ALBERT

Notizen: Abstract  The Hahajima Seamount, located at the junction between the Izu–Bonin and Mariana forearc slopes, is a notable rectangular shape and consists of various kinds of rocks. An elaborated bathymetric swath mapping with geophysical measurements and dredge hauls showed the Hahajima Seamount is cut by two predominating lineaments, northeast–southwest and northwest–southeast. These lineaments are of faults based on the topographic cross-sections and a 3-D view (whale's eye view). The former lineament is parallel to the transform faults of the Parece Vela Basin, whereas the latter is parallel to the nearby transform fault on the subducting Pacific Plate. The rocks constituting the seamount are ultramafic rocks (mostly harzburgite), boninite, basalt, andesite, gabbro, breccia and sedimentary rocks, which characterize an island arc and an ocean basin. Gravity measurement and seismic reflection survey offer neither a definite gravity anomaly at the seamount nor definite internal structures beneath the seamount. A northwest–southeast-trending fault and small-scale serpentine flows were observed during submersible dives at the Hahajima Seamount. The rectangular shape, size of the seamount, various kinds of rocks and geophysical measurements strongly suggest that the Hahajima Seamount is not a simple serpentine seamount controlled by various tectonic movements, as previously believed, but a tectonic block.

Notizen: Abstract  The Thimi Formation, constituting the upper part of the sedimentary sequence of the Kathmandu Valley, is characterized by alternation of fine- to medium-grained sand, silt, silty clay and clay deposited by a distal fluvial system in the Late Pleistocene. Palynostratigraphy based on 40 samples revealed the dominance of gymnosperm taxa over angiosperms and herbaceous members. As the different species Pinus and Quercus grow at different altitudes in Nepal today, an attempt was made to identify these taxa up to species level for climate interpretations. Gymnosperms, such as Pinus wallichiana, Pinus roxburghii, Abies spectabilis, Tsuga dumosa and Picea smithiana, were dominant over the woody angiosperms, such as Quercus lanata, Quercus lamellosa, Quercus leucotrichophora, Quercus semecarpifolia, Betula, Juglans, Myrica, Castanopsis and Symplocos. The pollen diagram of the Thimi Formation shows only minor fluctuations in assemblage. The pollen assemblages indicate the prevalence of a cool and temperate climate during the late Pleistocene. This is confirmed by the high percentages of Poaceae and other herbaceous plants, with very few woody angiosperms.

Notizen: Abstract  The 〈 6 Ma young Taitao ophiolite, exposed at the westernmost promontory of the Taitao Peninsula, is located approximately 40 km southeast of the Chile triple junction and consists of a complete sequence of oceanic lithosphere. Systematic sampling for paleomagnetic study was performed to understand the complex obduction processes of the ophiolite onto the forearc of the South American Plate. Two representative demagnetization paths of remanent magnetization vectors were observed. One is characterized by stable univectorial demagnetization paths and was observed in volcaniclastic rocks and dyke complexes. Orientations of their remanent magnetization vectors indicate various degrees of counterclockwise rotations. The other is characterized by multivectorial demagnetization paths and was observed in the plutonic units (gabbros and ultramafic rocks). From these, two distinct stable remanent magnetization vectors were isolated; one has high coercivity and the other has low coercivity along the demagnetization paths with little influence of viscous magnetizations. This suggests that the complex deformation history involved at least two rotational events. The clockwise rotation, inferred from high coercivity remanent magnetization vectors, was attributed to a ridge collision event and the counterclockwise rotation, inferred from the low coercivity remanent magnetization vectors, was attributed to an accommodation phase into the South American forearc during obduction and final emplacement of the ophiolite. Folds developed during this period. Paleomagnetic restorations of the internal structures of the plutonic units and dyke complexes suggest that they probably originated in a mid-oceanic ridge environment near a transform fault. The counterclockwise rotation of the plutonic and dyke complex units during the obduction generated tectonic gaps between these and the basement. The volcaniclastic rocks must have been deposited at nearly their present location, filling the tectonic gaps, as less effect of tectonic rotation was identified on these rocks.

Notizen: Abstract  The 1999 Chi-Chi earthquake in Taiwan (Mw = 7.6) produced a surface rupture along the north–south-striking Chelungpu thrust fault with pure dip-slip (east side up) and left lateral strike-slip displacements. Near-field strong-motion data for the northern part of the fault illustrate a distinct lack of the high-frequency seismic radiation associated with a large slip (10–15 m) and a rapid slip velocity (2–4 m/s), suggesting a smooth seismic slip associated with low dynamic frictional resistance on the fault. A drillhole was constructed at shallow depths in the possible fault zones of the northern part of the Chelungpu Fault, which may have slipped during the 1999 earthquake. One of the zones consists of a 20-cm-thick, unconsolidated fault breccia with a chaotic texture lacking both discrete slip surfaces (e.g. Riedel shears) and grain crushing. Other possible fault zones are marked by the narrow (less than a few centimeters) gouge zone in which clayey material intrudes into the damaged zone outside of the gouge zone. These characteristic fault rock textures suggest that the slip mechanisms at shallow levels during the earthquake involved either granular flow of initially unconsolidated material or slip localization under elevated pore pressure along the narrow clayey gouge zone. Because both mechanisms lead to low dynamic frictional resistance on the fault, the rapid seismic slip in the deep portions of the fault (i.e. the source region of strong-motion radiation) could have been accommodated by frictionless slip on the shallow portions of the fault. The combination of strong-motion data and fault rock analysis suggests that smooth slip associated with low dynamic friction occurred on both the deep and shallow portions of the fault, resulting in a large slip between the source region and the surface in the northern region.

Notizen: Abstract  The evolution of volcanism in Sumatra and Java during Tertiary and Quaternary time can be divided into three phases: (i) lava flows of the Early Tertiary event (43–33 Ma) consisting of island arc tholeiites; followed by (ii) eruption of tholeiitic pillow basalt at the beginning of the Late Tertiary (11 Ma); and succeeded by (iii) medium-K calc-alkaline magmatism in the Pliocene and Quaternary. The present available field data on the occurrence of Paleogene volcanic rocks and subsurface data in south Sumatra and northern west Java indicate a much larger area of distribution of the volcanic rocks than previously recognized. Because the eastward continuation of the northern west Java volcanic rocks had not been found, early investigators were inclined to assume that they continued to south Kalimantan. In contrast, the early Tertiary volcanic rocks that occupy the south coast of Java can be traced further east as far as Flores. The occurrence of Paleogene volcanics in south Sumatra and northern west Java can be interpreted as a Paleogene volcanic arc that was presumably related to the late Cretaceous–Paleogene trench parallel to Sumatra and west Java due to subduction of the Indian Plate toward the northeast (Meratus trend).

Notizen: Abstract  The break-up of Pangea began during the Triassic and was preceded by a generalized Permo-Triassic formation of continental rifts along the future margins between Africa and Europe, between Africa and North America, and between North and South America. During the Middle–Late Triassic, an ocean basin cutting the eastern equatorial portion of the Pangea opened as a prograding branch of the Paleotethys or as a new ocean (the Eastern Tethys); westwards, continental rift basins developed. The Western Tethys and Central Atlantic began to open only during the Middle Jurassic. The timing of the break-up can be hypothesized from data from the oceanic remnants of the peri-Mediterranean and peri-Caribbean regions (the Mesozoic ophiolites) and from the Atlantic ocean crust. In the Eastern Tethys, Middle–Late Triassic mid-oceanic ridge basalt (MORB) ophiolites, Middle–Upper Jurassic MORB, island arc tholeiite (IAT) supra-subduction ophiolites and Middle–Upper Jurassic metamorphic soles occur, suggesting that the ocean drifting was active from the Triassic to the Middle Jurassic. The compressive phases, as early as during the Middle Jurassic, were when the drifting was still active and caused the ocean closure at the Jurassic–Cretaceous boundary and, successively, the formation of the orogenic belts. The present scattering of the ophiolites is a consequence of the orogenesis: once the tectonic disturbances are removed, the Eastern Tethys ophiolites constitute a single alignment. In the Western Tethys only Middle–Upper Jurassic MORB ophiolites are present – this was the drifting time. The closure began during the Late Cretaceous and was completed during the Eocene. Along the area linking the Western Tethys to the Central Atlantic, the break-up was realized through left lateral wrench movements. In the Central Atlantic – the link between the Western Tethys and the Caribbean Tethys – the drifting began at the same time and is still continuing. The Caribbean Tethys opened probably during the Late Jurassic–Early Cretaceous. The general picture rising from the previous data suggest a Pangea break-up rejuvenating from east to west, from the Middle–Late Triassic to the Late Jurassic–Early Cretaceous.

Notizen: Abstract  The Mefjell plutonic complex consists of 500–550-Ma Pan-African plutonic rocks, which intrude into the Precambrian crystalline basement in the Sør Rondane Mountains, East Antarctica, and forms part of the Sør Rondane Suture Zone. The complex comprises syenitic and granitic (mostly monzogranitic) rocks, and is characterized by the presence of iron-rich hydrous mafic minerals and primary ilmenite, both of which imply its formation at high temperature and under low oxygen fugacity conditions. The syenitic rocks are metaluminous, and are high in alkalis, K2O/Na2O, Al2O3, FeOt/(FeOt + MgO) (0.88–0.98), K/Rb (800–1000), Ga (18–28 p.p.m.), Zr (up to 2100 p.p.m.) and Ba. They also have a low Mg♯ (Mg/[Mg + Fe2+]), Rb, Sr, Nb, Y and F, low to moderate light rare earth element (LREE)/heavy rare earth element (HREE) ratios and positive Eu anomalies in their rare earth element (REE) patterns. The granitic rocks are metaluminous to peraluminous, and have a high Rb content, high Sr/Ba and LREE/HREE ratios, low K/Rb and negative Eu anomalies. Most of the syenitic and granitic rocks have Y/Nb ratios greater than 1.2, and are depleted in Nb, Ti and Sr on the primitive mantle-normalized spider diagrams, indicating a crustal origin with subduction zone signatures. We interpret both the syenitic and granitic rocks to be derived from an iron-rich lower crustal source by dehydration melting induced by the heat of mantle-derived basaltic intrusion, after which they then underwent limited fractional crystallization. The Mefjell plutonic complex has a high Zr content and tectonic discrimination diagram signatures indicative of normal A-type granitic rocks. Both rock suites may have been generated under the same postorogenic tectonic setting. The Mefjell syenitic rocks are chemically comparable to charnockites in the Gjelsvikjella and western Mühlig-Hofmannfjella areas of East Antarctica, whereas the granitic rocks are comparable to aluminous A-type granitic rocks in South India, which were emplaced during formation and evolution of the Gondwanaland supercontinent.

Notizen: Abstract  A Middle Pleistocene widespread tephra referred to here as Hakkoda–Kokumoto Tephra (Hkd–Ku) has been newly recognized. Hkd–Ku, derived from the Hakkoda Caldera located in northernmost Honshu Is. of northeast Japan, covers much of Honshu Is. At the type locality in the proximal area, Hkd–Ku comprises Plinian pumice deposits and an immediately overlying ignimbrite. The fine vitric ash nature of the distal ash-fall deposits of Hkd–Ku suggests that they are coignimbrite ash-fall deposits. Hkd–Ku was identified using a combination of refractive indices and chemical compositions of major, trace and rare earth elements of glass shards, heavy mineral content, refractive indices of orthopyroxene and paleomagnetic polarity. On the basis of these properties, Hkd–Ku was identified in Oga and Boso Peninsulas and Osaka Plain, 830 km southwest of the source. Stratigraphic positions in Boso Peninsula and Osaka Plain within marine sediments that have a reliable chronology based on oxygen-isotope, and litho-, bio-, magneto- and tephrostratigraphy indicate that the age of Hkd–Ku is ca 760 ka, positioned in the transition between marine oxygen-isotope stages 19.1 and 18.4. The widespread occurrence of Hkd–Ku providing a tie line between many different Pleistocene sections over a distance of 800 km is a key marker horizon in the early part of the Middle Pleistocene. This tephra gives a time control point of ca 760 ka to marine sediments in the Oga Peninsula – where no datum plane exists between the Brunhes–Matuyama chron boundary and oxygen-isotope stage 12 – and to the volcanostratigraphy of the Hakkoda Caldera. The distribution of Hkd–Ku showing emplacement of coignimbrite ash-fall deposits in the area 830 km southwest of the source emphasizes the upwind transport direction, relative to the prevailing westerly winds, typical of other coignimbrite ash-fall deposits in the Japanese islands.

Notizen: Abstract  In this paper, a summary of the tectonic history of the Mirdita ophiolitic nappe, northern Albania, is proposed by geological and structural data. The Mirdita ophiolitic nappe includes a subophiolite mélange, the Rubik complex, overlain by two ophiolite units, referred to as the Western and Eastern units. Its history started in the Early Triassic with a rifting stage followed by a Middle to Late Triassic oceanic opening between the Adria and Eurasia continental margins. Subsequently, in Early Jurassic time, the oceanic basin was affected by convergence with the development of a subduction zone. The existence of this subduction zone is provided by the occurrence of the supra-subduction-zone-related magmatic sequences found in both the Western and Eastern units of the Mirdita ophiolitic nappe. During the Middle Jurassic, continuous convergence resulted in the obduction of the oceanic lithosphere, in two different stages – the intraoceanic and marginal stages. The intraoceanic stage is characterized by the westward thrusting of a young and still hot section of oceanic lithosphere leading to the development of a metamorphic sole. In the Late Jurassic, the marginal stage developed by the emplacement of the ophiolitic nappe onto the continental margin. During this second stage, the emplacement of the ophiolites resulted in the development of the Rubik complex. In the Early Cretaceous, the final emplacement of the ophiolites was followed by the unconformable sedimentation of the Barremian–Senonian platform carbonate. From the Late Cretaceous to the Middle Miocene, the Mirdita ophiolitic nappe was translated westward during the progressive migration of the deformation front toward the Adria Plate. In the Middle to Late Miocene, a thinning of the whole nappe pile was achieved by extensional tectonics, while the compression was still active in the westernmost areas of the Adria Plate. On the whole, the Miocene deformations resulted in the uplift and exposition of the Mirdita ophiolites as observed today.

Notizen: Abstract  The Solund-Stavfjord ophiolite complex (SSOC) in western Norway represents a remnant of the Late Ordovician oceanic lithosphere, which developed in an intermediate- to fast-spreading Caledonian back-arc basin. The internal architecture and magmatic features of its crustal component suggest that the SSOC has a complex, multistage sea floor spreading history in a supra-subduction zone environment. The youngest crustal section associated with the propagating rift tectonics consists of a relatively complete ophiolite pseudostratigraphy, including basaltic volcanic rocks, a transition zone between the sheeted dyke complex and the extrusive sequence, sheeted dykes, and high-level isotropic gabbros. Large-scale variations in major and trace element distributions indicate significant remobilization far beyond that which would result from magmatic processes, as a result of the hydrothermal alteration of crustal rocks. Whereas K2O is strongly enriched in volcanic rocks of the extrusive sequence, Cu and Zn show the largest enrichment in the dyke complex near the dyke–volcanic transition zone or within this transition zone. The δ18O values of the whole-rock samples show a general depletion structurally downwards in the ophiolite, with the largest and smallest variations observed in volcanic rocks and the transition zone, respectively. δ18O values of epidote–quartz mineral pairs indicate 260–290°C for volcanic rocks, 420°C for the transition zone, 280–345°C for the sheeted dyke complex and 290–475°C for the gabbros. The 87Sr/86Sr isotope ratios show the widest range and highest values in the extrusive rocks (0.70316–0.70495), and generally the lowest values and the narrowest range in the sheeted dyke complex (0.70338–0.70377). The minimum water/rock ratios calculated show the largest variations in volcanic rocks and gabbros (approximately 0–14), and generally the lowest values and range in the sheeted dyke complex (approximately 1–3). The δD values of epidote (−1 to −12‰), together with the δ18O calculated for Ordovician seawater, are similar to those of present-day seawater. Volcanic rocks experienced both cold and warm water circulation, resulting in the observed K2O-enrichment and the largest scatter in the δ18O values. As a result of metal leaching in the hot reaction zone above a magma chamber, Zn is strongly depleted in the gabbros but enriched in the sheeted dyke complex because of precipitation from upwelling of discharged hydrothermal fluids. The present study demonstrates that the near intact effect of ocean floor hydrothermal activity is preserved in the upper part of the SSOC crust, despite the influence of regional lower greenschist facies metamorphism.

Notizen: Abstract  During the Hirnantian period, the Yangtze Platform was situated in the western part of the South China block (SCB) before its later rotation, in the middle–low paleolatitudes of the southern hemisphere in the northeast side of peri-Gondwana. It is part of the Kosov faunal province as indicated by the Hirnantia fauna. Sedimentary evidence shows the domination of cool ventilated marine water from its offshore ramp and shelf. Hirnantian shallow-water carbonate facies (Kuanyinchiao Bed) overlie earlier Ashgill graptolitic black shales (Wufeng Formation) as a result of marine regression. In the Yangtze Platform, however, we have found local areas of intertidal to nearshore facies that lack the typical highly diverse Hirnantia fauna. Some warm-water features (radial oolites, peloids, diverse solitary rugose corals and other benthic shelly fauna) occur commonly in some limited shallow areas, forming grainstones and packstones. Although interglacial episodes within the Hirnantian glaciation could be responsible for these features, their limited occurrence within the interior of the platform leads us to interpret the deposits as indicating that cold-water currents from the southeastern high latitudes were partly excluded from the nearshore area of the Yangtze Platform. The landmass of the eastern SCB in the Hirnantian epoch prevented access to some areas of the cold marine water masses that flowed from higher latitudes of Gondwana; the result was a persistence of warm-water shallow marine facies in some areas.

Notizen: Abstract  Basalts and tonalites dredged from the Amami Plateau in the northern West Philippine Basin have the geochemical characteristics of intraoceanic island arc rocks: low 87Sr/86Sr (0.70297–0.70310), intermediate 143Nd/144Nd (0.51288–0.51292), moderate light rare earth element (LREE) enrichment (La/Yb = 4.1–6.6) and high La/Nb (1.4–4.3). The incremental heating of hornblende from tonalites yielded well-defined plateaus and 40Ar/39Ar isochron ages of 115.8 ± 0.5 Ma and 117.0 ± 1.1 Ma, while plagioclase yielded disturbed Ar release patterns, with ages ranging from 70 to 112 Ma. Taken together, these results show that the Amami Plateau was formed by subduction-related magmatism in the Early Cretaceous period, earlier than indicated by prior K/Ar results. The results support tectonic models in which the West Philippine Basin was opened within a complex of Jurassic–Paleocene island arc terranes, which are now scattered in the northern West Philippine Basin, the Philippine Islands and Halmahera. The Amami Plateau tonalites and basalts have higher Sr/Y and lower Y and 87Sr/86Sr compared with younger tonalitic rocks from the northern Kyushu–Palau Ridge and the Tanzawa complex, which were formed by the subduction of the Pacific Plate beneath the Philippine Sea Plate. Based on the geochemical characteristics of the basalts, the Early Cretaceous subduction zone that formed the Amami Plateau may have been the site of slab melting, which suggests that a younger and hotter plate was being subducted at that time. However, the Amami tonalites were probably formed from basaltic magma by fractional crystallization or by partial melting of basaltic arc crust, rather than by melting of the subducted slab.

Notizen: Abstract  Damage, destruction and casualties related to landslide and debris flow are common phenomena in the Himalaya, especially during the summer monsoon. This fact was tragically illustrated on 22 July 1996, when Larcha, situated at the 109-km mark of the Arniko Highway, upper Bhotekoshi Valley, central Nepal, experienced a catastrophic debris flow powered by the Bhairab Kunda Stream. Of the 22 houses in Larcha, 16 were swept away, two were partially damaged and 54 people were killed in a matter of a few minutes. The event attracted attention when media linked it to a glacial lake outburst flood as a result of the fact that the source of the stream is a glacial lake. To understand the cause, initiation mechanism and deposition process, the basin area was studied from geological, geomorphologic and engineering geological points of view and the role of precipitation was evaluated. A combination of rainfall, runoff from cliff faces and stream undercutting triggered failure of the bedrock and colluvium, both on the dip and counter-dip slopes, 500 m upstream from the highway. The landslide debris dammed the channel, which was eventually breached, and deposited approximately 104 000 m3 of coarse debris, dominated by the metasediments of the Lesser Himalayan origin, and overwhelmed the village of Larcha. The debris deposit was studied for clast size, composition, texture and dimensions. Lack of sorting and the presence of abundant silt and clay in the source area helped in the initiation of debris flow. The abundance of the Lesser Himalayan metasediment clasts together with the absence of debris traces upstream from the landslide site ruled out the possibility of a glacial lake outburst flood. The disaster was a result of landslide damming triggered by precipitation and stream undercutting and sudden bursting.

Notizen: Abstract  Since the mid-nineteenth century, devastating glacier lake outbursts have occurred in the Karambar Valley. The exact source areas of these floods are to date unknown. The present study uses geomorphologic field evidence and interviews of local inhabitants to reconstruct nine potential glacier dams in the Karambar Valley within a horizontal distance of only 40 km. The article focuses on the geomorphologic reconstruction of the highest glacier dams, the Chateboi and Saklei Shuyinj Glaciers. Their lake basins were connected in former times resulting in a complex interfingering of lake sediments, lake terraces and glacial deposits. The outbursts of these lakes could have triggered the drainage of one of the lower ice-dammed lakes (Sokther Rabot, Chillinji, Warghut or Karambar) and therefore initiated an outburst cascade in the upper Karambar Valley. Successive glacier dams are wide spread in the Karakoram, and cascading lakes might have also played a role in other lake outburst scenarios. In the Karambar Valley, even today the Chateboi Glacier blocks the Karambar River over a distance of 4 km and represents a permanent hazard for the villages located downstream.

Notizen: Abstract  Since 1973 new data have been obtained on the maximum extent of glaciation in High Asia. Evidence for an ice sheet covering Tibet during the last glacial period means a radical rethinking about glaciation in the northern hemisphere. The ice sheet's subtropical latitude, vast size (2.4 million km2) and high elevation (6000 m a.s.l.) are supposed to have resulted in a substantial, albedo-induced cooling of the Earth's atmosphere and the disruption of summer monsoon circulation. Moraines were found to reach down to 460 m a.s.l. on the southern flank of the Himalayas and to 2300 m a.s.l. on the northern slope of the Tibetan Plateau, in the Qilian Shan region. On the northern slopes of the Karakoram, Aghil and Kuen-Lun Mountains, moraines occur as far down as 1900 m a.s.l. In southern Tibet, radiographic analyses of erratics suggest a former ice thickness of at least 1200 m. Glacial polish and roches moutonnées in the Himalayas and Karakoram suggest former glaciers as thick as 1200–2700 m. On the basis of this evidence, a 1100–1600-m lower equilibrium line has been reconstructed, resulting in an ice sheet of 2.4 million km2, covering almost all of Tibet. Radiometric ages, obtained by different methods, classify this glaciation as isotope stage 3–2 in age (Würmian, the last glacial period, ca 60 000–18 000 years ago).

Notizen: Abstract  Prograde eclogites occur in the Tonaru epidote amphibolite mass in the Sambagawa Metamorphic Belt of central Shikoku. The Tonaru mass is considered to be a metamorphosed layered gabbro, and occurs as a large tectonic block (approximately 6.5 km × 1 km) in a high-grade portion of the Sambagawa schists. The Tonaru mass experienced high-P/low-T prograde metamorphism from the epidote-blueschist facies to the eclogite facies prior to its emplacement into the Sambagawa schists. The estimated P–T conditions are T = 300–450°C and P = 0.7–1.1 GPa for the epidote-blueschist facies, and the peak P–T conditions for the eclogite facies are T = 700–730°C and P ≥ 1.5 GPa. Following the eclogite facies metamorphism, the Tonaru mass was retrograded to the epidote amphibolite facies. It subsequently underwent additional prograde Sambagawa metamorphism, together with the surrounding Sambagawa schists, until the conditions of the oligoclase–biotite zone were reached. The high-P/low-T prograde metamorphism of the eclogite facies in the Tonaru mass and other tectonic blocks show similar steep dP/dT geothermal gradients despite their diverse peak P–T conditions, suggesting that these tectonic blocks reached different depths in the subduction zone. The individual rocks in each metamorphic zone of the Sambagawa schists also recorded steep dP/dT geothermal gradients during the early stages of the Sambagawa prograde metamorphism, and these gradients are similar to those of the eclogite-bearing tectonic blocks. Therefore, the eclogite-bearing tectonic blocks reached greater depths in the subduction zone than the Sambagawa schists. All the tectonic blocks were ultimately emplaced into the hanging wall side of the later-subducted Sambagawa high-grade schists during their exhumation.

Notizen: Abstract  The mantle-derived xenoliths entrained in the Pliocene basanite from Baengnyeong Island, South Korea, are spinel lherzolites and spinel harzburgites. The overall compositional range of the Baengnyeong xenoliths matches that of the post-Archean xenoliths of lithospheric mantle origin from eastern China, but without any compositional evidence for a refractory Archean mantle root. Mineral compositions of the xenoliths have been used to estimate the equilibrium temperatures and pressures, and to construct a paleogeothermal gradient of the source region. The xenolith-derived paleogeotherm is constrained from about 820°C at 7.3 kbar to 1000°C at 20.6 kbar. Like those from the post-Archean Chinese xenoliths of lithospheric mantle origin, the Baengnyeong geotherm is considerably elevated relative to the conductive models at the depth of the crust–mantle boundary, reflecting a thermal perturbation probably related to lithospheric thinning. There is no significant P/T difference between harzburgite and lherzolite, which suggests that the harzburgites are interlayered with lherzolites within the depth interval beneath Baengnyeong Island.

Notizen: Abstract  In southern New Caledonia, Late Oligocene granodiorite and adamellite are intruded into an ultramafic allochthon emplaced in the Late Eocene period. Previous studies of these granitoids proposed an origin associated with the melting of the underlying continental crust, but our new data show that these high-K to medium-K calc-alkaline granitoids display the geochemical and isotopic features of volcanic arc magmas uncontaminated by crust-derived melts. These magmas were probably generated in a post-Eocene and pre-Miocene subduction, the geophysical traces of which have been detected along the western coast of New Caledonia. Sr, Nd and Pb isotopic ratios indicate derivation from an almost isotopically homogeneous mantle wedge, but in contrast, some variation in trace element ratios uncorrelated to differentiation is indicative of source heterogeneity. Prominent heavy rare earth element (HREE) depletion of some of the younger granitoids may be the result of an equilibrium achieved with garnet-bearing subcrustal material (granulite) found as xenoliths, while a relative Nb, Ta and Hf enrichment, irrespective of crystal fractionation, may be related to either a modest contamination by previously underplated mafic material, heterogeneous hydration of the mantle wedge, or mixing with uplifted Nb-rich mantle. Post-obduction slab break-off can be proposed to have played a role in sublithospheric mantle mixing and the subsequent heterogeneity. The Late Oligocene subduction described here may be tentatively extended southward into northern New Zealand allochthons.

Notizen: Abstract  The Isabela ophiolite shows a complete ophiolite sequence exposed along the eastern coast of northern Luzon, the Philippines. It forms the Cretaceous basement complex for the northeastern Luzon block. This ophiolite is located at the northern end of a trail of ophiolites and ophiolitic bodies along the eastern margin of the Philippine Mobile Belt. This paper presents new findings regarding the nature and characteristics of the Isabela ophiolite. Peridotites from the Isabela ophiolite are relatively fresh and are composed of spinel lherzolites, clinopyroxene-rich harzburgites, depleted harzburgites and dunites. The modal composition, especially the pyroxene content, defines a northward depletion trend from fertile lherzolite to clinopyroxene-rich harzburgites and more refractory harzburgites. Variation in modal composition is accompanied by petrographic textural variations. The chromium number of spinel, an indicator of the degree of partial melting, concurs with petrographic observations. Furthermore, the Isabela ophiolite peridotites are similar in spinel and olivine major-element geochemistry and clinopyroxene rare earth-element composition to abyssal peridotites from modern mid-oceanic ridges. Petrological and mineral compositions suggest that the Isabela ophiolite is a transitional ophiolite subtype, with the fertile lherzolites representing lower sections of the mantle column that are usually absent in most ophiolitic massifs. The occurrence of the fertile peridotite presents a rare opportunity to document the lower sections of the ophiolitic mantle. The variability in composition of the peridotites in one continuous mantle section may also represent a good analogy of the melting column in the present-day mid-oceanic ridges.

Notizen: Abstract  The Mesozoic gold–silver deposits in South Korea are closely associated with the Mesozoic granitoids. The Jurassic gold–silver deposits can be distinguished from the Cretaceous ones in terms of occurrence, alteration style, gold fineness, associated mineral assemblage, fluid inclusion and stable isotopic compositions. The Jurassic deposits were formed in mesozonal environments related to deep-seated granitoids, whereas the Cretaceous ones were formed in epizonal environments related to shallow-level granitoids. The Jurassic auriferous deposits (about 165–145 Ma) show fluid characteristics typical of an orogenic-type gold deposit, and were probably generated in a compressional regime caused by an orthogonal convergence of the Izanagi oceanic plate into the Asiatic margin. However, strike-slip faults and caldera-related fractures, together with subvolcanic to volcanic activity, may have played an important role in the formation of Cretaceous gold–silver lode deposits (about 110–45 Ma) under a continental arc setting.

Notizen: Abstract  Refined numerical ages of the diatom biohorizons of the Early to Middle Miocene (11–18 Ma) period in the Neogene North Pacific are presented based on the direct correlation between biostratigraphy and magnetostratigraphy at Site 887 on the Patton–Murray Seamount in the northeastern Pacific. Sampling intervals of 0.02–0.04 my allowed the determination of the ages of the biohorizons to be more precise than previous studies. The secondary biohorizons established in the northwestern Pacific have been proven to be useful also in the northeastern Pacific, and are linked to magnetostratigraphy directly for the first time. The refined diatom biochronology established in this study will provide a vital basis for the study of the Neogene marine sediments of the middle- to high-latitude North Pacific, which rarely yield calcareous microfossils. Denticulopsis praedimorpha var. prima n. var. is described.

Notizen: Abstract  Early Cretaceous high-K calc-alkaline volcanism occurring in the Laiyang Basin north of the Sulu high-pressure to ultrahigh-pressure (HP-UHP) Metamorphic Belt, eastern China, comprises a wide spectrum of rock types, ranging from trachybasalts to trachydacites. The basaltic–andesitic rocks erupted at 107–105 Ma, spanning an SiO2 range of 50.1–59.6% and an MgO range of 2.6–7.2%, and are characterized by large ion lithophile element (LILE; e.g. Ba and K) and light rare earth element (LREE) enrichment, high field strength element (HFSE) depletion and highly radiogenic Sr but non-radiogenic Nd isotopic compositions (87Sr/86Sr(i) = 0.70750–0.70931; ɛNd(t) = −17.9 − −15.6). The geochemical similarities between these rocks and the earlier Sulu Belt lamprophyres suggest that both types of mafic rocks were derived from similar mantle sources with LILE and LREE enrichment. Thus, the Wulian–Qingdao–Yantai Fault that separates the two terranes at the surface should not be considered as a lithospheric boundary between the North China and Yangtze blocks. The felsic lavas erupted at 93–91 Ma, spanning an SiO2 range of 61.6–67.0% and an MgO range of 1.1–2.6%, and show a trace element geochemistry similar to the basaltic rocks, but with higher radiogenic Sr and even lower Nd isotopic compositions (87Sr/86Sr(i) = 0.70957–0.71109; ɛNd(t) = −19.1 − −17.5), similar to I-type granitoids in the Sulu Belt. A crustal origin was proposed to explain their compositions (which are comparable to those of experimental slab melts), the 〉10 Ma eruption interval and the compositional gaps in some elements (e.g. P, Ti and Sr) between them and the older basaltic–andesitic rocks. These melts were derived from predominant metaigneous protoliths containing mafic accumulative counterparts of the basaltic–andesitic and/or lamprophyric magmas. The extensive extrusion of Early Cretaceous high-K calc-alkaline rocks in the Laiyang Basin favored an extensional regime in response to the progressive attenuation of the thickened lithosphere and orogenic collapse, as reflected in the development of the basin from a foreland basin (before the end of the Jurassic period) to a fault basin (since the Early Cretaceous period).

Notizen: Abstract  The geology and geochemistry of pyroclastic flows and fallout tephras formed during the Karasugasen dome eruption in the Daisen–Hiruzen Volcano Group in southwest Japan have been examined in detail. The Karasugasen lava dome erupted at about 26 ka. The eruption began with a vulcanian ash fall, and this was followed by at least eight block and ash flows and a pumice flow. The block and ash flows were produced by the successive collapses of a growing lava dome. This main eruption phase was followed by an eruption of vulcanian ash falls, and finally ended with a sub-Plinian pumice fall. This eruption sequence is typical of the Daisen Volcano during the last three eruption events, which occurred at 58, 26 and 17 ka. The magma produced during the Karasugasen eruption was a typical adakite, with extremely high Sr/Y ratios and low HREE/LREE ratios compared to normal arc lavas. The chemistry of the Karasugasen lavas is almost identical to other Daisen–Hiruzen lavas that were produced from eruptions over an interval of a million years. The continuous supply of a huge amount of adakitic magma (〉100 km3) for such a long period suggests a massive homogeneous source material, such as molten Philippine Sea Plate slab. Slab melting is a plausible mechanism for the production of the adakitic lavas at Karasugasen, and hence the Daisen–Hiruzen Volcano Group.

Notizen: Abstract  Paleostress fields of the Late Paleozoic to Early Mesozoic Pyeongan Supergroup that is distributed along the northeastern part of the Ogcheon Belt in South Korea were investigated using the calcite strain gauge (CSG) technique. Combining the results of this study with those of other studies investigating the relationship between twin strain, twin density and width, which are used as indicators of deformation conditions in the natural low-temperature deformation of limestone, it was estimated that calcite twins in the study area were probably formed at temperatures lower than 170°C. From two samples, two different principal paleostress directions were inferred from calcite twins, while only one direction was inferred from two other samples. This result suggests that deformation occurred during two or more different tectonic events in the Pyeongan Supergroup during the Mesozoic era. The maximum shortening axis was oriented in two directions, northeast–southwest and northwest–southeast, respectively, which coincide well with the paleostress directions inferred from the stress inversion for many fault sets. Combining the results of the paleostress analysis from this and other studies, we hypothesize that the directions of the maximum shortening axis in the Pyeongan Supergroup changed from northeast–southwest during the pre-Daebo orogeny period (Late Triassic period) to northwest–southeast during the syn-Daebo orogeny period (Early Jurassic to Early Cretaceous period) in the Mesozoic era.

Notizen: Abstract  The structure, paleomagnetism and biostratigraphy of the Nishizaki and Kagamigaura formations on the southern Boso Peninsula, central Japan, were investigated to determine the chronographic constraints on the accretion, post-Late Miocene rotation and regional tectonics in the Izu–Bonin island arc collision zone. The geological structures on the southern Boso Peninsula are characterized by an east–west trending and south-verging fold and thrust belt that curves toward the northwest–southeast in the northwest extent of the Nishizaki Formation. Two stages of tectonic rotation were revealed by paleomagnetic and structural studies. The first is believed to have occurred after the accretion of the Nishizaki Formation and before the deposition of the Kagamigaura Formation, while the second is confidently correlated with the 1 Ma Izu block collision. The northwest extent of the Nishizaki Formation was rotated clockwise by approximately 65–80°, whereas the rotation was only 25–30° in the east, and 11–13° in the overlying Kagamigaura Formation. Radiolarian biostratigraphy suggests a depositional age of 9.9–6.8 Ma (Upper Miocene period) for the Nishizaki Formation and 4.19-3.75 Ma (Pliocene period) for the lower Kagamigaura Formation. These results indicate that the age of accretion and first-stage rotation of the Nishizaki Formation can be constrained to the interval of 6.80–3.75 Ma. This structure most likely represents the northward bending caused by collisions of the Tanzawa and Izu blocks with the Honshu island arc, and suggests rapid processes of accretion, collision, uplift and the formation of new sedimentary basins within a relatively short period of time (2.61–3.05 my).

Notizen: Abstract  River incision into bedrock results in the decrease of burial depths, which can be of critical importance, for example, in the safe long-term storage of high-level radioactive waste. For the long-term prediction of river erosion, it is essential to know the rate of incision during the Late Quaternary period. In the Abukuma Mountains on the forearc side of northeast Japan, a low-relief peneplain that was uplifted in the Pliocene period is widely developed. Degradational fluvial terraces that are discontinuously distributed along draining rivers are scattered in the study area. The fluvial sediments were mainly transported from the summit regions as debris flows or hyperconcentrated flows. The terrace deposits are capped by a series of eolian veneers containing key tephra beds. From the oldest to the youngest, these tephra beds are the 150–125 ka Iizuna–Kamitaru tephra, the 135–125 ka Hiuchigatake–Tagashira tephra, the 120 ka Adatara–Dake tephra, the 70–80 ka Bandai–Hayama-2 tephra, the 45 ka Numazawa–Mizunuma tephra and the 42 ka Bandai–Hayama-1 tephra. Using tephrochronological data, the terraces are divided into three groups: higher, middle and lower. The ages of formation of the higher, middle and lower terraces are estimated to be within marine isotope stage (MIS) 6, MIS 5.4–5.2 and MIS 3 to MIS 2, respectively. The incision rate, calculated from the relative height between the terrace surface and present-day valley floor fill, is 1.5–0.8 m/10 000 years in the elevations from 350 to 700 m. The calculated rate does not show significant differences between the higher, middle and lower terraces. All the relative heights decrease with increasing elevation, because the erosional rates of streams in the upper reaches are lower than those in downstream reaches where the discharge rates are higher. This value can be regarded as an estimate of the rate of incision in granitic mountains where there is no volcanic or distinct tectonic activity.

Notizen: Abstract  Small-volume plutons of Early to Late Cretaceous ages are widely distributed in the Yamizo Mountains, central Japan. These plutons consist predominantly of granitoids, classified into hornblende gabbro, quartz diorite, hornblende–biotite granodiorite and coarse-grained biotite granite. The quartz diorite (52–64 wt% of SiO2) is characterized by a high Sr content (606–769 p.p.m.) associated with a low Y (13–27 p.p.m.) and heavy rare earth element content (Yb content of 1.19–2.13 p.p.m.). On the Sr/Y versus Y diagram, this rock type mainly plots in the adakite and Archean high-Al tonalite, trondhjemite and granodiorite (TTG) field. Together with its initial Sr isotopic ratios, which range from 0.7038 to 0.7046, these data suggest that quartz diorite originated as slab melts. However, geochemical calculations assuming either eclogite or garnet amphibolite as the source material do not support this suggestion. Instead, the chemical compositions of quartz diorite are better explained by the fractional crystallization of hornblende, plagioclase and biotite from a primitive, basaltic melt in a magma chamber. In this case, the formation of the associated hornblende gabbro can also be explained by the accumulation of hornblende and plagioclase. Adakitic rocks of Early Cretaceous ages have also been reported in the Tamba Belt of the inner zone of southwest Japan, located ca 500 km west of the Yamizo Mountains. These rocks can be correlated to the adakitic rocks in the Yamizo Mountains based on the geology, petrography, geochemistry and radiometric ages. Therefore, we propose the possibility that the Early Cretaceous adakitic rocks in the inner zone of southwest Japan were produced by fractional crystallization from basaltic arc magmas generated by a partial melting of metasomatized wedge mantle peridotite.

Notizen: Abstract  The major element and compatible trace element compositions of the northwest Kyushu basalts (NWKBs) collected from Saga-Futagoyama were analyzed to examine the petrogenesis of these basalts. Although nepheline-normative alkaline basalts are not found in the basalts from Saga-Futagoyama, the Saga-Futagoyama basalts almost cover the major element variations of NWKBs. The basalts can be chemically divided into two groups: an Fe-poor group (IPG) and an Fe-rich group (IRG). The compositional variation of IPG basalts is essentially controlled by the partial melting of the source as suggested by the following: (i) bulk rock MgO, FeO and NiO compositions indicate that some IPG samples were equilibrated with mantle olivine; and (ii) correlations between Al2O3, CaO and MgO are consistent with those of experimental partial melts of peridotites. The inconsistent behaviors of the elements compatible with clinopyroxene (Cpx), such as V (Sc and Cu), preclude the significant role of the fractional crystallization of Cpx and spinel in IPG variation. IPG basalts have low Al and high Fe concentrations compared to the products of melting experiments involving peridotites and pyroxenites, suggesting that the IPG source would have a lithology and bulk rock composition different from those of typical peridotites and pyroxenites. IRG basalts have negative correlations between Fe2O3* and MgO, and between V and Fe2O3*/MgO, indicating that IRG basalts would have fractionated Cpx. However, the anomalously Fe-rich feature of IRG basalts compared with NWKBs collected from other areas suggests that the role of Cpx fractionation in NWKBs is minor. Relatively low melting temperatures would have principally caused the large chemical variation of NWKBs.

Notizen: Abstract  The fractality of fault zones of thickness T for the 248-m-long core from a borehole penetrating the northern segment of the seismic Chelungpu Fault, Taiwan, was analyzed. The frequency curve of T shows that the fractal dimension is normal when T is smaller than a characteristic thickness Tc, and it becomes abnormally large when T exceeds Tc. The fractal dimensions of size and spatial distributions of T increase as the mean distribution density of T increases, which is inconsistent with the evolution laws for ordinary brittle faults. This discrepancy implies that the thickening rate of T when T is more than Tc is not constant, but a decreasing function of fault displacement. The slow thickening rate is related to the elastohydrodynamic lubrication which was effective on the fault when T exceeds Tc. This slip instability mechanism can explain the large, fast and smooth slip on the northern segment of the Chelungpu Fault during the 1999 Chi-Chi earthquake.

Notizen: Abstract  This paper reviews the compositional data (major elements, platinum group element [PGE] concentrations, Os- and O-isotopes) for chromites from the mantle section of the Oman ophiolite. Chromites in chromitite from the Oman ophiolite lie on a compositional spectrum between high-Cr♯, boninite-like and low-Cr♯, mid-oceanic ridge basalt-like end-members. The high-Cr♯ end-member is low in Ti, has a fractionated PGE pattern and is enriched in iridium group-platinum group elements (IPGE). The low-Cr♯ end-member has higher Ti and an unfractionated PGE pattern. The compositional variation in the chromitites reflects their crystallization from a range of different melt compositions. It is proposed that this wide variation in melt compositions was produced by the process of a melt–rock reaction, whereby a basaltic melt has reacted with harzburgitic mantle to yield successively more Cr-rich melts. In contrast to previous models, this approach does not require a change in the tectonic environment to explain the different chromite types.

Notizen: Abstract  Ophiolites of the Mirdita–Subpelagonian zone form a nearly continuous belt in the Albanide–Hellenide orogen, including mid-ocean ridge basalt (MORB) associations in the western Mirdita sector and supra-subduction zone (SSZ) complexes, with prevalent island arc tholeiitic (IAT) and minor boninitic affinities in the eastern part of the belt (i.e. eastern Mirdita, Pindos, Vourinos). In addition, basalts with geochemical features intermediate between MORB and IAT (MORB/IAT) are found in the central Mirdita and in the Aspropotamos sequence (Pindos). These basalts alternate with pure MORB and are cut by boninitic dykes. The distinctive compositional characteristics of the mafic magmas parental to the different ophiolitic suites can be accounted for by partial melting of mantle sources progressively depleted by melt extractions. Partial melting processes (10–20%) of lherzolitic sources generated pure MORB, leaving clinopyroxene-poor lherzolite as a residuum. Approximately 10% water-assisted partial melting of this latter source, in an SSZ setting, may in turn generate basalts with MORB/IAT intermediate characteristics, whereas IAT basalts and boninites may have been derived from 10–20% and 30% partial melting, respectively, of the same source variably enriched by subduction-derived fluids. In addition, boninites may also have been derived by comparatively lower degrees of hydrated partial melting of more refractory harzburgitic sources. A generalized petrologic model based on mass balance calculations between bulk rock and mineral compositions, indicate that most of the intrusives (from ultramafic cumulates to gabbronorites and plagiogranites), as well as sheeted dykes and volcanics (from basalts to rhyodacites) forming the bulk crustal section of the SSZ ophiolites, may be accounted for by shallow fractional crystallization from low-Ti picritic parental magmas very similar in composition to IAT picrites from Pacific intraoceanic arcs. The most appropriate tectono-magmatic model for the generation of the SSZ Tethyan ophiolites implies low velocity plate-convergence of the intraoceanic subduction and generation of a nascent arc with IAT affinity and progressive slab roll-back, mantle diapirism and extension from the arc axis to the forearc region, with generation of MORB/IAT intermediate basalts and boninitic magmas.

Notizen: Abstract  Structures developed in metamorphic and plutonic blocks that occur as knockers in the Mineoka Ophiolite Belt in the Boso Peninsula, central Japan, were analyzed. The aim was to understand the incorporation processes of blocks of metamorphic and plutonic rocks with an arc signature into the serpentinite mélange of the Mineoka Ophiolite Belt in relation to changes in metamorphic conditions during emplacement. Several stages of deformation during retrogressive metamorphism were identified: the first faulting stage had two substage shearing events (mylonitization) under ductile conditions inside the crystalline blocks in relatively deeper levels; and the second stage had brittle faulting and brecciation along the boundaries between the host serpentinite bodies in relatively shallower levels (zeolite facies). The first deformation occurred during uplift before emplacement. The blocks were intensively sheared by the first deformation event, and developed numerous shear planes with spacing of a few centimeters. The displacement and width of each shear plane were a few centimeters and a few millimeters, respectively, at most. In contrast, the fault zone of the second shearing stage reached a few meters in width and developed during emplacement of the Mineoka Ophiolite. Both stages occurred under a right-lateral transpressional regime, in which thrust-faulting was associated with strike-slip faulting. Such displacement on an outcrop scale is consistent with the present tectonics of the Mineoka Belt. This implies that the same tectonic stress has been operating in the Boso trench–trench–trench-type triple junction area in the northwest corner of the Pacific since the emplacement of the Mineoka Ophiolite. The Mineoka Ophiolite Belt must have worked as a forearc sliver fault during the formation of a Neogene accretionary prism further south.

Notizen: Abstract  Calcretes can be observed on the surface of old moraines around Batura Glacier in the upper Hunza Valley, Karakoram Mountains, Pakistan. They develop as a calcareous crust cementing small gravels under boulders. In order to understand the genesis of the calcrete crust, a variety of methods were employed: (i) study of mineralogy and geochemistry of a calcrete crust precipitated on the lateral moraine using X-ray diffractometer and electron probe microanalysis; (ii) analysis of solute chemistry of surface water and ice bodies around the Batura Glacier; and (iii) accelerator mass spectrometry 14C dating of the crust itself. The results indicate that the calcrete crust has definite laminated layers composed of a fine-grain and compact calcite layer, and a mineral fragment layer. The chemical composition of the calcite layer is approximately 60% CaO and 1% MgO. The mineral fragment layer consists of rounded grain materials up to 0.2 mm in diameter. It shows a graded bedding structure with fine grains of quartz, albite and muscovite. Meanwhile, as the Paleozoic Pasu limestone is distributed around the terminal of Batura Glacier, Ca cations dissolve in the melt water of the glacier. Accordingly, the calcrete crust is precipitated by decreases in CO2 partial pressure from glacier ice and evaporation of the melt water, including high concentration of Ca2+ at ephemeral streams and small ponds stagnating between the moraine and glacial ice. On the basis of the AMS 14C age, the calcrete is considered to have formed approximately 8200 calibrated years bp under the Batura glacial stage.

Notizen: Abstract  The rates of the accumulated and continuous displacement of solifluction lobes in the Kangchenjunga area, eastern Nepal Himalaya, were determined using glass fiber tubes and a strain probe. Ground temperature, precipitation and soil moisture were monitored at two sites, whose altitude differed by approximately 100 m, to understand the solifluction process. The average movement rate of the glass fiber tubes on a 31° slope at altitudes of 5412–5414 m a.s.l. was approximately 11 mm/year, being almost threefold greater than that observed on a 22° slope at 5322–5325 ma.s.l. There was no significant difference in the depth of displacement at these sites. The continuous displacement measurement near the ground surface at 5414 m showed permanent downslope movement from early July. Such movement may be attributed to additional moisture supply during the monsoon season. The amplitude of the displacement cycle was highest at the ground surface, and decreased to virtually zero at and below 20 cm in depth. Probable factors leading to the relatively slow rates of downslope displacement at the surface and depth at the studied altitudes are the lack of concurrence of the freeze–thaw cycles and the high moisture condition in the soil, and the low moisture retention capacity of the soil because of steep slopes and superficial desiccation. The rate of displacement may be more pronounced at altitudes above 5600 m because of the freeze–thaw cycles during the summer season.

Notizen: Abstract  Soil profiles of the Kathmandu urban area exhibit significant variations in magnetic susceptibility (χ) and saturation isothermal remanence (SIRM), which can be used to discriminate environmental pollution. Magnetic susceptibility can be used to delineate soil intervals by depth into normal (〈 10−7 m3/kg), moderately enhanced (10−7–〈 10−6 m3/kg) and highly enhanced (≥ 10−6 m3/kg). Soils far from roads and industrial sites commonly fall into the ‘normal’ category. Close to a road corridor, soils at depths of several centimeters have the highest χ, which remains high within the upper 20 cm interval, and decreases with depth through ‘moderately magnetic’ to ‘normal’ at approximately 30–40 cm. Soils in the upper parts of profiles in urban recreational parks have moderate χ. Soil SIRM has three components of distinct median acquisition fields (B1/2): soft (30–50 mT, magnetite-like phase), intermediate (120–180 mT, probably maghemite or soft coercivity hematite) and hard (550–600 mT, hematite). Close to the daylight surface, SIRM is dominated by a soft component, implying that urban pollution results in enrichment by a magnetite-like phase. Atomic absorption spectrometry of soils from several profiles for heavy metals reveals remarkable variability (ratio of maximum to minimum contents) of Cu (16.3), Zn (14.8) and Pb (9.3). At Rani Pokhari, several metals are well correlated with χ, as shown by a linear relationship between the logarithmic values. At Ratna Park, however, both χ and SIRM show significant positive correlation with Zn, Pb and Cu, but poor and even negative correlation with Fe (Mn), Cr, Ni and Co. Such differences result from a variety of geogenic, pedogenic, biogenic and man-made factors, which vary in time and space. Nevertheless, for soil profiles affected by pollution (basically traffic-related), χ exhibits a significant linear relationship with a pollution index based on the contents of some urban elements (Cu, Pb, Zn), and therefore it serves as an effective parameter for quantifying the urban pollution.

Notizen: Abstract  Newly discovered peloidal limestone from the summit of Mount Qomolangma (Mount Everest) contains skeletal fragments of trilobites, ostracods and crinoids. They are small pebble-sized debris interbedded in micritic bedded limestone of the Qomolangma Formation, and are interpreted to have been derived from a bank margin and redeposited in peri-platform environments. An exposure of the Qomolangma detachment at the base of the first step (8520 m), on the northern slope of Mount Qomolangma was also found. Non-metamorphosed, strongly fractured Ordovician limestone is separated from underlying metamorphosed Yellow Band by a sharp fault with a breccia zone. The 40Ar–39Ar ages of muscovite from the Yellow Band show two-phase metamorphic events of approximately 33.3 and 24.5 Ma. The older age represents the peak of a Barrovian-type Eo-Himalayan metamorphic event and the younger age records a decompressional high-temperature Neo-Himalayan metamorphic event. A muscovite whole-rock 87Rb–86Sr isochron of the Yellow Band yielded 40.06 ± 0.81 Ma, which suggests a Pre-Himalayan metamorphism, probably caused by tectonic stacking of the Tibetan Tethys sediments in the leading margin of the Indian subcontinent. Zircon and apatite grains, separated from the Yellow Band, gave pooled fission-track ages of 14.4 ± 0.9 and 14.4 ± 1.4 Ma, respectively. These new chronologic data indicate rapid cooling of the hanging wall of the Qomolangma detachment from approximately 350°C to 130°C during a short period (15.5–14.4 Ma).

Notizen: Abstract  A multidisciplinary study was conducted on the section of the Siwalik Group sediments, approximately 5000 m thick, exposed along the Karnali River. Analysis of facies, clay mineralogy and neodymium isotope compositions revealed significant changes in the sedimentary record, allowing discussion of their tectonic or climatic origin. Two major changes within the sedimentary fill were detected: the change from a meandering to a braided river system at ca 9.5 Ma and the change from a deep sandy braided to a shallow sandy braided river system at ca 6.5 Ma. The 9.5-Ma change in fluvial style is contemporaneous with an abrupt increase of ɛNd(0) values following a ɛNd(0) minimum. This evolution indicates a change in source material and erosion of Lesser Himalayan rocks within the Karnali catchment basin between 13 and 10 Ma. The tectonic activity along the Ramgarh thrust caused this local exhumation. By changing the proximity and morphology of relief, the forward propagation of the basal detachment to the main boundary thrust was responsible for the high gradient and sediment load required for the development of the braided river system. The change from a deep sandy braided to a shallow sandy braided river system at approximately 6.5 Ma was contemporaneous with a change in clay mineralogy towards smectite-/kaolinite-dominant assemblages. As no source rock change and no burial effect are detected at that time, the change in clay mineralogy is interpreted as resulting from differences in environmental conditions. The facies analysis shows abruptly and frequently increasing discharges by 6.5 Ma, and could be linked to an increase in seasonality, induced by intensification of the monsoon climate. The major fluvial changes deciphered along the Karnali section have been recognized from central to western Nepal, although they are diachronous. The change in clay mineralogy towards smectite-/kaolinite-rich assemblages and the slight decrease of ɛNd(0) have also been detected in the Bengal Fan sedimentary record, showing the extent and importance of the two major events recorded along the Karnali section.

Notizen: Abstract  The focus in the present study is on characterizing spatial patterns of textural and petrological variabilities, and on evaluating mechanisms influencing the textural and petrological components of modern river, beach and shelf sands in a volcanically active back-arc tectonic setting. Abashiri Bay and the surrounding area in eastern Hokkaido, Japan, has volcanic source land within a back-arc region associated with subduction of the Pacific Plate beneath the Okhotsk (North American) Plate. A total of 41 river, beach and shelf sands were obtained for grain-size and modal composition analyses. Multivariate analytical techniques of hierarchical cluster and principal component analyses were performed on the textural and petrological data for investigating relations among quantitative variables. On the basis of grain-size data, four sedimentary zones were identified: zone I, palimpsest zone; zone II, relict zone; zone III, modern (proteric) zone; zone IV, coastal sedimentary zone. All sands are feldspatholithic and quartz-deficient. The framework (quartz, feldspar and rock fragment) modal compositions were also classified into four clusters, A–D. The characteristic components of each cluster are as follows: cluster A, felsic volcanic rock fragments; cluster B, andesitic–basaltic volcanic rock fragments; cluster C, mixed or plagioclase; cluster D, sedimentary rock fragments. Almost all sands in western and central Abashiri Bay belong to cluster A, where the original compositions are influenced by Kutcharo pyroclastic flow deposits. Andesitic–basaltic lava and Neogene volcaniclastic and sedimentary rocks have a major influence on the compositions of shelf sands in eastern Abashiri Bay. The modal compositions are basically controlled by the source lithology. Compositional maturity (percentage of quartz to feldspar and rock fragments; Q/FR%) slightly increased, in order, from river (1.2), zone IV (coastal, 1.7), zone II (relict, 2.2), zone I (palimpsest, 3.6), to zone III (modern proteric, 7.0). Greater maturity in the recycled sediments is indicative of weathering under the sea or abrasion by transportation induced by sea-level fluctuations, waves, or sea currents. Several controlling factors – (i) source lithological; (ii) mineralogical; (iii) climatic; and (iv) geomorphological controls – might still cause low maturity through all sedimentary zones other than the continental margin sands previously reported.

Notizen: Abstract  Ophiolitic mélanges associated with ophiolitic sequences are wide spread in the Mirdita–Subpelagonian zone (Albanide–Hellenide Orogenic Belt) and consist of tectonosedimentary ‘block-in-matrix-type’ mélanges. Volcanic and subvolcanic basaltic rocks included in the main mélange units are studied in this paper with the aim of assessing their chemistry and petrogenesis, as well as their original tectonic setting of formation. Basaltic rocks incorporated in these mélanges include (i) Triassic transitional to alkaline within-plate basalts (WPB); (ii) Triassic normal (N-MORB) and enriched (E-MORB) mid-oceanic ridge basalts; (iii) Jurassic N-MORB; (iv) Jurassic basalts with geochemical characteristics intermediate between MORB and island arc tholeiites (MORB/IAT); and (v) Jurassic boninitic rocks. These rocks record different igneous activities, which are related to the geodynamic and mantle evolution through time in the Mirdita–Subpelagonian sector of the Tethys. Mélange units formed mainly through sedimentary processes are characterized by the prevalence of materials derived from the supra-subduction zone (SSZ) environments, whereas in mélange units where tectonic processes prevail, oceanic materials predominate. In contrast, no compositional distinction between structurally similar mélange units is observed, suggesting that they may be regarded as a unique mélange belt extending from the Hellenides to the Albanides, whose formation was largely dominated by the mechanisms of incorporation of the different materials. Most of the basaltic rocks surfacing in the MOR and SSZ Albanide–Hellenide ophiolites are incorporated in mélanges. However, basalts with island arc tholeiitic affinity, although they are volumetrically the most abundant ophiolitic rock types, have not been found in mélanges so far. This implies that the rocks forming the main part of the intraoceanic arc do not seem to have contributed to the mélange formation, whereas rocks presumably formed in the forearc region are largely represented in sedimentary-dominated mélanges. In addition, Triassic E-MORB, N-MORB and WPB included in many mélanges are not presently found in the ophiolitic sequences. Nonetheless, they testify to the existence throughout the Albanide–Hellenide Belt of an oceanic basin since the Middle Triassic.

Notizen: Abstract  Magnetic susceptibility and the anisotropy of magnetic susceptibility were measured on an 800-cm-thick succession of cumulate gabbro in the Sadm area of the Oman ophiolite. The section contained three distinct cumulate units. The susceptibility tends to decrease upward in each from a melanocratic layer (several tens of centimeters thick) to a leucocratic layer (a few meters thick). The susceptibility decreases in accordance with the decreasing number of magnetite grains, which are the alteration product mainly of olivine minerals. This suggests the cyclic downward accumulation of olivine in the cumulate gabbro. The apparent strain deduced from the patterns of magnetic and grain fabrics was the result mostly of simple shear, so that the layering of gabbro is understood to be formed primarily by a crystal cumulus process followed by simple shear deformation.

Notizen: Abstract  An accretionary complex, which contains fragments of a remnant island arc, was newly recognized in the Cretaceous accretionary terranes in Hokkaido, Japan. It consists of volcanics, volcanic conglomerate, intermediate to ultramafic intrusive rocks with island-arc affinity including boninitic rocks, accompanied by chert and deformed terrigenous turbidites. Compared with the results of modern oceanic surveys, the preserved sequence from island-arc volcanics to chert, via reworked volcanics, is indicative of intraoceanic remnant arc, because the sequence suggests an inactive arc isolated within a pelagic environment before its accretion. The age of a subducting oceanic crust can be discontinuous before and after a remnant-arc subduction, resulting in abrupt changes in accretion style and metamorphism, as seen in Cretaceous Hokkaido. Subduction of such an intraoceanic remnant arc suggests that the subducted oceanic plate in the Cretaceous was not an extensive oceanic plate like the Izanagi and/or Kula Plates as previously believed by many authors, but a marginal basin plate having an arc–back-arc system like the present-day Philippine Sea Plate.

Notizen: Abstract  The Xialu chert radiolarian fauna is latest Jurassic–earliest Cretaceous in age (Pseudodictyomitra carpatica zone) and contains many taxa in common with coeval northern hemisphere middle-latitude (temperate) radiolarian faunas represented by the Torinosu fauna in southwest Japan. Common elements include Eucyrtidiellum pyramis (Aita), Protunuma japonicus Matsuoka & Yao, Sethocapsa pseudouterculus Aita, Sethocapsa (?) subcrassitestata Aita, Archaeodictyomitra minoensis (Mizutani), Stichocapsa praepulchella Hori and Xitus gifuensis (Mizutani). The Xialu fauna is less similar to low-latitude (tropical) assemblages represented by the Mariana fauna. For this reason, the Xialu fauna is regarded as representative of a southern hemisphere middle-latitude (temperate) fauna. A mirror-image bi-temperate provincialism to the equator in radiolarian faunas is reconstructed for the Ceno-Tethys and Pacific Ocean in latest Jurassic–earliest Cretaceous time.

Notizen: Abstract  The relationship between the altitude of the Tibetan Plateau and climate change in central Asia was investigated through a numeric experiment using the Meteorological Research Institute (MRI) coupled atmosphere–ocean general circulation model I (MRI-CGCM1). The results suggest that summer precipitation in central Asia decreased significantly as the Tibetan Plateau rose in height. Spring precipitation, however, increased during initial growth stages when the plateau height was up to 40% of its present-day height, and then decreased with further plateau growth. During the Tibetan Plateau uplift, the difference between precipitation and evaporation was minimal during spring. When the plateau attained a height exceeding 60% of its present height, relatively low precipitation but high evaporation in spring led to a lower amount of ground moisture. In the case of the high plateau, sensible heat flux during summer and fall largely exceeded latent heat flux. Change was particularly significant for cases when the plateau reached 40–60% of its present-day height. The duration of the predominant sensible heat flux became longer with the uplift of the Tibetan Plateau. The period in which latent heat exceeded sensible heat seems to have been restricted to winter and early spring. The numeric experiments suggest that a significant drying of central Asia corresponded to the period in which the Tibetan Plateau exceeded approximately half its present-day height.

Notizen: Abstract  The seismic slip that occurred during the 1999 Chi-Chi earthquake in Taiwan showed contrastive behaviors in different regions along the Chelungpu Fault: A large and smooth slip occurred in the north, while a relatively small slip associated with high-frequency seismic wave radiation occurred in the south. The core samples from shallow boreholes at northern (Fengyuan) and southern (Nantou) sites penetrating the seismic Chelungpu Fault were analyzed. The fault zones at the northern site are characterized by soft clayey material associated with clayey injection veins. This suggests that the fault zones were pressurized during ancient seismic slip events, and hence the elastohydrodynamic lubrication occurred effectively. In contrast, the fault rock from the southern site is old pseudotachylyte that has been shattered by repeated ancient seismic slip events. Statistical analysis of many pseudotachylyte fragments reveals that the degree of frictional melting tended to be low. In this case, the seismic slip is restrained by the mechanical barrier of a highly viscous melt layer. These contrastive fault rocks were produced by repeated ancient seismic slip events, but the two corresponding mechanisms of friction are likely to have also occurred during the 1999 Chi-Chi earthquake, thus causing the contrastive slip behaviors in the north and south.

Notizen: Abstract  The changes in the isotopic composition of, and the groundwater level in, the Choshui River alluvial fan near the ruptured Chelungpu Fault during and following the 1999 (Mw = 7.5) Chi-Chi earthquake in Taiwan are reported. Three aspects of the hydrological changes are noticed. First, following the Chi-Chi earthquake, the lower aquifers beneath the Choshui River fan showed a significant shift in isotopic composition towards that of the surface water in the Choshui River, suggesting enhanced exchanges of water between the river and the groundwater. Second, in some wells, water levels and isotopic compositions in different aquifers converged to the same respective values during the Chi-Chi earthquake, suggesting coseismic exchanges of water between the different aquifers, which implies enhanced permeability due perhaps to the fracturing and breaching of aquitards between the aquifers. Third, the pattern of the coseismic water-level response is distinctly different from that of the shift in the isotopic composition, suggesting that they were produced by different mechanisms.

Notizen: Abstract  Volcanic rocks consisting of adakite and Nb-enriched basalt are found in the early Devonian Tuoranggekuduke Group in the northern margin of the Kazakhstan-Junggar Plate, northern Xinjiang, northwest China. The geochemical characteristics of the andesitic and dacitic rocks in this area resemble that of adakites. The relatively high Al2O3, Na2O and MgO content and Mg♯ values indicate that the adakites were generated in relation to oceanic slab subduction rather than the partial melting of basaltic crust. A slightly higher SrI and a lower ɛNd(t = 375 Ma) compared to adakites of mid-oceanic ridge basalt (MORB) imply that slab sediments were incorporated into these adakites during slab melting. The Nb-enriched basalt lavas, which are intercalated in adakite lava suite, are silica saturated and are distinguished from the typical arc basalts by their higher Nb and Ti content (high field strength element enrichment). They are derived from the partial melting of the slab melt-metasomatized mantle wedge peridotite. Apparently, positive Sr anomalies and a slightly higher heavy rare earth element content in these adakites compared to their Cenozoic counterparts indicate that the geothermal gradient in the Paleo-Asian Oceanic subduction zone and the depth of the Paleo-Asian Oceanic slab melting are between those of their Archean and Cenozoic counterparts. The distribution of the adakites and Nb-enriched basalts in the northern margin of the Kazakhstan-Junggar Plate, northern Xinjiang, indicates that the Paleo-Asian Oceanic Plate subducted southward beneath the Kazakhstan-Junggar Plate in the early Devonian period.

Notizen: Carbon gases (methane, CH4, and carbon dioxide, CO2) were measured for the first time in sediments of the Lobo-Broa Reservoir, near São Carlos in São Paulo State, Brazil. It is believed these are the first measurements of this kind in any of the many reservoirs located in Brazil. Even though the Lobo-Broa Reservoir is classified as oligotrophic, the sediment gas concentrations were exceedingly high, ranging from 0.4–3 mmol L−1 for CH4 and 1–9 mmol L−1 for CO2. Both gases exceeded their in situ gas saturation values at these shallow water depths (7 m in central basin; 11 m at dam), resulting in numerous sediment bubbles. Organic matter was highly concentrated in the reservoir sediments, averaging 25.5% loss on ignition (LOI) (dam) to 26.9% LOI (central basin) for the 0–12 cm depth interval, with values as high as 29–30% LOI (12% organic carbon) in the surface 0–5 mm layer. The theoretical flux of dissolved pore water carbon gases to the sediment–water interface (SWI) averaged 3.4 mmol L−1 m−2 day−1 CH4 and 7.3 mmol L−1 m−2 day−1 CO2 for the surface 0–10 mm. From gas emission measurements at the water surface, it was calculated that 90% of CH4 is consumed either at the SWI or in the water column, resulting in a loss of 0.31 mmol L−1 m−2 day−1 of CH4 to the atmosphere. However, only 20% of the total CO2 gas transported across the water–atmosphere interface (36.3 mmol L−1 m−2 day−1, or 1600 mg CO2 m−2 day−1) was produced in the sediments. The remaining 80% of CO2 probably comes from other carbon sources. With CH4 oxidation in the aerobic water column, close to 30% of the carbon gas flux to the atmosphere could be accounted for by gas production of CO2 and CH4 in the sediments and their diffuse transport to the water column.

Notizen: The Volta River basin comprises ≈ 70% of mainland Ghana, being inhabited by a majority of the country's population. The purpose of this study was to analyse water and sediment samples at six locations in Volta Lake for residues of persistent organochlorine pesticides. Residues were extracted by use of two types of extractions, including a standardized solid phase extraction procedure for water samples and a Soxhlet extraction procedure for sediment samples. All samples were analysed by gas chromatography. Lindane and endosulfan were identified in concentrations ≤ 0.008 p.p.b. and 0.036 p.p.b., respectively, in water, and ≤ 2.3 p.p.b. and 0.36 p.p.b., respectively, in sediments. Dichlorodiphenyltrichloroethane and dichlorodiphenyldichloroethylene were also found in sediment samples (in concentrations ≤ 9.0 p.p.b. and 52.3 p.p.b., respectively). No significant contamination was noted in the lake. The distribution of pesticide residues in water and neighbouring sediment are briefly discussed. Different bioconcentration factors obtained in this study allowed the confirmation of the complex processes already reported in the literature regarding the partitioning of chemicals between sediment and water.

Notizen: Two aroid congeners, Alocasia odora and Alocasia cucullata, grow on Okinawa Island, Japan. Two floricolous species of Colocasiomyia alocasiae and Colocasiomyia xenalocasiae (Diptera: Drosophilidae), previously known to be specific pollinators for A. odora, were found pollinating A. cucullata. We collected the floral volatiles of A. odora and A. cucullata and compared them using gas chromatography and mass spectrometry because floral volatiles act as attractive signals for these pollinators. The volatile compositions detected were similar and dominated by methyl salicylate, 4,8-dimethyl-1,3,7-nonatriene, β-caryophyllene, bicyclogermacrene, methyl benzoate and α-humulene, which means it is likely that the flies cannot discriminate between the two plant species when they search for hosts. Interspecific hybridization did not occur when A. odora was hand pollinated with A. cucullata pollen, suggesting that the movement of flies from one host species to another will result in wastage of pollen. Adults of both Colocasiomyia flies emerged from A. cucullata inflorescences collected in the field, suggesting that their larvae can also develop on A. cucullata. We did not find any difference in larval performance of C. alocasiae on A. cucullata or A. odora. C. alocasiae does not appear to suffer any ill effects when using A. cucullata as a host plant. The partnership between A. cucullata and the two Colocasiomyia flies may be an example of exaptation, although other possibilities cannot be excluded.

Notizen: The effects of pollination competition between related species on pollen limitation, selfing ability and heterospecific incompatibility were studied in the alpine snowbed shrubs, Phyllodoce caerulea and Phyllodoce aleutica (Ericaceae) along local snowmelt gradients. The flowering season of these species highly overlapped and they shared the same method of pollination (via bumblebees). The floral density and nectar production were higher in P. caerulea in the early snowmelt habitat, but they were higher in P. aleutica in the late snowmelt habitat, reflecting the species-specific sensitivity to a short growing season. Bumblebee preference shifted from P. caerulea to P. aleutica along the snowmelt gradient, reflecting the changes in the relative reward level between the species. The extent of pollen limitation of P. caerulea was severe in the late snowmelt habitat, whereas that of P. aleutica was obvious in the early snowmelt habitat. A pollination experiment revealed that P. caerulea showed a consistently low selfing ability, whereas P. aleutica showed a high selfing ability in the early snowmelt habitat and shifted to an obligate outcrosser in the late snowmelt habitat. The frequency of interspecific bumblebee movement for P. caerulea from P. aleutica increased in the late snowmelt habitat. To the contrary, the frequency of interspecific movement for P. aleutica from P. caerulea decreased along the snowmelt gradient. P. caerulea did not indicate heterospecific incompatibility to P. aleutica pollen. In contrast, P. aleutica indicated heterospecific incompatibility to P. caerulea pollen, reflecting the high risk of receiving heterospecific pollen as a result of interspecific bumblebee movement. However, heterospecific compatibility of P. aleutica disappeared in the late snowmelt habitat, where the risk of heterospecific pollen receipt was low. Therefore, changes in interspecific bumblebee movement might have been responsible for the variation in heterospecific incompatibility among P. aleutica populations. The local snowmelt gradient creates diverse biological interactions and mating system evolution in the alpine ecosystem.

Notizen: Common wild rice (Oryza rufipogon Griff.), known as the ancestor of Asian cultivated rice (Oryza sativa L.), is the most important germplasm for rice improvement. The first male sterility gene was found in the wild rice, and introduced to the cultivated rice, which launched the fast development of the high-yielding hybrid rice. Other agronomically beneficial traits in the wild rice, such as rice tungro virus resistance, bacterial leaf blight (Xa21 gene) resistance and acid sulfate soil tolerance, have played important roles in rice breeding. China has the northernmost distribution area of wild rice possessing great genetic diversity. However, most of the populations of this species have disappeared in China over the last three decades, mainly caused by habitat loss, fragmentation and other human disturbances. Unfortunately, the decline of existing populations still continues. In the present study, we reviewed studies on genetic diversity and conservation of this wild rice in China, concentrating on population structure, pollen competition, pollen/gene flow from cultivated rice to wild rice, and ecological restoration in relation to in situ conservation. The relatively high genetic diversity of populations of O. rufipogon in China suggests that there is great value for conservation. Considerable gene flow from cultivated rice to wild rice may alter the genetic structure of natural populations of O. rufipogon and eventually lead to its genetic erosion. Pollen competition between wild and cultivated rice has caused a low rate of crop-to-wild gene flow, but it does not completely prevent gene flow from the crop. Effective isolation measures should be undertaken in the regions where in situ conservation of O. rufipogon is carried out. Reintroduction is an important alternative for the in situ conservation of wild rice species. As wild rice is an important genetic resource, both in situ and ex situ conservation strategies are needed.

Notizen: In current quantitative genetic models, the trade-off is viewed as a dynamic relationship between competing fitness components, which will evolve as a consequence of selection. Selection can change both the intercept and slope of the trade-off function, although it changes the former more strongly than the latter. We tested these predictions by examining two relationships among three clonal life-history traits (ramet number per plant and ramet production rate as a function of leaf number per ramet) in Iris pumila plants originating from an open and a shaded habitat. Our results support the hypothesis that the trade-off function will vary over environments, but not the expectation that the changes in the intercept are more likely than in the slope.

Notizen: Plantago asiatica L. (Plantaginaceae) is a perennial herb that is distributed over a wide range of habitats from exposed to shaded sites in lowlands to the subalpine zone in Japan. We investigated the patterns of biomass allocation and population structures based on the frequency distribution of individual plants in order to clarify the extent of plasticity in significant life-history traits and also population dynamics of this plantain species, which occurs under two contrasting light regimes—in exposed and shaded habitats—at Numappara, 1230 m a.s.l., Tochigi Prefecture, central Honshu. The plants at the shaded site allocated more biomass to leaves, but less to rhizomes than those at the exposed site. Increasing the biomass of the reproductive organs resulted in a reduction of the leaf and rhizome fractions. This trend is clearer in the shaded plants than in the exposed plants. In both exposed and shaded populations, the number of seedlings was greater in the first year, but the population structure was skewed more negatively in the second year during two consecutive study years. The possible effects of allocation traits of individuals on the population structures and regeneration mechanisms of P. asiatica at elevated habitats are discussed in terms of cyclic changes in population structure with the fluctuations of seeding activity over some years.

Notizen: Abstract  Although positive interactions among plants are believed to be common in primary succession, they have rarely been demonstrated on glacial moraines. In Patagonia, the prostrate shrub Empetrum rubrum is dominant in early succession in recently deglaciated valleys, eventually being replaced by the small tree Nothofagus antarctica. This study experimentally evaluates the effects of E. rubrum shrubs on density, biomass, growth and survival of N. antarctica seedlings. The initial density of the seedlings was significantly higher under the canopy of Empetrum than in open areas. A removal experiment was performed to evaluate the influence of Empetrum on survival and growth of seedlings that germinated naturally beneath the canopy of this species. The shrub cover was removed from half of a sample of randomly selected seedlings, and left intact above the remainder. One year later, seedlings with an intact cover of E. rubrum showed significantly higher survival, growth and leaf number than seedlings which had been exposed. The results suggest that the presence of E. rubrum facilitates the establishment of N. antarctica in post-glacial succession, mainly as a result of more favourable microclimatic conditions under the shrub canopy.

Notizen: Abstract  Cover provides shelter, food, nesting opportunities and protection from predators. The behavioural response of small mammals to reduced cover has been well documented. However, very little is known about the effect of cover on community and population dynamics. Australian small mammals generally inhabit extremely dynamic ecosystems, where cover and food supplies are greatly affected by fire. Species are described as early or late seral specialists, generally returning to a disturbed area once their habitat requirements are met. Habitat requirements have loosely been interpreted as cover and food supply, however, these factors are not mutually exclusive and few studies have attempted to determine the driving factors behind small mammal succession. In this study, we manipulated specific aspects of cover in the eucalypt forests of Fraser Island and show that the behaviour and population dynamics of small mammals were greatly affected. A reduction of cover from grass-trees (Xanthorrhoea johnsonii) did not affect small mammal species composition, however, the abundance and size structure distribution of the dominant species (Rattus fuscipes) decreased. Patch use by rodents also decreased after cover was reduced. Rattus fuscipes must trade-off remaining in an environment with increased risk of predation, or disperse to an area with greater cover but increased competition. Juveniles dominated (〉60%) populations of R. fuscipes after cover was reduced, however, size distributions of control sites were relatively more even (〈25% juvenile). While adult R. fuscipes are either killed by predators or disperse to other areas, juveniles that remained or immigrated to an area of reduced cover gained a selective advantage over those in control sites, because reduced competition with adults increased body condition of juvenile R. fuscipes.

Notizen: Abstract  We examine the role of the native fox, Pseudalopex culpaeus, as a frugivore and seed disperser in a semiarid thornscrub of Chile. We quantified the fruit and animal components in its diet versus the availability of fruits and small mammals in the field over a 2-year period (January 1998 through February 2000). We tested the legitimacy and effectiveness of foxes as dispersers by quantifying the percentages of seed viability and of germination of seeds that passed through fox gut versus those picked from plants. We also studied their efficiency as dispersers, monitoring the fate of seeds in faeces placed in the field. The highest frequencies of fruit consumption by foxes were observed when abundances of small mammal prey were 〈6 individuals per hectare, regardless of fruit abundance in the field. Thus, foxes consumed fruits as a supplementary food resource. Based on 326 faeces, the total number of fruits consumed was about 34 000 over the 2-year study period, and fruits from the alien shrub Schinus molle represented 98% of that total, with the native Porlieria chilensis a distant second. Germination and viability of defecated seeds of P. chilensis were reduced by 66% and 48%, respectively, in comparison to controls. In contrast, germination of seeds of S. molle increased by 50% and no effect on viability was observed. With regard to P. chilensis, foxes were legitimate (they defecated viable seeds), but ineffective (seeds in faeces had lower germination than those taken directly from parental plants and there was no seedling establishment in the field) and inefficient dispersers (seeds in faeces were deposited on microhabitats hostile to seed germination and seedling establishment). However, with regard to S. molle, foxes were legitimate, effective (seeds in faeces had higher germination than those taken directly from parental plants; there was germination but no establishment in the field), and efficient dispersers (over 41% of seeds were deposited on safe microsites). Thus, a native fox may be contributing to the spread of an alien shrub, co-opting existing community processes.

Notizen: Abstract  Habitat models are now broadly used in conservation planning on public lands. If implemented correctly, habitat modelling is a transparent and repeatable technique for describing and mapping biodiversity values, and its application in peri-urban and agricultural landscape planning is likely to expand rapidly. Conservation planning in such landscapes must be robust to the scrutiny that arises when biodiversity constraints are placed on developers and private landholders. A standardized modelling and model evaluation method based on widely accepted techniques will improve the robustness of conservation plans. We review current habitat modelling and model evaluation methods and provide a habitat modelling case study in the New South Wales central coast region that we hope will serve as a methodological template for conservation planners. We make recommendations on modelling methods that are appropriate when presence-absence and presence-only survey data are available and provide methodological details and a website with data and training material for modellers. Our aim is to provide practical guidelines that preserve methodological rigour and result in defendable habitat models and maps. The case study was undertaken in a rapidly developing area with substantial biodiversity values under urbanization pressure. Habitat maps for seven priority fauna species were developed using logistic regression models of species-habitat relationships and a bootstrapping methodology was used to evaluate model predictions. The modelled species were the koala, tiger quoll, squirrel glider, yellow-bellied glider, masked owl, powerful owl and sooty owl. Models ranked sites adequately in terms of habitat suitability and provided predictions of sufficient reliability for the purpose of identifying preliminary conservation priority areas. However, they are subject to multiple uncertainties and should not be viewed as a completely accurate representation of the distribution of species habitat. We recommend the use of model prediction in an adaptive framework whereby models are iteratively updated and refined as new data become available.

Notizen: Abstract  Intensive pastoralism with goats transforms semiarid thicket in the Eastern Cape, South Africa from a dense vegetation of tall shrubs to an open landscape dominated by ephemeral grasses and forbs. Approx. 800 000 ha of thicket (which prior to the introduction of goats had a closed canopy and a Portulacaria afra Jacq. component) have been transformed in this manner. Ecosystem C storage in intact thicket and loss of C due to transformation were quantified. Carbon storage in intact thicket was surprisingly high for a semiarid region, with an average of 76 t C ha−1 in living biomass and surface litter and 133 t C ha−1 in soils to a depth of 30 cm. Exceptional C accumulation in thicket may be a result of P. afra dominance. This succulent shrub switches between C3 and CAM photosynthesis, produces large quantities of leaf litter (approx. 450 g m−2 year−1) and shades the soil densely. Transformed thicket had approx. 35% less soil C to a depth of 10 cm and approx. 75% less biomass C than intact thicket. Restoration of transformed thicket landscapes could consequently recoup more than 80 t C ha−1.

Notizen: Abstract  Complex sociality is widespread in lizards, but the difficulties of directly observing social interactions in free-ranging snakes have precluded such studies for most snake species. However, a type of data already available from mark-recapture studies (dates of capture and recapture of individually marked animals) can reveal social substructure within snake populations. If individuals associate with each other in social groups, we expect synchrony in the dates of capture and recapture of those animals. A field study of turtle-headed sea snakes (Emydocephalus annulatus) in New Caledonia reveals exactly this phenomenon. For example, animals that were captured on the same day in one year often were recaptured on the same day the following year. Analysis rejects non-social interpretations of these data (such as spatial-temporal confounding in sampling, intrapopulation heterogeneity in cues for activity), suggesting instead that many individual sea snakes belong to ‘social’ groups that consistently move about together. The phenomenon of capture synchrony during mark-recapture studies can provide new insights into the occurrence and correlates of cryptic social aggregations.

Notizen: Abstract  The impact of feral Asian water buffalo (Bubalus bubalis) and season of fire on growth and survival of mature trees was monitored over 8 years in the eucalypt savannas of Kakadu National Park. Permanently marked plots were paired on either side of a 25-km-long buffalo-proof fence at three locations on an elevational gradient, from ridge-top to the edge of a floodplain; buffalo were removed from one side of the fence. All 750 trees ≥ 1.4 m height were permanently marked; survival and diameter of each tree was measured annually; 26 species were grouped into four eco-taxonomic groups. The buffalo experiment was maintained for 7 years; trees were monitored an additional year. Fires were excluded from all sites the first 3 years, allowed to occur opportunistically for 4 years and excluded for the final year. Fires were of two main types: low-intensity early dry season and high-intensity late dry season. Growth rates of trees were size-specific and positively related to diameters as exponential functions; trees grew slowest on the two ends of the gradient. Eucalypt mortality rates were 1.5 and 3 times lower than those of pantropics and of arborescent monocots, respectively, but the relative advantage was lost with fires or buffalo grazing. Without buffalo grazing, ground level biomass was 5–8 t ha−1 compared with 2–3 t ha−1, within 3 years. In buffalo-absent plots, trees grew significantly slower on the dry ridge and slope, and had higher mortality across the entire gradient, compared with trees in buffalo-present plots. At the floodplain margin, mortality of small palms was higher in buffalo-present sites, most likely due to associated heavy infestations of weeds. Low-intensity fires produced tree growth and mortality values similar to no-fire, in general, but, like buffalo, provided a ‘fertilization’ effect for Eucalyptus miniata and Eucalyptus tetrodonta, increasing growth in all size classes. High-intensity fires reduced growth and increased mortality of all functional groups, especially the smallest and largest (〉35 cm d.b.h.) trees. When buffalo and fires were excluded in the final year, there were no differences in growth or mortality between paired sites across the environmental gradient. After 8 years, the total numbers of trees in buffalo-absent plots were only 80% of the number in buffalo-present plots, due to relatively greater recruitment of new trees in buffalo-present plots; fire-sensitive pantropics were particularly disadvantaged. Since the removal of buffalo is disadvantageous, at least over the first years, to savanna tree growth and survival due to a rebound effect of the ground-level vegetation and subsequent changes in fire-vegetation interactions, process-orientated management aimed at reducing fuel loads and competitive pressure may be required in order to return the system to a previous state. The ‘footprint’ of 30 years of heavy grazing by buffalo has implications for the interpretation of previous studies on fire-vegetation dynamics and for current research on vegetation change in these savannas.

Notizen: This study was carried out to investigate the possibility of using the limnological characteristics of non-perennial reservoirs in Sri Lanka for the future management of culture-based fisheries. Forty-five reservoirs were randomly selected to study their limnology, out of which 32 were stocked with fish fingerlings of Chinese and Indian carps, tilapia and freshwater prawn at stocking densities ranging from 218–4372 fingerlings ha−1. Of these, 23 reservoirs were harvested at the end of the culture period (6–10 months). Thirteen limnological parameters were measured during the water retention period of each of the 45 reservoirs between November 2001 and January 2004. The mean values of the limnological parameters were used to ordinate the reservoirs through principal component analysis. Ordination showed a productivity gradient among reservoirs where Secchi disc depth, total phosphorus, chlorophyll-a, inorganic turbidity and organic turbidity were identified as key factors. The total fish yield of culture-based fisheries was positively correlated to the scores of the first principal component axis. This study reveals that it is possible to classify non-perennial reservoirs in Sri Lanka based on the above limnological parameters in order to develop culture-based fisheries and that they could be applicable in comparable water bodies elsewhere in the tropics.

Notizen: Water samples for bacterial analyses were taken, when possible, at 41 sites in Lebanon and Syria in the El-Kabir River watershed. Samples were analysed for total coliform (TC), faecal coliform (FC) and faecal streptococcus. The Lebanese samples also were analysed for the presence of sulphate-reducing bacteria. The TC and FC concentrations were extremely high throughout the watershed, rendering the water unfit for any human uses. The origin of the bacteria is the untreated sewage waste from the numerous settlements situated throughout the watershed. This primary origin is supported by high ratios of FC/faecal streptococcus, although impacts from animal wastes also were observed. The bacterial levels were higher in summer than in winter, indicating a high winter river flow that dilutes a relatively constant source of human sewage discharged to the system. Spring waters also exhibited elevated levels of bacteria, implicating surface land use and waste disposal practices upstream of the springs. The data clearly shows that human health is at a high risk and that strategies for improving water quality and protecting spring water must be expeditiously implemented.

Notizen: Abstract  We measured the plasticity of the response of photosynthesis to nutrient supply in seedlings of the dominant four conifer and broadleaved angiosperm tree species from an indigenous forest in South-westland, New Zealand. We hypothesized that the response of conifers to differing nutrient supply would be less than the response for the angiosperms because of greater adaptation to low fertility conditions. In Prumnopitys ferruginea (D. Don) de Laub. the maximum velocity of electron transport, Jmax, doubled with a 10-fold increase in concentration of nitrogen supply. In Dacrydium cupressinum Lamb. the maximum velocity of carboxylation, Vcmax, doubled with a 10-fold increase in phosphorus supply. In contrast, photosynthetic capacity for the angiosperm species Weinmannia racemosa L.f. was affected only by the interaction of nitrogen and phosphorus and photosynthetic capacity of Metrosideros umbellata Cav. was not affected by nutrient supply. The response of the conifers to increasing availability of nutrient suggests greater plasticity in photosynthetic capacity, a characteristic not generally associated with adaptation to soil infertility, thus invalidating our hypothesis. Our data suggest that photosynthetic response to nutrient supply cannot be broadly generalized between the two functional groups.

Notizen: Abstract  Although forested habitats in eastern Australia have attracted significant conservation-related research, this work has focused strongly on endothermic vertebrates. Threatened reptile taxa have received less attention, but information on their habitat requirements should be central to management planning. The arboreal elapid snake Hoplocephalus stephensii is largely restricted to remnant forests in eastern Australia, and is listed as a threatened species under wildlife legislation. We collated 84 records of the current New South Wales geographical distribution of H. stephensii, and compared attributes of these locations to those of randomly chosen points within the same forests, in adjacent forests, in timber plantations and on freehold land across the geographical range of the taxon. Data on climatic and topographic characteristics of these sites were obtained from Geographic Information Systems databases and entered into a principal components analysis. Unsurprisingly, locations where snakes were recorded differed from the random sites in several respects (e.g. rainfall, elevation, seasonality of precipitation). Within a given forest, H. stephensii was generally found in areas similar to randomly chosen points. Comparison of vegetation communities used with those available within forests provided no evidence for active habitat selection. Comparisons of Geographic Information Systems-derived data for snake-collection localities along roads versus those within the forest revealed significant biases, and we warn that such methodological errors could generate spurious conclusions about non-random habitat use by threatened species. In combination with previous data from radio-tracking, we conclude that although H. stephensii is highly specialized in its arboreality and dependence upon hollow trees, its broad tolerance with respect to other factors (climatic conditions, vegetation communities, food types, etc.) allows populations to persist so long as large areas of forest with high numbers of hollow-bearing trees are available. These requirements are similar to those of many other components of the Australian forest fauna. Thus, the findings of this study support the idea that the same kinds of management programmes can effectively conserve a wide range of taxa, if such programmes protect critical habitat components at suitable spatial scales.

Notizen: Abstract  Exotic plant invasions are a significant problem in urban bushland in Sydney, Australia. In low-nutrient Hawkesbury Sandstone communities, invasive plants are often associated with urban run-off and subsequent increases in soil nutrients, particularly phosphorus. Fire is an important aspect of community dynamics in Sydney vegetation, and is sometimes used in bush regeneration projects as a tool for weed control. This study addressed the question: ‘Are there differences in post-fire resprouting and germination of native and exotic species in nutrient-enriched communities, compared with communities not disturbed by nutrient enrichment?’ We found that in non-enriched areas, few exotic species emerged, and those that did were unable to achieve the rapid growth that was seen in exotic plants in the nutrient-enriched areas. Therefore, fire did not promote the invasion of exotic plants into areas that were not nutrient-enriched. In nutrient-enriched areas after fire, the diversity of native species was lower than in the non-enriched areas. Some native species were able to survive and compete with the exotic species in terms of abundance, per cent cover and plant height. However, these successful species were a different suite of natives to those commonly found in the non-enriched areas. We suggest that although fire can be a useful tool for short-term removal of exotic plant biomass from nutrient-enriched areas, it does not promote establishment of native species that were not already present.

Notizen: Abstract  Large predators play important ecological roles, but often are sensitive to habitat changes and thus are early casualties of habitat perturbation. Pythons are among the largest predators in many Australian environments, and hence warrant conservation-orientated research. Carpet pythons (Morelia spilota imbricata) have declined across much of south-western Australia presumably because of habitat clearance and degradation. Information on habitat use, home range sizes and movements is needed to plan for the conservation of this important predator. We studied pythons at two study sites (Garden Island and Dryandra Woodland) with markedly different climates, habitat types and disturbance histories. We surgically implanted radio-transmitters in 91 pythons and tracked them for periods of 1 month to 4 years. Dryandra pythons remained inactive inside tree hollows during cooler months (May–September), whereas some (especially small) pythons on Garden Island continued to move and feed. Overall weekly displacements (mean = 100–150 m) were similar at the two study sites and among sex/age classes, except that reproductive females were sedentary during summer while they were incubating eggs. Home ranges averaged 15–20 ha. Adult male pythons had larger home ranges than adult females at Dryandra, but not at Garden Island. Radio-tracked snakes at Dryandra exhibited high site fidelity, returning to previously occupied logs after long absences and reusing tree hollows for winter shelter. Many of the logs used by snakes had been felled during plantation establishment 〉70 years ago, with little subsequent regeneration of source trees. In contrast, Garden Island snakes usually sheltered under dense shrubs. Habitat usage was similar among different sex/age classes of snakes at each site, except that juvenile pythons were more arboreal than adults. Although carpet pythons demonstrate great flexibility in habitat use, certain habitat elements appear critical for the persistence of viable populations. Fire plays a central role in this process, albeit in complex ways. For example, low-intensity fires reduce the availability of hollow logs on the ground at Dryandra and fail to regenerate shrub thickets required by prey species. Paradoxically, high-intensity fires stimulate shrub thickets and fell trees creating new logs – but might also threaten overwinter trees. Thus, the impact of disturbances (such as wildfires) on the viability of python populations will be mediated in complex ways by alteration to important microhabitats such as vegetation cover or log availability. At Dryandra, landscape management should include occasional fire events to generate new logs as well as shrub thickets used by prey. Strategic burning may also be required at Garden Island to regenerate some vegetation communities.

Notizen: Abstract  The intensity of seed predation the invasive tropical legume Leucaena leucocephala by the bruchid Acanthoscelides macropthalmus was investigated in south-eastern Queensland, Australia. The number of seeds damaged by A. macropthalmus as a proportion of total seeds available was found to increase the longer the pods remained on the tree. Seed predation ranged from a mean of 10.75% of seeds on pods that remained on the plant for 1 month and increased to 53.54% for pods that remained of the plant for 4 months. The low bruchid populations at high pod densities results in ‘predator satiation’. However, pods dehisce over time and the proportion of pods available over time to the bruchid correspondingly declines. By the time bruchid densities build up, most pods have dehisced and the seeds consequently escape predation. As a result the number of seeds lost to bruchid damage increases only marginally over time. Despite the levels of seed predation observed over the course of the study, the number of seeds in the soil seedbank almost doubled over time increasing from 8.5 seeds m−3 to 15.5 seeds m−3 over a 4-month period. Levels of seed predation and addition of seeds to the soil seedbank were not correlated. The taxonomic (subspecies) status and apparency of host plants as measured by plant and patch traits (average plant height, density of podding plants and patch size) did not influence levels of seed predation. Pre-dispersal seed predation studies need to take into account the pod/seed retention behaviour of the plant. The ability of the bruchid to regulate the invasiveness of Leucaena through influencing its demography is likely to be diminished if the insect populations cannot increase rapidly enough to use the seeds before pod dehiscence.

Notizen: Abstract  The White-bellied Sea-Eagle Haliaeetus leucogaster (Accipitridae) is widespread within Australia. However, in a number of states it is thought to be declining locally in response to human induced disturbance. Here we analyse the Australian Bird Atlas data to identify the extent and pattern of change in range and density of the species between three Atlas Periods (1901–1976, 1977–1981 and 1998–2001) using a new standardized frequency measure, the Occupancy Index (OI) for 1° blocks (approx. 100 km2) across the continent. At the continental scale, there was no significant difference in the spatial extent of occupancy between Atlas Periods. However, there were considerable changes in frequency and range extent between defined regions, and there were distinct differences in the pattern of change in OI between coastal and inland blocks over time. Coastal blocks showed much more change than inland blocks, with a clear increase in the use of coastal blocks, accompanied by a decrease in inland blocks, during the 1977–1981 Atlas Period, relative to both other Atlas Periods. While there were slight (and not statistically significant) trends for OI to increase in areas containing dams, and to decrease in urbanized coastal areas, the over-riding factor associated with distributional shifts and frequency changes was apparently climatic fluctuation (the 1977–1981 period showing the influence of El Niño associated drought). Within this study, the impression of abundance was strongly dependent on both the temporal and spatial scale of analysis. This highlights the importance of large-scale analysis in interpreting change in distribution and abundance of widespread species.

Notizen: Platanthera lacera (Orchidaceae) is a moth-pollinated, loess prairie orchid producing a raceme of one to many whitish-green flowers. Field studies on a western Illinois population found the crepuscular visiting noctuid moth, Anagrapha falcifera (Noctuidae), to be the most frequent pollinator with occasional visits from Allagrapha aerea (Noctuidae). Visitation rates, assessed by removal of at least one pollinium, were relatively high (84.9%) and fruit production on experimentally outcrossed flowers (94.4%) was higher than open-pollinated plants (71.4%). Experimental pollination showed P. lacera to be highly self-compatible (94.1%) with a low level of autogamy (8.2%). Measurements taken from 598 spurs on 44 plants indicated that nectar spur length varied significantly among plants (10.9–17.1 mm, mean 14.3 mm), but was not under selective pressure from visitation by An. falcifera (mean proboscis length 11.1 mm). The absence of selective pressure on nectar spur length is likely to be explained by occasional pollinating visits from Al. aerea (proboscis length 18 mm) and a limited amount of autogamy. Electrophoretic analysis of 12 enzymes revealed seven polymorphic loci. Mean levels of heterozygosity were He = 0.3384, Ho = 0.3229 and F = 0.0458, indicating that P. lacera is primarily an outcrossing species dependent on noctuid moth pollination.

Notizen: Genetic variations of the facultatively autogamous species Ranunculus silerifolius, which show intraspecific chromosomal polymorphisms (Karatsu-cytotype, Matsuyama-cytotype, Mugi-cytotype and Otaru-cytotype), were investigated in 95 populations using allozymic analysis. Sixteen loci of nine enzyme systems were resolved. Three loci were monomorphic for all populations. On average, 26% of the loci were polymorphic; the 16 loci resolved gave a total of 49 alleles with a mean number of 1.29 alleles per locus. We could not detect any genetic differentiation estimated from allozymic polymorphisms among cytotypes distinguished by chromosome structures in this species. The average genetic distance between populations was large (D = 0.129), indicating a high level of genetic differentiation and a low level of gene flow (Nm = 0.171) among the populations, whereas that between cytotypes was very small (D = 0.008), possibly a result of the relatively short period of time after the occurrence of cytotypes. The overall levels of genetic variation were low as with other facultatively autogamous species. The gene differentiation coefficient among populations, GST, was high (0.579), which probably reflected the inbreeding in this species. The absence of a correlation between genetic distance and geographic distance may also have resulted from inbreeding.

Notizen: Abstract  The flowers of two species of threatened New Zealand mistletoes (Peraxilla tetrapetala and Peraxilla colensoi, Loranthaceae) have explosive buds that do not open unless force is applied by birds or two species of native short-tongued bees. Opened flowers are visited by a variety of birds and insects. Although both species of Peraxilla conform to a pollination syndrome of ornithophily, bees may be effective alternative pollinators. We investigated the effectiveness of bees and birds as pollinators of P. colensoi at one site and P. tetrapetala at two sites in the South Island. Bees and other insects outnumbered birds as flower visitors at all three sites. By excluding birds with wire cages, we showed that two bee species regularly open flowers of P. tetrapetala, but only rarely open flowers of P. colensoi. Few pollen grains were deposited when either birds or bees opened buds, so opening buds was not by itself sufficient for adequate pollination. Instead, pollen continued to accumulate over the next 6 or 7 days, even inside cages that excluded birds. Both populations of P. tetrapetala were regularly pollen-limited, but in different ways. At Ohau, opened flowers gained enough pollen to produce seeds, but many buds were not opened and hence failed to set seed. In contrast, at Craigieburn, nearly all buds were opened, but many of these did not receive enough pollen. These results demonstrate that native bees can partially replace birds as pollinators of mistletoes, despite their apparent ornithophilous syndrome. Ongoing reductions in New Zealand forest bird numbers means that the service bees provide may be important for the long-term future of these plants.

Notizen: Abstract  This study investigated the structure and properties of a tropical stream food web in a small spatial scale, characterizing its planktonic, epiphytic and benthic compartments. The study was carried out in the Potreirinho Creek, a second-order stream located in the south-east of Brazil. Some attributes of the three subwebs and of the conglomerate food web, composed by the trophic links of the three compartments plus the fish species, were determined. Among compartments, the food webs showed considerable variation in structure. The epiphytic food web was consistently more complex than the planktonic and benthic webs. The values of number of species, number of links and maximum food chain length were significantly higher in the epiphytic compartment than in the other two. Otherwise, the connectance was significantly lower in epiphyton. The significant differences of most food web parameters were determined by the increase in the number of trophic species, represented mainly by basal and intermediate species. High species richness, detritus-based system and high degree of omnivory characterized the stream food web studied. The aquatic macrophytes probably provide a substratum more stable and structurally complex than the sediment. We suggest that the greater species richness and trophic complexity in the epiphytic subweb might be due to the higher degree of habitat complexity supported by macrophyte substrate. Despite differences observed in the structure of the three subwebs, they are highly connected by trophic interactions, mainly by fishes. The high degree of fish omnivory associated with their movements at different spatial scales suggests that these animals have a significant role in the food web dynamic of Potreirinho Creek. This interface between macrophytes and the interconnections resultant from fish foraging, diluted the compartmentalization of the Potreirinho food web.

Notizen: Humboldt Lake, a hypertrophic prairie lake typical of many found on the Great Plains of North America, is usually ice-covered from early November to about mid-May. The lake is an important recreational fishery, now mainly stocked with walleye. It has a high potential risk of experiencing fish kills because of the very large cyanobacterial blooms that develop in it, the high rates of algal and bacterial production and the high concentrations of ammonia (NH3-N) and dissolved organic matter. Following the collapse of cyanobacterial blooms, shallow prairie lakes are known to undergo periods of anoxia that can lead to summer fish kills. In some of the lakes, anoxia forms during the long period of ice cover, causing winter fish kills. Two years of seasonal and diel data (total phosphorus, dissolved oxygen (DO), NH3-N and chlorophyll-a concentrations, and bacterial production) were analysed in this study to assess why significant fish kills did not occur during this period or during the ≈ 30 years of records from Saskatchewan Environment. Humboldt Lake did not become anaerobic, either following the collapse of the cyanobacterial bloom or under ice cover, indicating that the oxygen (O2) influx (strong mixing) and production processes were greater than the microbial and chemical O2 demands, both over seasonal and diel time scales. Several published risk threshold criteria to predict the probability of summer and/or winter fish kills were applied in this study. The threshold criteria of maximum summer chlorophyll and maximum winter NH3-N concentrations indicated that a summer fish kill was unlikely to occur in this hypertrophic prairie lake, provided its water quality remained similar to that during this study. Similarly, the threshold criteria of initial DO storage before ice cover and the rate of O2 depletion under ice cover also indicated a winter fish kill was unlikely. However, recent development in the watershed might have resulted in significant water quality deterioration and the winter fish kill that occurred in 2005.

Notizen: An assessment has been made of the stock conditions of five major component fishery species (Chrysichthys nigrodigitatus, Chrysichthys auratus, Hemisynodontis membranaceus, Oreochromis niloticus and Schilbe intermedius) exploited with illegal purse-seine (winch-net) gear in the Yeji sector of Lake Volta, Ghana. Chrysichthys nigrodigitatus was clearly found to be overexploited, but the others were being exploited near to, or under, optimum harvest levels. All five species were harvested at an inappropriate age-at-first-capture of ≈ 6 months, suggesting overfishing of young fishes. Consequently, the computed Lm:L∞ ratios were 〉 0.64. For most fish species, such a ratio implies their exploitation when at early maturity and at very small sizes. The estimated range of mesh sizes in the cod-ends was far lower (5–8 mm) than the legal mesh size of 25 mm, calling for urgent enforcement of rules and regulations. Single-species yield-per-recruit analyses indicated that yields could be improved by the reduction in the current fishing effort. As the fishery of the lake is not segmented to allow fish to be taken by the illegal small-mesh purse seines, studies on the interactions between the different fishery sectors need to be undertaken, alongside the proposed ban of the gear as enshrined in the Fisheries Law of Ghana.

Notizen: In order to assess the quality of the waters of the El-Kabir River, which forms the border between Lebanon and Syria, water samples were collected for phosphorus (P) and nitrogen analyses at 39 sample stations in the river watershed (18 in Syria, 21 in Lebanon). These samples were collected on the main stem and three major tributaries (Nahr al-Arous and Nahr Nasrive in Syria, Chadra River in Lebanon). Three major springs also were sampled. The sampling was carried out in September 2001, and January, April and August 2002. Nutrient analyses were carried out on samples taken in September 2001, January and April 2002 in Syria, and in September 2001 and August 2002 in Lebanon. The P concentrations were extremely high throughout the watershed, as were the ammonia-nitrogen and nitrate-nitrogen concentrations, indicating extensive pollution. Although the nitrite-nitrogen concentration was relatively low, it is at the upper end of what might be considered normal, thereby perhaps being indicative of some anthropogenic sources. The spring waters were found to be polluted by nutrients. The nutrient sources contributing to the river pollution were mainly from piped, direct sewage discharges from the many settlements throughout the basin. These were supplemented by diffuse sources directly from agricultural fertilizer use and from the indiscriminate disposal of solid wastes into the river and on the stream banks and lands adjacent to the roads of the watershed.

Notizen: Thirty-nine sampling sites were selected in the El-Kabir River watershed, including 18 in Syria and 21 in Lebanon. Three major tributaries, the Nahr al-Arous and the Nahr Nasrive in Syria, and the Chadra River in Lebanon, were included in the site selection, together with Wadi el-Aatchane and Wadi Khaled. Instrumental measurements for temperature, specific conductivity (Sp. Cond.), dissolved oxygen (DO) and pH were taken directly in the water at each site visit. Measurements were taken in both countries in May 2001, January, April and August 2002, and there was an additional sampling in Lebanon during September 2001. The interpretation of the data led to some specific conclusions on the conditions in the watershed. The waters of the El-Kabir River are derived almost exclusively from ground water, with many significant springs functioning throughout the year. The water that flows rapidly through the system is well-mixed and consistent in its major characteristics. The DO concentration 〉 5 mg L−1, averaging 8.53 mg L−1 (three DO values 〈 5 mg L−1 were observed, all at the same spring). Some variability in water character was observed for Sp. Cond.; these differences could be related to the spring-source waters originating in limestone or basaltic terrain. Furthermore, an increase in Sp. Cond. in the lower reaches of the river might be related to salinization, resulting from surface water and near-surface ground water withdrawals for anthropogenic use, particularly irrigation.