ALBERT

Description: 〈b〉Thermogeodynamic manifestations in the Caucasus and their genesis〈/b〉〈br〉 G. E. Gugunava, J. K. Kiria, and T. B. Bochorishvili〈br〉 eEarth Discuss., 4, 77-89, doi:10.5194/eed-4-77-2009, 2009〈br〉 〈b〉Publication in eE not foreseen〈/b〉 (discussion: closed, 2 comments)〈br〉 In the work two aspects of thermal character are considered: first of all this is the connection of subduction phenomena with thermal life of the Caucasus on the basis of over interpreted data of magnetotelluric sounding, and secondly, origin of thermostressed condition of the Caucasus and its geological aspects which is manifested in the following: 〈br〉〈br〉 1. in the zones of anomalous thermodisplacements thermofaults should occur (Le Pishon et al., 1977). These thermofaults are in good correlation with deep faults which are distinguished by geological and seismic methods, these thermofaults may be earthquake sources (Spitak, Racha, etc. earthquakes), also may be channels through which magma derivates (giving mineral deposits) may penetrate on surface (Gugunava and Gijeishvili, 1989); 〈br〉〈br〉 2. in the body of sedimentary complex thermostressed seals and seal failures occur, which are apparently traps for oil-gas fluids. Good correlation of thermodense anomalies with oil deposits of the Caucasus is shown (Alexidze et al., 1985; Gugunava, 1980). 〈br〉〈br〉 Everything above mentioned was carried out within frames of stationary thermal model which did not allow us to reveal time characteristics of interconnection of geological medium and thermal field. 〈br〉〈br〉 Now investigations are being carried out within the frames of stationary thermal model and its interconnection with geological environment.

Description: 〈b〉Morphology of the pore space in claystones – evidence from BIB/FIB ion beam sectioning and cryo-SEM observations〈/b〉〈br〉 G. Desbois, J. L. Urai, and P. A. Kukla〈br〉 eEarth, 4, 15-22, doi:10.5194/ee-4-15-2009, 2009〈br〉 The morphology of pore space has a strong effect on mechanical and transport properties of mudrocks and clay-rich fault gouge, but its characterization has been mostly indirect. We report on a study of Boom clay from a proposed disposal site of radioactive waste (Mol site, Belgium) using high resolution SEM at cryogenic temperature, with ion beam cross-sectioning to prepare smooth, damage free surfaces. Pores commonly have crack-like tips, preferred orientation parallel to bedding and power law size distribution. We define a number of pore types depending on shape and location in the microstructure: large jagged pores in strain shadows of clastic grains, high aspect ratio pores between similarly oriented phyllosilicate grains and crescent-shaped pores in saddle reefs of folded phyllosilicates. 3-D reconstruction by serial cross-sectioning shows 3-D connectivity of the pore space. These findings offer a new insight into the morphology of pores down to nano-scale in comparison to traditional pore size distributions calculated from mercury Injection experiments, explain slaking of clays by successive wetting and drying and provide the basis for microstructure-based models of transport in clays.

Description: 〈b〉Holocene evolution and sedimentation rate of Alikes Lagoon, Zakynthos island, Western Greece: preliminary results〈/b〉〈br〉 P. Avramidis and N. Kontopoulos〈br〉 eEarth, 4, 23-29, doi:10.5194/ee-4-23-2009, 2009〈br〉 In the present study we present preliminary results from Alikes lagoon in Zakynthos island, an area that is one of the most seismically active regions of Greece. In order to estimate – interpret the Holocene evolution of the area and to reconstruct the palaeoenvironmental changes, we based on data derived from a 21 m sediment core. Sediment types, structure, colour, as well as contact depths and bed characteristics were recorded in the field. Standarised sedimentological analysis was carried out, on 46 samples including grain size analysis, calculation of moment measures, and micro- and molluscan fossils of 17 selected samples. Moreover, radiocarbon age determinations have been made on individual 〈i〉Cardium〈/i〉 shells from two horizons and whole – core Magnetic Susceptibility (MS) measurements were taken. The interpretation of depositional environments suggests a coastal environment (restricted-shallow) with reduced salinity such as a lagoon margin and in a tidal flat and/or marsh particularly. The maximum age of the studied sediments is about 8500 BP. The rate of sedimentation between 8280 BP while 5590 BP was 5.3 mm/yr and between 5590 BP and modern times is on the order of 1.03 mm/yr. These sedimentation rates results are similar to other coastal areas of western Greece.

Description: 〈b〉Foraminiferal response to environmental changes in Kiel Fjord, SW Baltic Sea〈/b〉〈br〉 A. Nikulina, I. Polovodova, and J. Schönfeld〈br〉 eEarth, 3, 37-49, doi:10.5194/ee-3-37-2008, 2008〈br〉 The living benthic foraminiferal assemblages in Kiel Fjord (SW Baltic Sea) were investigated in the years 2005 and 2006. The faunal studies were accomplished by geochemical analyses of surface sediments. In general, sediment pollution by copper, zinc, tin and lead is assessed as moderate in comparison with levels reported from other areas of the Baltic Sea. However, the inner Kiel Fjord is still exposed to a high load of metals and organic matter due to enhanced accumulation of fine-grained sediments in conjunction with potential pollution sources as shipyards, harbours and intensive traffic. The results of our survey show that the dominant environmental forcing of benthic foraminifera is nutrients availability coupled with human impact. A comparison with faunal data from the 1960s reveals apparent changes in species composition and population densities. The stress-tolerant species 〈i〉Ammonia beccarii〈/i〉 invaded Kiel Fjord. 〈i〉Ammotium cassis〈/i〉 had disappeared that reflects apparently the changes in salinity over the last 10 years. These changes in foraminiferal community and a significant increase of test abnormalities indicate an intensified environmental stress since the 1960s.

Description: 〈b〉Palaeomagnetic investigations of sediments cores from Axios zone (N. Greece): implications of low inclinations in the Aegean〈/b〉〈br〉 E. Aidona, D. Kondopoulou, R. Scholger, A. Georgakopoulos, and A. Vafeidis〈br〉 eEarth, 3, 7-18, doi:10.5194/ee-3-7-2008, 2008〈br〉 Sediment cores from 13 deep boreholes (1–4.1 km) distributed within Axios zone in Northern Greece have been studied by means of palaeomagnetism. Both low field magnetic susceptibility and intensity of the natural remanent magnetization (NRM) indicate rather weakly magnetised materials. A set of 390 samples have been subjected to thermal and alternative field demagnetization. Isothermal remanent magnetization (IRM) acquisition curves and thermomagnetic analysis suggest the dominance of magnetite. Thin sections from 30 selected samples were studied in order to more precisely characterise their magnetic mineralogy. This investigation also reveals the presence of magnetite and pyrite in framboidal form. An attempt to re-orient some of the samples was partially successful by using the viscous component and the anisotropy method. These techniques were applied in order to correct the palaeomagnetic directions due to the orientation ambiguity of the core samples. The corrected mean direction converges towards an eastward value, in agreement with the overall pattern of the onshore results from previous investigations in the study area. 〈br〉〈br〉 Finally, the observed inclinations of characteristic remanences in these rocks are much lower than the expected ones but converge with those obtained from formations on land.

Description: 〈b〉Zoogeography of the bottom Foraminifera of the West-African coast〈/b〉〈br〉 V. Mikhalevich〈br〉 eEarth Discuss., 3, 1-9, doi:10.5194/eed-3-1-2008, 2008〈br〉 〈b〉Revised manuscript has not been submitted〈/b〉 (discussion: closed, 8 comments)〈br〉 The sediment samples from the continental shelf of West-Equatorial Africa (from the Strait of Gibraltar to the Niger estuary), depths ranging from 0 to 69 m were found to contain 176 bottom foraminiferal species. For the majority of them (126 species), their areas of occurrences were mapped and the peculiar features of the geographical range and distribution were studied. The species natural habitats were established based on the taxonomical revision of the species in study all over the World Ocean based on the collections of the Zoological Institute RAS and wide literary data. The method of perforated cards was used to mark the geographical locations of all of the species studied. In order to establish the species geographic zonal distribution (together with their depth habitat) the five characteristic groups of the species were separated: 1. pan-oceanic (cosmopolitan), 2. widely spread tropical-boreal, 3. tropical-law boreal, 4. tropical-subtropical, 5. tropical. The percent of the species of each group among the species composition was established for the fauna of each station and for the whole region.

Description: 〈b〉Geometry of the Turkey-Arabia and Africa-Arabia plate boundaries in the latest Miocene to Mid-Pliocene: the role of the Malatya-Ovacık Fault Zone in eastern Turkey〈/b〉〈br〉 R. Westaway, T. Demir, and A. Seyrek〈br〉 eEarth, 3, 27-35, doi:10.5194/ee-3-27-2008, 2008〈br〉 We suggest a working hypothesis for the geometry of the strike-slip faults that formed the boundaries between the Turkish, African and Arabian plates in the latest Miocene to Mid-Pliocene (LMMP), between ~7–6 Ma and ~3.5 Ma. This geometry differed significantly from the modern geometry; the northern Dead Sea Fault Zone (DSFZ) was located east of its present line and the TR-AR boundary was formed by the Malatya-Ovacık Fault Zone (MOFZ), located well north of the modern East Anatolian Fault Zone (EAFZ). The MOFZ is potentially the most problematic aspect of such a scheme, given the dramatically different interpretations of it that have been proposed. However, the presently-available evidence, albeit limited, is consistent with our proposed interpretation. Significant differences between the proposed LMMP fault geometry and the modern geometry include, first, the transtensional geometry of the MOFZ, the modern EAFZ being typically a left-lateral transform fault zone but with localized transpression. Second, the MOFZ slip rate was much lower than the ~9–10 mm a〈sup〉−1〈/sup〉 EAFZ slip rate; it is estimated as ~2–3 mm a〈sup〉−1〈/sup〉, having produced no more than ~8 km of slip during its approximately three million year long activity. The Euler vector is tentatively inferred to have involved relative rotation between the Turkish and Arabian Plates at ~0.85±0.15° Ma〈sup〉−1〈/sup〉 about a pole at ~37.75±0.15° N, ~38.8±0.3° E. Third, unlike at present, there was no throughgoing linkage of left-lateral faulting between the LMMP DSFZ and the MOFZ; instead, the DSFZ terminated northward, and the MOFZ terminated southward, in a zone of localised crustal shortening adjoining the suture of the former Neotethys Ocean in the Kahramanmaraş-Pazarcık region of SE Turkey. The different motion of the Turkish plate relative to Arabia, and, thus, relative to Eurasia, means that senses and rates of crustal deformation can be expected to have been different during the LMMP phase from at present, throughout the eastern Mediterranean region.

Description: 〈b〉Late Pleistocene palaeoproductivity patterns during the last climatic cycle in the Guyana Basin as revealed by calcareous nannoplankton〈/b〉〈br〉 G.-E. López-Otálvaro, J. A. Flores, F. J. Sierro, I. Cacho, J.-O. Grimalt, E. Michel, E. Cortijo, and L. Labeyrie〈br〉 eEarth, 4, 1-13, doi:10.5194/ee-4-1-2009, 2009〈br〉 Variations in the assemblage and abundance of coccoliths reveal changes in oceanic and atmospheric dynamics in the Guyana Basin over the last climatic cycle, mainly linked to latitudinal variations in the ITCZ (Intertropical Convergence Zone). Records of the N ratio (a palaeoproductivity index of coccolithophores) allowed us to monitor nutri-thermocline fluctuations. Nannofossil accumulation rates (NAR) vary closely with the N ratio, indicating a strong correlation between these two palaeoproductivity proxies. Decreases in the N ratio and NAR values suggest lower palaeoproductivity during glacial substages, indicating a deep nutri-thermocline (deep stratification of the mixed layer) as a consequence of the piling up of warm water dragged by the NEC. This setting was favoured by the southern shift of the ITCZ and Trade winds which blew perpendicular to the Guyana coast. By contrast, increases in the N ratio and NAR values revealed higher palaeoproductivity during interglacial substages, suggesting a shoaling of the nutri-thermocline. This scenario is favoured by a northward displacement of the ITCZ with the southeast Trade winds blowing alongshore. Additionally, palaeoproductivity changes during substages of Marine Isotope Stage (MIS) 6-5 are of much higher amplitude than those recorded in substages of MIS 4-2 and the early Holocene. Similarities between the palaeoproductivity and the 65° N summer insolation records, suggest a link between the depth of nutri-thermocline, the latitudinal migration of the ITCZ and ice-sheet changes in the Northern Hemisphere.

Description: 〈b〉Decline of coral reefs during late Paleocene to early Eocene global warming〈/b〉〈br〉 C. Scheibner and R. P. Speijer〈br〉 eEarth, 3, 19-26, doi:10.5194/ee-3-19-2008, 2008〈br〉 Since the 1980s the frequency of warming events has intensified and simultaneously widespread coral bleaching, and enhanced coral mortality have been observed. Yet, it remains unpredictable how tropical coral reef communities will react to prolonged adverse conditions. Possibly, coral reef systems are sufficiently robust to withstand continued environmental pressures. But if coral mortality increases, what will platform communities of the future look like? The co-evolution of early Paleogene carbonate platforms and palaeoclimate may provide insight. Here we document the impact of early Paleogene global warming on shallow-water carbonate platforms in the Tethys. Between 59 and 55 Ma, three discrete stages in platform development can be identified Tethys-wide: during the first stage carbonate platforms mainly consisted of coralgal reefs; during the second – transitional – stage coralgal reefs thrived only at middle latitudes and gave way to larger foraminifera as dominant carbonate producer in low latitudes; finally, during the third stage, newly developing larger foraminifera lineages completely took over the role as main carbonate-producing organisms in low to middle latitudes. We postulate that rising temperatures led to a stepwise demise of Paleocene coral reefs, giving way to an unprecedented expansion of larger foraminifera, dominating Tethyan platforms during the early Eocene.

Description: 〈b〉Characteristics of chlorites in seismogenic fault zones: the Taiwan Chelungpu Fault Drilling Project (TCDP) core sample〈/b〉〈br〉 Y. Hashimoto, O. Tadai, M. Tanimizu, W. Tanikawa, T. Hirono, W. Lin, T. Mishima, M. Sakaguchi, W. Soh, S. R. Song, K. Aoike, T. Ishikawa, M. Murayama, K. Fujimoto, T. Fukuchi, M. Ikehara, H. Ito, H. Kikuta, M. Kinoshita, K. Masuda, T. Matsubara, O. Matsubayashi, K. Mizoguchi, N. Nakamura, K. Otsuki, T. Shimamoto, H. Sone, and M. Takahashi〈br〉 eEarth, 3, 1-6, doi:10.5194/ee-3-1-2008, 2008〈br〉 The iron content and the asymmetry of iron and magnesium ions in chlorites are examined for the Chelungpu Fault in Taiwan, which is a seismogenic fault. The samples are collected from the cores drilled for the Taiwan Chelungpu Fault Drilling Project (TCDP, borehole B). Three fault zones are recognized as candidates for the source of seismogenic materials. The fault zones are composed of fractured-damaged rocks, breccia, gray gouge, black gouge, and black material. Chlorite from each type of rock was analyzed by using X-ray diffraction (XRD). The iron content and asymmetry of the iron and magnesium ions in the chlorites were estimated from the XRD peak ratios. The hydroxide and silicate layers of chlorite in the black gouge and black material have low iron contents. Many studies have suggested that a temperature rise occurred at the fault zones. In addition, the temperature rise can result in the production of iron oxides such as magnetite or maghemite, as reported by other studies. However, the temperature rise cannot explain the low value of iron content in the chlorites. Another reason for the low value of iron content is the variation in the pH of the fluid, which can be controlled by radical reactions. Therefore, on the basis of chlorite characteristics, the reactions at the seismogenic fault are due not only to the thermal decomposition resulting from the temperature rise and but also to rock-fluid interactions.