ALBERT

Beschreibung: North American and Pacific spore-pollen records show a major extinction event at the Cretaceous-Tertiary (K-T) boundary, and abrupt changes are similarly found in many marine organisms world-wide. In contrast, records from the Old World reveal little evidence of terrestrial vegetational change across the boundary. In order to improve the characterization of changes across the K-T boundary, palynological assemblages from two sections in the southern Pyrenees have been evaluated. The abundance and diversity of trilete fern spores are high in Maastrichtian samples and show a statistically significant decrease during the Danian. The fern spike' of low-diversity spores found elsewhere is not recorded in the Pyrenean region. Minor replacements of taxa across the K-T boundary are also noted, as well as an increase in inaperturate gymnosperm pollen in the Danian. Comparing our two examined sections with one another reveals important differences in angiosperm pollen composition.

Beschreibung: New insights into the palaeogeographical evolution of the Rifian Internides and their external surroundings are inferred from six key stratigraphic successions selected across the Internides-Externides front. These successions span a time interval ranging from the late Cretaceous to the early Burdigalian. The main results are: (1) important lost palaeogeographical domains should be located during the late Cretaceous-Eocene between the present-day Ghomarides and the Dorsale Calcaire, on one hand, and between the Predorsalian units and the Flysch Trough as isolated carbonate platforms, on the other hand; (2) during the late Eocene-early Oligocene an extensional tectonic event, well marked in the Dorsale Calcaire, caused the collapse of these platforms and resulted in olistostromes and coarse-grained breccias in both the Predorsalian and the Beni Ider areas; (3) by the beginning of mid-Oligocene, an overturning contractional event in the Ghomarides resulted in the regional onset of the siliciclastic depositional regime throughout these palaeogeographical areas; (4) during the Aquitanian-early Burdigalian, the stepwise return of pelagic deposition in the Ghomarides indicates extensional phases, whereas the homogenization of the same pelagic facies over the Dorsale Calcaire and its external surroundings may indicate that the previously distant palaeogeographical areas were brought nearer (i.e. just before large-scale thrusting).

Beschreibung: Solutions coming from two natural playalake saline systems located in Central Ebro Basin (NE Spain) have been evaporated in the laboratory, in order to obtain the precise path of chemical evolution followed until high concentration stages. The lakes belong to two chemically different neutral brines: La Playa (with NaCl solutions) and La Salada (NaMgSO4 type). Experimental evaporation has been carried out at 25 {degrees}C until total dryness, and samples collected along the experiment have been analysed for their major components. Application of geochemical modelling techniques allowed calculation of the saturation indexes for the main saline minerals using the PHRQPITZ program, which incorporates Pitzer's model. The mineral precipitation sequence for La Playa brines following the saturation data is: gypsum, halite, thenardite and epsomite. Brines reach saturation almost simultaneously with respect to both halite and thenardite, but halite precipitates more massively and hence the solid samples collected after total desiccation were composed mainly of halite. In the case of La Salada brines, the order of precipitation is somewhat different and is as follows: gypsum, mirabilite, thenardite and bloedite. Solid samples here consisted of bloedite and thenardite, this latter formed after subaquatic dehydration of mirabilite when brines attained a peritectic point. The evolution of saturation indexes is in good agreement with mineral determinations carried out on the solid experimental samples, and it allowed us to interpret the evaporative evolution of both La Playa and La Salada brines.

Beschreibung: This work analyses the present-day principal strain orientation on the downgoing slab of the South America Plate (SAM) beneath the Sandwich Plate (SAND). The strain regime was deduced from the study of 331 earthquake focal mechanism solutions examined by fault population analysis methods. In the slab, the maximum horizontal shortening direction (ey) rotates in trend in a clockwise direction from NE in the north, to SE in the south. Based on this rotation, three different areas were defined according to the prevailing focal mechanism type: (1) the North Zone, with ey oriented N058{degrees}E and reverse and strike-slip focal mechanisms; (2) the Central Zone, with only reverse focal mechanisms and ey striking N080{degrees}E; and (3) the South Zone, with ey oriented N106{degrees}E and reverse and strike-slip focal mechanisms. The strain field in the North Zone of the SAND involves decoupling of the slab at approximately 70 km depth. In contrast, the South Zone edge slab exhibits no decoupling and it exhibits different geometry (hook-like shaped) from the North Zone. Finally, we define the dextral strike-slip component acting at the South Sandwich Fracture Zone (SSFZ), according to focal mechanism solutions and the regional tectonic configuration.

Beschreibung: New structural, geochronological, and petrological data highlight which crustal sections of the North American-Caribbean Plate boundary in Guatemala and Honduras accommodated the large-scale sinistral offset. We develop the chronological and kinematic framework for these interactions and test for Palaeozoic to Recent geological correlations among the Maya Block, the Chortis Block, and the terranes of southern Mexico and the northern Caribbean. Our principal findings relate to how the North American-Caribbean Plate boundary partitioned deformation; whereas the southern Maya Block and the southern Chortis Block record the Late Cretaceous-Early Cenozoic collision and eastward sinistral translation of the Greater Antilles arc, the northern Chortis Block preserves evidence for northward stepping of the plate boundary with the translation of this block to its present position since the Late Eocene. Collision and translation are recorded in the ophiolite and subduction-accretion complex (North El Tambor complex), the continental margin (Rabinal and Chuacus complexes), and the Laramide foreland fold-thrust belt of the Maya Block as well as the overriding Greater Antilles arc complex. The Las Ovejas complex of the northern Chortis Block contains a significant part of the history of the eastward migration of the Chortis Block; it constitutes the southern part of the arc that facilitated the breakaway of the Chortis Block from the Xolapa complex of southern Mexico. While the Late Cretaceous collision is spectacularly sinistral transpressional, the Eocene-Recent translation of the Chortis Block is by sinistral wrenching with transtensional and transpressional episodes. Our reconstruction of the Late Mesozoic-Cenozoic evolution of the North American-Caribbean Plate boundary identified Proterozoic to Mesozoic connections among the southern Maya Block, the Chortis Block, and the terranes of southern Mexico: (i) in the Early-Middle Palaeozoic, the Acatlan complex of the southern Mexican Mixteca terrane, the Rabinal complex of the southern Maya Block, the Chuacus complex, and the Chortis Block were part of the Taconic-Acadian orogen along the northern margin of South America; (ii) after final amalgamation of Pangaea, an arc developed along its western margin, causing magmatism and regional amphibolite-facies metamorphism in southern Mexico, the Maya Block (including Rabinal complex), the Chuacus complex and the Chortis Block. The separation of North and South America also rifted the Chortis Block from southern Mexico. Rifting ultimately resulted in the formation of the Late Jurassic-Early Cretaceous oceanic crust of the South El Tambor complex; rifting and spreading terminated before the Hauterivian (c. 135 Ma). Remnants of the southwestern Mexican Guerrero complex, which also rifted from southern Mexico, remain in the Chortis Block (Sanarate complex); these complexes share Jurassic metamorphism. The South El Tambor subduction-accretion complex was emplaced onto the Chortis Block probably in the late Early Cretaceous and the Chortis Block collided with southern Mexico. Related arc magmatism and high-T/low-P metamorphism (Taxco-Viejo-Xolapa arc) of the Mixteca terrane spans all of southern Mexico. The Chortis Block shows continuous Early Cretaceous-Recent arc magmatism.

Beschreibung: The Late Permian to Early Triassic (P/T) transition represents one of the most important Phanerozoic mass extinction episodes. Data from this transitional period are very scarce in continental basins, and reliable correlation with marine series is still a matter of debate. In this paper, information on the P/T transition in the continental series of central and NE Spain and the Balearic Islands is presented and compared with some coeval western European basins. The Iberian Ranges sections contain detailed information on the P/T transition, with sediments interpreted as alluvial fans, sandy and gravelly braided rivers and high sinuosity rivers with extensive floodplains, dated by means of pollen and spore assemblages. However, the fossil record contains two barren intervals throughout the study area, one in the Late Permian (Thuringian) and another during the latest Permian to Early Triassic. The possible causes of these gaps include the very likely relationship with the emplacement of the basaltic large igneous provinces (LIP) of SE China and western Siberia during this period of time.

Beschreibung: Carboniferous-Permian magmatism in the Spanish Central System, Iberian Ranges, Cantabrian Chain, Pyrenees (Maladeta plutonic complex) and the French Massif Central includes a range of mafic calc-alkaline and shoshonitic rock types, as well as amphibole-bearing lamprophyres (spessartites) and minor alkaline lamprophyres (camptonites). Subalkaline basalts with intermediate characteristics between enriched mid-ocean ridge basalts (E-MORB) and the mafic calc-alkaline rocks also occur in the Pyrenees (Panticosa, Cinco Villas and La Rhune). The incompatible trace-element characteristics of the least differentiated subalkaline rocks and lamprophyres indicate that variably enriched mantle sources were involved in their genesis. High large ion lithophile element/high-field-strength element (LILE/HFSE), light rare earth element (LREE) HFSE and low Ce/Pb ratios in the calc-alkaline and shoshonitic rocks require either assimilation of crustal rocks plus fractional crystallization (AFC) of the parental mafic magmas or melting of a previously subduction-modified mantle source. In the Cantabrian Chain and the Massif Central, melting of a subduction-modified mantle source seems more likely. In the Central System, Iberian Ranges and Maladeta area the lack of any evidence for a contemporaneous subduction system suggests that AFC processes were more likely to be responsible for the crustal signature of the magmas. The alkaline camptonites from the Central System were generated from an enriched mantle source, which had lower LREE/HFSE and LILE/HFSE ratios than the source of the older calc-alkaline magmas from the same area. The incompatible trace-element patterns and ratios (e.g., Y/Nb, Zr/Nb) of the subalkaline basalts from Panticosa, Cinco Villas and La Rhune suggest that they were generated from similar parent magmas, formed by mixing of partial melts of an asthenospheric source and a crustal component.

Beschreibung: Regional considerations on the tectonic regime during the emplacement of the Early Devonian magmatic units in the Sierra de San Luis are inferred from combined field, petrographic and AMS observations. Devonian granitoids of the Sierra de San Luis, in central Argentina, constitute elliptical composite batholiths and make up the most voluminous magmatism that appears in the Sierra. Detailed fabric studies have been carried out on the La Totora batholith (33{degrees}09'S, 65{degrees}42'W), which complement previous studies on two of the largest plutons in the Sierra de San Luis: The Renca and Las Chacras-Potrerillos batholiths. The studies comprised systematic field surveys, petrographic observations and anisotropy of magnetic susceptibility (AMS) measurements. Microstructural studies indicate that the batholith rocks are mainly characterized by magmatic microstructures with limited sub-magmatic to high-temperature solid-state deformation. All three batholiths possess concentric foliation patterns. The average magnetic foliation patterns in the studied plutons agree well with the macroscopic fabrics measured in the field indicating that the AMS-data can be used to study the orientation of fabric elements. Bulk susceptibility indicates a predominance of ferromagnetic contributions, although some paramagnetic sub-units are also present. Most foliations and lineations reflect magmatic flow and their attitude is linked to the interference between regional deformation and batholith inflation, i.e. fabrics may be due to regional strain in combination with the internal dynamics of the magma bodies. Rock fabrics are mainly described by oblate magmetic fabric ellipsoids. Magnetic lineations generally show a NNE-SSW trend that is interpreted to be controlled by the opening transtensional pull-apart structures during batholith inflation. It turns out that the Devonian batholiths intruded the basement syn-kinematically with respect to the Achalian deformational cycle.

Beschreibung: This work describes the coseismic ceiling block collapse within Benis Cave (-213 m; Murcia, SE Spain), associated with the 1999 Mula earthquake (mb=4.8, MSK VII). The collapse occurred at -156 m into the Earthquake Hall, and as a consequence one small gallery became blind. We studied the geology, topography and active tectonic structures relevant to the cave. In addition, we carried out a seismotectonic analysis of the focal mechanism solutions, and also a fault population analysis on slickensides measured in fault planes in the cave. The stress and strain regime is interpreted as being congruent with the palaeoseismic evidence, and agrees with the fault kinematics established for cave galleries developed within fault planes and growth anomalies of coral flowstone. Our analysis suggests that one active segment (NNE-SSW) determined the morphology and topography of the Benis Cave, where strong to moderate palaeoearthquakes (6[≤]M[≤]7) took place. As a consequence of this intense seismic activity a small gallery collapsed. A new palaeoseismic structure, or seismothem, has been recognized, namely the effect of palaeoearthquakes affecting the pattern of development of the spatial coral flowstone distribution located at the bottom of the cave.

Beschreibung: Metamorphosed shales, heterolithic deposits and sandstones build up the Palaeoproterozoic Chaibasa Formation in east India. The shales (referred here to as the fine-grained facies) comprising mudstone (clay and silt size) with some minor amounts of very fine to fine sandstone were deposited below storm wave base in a deep marine basin that simultaneously underwent tectonic activity. This fine-grained facies contains strongly deformed layers, intercalated between undeformed layers. Sedimentological analysis of the deformations indicates that they formed while still in an unconsolidated or slightly consolidated state, partly during and after sedimentation, but before being covered by younger sediments. The types of deformation structures indicate an earthquake-induced origin. Thus, they should be considered as seismites. The soft-sediment deformation structures in the seismites show a wide variety of shapes and other characteristics that appear to depend on their relative position to the epicentre of the earthquake.