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Early Ilerdian (Early Eocene, Shallow Benthic Zones 5 and 6) carbonate systems of the Pyrenees shelf were deposited after a time of severe climatic ('Paleocene-Eocene Thermal Maximum, PETM') and phylogenetic ('Larger Foraminifer Turnover') changes. They reflect the radiation of nummulitid, alveolinid, and orbitolitid larger foraminifera after remarkable biotic changes at the end of the Paleocene, and announce their subsequent flourishing in the Middle Eocene. A paleoenvironmental model for tropical carbonate environments of this particular time interval is provided herein. During the Early Ilerdian, the inner and middle ramp deposits from Minerve, Campo and Serraduy revealed the end-member of a tropical carbonate factory with carbonate production dominated by the end-members of biotically (photo-autotrophic skeletal) controlled and biotically induced carbonate precipitation. Inner platform environments are dominated by alveolinids and in part by orbitolitids, middle platform environments are dominated by nummulitids. Corals are present, but they do not form reefs, which is a typical feature for the Eocene. Nummulite shoal complexes, which are well-known from the Middle Eocene are also absent during the studied Early Ilerdian interval, which may reflect the early evolutionary stage of this group
We report on a receiver function study of the crust and upper mantle within DESERT, a multidisciplinary geophysical project to study the lithosphere across the Dead Sea Transform (DST). A temporary seismic network was operated on both sides of the DST between 2000 April and 2001 June. The depth of the Moho increases smoothly from about 30 to 34-38 km towards the east across the DST, with significant north-south variations east of the DST. These Moho depth estimates from receiver functions are consistent with results from steep-and wide-angle controlled-source techniques. Steep-angle reflections and receiver functions reveal an additional discontinuity in the lower crust, but only east of the DST. This leads to the conclusion that the internal crustal structure east and west of the DST is different. The P to S converted phases from both discontinuities at 410 and 660 km are delayed by 2 s with respect to the IASP91 global reference model. This would indicate that the transition zone is consistent with the global average, but the upper mantle above 410 km is 3-4 per cent slower than the standard earth model
The interplay between topography and Indian summer monsoon circulation profoundly controls precipitation distribution, sediment transport, and river discharge along the Southern Himalayan Mountain Front (SHF). The Higher Himalayas form a major orographic barrier that separates humid sectors to the south and and regions to the north. During the Indian summer monsoon, vortices transport moisture from the Bay of Bengal, swirl along the SHF to the northwest, and cause heavy rainfall when colliding with the mountain front. In the eastern and central parts of the Himalaya, precipitation measurements derived from passive microwave analysis (SSM/I) show a strong gradient, with high values at medium elevations and extensive penetration of moisture along major river valleys into the orogen. The end of the monsoonal conveyer belt is near the Sutlej Valley in the NW Himalaya, where precipitation is lower and rainfall maxima move to lower elevations. This region thus comprises a climatic transition zone that is very sensitive to changes in Indian summer monsoon strength. To constrain magnitude, temporal, and spatial distribution of precipitation, we analyzed high-resolution passive microwave data from the last decade and identified an abnormal monsoon year (AMY) in 2002. During the 2002 AMY, violent rainstorms conquered orographic barriers and penetrated far into otherwise and regions in the northwest Himalaya at elevations in excess of 3 km asl. While precipitation in these regions was significantly increased and triggered extensive erosional processes (i.e., debris flows) on sparsely vegetated, steep hillslopes, mean rainfall along the low to medium elevations was not significantly greater in magnitude. This shift may thus play an important role in the overall sediment flux toward the Himalayan foreland. Using extended precipitation and sediment flux records for the last century, we show that these events have a decadal recurrence interval during the present-day monsoon circulation. Hence, episodically occurring AMYs control geomorphic processes primarily in the high-elevation and sectors of the orogen, while annual recurring monsoonal rainfall distribution dominates erosion in the low- to medium- elevation parts along the SHF. (C) 2004 Elsevier B.V. All rights reserved
Carpholite+chloritoid+pyrophyllite association occurs widely in the Triassic metaclastic rocks of the Afyon Zone in west-central Turkey. Fe-Mg-carpholite is associated with rare aragonite pseudomorphs and glaucophane in marbles and metabasites, respectively. The Afyon Zone consists stratigraphically of a Pan-African basement and an overlying Mesozoic cover sequence. The Pan-African basement, which shows Barrovian-type amphibolite-facies metamorphism, comprises garnet-mica schists, intruded by sodic amphibole-bearing metagabbros and leucocratic metagranites. It is unconformably overlain by a continuous metasedimentary sequence extending from Triassic to early Palaeocene. This cover sequence begins with metaconglomerates, which pass upwards into phyllites. Fe-Mg-carpholite occurs within this metaclastic sequence as rosette-like crystals in metapelites and fibres in quartz segregations. The metaclastic rocks are succeeded by metamorphosed platform carbonates, grading into Latest Mesozoic metamorphosed pelagic limestones, which in turn progress up to a Late Mesozoic-Early Tertiary olistostrome. This sequence is tectonically overlain by the blueschists of the Tavsanh Zone. Fe-Mg-carpholite-bearing assemblages imply temperatures of about 350 degrees C and minimum pressures of 6-9 kbar, corresponding to burial depths of about 30 km for the Mesozoic passive continental margin sediments and the underlying Pan-African supracrustal metasediments and metaintrusives. The metamorphic rocks of the Afyon Zone are unconformably overlain by Upper Palaeocene-Lower Eocene sedimentary rocks, indicating a Paleocene age for the regional HP/LT metamorphism. This implies continuous younging of HP/LT metamorphism in the Anatolides related to northward subduction of the Anatolide-Tauride platform beneath the Sakarya Zone. From north to south this involved the Tavsanh Zone (Campanian, 80 +/- 5 Ma), the Afyon Zone (Palaeocene?), the Menderes Massif (Middle Eocene) and the Lycian Nappes (Late Cretaceous-Eocene?), all of which were probably derived from the frontal part of the Anatolide-Tauride platform. (c) 2005 Elsevier B.V. All rights reserved
Alpine thermal and structural evolution of the highest external crystalline massif : the Mont Blanc
(2005)
The alpine structural evolution of the Mont Blanc, highest point of the Alps (4810 m), and of the surrounding area has been reexamined. The Mont Blanc and the Aiguilles Rouges external crystalline massifs are windows of Variscan basement within the Penninic and Helvetic nappes. New structural, Ar-40/Ar-39, and fission track data combined with a compilation of earlier P-T estimates and geochronological data give constraints on the amount and timing of the Mont Blanc and Aiguilles Rouges massifs exhumation. Alpine exhumation of the Aiguilles Rouges was limited to the thickness of the overlying nappes (similar to 10 km), while rocks now outcropping in the Mont Blanc have been exhumed from 15 to 20 km depth. Uplift of the two massifs started similar to 22 Myr ago, probably above an incipient thrust: the Alpine sole thrust. At similar to 12 Ma, the NE-SW trending Mont Blanc shear zone (MBsz) initiated. It is a major steep reverse fault with a dextral component, whose existence has been overlooked by most authors, that brings the Mont Blanc above the Aiguilles Rouges. Total vertical throw on the MBsz is estimated to be between 4 and 8 km. Fission track data suggest that relative motion between the Aiguilles Rouges and the Mont Blanc stopped similar to 4 Myr ago. Since that time, uplift of the Mont Blanc has mostly taken place along the Mont Blanc back thrust, a steep north dipping fault bounding the southern flank of the range. The "European roof'' is located where the back thrust intersects the MBsz. Uplift of the Mont Blanc and Aiguilles Rouges occurred toward the end of motion on the Helvetic basal decollement (HBD) at the base of the Helvetic nappes but is coeval with the Jura thin-skinned belt. Northwestward thrusting and uplift of the external crystalline massifs above the Alpine sole thrust deformed the overlying Helvetic nappes and formed a backstop, inducing the formation of the Jura arc. In that part of the external Alps, similar to NW-SE shortening with minor dextral NE-SW motions appears to have been continuous from similar to 22 Ma until at least similar to 4 Ma but may be still active today. A sequential history of the alpine structural evolution of the units now outcropping NW of the Pennine thrust is proposed
In a series of timed experiments, monazite inclusions are induced to form in the Durango fluorapatite using 1 and 2 N HCl and H2SO4 solutions at temperatures of 300, 600, and 900 degrees C and pressures of 500 and 1,000 MPa. The monazite inclusions form only in reacted areas, i.e. depleted in (Y+REE)+Si+Na+S+Cl. In the HCl experiments, the reaction front between the reacted and unreacted regions is sharp, whereas in the H2SO4 experiments it ranges from sharp to diffuse. In the 1 N HCl experiments, Ostwald ripening of the monazite inclusions took place both as a function of increased reaction time as well as increased temperature and pressure. Monazite growth was more sluggish in the H2SO4 experiments. Transmission electron microscopic (TEM) investigation of foils cut across the reaction boundary in a fluorapatite from the 1 N HCl experiment (600 degrees C and 500 MPa) indicate that the reacted region along the reaction front is characterized by numerous, sub-parallel, 10-20 nm diameter nano-channels. TEM investigation of foils cut from a reacted region in a fluorapatite from the 1 N H2SO4 experiment at 900 degrees C and 1,000 MPa indicates a pervasive nano- porosity, with the monazite inclusions being in direct contact with the surrounding fluorapatite. For either set of experiments, reacted areas in the fluorapatite are interpreted as replacement reactions, which proceed via a moving interface or reaction front associated with what is essentially a simultaneous dissolution-reprecipitation process. The formation of a micro- and nano-porosity in the metasomatised regions of the fluorapatite allows fluids to permeate the reacted areas. This permits rapid mass transfer in the form of fluid-aided diffusion of cations to and from the growing monazite inclusions. Nano-channels and nano-pores also serve as sites for nucleation and the subsequent growth of the monazite inclusions
About 24 % of the land surface in the northern hemisphere are underlayed by permafrost in various states. Permafrost aggradation occurs under special environmental conditions with overall low annual precipitation rates and very low mean annual temperatures. Because the general permafrost occurrence is mainly driven by large-scale climatic conditions, the distribution of permafrost deposits can be considered as an important climate indicator. The region with the most extensive continuous permafrost is Siberia. In northeast Siberia, the ice- and organic-rich permafrost deposits of the Ice Complex are widely distributed. These deposits consist mostly of silty to fine-grained sandy sediments that were accumulated during the Late Pleistocene in an extensive plain on the then subaerial Laptev Sea shelf. One important precondition for the Ice Complex sedimentation was, that the Laptev Sea shelf was not glaciated during the Late Pleistocene, resulting in a mostly continuous accumulation of permafrost sediments for at least this period. This shelf landscape became inundated and eroded in large parts by the Holocene marine transgression after the Last Glacial Maximum. Remnants of this landscape are preserved only in the present day coastal areas. Because the Ice Complex deposits contain a wide variety of palaeo-environmental proxies, it is an excellent palaeo-climate archive for the Late Quaternary in the region. Furthermore, the ice-rich Ice Complex deposits are sensible to climatic change, i.e. climate warming. Because of the large-scale climatic changes at the transition from the Pleistocene to the Holocene, the Ice Complex was subject to extensive thermokarst processes since the Early Holocene. Permafrost deposits are not only an environmental indicator, but also an important climate factor. Tundra wetlands, which have developed in environments with aggrading permafrost, are considered a net sink for carbon, as organic matter is stored in peat or is syn-sedimentary frozen with permafrost aggradation. Contrary, the Holocene thermokarst development resulted in permafrost degradation and thus the release of formerly stored organic carbon. Modern tundra wetlands are also considered an important source for the climate-driving gas methane, originating mainly from microbial activity in the seasonal active layer. Most scenarios for future global climate development predict a strong warming trend especially in the Arctic. Consequently, for the understanding of how permafrost deposits will react and contribute to such scenarios, it is necessary to investigate and evaluate ice-rich permafrost deposits like the widespread Ice Complex as climate indicator and climate factor during the Late Quaternary. Such investigations are a pre-condition for the precise modelling of future developments in permafrost distribution and the influence of permafrost degradation on global climate. The focus of this work, which was conducted within the frame of the multi-disciplinary joint German-Russian research projects "Laptev Sea 2000" (1998-2002) and "Dynamics of Permafrost" (2003-2005), was twofold. First, the possibilities of using remote sensing and terrain modelling techniques for the observation of periglacial landscapes in Northeast Siberia in their present state was evaluated and applied to key sites in the Laptev Sea coastal lowlands. The key sites were situated in the eastern Laptev Sea (Bykovsky Peninsula and Khorogor Valley) and the western Laptev Sea (Cape Mamontovy Klyk region). For this task, techniques using CORONA satellite imagery, Landsat-7 satellite imagery, and digital elevation models were developed for the mapping of periglacial structures, which are especially indicative of permafrost degradation. The major goals were to quantify the extent of permafrost degradation structures and their distribution in the investigated key areas, and to establish techniques, which can be used also for the investigation of other regions with thermokarst occurrence. Geographical information systems were employed for the mapping, the spatial analysis, and the enhancement of classification results by rule-based stratification. The results from the key sites show, that thermokarst, and related processes and structures, completely re-shaped the former accumulation plain to a strongly degraded landscape, which is characterised by extensive deep depressions and erosional remnants of the Late Pleistocene surface. As a results of this rapid process, which in large parts happened within a short period during the Early Holocene, the hydrological and sedimentological regime was completely changed on a large scale. These events resulted also in a release of large amounts of organic carbon. Thermokarst is now the major component in the modern periglacial landscapes in terms of spatial extent, but also in its influence on hydrology, sedimentation and the development of vegetation assemblages. Second, the possibilities of using remote sensing and terrain modelling as a supplementary tool for palaeo-environmental reconstructions in the investigated regions were explored. For this task additionally a comprehensive cryolithological field database was developed for the Bykovsky Peninsula and the Khorogor Valley, which contains previously published data from boreholes, outcrops sections, subsurface samples, and subsurface samples, as well as additional own field data. The period covered by this database is mainly the Late Pleistocene and the Holocene, but also the basal deposits of the sedimentary sequence, interpreted as Pliocene to Early Pleistocene, are contained. Remote sensing was applied for the observation of periglacial strucures, which then were successfully related to distinct landscape development stages or time intervals in the investigation area. Terrain modelling was used for providing a general context of the landscape development. Finally, a scheme was developed describing mainly the Late Quaternary landscape evolution in this area. A major finding was the possibility of connecting periglacial surface structures to distinct landscape development stages, and thus use them as additional palaeo-environmental indicator together with other proxies for area-related palaeo-environmental reconstructions. In the landscape evolution scheme, i.e. of the genesis of the Late Pleistocene Ice Complex and the Holocene thermokarst development, some new aspects are presented in terms of sediment source and general sedimentation conditions. This findings apply also for other sites in the Laptev Sea region.
Seismic tomography, imaging of seismic scatterers, and magnetotelluric soundings reveal a sharp lithologic contrast along a similar to 10 km long segment of the Arava Fault (AF), a prominent fault of the southern Dead Sea Transform (DST) in the Middle East. Low seismic velocities and resistivities occur on its western side and higher values east of it, and the boundary between the two units coincides partly with a seismic scattering image. At 1 - 4 km depth the boundary is offset to the east of the AF surface trace, suggesting that at least two fault strands exist, and that slip occurred on multiple strands throughout the margin's history. A westward fault jump, possibly associated with straightening of a fault bend, explains both our observations and the narrow fault zone observed by others
The rise and fall of the Classic Maya provides a textbook example of human social evolution. It is therefore significant to discover that the history of theMaya was so closely tied to environmental constraints. If Maya civilization could collapse under the weight of natural climate events, it is of more than academic interest to ponder how modem society will fare in the face of an uncertain climate in the years ahead. An understanding of how ancient cultures responded to climatic changes in the past may thus provide important lessons for humanity in the future