1,721,027 research outputs found
Spurensuche im Gestein – was uns geologische Archive über die Entstehung des Lebens auf der Erde verraten
No full text
Depositional dynamics of a bituminous carbonate facies in a tectonically induced intra-platform basin: the Shibantan Member (Dengying Formation, Ediacaran Period)
No full textThe Ediacaran Shibantan Member (Dengying Formation, South China) is characterised by a black, laminated bituminous limestone facies with diverse Ediacara-type organisms and trace fossils. However, still little is known about the evolution of the Shibantan basin and its sedimentary dynamics. A detailed sedimentological characterisation revealed that the Shibantan Member was deposited on a carbonate ramp system linked to an intra-platform basin. Evaporitic dolomites of the Hamajing Member (representing sub- to supratidal inner ramp environments above fair weather wave base) are sharply overlain by black, laminated limestones of the lower Shibantan Member, representing a subtidal lower- to middle ramp environment close to the storm wave base. This facies-shift implies a sudden local deepening event, probably due to a tectonically induced increase in subsidence. The Shibantan basin was subsequently filled as evidenced by the gradual transition into dark wavy dolomites deposited in a subtidal middle-ramp environment (i.e. between storm- and fair weather wave bases) and, eventually, the upper Dengying Formation (i.e. the Baimatuo Member), which represents the same depositional environments as the Hamajing Member. Sedimentation in the Shibantan basin was highly dynamic as evidenced by a distinct slumping horizon and mass-flow deposits, partly possibly due to synsedimentary tectonic processes. A microbial mat associated biota which includes Ediacara-type fossils is restricted to the lower Shibantan Member. The close spatial relationship between allochthonous event deposits and autochthonous fossil associations in this setting implies that the event deposits were not only important for the preservation of fossils, but probably also for the supply of nutrients
symposium ; Göttingen Academy of Sciences and Humanities and Courant Research Centre Geobiology, October, 16-18, 2014
No full textOpening up a window into ecosystems with Ediacara-type organisms: preservation of molecular fossils in the Khatyspyt Lagerstatte (Arctic Siberia)
No full textThe Khatyspyt Formation in Arctic Siberia is one of only two carbonate settings with Ediacara-type fossils. As a potential hydrocarbon source rock, it contains abundant molecular fossils that may help to expand our understanding of these ecosystems. Unfortunately, however, the molecular fossil record in geological materials is commonly biased by secondary processes such as thermal maturation, migration of bitumen compounds or surface contamination. In this study, we evaluate the preservation of molecular fossils in a sample from the Khatyspyt Formation and elucidate their paleobiological meaning. Our results reveal that the organic matter is remarkably immature (oil window maturity) and shows little effect of biodegradation. Petrographic observations, exterior/interior experiments, and the similarity between free bitumen, mineral-occluded bitumen, and kerogen pyrolysate point to the syngeneity of the molecular fossils. Abundant hopanes, cyclohexylalkanes, and methyl-branched alkanes indicate a bacterial source of the organic matter, likely including cyanobacteria and anaerobic bacteria. At the same time, a carbonaceous compression fossil on top of the sample and abundant steranes indicate the presence of eukaryotes. The steranes show typical distributions for the Ediacaran (i.e., dominance of stigmastane). Given the exceptional preservation of the body fossils, trace fossils, and molecular fossils, the Khatyspyt Formation can be considered a fossil lagerstatte sensu Seilacher (1970: Begriff und Bedeutung der Fossil-Lagerstatten. Neues Jahrbuch fur Geologie und Palaontologie, Monatshefte: 34-39). The combined analysis of sedimentary facies, paleontology (body, trace, and molecular fossils), and biogeochemistry will provide a more complete understanding of ecosystems with Ediacara-type fossils
Assessing Possibilities and Limitations for Biomarker Analyses on Outcrop Samples: A Case Study on Carbonates of the Shibantan Member (Ediacaran Period, Dengying Formation, South China)
No full textThe Shibantan Member (Dengying Formation, South China) represents one of only two carbonate settings with Ediacara-type organisms and offers a rare opportunity to study the biogeochemistry of these ecosystems. To evaluate possibilities and limitations for future biomarker studies on fossil-bearing outcrop samples of the Shibantan Member, we analysed the spatial distribution of hydrocarbons in extractable organic matter (i.e. bitumen) on a millimetre scale. Our study demonstrates that the sample and most likely also other rocks from the same setting are contaminated with petroleum-derived compounds that bear the potential for erroneous interpretations in palaeo-reconstructions. The contamination was revealed by distribution patterns and amounts of extractable n-alkanes and acyclic isoprenoids. The contamination is linked to the external weathering surfaces but also to cracks within the rock, and the extent most likely depends on concentration gradients between these contamination sources. Here we show that contamination can successfully be distinguished from syngenetic signals obtained from non-extractable organic matter (i.e. kerogen) using catalytic hydropyrolysis (HyPy). However, we observed that decalcification is necessary to achieve sufficient yields of kerogen-bound hydrocarbons and to avoid artificial alteration of the biomarker signals due to matrix effects
Organic matter influence on ooid formation: New insights into classic examples (Great Salt Lake, USA; Triassic Germanic Basin, Germany)
No full textsymposium ; Göttingen Academy of Sciences and Humanities and Courant Research Centre Geobiology, October, 16-18, 2014
No full textTracing the fate of steroids through a hypersaline microbial mat (Kiritimati, Kiribati/Central Pacific)
No full textEukaryotic steranes are typically absent or occur in very low concentrations in Precambrian sedimentary rocks. However, it is as yet unclear whether this may reflect low source inputs or a preservational bias. For instance, it has been proposed that eukaryotic lipids were profoundly degraded in benthic microbial mats that were ubiquitous prior to the advent of vertical bioturbation in the Cambrian ("mat-seal effect"). It is therefore important to test the microbial turnover and degradation of eukaryotic steroids in real-world microbial mats. Here we assessed steroid inventories in different layers of a microbial mat from a hypersaline lake on Kiritimati (Central Pacific). Various eukaryote-derived C27 -C30 steroids were detected in all mat layers. These compounds most likely entered the mat system as unsaturated sterols from the water column or the topmost mat, and were progressively altered during burial in the deeper, anoxic mat layers over c. 103 years. This is reflected by increasing proportions of saturated sterols and sterenes, as well as the presence of thiosteranes in certain horizons. Sterol alteration can partly be assigned to microbial transformation but is also due to chemical reactions promoted by the reducing environment in the deeper mat layers. Notably, however, compounds with a sterane skeleton were similarly abundant in all mat layers and their absolute concentrations did not show any systematic decrease. The observed decrease of steroid/hopanoid ratios with depth may thus rather indicate a progressive "dilution" by lipids derived from heterotrophic bacteria. Further, pyrolysis revealed that steroids, in contrast to hopanoids, were not sequestered into non-extractable organic matter. This may lead to a preservational bias against steroids during later stages of burial. Taken together, steroid preservation in the microbial mat is not only controlled by heterotrophic degradation, but rather reflects a complex interplay of taphonomic processes
Organic matter influence on ooid formation: New insights into classic examples (Great Salt Lake, USA; Triassic Germanic Basin, Germany)
No full textOoids are coated grains composed of a tangential or radial cortex growing around a nucleus. They are common in carbonate deposits of almost any geological age and provide insights into environmental conditions. However, abiotic or biotic factors influencing their formation remain unclear. This study aims to advance current understanding of ooid formation with a multi-analytical approach (for example, field emission scanning electron microscopy, Raman spectroscopy and micro X-ray fluorescence) to classic examples from Great Salt Lake, USA, and the Lower Triassic Germanic Buntsandstein Basin, Germany. Both of these deposits represent hypersaline shallow-water environments where ooids are closely associated with microbial mats. Great Salt Lake ooids are dominantly 0.2 to 1.0 mm in size, ellipsoidal to subspherical in shape, composed of aragonite and contain organic matter. Germanic Buntsandstein Basin ooids are mainly ≤4 mm in size, spherical to subspherical in shape, composed of calcite and currently contain little organic matter. Despite the differences, both ooids have the same cortex structures, likely reflecting similar formation processes. Some Great Salt Lake ooids formed around detrital grains while others exhibit micritic particles in their nuclei. In Germanic Basin ooids, detrital nuclei are rare, despite the abundance of siliciclastic particles of various sizes in the host rocks. Germanic Basin deposits also include ‘compound ooids’, i.e. adjacent ooids that coalesced with one another during growth, suggesting static in situ development, which is supported by the lack of detrital grains as nuclei. Germanic Basin ooids also grew into laminated microbial crusts with identical microstructures, further indicating a static formation. Such microbial crusts typically form through mineral precipitation associated with organic matter (for example, extracellular polymeric substances), suggesting a similar formation pathway for ooids. The inferred key-role of organic matter is further supported by features in radial ooids from the Great Salt Lake, which commonly exhibit, from their nuclei towards their surface, increasing organic matter contents and decreasing calcification.Göttingen Academy of Sciences and HumanitiesMinisterio de Ciencia e InnovaciónChina Scholarship CouncilUniversity of TübingenChina Postdoctoral Science FoundationAlexander von Humboldt FoundationDepto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu
- …
