Molekulare Fossilien: Schlüssel zum Ursprung diagenetischer Karbonatkonkretionen

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Diagenetic carbonate concretions commonly form during shallow burial via localized lithification of soft sediment and have long been recognized as a source of exceptionally preserved fossils. While concretions are common in many ancient sediments, modern equivalents are very rare and our understanding of the complex biogeochemical processes underlying their formation is incomplete. In this project the organic matter enclosed in ancient concretions is studied with organic geochemical techniques to provide further clues to the formation of these precipitates and test their significance as containers of exceptionally preserved molecular fossils. It is proposed that lipid biomarkers and kerogen locked in concretions may represent a "snapshot" of the original sedimentary OM, plus the early microbial processes as they once occurred in the freshly deposited sediment. A particular focus is placed on testing the role of Ca- and or Mg-salts of carboxylic acids (particularly fatty acids, "adipocere"), and their anaerobic degradation products as raw materials for the formation of carbonate concretions. For this purpose, ancient (Early Jurassic) carbonate concretions from Buttenheim (Bavaria) and Hondelage (Lower Saxony) will be studied in relation to their immediate host rocks using extract based (GC-MS, IRM-GC-MS) and pyrolysis techniques (Hypy; Py-GC-MS).