Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59.3731b&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 59, Issue 18, pp.3731-3747
Computer Science
7
Scientific paper
Recent studies revealed short-term cyclic variations (microcycles) in total organic carbon (TOC) and the hydrogen index (HI) in the Kimmeridge Clay Formation, an organic-rich deposit considered to be a lateral equivalent of the main source rocks of the North Sea. In addition, three different types of organic matter that all appear to be amorphous when observed by light microscopy (AOM) were recognized. Together, these AOM types account for over 80% of total kerogen and their relative abundances show large variations along each microcycle. In the present work, transmission electron microscopy (TEM) observations were carried out on samples (whole kerogens, kerogen subfractions only comprising a single type of AOM, selected rock fragments) corresponding to typical points within a microcycle and obtained via high resolution sampling. The nature and the relative abundances of the products generated by Curie-point Py-GC-MS and off-line pyrolyses of isolated kerogens were also determined for two selected samples corresponding to the beginning and the top of the microcycle. Combination of such ultrastructural observations, including some semiquantitative studies, and the analysis of pyrolysis products allowed (1) determination of the ultrastructural features of the three AOM types thus providing what we believe to be the first example of correlations between light microscopy (palynofacies, in situ maceral analysis) and TEM observations on "amorphous" fossil materials; (2) identification of the source organisms and elucidation of the mode of formation of the different AOM types in the Kimmeridge Clay; (3) explanation of the variations in their relative abundances taking place along a microcycle and establishment of tight correlations with TOC and HI changes; and (4) explanation of the origin of the microcyclic variations in kerogen quantity (TOC) and quality (III) occurring in the Kimmeridge Clay Formation. Interrelationships between primary productivity, sulphate reduction intensity, and lipid "vulcanization" likely played a major role in the control of such variations.
Bertrand Philippe
Boussafir M.
Derenne Sylvie
Gelin F.
Lallier-Vergès E.
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