TY - JOUR
T1 - Different response of δD values of n-alkanes, isoprenoids, and kerogen during thermal maturation
AU - Pedentchouk, Nikolai
AU - Freeman, Katherine H.
AU - Harris, Nicholas B.
N1 - Funding Information:
We thank members of the Penn State Congo Basin consortium, which include Anadarko, Arco, Chevron, Conoco, the Japan National Oil Corporation, Mobil, Norsk Hydro, Phillips and Texaco, for financial support of this project. We are grateful to Conoco for providing samples from well ONEZ-1 in Gabon. Arndt Schimmelmann and Peter Sauer contributed tremendously with their analytical and methodological input. Dennis Walizer, Pratigya Pollisar, Teresa Diel, and Chris Lernihan provided technical and laboratory assistance. We thank Gareth Mitchell for vitrinite reflectance analyses. We are grateful to Stephen Meyers for his assistance with statistical treatment of δD data. This research was supported by an ACS PRF research grant to K.H. Freeman as well as the BP Fellowship and the AAPG Grant-in-Aid to N. Pedentchouk. Alex Sessions, Arndt Schimmelmann, and one anonymous reviewer provided very constructive reviews which greatly improved the manuscript.
PY - 2006/4/15
Y1 - 2006/4/15
N2 - This study investigates the extent of post-depositional alteration of δD values of n-alkyl lipids, isoprenoids, and kerogen isolated from a continuous 450 m core that covers the transition from thermally immature to early mature sediments in the lacustrine Kissenda Formation, Lower Cretaceous, Gabon Basin. Large variations in δD values (up to 40‰ for nC17 and up to 30‰ for nC29 alkanes as well as up to 10‰ for kerogen) in closely spaced samples are evident throughout the core and remain preserved even at the bottom of the section. δD values of individual n-alkanes show a slight overall D-enrichment with depth, and a general trend of increasing δD values with increasing n-alkane chain length characterizes all samples, particularly in those below 600 m depth. Hydrogen isotopic compositions of kerogen samples overlap with those of n-alkanes throughout the section. δD values of pristane and phytane are more negative than those of nC17 alkane by as much as 120‰ at shallow depths but increase dramatically and approach δD values of nC17 alkane in the samples closest to the oil window. Integration of analytical and computational results indicates that: (1) n-alkanes and isoprenoids have the potential to preserve the original biological signal before the onset of oil generation; (2) isomeric and structural rearrangements taking place at the beginning stages of oil generation do not influence significantly the δD values of n-alkanes and kerogen. However, these processes have a major effect on the isotopic composition of isoprenoids, causing isotopic D-enrichment up to 90‰.
AB - This study investigates the extent of post-depositional alteration of δD values of n-alkyl lipids, isoprenoids, and kerogen isolated from a continuous 450 m core that covers the transition from thermally immature to early mature sediments in the lacustrine Kissenda Formation, Lower Cretaceous, Gabon Basin. Large variations in δD values (up to 40‰ for nC17 and up to 30‰ for nC29 alkanes as well as up to 10‰ for kerogen) in closely spaced samples are evident throughout the core and remain preserved even at the bottom of the section. δD values of individual n-alkanes show a slight overall D-enrichment with depth, and a general trend of increasing δD values with increasing n-alkane chain length characterizes all samples, particularly in those below 600 m depth. Hydrogen isotopic compositions of kerogen samples overlap with those of n-alkanes throughout the section. δD values of pristane and phytane are more negative than those of nC17 alkane by as much as 120‰ at shallow depths but increase dramatically and approach δD values of nC17 alkane in the samples closest to the oil window. Integration of analytical and computational results indicates that: (1) n-alkanes and isoprenoids have the potential to preserve the original biological signal before the onset of oil generation; (2) isomeric and structural rearrangements taking place at the beginning stages of oil generation do not influence significantly the δD values of n-alkanes and kerogen. However, these processes have a major effect on the isotopic composition of isoprenoids, causing isotopic D-enrichment up to 90‰.
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U2 - 10.1016/j.gca.2006.01.013
DO - 10.1016/j.gca.2006.01.013
M3 - Article
AN - SCOPUS:33645876740
SN - 0016-7037
VL - 70
SP - 2063
EP - 2072
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 8
ER -