TY - JOUR
T1 - Sources of alkylbenzenes in Lower Cretaceous lacustrine source rocks, West African rift basins
AU - Pedentchouk, Nikolai
AU - Freeman, Katherine H.
AU - Harris, Nicholas B.
AU - Clifford, David J.
AU - Grice, Kliti
N1 - Funding Information:
We thank corporate members of the Penn State Congo Basin consortium, which include Anadarko, Arco, Chevron, Conoco, Japan National Oil Corporation, Mobil, Norsk Hydro, Phillips and Texaco, for financial support of this research. We greatly appreciate the willingness of Conoco to provide samples from ONEZ-1 well in Gabon and Sonangol to provide samples from Well A in the Kwanza Basin, Angola. We are grateful to Stefan Schouten (NIOZ) for providing a sample containing isorenieratane as well as helpful discussions. Sylvie Derenne and one anonymous reviewer provided helpful comments that significantly improved the manuscript. NASA's Astrobiology Program (NCC2-1057) and a BP Fellowship provided support for N. Pedentchouk.
PY - 2004
Y1 - 2004
N2 - We conducted molecular biomarker and compound-specific carbon isotope analyses of off-line pyrolyzates from lacustrine samples recovered by ONEZ-1 well (the Kissenda Formation) in the Gabon Basin and Well A (the Maculungo Formation) in the Kwanza Basin in West Africa. Pyrolyzates from ONEZ-1 well contain isotopically depleted 1,2,3,4-tetramethylbenzene (1,2,3,4-TetraMB; -26. 1 to -29.4‰) and 1,2,4-trimethylbenzene (1,2,4-TriMB; -26.4 to -29.7‰), which are isotopically similar to aryl isoprenoids (-29.9 and -31.2‰) and β-carotane (-28.5 to -31.3‰) identified in the bitumen fractions. Pyrolyzates from 3 samples in the lower sections of Well A contain isotopically enriched 1,2,3,4-TetraMB (ca. -16‰) and 1,2,4-TriMB (ca. -14‰), consistent with an origin from diagenetic products of isorenieratene/chlorobactene biosynthesized by green sulfur bacteria (Chlorobiaceae). Pyrolyzates from five samples in the upper sections of Well A are characterized by the presence of intermediate carbon-isotope values of 1,2,3,4-TetraMB (-20.7 to -22.8‰) and 1,2,4-TriMB (-19.3 to -21.2‰) and isotopically enriched isorenieratane (ca. -14.5‰). Off-line pyrolyzates from these lacustrine source rocks represent two distinct end members: 13C-depleted diagenetic products of β-carotene derived from a lacustrine algal source and 13C-enriched diagenetic products of isorenieratene/chlorobactene derived from green sulfur bacteria. Organic matter (OM) from ONEZ-1 well shows a significant proportion of algal biomass with a 13C-depleted composition. The presence of 13C-enriched biomarkers derived from carotenoids of Chlorobiaceae from samples in the lower part of Well A indicates the development of photic zone euxinia and a significant biogeochemical role of sulfur. In the upper section of Well A, the 1,2,3,4-TetraMB and 1,2,4-TriMB have δ 13C values indicative of contributions from both Chlorobiaceae and algae to the OM.
AB - We conducted molecular biomarker and compound-specific carbon isotope analyses of off-line pyrolyzates from lacustrine samples recovered by ONEZ-1 well (the Kissenda Formation) in the Gabon Basin and Well A (the Maculungo Formation) in the Kwanza Basin in West Africa. Pyrolyzates from ONEZ-1 well contain isotopically depleted 1,2,3,4-tetramethylbenzene (1,2,3,4-TetraMB; -26. 1 to -29.4‰) and 1,2,4-trimethylbenzene (1,2,4-TriMB; -26.4 to -29.7‰), which are isotopically similar to aryl isoprenoids (-29.9 and -31.2‰) and β-carotane (-28.5 to -31.3‰) identified in the bitumen fractions. Pyrolyzates from 3 samples in the lower sections of Well A contain isotopically enriched 1,2,3,4-TetraMB (ca. -16‰) and 1,2,4-TriMB (ca. -14‰), consistent with an origin from diagenetic products of isorenieratene/chlorobactene biosynthesized by green sulfur bacteria (Chlorobiaceae). Pyrolyzates from five samples in the upper sections of Well A are characterized by the presence of intermediate carbon-isotope values of 1,2,3,4-TetraMB (-20.7 to -22.8‰) and 1,2,4-TriMB (-19.3 to -21.2‰) and isotopically enriched isorenieratane (ca. -14.5‰). Off-line pyrolyzates from these lacustrine source rocks represent two distinct end members: 13C-depleted diagenetic products of β-carotene derived from a lacustrine algal source and 13C-enriched diagenetic products of isorenieratene/chlorobactene derived from green sulfur bacteria. Organic matter (OM) from ONEZ-1 well shows a significant proportion of algal biomass with a 13C-depleted composition. The presence of 13C-enriched biomarkers derived from carotenoids of Chlorobiaceae from samples in the lower part of Well A indicates the development of photic zone euxinia and a significant biogeochemical role of sulfur. In the upper section of Well A, the 1,2,3,4-TetraMB and 1,2,4-TriMB have δ 13C values indicative of contributions from both Chlorobiaceae and algae to the OM.
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U2 - 10.1016/j.orggeochem.2003.04.001
DO - 10.1016/j.orggeochem.2003.04.001
M3 - Article
AN - SCOPUS:0347319553
SN - 0146-6380
VL - 35
SP - 33
EP - 45
JO - Organic Geochemistry
JF - Organic Geochemistry
IS - 1
ER -