by Schoell, M, McCaffrey, M A, Fago, F J and Moldowan, J M
Abstract:
An immature, tar-like oil (API approximately 3-degrees, delta-C-13 = -23.6 parts per thousand vs. PDB) from the Miocene Monterey Formation offshore California was selected for a study of carbon isotopic signatures of individual biomarkers. The three principal stereoisomers of 28,30-bisnorhopane (C28) have, within analytical precision, identical carbon isotopic compositions (average delta-C-13 = -32.3 +/- 0.4 parts per thousand) and are considerably depleted in C-13 compared to the whole oil. These 28,30-bisnorhopanes (BNH) differ isotopically from C29 and C30 17-alpha(H)-hopanes (-25.8 parts per thousand and -26.1 parts per thousand) and C31-C35 extended hopanes (delta-C-13 = -27.7 parts per thousand) and suggest different precursors for the C28 hopanes than for C29-C35 hopanes. The relative depletion of BNH of almost 9 parts per thousand compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria, possibly not yet identified H2S oxidizers, which utilize C-13-depleted substrates. The C29 and C30 hopanes are, within analytical precision, isotopically identical (approximately -26 parts per thousand) and similar to algal-derived compounds, e.g., C27 steranes (approximately -25.9 parts per thousand), which is consistent with a cyanobacterial source for these hopanes. An archaebacterial biomarker, 1,1'-biphytane (delta-C-13 = -25.5 parts per thousand), likely derived from methanogens, is also isotopically similar to C27 sterane. Norpristane, pristane, and phytane, liberated by desulfurization of the aromatic and polar maltene fractions, show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen (total range from -24.5 to -27.5 parts per thousand). This isotopic similarity supports a common origin for the free and sulfur-bound forms of these isoprenoids. This origin could be algal and/or archaebacterial lipids, which both show isotopic compositions within the range of the C18-C20 isoprenoids. Like other marine-derived organic matter, this Monterey oil does not show the strong C-13 depletion typical for methylotroph-derived compounds characteristically found in organic matter of lacustrine origin. This may indicate fundamental differences of methane recycling processes in marine (sulfate-dominated) as compared to lacustrine environments.
Reference:
Carbon Isotopic Compositions of 28,30-Bisnorhopanes and Other Biological Markers in a Monterey Crude-Oil (Schoell, M, McCaffrey, M A, Fago, F J and Moldowan, J M), In Geochimica et Cosmochimica Acta, volume 56, 1992.
Bibtex Entry:
@article{RefWorks:15336,
abstract = {An immature, tar-like oil (API approximately 3-degrees, delta-C-13 = -23.6 parts per thousand vs. PDB) from the Miocene Monterey Formation offshore California was selected for a study of carbon isotopic signatures of individual biomarkers. The three principal stereoisomers of 28,30-bisnorhopane (C28) have, within analytical precision, identical carbon isotopic compositions (average delta-C-13 = -32.3 +/- 0.4 parts per thousand) and are considerably depleted in C-13 compared to the whole oil. These 28,30-bisnorhopanes (BNH) differ isotopically from C29 and C30 17-alpha(H)-hopanes (-25.8 parts per thousand and -26.1 parts per thousand) and C31-C35 extended hopanes (delta-C-13 = -27.7 parts per thousand) and suggest different precursors for the C28 hopanes than for C29-C35 hopanes. The relative depletion of BNH of almost 9 parts per thousand compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria, possibly not yet identified H2S oxidizers, which utilize C-13-depleted substrates. The C29 and C30 hopanes are, within analytical precision, isotopically identical (approximately -26 parts per thousand) and similar to algal-derived compounds, e.g., C27 steranes (approximately -25.9 parts per thousand), which is consistent with a cyanobacterial source for these hopanes. An archaebacterial biomarker, 1,1'-biphytane (delta-C-13 = -25.5 parts per thousand), likely derived from methanogens, is also isotopically similar to C27 sterane. Norpristane, pristane, and phytane, liberated by desulfurization of the aromatic and polar maltene fractions, show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen (total range from -24.5 to -27.5 parts per thousand). This isotopic similarity supports a common origin for the free and sulfur-bound forms of these isoprenoids. This origin could be algal and/or archaebacterial lipids, which both show isotopic compositions within the range of the C18-C20 isoprenoids. Like other marine-derived organic matter, this Monterey oil does not show the strong C-13 depletion typical for methylotroph-derived compounds characteristically found in organic matter of lacustrine origin. This may indicate fundamental differences of methane recycling processes in marine (sulfate-dominated) as compared to lacustrine environments.},
annote = {PT: J; UT: WOS:A1992HJ96300039},
author = {Schoell, M and McCaffrey, M A and Fago, F J and Moldowan, J M},
doi = {10.1016/0016-7037(92)90070-Y},
isbn = {0016-7037},
journal = {Geochimica et Cosmochimica Acta},
month = {mar},
number = {3},
pages = {1391--1399},
title = {{Carbon Isotopic Compositions of 28,30-Bisnorhopanes and Other Biological Markers in a Monterey Crude-Oil}},
url = {http://www.sciencedirect.com/science/article/pii/001670379290070Y},
volume = {56},
year = {1992}
}