Geochemical evidence for an Early Cambrian origin of the ‘Q’ oils and some condensates from north Oman

Autor: Amy E. Kelly, Roger E. Summons, Paul N. Taylor, Gordon D. Love, Emmanuelle Grosjean
Rok vydání: 2012
Předmět:
Zdroj: Organic Geochemistry. 45:77-90
ISSN: 0146-6380
DOI: 10.1016/j.orggeochem.2011.12.006
Popis: The Q family of oils from Oman was previously recognized as highly unusual and distinct from the more prevalent Huqf oil family by having an extraordinarily high C27/C29 sterane ratio and δ13C values near −30‰. A re-evaluation of the hydrocarbon constituents of the Q oils using GC–MS–MS analyses resulted in identification of other useful geochemical discriminators that include gammacerane/hopane ratios between 0.5 and 0.9, C24T/C23T ⩾ 0.7 combined with C22T/C21T cheilanthane ratios Although we were unable to identify a source facies within the sediments of the South Oman Salt Basin that convincingly correlated with the hydrocarbons of the Q oils, the geochemistry of Q oils provided valuable clues about their origin. Sterane and terpane patterns indicated that the Q source rock is most likely a marine shale deposited under intermittently anoxic and hypersaline conditions. The absence of a carbon isotopic ordering anomaly for normal alkanes and isoprenoids points to a Cambrian age for the Q oils. Moreover, trends in the patterns of norsteranes in south Oman carbonate stringer oils suggest the Q oil source originates from one of the upper units of the Ara carbonate and evaporite sequence. More specifically, our results point to a siliciclastic source rock lying stratigraphically above the A6 carbonates from the Dhahaban Formation. The high relative abundances of 24-isopropylcholestanes in Q oils likely originate from demosponges and we hypothesize that the 17-methylpentatriacontane, which is so abundant in Q oils, is a biomarker for early arthropods that inhabited the salt basins of Oman at the very beginning of the Cambrian Period.
Databáze: OpenAIRE
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