Published 1996 as part of Memoir 66
Copyright © 1996 The American Association of Petroleum Geologists.  All Rights Reserved.
 

Evidence from large numbers of sediment cores collected on the continental slope of the U.S. Gulf of Mexico suggests that methane is generated by bacteria at depths of about 4 m from seepage petroleum. Marine sediment-dwelling methanogenic bacteria use carbon dioxide generated at shallow depths by aerobic and anaerobic bacteria from available organic material. Until the cores described here were evaluated, it appeared that shallow occurrences of biogenic methane in Pliocene, Pleistocene, and Recent sediments of the Gulf Coast were derived solely from organic detritus, both marine and terrestrial, of the same ages. However, circumstantial evidence indicates that a significant source of organic carbon for methanogenesis is provided by petroleum that frequently seeps into surface sediments. The relative scales of methane generation from these competing sources cannot yet be established.