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Phytotaphonomy in Subtropical to Temperate Bayhead Delta

Robert A. Gastaldo

Deltaic regimes act as sinks for hydrocarbon precursors of various organic origin. Most organic detritus incorporated into deltaic sediments is contributed by vegetation established in wetland environments. Processes that incorporate vegetational components in deltaic subenvironments vary, depending on the climate and geography of the sediment-receiving basin. Understanding the phytotaphonomy within the sedimentologic context of different deltas will help workers develop criteria to identify ancient deltaic subenvironments. Some subenvironments are richer in accumulated plant detritus than others; therefore, to plan exploration and exploitation programs, the relationships between sources and reservoirs must be understood.

The Mobile delta, Alabama, is a bayhead delta that began prograding through a drowned Pleistocene river valley before 9.5 k.y.B.P. Plant detritus accumulated--and is presently accumulating--in parts of the upper and lower delta flood basins. In the upper delta, large quantities of detritus are deposited in abandoned distributary channels, whereas litter is recycled in clastic swamps. Organic detritus is concentrated in the lower delta in interdistributary bays and marshes. These latter sites contain more productive source sediments for future hydrocarbon resources.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.