Lower to middle Cretaceous sediments in the eastern Gulf of Mexico are richer in organic matter and have a more marine organic facies than their counterparts in the nearby western North Atlantic, suggesting that the Gulf was the more productive of the two areas. As in the western North Atlantic, the rate of supply of terrestrial organic matter was high when the rate of supply of noncarbonate clastic materials was high (at times of low sea level) and diminished as sea level rose. The rate of supply of marine organic matter was lower in the Early Cretaceous than in the Cenomanian, perhaps in response to the global rise in sea level over this period. Where they are thermally mature, the organic matterrich units drilled at Sites 535 and 540 should be excellent sources for liquid hydrocarbons. The Pleistocene sediments of the eastern Gulf are dominated by terrestrial organic matter representing Mississippi River effluent.

Sediment depth is given in mbsf. Organic matter types by Th. C. Masran (in percent of kerogen fraction) using organic matter classification scheme of Masran and Pocock (1981).

Supplement to: Summerhayes, Colin P; Masran, Theodora C (1984): Organic facies of Cretaceous sediments from Deep Sea Drilling Project Sites 535 and 540, eastern Gulf of Mexico. In: Buffler, RT; Schlager, W; et al. (eds.), Initial Reports of the Deep Sea Drilling Project, Washington (U.S. Govt. Printing Office), 77, 451-457