Paleoenvironment and Petroleum Potential of Mid-Cretaceous Black Shales in Atlantic Basins: ABSTRACT

Abstract

Cores from the Deep Sea Drilling Project in the Atlantic Ocean have permitted recognition of widespread organic-rich black shales in the mid-Cretaceous. However, geochemical studies have proved that the origin and petroleum potential of this organic matter is highly variable. Three main types of organic material can be recognized in these sediments from kerogen studies: (a) marine planktonic, deposited in a reducing environment; (b) terrestrial higher plants, moderately degraded; and (c) residual organic matter, either oxidized in subaerial environments and/or recycled from older sediments. Vertical and horizontal variations of these three types of organic matter are illustrated by geochemical logs in each main basin of deposition. Paleogeography and environment of deposition of organic deposits are deduced from these data. The petroleum potential of the sediments is therefore a consequence of the paleogeographic setting. Thus, the zones favorable for oil and gas (given adequate maturation), or those devoid of any potential, can be delineated. Complementary studies of wells on the continental shelf of the North American continent tend to show that the organic characters in the deep basins can be correlated with those recognized in nearshore locations. End_of_Article - Last_Page 542------------