Journal of Petroleum Geology, Vol.11, No.3, pp. 347-354, 1988

©Copyright 2000 Scientific Press, Ltd.

ZOOPLANKTON FECAL PELLETS AS A SOURCE OF HYDROCARBONS IN CHALK

M.T. Moussa*

* Gulf Oil Exploration and Production Company, Houston Technology Center, Houston, Texas.
Present address: Chevron USA Inc., PO Box 599, Denver, CO 80201, USA.

Abstract

Evidence from biochemistry, marine geology and sedimentology shows that chalk could be a source of hydrocarbons, and that some hydrocarbons in some chalk reservoirs could have originated within the chalk. Coccolith ooze, the precursor of chalk, is deposited as the fecal (faecal) pellets of zooplankton, most probably copepods. These fecal pellets contain dihydrophytol which is a precursor of pristane;the latter is a precursor of some crude oil deposits. Zooplankton fecal pellets probably provided the organic source for some of the hydrocarbons in chalk. Some hydrocarbons in marine-and lacustrine-shale source rocks could have originated in much the same way.