BELIN, SOPHIE, and A. Y. HUC, Institut Francais Du Petrole, Rueil-Malmaison, France

ABSTRACT: Organic Matter Content and Microhabitat of Kerogen within the Lower Part of the Monterey Formation (Miocene of California)

The lower part of the Monterey Formation has been observed with scanning electron microscope (SEM) using backscattered electron mode (BSE), and local chemical analyses have been performed with an energy dispersive spectrometer associated withthe SEM.

Organic matter distribution is characterized by its close association with clay minerals. No well-delimited organic patches are visible. In the most organic-rich samples, organic matter is encountered as small isolated domains (<10 micrometers) and tends to form purely organic laminae ranging from 50 to 100 micrometers in length within the argillaceous-organic matrix.

The preservation of lamination indicates lack of bioturbation and a low energy depositional environment. The organic matter distribution observed in this sediment is a new organo-mineral microtexture pattern for a confined marine depositional environment, because such depositional conditions generally lead to a laminate organic matter repartition, even for similar organic carbon content, and organic matter particles have well defined boundaries. Sediments having high organic matter content are interpreted as derived from previously a soupy argillaceous groundmass in which detrital particles were incorporated. These organo-mineral aggregates could originate from fecal pellets. A systematic occurrence of silica within the organic matter itself has been noted. This could be an interestin clue concerning the origin of the organic matter suspected to come from diatoms body or protoplasm.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.