BENALIOULHAJ, SAID, and B. C. SCHRIEBER, Department of Geology, Queens College (C.U.N.Y.), Flushing, NY; J. TRICHET, Department Geologie, Universite d'Orleans, Orleans la Source, France; and R. P. PHILP, School of Geology and Geophysics, University of Oklahoma, Norman, OK

ABSTRACT: Factors Controlling Diagenetic Evolution of Organic Matter in the Septentrional Gulf (Morocco)

The sedimentary basins of Timahdit and Oulad-Abdoun, although very different in structural origins, were part of a single marine gulf that extended across Morocco for more than 500 km (west to east), from Upper Cretaceous through the Eocene. Overall reducing conditions prevalent in both basins are expressed by high amounts of organic matter that has been shown to have a marine phytoplanktonic origin and a very low diagenetic evolution. This immaturity of the organic matter is demonstrated by the yellow fluorescent color or the organic remains, by the low vitrinite reflectance (Ro <0.4), and by low pyrolysis maximum temperatures (around 4000 C). Subsidence has contolled the both the nature and the thickness of the deposits and also the accumulation and preservation of the associated organic matter. It has resulted in the deposition of a thick sequence of oil shale (300 m) very rich in clay and organic matter (TOC: 8-15%)in Timahdit, within the unstable zone of the Middle Atlas, while a condensed sequence (40 m) made up of dolomitic limestone, marls, shales and phosphates with a relatively low organic content (TOC: <4%) accumulated in the Oulad-Abdoun basin, within a stable platform along the Atlantic passive margin. Quantitative and qualitative analysis of Organic matter associated with a large variety of facies from both basins show the extreme sensitivity of organic compounds to processes that have affected them from the moment of their deposition and during early diagenesis. Among the critical parameters influencing the evolution of the organic matter and its egree of preservation are: mechanical reworking, Eh conditions, polymerization and condensation, and the nature of the organo-mineral associations. Interactions between metals and organic matter (Al, Si, Fe, Au, Ag, Cu, Zn, V, Ni, Co) was continuous during diagenesis. Integration of sulfur by the organic matter was very sensitive toboth Eh conditions and the concentration of chalcophile elements in the milieu of deposition.

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