MOSCA, FAUSTO, and DALLA STEFANO, AGIP S.P.A., Milano, Italy

ABSTRACT: Organic Matter Distribution in the Flysch Deposits of the Marnoso-Arenacea Formation, Miocene, Northern Apennines, Italy

The Marnoso-Arenacea Formation represents the filling of the Miocene Apennine foredeep by widespread and thick turbidite systems. Based on stratigraphic and sedimentologic considerations, two major sequences, related to the development of the Apennine orogene and to migration toward northeast of the depocenters, have been recognized. In both these units, respectively, upper Burdigalian-Serravallian and uppermost Serravallian-Tortonian, a major foredeep and a piggyback basin belt coexisted. The former is characterized by the development of depositional lobes down current passing to basin plain deposits; the latter were filled mostly by channel-levee-slope fine-grained deposits.

To evaluate the petroleum potential of the different facies associations recognized within the Marnoso-Arenacea Formation, 300 samples were collected along the Santerno Valley type section and analyzed by using the basic geochemical methods.

A preliminary space-time model concerning the distribution and nature of the naphtogenic facies in a foredeep basin has been developed. In particular, the average organic carbon content vs. hydrogen index and petroleum potential shows that the preservation of organic matter seems to be better in the basin plain than in the lobe area. Furthermore, it has been noticed that similar facies associations, but of different age, show significant variation in the petroleum potential (S2) and in the hydrogen index (HI). These variations do not reflect changes in the organic input, as pointed out by kerogen composition and gc-ms analyses, but are related to different sedimentation rates during the Miocene. The best condition for organic matter preservation seems to be related to medium to high s dimentation rates, whereas low rates lead to a more diffused oxidation. This is true for similar paleoenvironmental conditions with the same organic productivity. However, it is important to point out that very high sedimentation rates can lead to a dilution of the organic matter in the siliciclastic fraction.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.