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ABSTRACT: Analysis of Subsidence and Modeling of Oil Formation in the Ragusa Basin (Iblean Plateau, Southeast Sicily)

I. Moretti, E. Brosse, S. Delahaye, F. Roure, L. Mattavelli

The Iblean plateau (southeastern Sicily) was part of the Apulian (African) margin of the Ligurian Tethys during the Mesozoic and played the role of a foreland during the Tertiary Alpine compression. From the Tortonian until the Holocene, the Apulian platform has been subducting northward underneath the European plate. Both the thickness and nature of the Apulian crust are poorly known.

Subsurface data, from wildcat wells in the Ragusa petroleum basin, and backstripping have been used to quantify the vertical movements and thinning of the Apulian margin in southeastern Sicily.

After quiet tectonics during the Middle Triassic, a rifting phase was initiated in the Hettangien, and lasted until the end of the Lias. Tectonic synrift subsidence can be great (up to 800 m in the wells analyzed). By contrast, the postrift subsidence, which gives an image of the lithospheric thermal anomaly, is very low. Comparison with some other current passive margin evolution, such as the Gulf of Lions, suggests that the Iblean plateau remained quite far away from the main axis of the rift.

In this general tectonic context, the burial history of the source rocks, i.e., the Noto (Rhaetian) and Streppenosa (mainly Hettangien) formations are quite different from one area of the Ragusa basin to another. Early Jurassic subsidence rates were relatively higher in the center and in the south, and this could have resulted in early oil kitchens in local grabens. On the contrary, in the north, oil formation is a very recent phenomenon, induced by the overthrusting of the Maghrebidic (Apenninic) nappes.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990