Organic Matter in the Paleogene West European Rift: Bresse and Valence Salt Basins (France)

A. Curial, D. Dumas, R. Moretto

The Bresse and Valence basins are two adjacent segments of the West European rift. They contain thick Paleogene halite sequences including intercalated and interfingering siliciclastic material and carbonate and sulfate deposits. Source rock samples in this study were mainly taken from the depocenters because of maximum sampling coverage. Organic matter (OM) is generally immature and occurs primarily within intercalated nonhalitic beds. The Bresse basin seems to contain more OM in (1) the Intermediate Salt Formation (Priabonian), composed of alternating laminated carbonate and halite beds; (2) the upper part of the Upper Salt Formation (clayey carbonate beds; Rupelian), affected by synsedimentary halite solution; and (3) the solution breccia which immediate overlies the s lt sequence. In the Valence basin, the organic-rich layers are concentrated in the Subsalt Formation (carbonate beds; Priabonian), and the upper part of the Lower Salt Formation (laminites; Rupelian). In both basins, type III organic matter is associated with terrigenous facies. Type I is abundant in the Valence basin (laminites), and type II seems to be more abundant in the Bresse basin. The amount of OM varies considerably, and we suppose it is higher toward the basin margins. From studies made in evaporite basins in other region, which are also known to have significant amounts of organic matter, we find a similar range of organic composition. Such studies are of interest because of their petroleum potential and for understanding precise depositional environments and waste disposal pr blems (gas generation with local heat source).

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.