SEQUENCE ANALYTICAL APPROACH TO THE UPPER KIMMERIDGIAN LOWER TITHONIAN STORM-DOMINATED RAMP DEPOSITS OF THE BOULONNAIS (NORTHERN FRANCE) - A LANDWARD TIME-EQUIVALENT TO OFFSHORE MARINE SOURCE ROCKS

An interdisciplinary approach based on high-resolution physical strati graphy, biostratigraphy, organic matter analysis and clay mineralogy h as been applied to the mixed siliciclastic/carbonate Kimmeridgian/Tith onian deposits of the Boulonnais (north-western France). These rocks a re the age-equivalents of some of the offshore marine source rocks of the North Sea and were deposited in an overall storm-dominated homocli nal ramp setting which may represent one of the most shore-proximal se diments of this age cropping out in north-western Europe. Comparison w ith data from the Yorkshire, Dorset, Lorraine and Aquitaine areas allo ws the discrimination of three major transgressive-regressive sediment packages with disconformities of interregional extent: (1) from the B aylei Zone to top Eudoxus Zone; (2) from the Autissiodorensis Zone to base Scitulus Zone; (3) from the upper Scitulus Zone to the Pectinatus Zone. The lower two regionally correlative disconformities correspond to the sequence boundaries at the top of the Eudoxus Zone and the top of the Autissiodorensis Zone, formed by high-frequency relative sea-l evel variations during the periods of maximum transgression of the pla tform. The latter disconformity (the P1 nodule bed) reflects a major t ectonically induced reorganization of the north-west European intrashe lf sedimentary basin, characterized by a shift in both the location of the main depocentre and the sources of sediment production.