BASAL CRETACEOUS (MIDDLE BERRIASIAN) PALE OKARST IN THE WESTERN SWISSJURA (BIENNE REGION) - BOREAL AND TETHYAN CORRELATIONS

In the western Swiss Jura Mountains, the Bienne section (Purbeckian fa cies with lacustrine to brackish and shallow marine lagoonal environme nts of the earliest Cretaceous) contains in the Marbre batard pro pane (Unite inferieure oolithique and basal parr of the Unite moyenne calc aire massive; Middle Berriasian; occitanica Zone) a breccia, including a block of nearly 3 m(3). The formation of the breccia is the result of the collapse of an important karstic cave. The formation of the kar stic network implies an important emersive event and has great interes t for sequence stratigraphic interpretation within the framework of a reliable correlation with the middle Berriasian mass-hows (privasensis Subzone) in the Vocontian basin. The biostratigraphical data on the o stracods and the charophytes allow correlation of the Unite inferieure oolithique (subalpina Subzone; lowermost Middle Berriasian of the Tet hyan realm) with the Cinder Beds in the Middle Purbeck of southern Eng land (runctoni Zone; lowermost Ryazanian of the Boreal realm). Consequ ently, the Jurassic-Cretaceous Boundary corresponding to the basis of the Purbeckian in the French and Swiss Jura Mountains (jacobi-grandis Zone of the Tethyan Lower Berriasian) must be placed in the uppermost part of the Boreal Volgian (lower part of the English Lower Purbeck). (C) 1996 Academic Press Limited