Abstract
In the western Swiss Jura Mountains, the Bienne section (Purbeckian facies with lacustrine to brackish and shallow marine lagoonal environments of the earliest Cretaceous) contains in the Marbre bâtard pro parte(Unité inférieure oolithique and basal part of the Unité moyenne calcaire massive; batard pro parte (Unite inferieure oolithique and basal part of the Unite moyenne calcaire massive; Middle Berriasian; occitanicaZone) 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 karstic network implies an important emersive event and has great interest for sequence stratigraphic interpretation within the framework of a reliable correlation with the middle Berriasian mass-flows ( privasensisSubzone) in the Vocontian basin. The biostratigraphical data on the ostracods and the charophytes allow correlation of the Unité inférieure oolithique ( subalpinaSubzone; lowermost Middle Berriasian of the Tethyan realm) with the Cinder Beds in the Middle Purbeck of southern England ( runctoniZone; lowermost Ryazanian of the Boreal realm). Consequently, 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).
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