Shallow marine Lower and Middle Miocene deposits at the southern margin ofthe North Sea Basin (northern Belgium): dinoflagellate cyst biostratigraphy and depositional history

Detailed dinoflagellate cyst analysis of the Lower-Middle Miocene Berchem F ormation at the southernmost margin of the North Sea Basin (northern Belgiu m) allowed a precise biostratigraphical positioning and a reconstruction of the depositional history. The two lower members of the formation (Edegem S ands and decalcified Kiel Sands) are biostratigraphically regarded as one u nit since no significant break within the dinocyst assemblages is observed. The base of this late (or latest) Aquitanian-Burdigalian unit coincides wi th sequence boundary Aq3/Burl as defined by Hardenbol and others, in work p ublished in 1998. A hiatus at the Lower-Middle Miocene transition separates the upper member (the Antwerpen Sands) from the underlying member. The gre ater part of the Antwerpen Sands were deposited in a Langhian (latest Burdi galian?)-middle Serravallian interval. The base of this unit coincides with sequence boundary Bur5/Lan1. Biostratigraphical correlation points to a di achronous post-depositional decalcification within the formation since part s of the decalcified Kiel Sands can be correlated with parts of the calcare ous fossil-bearing section, up to now interpreted as Antwerpen Sands. The d inoflagellate cyst assemblages are dominated by species with a inner neriti c preference, although higher numbers of oceanic taxa in the upper part of the formation indicate incursions of oceanic watermasses into the confined depositional environment of the southern North Sea Basin.