Biostratigraphy and sequence stratigraphy of the Lower Cretaceous in central and SE Poland

Detailed biostratigraphy and sequence stratigraphy of the Lower Cretaceous deposits in central and southeastern Poland (the Warsaw and Lublin troughs and the Carpathian Foredeep) were established and refered to the cyclicity nature of the sedimentary basins filling. The surfaces of transgression and maximum flooding, and sequence boundaries were identified on the grounds of geophysical well-logs analysis, including: gamma (G), neutron (N), spontaneous potential (SP), and resistivity (R) logs. The analysis allowed us to distinguish sedimen-tary sequences of various scales and to correlate them precisely throughout the studied area. The chronostrati-graphic framework was based on analyses of ammonite, microfauna and calcareous nannoplankton assemblages analysed in the same series. Mixed, Tethyan and Boreal macro-and microfauna allowed us to identify biostrati-graphic zones of both, the Tethyan and Boreal realms. The recognised boreal ammonite zones included robustum, heteropleurum (lowermost Valanginian), polytomus-crassus, triptychoides (Upper Valanginian), amblygonium, noricum (Lower Hauterivian) and gottschei (Upper Hauterivian), as well as the Tethyan zones, such as petransiens (Lower Valanginian), verrucosum (Upper Valanginian) and radiatus (Upper Hauterivian). Eight foraminiferal assemblages were identified in the studied series. Some of them were correlated with the six Berriasian and Valanginian ostracod zones: Cypridea dunkeri, C. granulosa, C. vidrana, Protocythere propria emslandensis, P. aubersonensis and P. frankei. Thirteen calcareous nannoplankton zones have been distinguished, in reference to the stratigraphical zonal scheme of the Lower Saxony Basin. The microfossil data allowed us to recognise the position of the Jurassic/Cretaceous boundary. It was correlated with a sequence boundary by analysis of geophysical logs. This boundary was identified along the studied area, over a distance of more than 170 km. Genetically controlled third order sedimentary sequences (parasequences) were described in the Lower Cretaceous, which record the progress of the sedimentary basins filling. A local curve of relative sea-level changes presented in this paper was correlated with a global one. A re-construction of depositional sequences allowed us to indicate periods of tectonic activity in the studied area, adjacent to the Teisseyre-Tornquist Zone.