Integrated stratigraphy of an offshore succession influenced by intense siliciclastic supply: Implications for Coniacian tectono-sedimentary evolution of the West Sudetic area (NW Bohemian Cretaceous Basin, Czech Republic)

We present the interpretation of tectono-sedimentary evolution of the West Sudetic area (central Europe) during the latest Turonian–middle Coniacian as recorded by deposits of the NW part of the Bohemian Cretaceous Basin. This paper provides the first strontium isotope curve from the Upper Cretaceous of the Bohemian Massif. The exact stratigraphic framework was provided by combining of macrofossils (inoceramids) and calcareous nannofossils. Six inoceramid zones were distinguished, from Cremnoceramus deformis erectus Zone to Volviceramus koeneni Zone. Biostratigraphic data were combined with XRF curves and geophysical logs which allowed for correlation of several key sections within the study area. Using the genetic stratigraphy, contrasting parts of the depositional system interpreted as nearshore to deltaic were successfully correlated. Six elementary sequences were defined within the studied succession. These are TUR 7 (latest Turonian), backstepping, aggradation-dominated, with a short-term progradational episode and CON 1 to 5 (early–middle Coniacian), deposited during a period of increasing depth through time. The progradational pattern is most typical for the CON 4 sequence. Intensified sediment supply resulting in pronounced progradation is also evidenced by increased siliciclastic influx to the offshore zone and resulting changes in calcareous nannofossil assemblages.