Calcareous nannoplankton in the Upper Jurassic ma rine deposits of the Bohemian Massif: new data concerning the Boreal-Tethyan communication corridor
Abstrakt
Calcareous nannoplankton assemblages from the Jurassic relict deposits in the northern part of the Bohemian Massif are described here for the first time. They are generally of low diversity and dominated by watznaueriaceans.
Some of them are diagenetically affected, probably due to dolomitisation. Calcareous nannoplankton enables the stratigraphical range of the Northern Bohemia Jurassic succession to be extended to the Tithonian by reference to the stratigraphical range of Jurassic platform sequences in Central Poland and the eastern part of the Bohemian Massif.
The Oxfordian-Kimmeridgian nannofossil assemblages indicate a generally oligotrophic condition of the restricted sea with episodic fluvial input containing terrestrial nutrients. The character of the upper part of the water column was generally uniform and did not reflect variabil ity at the sea-floor expressed by lithofacies diversity.
The palaeoenvironment interpreted for the famous former palaeontological locality "Sternberk Quarry" was characterized by a higher nutrient content and more stable environment. The Tithonian nannofossil assemblages contain warm-water Tethyan taxa which suggest south-north migration of nannoplankton due to warming during the Jurassic-Cretaceous boundary interval.