Paleo-oxygenation in Tertiary epeiric seas: evidence from dinoflagellate cysts

The dinoflagellate cyst record from an epeiric setting in the Oligocene of Southwest Germany exhibits major changes associated with variations in pale o-oxygenation inferred from benthic foraminifera. Dinoflagellate cyst diver sity and equitability strongly decline in the case of extreme oxygen deplet ion. The relative abundance of the dinoflagellate cyst Thalassiphora pelagi ca inversely correlates with the availability of benthic oxygen. The T. pel agica spectrum consists of different morphotypes which are considered to re present different stages within the cystal part of the T. pelagica life cyc le following the concept of Benedek and Gocht. The distribution of these mo rphotypes is also linked to oxygen availability. Horizons with highest T. p elagica abundances are characterized by the occurrence of T. pelagica speci mens representing an early stage in cyst formation. A model is proposed tha t uses T. pelagica as a proxy to assess oxygenation both at the sediment su rface and in the water column. The occurrence of T. pelagica specimens repr esenting an early stage in cyst formation is interpreted to reflect the ext ension of oxygen-depletion upwards into the water column. Because T, pelagi ca is an easily recognized, globally distributed element of Paleogene and E arly Neogene dinoflagellate cyst assemblages, the application of this model may be of importance in the reconstruction of paleo-oxygenation in epeiric settings from these times. Its sensitivity to changes in benthic oxygenati on can be as high as (if not higher than) that of the approach based on for aminifera. Moreover, it is applicable to decalcified sediments. (C) 2001 El sevier Science B.V. All rights reserved.