Abstract:
To further understand the distribution and abundance of Apectodinium through space and time, dinoflagellate cyst (dinocyst) records from two well-calibrated Paleogene sections in the Tethys (Tunisia and Uzbekistan) have been examined. Apectodinium was present in the southern Tethys (Tunisia) by the late Paleocene (planktonic foraminiferal Subzone P4a), confirming earlier findings that the genus evolved in lower latitudes. Apectodinium abundance was frequent to dominant from the upper Paleocene to lower Eocene in the Tethys. The initial Eocene thermal maximum (IETM) at lower latitudes appears to be characterized by high percentages of Apectodinium, although it may not always have dominated assemblages. Other dinocyst genera with thermophilic preferences may be abundant during the IETM. At mid to high latitudes, Apectodinium has been sporadically recognized during the upper Paleocene. Nevertheless, the IETM at mid to high latitudes was still characterized by Apectodiniumdominated assemblages. Additional Apectodinium acmes occurred in the lower Eocene, although as yet it is unclear if these are globally isochronous. Intervals of Apectodinium-dominated assemblages are indicative of environmental conditions that were apparently markedly different to "normal background settings" of the late Paleocene-early Eocene. Sea surface temperature (SST) was probably the main control in distribution since Apectodinium acmes at mid to high latitudes seem to have occurred during intervals of highest SSTs, such as the IETM. In addition, the probable heterotrophic Apectodinium "blooms" were intricately linked to enhanced runoff and increased delivery of nutrients in surface waters, probably as a result of intensification of the weathering cycle and other possible specific oceanic conditions.
