Did the PETM trigger the first important radiation of wetzelielloideans? Evidence from France and northern Kazakhstan

Abstract

ABSTRACTUntil now it was presumed that the first major expansion of the dinoflagellate cyst subfamily Wetzelielloideae occurred during the Early Ypresian, with the appearance of Dracodinium (= Wetzeliella) astra at ∼55 Ma, i.e. ∼1 My after the Paleocene/Eocene boundary and after the onset of the negative Carbon Isotope Excursion (CIE), which is coeval with the Paleocene–Eocene Thermal Maximum (PETM) event. Palynological studies of lowest Eocene sections in northern Kazakhstan (former Turgay Strait) and France (southeastern part of the former North Sea Basin) indicate that the first strong radiation of the dinoflagellate cyst subfamily Wetzelielloideae occurred in two stages: the first major diversity corresponds to the late stage of the PETM (at least 16 new taxa from seven genera) at about 55.8 Ma and the second one a little later, after the PETM (three new taxa), but probably several hundred thousand years before the first appearance of Dracodinium astra. In both geographical areas, all newly described wetzelielloideans seem to disappear before the first occurrences of Dracodinium astra and Dracodinium lobiscum. Therefore, the first important radiation of the Wetzelielloideae occurred earlier (by about 800,000 y) than was previously postulated – thus closer to 56 than to 55 Ma. New wetzelielloidean taxa include 14 new formally described species, Axiodinium sparnacium, Dracodinium? modestum, Epelidinium brinkhuisii, Epelidinium leptotoichum, Epelidinium normandiense, Petalodinium lenisium, Stichodinium elegantulum, Stichodinium galliciense, Stichodinium parisiense, Stichodinium prostimus, Stichodinium sympagicum, Vallodinium heilmannii, Vallodinium picardicum and Wilsonidium modicum. The emended diagnosis of the genus Stichodinium is proposed.