Author	Head, M.J.
Year	1994
Journal	Micropaleontology vol. 40: 289-321Micropaleontology vol. 40: 289-321
Title	Morphology and paleoenvironmental significance of the Cenozoic dinoflagellate genera Tectatodinium and Habibacysta

Abstract Head, M.J., 1994; Morphology and paleoenvironmental significance of the Cenozoic dinoflagellate genera Tectatodinium and Habibacysta. Micropaleontology vol. 40: 289-321 Presence of the warm-water species Tectatodinium pellitum Wall 1967 emend. nov. is established for the mid Pliocene Coralline Crag Formation (about 3.75-3.55 Ma) at Rockhall Wood, Suffolk, in eastern England, when North Sea temperatures were 4¦ to 5¦C higher than today. The dinoflagellate assemblage reflects warm temperate conditions, as do other fossil groups. The reputed occurrence of Tectatodinium pellitum in post-2.6 Ma upper Pliocene through lower Pleistocene? deposits of eastern England is not substantiated: its apparent absence likely reflects cooling initiated at 2.6 Ma. The cool-tolerant species Habibacysta tectata Head et al. 1989 is documented for the first time from eastern England where it occurs commonly in the Royal Society borehole at Ludham, Norfolk (about 2.4-1.8 Ma) and Chillesford Sand Member (about 2.0 Ma) of the Norwich Crag Formation, Chillesford, Suffolk - two sections previously reported as containing Tectatodinium pellitum. The common presence of H. tectata seems to indicate mild- to cool-temperate marine conditions based on its fossil occurrences at high-latitude sites. Species determinations have been aided by restudy of the holotypes of T. pellitum and H. tectata. Previous misidentification of these species has obscured their paleoenvironmental significance. The holotype of Tectatodinium pellitum, the type of the genus, has a non-tegillate wall comprising a thin pedium and thick, spongy, distally open luxuria. The species, here emended to include new observations of wall structure and archeopyle margin, ranges from at least early Eocene to present day, occurring in deposits of 50 Ma in the Labrador Sea, Ocean Drilling Program Hole 647A. The genus Tectatodinium is here emended to include only those species with a lanate to spongy, distally open luxuria. Pyxidinopsis? pannonia (Lentin and Williams 1973) comb. nov. (al. Tectatodinium? pannonium) and Pyxidinopsis psilata (Wall and Dale in Wall et al. 1973) comb. nov. (al. Tectatodinium psilatum Wall and Dale in Wall et al. 1973) do not meet this requirement and are transferred accordingly. Barssidinium pliocenicum (Head 1993) comb. nov. (al. Sumatradinium pliocenicum), mentioned along with other species in the text, is transferred in compliance with the newly established taxonomy of Sumatradinium Lentin and Williams 1976 emend. Lentin et al. 1994 and Barssidinium Lentin et al. 1994.