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Radiolarian and foraminiferal events at the Albian-Cenomanian and Cenomanian-Turonian boundaries (Tethyan Province, Crimean Mountainsстатья
- Авторы: Vishnevskaya V., Bragina L.G., Kopaevich L.F.
- Сборник: Proc. Meeting “Global events during the quiet Aptian-Turonian superchron
- Год издания: 2005
- Место издания: Grenoble, France
- Первая страница: 201
- Последняя страница: 206
- Аннотация: The development of phylogenetic and morphological features of Albian-Turonian radiolarian skeletons are useful for biostratigraphic and paleoenvironmental interpretation. Evolution of radiolarians during the late Albian was marked by development and perfection of skeletal features necessary for floating in pelagic zone, The diversity and distinctive features of late Albian assemblages consist in abundance of high-conical tests with triangular and quadrangular distal sections and with lateral costae in the corners grading into terminal legs. The Albian-Cenomanian transition was a time of intense development of rotaliporids (planktonic foraminifers), a highly specialized group of planktonic foraminifers, which became extinct in the terminal Cenomanian. Rotapolirids coexisted with other groups of planktonic foraminifers, and this was the polytaxic stage in evolution of foraminifers. The less abundant calcareous planktonic microfossils and radiolarians from the bituminous member, a marker of anoxic event, are largely represented by dwarfish specimens in the upper Cenomanian. Remarkable are abundant small planktonic foraminifers of the Genus Hedbergella comparable in size with radiolarians and monstrous specimens. Radiolarians are accompanied by abundant siliceous sponge spicules often of irregular shape that is probably indicative of abnormal salinity in the basin of sedimentation. Radiolarians are largely represented by simple discoid forms and primitive Dictyomitra species.
- Добавил в систему: Копаевич Людмила Федоровна