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Speeton Beds

1911 Encyclopedia Britannica

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In English geology, a series of clays well exposed at Speeton, near Filey on the Yorkshire coast. Peculiar interest attaches to these beds for they are the principal representatives in Britain of the marine phase of the Lower Cretaceous system. The Speeton Clays pass downwards without break into the underlying Kimeridgian; they are capped by the Red Chalk, which may be regarded as the equivalent of the Upper Gault of southern England. These beds thus form a passage series between marine Jurassic strata and those belonging undoubtedly to the Cretaceous system; in this way they correspond with the Purbeck-Wealden rocks, which form a connecting link between estuarine Jurassic and Cretaceous strata.

Above the dark, bituminous, nodular shales with Kimeridge fossils at the base of the Speeton Clay comes the zone of Belemnites lateralis (34 ft.), with Olcostephanus gravesiformis, O. rotula, and species of Hoplites and Oxynoticeras; this is followed by the zone of Belemnites jaculum, with B. cristatus, Olcostephanus (Astieria) astieri, O. (Simbirskites) inversus and O. (S.) Speetonensis in ascending order; Echinospatagus cordiformis, a species found in the typical Neocomian area, also occurs in this zone. The next higher zone is that of Belemnites brunsvicensis (= semi-

canaliculatus ) (roo ft.), with B. Speetonensis, Hoplites deshayesii, and Amaltheus bicurvatus. The topmost zone is characterized by Belemnites minimus with Inoceramus concentricus and I. sulcatus; it consists of a few feet of mottled clays. It appears, therefore, that while the lower portions of the Speeton Clay are the equivalents of the Wealden and perhaps of the Purbeck beds, the higher portions are the equivalents of the Lower Greensand and part of the Gault. In Lincolnshire the upper Speeton beds are represented by the Carstone and Tealby Limestone and Clay, and the lower Speeton by the Claxby Ironstone, Spilsby Sandstone and lower part of the Tealby clay. A similar faunal horizon is recognized in Heligoland and Russia.

See Cretaceous; Neocomian; Kimeridgian; also G. W. Lamplugh, Q.J.G.S. (1889), xlv. (1896), lii.; Rep. Brit. Assoc. (1890); A. Pavlov and G. W. Lamplugh, Bull. soc. imp. nat. Moscow. (1891),(1891), and Q.J.G.S. (1897), liii.