THE MARL SLATE AND BASAL PERMIAN BRECCIA AT MIDDRIDGE, CO. DURHAM

Abstract

SUMMARY A study of the stratigraphy and palaeontology of the Basal Permian Breccia and Marl Slate at Middridge, south-east Durham, was recently made possible by the reopening of an old quarry. The Permian Breccia here, although originally deposited under terrestrial (desert) conditions, was subsequently partially redistributed during the transgression of the Zechstein Sea. Numerous specimens of invertebrates, fish and plants were collected and the assemblages as a whole demonstrate that the Marl Slate is of a near shore facies in this part of Durham. Sessile, shallow water invertebrate fossils are relatively abundant at the top of the Breccia and in a laminated limestone within the Marl Slate. Many of these fossils represent several years of in situ growth which contradicts the accepted palaeoenvironmental interpretation of seasonal toxic conditions. It is suggested that toxic conditions were less severe in the near shore environment which probably acted as a refuge for the deep and shallow water faunas during periods of unfavourable conditions in the offshore area. This interpretation is supported by other exposures of the Marl Slate in south Durham which yield a sparse invertebrate assemblage in contrast to the exposures to the north-east which yield few or no invertebrates and an essentially deep water fish fauna.