The Alteration of Detrital Minerals in the Mesozoic Rocks of Yorkshire

Abstract

Dr. R. H. Rastall (1932) has described the petrography of the Middle Jurassic sandstones of Eskdale and shown that they possess a remarkably restricted suite of detrital minerals, having for example no garnet or staurolite, but containing much anatase and brookite, both apparently of authigenic origin. The present writer (1934) showed that in other parts of North-East Yorkshire beds of the same age contain relatively rich heavy mineral assemblages. After a more detailed survey the writer was able to show (1939c, Text-fig. 2) that the peculiar restricted assemblage was confined to a belt or elongated oval area—which can be roughly defined as occupying the north-west and northeast quarters of Sheet 43 (Geol. Survey “one-inch” map) and the north-east quarter of Sheet 44—and that as one passed outward from this area one met with increasingly richer assemblages at all horizons in the Middle Jurassic.¹ This result, as well as the results of mapping certain other characteristics of the assemblage, led the writer to suggest that this belt, which coincides closely with the Cleveland axis, is a belt along which active decomposition and alteration has occurred in these deposits after they were laid down.