Mineralogy op yoredale series rocks in Upper Teesdale with special reference to clay minerals

Abstract

A description of the stratigraphy of the area studied is given in which the variations in lithology and sequence are illustrated. The methods of clay mineral analysis are discussed and it is concluded that X-ray analysis is most useful for the present work. The argillaceous rocks are classified into types on characteristics recognisable in the field and the results of petrographic and X-ray analyses are tabulated. Apart from kaolinite, which is post-depositional in origin, only three different clay minerals occur: illite, chlorite and mixed- layer. Different types of argillaceous rock have different clay mineral assemblages. Associated arenaceous and calcareous rocks are similarly classified on field characters and are analysed petrographically. A system of sandstone classification is proposed. The relationship between the clay mineralogy of a sedimentary rock and the origin, transport, deposition and post-depositional history of the minerals is discussed. Recent shallow water marine and deltaic sedimentation are reviewed and the various facies recognised in the Gulf of Mexico and the Mississippi Delta are enumerated. It is postulated that the Yoredale sediments were deposited in a shallow water marine environment from a series of small shoal-water deltas. The different sediment types and their mineralogies are related to different conditions in the various facies of the environment. Repetition of the sedimentation in the form of cycles is discussed briefly. An additional chapter deals with the igneous rocks intruding the sediments and the metamorphic effects of the Whin Sill upon the country rocks.