The concealed Upper Palaeozoic rocks of Berkshire and South Oxfordshire

Abstract

Lithological, sedimentological and biostratigraphical (mainly palynological) details are presented of Devonian and Carboniferous rocks proved in five boreholes in Berkshire. The Devonian rocks include both fluvial Old Red Sandstone and marine facies. Two boreholes proved Dinantian rocks, of Courceyan (Lower Limestone Shales) age in one and probable Holkerian limestones in the other. These are overlain unconformably by Westphalian A and B strata (Lower and Middle Coal Measures), with are locally dominated by basic volcanics and intrusives. The Upper Coal Measures (late Westphalian C to early Westphalian D), chiefly composed of coarse-grained and conglomeratic sub-greywacke and belonging to the Arenaceous Coal Formation, unconformably overlie and overlap the earlier Carboniferous strata. The Upper Palaeozoic rocks were deformed into broad open folds during the latter part of the Variscan Orogeny, but steep dips in the south suggest proximity to the Variscan Front. The intermittent periods of erosion through Upper Palaeozoic time, and the late Carboniferous sedimentary history, can probably be related to deformational events in the Variscan Fold-Belt to the south.