THE PALAEOECOLOGY OF THE FAUNA OVER THE PARK MINE (WESTPHALIAN B) NEAR WIGAN, LANCASHIRE

Abstract

Summary The cyclothem above the Park Mine (Lower similis-pulchra Zone) at the Amberswood opencast site near Wigan is composed of mudstones which can be divided into two parts of almost equal thickness. The lower half, dark grey in colour, contains abundant bivalves, mostly referable to the genera Anthracosia and Naiadites. The upper part is light grey and contains macroscopic plant debris, bivalves only occurring at the base. The variation shown by six assemblages of Anthracosia is demonstrated by means of a new type of diagram. The degree of water turbulence is determined by studying the percentage disarticulation, the orientation of shells, and the lithology of the sediments. It is concluded that an alteration in the growth pattern of Anthracosia and a shift of the entire size range to smaller values correlate with the change from a sulphate zone at the base to a carbonate zone above, together with increasing coarseness in texture and reduced carbon content. All the changes in fauna and sediment may be brought about by the gradual filling and freshening of a lagoon.