Westphalian B marine bands and their subsurface recognition using gamma-ray spectrometry

Abstract

Palaeogeographic reconstructions, marine band deposition and the variations of uranium enrichment in sediments enable marine bands to be divided into four types: (1) Namurian marine bands, which represent marine anoxic black shale events, with thick ammonoid acme phases that concentrate uranium; (2) Vanderbeckei marine bands have thin ammonoid acme zones and abundant benthos, resulting from shallower water depths and poorly developed anoxic events with negligible uranium enrichment; (3) Westphalian B/C marine bands are more marginal and have an abundance of land-derived plant fragments with adsorbed uranium, as well as uranium entrapped within phosphatic tests of Lingula; (4) brackish water Lingula beds with abundant terrigenous matter and negligible uranium response. This classification scheme provides a means of predicting the uranium response of individual marine bands which is attributed primarily to the type and amount of organic matter, and the salinity of the waters responsible for deposition. This approach allows marine bands to be recognized and identified in the subsurface from their gamma ray and spectral gamma response, and together with palynological analysis allows the marine band to be placed more accurately within the regional stratigraphic framework.