Interplay of mid-Carboniferous sediment sources on the northern margin of the Wales-Brabant High

Abstract

Heavy mineral analysis and garnet geochemistry of late Visean and Namurian sandstones in the southernmost part of the Pennine Basin show clear distinctions between sediment transported from a distant northern source and sediment derived from local sources to the south on the Wales-Brabant High. Monazite is common in northern sandstones, whereas it is rare in southern sandstones. Southern sandstones may also contain chrome spinel: variations in its abundance identify spatial and temporal variations in the southern supply. There is evidence in some sandstones that material from the two sources has become mixed. Feldspar content has been used historically as an indicator of provenance in the study area, but the new data show that it might not always be reliable. Detailed stratigraphical analysis across the region has allowed the identification of the interplay of different southern and northern sediment supplies through time. The integration of heavy mineral analysis with palaeocurrent data has enabled the approximate geographical distribution of lobes of northern and southern sediment to be mapped out for successive intervals of late Visean and Namurian time. The southern sediment was carried into the basin throughout the late Visean and Namurian by small river systems, several of which can be recognized within the study area. The northern sediment entered via two lobes; it first entered the region in mid-Namurian (late Kinderscoutian) times and continued through the later Namurian into the Westphalian.