Volcanogenic sediments of the East Kirkton Limestone (Viséan) of West Lothian, Scotland

Abstract

ABSTRACTVolcanogenic sediments form a significant part of the East Kirkton Limestone, with thin tuff units occurring at several levels and pyroclastic fragments being an important constituent of the coarser clastic limestone units.The tuffs have been extensively altered during diagenesis but recognisable pseudomorphs after olivine and plagioclase phenocrysts confirm the basaltic nature of the volcanism. The considerable lateral variations in thickness of the tuff horizons in conjunction with the poorly sorted and lithologically heterogeneous nature of the tuffs indicate an epiclastic origin for the volcanogenic sediments. Well-rounded volcanic rock fragments—products of erosion—occur with angular fragments within the tuffs. Blocky tuffs in the lower part of the formation contain charred wood fragments, rip-up clasts of limestone and disarticulated amphibian bones. Graded bedding at several horizons and the presence of ostracods within some tuffs confirms subaqueous deposition.The findings are consistent with the usual, dominantly epiclastic products of basaltic volcanism, in an equatorial, continental, humid environment, with assorted debris being washed from the flanks of a volcano into a shallow lake.