Etruria Formation (Westphalian C) palaeoenvironments and volcanicity on the southern margins of the Pennine Basin, South Staffordshire, England

Abstract

The Westphalian C Etruria Formation of Tansey Green, South Staffordshire, comprises three facies associations deposited during a period of extensional faulting. Subsequent to upper delta plain deposition during Westphalian A and B times, the lower Etruria Formation was deposited upon a poorly drained alluvial plain fed by low sinuousity, east- and northeast-flowing streams, which were periodically inactive. Whilst channel geometry remained unchanged, continued sedimentation resulted in relative lowering of the water table and development of a second facies association, characterized by well-drained alluvial plain conditions upon which conifers thrived. These alluvial associations include occasional well-developed palaeosol horizons indicative of variable drainage conditions. Continued extensional faulting culminated in alkaline basaltic and phreatomagmatic volcanism and deposition of the third facies association which comprises volcaniclastic and possible epiclastic rocks. Rapid deposition of the third association resulted in the excellent preservation of a Westphalian C conifer flora. Although extensional tectonism provided the dominant control on sedimentation, this is believed to be only of localized importance during a period of Variscan compression and associated uplift which characterizes much of the southern margin of the Pennine Basin.