Late Permian anoxia in central East Greenland

Abstract

Abstract The Upper Permian Foldvik Creek Group of the East Greenland Basin provides excellent possibilities for studying regional anoxia, because the basinal, anoxic facies of the Ravnefjeld Formation are well exposed throughout this 400 km long and more than 80 km wide basin. The shales of the Ravnefjeld Formation are dominated by two units of laminated, organic-rich, calcareous mudshales. The absence of a burrowing or benthonic fauna, and the high content of organic matter and sulphur suggest these units were formed during a basin-wide anoxic episode. The character of the graded laminae indicates deposition from suspension. In contrast, thin bioturbated units appear to have been deposited during episodes of more oxygenated bottom waters. The TOC, HI and sulphur content are all lower in these bioturbated units. The associated marine limestones of the Wegener Halvø Formation record a depositional history of transgressions and regressions that can be directly related to the laminated—bioturbated units of the Ravnefjeld Formation. The anoxic period can therefore be correlated with the maximum transgression of the basin, which induced rapid vertical growth of reefs. A stratified water column with anoxic bottom conditions and restricted circulation was apparently induced by the maximum flooding of the basin. The extensive vertical growth of carbonate platforms may have further restricted the circulation in the basin, producing a ‘silled basin’ effect.