Late Wolstonian and Ipswichian (MIS 6/5e) sediment fill in a limestone sinkhole, Askham Fell, northern England

Abstract

In 2019 a sinkhole (doline) occurred in Late Devensian till above fissured limestone in northern England. Most sediment plugging the fissure was evacuated down into a karstic drainage system. The residual sedimentary fill comprises three main lithofacies, dated using optically stimulated luminescence to between 170.7 ± 40.0 and 56.1 ± 13.5 ka. The earliest date demonstrates fissures were present in the limestone pavement at the time of Marine Isotope Stage (MIS) 6, or shortly thereafter. The fissure filled with fine sand and silt due to surface runoff and aeolian processes probably at the MIS 6 to MIS 5e transition after Wolstonian glacial ice had retreated. The deposits then collapsed into the karst system. Further fine sand and silt deposition occurred during MIS 3; this deposit filled the central cavity surrounded by residual MIS 6/5e deposits. The sequence was capped by till as Late Devensian (MIS 2) ice transgressed the area. Solution fissures in the karst surfaces of northern England may pre-date the Late Devensian glaciation. Moreover, fissures are repositories of pre-Devensian sediment deposits which survived the Late Devensian glaciation and the Ipswichian interglacial. Such sites should provide information on the nature and timing of pre-Devensian glacial–interglacial events and shed light on basal ice conditions and glaciokarst drainage behaviour.