Scratching the surface: Footprint of a late Carboniferous ice sheet

D.P Le Heron,P Dietrich,M.E Busfield,S Bermanschläger,B Grasemann,C Kettler

doi:10.1130/g46590.1

D.P Le Heron, P Dietrich + Show 4 more

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https://doi.org/10.1130/g46590.1

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Abstract

AbstractField observations in conjunction with aerial images from an unmanned aerial vehicle were used to create the first map of a glacial unconformity underlying the late Carboniferous Dwyka Group of South Africa. Crosscutting relationships reveal that the glacial unconformity at Oorlogskloof, in which flutes, grooves, and striae were ploughed into unconsolidated sand, formed in a three-phased process charting a periodic shift in the locus of subglacial erosion. The unconformity formed by a periodically decoupled ice sheet in a probable tidewater setting. This model contrasts with earlier views that the structures simply record progressive ice-margin liftoff during transgression, and they provide unique insight into the complex temporal development of a 300 Ma subglacial environment.

Highlights

Unconformities are increasingly understood as recording complex, evolving processes during basin evolution rather than stasis (Davies and Shillito, 2018)
Field observations in conjunction with aerial images from an unmanned aerial vehicle were used to create the first map of a glacial unconformity underlying the late Carboniferous Dwyka Group of South Africa
Crosscutting relationships reveal that the glacial unconformity at Oorlogskloof, in which flutes, grooves, and striae were ploughed into unconsolidated sand, formed in a three-phased process charting a periodic shift in the locus of subglacial erosion

Summary

Introduction

Unconformities are increasingly understood as recording complex, evolving processes during basin evolution rather than stasis (Davies and Shillito, 2018). Where cut into soft sediments, glacial unconformities may record the degree of basal coupling or changes in ice-flow velocity (Le Heron et al, 2005; Vesely and Assine, 2014). -called “soft-sediment striated surfaces” are extremely common in the glaciogenic Late Ordovician (Deynoux and Ghienne, 2004; Le Heron et al, 2005; Denis et al, 2010; Girard et al, 2015; Tofaif et al, 2019) and Carboniferous–Permian (Visser, 1987, 1990; Assine et al, 2018; Dietrich and Hofmann, 2019) records alike. We produced the first detailed map of a LPIA glacial unconformity from Oorlogskloof, Northern Cape Province, South Africa (Fig. 1), integrating data from an unmanned aerial vehicle (UAV) and field observations

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