Reinterpreting Rotherslade, Gower Peninsula: implications for Last Glacial ice limits and Quaternary stratigraphy of the British Isles JOHN F. HIEMSTRA, 1 * KENNETH F. RIJSDIJK, 2,3,4 RICHARD A. SHAKESBY 1 and DANNY MCCARROLL 1 1 School of the Environment and Society, Swansea University, Swansea, UK 2 Naturalis (National Museum of Natural History), University of Amsterdam, Amsterdam, The Netherlands 3 IBED, University of Amsterdam, Amsterdam, The Netherlands 4 TNO-NITG, Utrecht, The Netherlands Hiemstra, J. F., Rijsdijk, K. F., Shakesby, R. A. and McCarroll, D. Reinterpreting Rotherslade, Gower Peninsula: implications for Last Glacial ice limits and Quaternary stratigraphy of the British Isles. J. Quaternary Sci., (2008). ISSN 0267-8179. Received 20 March 2008; Revised 22 August 2008; Accepted 27 August 2008 ABSTRACT: Rotherslade on the Gower Peninsula in south Wales has been viewed as a key site for the reconstruction of Quaternary depositional environments in the British Isles. Since the early 20th century, and certainly since the 1980s, the accepted view has been that Rotherslade is the most westerly location on the south Gower coast where there is in situ basal till exposed and that, logically, this location marks the position of the LGM ice limit. However, reinvestigation of the sediments and their architecture, and analysis of clast fabrics and thin sections of critical sedimentary units, show that none of the exposed sediments has properties diagnostic of subglacial deposition or deformation. We postulate here that LGM ice terminated at the western side of Swansea Bay, a few kilometres to the north-east of Rotherslade, and propose that the sedimentary sequence comprises Early to Middle Devensian periglacial sediments, overlain by a complex of Late Devensian, ice-proximal outwash fan deposits, an assemblage of paraglacial debris and, finally, periglacial mass movement deposits. The proposed repositioning of the Late Devensian ice limit and the associated new subaerial interpretation of the sediments suggest that a reassessment of sedimentary sequences (Hunts Bay, Western Slade) and landforms (Paviland Moraine) farther west on Gower, which have attained similar stratigraphical status, is now warranted. Copyright # 2008 John Wiley & Sons, Ltd. KEYWORDS: Rotherslade; Gower Peninsula; glacial sedimentology; LGM ice limits; Devensian stratigraphy. Introduction During recent decades, the coastal exposures and cave deposits of the Gower Peninsula in south-west Wales have come to be viewed as key evidence for interpreting late Quaternary environmental change, with implications for constructing not only the British Isles stratigraphy but also the North West Europe stratigraphy (Bowen, 1970; Bowen and Sykes, 1988). The cliff section at Rotherslade on the south coast (SS612872; Fig. 1) has played a pivotal role in such constructions. The exposed sediments have been interpreted as comprising in part an in situ basal till, making this site ostensibly the only place on Gower’s south coast with evidence of ice presence. Age control is provided by an Ipswichian (Eemian) raised beach at the base of the sequence (Davies, 1983; Bowen et al., 1985), which logically constrains the age of the overlying sediments, including the supposed basal till, to the last glaciation. Although the sedimentological, faunal and dating evidence for Last Glacial Maximum (LGM) ice is far stronger at Broughton Bay in north-west Gower (SS424932; Campbell et al., 1982; Campbell and Shakesby, 1994; Shakesby et al., 2000), the focus of workers for nearly 80 years has been Rotherslade and its supposed position marking the ice limit. The idea of an in situ till in the sequence has a long history. In the early 20th century, Strahan (1907) suggested a subglacial origin for the ’gravelly boulder clay’ deposits and recognised the importance of their stratigraphic relation to the raised beach. Later, George (1933) and Griffiths (1939) proposed a model of two glaciations to explain the sequence, an idea that mirrored Charlesworth’s (1929) model of ’Older’ and ’Newer Drift’ in Wales. In the 1980s, following amino acid dating of the raised beach to the last interglacial, this idea of two separate glaciations was replaced by a model involving a single glaciation. Most researchers now agree that during the Late Devensian, ice from the Tawe-Nedd glacial system occupied Swansea Bay and overrode the southeastern part of Gower (see Evans et al., 2005, for review). The main sedimentological evidence supporting this view remains the supposed presence of a basal till at Rotherslade and its absence at any location west of this site on the Gower south coast (e.g. Bowen, 1970, 1977, 1981, 1982; Campbell, 1984; Bowen et al., 1985; Campbell and Bowen, 1989; Harris and Donnelly, 1991). Although sedimentary sequences at several Gower sites have been the subject of JOURNAL OF QUATERNARY SCIENCE (2008) Copyright ß 2008 John Wiley & Sons, Ltd. Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jqs.1238 * Correspondence to: J. F. Hiemstra, School of the Environment and Society, Swansea University, Singleton Park, Swansea SA2 8PP, UK. E-mail: j.hiemstra@swansea.ac.uk