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Loch lomond stadial glacier at Fan Hir, Mynydd Du (Brecon Beacons), South Wales: Critical evidence and palaeoclimatic implications
Author(s) -
Shakesby Richard A.,
Matthews John A.
Publication year - 1993
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3350280106
Subject(s) - geology , moraine , stadial , ridge , fault scarp , glacier , geomorphology , paleontology , glacial period , snow , fault (geology)
The c. 1·2 km long, up to c. 25 m high ridge east of the almost north‐south aligned Fan Hir scarp, Mynydd Du, South Wales has been regarded as a remarkable protalus rampart formed in the Loch Lomond Stadial ( c. 11–10000 years BP ). New data are presented which indicate that it is a moraine. The main points supporting this glacigenic origin are: its curved plan form at the lower, southern end; its scale and the ample depth for snow to glacier ice transformation; the presence of subsidiary ridges interpreted as recessional moraines; the exceptional rate of rockwall retreat required if it were a protalus rampart; and, most importantly, the presence in the ridge of matrix‐supported abraded clasts, up to 20% of which are striated. Useful criteria for differentiating moraines and protalus ramparts are thereby proposed and a sound basis is provided for palaeoclimatic reconstruction. Palaeoclimatic inferences imply that the glacier owed its existence to the combined effect of a mean July temperature of c. 8·5°C and topographically enhanced accumulation, nearly half of which was from wind‐blown snow.