Characteristics and palaeoenvironmental significance of relict sorted patterned ground, Drakensberg plateau, southern Africa

Relict large sorted periglacial circles are described from the Drakensberg plateau of southern Africa. Morphological and sedimentological data for three populations of patterns occurring on high summit ( > 3400 m a.s.l.) interfluves are presented. The patterns range between 8 5 and 904 cm in diameter, with centres encircled by primary and, in some cases, secondary borders. Patterns are sorted to maximum depths of 85 cm or more, with borders occupying trough-like depressions to a depth of 26 cm. Although it is found that contemporary freeze to 40cm depth still permits some cryogenic activity within smaller patterns, it is argued that the larger patterns are degrading owing to limited moisture and freeze duration and intensity. The paper provides a literature summary of contemporary environmental parameters from 10 northern hemisphere localities where active/relict large periglacial patterns occur. Findings suggest that patterns over 80 cm in diameter develop where the MAAT is - 1.6degreesC or less. It is demonstrated that the Drakensberg palaeo-MAAT reached such low temperatures during the LGM. It is thus argued that the patterns developed during the LGM and that smaller varieties became reactivated during Holocene cold phases. The relict sorted circles provide confirmation for Late Quaternary permafrost above 3400m a.s.l. in southern Africa. The results further suggest pronounced palaeo-climatic/ environmental variation over short spacial scales over southern Africa's high plateau. (C) 2002 Elsevier Science Ltd. All rights reserved.