Reconstruction of the ordovician pakhuis ice sheet, South Africa
dc.contributor.author | Blignault H.J. | |
dc.contributor.author | Theron J.N. | |
dc.date.accessioned | 2011-05-15T16:00:33Z | |
dc.date.available | 2011-05-15T16:00:33Z | |
dc.date.issued | 2010 | |
dc.description.abstract | This reconstruction of the Late Ordovician, glacigenic Pakhuis Formation of the Table Mountain Group is based on a variety of diverse datasets. Field observations were made over the full 300 km extent of exposure in a north-south direction. The thin glacigenic package constitutes a minor interlude in the development of a subcontinental, Palaeozoic, siliciclastic basin. The Pakhuis Formation is of special interest because it includes features like the extensive penecontemporaneous folding, an erosional unconformity and the uniform lithological character of the sandy diamictites. A model is presented by which an unusual concurrence of circumstances produced the special features of the Pakhuis glacigenics. These are the ice invasion of a developing basin, an onset zone within basin and a deep trough harboring an ice-stream. Subglacial, grounding zone and iceberg facies associations with their lateral variations are developed. The temperate, glaciation of relative short duration, comprised one major and a second minor advance. During the first advance the grounded ice sheet with slow-moving sheet-flow reached ice-stream characteristics along at least part of a trough. The occurrence of an ice-stream within a slow-moving, low-profile ice sheet provides the glaciological environment for ice-stream draw-down, flanking infill of ice, resulting in compressional ice-flow from the sides. The fundamental requirement for buckling (i.e. the development of the Fold Zone) is layer parallel shortening achieved by the compressional ice-flow. Ice-bed interface features like deforming-bed structures are developed, as well as outsize flutes for which an alternative bulk strain model is proposed. The glacial retreat was rapid, interrupted only by the second, minor advance. A marine environment is attested by the postglacial fauna of a black shale. © 2010 September Geological Society of South Africa. | |
dc.description.version | Article | |
dc.identifier.citation | South African Journal of Geology | |
dc.identifier.citation | 113 | |
dc.identifier.citation | 3 | |
dc.identifier.issn | 10120750 | |
dc.identifier.other | 10.2113/gssajg.113.3.335 | |
dc.identifier.uri | http://hdl.handle.net/10019.1/11760 | |
dc.subject | basin evolution | |
dc.subject | glacier advance | |
dc.subject | glacier retreat | |
dc.subject | ice sheet | |
dc.subject | ice stream | |
dc.subject | Ordovician | |
dc.subject | reconstruction | |
dc.subject | sequence stratigraphy | |
dc.subject | unconformity | |
dc.subject | South Africa | |
dc.title | Reconstruction of the ordovician pakhuis ice sheet, South Africa | |
dc.type | Article |