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Paper No. 13
Presentation Time: 9:00 AM-6:30 PM

EVIDENCE FOR CLIMATIC VARIATION WITHIN THE ~2.0 GA UPPER MAKGABENG FORMATION, SOUTH AFRICA


HENESS, Elizabeth A.1, SIMPSON, Edward L.2, BUMBY, Adam J.3, ERIKSSON, Patrick G.4, ERIKSSON, Kenneth A.5, LINNEVELT, Sarah4 and MODUNGWA, Tshepiso4, (1)Department of Physical Science, Kutztown University, 425 Boehm, P.O. Box 730, Kutztown, PA 19530, (2)Physical Sciences, Kutztown University, Kutztown, PA 19530, (3)Geology, University of Pretoria, Pretoria, South Africa, (4)Department of Geology, University of Pretoria, Pretoria, 0002, South Africa, (5)Department of Geosciences, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061, ehene946@live.kutztown.edu

Eolian dune fields and associated environs are extremely sensitive to short- and long-term changes in climate, such as differences in precipitation. One of the oldest erg deposits is present in the ~2.0 Ga Makgabeng Formation, Limpopo Province, South Africa. Within the formation various facies are distinguished that reflect one of the earliest recordings in Earth’s History of definitive climatic shifts in a terrestrial setting.

The upper Makgabeng Formation is broken into a lower and upper paleo-dune field/erg by a playa or saline pan deposit. The lower dune field consists of meter-scale dune sets with interbedded lenses of wet interdune strata, up to 60 cm in thickness and traceable to a maximum of 55 m. The overlying inferred playa reflects considerable variation in precipitation. The basal playa deposit consists of alternating mud and sandstone beds with both deep and shallow penetrating mud cracks. Above this lower mud-phase, the playa is fully sand dominated, featuring wave- and current-ripples, low-angle eolian wind-ripple stratification, scour marks, potential evaporitic crust features and evaporite dissolution structures. Overlying the playa is the upper dune field that consists of laterally continuous thick eolian sets with sparse, thin lenses of dry interdune deposits. Characterizing the upper dune field is a vertical transition from medium- to coarse-grained sandstone. In addition to the grain size change, fluvial, sheet-flood deposits, eolian cross-beds sculpted by mass flows, and a geographically restricted playa sequence is recognizable.

These facies demonstrate shifts in precipitation that are reflected in changing water table levels. Fluvial and playa facies record high water tables. Low water tables are reflected in the erg deposits. The transition from low to higher water tables is recorded in the appearance of wet interdunes and massive flow interspersed within the dune strata. These climatic alterations, in precipitation levels, radically changed the Makgabeng landscape through time.

Session No. 41

T182. The Next Generation—Sedimentary Geology Student Poster Session (Posters)
Sunday, 4 November 2012: 9:00 AM-6:30 PM
Hall B (Charlotte Convention Center)
Geological Society of America Abstracts with Programs. Vol. 44, No. 7, p.131
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