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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 1000

Last Page: 1000

Title: Wave-Dominated Deltaic Sedimentation in Devonian Bokkeveld Basin of South Africa: ABSTRACT

Author(s): Anthony J. Tankard, John H. Barwis

Article Type: Meeting abstract


In the Devonian Bokkeveld basin on the southwestern periphery of Gondwanaland, over 3,000 m of mudstones and sandstones were deposited as a southerly prograding clastic wedge. Five thick regressive sequences record processes on arcuate deltas along a mixed wave and tidal energy coastline. Variations among the upward-coarsening sequences are the result of differential preservation and transgressive reworking caused by uneven rates of relative sea level rise.

The base of each sequence is represented by dark shelf-prodelta shales which grade upward through mudstones to graywackes and lithic arenites of river-mouth bar facies. This upward-coarsening deltaic package is topped by tidal flat, shallow subtidal, and interdistributary bay deposits of the delta plain. These delta plain deposits are extensively bioturbated and contain brackish invertebrate taxa of the Malvinocaffric province. Reworked sands are present largely as tidal channel and tidal inlet quartzarenites that unconformably overlie the distributary-mouth bar facies and in places the delta plain facies. Plane-bedded sheet sands locally occur below the quartzarenites and are attributed to storm washover processes.

It is suggested that deposition of the Bokkeveld Group occurred on arcuate deltas similar to the modern Brazos and Niger deltas. Rates of relative sea level rise were high and were punctuated by periods of near stillstand. The duration of these stable periods increased through time, culminating in stable shelf conditions in Witteberg time.

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