The stratigraphy of the Witteberg-Dwyka contact beds

[摘要] Effective use is made of a multiple system to subdivide theportion of the Cape-Karroo stratigraphical column investigated intorock, time and in a lesser degree, biostratigraphic units.Heavy mineral studies reveal that distinct vertical variationtrends exist for tourmaline. The steady increase in the frequencyof brown tourmaline over other types makes this mineral speciallysuited for correlation, even over long distances. Garnet is indicative of the Dwyka Group.In the southern outcrop areas the Cape and Karroo Supergroupsare structurally conformable to each other.Continuity in deposition was the rule.The sandstones of the Wittepoort Formation are interpreted as stableshelf deposits. The mixed sediments of the Lake Mentz Formationmark the rapid transition to a large interior basin with more restrictedcirculation. The fine-grained proglacial sediments of theKommadagga Formation were deposited in a basin inherited from theWitteberg Epoch. The overlying tillites were deposited in a marineenvironment. An interpretation of the tectonic history of the Cape-Karroo sequence indicates that a peneplanation stage was present upto the end of the Witteberg Epoch. A geosynclinal stage then set in.It is convenient to divide the sequence into two major timestratigraphicunits of system rank. The base of the Karroo System ischosen in view of historical, lithological, geographical and paleontologicalconsiderations.

[发布机构] University of the Witwatersrand