A geological investigation of upper Transvaal sequence rocks in the northern portion of the Rooiberg fragment

[摘要] The stratigraphy , sedimentology and geochemistry of. the upper TransvaalSequence rocks in the northern portion of the Rooiberg Fragment areresearched.The Leeuwpoort Formation of the Pretoria Group was deposited in a fluvialpalaeoenvironment. The basal arkosites in this unit reflect braided streamdeposition, whereas the overlying shaly arkosi tes represent upward- finingcycles of point bar sedimentation. The uppermost main Leeuwpoort shaleprobably formed in a floodplain palaeoenvironment. The overlyingSmelterskop Formation arenites indicate high energy flood conditions in aproximal fluvial palaeoenvironment. The extrusion of andesi tic lavas actedas an agent of change during the deposition of Smelterskop Formationsedimentary rocks.The upper and lower contacts of the Smelterskop Formation are disconformableand conformable, respectively. However, non-deposition of the main shale ofthe upper Leeuwpoort Formation and erosion by succeeding Smelterskopsedimentation in some areas, created local disconformities at the base ofthe Smelterskop Formation.The scattering of Si02 binary plots recorded in the geochemistry of theRooiberg Group rhyolites indicates extensive alteration of these rocks.Petrogenetic conclusions drawn from the geochemistry must therefore betreated with caution. However, empirical data indicates two lava types,defined by major and trace element geochemistry and geographical position.

[发布机构] University of Pretoria