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Victoria University Antarctic Research Expedition Science and Logistics Reports 1990-91: VUWAE 35

Enigmatic Sandstone Geometries

Enigmatic Sandstone Geometries

Field relationships and paleocurrent analysis has shown that the apparently enigmatic sandstone geometries resulted from the interaction of two different sedimentary systems. Some of the sheetlike geometries probably represent episodic advances of a sandy alluvial fan originating in highland to the east while other originated within the meandering system itself.

This interpretation leads to two significant findings. Firstly, paleocurrent analysis of the fan derived sheets show that highlands of crystalline basement rocks existed to the East of Allan Hills during the Permian. Of more significance is the finding that meandering rivers can deposit extensive sandstone sheets with internally complex geometries and diverse paleocurrent directions. This contrasts strongly with accepted models of meandering river deposition and suggests that a previously unrecognised process was occurring.

Further work is required to fully document an alternative model. However, it is envisaged that the sheet sandstones were deposited by blind swamp-draining meandering rivers. The unusual bed geometry results from biogenic aggradation of the flood plain (swamp) exceeding the clastic accumulation of the meandering system (Woolfe et al submitted).