Relationship between Callanna Beds and Adelaidean Cover, and the effect of syn- and post­sedimentary diapirism, Mt. Bayley Range area Flinders Ranges, South Australia

Abstract

Late Precambrian sedimentation in the Mt. Bayley Range area, Northern Flinders Ranges, was largely controlled by tectonism involving the Beltana Diapir. Diapiric uplift caused development of a small syn­sedimentary basin adjacent to the north-western side of the diapir. Sediments deposited within this basin, the Mt. Bayley Trough, exhibit lateral thinning and shallowing of facies and progressive onlapping of the Callanna Beds and breccia constituting the diapir. Conglomerates in the Brachina Formation show a bi-directional inflow of detritus, derived locally from the diapir. Basinal instability, pertaining to pulses of diapiric movement, occur within the Bunyeroo Formation, with the presence of diapiric detritus in non-glacial diamictites and conglomerates, and sedimentary slumping suggesting gravity transport.

Diapiric activity caused the development of local shallowing in a generally transgressive sequence within the Bunyeroo Formation. These diapiric bodies have later pierced the cover as thrust-faulted blocks.

A region to the north of the Mt. Bayley Range presents findings that concur with those of the Mt. Bayley Trough. A sedimentary contact between the diapir and the Bunyeroo Formation exists, with a transgressive rim dolomite unconformably overlying more intensely folded Callanna Beds. This region shows evidence of syn-sedimentary faulting during the deposition of the basal Bunyeroo Formation with resulting facies and thickness changes across faults.