Controls on organic carbon enrichment in a Permian periglacial setting (Arckaringa Basin)

In the Arckaringa Basin, organic carbon (OC) enrichment within the Permo-Carboniferous Stuart Range Formation occurred within syn-sedimentary fault troughs that were scoured by glaciers. This enrichment was facilitated by sytematic variations in water chemistry within these troughs identifying periods of restriction and open water exchange with the ocean to the south. The U-shaped morphology of some of these troughs apparent in seismic profiles along with the presence of lonestones, dropstones, and feldspathic, angular sediment identifies a cold palaeoclimate depositional setting that is unusual for the organic enrichments of up to 12% total organic carbon (TOC). It is hypothesised that episodic restriction within these fjord-like troughs led to cyclical variations in sulphur concentration within the water column, driving sulfurization reactions that preserved organic matter in discreet laminae. Abundant pyrite (up to 20 wt%) and the distribution of organosulphur compounds with TOC supports this hypothesis. Cyclical oxygenation of bottom waters and alkalinity from OM mineralisation by bacterial sulphate reducers resulted in the formation of manganese carbonate (kutnohorite) during periods of ventilation. Organic-lean sediments in the adjacent lacustrine Cooper Basin that lacked a source of marine sulphur do not show vulcanization nor preservation of labile organic matter.