Australia: The Land Where Time Began

A biography of the Australian continent 

Oodnaminta Hut and Illinawortina regions

The Tapley Hill Formation

The Tapley Hill Formation has a stratigraphy in the Oodnaminta region that is similar to that near Mt Jacob, all of the 5 informal stratigraphic units being recognisable, though not all units are present in all sections and significant differences exist between successions either side of the Paralana Fault, reflecting the different histories of the 2 regions.

There is a significant difference between the cap carbonate in the Oodnaminta Hut-Illinawortina region  and the area near Mt Jacob. It is micritic limestone that is finely laminated and has thin, less than 1 mm, interlaminations of quartz-silt that interbedded with calcareous shale, in the Oodnaminta Hut section (A-C). It is about 5-10 m thick and in general is richer in shale than that of the Mt jacob region. The cap is highly lenticular in the Illinawortina region, and often there is only calcareous shale.

According to the authors¹ the overall thickness of the Tindelpina Shale Member, the siltstone unit, the cyclic unit and quartz-sandstone unit in the Oodnaminta Hut sections are of comparable thickness to those of the Mt jacob region. In the Illinawortina section the siltstone unit, the quartz-sandstone unit and transitional shale unit are absent. The Oodnaminta Hut section C also has no transitional shale unit, and in the region of the Oodnaminta Hut sections A and B (80-100 m) the transitional unit varies in thickness. The authors say there is a sharp, erosional upper contact with the Balcanoona Shale.

See Interglacial Carbonates, Umberatana Group, Flinders Ranges, South Australia

Sources & Further reading

1. Giddings, J.A., Wallace, M.W. and Woon, E.M.S., 2009, Interglacial carbonates of the Cryogenian Umberatana Group, Flinders Ranges, South Australia, Australian Journal of Earth Science (2009) 56 (907-925).