The Holowilena Ironstone and the overlying Wilyerpa Formation are believed to represent the Sturtian glaciations - the Holowilena Ironstone was probably deposited towards the end of the first Sturtian glaciation by chemical precipitation, and the Wilyerpa Formation during the second Sturtian glaciation (Coats and Preiss, 1987).
The Holowilena Ironstone and Wilyerpa Formation are exposed between the Oraparinna and Enorama Diapirs in the central Flinders zone (Figure 2B - site 1 on satellite image). The Wilyerpa Formation is 90% mudstone, shale, siltstone, arenites and only 10% tillite and pebbly mudstone.
The base of the Tindelpina Shale Member at the base of the Tapley Hill Formation is considered to be a 'cap dolomite', which is often sharply defined by thin, continuous dolomite bands that conformably overlie the diamictites, siltstones and sandstones of the Sturtian glacial deposits. Total thickness of this unit reaches ~60m, comprising dark grey, pyritic, carbonaceous, or dolomitic silty shale.
Figure 2. Locality map
(A) Geography of the area surrounding the Enorama Diapir.
(B) Satellite image of this area with key field localities in the Umberatana Group marked, in addition to geologic units discussed in the text.
The glacigenic Elatina Formation consists of a lower unit of massive, pink, fine - medium grained arkosic sandstone, overlain by a red-brown, massive, pebbly to bouldery sandy siltstone interpreted as a tillite. The Elatina Formation is exposed along Enorama Creek, south-west of the Enorama Diapir. Close to Elatina Hut, it is exposed as a pebbly siltstone with a fine reddish matrix containing scattered clasts of basic igneous origin, and according to Coats and Preiss (1987), some of these clasts are polished and striated indicating their glacial origin (site 2 on satellite image).
Directly overlying this is the thin (less than 5-10m thick), commonly discontinuously lensed 'cap carbonate' at the base of the Nuccaleena Formation. At Enorama Creek (site 3), the Nuccaleena Formation is a pale reddish dolomite, ~5m thick grading down abruptly into a 0.15m thick, well banded reddish fine sandstone at the top of the Elatina Formation (Forbes and Preiss, 1987). In the Flinders Ranges, the Nuccaleena Formation is widespread marker bed being readily recognizable over a large area.