Definition card for: Purni Formation State(s): NT, SA, Status of unit: Formal Usage: Defined Stratno: 15684
Reserved by: Youngs B.C. on: 03-DEC-74 Approved: Y Approved by: on: 09-DEC-74 Age and Evidence: Early Permian. Palynological evidence suggests it is restricted to Stage 3, but it could extend down to Stage 2 (Harris, 1972). Comments: The Purni Formation is divisable into three members, these are defined briefly below: Upper Member - F.P.C.(A). Purni No. 1 well between 1417 and 1536 m. Fine, white, kaolinitic sandstones; silts; grey shales; carbonaceous shales. Middle Member - F.P.C.(A) Purni No. 1 well between 1536 and 1603 m. Fine to medium, grey-brown, well sorted, kaolinitic sandstone. Occasional thin interbeds of silts and carbonaceous shales. Lower Member - F.P.C.(A). Purni No. 1 well between 1603 and 1698 m. Thinly bedded, grey shales with lenses of fine to medium, grey, kaolinitic sandstones and occasional conglomerates. Rare coal bands. *The Purni Formation is also known from Mokari No. 1, McDills No. 1 and Hale River No. 1. Distribution/extent: The formation is not known in outcrop. Its subcrop is believed to extend over the thicker parts of the Pedirka Basin (Youngs, in press)*. Lithology: Beds of white kaolinitic sandstone; occasional thin conglomerates; thinly bedded grey shales, frequently carbonaceous; siltstones; thin coals and very carbonaceous shales.
Deriviation of name: French Petroleum Co. (Australia) Ltd. Purni No. 1 well. Dalhousie 1:250 000 sheeet area. Grid Ref. 412736. Relationships and boundary criteria: It disconformably overlies the Crown Point Formation (except in Amerada Hale River No. 1) and is unconformably overlain by Mesozoic strata. The base is defined by a conglomeratic, silty, grey to black shale with minor coal lenses. The top of the formation at the type section, is marked by beds of black coal, interbedded with thin silty shales. Thickness: 3-350 m. Type-section locality: F.P.C.(A) Purni No. 1 well between 1417 m and 1698 m.
