Lower Palaeozoic Unconformities in South-western Tasmania

Recent geological work in south-west Tasmania on a regional scale has allowed the compilation of existing information regarding Lower Palaeozoic unconformities, namely the description of new localities and in some cases the amplification and extension of previously described exposures. Carey and Banks (1954, p. 245) provide a review of information to 1954 and their classification of unconformities has been adopted in this paper. These are repeated here (op. cit. p. 264) : Tyennan lTnconformity.-The Tyennan Unconformity may be defined as an angular discordance between pre-Dundas rocks below and the Junee Group above as revealed on the south-eastern slope of Tim Shea, at the head of Tyenna Valley. Stratigraphically it may be considered as the erosional surface in pre-Dundas rocks on which the Juneo Group was deposited. The orogenic movements occurring within the of time represented by this is to as the Tyennan Orogeny. This is a minimum of that during which the Dundas Group was deposited (at least lower Upper Cambrian to upper Middle Cambrian, Opi!~, 1951a, 1951bJ. The base of the Junee Group (Owen type Conglomerate) indicates a Lower Canadian age (Opik, 1951aJ so that the Tyennan Orogeny must precede this, Stiehtan Unconformity.-The Stichtan Unconformity has been defined as the angular discordance between the Carbine Group below and the Dundas Group above as revealed on the western flank of the Sticht Range and its southern continuation to a point east of Lake Dora in the West Coast Range. Stratigraphically the Stich tan Unconformity may be considered as the erosional surface on wbich the Dundas Group was deposited. It is an expression or orogenic movement of pre-upper Middle Cambrian age, followed by a period of erosion or nondeposition to the deposition of the Dundas Group. movement is referred to as the SticMan Movement of the Tyennan Orogeny. I would one minor modification to this definition by and Banks in the substitution of "Precambrian for" Carbine Group" at the beginning of the paragraph above. At the present time the term Carbine Group as a division of the Precambrian has never been sufficiently well defined to allow its use beyond the type area at Dundas.