Conodonts from the Wombat Creek Group and "Wibenduck Limestone" (Silurian) of eastern Victoria

Conodonts from four carbonate occurrences in the Wombat Creek Group - of the Wombat Creek Graben - a unit closely associated with the "type locality" of the inferred Benambran Orogeny, demonstrate that it includes horizons at least as old as celloni Zone (Early Silurian, late Llandovery, Telychian) as well as latest Silurian (Přídolí). Two and possibly three of the most prominent Wombat Creek Group limestones align chronologically with two of the oldest carbonate intervals of the Enano Group (of the Limestone Creek Half-graben) farther east in Victoria, specifically the Lobelia and Farquhar limestones. They also align chronologically with portion of the McCarty's limestone on the right flank of the Indi (= upper Murray) River in southeast New South Wales. The last of these documents carbonate sedimentation commencing earlier, in the early Llandovery (Rhuddanian). The youngest of the four Wombat Creek Group carbonate occurrences to have produced conodonts, Pyle's limestone deposit, is tectonically problematic, but its age is Přídolí (latest Silurian). The Wombat Creek Group and Enano Group sedimentation (and flanking "lost" carbonate platform accumulations) thus appear to have extended through most of Silurian time, from Llandovery to somewhere close to the Silurian-Devonian boundary. The Silurian sedimentary packages of the Wombat Creek Graben and Limestone Creek Half-graben have been regarded as developmentally discrete, but salient similarities in depositional sequence and in chronologic alignments are consistent with them being now-disjunct portions of a formerly continuous sedimentary accumulation, i.e. their preservation in separate tracts may be an artifact of post-depositional tectonics. Conodont data from an isolated occurrence, the "Wibenduck Limestone", indicate probable mid-Ludlow age (probable latest Gorstian to earliest Ludfordian). It consists of limestone clasts and olistoliths and possibly equates with submarine fans of Lochkovian age elsewhere, such as the Sharpeningstone Conglomerate of the Yass area, southern New South Wales.