Stratigraphy, structure and tectonics of Lower Ordovician and Devonian strata of the central part of the Wonominta Block, western New South Wales

Cover strata of the 40 km-wide north-northwest-trending Wonominta Block are sandstone-dominated and Palaeozoic in age. The block is bounded by the Koonenberry and Mootwingee Faults, and cut by the Mt Wright Fault, and it has a basement of mildly metamorphosed and deformed siliciclastic Neoproterozoic and Lower Cambrian rocks. The cover strata of the block, mostly well-sorted quartz arenites to arkoses, are represented by: (i) the Lower Ordovician Yandaminta (marine) and Rowena Formations (mostly non-marine), which in the north form a shoreline of an Ordovician island (Wertago Island); (ii) the Middle Devonian, Snake Cave Sandstone (Emsian–Eifelian) and Waverley Creek beds (Givetian), and the largely Upper Devonian Ravendale Formation. On Koonawarra Station the Ravendale Formation has lower (Upper Givetian – Frasnian?) and upper (Famennian?) parts, which are separated by a local unconformity and were deposited mainly by braided streams. The arcuate, northwest-trending Koonawarra Syncline formed during northeast–southwest compression. Its growth commenced prior to the Givetian (Middle Devonian) and continued during the Late Devonian (?late Frasnian), post-dating the deposition of the lower part of the Ravendale Formation. The fold was subsequently truncated by erosion, which was followed in the ?Famennian by the deposition of the upper Ravendale Formation, preserved in the core of the Mt Lynn Syncline (which refolds the Koonawarra Syncline). The Mt Lynn Syncline was cut by the Mt Wright Fault and the western and eastern parts of the fold were displaced ~6 km dextrally by the fault during, or following, a late phase of the Kanimblan Orogeny.