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 Koo nenberry and Mootwingee Faults, and cut by the Mt Wright Fault, and it has a basement of mildly metamorphosed and deformed siliciclastic Neoproterozoi c and Lower Cambrian rocks. The cover strata of the block, mostly well-sort ed 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 Koo nawarra Station the Ravendale Formation has lower (Upper Givetian - Frasnia n?) and upper (Famennian?) parts, which are separated by a local unconformi ty and were deposited mainly by braided streams. The arcuate, northwest-tre nding Koonawarra Syncline formed during northeast-southwest compression. It s growth commenced prior to the Givetian (Middle Devonian) and continued du ring 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 u pper Ravendale Formation, preserved in the core of the Mt Lynn Syncline (wh ich refolds the Koonawarra Syncline). The Mt Lynn Syncline was cut by the M t Wright Fault and the western and eastern parts of the fold were displaced similar to6 km dextrally by the fault during, or following, a late phase o f the Kanimblan Orogeny.