Late Paleozoic middle-latitude Gondwana environment-stable isotope records from Western Australia

One hundred and twelve Permian fossil brachiopod samples from two Western Australian basins (Carnarvon and Canning Basins) have been analyzed for oxygen and carbon isotopes to study the middle paleolatitude environment in the Permian. All samples were thin sectioned and examined using petrography and cathodoluminescence microscopy for evaluating shell preservation. A total of 249 isotopic analyses from the best preserved portion (nonluminescent; NL) of shells were found useful for inferring paleoenvironments. For the Carnarvon Basin, average delta C-13 values of NL shells were between 4.2 and 4.5 parts per thousand for the Callytharra Formation (N = 123; late Sakmarian-early Artinskian), Jimba Jimba Calcarenite (N = 7; early Artinskian), Coyrie/Madeline Formations (N = 71; both late Artinskian-early Kungurian), and Wandagee Formation (N = 18; late Kungurian). Average delta C-13 values of NL shells were 5.0 +/- 0.4 parts per thousand. (N = 9) for the Quinnanie Shale/Cundlego Formations (both Kungurian). For the Canning Basin, mean delta C-13 values of NL shells were 5.1 +/- 1.1 parts per thousand. (N = 11), 5.3 +/- 0.2 parts per thousand. (N = 4), and 4.8 +/- 0.5 parts per thousand (N = 6) for the Noonkanbah Formation. (Artinskian-Kungurian), Lightjack Formation (Roadian-Capitanian), and Hardman Formation (Wuchiapingian), respectively. Within the uncertainty of the stratigraphical correlation, the carbon isotope values spanning Late Sakmarian to Kungurian in middle latitude Western Australia are comparable to those of coeval low latitude Urals. Average delta O-18 values of NL shells were about 0 parts per thousand (-0.1 to 0.1 parts per thousand) for the Callytharra Formation, Jimba Jimba Calcarenite, Coyrie/Madeline Formations, Quinnanie Shale/Cundlego Formations, Noonkanbah Formation, and Hardman Formation; and were -0.5 +/- 0.7 parts per thousand and -0.3 +/- 0.7 parts per thousand for the Wandagee Formation and Lightjack Formation, respectively. These oxygen isotope values are overall higher than the coeval values reported for low latitude regions and for eastern Australia. The positive oxygen isotope values are here interpreted to indicate a cool temperature and/or a possibly moderately high salinity condition for the two studied basins in Western Australia during the Permian. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.