Permian Gondwanaland paleoenvironment inferred from carbon and oxygen isotope records of brachiopod fossils from Sydney Basin, southeast Australia

The delta C-13 and delta O-18 records of Permian fossil brachiopods with biostratigraphical age control from southeastern Australia have been constructed to investigate the high latitude paleoenvironment of Gondwanaland. All samples were thin sectioned and examined using petrographic and cathodoluminescence microscopy for evaluating shell preservation. Elemental compositions of select brachiopod shells were measured using electron probe microanalysis to further evaluate shell preservation. Within these intervals the average delta C-13 values of the best preserved (non-luminescent; NL) portion of the brachiopod shells are all greater than +5.1 parts per thousand with the highest value, + 7.0 parts per thousand, at Lower Wandrawandian Silt-stone (late Kungurian). These carbon isotope values are similar to those of contemporaneous tropical eastern Pangea (Russian Platform) but heavier than those of western Pangea (North America). The oxygen isotope difference between brachiopods of high southern latitudes and low latitudes fluctuated during Early to Middle Permian. The mean delta O-18 values of the high-latitude NL brachiopod shells were more positive than those of the low latitudes in early Sakmarian (-0.3 parts per thousand), early Late Artinskian (-1.1 parts per thousand), late Kungurian (-1.0 parts per thousand), Roadian (-0.2 parts per thousand), and Wordian (-0.7 parts per thousand); comparable to those of tropical western Pangea in early Artinskian (-2.1 parts per thousand) and early Kungurian (-2.5 parts per thousand); and more negative than those of tropical western Pangea in late Late Artinskian (-3.9 parts per thousand). Assuming the oxygen isotope value for Permian seawater in southeast Australia was -1 parts per thousand, the calculated oxygen isotope temperatures were mostly between 12 degrees C and 16 degrees C reflecting southeast Australia's cool high latitude temperature conditions. Higher apparent oxygen isotope temperatures for the Upper Pebbly Beach Formation (29 degrees C. late Late Artinskian), Berriedale Limestone (21 degrees C, early Artinskian), and Snapper Point Formation (22 degrees C, early Kungurian) may be attributed to a combination of warmer climate and lower seawater delta O-18 in this region. (C) 2011 Elsevier B.V. All rights reserved.