TY - JOUR
T1 - Gradients in seasonality and seawater oxygen isotopic composition along the early Permian Gondwanan coast, SE Australia
AU - Beard, J. Andrew
AU - Ivany, Linda C.
AU - Runnegar, Bruce
N1 - Funding Information:
Dan Petrizzo is gratefully acknowledged for collaboration on the field portion of this study. Special thanks go to Peter and Kaye Makeig (Bimbadeen), Warwick Denshire (Greenlees), Steve Hall, Simone Meakin, and Ian Percival (Geological Survey of New South Wales), Matthew Billings (Hunter 8 Alliance), Phil Smart (Mollymook), Mike Clarke (Taroona), Trevor and Pat Hanigan (Derwent Estate Wines), Michael Comfort (Primary Industries, Parks, Water and Environment, Tasmania), and Pete Lingard (Maria Island National Park) for assistance, for access to the Allandale project, the DM Tangorin 1 core, and field sites, and for permissions to sample and collect. We thank Paul Tomascak at SUNY-Oswego for help with ICP-MS work, David Linsley at Colgate University for preparing the thin sections, Jack Hietpas and Melissa Hicks for help interpreting textures, Maddie O'Connor for help in sampling, and Artem Kouchinsky for some isotopic analyses carried out at UCLA in the E.D. Young Laboratory. All other stable isotope analyses were done at the Keck Paleoenvironmental and Environmental Stable Isotope Laboratory at the University of Kansas. This work benefited from meaningful discussions with Scott Samson, Bruce Wilkinson, and Paul Tomascak, and from substantive and thoughtful comments by three anonymous reviewers. Research was supported by the Department of Earth Sciences at Syracuse University and a Stephen Jay Gould Research Grant from the Paleontological Society (to JAB), the American Federation of Mineralogical Societies and the College of Arts and Sciences at Syracuse University (to LCI), the NASA Astrobiology Institute and the Committee on Research at UCLA (to BR). Collections used in this study were assembled at the University of New England, Armidale and UCLA by BR with financial assistance from the Australian Research Council , Dolf Seilacher (Tübingen), and the U.S. National Science Foundation .
Publisher Copyright:
© 2015 Elsevier B.V.
PY - 2015/9/1
Y1 - 2015/9/1
N2 - Oxygen isotope compositions of marine carbonates are commonly employed for understanding ancient temperatures, but this approach is complicated in the very distant past due to uncertainties about the effects of diagenesis and the isotopic composition of seawater, both locally and globally. Microsampled accretionary calcite from two species of the fossil bivalve Eurydesma Sowerby and Morris 1845 collected from sediments of Cisuralian age in high latitude marine sediments along the SE coast of Australia records cyclic seasonal fluctuations in shell δ18O values during growth, demonstrating the primary nature of the isotope signal and thus allowing investigation of early Permian seawater isotopic composition and water temperature in the high southern latitudes. The mean and seasonal range of δ18Ocarb decreases poleward across about 10° of paleolatitude (~67°S-77°S). The presence of co-occurring dropstones and stratigraphically associated glendonites constrains winter temperatures across the region to near-freezing, thus permitting calculation of realistic estimates of water composition and summer temperatures. Summer δ18Ocarb values indicate water temperatures between 5 °C and 12 °C, with warmer values at lower latitudes. The decrease in both mean sea surface temperature and seasonal amplitude with increasing latitude on the Gondwanan coast is much like that observed along high-latitude coastlines today. Calculated δ18Owater decreases toward the pole, likely associated with an increasing contribution of isotopically light fresh water derived from summer snow-melt. The gradient in δ18Owater is similar to that documented over a similar span of latitude on the modern SE Greenland coast. We infer the presence of a north-flowing coastal current of cold, O18-depleted water that entrains progressively greater amounts of more typical seawater as it moves away from the pole. δ18O values in SE Australia, however, are about 3‰ lower than those off Greenland, suggesting comparatively lower salinity water or more O18-depleted glacial ice/runoff in the Permian Gondwanan high latitudes, perhaps augmented by more depleted (negative) global average seawater. Conditions in southeastern Australia during the largest of the Permian deglaciations were warmer than present-day Antarctica at similar latitudes, but may approximate those of early-mid Miocene Antarctica, with frozen winters but summers closer to 10 °C.
AB - Oxygen isotope compositions of marine carbonates are commonly employed for understanding ancient temperatures, but this approach is complicated in the very distant past due to uncertainties about the effects of diagenesis and the isotopic composition of seawater, both locally and globally. Microsampled accretionary calcite from two species of the fossil bivalve Eurydesma Sowerby and Morris 1845 collected from sediments of Cisuralian age in high latitude marine sediments along the SE coast of Australia records cyclic seasonal fluctuations in shell δ18O values during growth, demonstrating the primary nature of the isotope signal and thus allowing investigation of early Permian seawater isotopic composition and water temperature in the high southern latitudes. The mean and seasonal range of δ18Ocarb decreases poleward across about 10° of paleolatitude (~67°S-77°S). The presence of co-occurring dropstones and stratigraphically associated glendonites constrains winter temperatures across the region to near-freezing, thus permitting calculation of realistic estimates of water composition and summer temperatures. Summer δ18Ocarb values indicate water temperatures between 5 °C and 12 °C, with warmer values at lower latitudes. The decrease in both mean sea surface temperature and seasonal amplitude with increasing latitude on the Gondwanan coast is much like that observed along high-latitude coastlines today. Calculated δ18Owater decreases toward the pole, likely associated with an increasing contribution of isotopically light fresh water derived from summer snow-melt. The gradient in δ18Owater is similar to that documented over a similar span of latitude on the modern SE Greenland coast. We infer the presence of a north-flowing coastal current of cold, O18-depleted water that entrains progressively greater amounts of more typical seawater as it moves away from the pole. δ18O values in SE Australia, however, are about 3‰ lower than those off Greenland, suggesting comparatively lower salinity water or more O18-depleted glacial ice/runoff in the Permian Gondwanan high latitudes, perhaps augmented by more depleted (negative) global average seawater. Conditions in southeastern Australia during the largest of the Permian deglaciations were warmer than present-day Antarctica at similar latitudes, but may approximate those of early-mid Miocene Antarctica, with frozen winters but summers closer to 10 °C.
KW - Eurydesma
KW - Gondwana
KW - Oxygen isotope
KW - Permian
KW - Seasonality
KW - Seawater
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U2 - 10.1016/j.epsl.2015.06.004
DO - 10.1016/j.epsl.2015.06.004
M3 - Article
AN - SCOPUS:84931287822
SN - 0012-821X
VL - 425
SP - 219
EP - 231
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -