Temperate shelf carbonates reflect mixing of distinct water masses, eastern Tasmania, Australia
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In cold shallow seas undersaturated with CaCO3, carbonates disintegrate and dissolve away within a short period of time. Understanding the mixing of water masses from oceanographic and isotope point of view is important because these water masses provide nutrients and maintain CaCO3 in cold shallow seawater.
Temperature and salinity variations in surface seawater off the coast of eastern Tasmania are caused by influxes of different waters. Water from Coral Sea water provided by the East Australian Current prevails in the summer, whereas Subantarctic water dominates during the winter. Throughout the year the Tasman Sea water is mixed with low salinity and low temperature deep Antarctic Intermediate water. The Antarctic Intermediate water and Subantarctic water contain an admixture of about 4% glacial melt water, resulting in δ18O values that range from −0.8 to −1.7‰ SMOW. The δ13C values are ∼0‰ in Antarctic Intermediate water and they are ∼1‰ in Subantarctic water.
The Tasmanian carbonates consist mainly of reworked calcitic fauna, such as bryozoans, foraminifera, echinoderms and red algae with variable intragranular CaCO3 cements. The δ18O and δ13C isotope fields of eastern Tasmanian bulk carbonates, bryozoans, benthic foraminifera and brachiopods overlap and all grade into the field typical of deep-sea carbonates. The trend lines of seafloor diagenesis and upwelling water pass through fields of temperate skeletons and bulk carbonates because they are in equilibrium with mixed seawaters having δ18O values of −1 to 0‰ and δ13C values of 0 to 1‰. They are forming at a slower rate than tropical water carbonates. Temperate carbonates form in zones of mixing of nutrient rich cold waters saturated with CaCO3 and warmer shelf waters.
KeywordsAragonite Temperate Carbonate Bulk Carbonate East Australian Current Subantarctic Water
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- CRAIG, H. and GORDON, L.I., 1965, Deuterium and oxygen-18 variations in the ocean and marine atmosphere,in StableIsotopes in Oceanographic Studies and Paleotemperatures, Spoleto, CNR. Lab. Geol. Nucl., Pisda, p. 1–22.Google Scholar
- DAVIES, P.J. and MARSHALL, J.F., 1973, BMR marine geology cruise in Bass Strait and Tasmanian waters-February to May, 1973.Bur. Miner. Resour. Australia, Record 134, 19 p.Google Scholar
- EDWARDS, R.J., 1979, Tasman and Coral sea ten year mean temperature and salinity fields, 1967–1976. CSIRO Div. Fish. Oceanogr. Report No. 88, 4 p.Google Scholar
- FRANCIS, R.J., 1980, Reconstruction of atmospheric CO2 levels from C13/C12 in tree-rings,in Pearman, G.I., (ed), Carbon dioxide and climate, Australian Research. Aust. Acad Sci., Canberra. p. 95–104.Google Scholar
- FRIEDMAN, I. and O’NEIL, J.R., 1977, Compilation of stable isotope fractionation factors of geochemical interest, Data of Geochemistry, 6th ed., Fleischer, M., (ed.) U.S. Geol. Surv. Prop. Paper, 440-KK, p. 1–12.Google Scholar
- JAMES, N.P. and BONE, Y., 1989, Petrogenesis of Cenozoic temperate water calcarenites, South Australia:Journal of Sedimentary Petrology, v. 59, p. 191–203.Google Scholar
- KROOPNICK, P.M., MARGOLIS, S.V. and WONG, C.S., 1977, δ13C variations in marine carbonate sediments as indicators of the CO2 balance between the atmosphere and the oceans,in Anderson N.R. and Malahoff, A., (eds.), The Fate of Fossil Fuel CO2, in the Oceans. Plenum Press, New York, N.Y., p. 305–321.Google Scholar
- MORSE, J.W., and MACKENZIE, F.T., 1990, Geochemistry of sedimentary carbonates, Elsevier, Amsterdam, 707 p.Google Scholar
- NEWELL, B.S., 1961, Hydrology of S-E Australian waters: Bass Strait and New South Wales Tuna Fishing Area. CSIRO Div. Fish. Oceanogr. Tech. Pap. 10, 20 p.Google Scholar
- RAO, C.P., 1981b, Criteria for recognition of cold-water carbonate sedimentation: Berriedale Limestone (Lower Permian), Tasmania, Australia:Journal of Sedimentary Petrology, v. 51, p. 491–506.Google Scholar
- RAO, C.P., 1988a, Paleoclimate of some Permo-Triassic carbonates of Malaysia:Sedimentary Geology, v. 60, p. 117–129.Google Scholar
- RAO, C.P., 1993b, Mixing water masses: the key in understanding the origin of temperate carbonates. Australian Marine Geoscience Workshop Abstracts, p. 50.Google Scholar
- RAO, C.P. and GREEN, D.C., 1982, Oxygen and carbon isotopes of Early Permian cold-water carbonates, Tasmania, Australia:Journal of Sedimentary Petrology, v. 52, p. 1111–1125.Google Scholar
- RAO, C.P. and JAYAWARDANE, M.P.J., 1994, Major minerals, elemental and isotopic composition in modern temperate shelf carbonates, eastern Tasmania, Australia: Implication for the occurrence of extensive ancient nontropical carbonates:Paleogeo. Paleoclim. Paleoecology, v. 107, p. 49–63.CrossRefGoogle Scholar
- RAO, C.P. and ADABI, M.H., 1994, Oxygen and carbon isotope cr for the recognition of aragonite from calcite of Recent and ancient (Tertiary, Jurassic and Ordovician) carbonates: Imlications for water temperatures:Paleogeo. Paleoclim. Paleoecology (submitted).Google Scholar
- ROCHFORD, D.J., 1977, The surface salinity regime of the Tasman and Coral seas. CSIRO Div. Fish. Oceanogr., Report No. 84, 12 p.Google Scholar
- SHACKLETON, N.J. and KENNETT, J.P., 1974, Paleo-temperature history of the Cenozoic and the initiation of Antarctic glaciation: oxygen and carbon isotope analyses in DSDP sites 277, 279 and 281,in Kennett, J.P. and Houtz, R.E., Initial Reports of the Deep-Sea Drilling Project, XXIX, U.S. Govt. Printing Office, Washington D.C., p. 743–755.Google Scholar