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Carbonates and Evaporites

, Volume 10, Issue 1, pp 114–123 | Cite as

Faunal relationship to grain-size, mineralogy and geochemistry in recent temperate shelf carbonates, western Tasmania, Australia

  • C. Prasada Rao
  • Zahra Z. Amini
Article

Abstract

In western Tasmania cool temperate shelf carbonates predominate over siliciclastics and contain mainly bryozoan-molluscaforaminifera assemblages with minor algae, echinoderms, worm tubes, sponge spicules and ostracodes. Skeletons are mainly in gravel to sand fractions and minor in silt-clay fractions. Bryozoans are the main constituent in sand to gravel-size, foraminifera are the main constituent in fine sand-size and molluscans are mainly in the gravel-size fraction. Echinoderms and algae are in sand fraction, whereas sponge spicules occur in fine to very fine sand fractions.

X-ray analysis of Tasmanian bulk sediments indicate that calcite (high-Mg to low-Mg calcite; mean 69%) and quartz (mean 22%) are the major minerals with minor aragonite content (mean 9%). Mg, Sr, and Na contents in bulk sediments are positively related to high-Mg calcite bryozoans. Sr and Na contents exceed abiotic calcite values due to biotic source of these elements. Compared to tropical bryozoans, the higher Sr contents in Tasmanian bryozoans indicate a higher rate of bryozoan skeletal formation in temperate waters. Mn and Fe contents of bulk sediments are closely correlated with r2 value of 0.85. These elements are derived mainly from terrigenous source and were incorporated into calcite in a dysaerobic marine environment.

Tasmanian temperate bryozoan faunal assemblages differ from tropical chlorozoan assemblages due to variation in seawater temperatures. Bryozoans break down into fragments and are redistributed mainly as gravel to sand-size grains by currents. Normal salinity of seawater (34–35%) and nutrients in temperate waters allow abundant growth of fauna. Mixing of water masses maintain sufficent saturation of CaCO3 and thus preserve temperate carbonates.

Keywords

Calcite Sponge Bivalve Foraminifera Aragonite 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer 1995

Authors and Affiliations

  • C. Prasada Rao
    • 1
  • Zahra Z. Amini
    • 1
  1. 1.Department of GeologyUniversity of TasmaniaHobartAustralia

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