Abstract

The Ordovician Gordon Limestone in Tasmania is a low-paleolatitude (10°N) peritidal carbonate with a tropical chlorozoan assemblage (calcareous green algae and corals), diverse nonskeletal grains, extensive early diagenetic dolomites, and some evaporites. It is characterized by small Mn, moderate Na, and large Sr concentrations as in Holocene tropical aragonitic carbonates. The range of Sr/Na (2.6 to 4.6) in the Gordon Limestone is related to aragonitic original mineralogy, dolomitization, and evaporite formation and to channel, prograding tidal flat, and stratigraphic reef environments.

The Upper Permian Berriedale Limestone is a sequence of inter-bedded limestones and calcareous shales deposited at a paleolatitude near 80° S during the Gondwanan ice age. The shallow-marine limestone beds formed during the lowering of sea level in colder periods. As sea level rose in warmer periods, a shower of dropstones preceded shale deposition. The Berriedale Limestone contains a cold-water foramol fauna (bryozoans, brachiopods, and pelecypods), intraclasts, and abundant orthochems. Low Mg, equal amounts of Sr and Na (Sr/Na = 1.0), and large Mn concentrations in this limestone indicate original low-Mg calcite precipitation from sea water at a temperature <3 °C.

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