A note on calcite precipitates as encrustations around sea rush roots and rhizomes and as laminae in high tidal zones of western Leschenault Inlet estuary

摘要

Precipitates of calcite occur in the high tidal zone of the western shore of the Leschenault Inlet estuary as encrustations around roots and rhizomes of the sea rush Juncus kraussii, as permineralised plant and fungal material, as laminae transgressing the encrustations, and as laminae in mud and muddy sand. The calcite forms crusts around the roots and rhizomes, as bladed crystals 0.5-1.0 mm in length, preserving the roots/rhizomes as casts, as thin horizontal sheets and micro-lenses within the sediment, and cementing the sediment. Mineralogically the precipitates are calcite and some Mg-calcite. Crystallographically, the crusts are layered, with crystal growth hiatuses marked by dissolution of calcite and by Fe-oxide and Mn-oxide precipitates. The hydrological and hydrochemical setting of the calcite precipitates is where freshwater seepage from the quartz and calcareous sand of the dune barrier delivers calcium carbonate-charged waters to the high-tidal flat. These types of encrustations and calcite laminae are absent from the eastern quartz sand shore of the estuary.