Abstract

Calcrete formation is intimately associated with a near surface soil zone of intense plant root growth and an abundant soil biota. The calcretes contain many fabrics indicative of caliche formation including meniscus cements, micrite envelopes, rhizoconcretions, dissolved grains, nodules, zones of fractured sediment and intraclast breccias. Within Pleistocene dunes and especially within calcrete zones, sand grains are often coated with a rind or envelope of micrite. On the mesoscale many South Australian coastal calcretes contain intraclast horizons with "clast-within-clast" fabrics, and some of the clasts show an unusual stellate form. The formation of these intraclasts is controlled by the episodic nature of calcrete development and dune-sand emplacement within a coastal dune setting. Recognition of calcrete fabrics in pre-Quaternary carbonate sequences can be used to refine further the distinction between subaerial exposure surfaces and marine hardgrounds.--Modified journal abstract.

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