Abstract

Multiple calcrete horizons previously considered representative of true subaerial exposures may, in fact, be false penetrative calcretes related to only one subaerial exposure event. Individual subaerial exposure periods can produce a true surficial calcrete plus a series of penetrative calcretes. Although penetrative calcrete horizons are not laterally traceable over long distances, they are very similar to surficial calcretes, are commonly found at sequence and/or lithologic boundaries (permeability anomalies), and can be easily misinterpreted in core borings as representing individual exposure events. Recent penetrative calcretes are common on elevated limestone ridges of the Caicos Islands where roots penetrate downward, seeking ground-water moisture. In glacial times, penetrative calcretes may have been present throughout carbonate platforms, as ground-water levels were much lower. Penetrative and surficial calcretes can be differentiated by the lower concentrations of insoluble AI and Fe in penetrative calcretes.

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