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Annona Chalk

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Type  Formation
Country  United States
Thickness  30 m
Primary  Chalk
Underlies  Ozan Formation
Sub-units  Austin Group
Named for  Annona, TX
Region  Arkansas
Overlies  Brownstown Marl
Annona Chalk httpsuploadwikimediaorgwikipediacommonsthu

The Annona Chalk is a geologic formation in Arkansas, Texas, Louisiana, and Oklahoma. It preserves fossils dating back to the Cretaceous period. The formation is a hard, thick-bedded to massive, slightly fossiliferous chalk. It weathers white, but is blue-gray when freshly exposed. The unit is commercially mined for cement. Fossils in the Annona Chalk include coelenterates, echinoderms, annelids, bivalves, gastropods, cephalopods, and some vertebrate traces. The beds range in thickness, up to over 100 feet in depth in some areas (such as the White Cliffs). There is a gradual transition between the Annona chalk and the underlying Brownstown formation, where chalk and marl are interbedded.

References

Annona Chalk Wikipedia


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