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 | |
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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(Text) CC BY-SA