Abstract

Cortices of ooids in a bed in the upper part of the Bangor Limestone (Upper Mississippian) in northwestern Georgia are composed of neomorphic pseudospar which is mostly in a mosaic pattern but also occurs as single crystals in crystallographic continuity with nuclei consisting of echinoderm fragments. Locally common are single crystals of neomorphic spar which are shared by cortices of adjoining ooids. A void-filling origin for the calcite in the ooid cortices is ruled out, for the most part, because of good preservation of concentric structure in the ooids. The tentative conclusion is drawn that the cortices of the ooids originated as aragonite and that echinoderm fragments, where present as nuclei of ooids or as uncoated grains adjacent to ooids, strongly influenced the crystallographic orientation of neomorphic calcite in the cortices.

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