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Abstract: Recognition of Hardgrounds in Terrigenous Stratigraphic Sections: The Moseley Limestone, Middle Eocene, Southeast Texas

C. A. Thornton, R. J. Stanton, Jr.

At Stone City Bluff in southeast Texas, the contact between the Stone City Formation and the Cook Mountain Formation lies at the top of the Moseley limestone. The contact is significant because it has been interpreted both as a regional disconformity marked by lithoclasts and alternatively as a conformable surface marked by burrow-fill structures protruding through the top of the limestone. The true nature of this contact is important because it may yield insight into the recognition of breaks in sedimentation within sections consisting of terrigenous marine sediments. The former interpretation is correct. Lithoclasts are of two types: rounded clasts of "glauconite" arenite and irregularly shaped clasts of dark limestone, both of which are similar to rock types found within the Mosele limestone. Both types of clasts were exposed as lithified objects on the sea floor because they have epibionts and endolithic traces preserved on them. The clasts originated by early diagenetic cementation in the form of concretions and lithified burrow fillings, which were then exposed by sea-floor erosion. During a subsequent interval of nondeposition, encrusting and boring biota colonized the clast surfaces. The Moseley limestone was pervasively cemented after final burial, with the clasts cemented to the upper surface. These relationships provide a more thorough understanding of the depositional history of the Moseley limestone, and provide criteria useful in recognizing sedimentation breaks in terrigenous strata.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994