Abstract: Microfacies Analysis of Early Pennsylvanian Microproblematica Donezella Bioherm

CHOH, SUK-JOO, The University of Texas at Austin, Department of Geological Sciences, Austin, TX

Donezella emerged as an important bioherm builder in the middle Carboniferous, after the demise of many Cambrian to Devonian reef-building algae such as the Epiphyton - Renalcis assemblages. The biologic affinity of Donezella is still poorly understood. It was considered to be a rhodophyte, chlorophyte, codiacean, or an encrusting foraminifera. Donezella is capable of building small, oncoid-type colonies as well as spectacular carbonate buildups more than 30 m thick and 200 m long.

The primary objective of this study is to provide a detailed petrographic and sedimentologic analysis of Donezella-bearing formations by means of microfacies analysis. This will allow recognition of the specific depositional environments and an understanding of the mechanism of Donezella carbonate buildup development.

Four stratigraphic sections from the Wapanucka Formation (southeast Oklahoma), Marble Falls Formation (central Texas), and Magdalena Formation (West Texas) will be investigated. In order to aid the rapid determination of the microfacies, a new method of digitizing thin sections is being developed. Integration of microfacies analysis and meter-scale shallowing-upward cycle analysis allows for detailed interpretation of depositional environments of Donezella bioherms and associated facies.

Initial results from the Wapanucka Formation indicate that the Donezella-bearing interval is generally underlain by open marine, siliceous spicule-rich microfacies and overlain by shoal and lagoonal deposits. This may indicate that Donezella probably occupied a facies belt between the open marine and shoal area near the carbonate platform margin.

AAPG Search and Discovery Article #90931©1998 AAPG Foundation Grants-in-Aid