BENSON, D. J., E. C. BATCHELDER, and J. D. HOOKS, The University of Alabama, Tuscaloosa, AL

ABSTRACT: Deposition and Diagenesis of the Knox Group in the Southernmost Appalachians

The recent success of exploration activities in Arbuckle and Ellenburger carbonates in Texas and Oklahoma has increased interest in the hydrocarbon

potential of Lower Paleozoic carbonates in other basins. One potential area of interest is the Black Warrior Basin. Unfortunately, because of a lack of prior drilling, little is known about these rocks in the basin itself. This study describes Lower Paleozoic carbonates from 10 wells and 5 outcrop exposures in the southernmost Appalachians adjacent to the Warrior Basin.

The Lower Paleozoic carbonates, which include rocks ranging inage from Middle Cambrian through Lower Ordovician, overlie Middle Cambrian clastics and are bounded above by a major regional unconformity. The interval, which ranges from 1,500 to 2,300 meters in thickness, consists of seven formations, the Brier field, Ketona, Bibb, Copper Ridge, Chepultepec, Longview, and Newala Formations.

Nine major depositional facies dominate the interval and represent deposition on a broad, shallow carbonate platform under humid to semi-arid climatic conditions. These nine depositional facies occur in a series of stacked 2 to 15 meter thick, shallowing-upward cycles. The nature of the cycles varies throughout the section reflecting larger-scale changes in eustatic sea level. Three major highstands and four major lowstands are present in the interval. Highstand events are marked by an abundance of subtidally-dominated, open marine cycles. Lowstand events are marked by peritidally-dominated, restricted marine cycles capped by exposure surfaces. The introduction of meteoric waters into the sediment during lowstands resulted in dolomitization and silicification and extensive dissolution resulting in the formation of both solution collapse and lag breccias.

Megascopic porosity is relatively rare in the Knox sequence in the study area. The majority of reservoir-grade porosity present is fracture porosity developed in the brittle, siliceous dolomites and breccia porosity occurring in the solution collapse and lag breccias.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.