Alternative Stratigraphic Interpretations for Thrust Sheets Beneath Southern Appalachian Crystalline Overthrust

John M. Dennison, William A. Thomas

In eastern Tennessee, strata as young as Mississippian lie directly beneath the Great Smoky thrust. There, a stack of three sheets (Pulaski, Saltville, and Copper Creek) contains an estimated thickness of 19,000 ft of sedimentary rocks above Precambrian basement. Seismic profiles obtained as part of the site study for the proposed Appalachian Ultra-deep Core Hole (ADCOH), 85 mi southeast of the Great Smoky fault, have been interpreted to reflect subhorizontal Paleozoic strata about 5,000 ft thick beneath overthrust crystalline rocks and above autochthonous crystalline basement. The most remarkable relationship to be explained is not that subhorizontal Paleozoic strata extend southeastward to the ADCOH site east of the Brevard zone, but rather by what mechanism such a grea thickness of Paleozoic strata in several thrust sheets is lost southeastward.

Six alternative scenarios of a structural cross section from eastern Tennessee to the ADCOH site show the proposed core piercing a single subhorizontal stratigraphic succession formed by (1) attached platform strata, (2) the Copper Creek thrust sheet, (3) the Saltville thrust sheet, (4) the Pulaski thrust sheet, (5) a previously unknown thrust sheet that came from the eastern platform margin slope of North America, and (6) a thrust sheet of terrane accreted from another continent, probably Africa. The subhorizontal strata at the ADCOH site also may represent a stacking of thrust sheets, each containing only part of the stratigraphic thickness preserved farther northwest. Stratigraphic criteria will permit identification of a specific thrust sheet or of stacked thrust sheets in the cor hole. The indicated southeastward thinning of strata in thrust sheets beneath the crystalline overthrust raises questions about foreland thrusting mechanisms.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.