Abstract: The Southern-Central Appalachian Triangle Zone: An Unexplored Potential Hydrocarbon Play from Alabama to Pennsylvania

ROBERT D. HATCHER, JR.
University of Tennessee, Knoxville, TN, and Oak Ridge National Laboratory, Oak Ridge, TN
ROBERT C. MILICI
U.S. Geological Survey, Reston, VA
and JENNIFER B. WHISNER
University of Tennessee, Knoxville, TN

Triangle zones consist of a dominant foreland-vergent thrust that truncates a hinterlandvergent passive-roof duplex. They form in the outer parts of foreland fold-thrust belts, marking the transition from more complex deformation of the internal parts to the less complex outer parts. The best studied triangle zone is located in the transition between the Alberta Rockies and Foothills in the Canadian Cordillera. Triangle zones also occur in the southern and central Appalachians from the Jacksboro fault the Pine Mountain block to Alabama and northeastward to Pennsylvania where Lower Cambrian (Rome Formation) to Lower Ordovician (Knox Group) rocks were thrust over Carboniferous siliciclastic rocks. An exposed section through the southernmost triangle zone near Rockwood, Tennessee reveals an intensely deformed core probably the result of solving the room problem, but this deformation decreases to zero 100 m to the west. Regionally, intense brittle deformation in triangle zone cores could yield fractured reservoirs sealed by shale in different parts of the section. Source rocks for hydrocarbons include Devonian-Mississippian and Middle Ordovician black shale; potential reservoirs include the fractured Mississippian carbonate rocks, fractured Middle Ordovician limestone buildups, and the Cambro-Ordovician Knox Group. Drilling in Appalachian triangle zones has to date been limited. The regional oil-gas window boundary (based on conodont alteration index and vitrinite reflectance data) trends almost northsouth in the southern Appalachians and occurs to the east of the southern triangle zone. The northeastern end of the triangle zone mostly is in the gas realm. The southern triangle zone and the southern part of the northern may provide the best opportunities for exploration.

AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio