Sand Distribution, Facies Relationships, and Structural Styles of the Spiro Formation, Frontal Ouachita Mountains, Southeastern Oklahoma
HINDE, LAWRENCE K., Baylor University, Waco, TX
Ongoing gas exploration in the overthrusted portion of the Arkoma basin continues to demonstrate the excellent reservoir characteristics of the early Atokan Spiro Formation. This activity is providing valuable new data for a comprehensive surface-to-subsurface study.
The Spiro Formation represents a mixed carbonate and terrigenous clastic platform complex that consists of laterally interfingering sandstone, shale, and limestone. Quartz sand derived from reworking of the previously deposited fluviodeltaic Foster "channel sands" was transported southwestward across the shelf where it accumulated as marine shelf bars and associated interbar facies. Spiro carbonate facies that developed between areas of sand bar accumulation indicate sediment bypass.
Three sand bar tracts can be delineated within the Spiro based primarily on surface control. The easternmost tract is the most areally extensive, and it is characterized by sand thickness in excess of 150 ft. There, Spiro sandstones consist predominantly of bar crest and bar flank facies. To the west, sand bar tracts are smaller in areal extent, sand thickness is less, and sandstone units consist mostly of bar margin and interbar facies.
South of the present-day Pine Mountain fault, terrigenous clastic and spiculitic slope and basinal sediments accumulated, whereas east of the surface exposures (along the frontal zone), the Spiro grades into a shale facies.
Late Pennsylvanian thrust faulting produced a narrow belt of fault repeated sequences that crop out only in the frontal Ouachita Mountains. Differences in thrusting styles between the eastern and western parts of the outcrop belt reflect variations in lithologic character and probably in subthrust structure.
Palinspastic restoration of thrust sheets established a basis to extend paleodepositional trends and sand bar geometries from the surface into the subsurface.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)