DEPOSITIONAL ENVIRONMENTS OF THE STE. GENEVIEVE LIMESTONE, UPPER MISSISSIPPIAN, S.W. VIRGINIA

The Upper Mississippian Ste. Genevieve Limestone crops out along the flanks of the Powell Valley Anticline in Wise and Lee Counties, Virginia, and is composed of several shallowing upward cycles. These shallowing upward cycles of the Ste. Genevieve in this region contain four facies associations: shoal, intershoal, restricted/backshoal and open ramp/foreshoal. The shoal facies, which is dominant in the Ste. Genevieve, is composed of oolitic grainstone and has an average ooid content of 40%. The intershoal facies (12% average ooid content) is mainly composed of ooid packstones and minor skeletal packstones. Lithologies representing deposition in low energy areas of the backshoal/restricted facies range from skeletal wackestones to dolomitized mudstone, with no ooids and moderate amounts of quartz silt. The open ramp/foreshoal facies, represented by skeletal grainstones and minor skeletal packstones with an average of °Ö 6% ooid content, occurs only at the base of the unit. These facies suggest deposition on a broad, shallow, distally steepened ramp, punctuated by shoaling oolite bodies and restricted lower energy environments. This marks the transition from shallow water sedimentation of mainly oolitic compositions to the west, to deeper water carbonates to the east.