Thomas C. Wynn1,
J. Fred Read1
(1) Virginia Tech, Blacksburg, VA
Abstract: Subsurface high resolution sequence stratigraphy for Mississippian mixed carbonate-siliciclastics using well-cuttings and wireline log analysis Appalachian Basin, West Virginia
The high resolution, outcrop-base sequence stratigraphy of the Mississippian Greenbrier Group (50 to 500m thick) of Al-Tawil (1998) is being extended throughout the subsurface of West Virginia, using well-cuttings and wireline logs. Percent of each lithology in each sample interval have been plotted to form computer-generated graphical logs and some of the lithologies repositioned using the wireline logs for 100 out of a targeted 200 wells.
This methodology has allowed us to construct, for the first time, regional 150 km-long, detailed cross-sections through the basin. Subsurface analysis shows five major 3rd order sequences 10m to 50m thick each composed of two to five, regionally mappable 4th order sequences. Third order sequences are bounded by late highstand to lowstand red beds. Third and 4th order sequences contain lowstand shallow-marine sands/quartz-calcisilts along the ramp margin, semi-regional transgressive shales, and high-stand quartz peloidal grainstone (dominantly eolian), peritidal lime mudstone, peloid grainstone and oolite, skeletal grainstone, open marine skeletal wackestone/mudstone and argillaceous slope mudstone. Sequence boundaries updip are marked by caliche and/or eolianite lithologies in the cuttings and also occur at the change from upward shallowing to upward deeping trends. Transgressive shales commonly overlie sequence boundaries.
The cuttings data is enabling us to map out regional trends and spatial distribution of the major facies (including oolite and sandstone reservoirs) throughout the subsurface within this sequence stratigraphic framework. This will provide the first, detailed high-resolution time-slice maps for the Mississippian in the basin. In addition it is allowing us to refine our Mississippian sea level curve for the basin, which shows increased magnitude upsection, concomitant with buildup of Gondwana glaciation.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana