DENNISON, JOHN M., University of North Carolina, Chapel Hill, NC; FILER, JONATHAN K., College of William and Mary, Williamsburg, VA; CAVALLO, LARRY J., Dominion Appalachian Development, Jane Lew, WV; DRAKE, ROBERT A., Auburn University, Auburn, AL; and MIDDLETON, JEREMY D., University of Kentucky, Lexington, KY
Three examples illustrate how gamma-ray logs constructed from scintillometer
measurements of outcrops can clarify structural interpretations of monotonous
strata lacking distinct marker beds. Scintillometer readings were taken
every two stratigraphic feet and compared with gamma-ray logs from nearby
wells in horizontal strata.
The Brallier Formation near Dailey, WV is folded into three anticlines
and two synclines in monotonous turbidites. Stratigraphic position differed
by hundreds of feet from the first field estimate. This outcrop was tied
to a nearby borehole reaching the Oriskany Sandstone, and structure of
the Elkins Valley anticline was clarified.
Brallier Formation strata near Bluefield, WV are anomalously thin and
are cut by numerous extensional faults in overturned beds, which cause
small amounts of thinning. An outcrop gamma-ray log reveals that a major
omission of 2,000 feet of strata occurs in one covered interval, which
is the major offset of the Lindside normal faulting zone.
Chattanooga Shale at Hagan, VA, was interpreted by Miller and others
(1954) to contain an underthrust, duplicating much Chattanooga Shale on
the upturned, southern edge of the Pine Mountain block (also called a reverse
fault in Brallier Shale upthrust to the south). The presumed duplication
is a couplet of very black shale overlying lighter gray-weathering shale.
The strata are intensely contorted and slickensided in places. The two
dark shales interpreted as zones of fault duplication have distinctly different
signatures, and these two dark zones can be clearly identified in the normal
sequence of middle Chattanooga. Underthrusting duplication is rejected,
in favor of bedding surface slippage in the shale toward the axis of the
Powell Valley anticline.
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