Setting of the Devine Test Site
The Devine Test Site
is located in Medina County, approximately 2 miles southwest of Yancey,
Texas (Figure 1). The site is located on the northern margin of the Luling
Fault Zone (Figures 2 and 3), which is the southern segment of the Luling-Mexia-Talco
Fault Zone (LMT) that strikes approximately northeast from the test site
area and extends into the northeastern corner of Texas.
1. Locations of the Devine Test Site (DTs) and
Superconducting Super Collider (SSC) site within the extensional fault
zones (Balcones-Luling-Mexia-Talco) that rim the Gulf Coast Basin.
The LMT is east and
south of, and parallel to, the Balcones Fault Zone. Both fault zones are
characterized by large Cretaceous to Tertiary normal faults, commonly
with throws of over 100 ft, and associated smaller faults that mark extension
along the margin of the Gulf Coastal Basin (Collins and others, 1992).
2. Structure map on the top of the Edwards aquifer with location of
the Devine Test Site. Major faults of the Luling Fault Zone trend
northeast (from Hovorka and others, 1995).
3. Location of experimental wells at the Devine Test Site. Wells are
aligned approximately normal to local fault trends (compare with Figure
At the Devine Test
Site, the top of Austin Chalk is 2,250 ft deep, with a thickness of 320
ft (Figure 4). The Austin Chalk is overlain by younger Upper Cretaceous
and Eocene rocks, with rocks of the Wilcox Group exposed at the surface.
Austin Chalk is a deep-water deposit (Scholle, 1977; Hovorka and Nance,
1994) and has a very fine texture composition throughout its range in
Texas, except on the San Marcos Arch (northeast of the test site) where
shallow-water, generally coarser grained facies are common (Young and
4. Photograph of tunnel exposure in lower Lower Austin Chalk, SSC site,
Ellis County, Texas, showing uniformly thick chalk-marl intervals (typical
Austin Chalk), a submarine channel (behind the person), and several
normal faults. Note slight marl smears along faults. (Enlarged photo
of channel is shown under Vertical Heterogeneity of Austin Chalk, Figure
of chalk mapped inside the large tunnels (incrop exposures rather than
outcrop exposures??) at the abandoned Superconducting Super Collider (SSC)
site, located in the northern extension of the Balcones Fault Zone (Figure
2, above) in north Texas, are useful for describing the chalk at the Test
Site because both sites reside in relatively shallow subsurface settings
(SSC at a depth of 200 to 400 ft; Devine Test Site at depths of 2250 to
2580 ft) and in extensional fault zones. The Austin Chalk has a similar
deep-water depositional origin and composition at both sites (Collins
and others, 1992; Nance and others, 1994).