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Presented at the 1997
Annual Meeting of the Southeastern Section, Geological Society of
America, Auburn, Alabama
High
resolution vibroseis seismic reflection data
were collected during 1996 to investigate
the Crackerneck fault, a southeast dipping
high-angle reverse fault known to originate
within the crystalline basement and offset
overlying Cretaceous age Coastal Plain
sediments in the A and M areas of the
northwestern part of SRS. The seismic
survey, comprised of 8 profiles, was
designed to image from top-of-basement
(approx. 300 m) to the Tertiary age
Ellenton-Congaree Formations (approx. 100-50
m) to enable detailed mapping of the
Crackerneck fault and associated structures.
Of particular importance is limit of upward
penetration of the fault into the Tertiary
section were important aquifers could be
breached. These data were combined with
earlier seismic refection and borehole data
in the overall interpretation.
The
Crackerneck fault is intersected by four of
the new profiles and is now imaged on six
seismic lines. The Crackerneck fault is the
main throughgoing structure in a 1 km wide
N16E trending fault zone that can be mapped
for a minimum distance of 4.6 km. The trend
of the fault zone is parallel to gravity and
magnetic anomalies associated with presumed
Alleghanian structures and suggests
reactivation of these structures during the
Cretaceous and Tertiary similar to other
major faults at SRS. Patterns of faulting
with the Coastal Plain sediments suggest
that reactivation was transpressional in
origin. In general, deformation along the
fault increases from northwest to southeast
along the fault zone and decreases upward
into the overlying sediments. In the GCB-1
borehole interpreted offset of base
Cretaceous unconformity is 24 m, whereas 3.4
km to the northeast the interpreted offset
from seismic data is only 12 m. Typically,
no clear offsets of reflections younger than
the Middendorf Formation are noted; however,
upwarping of reflections from Tertiary age
formations are observed. The deformation of
Tertiary age formations by the Crackerneck
fault may have implications for
environmental remediation programs at SRS.
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