Trends in Late Cretaceous Seismites: Upper
and Capping Sandstone Members, Wahweap Formation, Kaiparowits Basin,
Utah
Wolf, Hannah L.,
Simpson,
Wendy
S.,
Simpson,
Edward
L., and Tindall,
Sarah
E.,,
2007, Trends
in
Late
Cretaceous
Seismites: Upper and Capping Sandstone Members,
Wahweap Formation, Kaiparowits Basin, Utah [abs]: 2007 GSA Denver
Annual Meeting (28–31 October 2007), Geological Society of America
Abstracts with Programs, Vol. 39, No. 6, p. 310.
The
Late Cretaceous upper and capping sandstone members of the Wahweap
Formation accumulated in a subsiding foreland basin. This study
demonstrates the utility of mapping seismites in detail to separate the
influence of regional versus local tectonic activity influencing
foreland basin sedimentation.
Soft-sediment deformation structures have been reported in the capping
sandstone member. The vertical and horizontal distribution of these
soft-sediment deformation structures was systematically studied and
their origin was determined to be seismogenic by comparison to well
established criteria. A qualitative scale applied to these seismites
uses a scheme from 1 to 4 that is based on the predominance of
liquefaction versus fluidization processes, and on scales and types of
sedimentary structures. In addition, orientations of soft-sediment fold
axes were recorded. Construction of a northwest to southeast
cross-section demonstrates: 1) a reduction in stratigraphic thickness
and percentage of conglomerates to the southeast, 2) the presence of a
lower seismite, a middle aseismic zone and an upper seismite zone
within the capping sandstone, 3) merging of the lower and upper
seismite zones to the southeast, and 4) the utility of seismite zones
as a possible correlation tool in nonfossiliferous strata. Isoseismal
maps generated from the qualitative scale indicate a decrease in
overall intensity from west-northwest to southeast in both the upper
and lower seismic zones and along the contact between the upper and
capping sandstone members. Local normal fault effects are superimposed
on the regional trends. In addition, cumulative fold orientations
indicate west-northwest regional epicenters.
