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.