Structural
evidence for syntectonic sedimentation within the Cretaceous
Wahweap Formation, Kaibab Uplift, Utah
Zellner, G.
C. and Tindall,
S.E., 2004, Structural
evidence
for
syntectonic
sedimentation
within the Cretaceous Wahweap Formation, Kaibab Uplift, Utah [abs]:
Northeastern Section (39th Annual) and Southeastern Section (53rd
Annual) Joint Meeting (March 25–27, 2004), Geological Society of
America Abstracts with Programs, Vol. 36, No. 2, p. 102.
The
East Kaibab monocline on the Colorado Plateau trends NNE and extends
from the Grand Canyon in northern Arizona to near Bryce Canyon in
southern Utah. Near the northern terminus of the monocline two
curved faults, each more than 2 km in strike length, display
approximately 0.5 km of apparent right-lateral offset of
east-dipping Jurassic and Cretaceous strata exposed in the steep
limb of the monocline. The faults strike ~N50E and dip 60W-80E;
previous workers interpreted them as reverse, right-lateral faults
that formed late during Laramide development of the East Kaibab
monocline.
The Cretaceous Wahweap Formation appears to be approximately three
times thicker on the southeastern side of each fault than on the
northwestern side. Apparent thickness of the Wahweap is greatest
immediately adjacent to each fault, and becomes thinner with
distance south of the faults. In order to determine whether the
apparent thickness change is an illusion caused by a shallowing of
bedding dip in the steep limb of the monocline, or represents
thickening possibly resulting from deposition during fault movement,
we measured strike and dip of bedding along three transects at
distances between 0.5 km and 3 km south of one of the curved faults.
The upper and lower stratigraphic boundaries of each transect
correspond with distinctive marker beds in the Cretaceous
stratigraphy. Cross sections constructed using transect data show
that thickness of bedding adjacent to the fault is between 400-520
ft, whereas 3 km south of the fault the thickness is180-190 ft.
Different subsurface interpretations along each transect result in
slightly different calculations of sediment thickness, producing the
thickness ranges noted above, but constraints provided by surface
data indicate that a change in bedding orientation is not sufficient
to account for the apparent thickening of the Wahweap Formation
adjacent to the fault. Based on these new data, we hypothesize that
stratigraphic thickening on the southeastern side of each fault
represents syntectonic sedimentation during the Cretaceous, and that
the steeply dipping, curved faults formed as listric normal faults
before being rotated to their current orientations in the steep limb
of the East Kaibab monocline.