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.
