Syntectonic
sedimentation in the East Kaibab Monocline: Evidence for the
timing of the onset of Laramide deformation in South-Central
Utah
Storm,
Lauren P., Tindall,
Sarah E., Simpson,
Edward
L., and Wizevich, Michael C.,, 2008, Syntectonic
sedimentation
in
the
East
Kaibab Monocline: Evidence for the timing of the onset of Laramide
deformation in South-Central Utah [abs]: Cordilleran Section
(104th Annual) and Rocky Mountain Section (60th Annual) Joint
Meeting (19–21 March 2008), Geological Society of America
Abstracts with Programs, Vol. 40, No. 1, p. 65.
The
East
Kaibab monocline on the Colorado Plateau formed by faulting and
folding during the Late Cretaceous and early Tertiary Laramide
orogeny. Two northwest-dipping faults, each with ~0.5 km of
right-lateral separation, offset Cretaceous strata in the steep limb
of the monocline, where it trends northward along the western margin
of the Kaiparowits basin in southern Utah. Aerial photographs and
maps of the East Kaibab monocline show apparent differences in
thickness of the upper member of the Cretaceous Wahweap Formation
across each fault trace. Changes in true thickness across the faults
would indicate that the area experienced syntectonic sedimentation
during Cretaceous faulting, and that the faults were originally
southeast-dipping normal faults associated with the onset of
monoclinal uplift. If this hypothesis is correct, then sediments
should increase in thickness from north to south across each fault
trace. Alternatively, it is possible that faulting occurred after
the deposition of sediment, and differences in outcrop width
represent dip variation and structural position within the
monocline. To evaluate the importance of true thickness variation
versus structural position, we collected GPS locations and bedding
orientations across the upper member along three transects: 1) north
of the faults; 2) between the faults; and 3) south of the two
faults. Data were used to construct cross sections showing dip
variation and structural position within the steep monoclinal limb.
Precise measurement of the upper member thickness revealed that the
thinnest sediment package (92m) lies north of the faults. Between
the faults, the upper member is 132m thick, and south of the
southern fault it is 262m thick. Our data confirm that faulting was
active during the deposition of the upper member of the Wahweap
Formation, causing thickness variations across normal faults
immediately before monoclinal uplift. This newly-recognized
syntectonic sedimentation associated with the East Kaibab monocline
pinpoints the timing of onset of Laramide deformation on the western
margin of the Colorado Plateau.