Effects
of local faulting on sedimentation of the Late Cretaceous Upper
and Capping Sandstone Members of the Wahweap Formation, Kaibab
Uplift, Utah
Orsulak,
Megan, Tester, Edward, Jenesky, Timothy, Bernard, Jonathan,
Tindall, Sarah E.,
Simpson,
Edward
L., 2006, Effects
of
local
faulting
on
sedimentation of the Late Cretaceous Upper and Capping Sandstone
Members of the Wahweap Formation, Kaibab Uplift, Utah [abs]:
Rocky Mountain Section–58th Annual Meeting (17–19 May 2006)
Geological Society of America Abstracts with Programs, Vol. 38,
No.6, p. 33.
Sedimentologic
and
stratigraphic examination of Late Cretaceous upper and capping
sandstone members of the Wahweap Formation at the northern end of
the East Kaibab monocline indicate tectonically influenced
sedimentation occurred adjacent to three northeast striking faults.
Variations in clast size and composition, stratigraphic thickness,
and bedding orientations across fault surfaces support active
faulting during sedimentation.
Trough crossbeds and planar foresets in the capping sandstone member
show southeast paleocurrent directions, crossing northeast-striking
faults from the northwestern, upthrown block to the down-dropped
southeastern side. From northwest to southeast across fault
surfaces, conglomerate clast composition changes from
chert-dominated to sandstone- and mudstone-dominated. Sandstone and
mudstone clast size increases dramatically on the down-dropped side
of at least one of the faults. Rounded chert clasts represent
extrabasinal sediment from the Sevier mountains to the west, while
sandstone and mudstone clasts represent locally derived sediment
shed from uplifted fault blocks within the field area.
Correlation of measured stratigraphic sections in the capping
sandstone highlights distinct, laterally continuous conglomerate
beds and seismite horizons, implying that episodes of local fault
movement affected sedimentation. Further evidence is provided by
significant changes in stratigraphic thickness in the capping
sandstone and by a fan of bedding orientations in upper and capping
sandstone members on the downthrown side of the faults.
Late Cretaceous surface faulting on the margin of the Laramide
Kaibab uplift influenced local stratigraphy and sedimentation during
deposition of the upper and capping sandstone members of the Wahweap
Formation. The tectonic significance of the faults is the subject of
ongoing research.