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.
