EFFECTS OF LOCAL FAULTING ON SEDIMENTATION OF THE LATE CRETACEOUS UPPER AND CAPPING SANDSTONE MEMBERS OF THE WAHWEAP FORMATION, KAIBAB UPLIFT, UTAH

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.