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The Upper Cretaceous Wahweap Formation accumulated in the active Cordilleran foreland basin of Utah. Soft-sediment deformation structures are abundant in the capping sandstone member of the Wahweap Formation. By comparing with well-established criteria, a seismogenic origin was determined for the majority of structures, which places these soft-sediment deformation features in a class of sedimentary features referred to as seismites. A systematic study of the seismite trends included their vertical and horizontal distribution and a semi-quantitative intensity analysis using a scale from 1 to 5 that is based on magnitude, sedimentary structure type, and the predominance of inferred process of hydroplastic deformation, liquefaction or £uidization. In addition, orientations of soft-sediment fold axes were recorded. Construction of a northwest-to -southeast stratigraphic and seismite intensity cross-section demonstrates: (1) reduction in stratigraphic thickness and percentage of conglomerates to the southeast, (2) the presence of lower seismite, middle nonseismite, and upper seismite zones within the capping sandstone (permitting subdivision of the capping sandstone member), and (3) elimination of the nonseismite zone and amalgamation of the lower and upper seismite zones to the southeast. Regional isoseismal contour maps generated from the semiquantitative analysis indicate a decrease in overall intensity from northwest to southeast in the upper and lower seismic zones and in sandstone within 5 m stratigraphically of the contact between the upper and capping sandstone members. In addition, cumulative seismite fold orientations support a west^northwest direction towards regional epicentres. Isoseismal maps are used to distinguish the e¡ects of intrabasinal normal faulting from those of regional orogenic thrusting.Thus, this study demonstrates the utility of mapping seismites to separate the importance of regional vs. local tectonic activity in£uencing foreland basin sedimentation by identifying patterns that delineate palaeoepicentres associated with speci¢c local intrabasinal normal faults vs. regional trends in softsediment deformation related to Sevier belt earthquakes.

Growth faults and synorogenic sedimentary strata preserved in Upper Cretaceous units on the margin of the Kaiparowits Basin in southern Utah pinpoint the timing of onset of the Laramide orogeny in this region between 80 and 76 Ma. The newly identifi ed listric normal faults, exposed in the steep limb of the East Kaibab monocline, sole into shales and evaporites of the Jurassic Carmel Formation. Faults lose displacement up-section through the Cretaceous Wahweap Formation and are associated with numerous coseismic sedimentary features. Fault orientations and slip vectors yield strain directions consistent with fold-related extension parallel to the axis of the growing East Kaibab monocline, or with development of a pull-apart basin at a bend in the trend of the fold. The association of the faults with the steep limb of a major basement-cored structure links them to initial Laramide movement along the Kaibab Uplift. When combined with recent radiometric ages of rock units bracketing the fault-induced growth strata, these sedimentary and structural features narrowly defi ne the onset of Laramide deformation in the western Colorado Plateau.

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