Insights into syndepositional fault movement in a foreland basin; trends in seismites of the Upper Cretaceous, Wahweap Formation, Kaiparowits Basin, Utah, USA

Abstract

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 in the Kaiparowits Basin, Utah, pinpoint initial Laramide deformation in the western Colorado Plateau

“…For example, Hilbert- described extensive seismites in the capping sandstone along the northern East Kaibab monocline, and attributed fl uidization features and largeamplitude soft-sediment folds to proximal faulting before lithifi cation. The normal faults in our fi eld area were active during the deposition of the upper member and through to the beginning of capping sandstone deposition, and they are the most likely source of some of the local seismicity Hilbert-Wolf et al, 2009). Orsulak et al (2006) described an increase in locally derived sandstone and mudstone clasts in conglomerates of the capping sandstone from north to south across the traces of the two faults.…”

Syndepositional tectonic activity in an epicontinental basin revealed by deformation of subaqueous carbonate laminites and evaporites: Seismites in Red River strata (Upper Ordovician) of southern Saskatchewan, Canada

“…Hilbert-Wolf, 2009). The episodic movement along known or approximated fault zones can be gauged by seismite-bearing intervals in stratigraphic sections.…”

Soft-sediment deformation structures in seismically affected deep-sea Miocene turbidites (Cilento Basin, southern Italy)

“…Owen, 1996;Moretti et al, 1999) However, it must be kept in mind that some SSDS must be attributed to liquefaction and others to fluidisation. The former process develops with a lower intensity than the latter (seismite intensity scale of Hilbert-Wolf et al, 2009). Therefore, the convolutions, the dish and pillar structures, as well as some of the vertical tubular structures must have developed with less frequency than tubes associated with sills and fluidised beds.…”