Stacked Late Devonian lowstand shorelines and their relation to tectonic subsidence at the Cordilleran Hingeline, western Utah

The Upper Devonian (lower Famennian) Cove Fort Quartzite and associated str ata of western Utah comprise three stratigraphic sequences, each containing a thick (as much as 65 m) lowstand systems tract. Coarse-grained shoreface quartz arenite and lagoonal dolomicrite of the lowstand systems tracts dis play the following features characteristic of forced regression: (1) they c ontain coarse-grained proximal shoreline deposits that overlie an erosional surface (sequence-bounding unconformity) cut into fine-grained distal-mari ne carbonate facies; (2) they lie seaward of a zone of sediment bypass, and are spatially detached and separated from the previous highstand shoreface ; (3) they are confined geographically to a relatively narrow zone less tha n 30 km wide; (4) they are onlapped and overlain by transgressive systems t ract deposits consisting of deep subtidal carbonates (West Range Limestone) ; and (5) landward of the lowstand shoreline pinch-out, the sequence boundi ng unconformity beneath them merges with a transgressive surface of erosion above them. A thick wedge of siliciclastic forced-regression deposits is present at the base of each depositional sequence. The stratigraphic position of each wed ge above the basal sequence boundary was controlled by eustatic sea-level f all. The forced regression deposits are geographically restricted to a narr ow strike belt along the eastern margin of the Pilot basin, which coincides with the trace of the Cordilleran Hingeline, a zone of crustal discontinui ty. The geographic confinement and unusual stratal thickness of barrier-bar complexes in the lowstand systems tract, as well as the stratigraphic stac king of the forced-regression deposits, were controlled by flexurally induc ed high subsidence rates focused at the Cordilleran Hingeline.