Abstract
AbstractAnomalous features of Upper Cretaceous strata in southern Utah challenge existing tectonic and depositional models of the Cordilleran foreland basin. Extreme thickness variations, net to gross changes, and facies distributions of nonmarine to marginal marine strata of the Turonian–early Campanian Straight Cliffs Formation are documented across the Southwestern High Plateaus. Contrary to most traditional models of foreland basin architecture, regional correlations demonstrate abrupt stepwise thickening, with a punctuated increase in average grain size of key intervals from west to east, i.e., proximal to distal relative to the fold-thrust belt. Except in the most proximal sections, fluvial drainage systems were oriented predominantly subparallel to the fold-thrust belt. Combined, these results suggest that modern plateau-bounding faults may have had topographic expressions as early as Cenomanian time, and influenced the position of the main axial river system by creating northeast-trending paleotopography and sub-basins. Laramide-style tectonism (e.g., basement-involved faults) is already cited as a driver for sub-basin development in latest Cretaceous–Cenozoic time, but new data presented here suggest that this part of the foredeep was “broken” into distinct sub-basins from its earliest stages. We suggest that flexural foundering of the lithosphere may have caused early stage normal faulting in the foredeep. Regional implications of these new data indicate that both detachment-style and basement-involved structures were simultaneously active in southern Utah earlier than previously recognized. These structures were likely influenced by inherited Proterozoic basement heterogeneities along the edge of the Colorado Plateau. This interpretation suggests that tectonic models for the region should be reevaluated and has broader implications for understanding variability and geodynamics of foreland basin evolution.
Highlights
Global archives suggest that retroarc foreland basins are broadly defined by several common characteristics (Jordan, 1981; DeCelles and Giles, 1996; Catuneanu, 2004; DeCelles, 2012)
Thirteen lithofacies were identified through field observations (Table 1), and these were grouped into four facies associations (Table 2: Facies association 1 (FA-1) to FA-4) that are distinguished by distinct channel architectural patterns and recurring associations of lithofacies
This proximal eastward-thinning trend is reversed across the Paunsaugunt Plateau where John Henry Member sections thicken from ∼270 m at Heward Creek to over ∼450 m at Shakespeare Mine over a distance of ∼25 km (Fig. 7)
Summary
Global archives suggest that retroarc foreland basins are broadly defined by several common characteristics (Jordan, 1981; DeCelles and Giles, 1996; Catuneanu, 2004; DeCelles, 2012) These fundamental attributes include (Fig. 1): a basinward-propagating, thin-skinned (detachment-style) fold-thrust belt; concomitant migration of four main depositional zones (wedge-top, foredeep, forebulge, and backbulge); a strongly asymmetric, continuous foredeep with greatest subsidence most proximal to the flexural load; clastic material sourced largely from the foldthrust belt ( in proximal sections); and general coarse to fine-grained facies transitions across the depozones from proximal to distal. Onset of Laramide-style (basement-involved) tectonism in latest Cretaceous time (ca. 75–50 Ma; Dumitru et al, 1994; Crowley et al, 2002; Saleeby, 2003; Tindall et al, 2010; Peyton et al, 2012; Weil and Yonkee, 2012; Yonkee and Weil, 2015) fundamentally changed Cordilleran foreland basin architecture, subdividing the foredeep into multiple isolated basins forming a “broken foreland” (Dickinson et al, 1988; Schmidt et al, 1993; Erslev, 1993; Strecker et al, 2011; Dávila and Carter, 2013)
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