Sevier orogenesis and nonmarine basin filling: Implications of new stratigraphic correlations of Lower Cretaceous strata throughout Wyoming, USA

Abstract

Lower Cretaceous nonmarine rocks throughout Wyoming have been used to date movements on major thrusts during the Sevier orogeny, evaluate the sedimentary response in the adjacent foreland basin, reconstruct subsidence histories, evaluate the driving mechanisms of that subsidence, and have been applied to basin modeling studies. However, detailed correlation and dating of these strata have been problematic for a century, making most detailed interpretations equivocal. New age data and correlations presented here have important implications for the evolution of the Sevier orogen and controls on basin fi lling.Lower Cretaceous strata in Wyoming show the former existence of a foreland basin fi ll that displays a thick foredeep depozone to the west (the Gannett Group), a thin forebulge depozone throughout central Wyoming (the Cloverly Formation), and thickening into a backbulge depozone in the Black Hills area to the east (the Lakota Formation). Basin subsidence is attributable not only to orogenic loading, but to dynamic loading as well.New data and correlations indicate that a thrust load was in place during the Neocomian (attributable to movement on the Paris-Willard thrust system) and that sediment supply was high (as represented by the upper Ephraim Formation). Subsequent deposition of the Peterson Limestone in the foredeep during the latest Neocomian and Aptian, and the development of a regional unconformity elsewhere, indicate a reduction in sediment supply that may have been caused by (1) a change to a drier climate, possibly related to progressive mountain-belt uplift and development or intensifi cation of an orographic rain shadow, or (2) a decrease in mountain-belt uplift rate and a reduction in mountain-belt relief. Unconformity development on the forebulge is consistent with the fi rst scenario. Subsequent deposition of the Bechler, upper Cloverly, and upper Lakota Formations during the Early to Middle Albian indicates increased sediment supply, progressive unroofi ng of the mountain belt, and movement on the Meade-Laketown-Paris-Willard thrust system. These events suggest renewed or accelerated mountainbelt uplift during the early to middle Albian. The Draney Limestone, which overlies the Bechler, correlates with an unconformity at the top of the Cloverly and Lakota Formations and is Albian in age. The Draney Limestone and the unconformity signify a return to conditions similar to those that existed during deposition of the Peterson Limestone. The results presented here differ from those of some researchers who contend that a foredeep did not exist during initial deposition of these strata, and that deposition was not coincident with thrusting during early stages of the Sevier orogeny.

Tectonically induced climate and its control on the distribution of depositional systems in a continental foreland basin, Cloverly and Lakota Formations (Lower Cretaceous) of Wyoming, U.S.A.

“…3). This age range is supported by zircon ages, palynology, and magnetostratigraphy (May et al, 1995;Chen and Lubin, 1997;Zaleha, 2006). Furthermore, this age designation is consistent with a new age of 108.5 ± 0.2 Ma from the Himes Member of the Cloverly Formation in the Bighorn Basin (Burton et al, 2006).…”

“…Conglomerates of the Cloverly Formation extend up to 1000 km eastward from the Sevier fold-and-thrust belt in western Wyoming. Provenance studies of Cloverly sandstones and conglomerates indicate that they were sourced from lower Mesozoic and Paleozoic rocks exposed by Late Jurassic to Early Cretaceous thrusting in western Wyoming and central Utah (Mirsky, 1962;Furer, 1970;DeCelles and Burden, 1992;May et al, 1995;Zaleha, 2006). The provenance and distribution of coarse-grained sediments in this continental foreland basin is consistent with northeast paleoflow of Cloverly rivers (May, 1992;O'Malley, 1994;Way et al, 1994;May et al, 1995;Zaleha et al, 2001).…”

“…2). The thickening of these sediments in a proximal position to the Sevier fold-and-thrust belt is related to increased accommodation from thrust loading, forming the Early Cretaceous Cordilleran retroarc foreland basin in Wyoming (DeCelles and Burden, 1992;Zaleha, 2006).…”

The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia

“…The age of the Cloverly Formation is not well-constrained, but several studies regarding Ostrom's (1970) units V-VII have found an Aptian-Albian age for those sediments with dates that range from about 113-108 Ma (Burton et al, 2006;Zaleha, 2006;Farke et al, 2014). However, D'Emic and Britt (2012) found a much younger age of about 103 Ma for sediments corresponding to unit VI or VII of Ostrom (1970) (Farke et al, 2014).…”

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“…Once work was completed, the (Darton, 1901;Rubey, 1931; Waage, 120 1959;Post and Bell, 1961). The Lakota Formation is interpreted to be temporally equivalent to 121 portions of both the Cloverly Formation of Wyoming and Montana, and the Cedar Mountain 122 Formation of eastern Utah (Way et al, 1998;Zaleha, 2006;Sames et al, 2010; Martin-Closas et 123 al., 2013;Cifelli et al, 2014). (Sohn, 1958;1979;Anderson, 1973;Cook and Bally, 1975 170 et al, 2014).…”