Tectonic Control on the Sequence Stratigraphy of Nonmarine Retroarc Foreland Basin Fills: Insights from the Upper Jurassic of Central Utah, U.S.A.

Abstract

Continental successions of the North American Western Interior retroarc foreland basin provide an excellent opportunity to evaluate the tectonic controls on nonmarine sequence stratigraphy. The transition between the Upper Jurassic Brushy Basin Member anastomosed fluvial system of the Morrison Formation and the gravelly braided-river deposits of the Buckhorn Conglomerate has been studied to assess the dispersal of coarse clastics and the development of associated basin-wide unconformities in a sequence stratigraphic framework. The sharp contact between the two members is interpreted to be conformable based on stratigraphic, sedimentologic, and petrologic data collected at and near Cedar Mountain in central Utah, while a regional, mature paleosol at the top of the Buckhorn Conglomerate indicates the presence of a major sequence boundary. These interpretations are combined with paleoflow data and fluvial architectural analysis to reconstruct the evolution of the alluvial equilibrium profiles that controlled deposition of the succession. The Buckhorn Conglomerate is interpreted as an example of a post-orogenic deposit on the basis of (1) its tabular geometry, (2) distance from the contemporaneous thrust belt, (3) shift to transverse paleoflow direction from the preceding Brushy Basin axial drainage, (4) conformable lower contact, and (5) presence of an overlying sequence boundary with a westward-expanding hiatus eroding the coeval foredeep. The onset of a protracted period of low rate of orthogonal convergence between the Farallon and North American Plates resulted in tectonic quiescence and consequent isostatic rebound of the Middle to Late Jurassic thrust belt and the contiguous contemporaneous foredeep, as well as dynamic uplift. The ensuing basin-wide decrease in subsidence rate induced the progradation of the Buckhorn alluvial plain into the Morrison back-bulge depozone, and the subsequent generation of the overlying pedogenic unconformity, which separates the deposits of the Jurassic flexural event from the overlying Sevier tectonostratigraphic unit.

Evolution of the Cordilleran foreland basin system in northwestern Montana, U.S.A.

“…In particular, a detrital zircon sample from the basal conglomeratic sandstone yielded two grains with Hauterivian ages (131.6 ± 4.5 and 133.5 ± 1.8 Ma), providing a maximum possible age for this interval. These data confl ict with recent suggestions by Roca and Nadon (2007) for continuous deposition between the Morrison Formation and the overlying conglomeratic beds, and the proposition that the K-1 unconformity is higher in the section. A detrital zircon sample from the upper part of the Kootenai contained a population of euhedral crystals that yielded early Albian ages, refl ecting syndepositional volcanism.…”

The evolution of volcano-hosted geothermal systems based on deep wells from Karaha-Telaga Bodas, Indonesia

“…2 and 5). A prominent calcrete paleosol separates Buckhorn Conglomerate from the remainder of the Cedar Mountain Formation (Currie, 1998), suggesting that the Buckhorn might represent a closing phase of Morrison sedimentation (Roca and Nadon, 2007), and an analogous calcrete horizon overlies basal sandstone bodies of the Burro Canyon Formation (Aubrey, 1998). The Buckhorn Conglomerate Member extends eastward, however, past an arbitrary change in nomenclature at the Green River, into the Poison Strip Sandstone Member, which overlies the Yellow Cat Member containing Early Cretaceous (Barremian) dinosaur remains (Kirkland and others, 1997;Kirkland and Madsen, 2007).…”

Sand composition changes across key boundaries of siliciclastic and hybrid depositional sequences

“…Subaerial exposure due to sea-level fall causes pedogenesis and erosion of early deposited marine sediments, especially in coincidence of interfluvial sequence boundaries (Van Wagoner et al, 1990;Aitken and Flint, 1996;McCarthy and Plint, 1998;Roca and Nadon, 2007).…”

“…The development of basin-wide unconformities due to active tectonics is commonly accompanied by deposition of sand units that differ markedly in composition, and different petrofacies may permit the characterization of each sequence in terms of both clastic constituents and provenance (Arribas et al, 2003). Compositional changes at sequence-bounding unconformities generally mark abrupt paleodrainage reorganization in response to tectonic uplift (Ryu and Niem, 1999;Roca and Nadon, 2007;Vezzoli and Garzanti, 2009). In terms of sequence stratigraphy, changes in arenite composition at sequence boundaries are likely to be recorded (i) at the basin margin, by sharp petrofacies changes within fluvial and transgressive estuarine to littoral and shelfal sand bodies directly overlying the subaerial unconformity, (ii) in deep-water settings, at the base of thick successions of falling-stage turbidites (correlative conformity), in association with diagnostic changes in lithofacies patterns (e.g., abrupt increase in the sandstone to shale ratio).…”