A Late Jurassic to Early Cretaceous record of orogenic wedge evolution in the Western Interior basin, USA and Canada

The Late Jurassic to Early Cretaceous fill of the Western Interior foreland basin is characterized using geochronological data in order to assess the stratigraphic expression of wedge-top geomorphology, as controlled by sediment cover and denudation. In northern Montana, USA, and Alberta, Canada, wedge-top deposits are poorly preserved; however, their former presence may be inferred from the detrital record in the foreland basin. We present new U/Pb detrital zircon data from nine samples collected near Great Falls, Montana, augmented with field data. The stratigraphy at Great Falls is characterized by Late Jurassic marine and nonmarine deposits, which are truncated by a basinwide sub-Cretaceous unconformity. Aptian and lower Albian strata overlying the unconformity are dominated by nonmarine deposits, which transition up-section into a predominantly marine succession related to a major transgression of the Boreal Seaway in the Albian. Detrital zircon grains from Great Falls strata yield age spectra that can be subdivided into three groups using multidimensional scaling. Group 1 is characterized by diverse zircon populations, which are interpreted to record recycling of pre-Cordilleran sedimentary strata transported via foreland basin-axial river systems with headwaters in the southwestern United States. Group 2 is characterized by the dominance of Mesozoic detrital zircon grains, which are interpreted to record sediment dispersal by fluvial systems with headwaters in the Cordillera. Group 3 is intermediate between groups 1 and 2, based on its proportion of Mesozoic zircon grains. This group records a diversification of the provenance from one dominated by Cordilleran igneous rocks to include recycled sedimentary strata. New data are integrated with three other data sets from Montana and Alberta such that stratal thicknesses (a proxy for accommodation development) and provenance evolution can be compared across the basin. The detrital record in each area, which transitions from diverse provenance to predominantly Cordilleran through the entire stratigraphic section, can be linked to the burial of the pre-foreland strata in the wedge-top depozone. This record elucidates a period of evolution of the western margin of North America to a more Andean-type system with primary input to the basin from an active magmatic arc. INTRODUCTION Aggradation and denudation of proximal foreland basin deposits in the wedge-top depozone are first-order controls on sediment flux to more-distal parts of foreland basin systems (Ben-Avraham and Emery, 1973; DeCelles, 1994; DeCelles and Giles, 1996; Roddaz et al., 2005; Ross et al., 2005; Horton, 2018). Burial of the frontal toe of the orogen can heal complex topography and enhance direct sediment transfer from the orogenic hinterland to a basin. Conversely, denudation of these wedge-top sediments can lead to structural control of river pathways; the process also can expose older stratigraphy in the orogenic wedge, which can be reflected by provenance changes in the adjacent foreland basin (Ross et al., 2005; Lawton et al., 2010). Sediments in the wedge-top depozone accumulate on top of orogenic structures and are part of the frontal toe of the orogenic wedge (DeCelles and Giles, 1996). These synorogenic strata accumulate near the erosional/depositional surface and are characterized by low preservation potential such that the history of sedimentation in this zone is difficult to discern (e.g., Coogan, 1992; Frisch et al., 2001; McMechan et al., 2018). More distal parts of the foreland basin contain well-established records of orogenic processes (e.g., Heller and Paola, 1989; Ross et al., 2005; Quinn et al., 2016). Therefore, we hypothesize that the history of the wedge-top depozone can be elucidated by investigating strata in more-distal parts of the foreland basin. This is particularly relevant to understanding topographic evolution in fold-thrust belts that have been deeply incised during subsequent orogenesis and glaciation (Osborn et al., 2006). We present a detrital zircon data set from Western Interior basin strata exposed near Great Falls, Montana, USA. The units provide a unique window into the Late Jurassic–Early Cretaceous evolution of the foreland basin because outcrops of these strata are rare except within the fold-thrust belt, which is ~100 km west of the study area. New data are integrated with previously presented data sets from across the basin in order to consider the history of burial and exhumation of the frontal toe of the orogenic wedge (Fig. 1) ( Fuentes et al., 2011; Leier and Gehrels, 2011; Raines et al., 2013; Benyon et al., 2014; Blum and Pecha, 2014; Quinn et al., 2016). This study emphasizes the potential impact of wedge-top dynamics on sediment dispersal across foreland basins and the structural evolution of the orogen. GEOSPHERE GEOSPHERE; v. 14, no. 3 https://doi.org/10.1130/GES01606.1 12 figures; 1 table; 1 supplemental file CORRESPONDENCE: garrett . quinn@ ucalgary.ca; gquinn7@ gmail . com CITATION: Quinn, G.M. , Hubbard, S.M. , Putnam, P.E. , Matthews, W.A. , Daniels, B.G. , and Guest, B. , 2018, A Late Jurassic to Early Cretaceous record of orogenic wedge evolution in the Western Interior basin, USA and Canada: Geosphere, v. 14, no. 3, p. 1187–1206, https:// doi . org /10 . 1130 /GES01606.1. Science Editor: Raymond M. Russo Received 24 August 2017 Revision received 21 February 2018 Accepted 16 April 2018 Published online 7 May 2018