Early Cretaceous Provenance, Sediment Dispersal, and Foreland Basin Development in Southwestern Montana, North American Cordillera

Abstract

Retroforeland basins form adjacent to fold-thrust belts and contain the stratigraphic record of mountain building (DeCelles, 2012;Ingersoll, 2012). In some cases, where portions of the hinterland have been displaced along major strike-slip faults, the foreland basin system may hold key information for unraveling complex geological histories as it remained stationary on the continent during orogenesis (e.g., Wyld et al., 2006). During Early Cretaceous time, the western margin of the Idaho-Montana sector of the North America Cordillera was subject to outboard terrane accretion and translation, decreased arc magmatism, growth of the Sevier orogenic belt, and development of a retroforeland basin system on the stable portion of the continent (Figure 1; DeCelles, 2004;Gehrels et al., 2009;Gray et al., 2019;Wyld et al., 2006). During this time, this foreland basin system expanded to several hundred kilometers in width, developed an asymmetric geometry, and spanned the length of the continent (DeCelles, 2004).Numerous models for North American sediment dispersal during Early Cretaceous time have been proposed. However, there is a notable gap in U-Pb detrital zircon data from the Idaho-Montana sector of the foreland basin system (e.g., Blum & Pecha, 2014;Leier & Gehrels, 2011;Schwartz & DeCelles, 1988). Some regional models for this time interval have focused on complexity in southwestern Montana, where early activity along thick-skinned thrusts has been documented in the distal parts of the foreland; these prior studies suggest that the record of basement-involved deformation may substantially predate activity along similar thick-skinned structures elsewhere in the Laramide province (

Middle Albian provenance, sediment dispersal and foreland basin dynamics in southwestern Montana, North American Cordillera

“…Our mixture model for the Group 2 U-Pb detrital zircon composite (Figure 9b) suggests a similar, but slightly more complex provenance than that of the underlying Kootenai Formation (Rosenblume et al, 2021). The Group 2 mixture model includes ages between 200 and 3500 Ma; it results in a best fit with R 2 = 0.926 and indicates major contributions of 39% Ordovician-Devonian-Mississippian, 18% Cambrian, 17% Kootenai Formation and minor contributions from other potential source strata.…”

“…Grey-shaded region highlights the study interval, which is separated into a western and eastern region based on previous work (Schwartz, 1972). Maximum depositional ages of underlying Kootenai Formation are based on previous work Rosenblume et al, 2021) Blackleaf locality to provide context for samples (Figure 3), which are identified by an abbreviation for the locality followed by the stratigraphic level in metres from which they were collected. For the sample at the Buffalo Jump locality (Table 1; KcBJ), a stratigraphic section was not measured.…”

“…A potential source for the first cycle detrital zircon grains is the portion of the Cordilleran arc in the southern Omineca belt (cf. Rosenblume et al, 2021). For first-cycle sources, we were unable to include U-Pb age composites in the mixture models because data from igneous rocks are typically high-precision, low-n ages, which may not be accurately reflected in the detrital zircon record (Schwartz et al, 2021).…”

“…Composite U-Pb detrital zircon age spectrum from Appalachian region compared with samples that show similar detrital age spectra from Iowa-Nebraska, the Black Hills, the Bighorn Basin, western Montana and northeastern Alberta, Canada. Shaded grey regions behind probability density plots highlight the two key populations present in all samples along the transect of the transcontinental Cambrian source strata (Figure9b), which signal continued unroofing or deeper fluvial incision in the Sevier fold-thrust belt, because lower-middle Palaeozoic strata were exposed prior to this time based on the provenance of the Kootenai Formation(Rosenblume et al, 2021). for the Group 3 U-Pb detrital zircon composite (Figure9c) suggests the arrival of detritus from a combination of Triassic and upper Palaeozoic strata that were exhumed within the Idaho sector of the Sevier belt.…”

Pre‐Thrusting Stratigraphic Control on the Transition From a Thin‐Skinned to Thick‐Skinned Structural Style: An Example From the Double‐Decker Idaho‐Montana Fold‐Thrust Belt

“…The absolute age of deformation within these two packages is less constrained. A basal angular unconformity, isopach maps, and reconstructed paleocurrent data from the lower‐Cretaceous to mid‐Cretaceous Kootenai Formation in the southwestern Montana foreland may suggest early, low‐magnitude exhumation related to thick‐skinned thrusting (Decelles, 1986; Scholten, 1982; Schwartz, 1982), but within a regionally continuous foreland basin setting with extrabasinal sources (Rosenblume et al., 2021). Provenance studies of the Late Cretaceous to Paleocene Beaverhead Group (Garber et al., 2020; Haley et al., 1991; Perry & Sando, 1982; Ryder & Scholten, 1973) and low‐temperature thermochronologic data (Carrapa et al., 2019) suggest mid to Late Cretaceous exhumation of the Blacktail‐Snowcrest arch, followed by in‐sequence slip along the thin‐skinned Medicine Lodge and Tendoy thrusts.…”