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 … Show more
“…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.…”
Section: Group 2 Provenance-lowermiddle Palaeozoic Strata In Idaho Se...mentioning
confidence: 77%
“…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.…”
Section: Field Methodsmentioning
confidence: 99%
“…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).…”
Section: Potential Sediment Sourcesmentioning
confidence: 99%
“…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.…”
The Lower Cretaceous Blackleaf Formation in southwestern Montana records sedimentation in the Idaho‐Montana retroforeland basin of the North American Cordillera. Regional‐scale sedimentology suggests that during Albian time southwestern Montana was partially flooded by an early marine incursion of the Western Interior Seaway during deposition of the Blackleaf Formation. We use sandstone petrography, large‐n (n = 600) U‐Pb detrital zircon geochronology and mixture modelling to determine the provenance of these strata. Our analysis suggests three distinct provenance groups: Group 1 sandstones occur in the eastern region of the study area, are quartz‐rich and have zircon age‐probability peaks of ca. 110, 160, 420–450, 1050 and 1160 Ma; these sandstones match with a primarily Appalachian provenance. Group 2 sandstones occur in the western region of study area, are lithic‐rich and have peaks of ca. 110, 160, 1780, 1840, 1920, 2080 and 2700 Ma; the primary source for these sandstones was exhumed lower‐middle Palaeozoic strata from the Idaho sector of the Sevier belt. Group 3 sandstones occur in the western region of the study area, are lithic‐rich and have prominent peaks of ca. 115, 170, 430, 600, 1085, 1170, 1670 and 1790 Ma; the primary source for these sandstones was exhumed Triassic‐upper Palaeozoic strata from the Idaho sector of the Sevier belt. Our provenance data record a sharp change that coincides with the western shoreline of the seaway, and we infer that it may indicate the position of an irregular, submarine forebulge depozone influenced by dynamic subsidence during a period of reduced thrusting in the adjacent fold‐thrust belt. Albian‐aged sediments in southwestern Montana were delivered by rivers with headwaters in the Sevier belt as well as transcontinental river systems with headwaters in eastern North America. In southwestern Montana, west‐flowing transcontinental fluvial systems were flooded by the Western Interior Seaway as it encroached from the north.
“…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.…”
Section: Group 2 Provenance-lowermiddle Palaeozoic Strata In Idaho Se...mentioning
confidence: 77%
“…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.…”
Section: Field Methodsmentioning
confidence: 99%
“…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).…”
Section: Potential Sediment Sourcesmentioning
confidence: 99%
“…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.…”
The Lower Cretaceous Blackleaf Formation in southwestern Montana records sedimentation in the Idaho‐Montana retroforeland basin of the North American Cordillera. Regional‐scale sedimentology suggests that during Albian time southwestern Montana was partially flooded by an early marine incursion of the Western Interior Seaway during deposition of the Blackleaf Formation. We use sandstone petrography, large‐n (n = 600) U‐Pb detrital zircon geochronology and mixture modelling to determine the provenance of these strata. Our analysis suggests three distinct provenance groups: Group 1 sandstones occur in the eastern region of the study area, are quartz‐rich and have zircon age‐probability peaks of ca. 110, 160, 420–450, 1050 and 1160 Ma; these sandstones match with a primarily Appalachian provenance. Group 2 sandstones occur in the western region of study area, are lithic‐rich and have peaks of ca. 110, 160, 1780, 1840, 1920, 2080 and 2700 Ma; the primary source for these sandstones was exhumed lower‐middle Palaeozoic strata from the Idaho sector of the Sevier belt. Group 3 sandstones occur in the western region of the study area, are lithic‐rich and have prominent peaks of ca. 115, 170, 430, 600, 1085, 1170, 1670 and 1790 Ma; the primary source for these sandstones was exhumed Triassic‐upper Palaeozoic strata from the Idaho sector of the Sevier belt. Our provenance data record a sharp change that coincides with the western shoreline of the seaway, and we infer that it may indicate the position of an irregular, submarine forebulge depozone influenced by dynamic subsidence during a period of reduced thrusting in the adjacent fold‐thrust belt. Albian‐aged sediments in southwestern Montana were delivered by rivers with headwaters in the Sevier belt as well as transcontinental river systems with headwaters in eastern North America. In southwestern Montana, west‐flowing transcontinental fluvial systems were flooded by the Western Interior Seaway as it encroached from the north.
“…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.…”
Continental fold-thrust belts are often modeled as wedges of deformed rock that structurally overlie and are detached from underlying basement rocks (e.g.
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