Mesoproterozoic–Early Cretaceous provenance and paleogeographic evolution of the Northern Rocky Mountains: Insights from the detrital zircon record of the Bridger Range, Montana, USA

Abstract

The Bridger Range of southwest Montana, USA, preserves one of the most temporally extensive sedimentary sections in North America, with strata ranging from Mesoproterozoic to Cretaceous in age. This study presents new detrital zircon geochronologic data from eight samples collected across this mountain range. Multidimensional scaling and non-negative matrix factorization statistical analyses are used to quantitatively unmix potential sediment sources from these and 54 samples compiled from previous studies on regional correlative strata. We interpret these sources based on reference data from preserved strata with detrital zircon signatures likely representative of ancient sediment sources. We link these sources to their sinks along sediment dispersal pathways interpreted using available paleogeographic constraints. Our results show that Mesoproterozoic strata in southwest Montana contain detritus derived from the nearby craton exposed along the southern margin of the fault-bounded Helena Embayment. Middle Cambrian strata were dominated by the recycling of local sources eroded during the development of the Great Unconformity. In Devonian−Pennsylvanian time, provenance in southwest Montana shifted to more distal sources along the northeastern to southeastern margins of Laurentia, but more western basins received detritus from outboard sources along a tectonically complicated margin. By the Late Jurassic, provenance in the developing retroarc foreland basin system was dominated by Cordilleran magmatic arcs and fold-thrust belt sources to the west. Eastward propagation of the fold-thrust belt caused recycling of Paleozoic and Jurassic detritus into the foreland basin to dominate by the Early Cretaceous.

Orogens of Big Sky Country: Reconstructing the Deep‐Time Tectonothermal History of the Beartooth Mountains, Montana and Wyoming, USA

“…The detrital zircon record from the eastern Belt Supergroup is consistent with this interpretation. A paucity of ∼2.8 Ga zircons in eastern Belt Supergroup units suggests the BBMP was not an important sediment source to the basin (Fox, 2017; Mueller et al., 2016; Ronemus et al., 2020), consistent with a lack of erosion of BBMP basement during Belt Supergroup deposition. Coupled with these lines of evidence, modeled Mesoproterozoic reheating of rocks in the Beartooth Mountains may support Mesoproterozoic deposition within the study area (Figure 6).…”

“…Modified from Ronemus et al. (2020) after Whitmeyer and Karlstrom (2007) and Yonkee and Weil (2015). Other tectonic elements adapted from: Basement‐cored ranges—Peyton et al.…”

“…Dashed line divides provinces of the Wyoming craton (e.g., Mogk et al, 1992). Modified from Ronemus et al (2020) after Whitmeyer and Karlstrom (2007) and Yonkee and Weil (2015). can reconstruct broadly continuous Precambrian-to-recent thermal histories, even in regions that have experienced significant Phanerozoic burial and tectonism.…”

New Timing Constraints for the Onset of Laramide Deformation in Southwest Montana Challenge our Understanding of the Development of a Thick‐Skinned Structural Style During Flat‐Slab Subduction

“…(a) Simplified geologic map of the Northern Rocky Mountain region showing the location of major tectonic features, including major basement‐cored mountain ranges in southwest Montana and Wyoming (modified from Ronemus et al, 2020, and Peyton & Carrapa, 2013); star denotes study locale of Garber et al (2020). (b) Stratigraphy of the Tendoy Thrust sheet near Lima, Montana, reproduced from Garber et al (2020).…”

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

“…In western Montana, most workers have interpreted the basal conglomerate of the Kootenai Formation to be sourced from recycled Jurassic aeolianite strata from the southwestern US based on detrital zircon U-Pb analysis (e.g., Dickinson & Gehrels, 2009a;Laskowski et al, 2013;Leier & Gehrels, 2011;Quinn et al, 2018;Ronemus et al, 2020). In our new and compiled data set, this detrital zircon signature mainly occurs near the base of the Kootenai Formation and only locally upsection throughout southwestern Montana; it is less common in the west than the east.…”