Mesoproterozoic–Early Cretaceous provenance and paleogeographic evolution of the Northern Rocky Mountains: Insights from the detrital zircon record of the Bridger Range, Montana, USA Chance B. Ronemus†, Devon A. Orme, Saré Campbell, Sophie R. Black, and John Cook Department of Earth Sciences, Montana State University, P.O. Box 173480, Bozeman, Montana 59717-3480, USA ABSTRACT Jurassic detritus into the foreland basin to rels et al., 1996, 2011; Gehrels and Ross, 1998; dominate by the Early Cretaceous. Park et al., 2010; Laskowski et al., 2013). These The Bridger Range of southwest Montana, ancient sources may consist of first-cycle grains USA, preserves one of the most temporally INTRODUCTION derived from Precambrian basement provinces extensive sedimentary sections in North or more recent magmatism. However, zircons America, with strata ranging from Meso- Sedimentary rocks in the Bridger Range of are more commonly sourced from erosion and proterozoic to Cretaceous in age. This study southwest Montana, USA, record the Mesopro- recycling of previously deposited sedimentary presents new detrital zircon geochronologic terozoic–Mesozoic history of sedimentation in rock (e.g., Schwartz et al., 2019). data from eight samples collected across this this region of North America, with Mesopro- The evolution of sedimentary provenance is mountain range. Multidimensional scaling terozoic to Cretaceous stratigraphy exposed as strongly influenced by tectonic factors (Gehrels, and non-negative matrix factorization sta- a generally eastward dipping homoclinal panel 2014). Tectonic events, such as rifting and moun- tistical analyses are used to quantitatively across the range (Fig. 1). The >8 km of stratig- tain building, trigger drainage reorganization unmix potential sediment sources from these raphy collectively record critical information and uplift new sediment sources. These changes and 54 samples compiled from previous stud- about source-to-sink relationships in this portion are recorded in the detrital zircon record, which ies on regional correlative strata. We inter- of Laurentia during much of the Mesoprotero- can be used to assess the tectonic and paleo- pret these sources based on reference data zoic, Paleozoic, and Mesozoic. During this time geographic evolution of the region (e.g., Fuentes from preserved strata with detrital zircon interval, the western margin of North America et al., 2011; Doe et al., 2012; Laskowski et al., signatures likely representative of ancient underwent rifting associated with the breakup 2013; Beranek et al., 2016). While similar sediment sources. We link these sources to of Proterozoic supercontinents and subsequent analyses have been conducted on some correla- their sinks along sediment dispersal path- thermal relaxation and early Paleozoic passive tive strata across the North American continent ways interpreted using available paleo- margin sedimentation (e.g., Devlin and Bond, (e.g., Fuentes et al., 2011; Gehrels et al., 2011; geographic constraints. Our results show 1988; Sears et al., 1998). The western margin of Laskowski et al., 2013; May et al., 2013; Geh- that Mesoproterozoic strata in southwest North America transitioned to an active margin rels and Pecha, 2014), southwestern Montana is Montana contain detritus derived from the likely beginning in the Devonian (e.g., Dorobek comparatively less studied. Our new data from nearby craton exposed along the southern et al., 1991; Crafford, 2008; Beranek et al., this region provide new constraints on the evo- margin of the fault-bounded Helena Embay- 2016). This margin became tectonically consoli- lution of the provenance of sediment feeding ment. Middle Cambrian strata were domi- dated with eastward subduction of the Farallon basins occupying this region and the coupled nated by the recycling of local sources eroded plate underneath North America by Late Juras- tectonic evolution driving these changes. Spe- during the development of the Great Uncon- sic time, culminating in Cordilleran orogenesis cifically, we test or constrain: (1) the hypothesis formity. In Devonian–Pennsylvanian time, and the creation of a ∼3000 km fold-thrust belt that Middle Cambrian strata deposited during provenance in southwest Montana shifted to and foreland basin system (e.g., DeCelles, 2004; the Sauk transgression sourced most of their more distal sources along the northeastern Yonkee and Weil, 2015). Throughout this evolu- detritus from the underlying basement (e.g., to southeastern margins of Laurentia, but tion, southwestern Montana occupied a central Malone et al., 2017; Matthews et al., 2018); (2) more western basins received detritus from position near the western margin of Laurentia. the timing and nature of the regional transition outboard sources along a tectonically com- Consequently, the strata deposited there provide from northern/northeastern-dominated sedi- plicated margin. By the Late Jurassic, prov- a crucial record of this tectonic history. mentary provenance (i.e., Gehrels and Pecha, enance in the developing retroarc foreland Siliciclastic intervals in these rocks contain 2014) to eastern/southeastern-dominated prov- basin system was dominated by Cordilleran detrital zircons, which can be radiometrically enance (i.e., Chapman and Laskowski, 2019) magmatic arcs and fold-thrust belt sources to dated to determine their crystallization age (e.g., during the Paleozoic; (3) the hypothesis that the west. Eastward propagation of the fold- Gehrels et al., 2006). Sampling large populations exotic terranes off the west coast of Laurentia thrust belt caused recycling of Paleozoic and of zircons from strata spanning a broad tempo- provided sediment to Paleozoic strata preserved ral and spatial interval can reveal changes in in the Northern Rocky Mountains (e.g., Beranek Chance B. Ronemus http://orcid.org/0000-0001- regional sediment routing systems through com- et al., 2016); (4) the timing of the shift from 6345-9589 parison of the distributions of detrital zircon ages eastern- to western-dominated provenance in †[email protected]. to potential ancient sediment sources (e.g., Geh- the Jurassic foreland basin system (e.g., Fuentes GSA Bulletin; March/April 2021; v. 133; no. 3/4; p. 777–801; https://doi.org/10.1130/B35628.1; 8 figures; 2 tables; 1 supplemental file. published online 14 August 2020 © 2020 The Authors. Gold Open Access: 777 This paper is published under the terms of the CC-BY license Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/133/3-4/777/5236215/777.pdf by guest on 29 September 2021 Ronemus et al. et al., 2011); and (5) the hypothesis that Early in the Bridger Range spanning Mesoprotero- Rocky Mountain region (Northern Rockies), Cretaceous intraforeland uplifts controlled zoic through Cretaceous time. This data set, herein considered from southern Wyoming, regional provenance patterns (DeCelles, 1986). consisting of 2133 analyses from eight original USA to southern Alberta/British Columbia, In this paper, we present a detrital zircon samples, is coupled with 8691 analyses from 54 Canada. This study couples descriptive statisti- data set sampled from a stratigraphic section samples (Table 1) compiled from the Northern cal analysis (e.g., Vermeesch, 2013; Saylor and 778 Geological Society of America Bulletin, v. 133, no. 3/4 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/133/3-4/777/5236215/777.pdf by guest on 29 September 2021 Mesoproterozoic–Early Cretaceous provenance and paleogeographic evolution of the Northern Rocky Mountains Figure 1. (A) Generalized map of the North- region through time and test existing hypotheses a passive margin along the western margin of ern Rocky Mountain regions shows the dis- for the tectonic processes driving this evolution. Laurentia (Bogdanova et al., 2009). In Middle tribution of major Precambrian–Mesozoic Cambrian time, thermal relaxation of this rifted tectonic features. The Bridger Range, Mon- GEOLOGIC SETTING margin along with rising eustatic sea levels led to tana, USA (yellow) lies at the intersection of a period of transgressive sedimentation referred the Wyoming Province, the Belt Basin, the The north-trending Bridger Range, adjacent to as the Sauk transgression (Sloss, 1963). The Sevier Belt, the Laramide Province, and the to Bozeman in southwest Montana, exposes oldest Phanerozoic rocks in the Bridger Range “Basin and Range” province of Neogene Archean metamorphic and Mesoproterozoic were depositing during this period (McMannis, extension (not depicted). HM—Highland through Cretaceous sedimentary rocks (Fig. 1). 1955). Throughout Paleozoic time, this domi- Mountains; TR—Tobacco Root Mountains; This range is situated in a region of overlap nantly passive margin-style marine sedimenta- RR—Ruby Range; GR—Gravelly Range; among four major tectonic provinces each with tion on the stable shelf of the North American MGR—Madison and Gallatin ranges; its own distinctive structural style (Fig. 1A). craton gradually transitioned to an active colli- BT—Beartooth Mountains; BT Shelf— These are: (1) a series of extensional structures sional margin, marked by terrane accretion and Beartooth shelf; NA—North America. Can- in the cratonic basement associated with the enigmatic mountain building events on the west- ada: BC—British Columbia; AB—Alberta; Mesoproterozoic development of the Belt Basin ern margin of Laurentia (Dickinson, 2006). In SK—Saskatchewan. USA: WA—Wash- (Winston, 1986); (2) a fold-thrust belt active in the Late Devonian–early Mississippian,