Sedimentary record of Late Paleozoic tectonism in the Monitor Range, central Nevada: Implications for convergence along the western Laurentian margin
Introduction
During the late Paleozoic assembly of Pangaea, the southern Laurentian continent was bounded on three sides by collisional and/or compressional boundaries (Bird and Dewey, 1970; Thomas, 1977; Ketner, 1977; Scotese et al., 1999; Domeier and Torsvik, 2014; Young et al., 2019). Stress generated along one or more of these margins has been interpreted to have driven Pennsylvanian-Permian intracontinental deformation across a wide area of the Laurentian continent including the North American mid-continent (Quinlan and Beaumont, 1984; Craddock et al., 2017), Southern Plains and Gulf region (Ham and Wilson, 1967; McConnell, 1989; Soreghan et al., 2012), and Ancestral Rocky Mountains (Kluth and Coney, 1981; Ye et al., 1996; Dickinson and Lawton, 2003).
Early work on the western (modern reference frame) margin of Laurentia, now central Nevada, USA, interpreted compressional tectonism to have occurred in discrete pulses associated with the Antler and Sonoma Orogenies (Roberts et al., 1958; Silberling and Roberts, 1962), but more recent work has interpreted compressional deformation along the Nevada margin to have occurred more or less continuously throughout the late Paleozoic (Erickson and Marsh, 1974; Trexler et al., 2004; Cashman et al., 2011), and many workers have interpreted this deformation to have been driven by sinistral transpression along the Nevada margin (Link et al., 1996; Beranek et al., 2016; Linde et al., 2016; Lawton et al., 2017). This deformation is preserved as numerous regional unconformities and isolated thrust faulting in northern Nevada (Trexler et al., 2004; Cashman et al., 2011), but the full spatial extent of these features remains underconstrained. This is in part due to a lack of study of syn-tectonic strata, particularly corresponding to the upper Permian-Lower Triassic Sonoma Orogeny (Gabrielse et al., 1983; Dickinson, 2006; Caravaca et al., 2018).
Understanding the full spatial extent of Permian-Triassic tectonism along the western margin of Laurentia is important in understanding the broader tectonics of the western Laurentian margin and in reconciling a number of conflicting tectonic models for the evolution of this margin (e.g. Burchfiel and Davis, 1975; Speed, 1979). A Permian-Triassic arc collision in the Yukon ~3000 km north of central Nevada is well-documented as the result of closure of the Slide Mountain Ocean (Beranek and Mortensen, 2011). This event, named the Klondike Orogeny (Beranek and Mortensen, 2011), has been correlated to the closure of the Havallah Basin and the emplacement of the Golconda Allochthon in central and northern Nevada (Colpron et al., 2007; Beranek and Mortensen, 2011). Correlation of these events suggests that large-scale synchronous tectonism occurred along this margin during Permian-Triassic time. However, one challenge in this interpretation is a paucity of geological data from intervening areas (Beranek and Mortensen, 2011). Moreover, the sedimentary record of the Sonoma Orogeny is less-studied than that of the Klondike Orogeny (e.g. Gabrielse et al., 1983; Dickinson, 2006; Caravaca et al., 2018). Lawton (1994) suggested that transpressional emplacement of the Golconda Allochthon may have resulted in heterogeneous flexural loading in Nevada and discontinuous foreland basin formation. Caravaca et al. (2018) used backstripping and flexural modelling to suggest that underlying lithospheric heterogeneities were responsible for relatively thick Lower Triassic (252–250.7 Ma) foreland basin deposits during the Sonoma Orogeny in northern Utah/Nevada and southern Idaho and thinner, coarser grained foreland deposits in central Nevada and Utah. However, their study did not extend south and west into the current study area.
In this study, we present a detailed analysis of the lowermost Permian to uppermost Permian/Triassic Garden Valley Formation exposed in the Monitor Range of central Nevada, USA, in order to document deformation and basin formation related to marginal tectonic processes. We present sedimentologic, petrographic, fusulinid, conodont, and detrital zircon U-Pb data for these rocks that show that ~0.5 km of sediment of the Garden Valley Formation accumulated in this area during the Sonoma Orogeny. The Sonoma Orogeny produced a widespread unconformity across most Nevada basins (Tr1 of Cashman et al., 2011), so our results suggest that the Garden Valley Formation may represent one of the more complete stratigraphic records of this event. This work advances the current understanding of the late Paleozoic evolution of western Laurentia by dating and interpreting previously poorly understood strata of this age and adding new constraints to paleogeographic and paleotectonic maps of this region.
Section snippets
Geologic background and regional stratigraphy
The Monitor Range is located near the geographical center of Nevada, USA (Fig. 1, Fig. 2). The modern topography of the range exposes Ordovician through Permian sedimentary rocks, capped by thick Cenozoic sequence of volcanic rocks (Fig. 2, Fig. 3). Exposure of Paleozoic rocks is due to a system of Basin and Range normal faults that bound the range on its eastern side and have created the Little Fish Lake Valley to the east (Fig. 1, Fig. 2).
From Neoproterozoic to Late Devonian time, central and
Regional stratigraphy
Over 100 years of geological work in Nevada has resulted in a diverse range of stratigraphic nomenclature for Permian strata in part because these rocks are laterally diverse and are exposed in discrete ranges separated by extensional basins (Nolan et al., 1956; Merriam, 1963; Bissell, 1964; Stevens, 1979). However, in the vicinity of Eureka, NV where rocks of this age have been well-studied, Permian strata have generally been assigned to the Garden Valley Formation and the Carbon Ridge
Sampling and methods
Pennsylvanian-Permian strata within Clear Creek Canyon and the surrounding area were mapped in detail at a scale of 1:24,000 (Fig. 2). Pennsylvanian-Permian strata were sedimentologically described at the cm-scale in sections measured with a Brunton and Jacob Staff. Samples were collected for thin-section petrography, detrital zircon analysis, and conodont and fusulinid biostratigraphy.
Sediment composition and provenance were determined using clast counts for conglomerates and breccias and thin
Sedimentology description
Paleozoic strata documented in this study were previously mapped as Mississippian to Pennsylvanian (Fig. 1; Stewart and Carlson, 1978); however, new data presented here date these rocks as Permian (see below). Based on similarity in age and previous work in the Monitor Range and surrounding area, we interpret these rocks to be equivalent to the Garden Valley Formation (Nolan et al., 1956; Merriam, 1963; Wise, 1977; Wardlaw et al., 2015), and we refer to them by this name throughout this study.
Basin evolution and paleogeography
The Garden Valley Formation is interpreted to have been deposited along the west flank of the remnant Antler Basin (Stevens, 1979; French et al., 2020), and Garden Valley sedimentation overlaps temporally with the deposition in the Strathearn basin, Dry Mountain Trough, Park City basin, and Phosphoria basin (Trexler et al., 2004; Cashman et al., 2011; Fig. 13B, C).
We interpret lowest Permian strata of the Garden Valley Formation to represent deposition of shallow marine shelf strata above an
Conclusions
Based on detailed sedimentologic, provenance, and biostratigraphic analysis of the Garden Valley Formation exposed in the Monitor Range, central Nevada, USA, we conclude that:
- 1)
The Garden Valley Formation records the transition from shallow marine shelf, to fan-deltoid, to wedge-top/proximal foredeep depositional zones from earliest Permian through latest Permian/earliest Triassic time.
- 2)
The Garden Valley formation continued accumulating sediment during emplacement of the Golconda Thrust (latest
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported in part by generous contributions from Pioneer Natural Resources, and we thank Bill Briners and Larry Lackey of Noranda Corporation for support of early geologic studies of the area. The area hosted the University of Arizona summer field camp for many years, and we acknowledge the feedback of many students in improving the geologic details of the work. We thank Dan Sturmer for editorial handling of this manuscript and Luke Beranek and an anonymous reviewer for thoughtful
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