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Late Paleozoic Tectonism in Nevada: Timing, Kinematics, and Tectonic Signi®Cance

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Late Paleozoic Tectonism in Nevada: Timing, Kinematics, and Tectonic Signi®Cance Late Paleozoic tectonism in Nevada: Timing, kinematics, and tectonic signi®cance James H. Trexler, Jr.² Patricia H. Cashman Department of Geological Sciences, University of Nevada, Reno, Nevada 89557-0180, USA Walter S. Snyder Vladimir I. Davydov Department of Geology and Geophysics, Boise State University, 1910 University Drive, Boise, Idaho 83725, USA ABSTRACT INTRODUCTION tail in this paper; see Trexler et al., 2003), a Middle Pennsylvanian deformation event, and Three late Paleozoic, angular unconfor- Although the tectonic evolution of south- another in earliest Permian time. Although ev- mities, each tightly constrained in age by western North America (present-day United idence for late Paleozoic deformation of Ant- biostratigraphy, are exposed in Carlin Can- States) is generally thought to include only ler foreland sedimentary deposits has long yon, Nevada. These record deformation as two Paleozoic orogenies, the latest Devonian± been recognized here (e.g., Dott, 1955; Ketner, well as erosion. Folding associated with Early Mississippian Antler orogeny and the 1977), it has generally been overlooked in these deformation events is roughly coaxial; Late Permian±earliest Triassic Sonoma orog- discussions of the tectonic evolution of west- all three sets of fold axes trend northeast. eny, many workers have shown that there is ern North America. Deformation events that Each unconformity represents tectonic dis- considerable evidence for deformation at other cannot be attributed to either a narrowly de- ruption of the middle part of the western times in the late Paleozoic. Mechanisms for ®ned, Late Devonian Antler orogeny or the Permian±Triassic Sonoma orogeny have also North American margin between the times this deformation fall into two groups: (1) evo- been documented elsewhere in Nevada (e.g., of the initiation of the Antler orogeny (Late lution or continuation of the Antler orogeny, Erickson and Marsh, 1974; Silberling et al., Devonian±Early Mississippian) and the or (2) new orogenic events resulting from a 1997; Ketner, 1998; Theodore, 1999, personal Permian±Triassic Sonoma orogeny. This changed tectonic setting. commun.). The geologic relationships at Car- paper focuses on one of these unconformi- Both the Antler and Sonoma orogenies are lin Canyon are signi®cant for two reasons: ties in the Middle PennsylvanianÐthe C6 interpreted to have resulted in the tectonic em- they record the geometry of the contractional unconformityÐand the deformation and placement of deep-marine strata and volcanic deformation, and they narrowly constrain that age constraints associated with it. rocks eastward onto the continental margin of deformation in time. In Carlin Canyon, it is Our data from Carlin Canyon yield de- western North America. However, identifying also possible to distinguish between the less tailed glimpses of how the Antler foreland speci®c structures (and particularly the origi- intense Mesozoic overprint and the late Paleo- evolved tectonically in Mississippian and nal basal thrust fault or suture) unequivocally zoic deformations and to determine the ge- Pennsylvanian time. Middle Pennsylvanian associated with these events has been dif®cult. ometry of the Mesozoic deformation. (Desmoinesian) northwest-southeast con- In contrast, the Middle Pennsylvanian and earliest Permian deformations we describe In this paper, we present evidence for Mid- traction resulted in thin-skinned folding here include folding and thrust faulting that dle Pennsylvanian and Permian deformation and faulting, uplift, and erosion. These data are well constrained in style and timing. in Nevada, and we then discuss the signi®- require reinterpretation of the tectonic set- This widespread, late Paleozoic contractional cance of these events for our understanding of ting at the time of the Ancestral Rocky deformation appears to require poorly under- the tectonic evolution of North America. We Mountains orogeny and suggest that plate stood (and in some places unrecognized) tec- ®rst summarize (1) the generally accepted Pa- convergence on the west side of the conti- tonic activity, thus adding a phase of defor- leozoic history of the Antler foreland, and (2) nent played a signi®cant role in late Paleo- mation whose timing is well constrainedÐbut our approach to reexamining part of this his- zoic tectonics of the North American whose nature is poorly knownÐto the evolu- tory by using detailed biostratigraphy to rec- continent. tion of western North America. ognize and correlate widespread unconformi- Unusually good exposure and age control ties in the stratigraphic record. Next, we Keywords: tectonics, stratigraphy, struc- in Carlin Canyon, north-central Nevada (Fig. present the structural and stratigraphic results ture, Great Basin, Nevada, Pennsylvanian, 1), allow us to document the geometry, kine- of our detailed studies at Carlin Canyon. We Ancestral Rocky Mountains. matics, and timing for three episodes of late then brie¯y summarize evidence for late Pa- Paleozoic tectonism in central Nevada: a mid- leozoic deformation elsewhere in Nevada. We ²E-mail: [email protected]. dle Mississippian event (not discussed in de- conclude with a short discussion of the im- GSA Bulletin; May/June 2004; v. 116; no. 5/6; p. 525±538; doi: 10.1130/B25295.1; 11 ®gures. For permission to copy, contact [email protected] q 2004 Geological Society of America 525 TREXLER et al. tains allochthon occurred before Middle Penn- sylvanian time (e.g., Poole and Sandberg, 1977; Rich, 1977; Dickinson et al., 1983; McFarlane, 1997; McFarlane and Trexler, 1997; Trexler and Giles, 2000). Thus, the Ant- ler orogeny is currently de®ned by syntectonic sedimentary rocks ranging in age from Late Devonian through Early Pennsylvanian and by deformation that is only known to be pre± Middle Pennsylvanian. Deformation of the foreland-basin rocks (in contrast to those of the allochthon) as young as middle Mississippian has been attributed to either the Antler orogeny or to an unrecog- nized younger event. Lower Mississippian rocks in the PinÄon Range are deformed, then overlapped by Upper Mississippian strata (for locations of places discussed in text, see Fig. 1) (Silberling et al., 1997; Johnson and Pen- dergast, 1981; Johnson and Visconti, 1992). Johnson and Pendergast (1981) interpreted this deformation as part of the Antler orogeny in earliest Osagean (middle Early Mississip- pian) time. Alternatively, where the same re- lationship occurs in the Diamond Mountains, it was interpreted to postdate Antler defor- mation, because Antler foreland-basin strata are folded beneath the unconformity (Trexler and Nitchman, 1990). Newer models for evo- lution of foreland systems in which strata of the foreland basin are deformed as contraction propagates inboard (e.g., DeCelles and Giles, 1996) suggest that the Antler orogeny might have lasted longer than previously thoughtÐ i.e., Late Devonian through middle Mississippian. Figure 1. Location map for northeast and north-central Nevada. SquaresÐsections de- The Antler orogeny created a long-lived picted in Figure 10. StarÐCarlin Canyon (geologic map in Fig. 5). contractional foreland basin that ®lled with syntectonic and posttectonic sedimentary de- posits. These strata record most of what we portance of late Paleozoic deformation and margin (e.g., Burch®el and Davis, 1975; Dick- know about the orogeny (citations above, and some possible implications of this deforma- inson, 1977; Speed and Sleep, 1982). reviewed in Trexler et al., 2003). In central tion for the tectonic evolution of North Antler tectonism began in latest Devonian Nevada, siliciclastic rocks of the foreland con- America. to earliest Mississippian time, as recorded by sist of conglomerate, sandstone, and shale that the initiation of a foreland basin with sedi- were subjected to at least two sedimentary cy- BACKGROUND ments derived from the west (Poole, 1974; cles within the Antler foreland system (Fig. Smith and Ketner, 1977; Poole and Sandberg, 2). Older basin ®ll is immature, deep-marine, Paleozoic History of the Antler Foreland 1977; Ketner and Smith, 1982; Johnson and and turbiditic, especially to the west in the Visconti, 1992; Carpenter et al., 1993). In the foredeep keel. Later sedimentary ®ll is more The western edge of Paleozoic North Amer- offshore basin that is now the Roberts Moun- mature and was deposited in ¯uvial, fan-delta, ica is thought to have been a passive margin tains allochthon, deposition continued until and shallow-marine environments; the com- until the Late Devonian±Early Mississippian Late Devonian (Famennian) to Early Missis- mon limestone interbeds in most places pre- Antler orogeny (e.g., Roberts et al., 1958; sippian (Kinderhookian) time (Coles and Sny- serve foraminifera. (Foraminifera [including Burch®el and Davis, 1972, 1975). The Antler der, 1985). The rocks of the allochthon are fusulinids] are ideal for age control. They are orogeny is marked by the formation of a fore- now strongly deformed, and that deformation rapidly evolving, cosmopolitan, and do not land basin in Nevada and by a deep strike-slip is widely thought to be ``Antler'' in age. How- survive recycling.) In some areas, the crustal basin in Idaho (Link et al., 1996). Most work- ever, attempts to ®nd the oldest overlap units response was quite different, e.g., strike-slip ers think that it also entailed the eastward ob- on the allochthon (bracketing the end of de- tectonics in Idaho (Link et al., 1996) and a duction of the internally deformed Roberts formation) have so far demonstrated
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