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

Home , Mountain formation, Sonoma orogeny, Syncline

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] ᭧ 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 unrecognized 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 relationship occurs in the Diamond Mountains, it was interpreted to postdate Antler deformation, because Antler foreland-basin strata are folded beneath the unconformity (Trexler and Nitchman, 1990). Newer models for evolution 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 deposits. 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 only that remnant foredeep in southern Nevada (Trexler Mountains allochthon onto the continental the internal deformation of the Roberts Moun- et al., 1996).

526 Geological Society of America Bulletin, May/June 2004 LATE PALEOZOIC TECTONISM IN NEVADA

Figure 2. Tectonostratigraphic boundaries, C1 through P2, in the upper Paleozoic section of the Great Basin and correlation of regional stratigraphy discussed in text. The basis for this unconformity-based organization is discussed thoroughly in Trexler et al. (2003).

Intermittent post-Antler (informally de®ned of basin formation and two phases of Early is greatest (the orogenic belt), and both the here as Middle Pennsylvanian through middle Permian folding and thrusting (Stevens et al., angularity and the lacuna typically decrease Permian time) deformation has been demon- 1997). In Utah and Idaho, important aspects away from the orogenic belt. We recognize strated in many places, although much of this of Pennsylvanian and Permian tectonics and several widespread late Paleozoic unconfor- deformation has been interpreted to be local sedimentation have been documented by Jor- mities in the Great Basin that separate pack- in extent (e.g., Dott, 1955; Stevens et al., dan and Douglas (1980), Geslin (1998), and ages of genetically related sedimentary rocks 1997). Some, however, have suggested that it Mahoney et al. (1991). In summary, there is (Fig. 2). We have adopted a numbering re¯ects regional phases of tectonism (e.g., considerable evidence in the literature for scheme for the unconformities similar to that Snyder et al., 1991, 1995; Trexler et al., 1991; Pennsylvanian and Permian deformation in used for the Mesozoic of the Colorado Plateau Ketner, 1977). In the Carlin area, Dott (1955) the region, enough to warrant an examination (e.g., Pipiringos and O'Sullivan, 1978). They and Ketner (1977) mapped angular unconfor- of whether one or more regional, rather than are numbered sequentially from oldest to mities in the upper Paleozoic section. In cen- local, tectonic events are represented. youngest within each time period (for the late tral Nevada, Snyder et al. (1991), Gallegos et Paleozoic, we use Carboniferous ϭ C and al. (1991), Perry (1994, 1995), Trexler et al. Unconformities in the Stratigraphic Permian ϭ P) (Snyder et al., 2000). (1995), and Crosbie (1997) documented Mis- RecordÐEvidence for Tectonism in the At Carlin Canyon, three of these late Paleo- sissippian through Permian unconformities Antler Foreland zoic unconformities are particularly easy to and syntectonic strata. In southwestern Neva- recognize because they are angular. With the da, there are tectonic as well as eustatic con- Tectonism is recorded by deformation, by aid of detailed biostratigraphy, these can be trols on sedimentation in the southern Antler syntectonic basin formation, and by unconfor- traced laterally into their correlative discon- foreland basin (Trexler et al., 1996; Trexler mities that result from uplift and erosion. Tec- formities. The middle Mississippian (C2) un- and Cashman, 1997; Schiappa et al., 1999). In tonically induced unconformities related to conformity is an angular unconformity southeastern California, tectonism included a collisional orogenies can be recognized be- throughout much of the PinÄon Range and Di- Desmoinesian (Middle Pennsylvanian) phase cause they are angular where the deformation amond Mountains (Figs. 1, 2, and 3) (Trexler

Geological Society of America Bulletin, May/June 2004 527 TREXLER et al.

west, removing the Tomera and Moleen en- tirely in the western part of the map area (Fig. 5) and placing Strathearn directly on the upper part of the Tonka. This angular relationshipÐ Strathearn over TonkaÐwas recognized by Dott (1955) as evidence for Pennsylvanian deformation in the Carlin area. A third angular unconformity (P1) occurs within the Stra- thearn and therefore requires a rede®nition of the Strathearn. This surface cuts down section toward the east; in the eastern part of the map area, it has removed all of the lower Strathearn and has placed the upper part of the Strathearn directly on Moleen-Tomera. A fourth unconformity (P2), not obviously angular here, places Buckskin Mountain Formation over Stra- Figure 3. North wall of Carlin Canyon at the west end. Both the C6 and C2 angular thearn and cuts down section toward the east unconformities are visible, at right and center, respectively. Here, the C6 unconformity in the Carlin Canyon area. This is a major has removed all intervening boundaries. unconformity at a regional scale; it occurs throughout northern Nevada (Snyder et al., 1991; Sweet et al., 2001; Sweet and Snyder, et al., 2003) and a disconformity in the Spot- Mississippian±Middle Pennsylvanian coarse 2002). ted Range of southern Nevada (Trexler et al., clastic and carbonate strata (Tonka, Moleen, The C6 and P1 unconformities truncate me- 1996). The Late Pennsylvanian (C6) uncon- and Tomera Formations) and overlying Upper soscopic and macroscopic structures that re- formity is a dramatic angular unconformity at Pennsylvanian±Lower Permian limestone cord the geometry and kinematics of two de- Carlin Canyon and throughout the PinÄon and (Strathearn Formation) (Fig. 3; see Fig. 4 for formation events, one occurring in the Middle Adobe Ranges. The earliest Permian (P1) un- stratigraphy). Dott (1955) recognized this re- Pennsylvanian and the other in earliest Perm- conformity is a low-angle unconformity at lationship as an angular unconformity. Ketner ian. The Middle Pennsylvanian (C6) defor- Carlin Canyon, detectable here only through (1977) and Smith and Ketner (1977) attributed mation includes thrust faults and macroscopic detailed biostratigraphy that shows stratal it to a Pennsylvanian ``Humboldt orogeny'' overturned folds in addition to mesoscopic trimming (down to the east) of the underlying and presumed uplift to the west. The concept structures. It records more contraction (at least lower Strathearn Formation, which is Mis- of the Humboldt orogeny was challenged by locally) than the other deformation events ex- sourian. The detailed work necessary to re- Snyder et al. (1991, 1995) and has been aban- posed in Carlin Canyon. The earliest Permian solve the P1 relationship elsewhere is in prog- doned by Ketner, who now favors exclusively (P1) deformation is expressed as open, upright ress (W.S. Snyder and J.H. Trexler, Jr., Mesozoic deformation in the region (Ketner, macroscopic folds. Both fold sets have gently unpublished mapping). 1998). Jansma and Speed (1990) reinterpreted northeast-plunging axes, but these folds can this contact as a Mesozoic omissional fault, a be distinguished at Carlin Canyon on the basis RESULTS proposition since challenged by Schwarz et al. of details of fold geometry and kinematics (1994). (see section on Kinematics of Pennsylvanian Geologic Relationships at Carlin Our new mapping at Carlin Canyon, using and Permian Deformations). CanyonÐOverview detailed biostratigraphic age control, reveals The presence of these late Paleozoic uncon- three angular unconformities in the upper Pa- formities requires revision of the local strati- Carlin Canyon, along the Humboldt River leozoic section (Fig. 2). The stratigraphically graphic nomenclature, in particular, the Tonka and Interstate 80 in western Elko County, Ne- lowest (C2 in Figs. 2 and 4) occurs within and Strathearn Formations. Original mapping vada, exposes the Mississippian through coarse-grained conglomerates mapped as the in the area (Dott, 1955) designated all Missis- Permian section in the heart of the Antler fore- Tonka Formation by Dott (1955) and therefore sippian conglomerate sections as Tonka For- land basin (Figs. 1, 4, and 5). Strata dip steep- requires a rede®nition of the Tonka. We call mation, de®ned at Tonka siding in Carlin ly throughout the canyon and display both me- the rocks below the unconformity Melandco Canyon. The unconformity within the Missis- soscopic and macroscopic folds and faults. Formation, and those above, Tonka Formation sippian section was not recognized, and the Most workers have assumed that all of the de- (Trexler et al., 2003). This angular unconfor- lower section has no known fossil occurrences formation there is Mesozoic or Cenozoic in mity is Mississippian in age and cuts down that would allow biostratigraphic recognition age (e.g., Ketner and Smith, 1974; Smith and section to the west. Although it does not crop of the older conglomerates. We use the name Ketner, 1977; Thorman et al., 1991; Schwarz out elsewhere in the Carlin area, it is found Melandco Formation for these Lower and et al., 1994). This assumption was based on throughout much of central Nevada (Trexler middle Mississippian rocks, consistent with the observation that rocks as young as Triassic et al., 2003). The next younger unconformity unit names nearby to the east (Trexler et al., are deformed nearby in the northern Adobe preserved in Carlin Canyon, C6, separates the 2003). The unconformity within the Missis- Range, rather than on ®eld relationships in or Moleen and Tomera Formations (local equiv- sippian conglomerate section is expressed as near Carlin Canyon. alents of the lower and upper Ely Limestone) an angular discordance accompanied by a fa- The most conspicuous geologic feature in from the overlying Strathearn Formation. This cies change at the west end of Carlin Canyon, the canyon is the angular contact between unconformity cuts down section toward the west of the highway and railroad tunnels

528 Geological Society of America Bulletin, May/June 2004 LATE PALEOZOIC TECTONISM IN NEVADA d . Figure 4. Geologic mapat of the the star Carlin in CanyonFig. Figure area, 9B 1. Elko for The County, a grid Nevada; stereogram is locations of UTM and this zone ages syncline). of 11. Included biostratigraphic The is control box Carboniferous are outlined and shown. by Permian The a stratigraphy map white, in area dashed the is line Carlin locate shows Canyon a area; pre-P1 units syncline, are truncated color-keyed by to the map P1 unconformity (see

Geological Society of America Bulletin, May/June 2004 529 TREXLER et al.

(away ؍) toward) and A ؍) Figure 5. Two cross sections; for locations see Figure 4. Sense of motion on strike-slip faults is shown by T from the viewer.

(Figs. 3 and 5). Melandco strata are polymict ing recognition and mapping of the two rusty-colored, iron oxide±rich regolith zone conglomerate and sandstone that are matrix- members very dif®cult where they are con- about 1 m thick. This zone contains clasts de- rich to matrix-supported and that generally formable. We have not yet renamed these rived from the subjacent strata. Where the reg- lack sedimentary fabric. The overlying Tonka units and have referred to them informally as olith zone overlies the Tonka, the number and strata are well bedded; they consist of clean, upper and lower members of the Strathearn size of Tonka clasts increases downward with- chert±quartzite±lithic conglomerate and sand- Formation. in the zone, until the rock becomes a recog- stone with interbedded calcareous litharenite. nizable paleosol C-horizon developed on in- Our detailed biostratigraphy also documents Evidence for Erosion at the Mapped tact Tonka Formation. Vertical, open a hiatus within the Strathearn Formation. In UnconformityÐIt Is Not a Fault paleofractures in the Tonka are ®lled with reg- Carlin Canyon, the lower Strathearn Forma- olith material. The same regolith zone can be tion was folded and erosionally trimmed prior Our ®eld work has convinced us that the mapped laterally along the base of the Stra- to deposition of the upper Strathearn. The angular contact at the base of the Strathearn thearn to where the Strathearn overlies other Strathearn, de®ned southeast of Carlin Canyon in Carlin Canyon is the regionally important units such as the Moleen and Tomera For- at Grindstone Mountain (Dott, 1955), is lith- C6 unconformity. Locally, the basal part of mations. The regolith zone is overlain para- ologically uniform from bottom to top, mak- the Strathearn Formation is characterized by a conformably by quartz-arenaceous limestone

530 Geological Society of America Bulletin, May/June 2004 LATE PALEOZOIC TECTONISM IN NEVADA of the lower and/or upper Strathearn Forma- tion. No recognizable clasts of Strathearn limestone occur in this regolith zone, making it unlikely that the zone is, or contains, a fault- slip breccia. We have not found evidence of organic activity in the regolith zone, although it has extensive iron oxide development suggesting an aridisol. Our ®eld observations do not support a fault interpretation (Jansma and Speed, 1990) for the sub-Strathearn contact. Although there appears to have been local slip on the contact during subsequent folding, throughgoing, well-developed slip surfaces are absent, and there is no evidence for measurable offset along the base of the Strathearn. We were un- able to ®nd any kinematic features consistent with fault-zone deformation along or near the contact. Instead, the base of the Strathearn is a mappable regolith zone. We conclude that any slip along this contact is insigni®cant.

Age Control on Pennsylvanian and Permian Deformations

The strata that most tightly bracket the C6 unconformity in Carlin Canyon are the subjacent Middle Pennsylvanian Tomera Forma- tion (sensu Dott, 1955), and the superjacent, Upper Pennsylvanian±Lower Permian Stra- thearn Formation (Fig. 4). Below the unconformity, the youngest sub-C6 strata in Carlin Canyon are Atokan (Fig. 4), and angular trimming of the section suggests that younger strata may be preserved nearby. On a regional scale, we have shown that sub-C6 strata are as young as medial to possibly late Desmoi- nesian (Bissel, 1964; our unpublished work). The oldest Strathearn rocks overlying C6 in Carlin Canyon are lower to middle Missourian (Fig. 4). Therefore, the C6 hiatus in Carlin Canyon (and the tectonic event it records) is bracketed to be 5 m.y. or less in duration, de- pending on the time scale used for the extrap- olation of numerical ages from biostratigraph- Figure 6. Panoramic photograph looking at the north wall of east-central Carlin Canyon ic ages. (``the amphitheater''). ``Duplex Canyon'' is the southwest-trending gulch on the left (west) All Mississippian±Pennsylvanian strata in end of the amphitheater. Mesoscopic folds are asymmetric to overturned and have am- Carlin Canyon were folded again in the ear- plitudes of meters to tens of meters and northeast-plunging axes (see Fig. 9A for a ste- liest Permian, during an event bracketed by reogram of this folding). Vergence is toward the northwest for some structures and south- the lower Strathearn Formation, below, and east for others (see Fig. 5). For example, the lowest of the three closely spaced thrust faults the upper Strathearn Formation, above. The near the center of Figure 6 cuts upsection to the northwest and has a northwest-vergent resulting angular unconformity is the P1 hanging-wall anticline. The middle thrust cuts upsection to the northwest in the footwall boundary. Fusulinids from the upper Stra- here and cuts upsection to the northwest in the hanging wall in ``Duplex Canyon'' (see thearn are upper Asselian to lower Sakmarian the hanging-wall ramp in the upper thrust in Fig. 8). The upper thrust has a southeast- in age (Fig. 4). Therefore, in Carlin Canyon, vergent hanging-wall anticline and cuts upsection to the southeast. Stratigraphic throw on the P1 hiatus is 5 to 7 m.y. in duration. these thrust faults is tens to hundreds of meters; faulting duplicates the Lower Pennsyl- Still higher in the section at Carlin Canyon, vanian section at least hundreds of meters. Horizontal displacement is unknown, but may the P2 boundary is de®ned at the base of the be large. Buckskin Mountain Formation, where it overlies the upper Strathearn Formation. The old-

Geological Society of America Bulletin, May/June 2004 531 TREXLER et al. est Buckskin Mountain strata are early Artin- skian in age. The P2 unconformity trims the section down to rocks as old as Sakmarian at Carlin Canyon, but regionally (e.g., Secret Canyon, in the Fish Creek Range) the erosional surface cuts as far down as Chesterian rocks (Schwarz, 1987; Snyder et al., 1991). Where the P2 hiatus is the most tightly constrained, it is possibly as short as 5 m.y.

Kinematics of Pennsylvanian and Permian Deformations

Deformation, expressed as angular discordance, folding, or imbricate thrusting, can be documented below the unconformities in the upper Paleozoic section at Carlin Canyon (Fig. 6). Wherever fold axis orientations can be determined, they trend northeast, making it dif®cult to distinguish between the folding events on the basis of their general orientation. However, there are consistent differences in both fold style and precise axis orientation that make it possible to distinguish these deformations, even where good age control is absent. In the following paragraphs we document the geometry and kinematics of each deformation event, namedÐfor simplicityÐ after the unconformity that represents it (Fig. 2). The events are discussed in chronologic order, from oldest to youngest.

C2 Event The pre±late Late Mississippian (Chesteri- an) C2 unconformity is marked by Melandco Ely ؍) lower Tonka) below and (upper) Tonka Figure 7. View toward the south, showing deformation in the Moleen and Tomera) above. Deformation below the C2 unconfor- Limestone) Formations at the east end of Carlin Canyon. Vertical bedding occurs in the mity in Carlin Canyon is expressed only as an foreground and across the Humboldt River on the south canyon wall in the distance. angular truncation (Fig. 3). After the steep tilt Stratigraphic ``tops'' are toward the northwest, indicating that this large fold is northwest- of the overlying Tonka is removed, the bed- vergent. This macroscopic fold is coaxial with the thrust-related folds (see Figs. 6 and ding in the Melandco dips east, and the un- 9A); all are consistent with a single northwest-southeast shortening event. conformity cuts down section to the west. The contact between the Melandco and Tonka is not exposed over a wide enough area in Carlin Canyon to determine the geometry of the pre- boundaries are conformable contacts, are con- folding and imbricate thrusting within the Chesterian deformation. However, this defor- tained within other unconformities, or are oth- Tonka, Moleen, and Tomera Formations at mation event is regional in extent (Trexler et erwise not preserved. Each is expressed else- Carlin Canyon. Faulting and folding are de- al., 2003) and has also been mapped in the where, however, and is a stratigraphic veloped at both the macroscopic (Fig. 7) and northern PinÄon Range ϳ30 km to the south boundary that is of potential tectonic signi®- mesoscopic (Figs. 6 and 8) scales and are where there is middle Mississippian folding cance. These unconformities, not preserved at dominantly northwest vergent. Mesoscopic and thrusting (Silberling et al., 1997; R.M. Carlin Canyon, are not described in detail folds visible on the north side of I-80 (Fig. 6) Tosdal's mapping in Trexler et al., 2003) and here. have northeast-trending axes and verge both in the Diamond Mountains 120 km to the northwest and southeast; some are fault- south where an angular truncation exists be- C6 Event propagation folds preserved in the hanging low the C2 unconformity (Trexler and Nitch- The post±early Middle Pennsylvanian (mid- walls of mesoscopic thrusts. Imbricate thrust- man, 1990). dle Desmoinesian), pre±late Late Pennsylva- ing in ``Duplex Canyon'' is the best evi- nian (middle Missourian) C6 event has jux- dence that the deformation was dominantly C3, C4, and C5 Events taposed the Tonka, Moleen, and Tomera northwest-directed. Here, individual thrusts At Carlin Canyon, the Late Mississippian Formations below and Strathearn Formation step up-section to the northwest, and folds as- and Early Pennsylvanian C3, C4, and C5 above. The deformation involves overturned sociated with hanging-wall ramps, which oc-

532 Geological Society of America Bulletin, May/June 2004 LATE PALEOZOIC TECTONISM IN NEVADA

P2 Event The post±early Early Permian (late Asselian± early Sakmarian), pre±late Early Permian (early Artinskian) P2 unconformity separates upper Strathearn Formation below from Buck- skin Mountain Formation above. The deformation features in the upper Strathearn are not as well developed as those of the preced- ing two deformations in the Carlin Canyon area. The unconformity below the Buckskin Mountain Formation cuts down section toward the east in Carlin Canyon. We have not yet collected enough structural data along this contact to determine the geometry of the deformation below the unconformity. Although not dramatic in the Carlin Canyon area, the P2 is a major unconformity at a regional scale; Figure 8. ``Duplex Canyon'' in the north wall of Carlin Canyon; see Figure 6 for location. it occurs throughout northern Nevada (Snyder View is toward the east. Although the thrust faults now dip gently toward the northwest, et al., 1991; Sweet et al., 2001; Sweet and the truncation of hanging-wall bedding into the thrusts represents hanging-wall ramps Snyder, 2002). and documents northwest-directed thrusting. Post±Late Early Permian (Late Artinskian) Events cur in several of the imbricate sheets, all verge and this synform terminates against the homo- In the Carlin Canyon area, the Permian sec- northwest. clinal upper Strathearn on the east side of the tion is deformed. The immediately overlying Macroscopic folding also records northwest river (see box on map, Fig. 4). Note that the Tertiary Humboldt Formation remains unde- vergence. A macroscopic anticline-syncline Mesozoic ``Adobe syncline'' has been mapped formed. Therefore, the timing of the open, up- pair that is coaxial with the mesoscopic fold- through this area (Ketner and Ross, 1990), and right folding exhibited in the younger Permian ing is well exposed along I-80 east of the tun- bedding orientations within the highest pre- section is not well constrainedÐit postdates nels. It crops out adjacent to the hoodoos of served part of the section (Permian) are con- all of the Permian units present in this area Tertiary Humboldt Formation on the north sistent with a large syncline. This syncline is (upper Strathearn, Buckskin Mountain, Bea- side of the highway and continues along strike a different, and later, structure than the ero- con Flat, and Carlin Canyon Formations) and south of the highway (Fig. 7). The subvertical sionally truncated syncline below the P1 un- predates the Tertiary Humboldt Formation. In limb of this fold has stratigraphic ``tops'' to conformity. The overlying unconformity cuts their present orientation, the folds are open the northwest, indicating northwest vergence. down section to the east, removing the entire and upright, and fold axes plunge gently (25Њ) The overlying Strathearn Formation is not lower Strathearn 1.5 km east of the east por- toward the north-northeast (020Њ) (Fig. 9C). preserved immediately above many of these tals of the I-80 tunnels and suggesting that These folds are commonly meters to tens of structures, so the later deformation cannot be deformation-related uplift might have been meters in amplitude. A set of open, upright removed with con®dence. In their present ori- greater farther to the east. folds in the Moleen and Tomera Formations entation, however, fold axes characteristic of High-angle normal faults of late Paleozoic is also attributed to the post±Early Permian this deformation are subhorizontal and trend age are locally developed in Carlin Canyon deformation event on the basis of their fold 040Њ±065Њ (usually 060Њ±065Њ) (Fig. 9A). and have meters to hundreds of meters of dis- style and orientation; the axes are subhorizon- placement (Fig. 6). Brecciation is typical tal or plunging gently toward 025Њ (Fig. 9C). P1 Event along these faults, and drag folding occurs lo- Open, upright folding is demonstrably post- The post±late Late Pennsylvanian (middle± cally. A normal sense of motion is shown both Triassic elsewhere in the region, but this age upper Virgilian), pre±middle Early Permian by the offset of marker units across the faults (late Asselian) P1 event is expressed as an un- and by steeply plunging oblique-slip striae control is not available in the Carlin Canyon conformity separating lower Strathearn below along the fault surfaces. The high-angle faults area. In the northern Adobe Range, the Adobe and upper Strathearn above. The deformation cut thrust-related structures, but they are older syncline involves rocks as young as Triassic within the lower Strathearn is expressed as up- than the sub±upper Strathearn (P1) unconfor- (Ketner and Smith, 1974; Smith and Ketner, right, open folding. After the tilt of the over- mity. At least one of these high-angle faults 1977; Thorman et al., 1991). Broad folding in lying upper Strathearn has been removed, the has been reactivated by post-Pennsylvanian the Carlin Canyon area has been correlated fold axes plunge gently toward 030Њ±035Њ deformation. Although this fault can be with the Adobe syncline, but the youngest (Fig. 9B). This folding is easily visible in the mapped across the unconformity into the base rocks involved are Early Permian in age. Fold- eastern half of the big meander loop of the of the upper Strathearn Formation (Fig. 5), ing cannot be directly connected between the Humboldt River at the I-80 tunnels. Here, in- displacement of the Strathearn is an order of northern Adobe Range and Carlin Canyon; terbedded conglomerate and limestone of the magnitude smaller than displacement of the therefore, we can only constrain the latest lower Strathearn are folded into a broad syn- underlying Moleen Formation (lower Ely folding seen at Carlin Canyon to be late Early form on the west side of the Humboldt River, Limestone). Permian or younger in age.

Geological Society of America Bulletin, May/June 2004 533 TREXLER et al.

Evidence for Pennsylvanian and Permian Deformations Elsewhere in Nevada

The relationships we document at Carlin Canyon are also found both west and east of Carlin Canyon (Figs. 1, 10). Map relationships document unequivocal Pennsylvanian or Permian tectonism and indicate that late Pa- leozoic deformation is widespread. In some cases, the deformation is in rocks of the Antler foreland basinÐso it either postdates the Ant- ler orogeny or represents propagation of Ant- ler contraction into the foreland basin. In other cases, deformation is in rocks of the Antler allochthon and would probably be attributed to the narrowly de®ned Antler orogeny (i.e., Late Devonian±Early Mississippian) except that rocks of Carboniferous age are involved in the deformation. In both cases, it is the presence of Pennsylvanian or Permian sedimentary rocks unconformably overlying the deformation that demonstrates the late Paleo- zoic age. These ``overlap assemblage'' rocks are absent in most places, so interpretation of the age of deformation has often been based on inference: Antler deformation for rocks of the allochthon and Mesozoic deformation for rocks of the Antler foreland basin. At Beaver Peak west of Carlin Canyon, both members of the Strathearn Formation have been identi®ed and mapped (Figs. 1, 10) (Berger et al., 2001). There they are both con- glomeratic, and conodont ages there con®rm our fusulinid dates for both units. The lower member of the Strathearn, along with lower Paleozoic rocks of the Roberts Mountains al- Figure 9. Stereograms of the three different fold sets in the Carlin Canyon map area. All lochthon, is involved in thrusting on a fault are lower-hemisphere, equal-area plots; poles to bedding are shown as circles, squares, or that is unconformably overlapped by the upper open triangles. Different symbols represent individual mesoscopic or macroscopic folds. Strathearn, tightly bracketing the age of Fold axes for individual folds are shown as ®lled triangles. (A) Pennsylvanian (C6) defor- thrusting as middle to late Asselian (Early mation, characterized by asymmetric to overturned folding and northwest-directed thrust Permian), equivalent to the deformation at faulting. Stereogram shows poles to bedding in macroscopic, mesoscopic, and hanging- Carlin Canyon below the P1 boundary. wall folds; also plotted are individual fold axes. Fold axes most commonly trend east- The age of the folding and thrusting can be northeast (050؇±065؇). Note: The subsequent deformation has not been rotated out for constrained only to pre-Permian at Coal Mine most of these folds, because the overlying Strathearn Formation is not preserved. How- Canyon, in the northern Adobe Range (Fig. 1). ever, the three folds where subsequent tilt has been removed do not differ systematically There, Mississippian shale of the Antler from the other folds on this stereogram, indicating that subsequent rotation is not signif- foreland basin is in the footwall of a thrust icant here. (Fold axis orientations, presented as plunge/trend: 11/037, 08/039, 04/056, 04/ fault (Ketner and Ross, 1990) that clearly 063, 18/059, 02/246, 12/228.) (B) Lower Permian (P1) deformation, characterized by open, postdates the Antler foreland basin. Meso- upright folds (see also box, Fig. 5). The tilt of the overlying upper Strathearn has been ,scopic northeast-trending folds in the upper removed, and the P1 fold axes plunge gently toward 030؇±032؇. (Fold axis orientations plate and in the thrust itself are erosionally presented as plunge/trend: 16/032, 13/030.) (C) Post-Permian deformation, characterized trimmed and overlain by silici®ed sandy car- by open, upright folds. The tilt of the overlying upper Strathearn has been removed, and bonates dated only as ``Permian'' on the basis the P1 fold axes plunge gently toward 020؇±026؇. (Fold axis orientations, presented as of macrofossils (Ketner and Ross, 1990). Our plunge/trend: 21/026, 25/020, 05/205.) attempts to re®ne this age by using small foraminifera or fusulinids were unsuccessful because of poor fossil preservation in these si- erts Mountains allochthon and recognized that Permian rocks that overlap pre-Pennsylvanian lici®ed, coarse-grained rocks. this orogenic event could not be attributed to (Antler age?) deformation in the Edna Moun- Erickson and Marsh (1974) documented Pa- either the Antler or Sonoma orogenies as then tain quadrangle, in Humboldt County, Neva- leozoic deformation in the rocks of the Rob- conceived. Lower Pennsylvanian to Lower da, are asymmetrically folded and thrust fault-

534 Geological Society of America Bulletin, May/June 2004 LATE PALEOZOIC TECTONISM IN NEVADA

Figure 10. Measured sections in upper Paleozoic strata of central and northeast Nevada discussed in the text. Locations of measured sections are shown in Figure 1. Data for Beaver Peak are from Berger et al. (2001). All other sections are from our unpublished work. Note that unconformities generally span less time in eastern sections than they do in western ones. RMAÐRoberts Mountains allochthon. ed and are themselves unconformably overlain allochthon is erosionally truncated and over- the evidence of earlier deformations. Finally, by Upper Permian rocks. Erickson and Marsh lain by Missourian Strathearn Formation many of the upper Paleozoic sedimentary (1974) emphasized that ``orogenic movements (along the C6 unconformity). rocks, and particularly the syntectonic sedi- which do not conveniently relate to either the mentary rocks, are clastic rocks that are un- Antler or Sonoma orogeny deserve more DISCUSSION likely to contain or preserve age-diagnostic attention and must be accounted for in the fossils. However, all of the necessary condi- geologic history of the southern Cordillera'' The fortuitous combination of exposure, tions are met in the Carlin Canyon area, and (p. 336). preservation, and datable rocks is the reason earlier workers correctly interpreted the upper In northeastern Nevada, the C5 and C6 that several late Paleozoic deformation events Paleozoic rocks there to record deformation in boundaries have been documented indepen- can be unequivocally documented in Carlin Pennsylvanian and/or Permian time (e.g., dently by Sweet et al. (2001) and Sweet and Canyon, although they have not yet been Dott, 1955; Ketner, 1977). Snyder (2002) in the Pequop Mountains (Fig. widely recognized elsewhere. Paleozoic rocks Even within the Carlin Canyon area, the ev- 1) and by McFarlane (1997) and McFarlane are exposed discontinuously and poorly idence for some of the late Paleozoic defor- and Trexler (1997, 2000) in the Snake Moun- throughout central and western Nevada be- mation is cut out laterally by higher uncon- tains. In the southern Pequop Mountains, the cause of widespread Tertiary volcanic cover in formities. For example, the P1 unconformity Ely Limestone is folded and faulted, erosion- the ranges and Tertiary and Quaternary sedi- cuts down section toward the east, eventually ally truncated, and overlain by the Hogan For- mentary cover in the basins. Furthermore, placing the upper Strathearn Formation di- mation (C5). In the Snake Mountains north of clear preservation of a complex deformational rectly on the Moleen and Tomera Formations, Wells, Nevada, an imbricate stack of thrust record is unlikely because of the very nature completely removing the lower Strathearn sheets containing rocks of both the continental- of the late Paleozoic deformations; the accom- Formation and with it, all evidence of the C6 shelf autochthon and the Roberts Mountains panying uplift and erosion remove or obscure unconformity (Fig. 4). On the basis of the dis-

Geological Society of America Bulletin, May/June 2004 535 TREXLER et al. tribution of unconformities in Carlin Canyon, even with 100% exposure one would not ex- pect to ®nd the C6 unconformity east of the map area or the C3 unconformity west of the map area. The problem is not unique to Carlin CanyonÐSweet et al. (2001) and Sweet and Snyder (2002) described similar relationships in the Pequop Range. There, a higher unconformity (C6) cuts deeply enough that it locally removes all record of an older unconformity (C5) that is preserved elsewhere in the range. This repeated erosional trimming (due to uplift during later tectonic events) is probably the reason that the late Paleozoic deformation events have not been widely recognized, in spite of the accurate interpretations by early workers in the area (e.g., Dott, 1955; Ketner, 1977). Structures we have mapped in Carlin Canyon may (understandably) have been seen but misinterpreted as to age elsewhere in Nevada, especially where age control is Figure 11. Tectonic setting for North America during the Pennsylvanian Ancestral Rocky limited. In Carlin Canyon, three fold sets Mountains orogeny. Many workers have contributed to the ideas present in this conceptual (two unequivocally late Paleozoic and the map (see Discussion in the text). third probably Mesozoic) all have generally northeast-plunging axes. It would be hard to distinguish them in the absence of datable Ancestral Rocky Mountains structures gener- re®ned by Dickinson (2000), who suggests a Pennsylvanian and Permian rocks that occur ally comprise steep thrust faults involving northeast-southwest trend. in overlap relationships. basement and very thick sedimentary sections The recurrent and well-dated deformation We suggest that much of the deformation documenting rapid and deep subsidence (e.g., events at Carlin Canyon appear to require an attributed to the Antler orogeny in Nevada Paradox basin). In addition, Ancestral Rocky active orogenic belt to the west of North may in fact be Pennsylvanian or Permian in Mountains±related structures are generally America at the latitude of the Great Basin in age (see also Trexler et al., 1999; Snyder et oriented northwest-southeast, orthogonal to Carboniferous and Permian time. Continued al., 2000). This possibility may be particularly the folds and thrusts in Carlin Canyon. shortening during the late Paleozoic may have true within the Antler allochthon, where Or- Several plate boundaries may have in¯u- reactivated older structures in the Antler fore- dovician to Devonian chert, argillite, and vol- enced the tectonic development of western land and orogenic belt as well as producing canic rocks are folded, but usually there is no North America in Pennsylvanian time (Fig. overprinted folding, thrusting, and erosion sedimentary overlap assemblage to constrain 11). On the south and east, the Marathon- such as that at Carlin Canyon. Although tra- the time of folding. Our interpretation requires Ouachita orogenic belt is a complex and well- ditional ``Antler age'' (Late Devonian) struc- signi®cant revision to the conventional under- documented record of the collision of North tures may have been reactivated during this standing of the Antler orogenic event, extend- America with Africa and South America (e.g., shortening, we prefer the interpretation that ing the activity of this orogen well into the Kluth and Coney, 1981; Ross, 1991). To the most, or all, of the structures originated in late Pennsylvanian. south or southwest, Ye et al. (1996) have sug- Paleozoic time. The contrasting deformation Although the Pennsylvanian (C6) defor- gested a Pennsylvanian low-angle, northeast- style in Nevada relative to coeval deformation mation in Nevada is synchronous with the An- dipping subduction zone (not shown in Fig. in Utah and Colorado may result from the cestral Rocky Mountains orogeny, the style, 11), although subsequent work has failed to marked difference in crust: old, thinned, pas- intensity, and orientation of deformation sug- corroborate this hypothesis. To the southwest sive continental margin and accreted terranes gest that, unlike the Ancestral Rocky Moun- and west, Stone and Stevens (1988) and Ste- tains, it could not be a far-®eld effect of col- vens et al. (1998) have proposed a left-lateral to the west and thick, homogeneous, largely lision with Gondwana along the southeastern truncation of the continental margin in Penn- crystalline continental crust to the east. Also, continental margin (Kluth, 1986). The defor- sylvanian time. Dickinson and Lawton (2001) note that the Oquirrh basin of western Utah, mation style we describe here is thin-skinned also invoke a sinistral transform fault along usually thought to be the westernmost expres- contraction, similar to the Rocky Mountain the western edge of North America, and sug- sion of the Ancestral Rocky Mountains, is also fold-and-thrust belt of late Mesozoic age. We gest that the major displacement along the among the thickest of the Ancestral Rocky do not yet know whether the scale approaches transform occurred from Early Permian to Mountains basins (Erskine, 1997). This, like that of the Sevier thrust belt; that determina- Middle Triassic time. Walker (1988) suggests the northwest-southeast shortening at Carlin tion will require detailed work to de®ne the that this transform margin was initiated as ear- Canyon, is an unexplained anomaly if for- ages of potentially correlative structures ly as Pennsylvanian time. Convergence along mation of the Oquirrh basin resulted solely throughout the Great Basin. In contrast to the the western margin is a consistent theme from plate convergence along the southern thin-skinned deformation in Carlin Canyon, among many workers, and has recently been margin of the continent (Geslin, 1998), but is

536 Geological Society of America Bulletin, May/June 2004 LATE PALEOZOIC TECTONISM IN NEVADA

consistent with convergence along the western evolution of the Cordilleran continental margin, in the Roberts Mountains thrust unsettled by new data Stewart, J.H., Stevens, C.H., and Fritsche, A.E., eds., from northern Nevada: Geology, v. 10, p. 298±303. margin of North America. Paleozoic paleogeography of the western United Kluth, C.F., 1986, The plate tectonics of the Ancestral In conclusion, we think that late Paleozoic States, Volume 1: Los Angeles, Paci®c Section, So- Rocky Mountains, in Peterson, J.A., ed., Paleotecton- deformation in the Great Basin is much more ciety of Economic Paleontologists and Mineralogists, ics and sedimentation in the Rocky Mountain region: p. 137±156. Tulsa, American Association of Petroleum Geologists widespread and important than has been rec- Dickinson, W.R., 2000, Geodynamic interpretation of Pa- Memoir 41, p. 353±369. ognized. This contractional deformation oc- leozoic tectonic trends oriented oblique to the Meso- Kluth, C.J., and Coney, P.J., 1981, Plate tectonics of the zoic Klamath-Sierran continental margin: Geological Ancestral Rocky Mountains: Geology, v. 9, p. 10±15. curred repeatedly between the times generally Society of America Special Paper 347, p. 209±245. Link, P.K., Warren, I., Preacher, J.M., and Skipp, B., 1996, accepted for the Antler and Sonoma oroge- Dickinson, W.R., Harbaugh, D.W., Saller, A.H., and Snyder, Stratigraphic analysis and interpretation of the Missis- nies. Continent-continent collision along the W.S., 1983, Detrital modes of upper Paleozoic sand- sippian Copper Basin Group, McGowan Creek For- stones from Antler orogen in Nevada: Implications for mation, and White Knob Limestone, south-central Ida- Marathon-Ouachita orogenic belt, widely cited nature of the Antler orogeny: American Journal of ho, in Longman, M.W., and Sonnenfeld, M.D., eds., as the driving force for the Ancestral Rocky Science, v. 283, p. 481±509. Paleozoic systems of the Rocky Mountain region: Tul- Mountains orogeny, cannot alone explain con- Dickinson, W.R., and Lawton, T.F., 2001, Carboniferous to sa, Rocky Mountain Section, SEPM (Society for Sed- Cretaceous assembly and fragmentation of Mexico: imentary Geology), p. 117±114. current deformation in the Great Basin. We Geological Society of America Bulletin, v. 113, Mahoney, J.B., Link, P.K., Burton, B.R., Geslin, J.K., and conclude that plate convergence along the p. 1142±1160. O'Brien, J.P., 1991, Pennsylvanian and Permian Sun western margin of the continent must have Dott, R.H., 1955, Pennsylvanian stratigraphy of the Elko Valley Group, Wood River basin, south-central Idaho, and northern Diamond Ranges, northeast Nevada: in Cooper, J.D., and Stevens, C.H., eds., Paleozoic pa- played a signi®cant role deformation and sed- American Association of Petroleum Geologists Bul- leogeography of the western United States, Volume II: imentation in western North America during letin, v. 39, p. 2211±2305. Los Angeles, Paci®c Section, SEPM (Society for Sed- the late Paleozoic. Erickson, R.L., and Marsh, P., 1974, Paleozoic tectonics in imentary Geology), p. 551±579. the Edna Mountain Quadrangle, Nevada: U.S. Geo- McFarlane, M.J., 1997, The Roberts Mountains thrust in logical Survey Journal of Research, v. 2, no. 3, the northern Snake Mountains, Elko County, Nevada, ACKNOWLEDGMENTS p. 331±337. in Perry, A.J., and Abbott, E.W., eds., The Roberts Erskine, M.C., 1997, The Oquirrh basin revisited: American Mountains thrust, Elko and Eureka Counties, Nevada: National Science Foundation grants to Trexler, Association of Petroleum Geologists Bulletin, v. 81, Nevada Petroleum Society Field Trip Guidebook: Cashman, and Snyder (EAR-9304972, EAR- p. 624±636. Reno, Nevada Petroleum Society, p. 17±34. 9305097, EAR-9903006) funded much of the re- Gallegos, D.M., Snyder, W.S., and Spinosa, C., 1991, Tec- McFarlane, M., and Trexler, J.H., Jr., 1997, Antler tecto- search that led to this paper. Our attention was tonic implications of facies patterns, Lower Permian nism in the northern Snake Mountains, Elko County, drawn to this area by the spectacular exposure, but Dry Mountain trough, east-central Nevada, in Cooper, Nevada: Geological Society of America Abstracts J.D., and Stevens, C.H., eds., Paleozoic paleogeogra- with Programs, v. 29, no. 6, 233 p. the thorough and prescient work by Bob Dott made phy of the western United States, Volume II: Los An- McFarlane, M., and Trexler, J.H., Jr., 2000, Extension or it possible to begin to understand it; his mapping geles, Paci®c Section, Society of Economic Paleon- contraction in earliest Antler tectonism?: Geological was our starting point to unravel the stratigraphy tologists and Mineralogists, p. 343±356. Society of America Abstracts with Programs, v. 32, and structure. We thank Scott Ritter and Dave Geslin, J.K., 1998, Distal Ancestral Rocky Mountain tec- no. 7, p. A-383. Schwarz for their help in the ®eld early in the proj- tonism: Evolution of the Pennsylvanian±Permian Perry, A.J., 1994, Stratigraphic and sedimentologic analysis ect. Mapping and paleontology by graduate students Oquirrh±Wood River basin, southern Idaho: Geologi- of the (Upper Mississippian) lower Newark Valley se- at both Boise State University and the University of cal Society of America Bulletin, v. 110, p. 644±663. quence, Diamond Range, Eureka and White Pine Nevada, Reno, played a role in sorting out this com- Jansma, P.E., and Speed, R.C., 1990, Omissional faulting Counties, Nevada [M.S. thesis]: Reno, University of plex locality. The manuscript was much improved during Mesozoic regional contraction at Carlin Can- Nevada, 243 p. yon, Nevada: Geological Society of America Bulletin, Perry, A.J., 1995, Depositional setting of the Upper Mis- by reviews from Tim Lawton, Paul Link, and Joan v. 102, p. 417±427. sissippian to Lower Pennsylvanian Newark Valley se- Fryxell. 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Stevens, C.H., Stone, P., Dunne, G.C., Greene, D.C., Walk- leogeography of the western United States, Volume II: Schwarz, D.L., Carpenter, J.A., and Snyder, W.S., 1994, Re- er, J.D., and Swanson, B.J., 1998, Paleozoic and Me- Los Angeles, Paci®c Section, SEPM (Society for Sed- examination of critical geological relations in the Car- sozoic evolution of east-central California, in Ernst, imentary Geology), p. 317±330. lin Canyon area, Elko County, Nevada, in Dobbs, W.G., and Nelson, C.A., eds., Integrated Earth and Trexler, J.H., Jr., Snyder, W.S., Schwarz, D., Kurka, M.T., S.W., and Taylor, W.J., ed., Structural and stratigraphic Environmental Evolution of the Southwestern United and Crosbie, R.A., 1995, An overview of the Missis- investigations and petroleum potential of Nevada, with States: Columbia, Maryland, Bellwether Publishing. sippian Chainman Shale, in Hansen, M.W., Walker, special emphasis south of the Railroad Valley produc- p. 119±160. J.P., and Trexler, J.H., Jr., eds., Mississippian source ing trend, Volume II): Reno, Nevada Petroleum So- Stone, P., and Stevens, C.H., 1988, Pennsylvanian and Early rocks in the Antler basin of Nevada and associated ciety, p. 255±272. Permian paleogeography of east-central California: structural traps: Reno, Nevada Petroleum Society, Silberling, N.J., Nichols, K.M., Trexler, J.H., Jr., Jewell, Implications for the shape of the continental margin p. 45±60. P.W., and Crosbie, R.A., 1997, Overview of Missis- and the timing of continental truncation: Geology, Trexler, J.H., Jr., Cole, J.C., and Cashman, P.H., 1996, Mid- sippian depositional and paleotectonic history of the v. 16, p. 330±333. dle Devonian±Mississippian stratigraphy on and near Antler foreland, eastern Nevada and western Utah, in Sweet, D., and Snyder, W.S., 2002, Middle Pennsylvanian the Nevada Test Site: Implications for hydrocarbon Link, P.K., and Kowalis, B.J., ed., Geological Society through Early Permian tectonically controlled basins: potential: American Association of Petroleum Geolo- of America Fieldtrip Guidebook: Provo, Brigham Evidence from the central Pequop Mountains, north- gists Bulletin, v. 80, p. 1736±1762. Young University Geology Studies, v. 42, no. 1, east Nevada: Late Paleozoic tectonics and hydrocar- Trexler, J.H., Jr., Snyder, W.S., and Cashman, P.H., 1999, p. 161±196. bon systems of western North AmericaÐThe greater Pennsylvanian deformation right under our noses all Smith, J.F., Jr., and Ketner, K.B., 1977, Tectonic events Ancestral Rocky Mountains: Tulsa, AAPG Hedberg this time!: Geological Society of America Abstracts since early Paleozoic in the Carlin±Pinon Range area, Research Conference, p. 74±77. with Programs, v. 31, no. 4, p. A-59. Nevada: U.S. Geological Survey Professional Paper Sweet, D., Snyder, W.S., Davydov, V.I., Trexler, J.H., Jr., Trexler, J.H., Jr., Cashman, P.H., Cole, J.C., Snyder, W.S., 876C, 18 p. and Groves, J.R., 2001, Upper Paleozoic Tectonic un- Tosdal, R.M., Davydov, V.I., 2003, Widespread effects Snyder, W.S., Spinosa, C., and Gallegos, D.M., 1991, conformities in the central Pequop Mountains, Neva- of middle Mississippian deformation in the Great Ba- Pennsylvanian±Permian tectonism along the western da: Geological Society of America Abstracts with Pro- sin of western North America: Geological Society of United States continental margin: Recognition of a grams, v. 33, no. 5, p. 47. America Bulletin, v. 115, p. 1278±1288. new event, in Raines, G.L., Lisle, R.E., Schafer, Thorman, C.H., Ketner, K.B., Brooks, W.E., Snee, L.W., and Walker, J.D., 1988, Permian, and Triassic rocks of the Mo- R.W., and Wilkinson, W.H., eds., Geology and ore Zimmermann, R.A., 1991, Late Mesozoic±Cenozoic jave Desert and their implications for timing and deposits of the Great Basin, Symposium Proceed- tectonics in northeastern Nevada, in Raines, G.L., mechanisms of continental truncation: Tectonics, v. 7, ings: Reno, Geological Society of Nevada, p. 5±20. Lisle, R.E., Schafer, R.W., and Wilkinson, W.H., eds., p. 685±709. Snyder, W.S., Schwarz, D.L., Spinosa, C., and Torrealday, Geology and ore deposits of the Great Basin, Sym- Ye, H., Royden, L., Burch®el, B.C., and Schuepbach, M., H., 1995, Pennsylvanian±Permian tectonic sequence posium Proceedings: Reno, Geological Society of Ne- 1996, Late Paleozoic deformation of interior North stratigraphy: Implications for the structure and stratig- vada, p. 25±45. America: American Association of Petroleum Geolo- raphy of eastern Nevada, in Hansen, M., ed., Missis- Trexler, J.H., Jr., and Cashman, P.H., 1997, A southern Ant- gists Bulletin, v. 80, p. 1397±1432. sippian source rocks in the Antler foreland basin of ler foredeep submarine fan: The Mississippian Eleana MANUSCRIPT RECEIVED BY THE SOCIETY 14 NOVEMBER 2002 Nevada and associated structural and stratigraphic Formation, Nevada Test Site: Journal of Sedimentary REVISED MANUSCRIPT RECEIVED 3JUNE 2003 traps: Reno, Nevada Petroleum Society, p. 125±134. Research, v. 67, p. 1044±1059. MANUSCRIPT ACCEPTED 14 AUGUST 2003 Snyder, W.S., Trexler, J.H., Jr., Cashman, P.H., and Davy- Trexler, J.H., Jr., and Giles, K., 2000, The Antler orogeny dov, V.I., 2000, Tectonostratigraphic framework of the in the Great Basin: A review of the data: Geological Printed in the USA

538 Geological Society of America Bulletin, May/June 2004