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Chapter 2 PDF File Geological Field Trips in Southern Idaho, Eastern Oregon, and Northern Nevada Edited by Kathleen M. Haller and Spencer H. Wood Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government Open-File Report 2004-1222 U.S. Department of the Interior U.S. Geological Survey 20 Geologic Field Trips to Central and Southwestern Idaho, Central Nevada, and Eastern Oregon Coal Mine Canyon Carlin Canyon Ferdelford Canyon approximate trend of the eastern 0 10 20 30 40 50 60 mi edge of the Roberts Mountains allochthon 0 20 40 60 80 km Nevada Figure 1. Map of northern Nevada showing the location of areas described in the road log. 20 Geologic Field Trips to Central and Southwestern Idaho, Central Nevada, and Eastern Oregon The Western Margin of North America After the Antler Orogeny: Mississippian Through Late Permian History in the Basin and Range, Nevada By James H. Trexler, Jr.1, Patricia H. Cashman1, Walter S. Snyder2, and Vladimir I. Davydov2 Overview book paper, but is presented in two recent publications: Trex- ler and others (2003) and Trexler and others (2004). Reprints of these papers will be provided to field-trip participants. This field trip will examine the evidence for Mississip- pian, Pennsylvanian and Permian deformation events in north- central Nevada. These events are notable for their timing— after the Antler orogeny and well before the Sonoma orogeny Background (both as traditionally defined)—and, locally, for their intensity. On this trip, we will demonstrate that these deformation events The conventional tectonic interpretation of the evolu- are linked to unconformities that separate genetically related tion of western North America is that there were two major stratigraphic packages in the upper Paleozoic section. These orogenies in Paleozoic time; however, this does not explain unconformities can be recognized over wide areas, can be the numerous local and regional-scale tectonic events recorded correlated at a regional scale, are synchronous (within the in Late Paleozoic rocks. The Late Devonian Antler orogeny resolution of biostratigraphy), and are accompanied by marked and the Permo-Triassic Sonoma orogeny are both character- facies changes. In each case, the subunconformity rocks or ized as the eastward emplacement of oceanic facies sedimen- their correlatives have a deformation history not recorded tary and volcanic rocks over continental margin sedimentary in the overlying rocks. These unconformities are, therefore, rocks (Roberts, 1951; Roberts and others, 1958; Silberling and important stratigraphic markers with tectonic significance. We Roberts, 1962). Many syntheses (e.g., Burchfiel and Davis, refer to these as tectonostratigraphic boundaries. 1972, 1975; Speed and Sleep, 1982) propose that a long-lived On the first day, we will drive from Boise to Elko, with subduction zone oriented down-to-the-northwest, possibly a possible Stop along Nevada State Highway 225 in the accompanied by slab roll-back to the east (e.g., Dickinson, northern Adobe Range (approximately 4 mi west of Elko) to 2000), was responsible for the east-directed Antler and see Mississippian rocks of the Antler foreland and Permian Sonoma orogenies and all activity in between. This model is overlap strata. On the second day, we will see mid-Mississip- not robust in predicting the angular unconformities, discon- pian deformation at Ferdelford Canyon in the Piñon Range, formities, and deformation documented by many workers in and mid-Mississippian, mid-Pennsylvanian and early Perm- upper Paleozoic rocks (e.g., Dott, 1955; Johnson and Visconti, ian deformations at Carlin Canyon in the southern Adobe 1992; Schwarz and others, 1994; Snyder and others, 1997; Sil- Range. Here, the deformations have distinctive fold styles berling and others, 1997; Ketner, 1998; Schiappa and others, and geometries, as well as different ages. On the third day, we 1999; Trexler and Giles, 2000). In this study, our objective has will drive through a thick succession of Early Mississippian been to constrain tectonic models by determining the timing, foreland basin strata structurally overlain by Roberts Moun- extent, and kinematics of these short-lived upper Paleozoic tains allochthon, all depositionally overlapped by Middle (?) tectonic events. Permian strata. Our work throughout Nevada has shown that there are a Our interpretations are the product of a truly multidisci- number of regional unconformities from middle Mississippian plinary study and would not have been possible without the through Permian time, and that they all represent genetically full participation of sedimentologists, biostratigraphers, and important breaks in the stratigraphic record (fig. 2) (Snyder, structural geologists. Complete documentation of the map 2000; Trexler and others, 2003, 2004). These unconformities relationships, age control, stratigraphic revisions, and struc- are tectonically generated and are nearly isochronous (to the tural analyses in this study is beyond the scope of this guide- resolution of Upper Paleozoic biostratigraphic control, ±~1 to 5 m.y.). More importantly, these unconformities can be cor- 1Department of Geological Sciences, University of Nevada, Reno, NV 89557, related laterally to “event horizons” (e.g., lithofacies shifts) [email protected] that have the same origin. This feature makes them useful far 2Department of Geology and Geophysics, Boise State University, Boise, ID beyond the areas of actual uplift, deformation, and erosion. 83725 22 Geologic Field Trips to Central and Southwestern Idaho, Central Nevada, and Eastern Oregon 23 �� ������������� �� �������� �������������� � ������ ������ ������������ ��������� �� ����� (1) The Mississippian C2 un- . TRIASSIC E N 1 A 5 conformity records Meramecian I 2 G E CHANGXINGIAN N Carlin Canyon / N. I T Eastern Nevada P A ������ ������� ��������� deformation of Antler foreland L O WUCHIAPINGIAN OCHOAN Adobe R. L N CAPITANIAN basin deposits, overlapped by E A T L I N P D WORDIAN A I U D PARK CITY- PHOSPHORIA I L Chesterian strata. It is particu- M A P5? Park City, Arcturus M ROADIAN Buckskin Mtn, etc. & R 2 D BASINS E 7 A P 2 unnamed Units or Pequop U KUNGURIAN P4 larly well developed in the Piñon G LEONARDIAN P3 DRY MOUNTAIN TROUGH N ARTINSKIAN 0 Y A 8 L Range. I P2 2 L R SAKMARIAN A A R E WOLFCAMPIAN U. Strathearn U (2) The Pennsylvanian C6 un- S P1 I ASSELIAN C 1 9 conformity (recognized by Dott, 2 STRATHEARN GZHELIAN VIRGILIAN BASIN E E 1955) truncates thrust-related T T A L. Strathearn A N L L A MISSOURIAN I KASIMOVIAN deformation in rocks as young as N C6 6 A 0 V DESMOINESIAN 3 Hogan L D I Atokan and is overlain by middle Y MOSCOVIAN E C5 M S L 2 ATOKAN S 1 N D U ELY BASIN Tomera Upper Ely 3 Y N D O I L C4 Missourian strata. E R R M BASHKIRIAN P MORROWAN E A Moleen F E 0 I Lower Ely 2 C3 (3) The early Permian P1 un- N 3 O SERPUKHOVIAN 5 B CHESTERIAN 2 R ANTLER SUCCESSOR BASIN Tonka conformity post-dates folding in 3 Diamond Peak A E N C T A I A Y C2 P L the Virgilian (and older) section L P I R MERAMECIAN S VISEAN A S E I Melandco and is covered by Wolfcampian S ANTLER FORELAND BASIN Dale Canyon S I Y M OSAGEAN L (upper Asselian-lower Sakmar- 5 R 4 A 3 E TOURNAISIAN C1 5 KINDERHOOK' ian) sedimentary rocks. The latter 5 3 N A FAMENNIAN 0 I E two deformation events are vis- 7 ������ ������� ��������� N T 3 O A FRASNIAN V L 5 E 7 ible at Carlin Canyon. 3 D Recognition and widespread Figure 2. Regional stratigraphy of northern Nevada, showing the major tectonostratigraphic correlation of tectonic boundar- boundaries discussed in the text. ies would not be possible without biostratigraphic age control. We We have adopted a numbering scheme for the regional are fortunate in this part of the unconformities, using a system much like that used for the section to have high-resolution biostratigraphy provided by Mesozoic section on the Colorado plateau (Pipiringos and small foraminifera and fusulinids. These fossils provide age OʼSullivan, 1978; Peterson and Pipiringos, 1979). They are resolution on the order of ±1 m.y. numbered sequentially from oldest to youngest within each time period (fig. 2). For the upper Paleozoic, we use the Part 1: Deformation of the Antler foreland in the time periods C = Carboniferous, P = Permian (Snyder, 2000; northern Piñon Range Trexler and others, 2003, 2004). Our reassessment of the late Paleozoic stratigraphy in Nevada uses these unconformities and their correlative event horizons as natural breaks that separate packages of genetically related strata. Unconformity-bounded stratigraphic packages We have revised the regional stratigraphy based on our in the Mississippian and Pennsylvanian–A quick recognition of widespread unconformities in the Upper Paleo- summary zoic record. In many cases, these unconformities occur within existing mapped formations (Trexler and others, 2003, 2004). Mississippian and Pennsylvanian-Early Permian strata in Each unconformity is, by definition, a boundary of at least for- the Carlin area are characterized by genetic stratigraphic pack- mation rank; it, therefore, requires stratigraphic revision where ages that were deposited in response to tectonic deformation, it breaks an existing formation. Some of the unconformities uplift, erosion, and subsidence. The angular unconformities can be mapped laterally into areas where the underlying rocks between these packages provide an opportunity to determine are deformed; these we have identified as key stratigraphic the kinematics of deformation at each stage of this history markers with tectonic significance. Some unconformities can (fig. 2). also be traced laterally into areas where they are conformable surfaces with minor or no hiatus. Even in these cases, a signal Continental margin strata and Antler foreland onlap may exist in the form of a facies change forced by the same sequence – C1 tectonic disruption. Correlation of the unconformities with their correlative conformable surfaces is made possible by The Antler orogeny, commonly defined as Late Devo- detailed biostratigraphy.
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