The Antler orogeny was a tectonic event that began in the early Late Devonian with widespread effects continuing into the Mississippian and early Pennsylvanian . Most of the evidence for this event is in Nevada but the limits of its reach are unknown. A great volume of conglomeratic deposits of mainly Mississippian age in Nevada and adjacent areas testifies to the existence of an important tectonic event, and implies nearby areas of uplift and erosion, but the nature and cause of that event are uncertain and in dispute. Although it is known as an orogeny (mountain building event), some of the classic features of orogeny as commonly defined such as metamorphism , and granitic intrusives have not been linked to it. In spite of this, the event is universally designated as an orogeny and that practice is continued here. This article outlines what is known and unknown about the Antler orogeny and describes three current theories regarding its nature and origin.
33-492: There are two principal facies of lower Paleozoic rocks in Nevada. In the eastern part of the state, a north-trending fossil-rich carbonate shelf of Ordovician to Devonian age, termed the carbonate or eastern assemblage, gives way westward to a contemporaneous expanse of siliceous sedimentary deposits and minor mafic volcanic rocks termed the siliceous or western assemblage. Crafford assigned these two facies respectively to
66-422: A back-arc basin between the western continental margin and a volcanic arc over an east-dipping subduction zone. A second theory involved collision of the continent with an island arc above a west-dipping subduction zone. Both were based on the basic understanding that the western facies assemblage is composed of oceanic deposits and that it is underlain by an extensive thrust fault. Burchfiel and Davis presented
99-419: A facies ( / ˈ f eɪ ʃ ɪ . iː z / FAY -shih-eez , US also / ˈ f eɪ ʃ iː z / FAY -sheez ; same pronunciation and spelling in the plural) is a body of rock with distinctive characteristics. The characteristics can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formation) and the changes that may occur in those attributes over
132-585: A facies series . Roberts Mountains The Roberts Mountains are located in central Nevada in the western United States. The mountains are found in Eureka County , east of the Simpson Park Mountains and west and southwest of the Sulphur Spring Range . The range reaches a peak at Roberts Creek Mountain at 10,133 feet (3,089 m). Nevada State Route 278 passes the east margin of
165-415: A distinct kind of sediment for that area or environment. Since its inception in 1838, the facies concept has been extended to related geological concepts. For example, characteristic associations of organic microfossils, and particulate organic material, in rocks or sediments, are called palynofacies . Discrete seismic units are similarly referred to as seismic facies. Sedimentary facies are described in
198-510: A geographic area. A facies encompasses all the characteristics of a rock including its chemical, physical, and biological features that distinguish it from adjacent rock. The term "facies" was introduced by the Swiss geologist Amanz Gressly in 1838 and was part of his significant contribution to the foundations of modern stratigraphy , which replaced the earlier notions of Neptunism . Walther's law of facies, or simply Walther's law, named after
231-435: A group of "facies descriptors" which must be distinct, reproducible and exhaustive. A reliable facies description of an outcrop in the field would include: composition, texture, sedimentary structure(s), bedding geometry, nature of bedding contact, fossil content and colour. The sequence of minerals that develop during progressive metamorphism (that is, metamorphism at progressively higher temperatures and/or pressures) define
264-574: A major thrust fault as follows: A belt along the 116°-118° meridians—the Antler orogenic belt—was the locus of intense folding and faulting that culminated in the Roberts Mountains thrust fault... That age range and connection with the Roberts Mountains thrust were confirmed in a widely quoted paper by Silberling and Roberts: During the Late Devonian or Early Mississippian ... the Antler orogenic belt
297-506: Is that the western facies domain is dotted with anomalous blocky exposures of contemporaneous eastern facies shelf strata, some of mountain size, surrounded by exposures of western facies rocks. These have been interpreted almost universally as exposures of the carbonate shelf facies in windows of the Roberts Mountains thrust sheet, and to prove the existence of that thrust sheet. From an early date, geologists have struggled to explain
330-522: Is the vertical stratigraphic succession that typifies marine transgressions and regressions . Ideally, a sedimentary facies is a distinctive rock unit that forms under certain conditions of sedimentation , reflecting a particular process or environment. Sedimentary facies are either descriptive or interpretative. Sedimentary facies are bodies of sediment that are recognizably distinct from adjacent sediments that resulted from different depositional environments. Generally, geologists distinguish facies by
363-521: The Battle Mountains , Roberts introduced the term Antler orogeny in an abstract as follows: The earliest orogeny, here named the Antler orogeny ... took place during Mississippian (?) and early Pennsylvanian time. That abstract was followed in 1951 by his geologic map of the Antler Peak quadrangle in the text of which he described the Antler orogeny in detail and somewhat refined its age span: During
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#1732855366022396-457: The aspect of the rock or sediment being studied. Facies based on petrological characters (such as grain size and mineralogy ) are called lithofacies , whereas facies based on fossil content are called biofacies . A facies is usually further subdivided. The characteristics of the rock unit come from the depositional environment and from the original composition. Sedimentary facies reflect their depositional environment, each facies being
429-583: The Antler orogeny, formations in Battle Mountain ranging in age from Ordovician to Mississippian (?) were complexly folded and faulted. As these rocks are unconformably overlain by the Battle Formation of Early Pennsylvanian (Des Moines) age, the orogeny probably took place during the Late Mississippian. The orogeny may have continued into Early Pennsylvanian, however, for the coarse conglomerates of
462-418: The Antler orogeny. Their term "miogeoclinal terrane" referred to the eastern facies assemblage. This was followed by papers offering modified versions of the same theory. Other papers supplied definitive reviews and confirmed the Antler orogeny as a result of plate convergence. As an alternative to the two conventional theories described above, Ketner proposed that (1) left-lateral strike-slip faulting along
495-419: The Battle Formation indicate derivation from a rugged highland area. In a subsequent influential paper, Roberts and others adjusted the age of the Antler orogeny as follows: This belt is now known to have been the locus of intense folding and faulting during the Antler orogeny in latest Devonian or Early Mississippian time ... In the same paper the authors established a connection between the Antler orogeny and
528-548: The Cordilleran geosyncline—the Mid-Paleozoic Antler orogeny—was characterized by the eastward displacement (Roberts Mountains thrust) of eugeosynclinal units from within the small ocean basin over miogeosynclinal strata deposited on the continental shelf. Their now-outdated terms eugeosynclinal and miogeosynclinal refer respectively to the western facies and eastern facies domains. In that paper, Burchfiel and Davis set
561-489: The North American continent in the Late Devonian has been offered as the cause of the orogeny and three varieties of it have been tried—east dipping subduction , west-dipping subduction, and strike-slip motion. None of them is without serious problems and the nature and driving force of the orogeny remain uncertain. This much is known concerning the Antler orogeny: Based on stratigraphic relations near Antler Peak, of
594-546: The Roberts Mountains thrust fault was post-Paleozoic. However, with publication of the 1958 and 1962 papers cited above, the authors revised the age of the Roberts Mountains thrust to coincide with the Late Devonian to Mississippian Antler orogeny and to extend the name far beyond the Roberts Mountains . Over a period of 22 years numerous reports relating the Antler orogeny and Roberts Mountains thrust to plate convergence were published in various journals, and because their basic tenets have been widely accepted, they are here termed
627-443: The big jumping mouse . The large spotted leopard lizard can also be found in the mountains. Trees found in the range include: western juniper ( Juniperus occidentalis ), Utah juniper ( Juniperus osteosperma ), and single-leaf pinyon ( Pinus monophylla ). "Roberts Mountain" . Biological Resources Research Center. Archived from the original on 2005-01-21. This Eureka County , Nevada state location article
660-519: The carbonate shelf. The slide blocks probably were dislodged by the Alamo impact event of Late Devonian age. In this scheme, the deep-water aspects of the western facies assemblage are due to sea-level rise in the Cambrian rather than displacement from an ocean basin. The sedimentary effects of the Antler orogeny are well known and well described in many published reports, but the exact nature of that event and
693-578: The conventional theories. The earliest effort to relate plate tectonics specifically to the Antler orogeny was briefly outlined by E.M. Moores: A collision of this continental margin with a subduction zone dipping away from it in late Devonian-early Mississippian time ... resulted in deformation of the pre-existing continental marginal rocks in the Antler Orogeny. Two principal contrasting tectonic theories were published in greater detail between 1972 and 1992 as related below. One theory involved closure of
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#1732855366022726-410: The driving force remain unsettled. Among the unanswered questions are these: what aspect of plate tectonics was involved; what effect did the Alamo impact event have; why did marine basins appear in the area of general uplift; why did the western facies assemblage, and not the eastern assemblage, include bedded chert, basaltic bodies, barite deposits, and sulfide deposits. Facies In geology ,
759-402: The first detailed paper that explained the Antler orogeny and the Roberts Mountains thrust in terms of the subduction aspect of plate tectonics, stating: ... the paleogeography of this part of the Cordilleran geosyncline probably consisted of an offshore island complex separated from the continental slope and shelf by a small ocean basin of behind-the-arc type. Initial regional deformation within
792-403: The geologist Johannes Walther , states that the vertical succession of facies reflects lateral changes in environment. Conversely, it states that when a depositional environment "migrates" laterally, sediments of one depositional environment come to lie on top of another. In Russia the law is known as Golovkinsky-Walther's law, honoring also Nikolai A. Golovkinsky . A classic example of this law
825-472: The parameters for future discussions of the nature and origins of the Antler orogeny and associated thrusts. Their basic concept of east-dipping subduction was reflected in modified form by others, including Miller and others. Dickinson and others argued for an opposing theory, that west-dipping subduction and volcanic arc-continent collision were the fundamental processes. They stated in the abstract of their 1983 report that The Roberts Mountains allochthon
858-400: The presence in Nevada and adjacent areas of the Antler orogenic deposits without achieving a consensus. The advent of plate tectonic theory provided a variety of possible mechanisms by which the Roberts Mountains thrust and the orogenic deposits could be explained, but none of them has been universally accepted. As outlined in the following paragraphs, plate motion along the western margin of
891-631: The range in Garden Valley and continues about 25 miles (40 km) southeast to Eureka . Roberts Mountains was named after Bolivar Roberts, a division superintendent of the Pony Express. The western Peak is located to the west of these mountains. The range contains rocks deformed by the Antler orogeny of Late Devonian to early Mississippian age. Along the Roberts Mountain thrust fault , which
924-416: The shelf domain and the basin domain. The dark color of the western assemblage, the scarcity of carbonate rocks , and a near absence of shelly fossils, are generally interpreted to indicate a relatively deep-water depositional environment. The western assemblage also differs from the eastern assemblage in its components of bedded chert , basalt bodies, barite deposits, and sulfide deposits. The nature of
957-401: The two assemblages and their relation to one another are critical for an understanding of the Antler orogeny. The western facies assemblage is generally thought to be displaced from the west and to constitute the upper plate of an extensive thrust fault —the Roberts Mountains thrust . The eastern facies assemblage is thought to extend westward under the thrust plate. The basis for this belief
990-498: The western margin of the North American continent, rather than plate convergence, was the engine of Paleozoic tectonics in the region; (2) the Roberts Mountains allochthon, as such, does not exist, and the Ordovician to Devonian western facies assemblage was deposited essentially in situ; and (3) blocks of shelf carbonate rocks earlier thought to be exposures of the shelf in windows of the Roberts Mountains allochthon are slide blocks from
1023-477: Was intensely folded and faulted, and during Mississippian time the Roberts Mountains thrust sheet was emplaced. The effect of this revision in the age of the orogeny was to exclude the evidence in the Antler Peak quadrangle cited above for a Late Mississippian to mid-Pennsylvanian age, on which the concept of the Antler orogeny originally had been based, and to establish the conventional age of that orogeny as Late Devonian to Early Mississippian. The original date of
Antler orogeny - Misplaced Pages Continue
1056-444: Was named for the range, a terrane of oceanic island arc volcanic rocks and sediments were emplaced over the pre-existing Devonian to Silurian carbonates , sandstones and shales of the coastal margin of the continent. The Bureau of Land Management manages 99.4% of the Roberts Mountains, and 0.6% is privately held. Mammals found in the range include: the long-tailed vole , Great Basin pocket mouse , water shrew , and
1089-406: Was probably the subduction complex or accretionary prism of an intra-oceanic Antler arc-trench system that faced east (west-dipping), with subduction downward to the west. Its emplacement by thrusting over the Cordilleran miogeoclinal terrane of lower Paleozoic strata occurred in earliest Mississippian time during an inferred arc-continent collision that began in latest Devonian time and is termed
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