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Keith B. Ketner

Publications and source records attributed to Keith B. Ketner.

At least 19 recordsLinked to original sources
USGS2013

Stratigraphy of lower to middle Paleozoic rocks of northern Nevada and the Antler orogeny

Commonly accepted concepts concerning the lower Paleozoic stratigraphy of northern Nevada are based on the assumption that the deep-water aspects of Ordovician to Devonian siliceous strata are due to their origin in a distant oceanic environment, and their presence where we find them is due to tectonic emplacement by the Roberts Mountains thrust. The concept adopted here is based on the assumption that their deep-water aspects are the result of sea-level rise in the Cambrian, and all of the Paleozoic strata in northern Nevada are indigenous to that area. The lower part of the Cambrian consists mainly of shallow-water cross-bedded sands derived from the craton. The upper part of the Cambrian, and part of the Ordovician, consists mainly of deep-water carbonate clastics carried by turbidity currents from the carbonate shelf in eastern Nevada, newly constructed as a result of sea-level rise. Ordovician to mid-Devonian strata are relatively deep-water siliceous deposits, which are the western facies assemblage. The basal contact of this assemblage on autochthonous Cambrian rocks is exposed in three mountain ranges and is clearly depositional in all three. The western facies assemblage can be divided into distinct stratigraphic units of regional extent. Many stratigraphic details can be explained simply by known changes in sea level. Upper Devonian to Mississippian strata are locally and westerly derived orogenic clastic beds deposited disconformably on the western facies assemblage. This disconformity, clearly exposed in 10 mountain ranges, indicates regional uplift and erosion of the western facies assemblage and absence of local deformation. The disconformity represents the Antler orogeny.

Nevada↗
USGS2012

An alternative hypothesis for the mid-Paleozoic Antler orogeny in Nevada

A great volume of Mississippian orogenic deposits supports the concept of a mid-Paleozoic orogeny in Nevada, and the existence and timing of that event are not questioned here. The nature of the orogeny is problematic, however, and new ideas are called for. The cause of the Antler orogeny, long ascribed to plate convergence, is here attributed to left-lateral north-south strike-slip faulting in northwestern Nevada. The stratigraphic evidence originally provided in support of an associated regional thrust fault, the Roberts Mountains thrust, is now known to be invalid, and abundant, detailed map evidence testifies to post-Antler ages of virtually all large folds and thrust faults in the region. The Antler orogeny was not characterized by obduction of the Roberts Mountains allochthon; rocks composing the "allochthon" essentially were deposited in situ. Instead, the orogeny was characterized by appearance of an elongate north-northeast-trending uplift through central Nevada and by two parallel flanking depressions. The eastern depression was the Antler foreland trough, into which sediments flowed from both east and west in the Mississippian. The western depression was the Antler hinterland trough into which sediments also flowed from both east and west during the Mississippian. West of the hinterland trough, across a left-lateral strike-slip fault, an exotic landmass originally attached to the northwestern part of the North American continent was moved southward 1700 km along a strike-slip fault. An array of isolated blocks of shelf carbonate rocks, long thought to be autochthonous exposures in windows of the Roberts Mountains allochthon, is proposed here as an array of gravity-driven slide blocks dislodged from the shelf, probably initiated by the Late Devonian Alamo impact event.

Nevada↗
USGS2011

Ordovician graptolites from the northern Sierra de Cobachi, Sonora, Mexico

Two Ordovician graptolite assemblages are recognised and described for the first time in the allochthonous siliceous assemblage or succession forming the Guayacan Group of central Sonora in northwestern Mexico. A Middle Ordovician assemblage referable to the Nemagraptus gracilis-Climacograptus wilsoni zonal interval occurs in the upper siliceous shale of unit 1 of the Guayacan Group and an Upper Ordovician assemblage representative of the Dicellograptus ornatus Zone of the Pacific faunal province has been collected from shaly partings in the bedded radiolarian chert constituting unit 2. The stratigraphical make-up of the siliceous assemblage bears a striking similarity to the better known—and correlative—Lower Palaeozoic siliceous succession of central and northern Nevada, giving credence to the hypothesis that the Palaeozoic siliceous assemblage in northwestern Mexico was originally the extension of the Nevadan assemblage into California, which has been transposed to its present position along a left-lateral megashear of the magnitude of at least 1000 km. A review of the proximal development of the spinose species remaining in the form genus Climacograptus Hall has led to the proposal to restrict the genus to Climacograptus bicornis (Hall), its type species, and to two other septate species of early Middle Ordovician age (Llandeilo-early Caradoc) with a primitive type of proximal-end development. The genus Euclimacograptus , with Climacograptus hastatus T. S. Hall as the type species, is proposed for spinose Upper Ordovician climacograptids with an advanced proximal-end development. The genus Ensigraptus , with Climacograptus caudatus Lapworth as the type species, is also proposed for species homeomorphic with those included in Normalograptus Legrand but with a less advanced proximal-end development. Five species are described.

Sonora↗
USGS2009

Mid-Permian Phosphoria Sea in Nevada and the upwelling model

The Phosphoria Sea extended at least 500 km westward and at least 700 km southwestward from its core area centered in southeastern Idaho. Throughout that extent it displayed many characteristic features of the core: the same fauna, the same unique sedimentary assemblage including phosphate in mostly pelletal form, chert composed mainly of sponge spicules, and an association with dolomite. Phosphoria-age sediments in Nevada display ample evidence of deposition in shallow water. The chief difference between the sediments in Nevada and those of the core area is the greater admixture of sandstone and conglomerate in Nevada. Evidence of the western margin of the Phosphoria Sea where the water deepened and began to lose its essential characteristics is located in the uppermost part of the Upper Devonian to Permian Havallah sequence, which has been displaced tectonically eastward an unknown distance. The relatively deep water in which the mid-Permian part of the Havallah was deposited was a sea of probably restricted east-west width and was floored by a very thick sequence of mainly terrigenous sedimentary rocks. The phosphate content of mid-Permian strata in western exposures tends to be relatively low as a percentage, but the thickness of those strata tends to be high. The core area in and near southeastern Idaho where the concentration of phosphate is highest was separated from any possible site of upwelling oceanic waters by a great expanse of shallow sea.

Professional Paper↗
USGS2008

The Inskip Formation, the Harmony Formation, and the Havallah sequence of Northwestern Nevada — An interrelated Paleozoic assemblage in the home of the Sonoma orogeny

An area between the towns of Winnemucca and Battle Mountain in northwestern Nevada, termed the arkosic triangle, includes the type areas of the middle to upper Paleozoic Inskip Formation and Havallah sequence, the Upper Devonian to Mississippian Harmony Formation, the Sonoma orogeny, and the Golconda thrust. According to an extensive body of scientific literature, the Havallah sequence, a diverse assemblage of oceanic rocks, was obducted onto the continent during the latest Permian or earliest Triassic Sonoma orogeny by way of the Golconda thrust. This has been the most commonly accepted theory for half a century, often cited but rarely challenged. The tectonic roles of the Inskip and Harmony Formations have remained uncertain, and they have never been fully integrated into the accepted theory. New, and newly interpreted, data are incompatible with the accepted theory and force comprehensive stratigraphic and tectonic concepts that include the Inskip and Harmony Formations as follows: middle to upper Paleozoic strata, including the Inskip, Harmony, and Havallah, form an interrelated assemblage that was deposited in a single basin on an autochthonous sequence of Cambrian, Ordovician, and lowest Silurian strata of the outer miogeocline. Sediments composing the Upper Devonian to Permian sequence entered the basin from both sides, arkosic sands, gravel, limestone olistoliths, and other detrital components entered from the west, and quartz, quartzite, chert, and other clasts from the east. Tectonic activity was expressed as: (1) Devonian uplift and erosion of part of the outer miogeocline; (2) Late Devonian depression of the same area, forming a trough, probably fault-bounded, in which the Inskip, Harmony, and Havallah were deposited; (3) production of intraformational and extrabasinal conglomerates derived from the basinal rocks; and (4) folding or tilting of the east side of the depositional basin in the Pennsylvanian. These middle to upper Paleozoic deposits were compressed in the Jurassic, causing east-verging thrusts in the eastern part of the depositional basin (Golconda thrust) and west-verging thrusts and folds in the western part. Hypotheses involving a far-traveled allochthon that was obducted from an ocean or back-arc basin are incompatible with modern observations and concepts.

Nevada↗
USGS2007

Geologic Map of the Gold Creek Gold District, Elko County, Nevada

The Gold Creek, Nev. area displays important stratigraphic and structural relationships between Paleozoic and early Tertiary sedimentary strata in an area dominated by large intrusive bodies of Mesozoic age and extensive volcanic fields of middle to late Tertiary age. An autochthonous sequence includes the Cambrian and Proterozoic(?) Prospect Mountain Quartzite and the overlying Cambrian and Ordovician Tennessee Mountain Formation. This autochthon is overlain by three allochthonous plates each composed of a distinctive sequence of strata and having a distinctive internal structure. The structurally lowest plate is composed of the Havallah sequence, locally of Mississippian and Pennsylvanian age, which is folded on north-south trending axes. The next higher plate is composed of somewhat younger Pennsylvanian and Permian strata cut by east-west trending low-angle faults. The highest plate is composed of early Tertiary non-marine sedimentary and igneous rocks folded on varied but mainly north-south trending axes. The question of whether the allochthonous plates were emplaced by contractional or extensional forces is indeterminate from the local evidence. Mineral deposits include gold placers of moderate size and small pockets of base metals, none of which is currently being exploited.

Scientific Investigations Map↗
USGS2002

Cordilleran-margin quartzites in Baja California – implications for tectonic transport

One of the current controversies in Cordilleran tectonics concerns the position of Baja California prior to ∼300 km of opening of the Gulf of California. Geologic arguments, together with paleomagnetic results from Lower Cretaceous volcanic rocks, suggest that the rocks of the Baja Peninsula formed and evolved along the coast of northwestern Mexico prior to opening of the Gulf. In contrast, paleomagnetic data from Cretaceous–early Tertiary plutonic rocks and clastic strata have been interpreted by some workers to suggest that Baja was located near southern Mexico at approximately 80 Ma. The presence of similar detrital zircon ages in lower Paleozoic quartzites of northeast Baja and in lower Paleozoic strata east of the Gulf, in northwestern Mexico and southwestern US, provides strong support for the northern paleoposition, suggesting that Baja has been transported northward by only ∼300 km

Earth and Planetary Science Letters↗
USGS2000

The East Range, northwestern Nevada: A neglected key to the tectonic history of the region

The East Range occupies a strategic position at the western edge of the exposed western facies terrane near the Paleozoic continental margin. There a Cambrian and Ordovician deep-water sequence including the Preble and Valmy Formations is overlain by middle to upper Paleozoic strata that are assigned to three separate stratigraphic sequences on published geologic maps of the range. The three sequences, which include the Havallah sequence, the Inskip Formation, and the Harmony Formation, originally were perceived to be of different ages and lithic composition. The strata assigned to the Havallah are now known to contain conodonts of Late Devonian to Permian ages, and fusulinids of Permian age; those assigned to the Inskip contain conodonts of Early Mississippian and Permian ages and corals of Mississippian age. Strata assigned to the Harmony are undated paleontologically. All three are composed mainly of siliceous deep-water sedimentary deposits. Lower beds of the Havallah and Inskip totalling hundreds of meters in thickness are composed of arkosic sandstone and conglomerate identical to that composing most of the Harmony. The Havallah and Inskip lie disconformably on the quartzitic, middle part of the Valmy Formation. The Harmony lies concordantly on distinctive chert beds at the top of the Valmy Formation. Assuming the latter contact is disconformable rather than a bedding-parallel fault, the East Range displays the stratigraphic bases of all three arkosic map units. The disconformable relation of the Havallah and Inskip to the Valmy Formation indicates elevation of deep-water deposits, subaerial erosion down to Middle Ordovician, and in Late Devonian a return to deep immersion. There is no evidence here of Late Devonian to Early Mississippian folding. Major folds in the East Range must be of Jurassic or younger age because Upper Triassic strata are involved. Evidence of large-scale thrust-faulting is notably scarce. The existence of the Willow Creek thrust shown on published maps of the East Range was based on the mistaken belief that strata below the Valmy Formation are of Triassic age whereas they are actually of Cambrian and earliest Ordovician age.

Nevada↗
USGS1997

Early Silurian radiolaria from northern Nevada, USA

Radiolarians recovered from three sites in the early Llandoverian Cherry Spring chert, north-central Nevada, provide the first Early Silurian radiolarian data from the conterminous United States. Two assemblages were recovered that contain abundant pylomate sphaerellarians, rotasphaerids, inaniguttids, and possible palaeoactinosphaerids. The pylomate taxa have an intermediate spine morphology with Cessipylorum and Aciferopylorum , bringing into question the present criteria for distinguishing these two genera. Rotasphaerids include both species of Rotasphaera and Secuicollacta , that have five primary rods per spine unit, similar to those present in Ordovician assemblages (Caradocian-Ashgillian) reported from Nevada and Australia. Oriundogutta is another common component shared between the Cherry Spring and Caradocian-Ashgillian age faunas. To a lesser extent, the Cherry Spring fauna resembles late Early-Late Silurian (Wenlockian-Ludlovian) assemblages that contain abundant inaniguttids and rotasphaerids. None of the younger species of inaniguttids have been recognized, however, and younger species of rotasphaerids differ in that they have six primary rods per spine unit and a more diverse spine morphology. These preliminary data indicate a stronger similarity between Late Ordovician and early Llandoverian assemblages than between early Llandoverian and Wenlockian-Ludlovian assemblages. The Cherry Spring chert faunas contain several distinct forms, such as Cessipylorum (?) sp. A and B, that may prove useful for biostratigraphic correlation.

Nevada↗
USGS1984

Recent studies indicate that major structures in northeastern Nevada and the Golconda thrust in north-central Nevada are of Jurassic or Cretaceous age

Geologic mapping recently completed in four areas of northeastern Nevada indicates that major folds and thrusts are of post-Early Triassic age and probably are Jurassic or Cretaceous. Previously published data for northeastern Nevada lead to, or permit, the same conclusion. Basinal deposits of Early Triassic age in the northern Adobe Range are easterly derived clay and carbonate. The apparent lack of westerly derived siliceous orogenic sediments of Sonoma age (Late Permian to Early Triassic) suggests that the Sonoma orogeny took place at some unknown location far from northeastern Nevada and that rocks deformed then, the Golconda allochthon, were emplaced in northern Nevada at a later date.

Nevada↗