Pennsylvanian Permian Research Articles

Unexpected trend in the compositional maturity of second-cycle sand

It is generally accepted that recycling of sandstone generates relatively more mature sand than its parent sandstone. Such maturity is accomplished mainly through chemical weathering as the chemically unstable minerals are eliminated. Because chemical weathering is ubiquitous on the Earth's surface, maturity due to recycling is expected in most geological settings. However, contrary to one's expectation, second-cycle Holocene sand, exclusively derived from sandy facies of the first-cycle Pennsylvanian–Permian Cutler Formation, is actually less mature than its first-cycle parent near Gateway, Colorado. Both the Cutler sandstone and Holocene sand were the products of similar geological processes that controlled their respective composition. In spite of such similarities, a significant difference in composition is observed. We propose that the unexpected immaturity in second-cycle Holocene sand may be due to mechanical disintegration of coarse-grained feldspar and feldspar-rich rock fragments into relatively smaller fractions. Results presented in this paper are the first quantitative estimation of recycling of parent sandstone into daughter sand, and the first observed reverse maturity trend in second-cycle sand. These unexpected results suggest the need for further research to quantitatively understand the recycling process.

Effects of late Paleozoic foreland deformation on underground coal mine ground instability, Illinois and Appalachian Basins

Slickensides are commonly associated with potentially hazardous ground conditions in underground coal mines. Investigations by the Mine Safety and Health Administration's Roof Control Division indicate that slickensided drag folds in the immediate roof of Pennsylvanian-age coal seams represent instances of ground instability of various scales, from skin control hazards to roof falls that block travelways and belt entries. The occurrence of features in the roof of the Illinois Basin's Springfield coal seam that are identical to structures interpreted as drag folds in Pennsylvanian-age coal measure rocks of the Appalachian Basin suggests that tectonic stress associated with the late Pennsylvanian–Permian Alleghanian orogeny was transmitted into the mid-continent. This paper relates slickenside occurrences in the Pennsylvanian-age Springfield coal seam to local structural geologic features that are associated with the late Pennsylvanian–Permian Alleghanian orogeny. Because the slickensides discussed are interpreted to have formed in response to regional tectonic stress, small-scale controls on coal mine ground instability can be related to large-scale, regional tectonic processes. Field investigations indicate that mine-wide geologic mapping of structural geologic features can be used to project zones of subtle, yet problematic, structural weakness in advance of face positions. By incorporating this style of structural geologic hazard mapping in mine planning and operation, miners can be prepared to install appropriate supplemental support, or reduce the effects of structural weaknesses with local modifications to mine design.

Depositional environment and biofacies characterization of the Upper Pennsylvanian–Lower Permian deposits of the San Salvador Patlanoaya section (Puebla, Mexico)

The San Salvador Patlanoaya section (Puebla State of Mexico) has been subdivided into seven informal members labeled A–F. Members C–F have been dated as Missourian to Leonardian (equivalent to Kasimovian to Kungurian, i.e. lower Upper Pennsylvanian to upper Lower Permian). Members C–E display a shallowing-upward trend as does member F. The biodiversity of these carbonate deposits outcropping in the San Salvador Patlanoaya section is relatively low, although multiple microfossils (algae, small foraminifera, fusulinids and fish remains) are represented. Member C consists of calcarenitic limestone interpreted as distal tempestites interbedded with shaly limestone facies. These storm beds are composed mainly of silt, sand-sized quartz grains and bioclasts. Member D corresponds to coarse bioclastic limestones represented by calcareous tempestites and channel beds with erosional bases. Member E is composed of green shales and cross-bedded sandstones and gravelly conglomerates. Member F corresponds to a condensed package of limestones and interbedded siliciclastics and is Cisuralian (Early Permian) in age. Member G consists of condensed black shales and limestone nodules. The results of the study have significant implications for recognition of climatic and/or sea-level fluctuations in bioclastic–siliciclastic facies during the Late Pennsylvanian–Early Permian. The skeletal limestones and channel sandstones, common throughout the Pennsylvanian–Permian section, provide a constraint on palaeobathymetry, with the water depth fluctuating frequently around a position below, but near, the storm wave base.

Superimposed Quesnel (late Paleozoic–Jurassic) and Yukon–Tanana (Devonian–Mississippian) arc assemblages, Cassiar Mountains, northern British Columbia: field, U–Pb, and igneous petrochemical evidence

Allochthons in the Cassiar Mountains of northern British Columbia contain assemblages belonging to two distinct Canadian Cordilleran terranes, Yukon–Tanana (YTT) and Quesnellia. These assemblages, of pre-Late Devonian, Devonian–Mississippian, Pennsylvanian–Permian, and Early Jurassic age, occur in intrusive and depositional, as well as structural, contact with each other. The allochthons are gently dipping thrust panels, interrupted by the mid-Cretaceous Cassiar Batholith. A key element for correlation across the batholith is the Mississippian and older pericratonic Dorsey Complex. New Devonian–Mississippian U–Pb ages for deformed plutons within it document an igneous suite like those in type Yukon–Tanana exposures farther north. Other characteristics of the Dorsey Complex that ally it with YTT are orthoquartzites and grits, and amphibolite bodies with transitional mid-ocean ridge basalt (MORB) to ocean-island basalt (OIB) petrochemical signatures. Unconformities, deformed clasts in the late Paleozoic sequences, and a shared mid-Permian intrusive suite show that later arcs onlapped the mid-Paleozoic and older YTT assemblage. The Early Jurassic intrusive suite cuts all major contacts and fabrics except the terrane-bounding fault between the Slide Mountain and combined YTT–Quesnel terranes. It represents a northern continuation of a plutonic belt that extends the length of the Mesozoic Quesnel magmatic arc. These relationships carry important implications for Cordilleran terrane history and the tectonic evolution of the North American margin. At least some of the major terranes were not unrelated entities prior to their accretion to the continent, but a system of superimposed and interconnected arcs that developed over a protracted time interval, with complex and evolving paleogeographic configurations much like the modern western Pacific province.

Implications of Latest Pennsylvanian to Middle Permian Paleontological and U-Pb SHRIMP Data from the Tecomate Formation to Re-dating Tectonothermal Events in the Acatlán Complex, Southern Mexico

Limestones in the highly deformed Tecomate Formation, uppermost unit of the Acatlán Complex, are latest Pennsylvanian—earliest Middle Permian in age rather than Devonian, the latter based on less diagnostic fossils. Conodont collections from two marble horizons now constrain its age to range from latest Pennsylvanian to latest Early Permian or early Middle Permian. The older collection contains Gondolella sp., Neostreptognathodus sp., and Streptognathodus sp., suggesting an oldest age limit close to the Pennsylvanian—Permian time boundary. The other collection contains Sweetognathus subsymmetricus, a short-lived species ranging only from Kungurian (latest Leonardian) to Wordian (earliest Guadelupian: 272 ± 4 to 264 ± 2 Ma). A fusilinid, Parafusulina c.f. P. antimonioensis Dunbar, in a third Tecomate marble horizon is probably Wordian (early Guadelupian, early Middle Permian). Furthermore, granite pebbles in a Tecomate conglomerate have yielded ~320-264 Ma U-Pb SHRIMP ages probably derived from the ~288 Ma, arc-related Totoltepec pluton. Collectively, these data suggest a correlation with two nearby units: (1) the Missourian—Leonardian carbonate horizons separated by a Wolfcampian(?) conglomerate in the upper part of the less deformed San Salvador Patlanoaya Formation; and (2) the clastic, Westphalian—Leonardian Matzitzi Formation. This requires that deformation in the Tecomate Formation be of Early—Middle Permian age rather than Devonian. These three formations are re-interpreted as periarc deposits with deformation related to oblique subduction. The revised dating of the Tecomate Formation is consistent with new data, which indicates that the unconformity between the Tecomate and the Piaxtla Group is mid-Carboniferous and corresponds to a tectonothermal event.

A flexural model for the Paradox Basin: implications for the tectonics of the Ancestral Rocky Mountains

ABSTRACTThe Paradox Basin is a large (190 km × 265 km) asymmetric basin that developed along the southwestern flank of the basement‐involved Uncompahgre uplift in Utah and Colorado, USA during the Pennsylvanian–Permian Ancestral Rocky Mountain (ARM) orogenic event. Previously interpreted as a pull‐apart basin, the Paradox Basin more closely resembles intraforeland flexural basins such as those that developed between the basement‐cored uplifts of the Late Cretaceous–Eocene Laramide orogeny in the western interior USA. The shape, subsidence history, facies architecture, and structural relationships of the Uncompahgre–Paradox system are exemplary of typical ‘immobile’ foreland basin systems.Along the southwest‐vergent Uncompahgre thrust, ∼5 km of coarse‐grained syntectonic Desmoinesian–Wolfcampian (mid‐Pennsylvanian to early Permian; ∼310–260 Ma) sediments were shed from the Uncompahgre uplift by alluvial fans and reworked by aeolian‐modified fluvial megafan deposystems in the proximal Paradox Basin. The coeval rise of an uplift‐parallel barrier ∼200 km southwest of the Uncompahgre front restricted reflux from the open ocean south and west of the basin, and promoted deposition of thick evaporite‐shale and biohermal carbonate facies in the medial and distal submarine parts of the basin, respectively. Nearshore carbonate shoal and terrestrial siliciclastic deposystems overtopped the basin during the late stages of subsidence during the Missourian through Wolfcampian (∼300–260 Ma) as sediment flux outpaced the rate of generation of accommodation space. Reconstruction of an end‐Permian two‐dimensional basin profile from seismic, borehole, and outcrop data depicts the relationship of these deposystems to the differential accommodation space generated by Pennsylvanian–Permian subsidence, highlighting the similarities between the Paradox basin‐fill and that of other ancient and modern foreland basins. Flexural modeling of the restored basin profile indicates that the Paradox Basin can be described by flexural loading of a fully broken continental crust by a model Uncompahgre uplift and accompanying synorogenic sediments. Other thrust‐bounded basins of the ARM have similar basin profiles and facies architectures to those of the Paradox Basin, suggesting that many ARM basins may share a flexural geodynamic mechanism. Therefore, plate tectonic models that attempt to explain the development of ARM uplifts need to incorporate a mechanism for the widespread generation of flexural basins.

The control of coal bed decollement-related slickensides on roof falls in North American Late Paleozoic coal basins

Slickensides cause potentially hazardous ground conditions in underground coal mines. Investigations by the Mine Safety and Health Administration's (MSHA) Roof Control Division indicate that many slickensides represent bedding plane faults and drag folds that formed during coal bed decollement, a style of bedding plane faulting that occurs in shale units above coal seams. These slickensides formed in response to regional tectonic stresses, rather than by differential compaction, and strike parallel to local and regional fold axes and thrust faults. This paper relates some slickensides in the Appalachian, Illinois, Arkoma, and Black Warrior basins to the structural grain developed during the Late Pennsylvanian–Permian Alleghanian orogeny, provides descriptions of slickensides, and advocates geologic mapping as a predictive method for identifying adverse ground conditions associated with tectonically formed slickensides.

Discovery of radiolaria and conodonts in the Carboniferous–Permian of San Salvador Patlanoaya (Puebla, Mexico); biostratigraphic implications

New identifications of radiolaria and conodonts allow clarifying the biostratigraphy of the Pennsylvanian and Permian deposits in San Salvador Patlanoaya (Puebla State, Mexico). The radiolaria are sometimes relatively common in the series, but weakly diversified and endemic. Among the conodonts, Streptognathodus bellus is characteristic of the Late ‘Virgilian’ sensu Baars, probably coeval with the Early Wolfcampian sensu Thompson or Wilde, the Bursumian of Ross & Ross or the Orenburgian–Asselian stage or substage of Russia (sensu Davydov). San Salvador Patlanoaya is a key-section for the Pennsylvanian–Permian boundary in Mexico.

Syndepositional thrust-related deformation and sedimentation in an Ancestral Rocky Mountains basin, Central Colorado trough, Colorado, USA

Pennsylvanian–Permian synorogenic deposits (Minturn and Sangre de Cristo Formations) of the Central Colorado trough record an interplay of deformation and sedimentation in an Ancestral Rocky Mountains basin. The Central Colorado trough was a north-trending basin bordered by basement-involved highlands of the Uncompahgre uplift on the west and the Ancestral Front Range and Apishapa uplift on the east. Stratigraphic data show that the Central Colorado trough was an asymmetric basin in which coarse-grained sediments were deposited adjacent to the Sand Creek–Crestone thrust fault system of the Uncompahgre uplift. These deposits pinch out eastward against the Apishapa uplift along the eastern margin of the basin. Lithofacies analysis shows that the Central Colorado trough was filled by fan-delta, fluvial-delta, and turbidite deposits of the Middle Pennsylvanian Minturn Formation and by alluvial-fan, braided-stream, and meandering-stream deposits of the Upper Pennsylvanian–Permian Sangre de Cristo Formation. Geologic mapping has identified three syndepositional structures in the strata of the Central Colorado trough that indicate Pennsylvanian–Permian shortening: (1) the Gibson Peak growth syncline in the footwall of the Crestone thrust fault, which formed by syndepositional rotation of the Crestone Conglomerate Member of the Sangre de Cristo Formation during thrust displacement; (2) the Sand Creek thrust fault, which cuts the lower part of the Crestone Conglomerate Member but is covered by younger deposits of the Crestone Conglomerate Member; and (3) an intraformational angular unconformity in the Sangre de Cristo Formation that separates folded strata from overlying less deformed strata. All three structures indicate general east-west shortening during deposition. We interpret the Central Colorado trough as a flexural basin on the basis of syndepositional thrust-related structures, basin asymmetry, and lithofacies distribution. Displacement on the east-verging Sand Creek–Crestone thrust fault system appears to have controlled uplift of the central part of the Uncompahgre uplift and also subsidence in the adjacent basin. The Apishapa uplift, located along the eastern margin of the basin, is interpreted as a possible flexural forebulge related to crustal loading of thrust sheets along the western margin of the Central Colorado trough. Geologic mapping, subsurface data, and identification of syndepositional structures has also led to a better understanding of post-Paleozoic deformation of Pennsylvanian–Permian strata of the Central Colorado trough and the structural evolution of the present Sangre de Cristo Mountains.

Paleoenvironmental reconstruction from chemical and isotopic compositions of Permo-Pennsylvanian pedogenic minerals

Mineralogical and chemical analysis of Late Pennsylvanian and Early Permian paleosols from the eastern shelf of the Midland basin, north-central Texas, USA, are used to test hypothesized climate change in Late Paleozoic western equatorial Pangea, previously defined independently on the bases of sedimentologic and paleontologic proxies and climate models. The <0.2-μm size phyllosilicate fraction in the studied paleosols exhibits down-profile trends in mineralogy and chemical composition that are consistent with modern weathering profiles suggesting a dominantly pedogenic origin. A stratigraphic trend from kaolinite-dominated profiles in Upper Pennsylvanian paleosols to profiles dominated by smectite and hydroxy-interlayered 2:1 phyllosilicates in Lower Permian paleosols indicates a relatively rapid decrease in soil weathering and leaching in the latest Pennsylvanian followed by a more gradual decrease in leaching throughout the Early Permian. The chemical composition (cation ratios and exchange capacity) of these phyllosilicates further corroborates this shift toward less intensive leaching, presumably in response to climate change from humid to progressively more arid conditions. The phyllosilicates in the <0.2-μm size fraction and contemporaneous pedogenic calcites from the Permo-Pennsylvanian paleosols exhibit a long-term stratigraphic increase in their δ 18O values of as much as ∼3.2‰ and ∼5.2‰, respectively. This long-term trend is consistent with a transition throughout the latest Pennsylvanian through Early Permian toward progressively more evaporatively enriched soil waters. Superimposed on the long-term trend is an apparent rapid enrichment (1.5 to 2‰) in phyllosilicate δ 18O values immediately above the Pennsylvanian–Permian boundary. Observed oxygen isotope fractionation between the phyllosilicates and calcites within individual paleosols indicate isotopic disequilibrium between mineral pairs. This is attributed to a minor detrital component in the pedogenic clay-dominated phyllosilicate fraction coupled with the effects of seasonality of mineral formation. Inferred δ 18O compositions of Late Paleozoic meteoric water (−2‰ to +4‰) are compatible with less intensive soil leaching under conditions of increasing aridity, possibly coupled with a shift in local precipitation from a continental source to a marine source.

A new terrane subdivision for Mongolia: implications for the Phanerozoic crustal growth of Central Asia

We present a new terrane synthesis for Mongolia that incorporates geological, geochemical and geochronological data from more than 60 years of Mongolian, Russian and joint international studies. Forty-four terranes are distinguished and classified into cratonal, metamorphic, passive margin, island arc, forearc/backarc, accretionary complex, or ophiolitic types. New detailed stratigraphic columns for all terranes are presented which summarize the geological evolution of each terrane. Our analysis reveals that small Precambrian cratonic blocks in the Hangay region acted as a central nucleus around which Paleozoic arcs, backarc/forearc basin assemblages, associated subduction complexes and continental slivers were accreted. The temporal and spatial order of accretion and amalgamation was complex and probably not simply from north to south with time. The timing of terrane accretion is partly constrained by sedimentary overlap assemblages and post-amalgamation intrusive complexes. The main stages of amalgamation occurred during the Neoproterozoic, Cambrian–Ordovician, Devonian, Pennsylvanian–Permian and Triassic. The arcuate trends of terranes around the central Hangay region provide the first-order structural grain for Mongolia. This crustal anisotropy has played a major role in controlling the geometry and kinematics of all subsequent Phanerozoic deformation and reactivation of structures in the region, including the Cenozoic development of the Altai and Gobi Altai. Our results provide the most detailed synthesis to date of the basement geology of Mongolia which should provide an important crustal framework for interpreting the Phanerozoic tectonic evolution of a large part of Central Asia. In addition, our synthesis allows the economic resources of Mongolia to be placed in a modern tectonic context.

The geochemistry of shales, siltstones and sandstones of Pennsylvanian–Permian age, Colorado, USA: implications for provenance and metamorphic studies

A series of shales and sandstones found near the source of the Sangre de Cristo, Belden, and Maroon Formations from central Colorado were examined petrographically and were analyzed for major and selected trace elements, including the REE. The sandstones from the Belden Formation have higher quartz/feldspar ratios than do those from the Maroon and Sangre de Cristo Formations. Also, the alkali feldspar (i.e., orthoclase, microcline, perthite)/plagioclase ratio decreases in the order Sangre de Cristo Formation>Maroon Formation>Belden Formation, but the CIW′ (chemical index of weathering=molecular [Al 2O 3/(Al 2O 3+Na 2O)]∗100) decreases in the order Belden Formation>Sangre de Cristo Formation>Maroon Formation. This suggests that the Belden Formation had a more plagioclase-rich granitoid source and more intense weathering of the source than did the Maroon and Sangre de Cristo Formations. Also, the variation in the elemental composition within the terrigenous sediment may be explained in terms of the variation in the observed minerals. Elemental ratios critical of provenance are statistically the same between the finer sediment of the Maroon and Sangre de Cristo Formations and fall within the range of a granitoid provenance, suggesting a similar granitoid source composition for the two formations. The fine sediment from the Belden Formation, however, has significantly more negative Eu anomalies and lower La/Sc and Th/Cr ratios than those of the Maroon and Sangre de Cristo Formations, suggesting a more differentiated granitoid source for the Belden than for the Maroon and Sangre de Cristo Formations. Most elemental concentrations or ratios vary by a factor of 0.12 to 60 between adjacent fine and coarse sediment (<1-m distances). Thus, it is not recommended that metasedimentary sequences similar in composition to this study be examined to determine element mobility during metamorphism as the variation due to sedimentary processes is so large.

Abstract: Sequence Stratigraphy and Phylloid Mound Development in Pennsylvanian and Lower Permian Limestones, Midland Basin, West Texas, USA&amp;nbsp;

Abstract: Sequence Stratigraphy and Phylloid Mound Development in Pennsylvanian and Lower Permian Limestones, Midland Basin, West Texas, USA&amp;nbsp;

Carbon and oxygen isotope zoning around Carlin-type gold deposits: a reconnaissance survey at Twin Creeks, Nevada

This study was undertaken to determine whether wallrocks around the Twin Creeks Carlin-type gold deposits exhibit oxygen isotope haloes similar to those found around other types of hydrothermal deposits. Mineralization at Twin Creeks is hosted by Ordovician Sequence shales containing some carbonate minerals and by Pennsylvanian–Permian Etchart Formation limestone. Analysis of orthophosphate-soluble carbonate from these rocks shows that oxygen isotope haloes are detectable in Ordovician Sequence shales but not in Etchart Formation limestone. The soluble fraction of Ordovician Sequence shales at Twin Creeks has δ 18O values of 12 to 24‰ and δ 13C values of 0 to −10‰. Most samples fall along a poorly defined trend that extends from δ 18O of about 24‰ and δ 13C values of about 0, which are typical of unaltered limestones, toward lower values for both isotope systems, which are typical of rocks that have undergone alteration by hydrothermal fluids. Plots of these values along two sections through the ore body show that δ 18O values of wallrocks are lowest in the ore zone and increase outward, forming a halo several hundred meters in size. In the same plots, δ 13C values of the wallrocks do not show systematic spatial variations. The soluble fraction of Etchart Formation limestones at Twin Creeks have δ 18O values of 25 to 5‰ and δ 13C values of 4 to −10‰, but do not show any systematic spatial variation relative to mineralization at the scale of our samples. Failure of the Etchart Formation samples to show detectable haloes is probably related to deposition of post-ore carbonate minerals or lower ore fluid : rock ratios. Material balance calculations used to model the isotopic composition of average Ordovician Sequence shales indicate that changes in temperature and water : rock ratio were probably not sufficient to account for the wide range of isotope compositions observed in these rocks. The most likely additional factor contributing to this range of values was a change in the composition of the altering fluid, probably by mixing of the ore fluid with surrounding meteoric water. These results suggest that Carlin-type gold deposits are surrounded by haloes of low δ 18O values, but that detection of these haloes could be complicated by local compositional variations and post-ore modification of the wallrocks.

Redevelopment of Old Fields - Upper Pennsylvanian and Lower Permian of Southeast New Mexico : ABSTRACTS

Redevelopment of Old Fields - Upper Pennsylvanian and Lower Permian of Southeast New Mexico : ABSTRACTS

An eugeneodontid elasmobranch from the Late Paleozoic of Kansas

A tooth battery, palatoquadrate, and a gill-arch element of Bobbodus schaefferi were collected from Late Pennsylvanian/Early Permian (Asselian) rocks near Manhattan, Kansas. Depending on the placement of the Pennsylvanian–Permian boundary, this specimen extends the upper limit of the species from the Virgilian (Gzelian) into the Gearyan (Asselian). The new range thus is Kasimovian to Asselian, a 15 my interval. Based on features of the palatoquadrate, the diagnoses of the order Eugeneodontida and the superfamily Caseodontoidea are revised. Bobbodus is the most primitive genus of the order Eugeneodontida.

Cycle Stratigraphy and Porosity in Pennsylvanian and Lower Permian Shelf Limestones, Eastern Central Basin Platform, Texas

Pennsylvanian and Lower Permian shelfal limestones were studied in core and wireline logs on the eastern side of the Central Basin platform in west Texas. Sixty-three (63) cycles were delineated in the study interval, which includes 200250 m of Canyon (Missourian), Cisco (Virgilian), and Wolfcamp strata. Four general lithofacies are present: fossiliferous wackestones and packstones, grainstones, phylloid algal boundstones, and shales. These lithologies typically occur in 118-m-thick cycles bounded by subaerial exposure surfaces. Grainstones in the upper part of some cycles indicate a shallowing of environments prior to subaerial exposure. Many cycles have subaerial exposure surfaces developed on subtidal fossiliferous wackestones or packstones suggesting rapid falls in se level. Long-term transgressive intervals (transgressive systems tracts or TST) are dominated by thick (>4 m) cycles, whereas long-term regressive intervals (highstand systems tracts or HST) are dominated by thinner cycles. Stable carbon isotope data suggest that thick cycles in TSTs were subjected to short periods of subaerial exposure, whereas thin cycles in the HSTs were subjected to much longer subaerial exposure. Porosity is quite variable beneath subaerial exposure surfaces. At any given well, reservoir-grade porosity (>4%) is present below only 1045% of the identified subaerial exposure surfaces. Where pres-ent, reservoir-grade porosity occurs in the upper part of cycles, 0.35 m below subaerial exposure surfaces. Porosity in thick cycles of the TST is relatively widespread and not facies-selective. Porosity is less abundant and facies-selective in the HST, with porosity occurring only in relatively thick (1.54 m) grainstones, which are concentrated near the shelf margin. Thin (

Paleomagnetism of the late Paleozoic Slide Mountain terrane, northern and central British Columbia

Paleomagnetic samples were collected from Mid-Pennsylvanian to Lower Permian red argillaceous cherts at two localities of the Slide Mountain terrane: 18 sites from the Sylvester allochthon in northern British Columbia and 11 sites from Sliding Mountain in central British Columbia. A secondary component of natural remanent magnetization in the Sylvester samples yields a paleomagnetic pole that can be brought into coincidence with the Jurassic portion of the North American apparent polar wander path by inferring vertical-axis rotation during obduction of the allochthon. Both localities yield a characteristic component (ChRM) with unblocking temperatures from 650 to 680 °C. After structural correction for bedding tilt, all inclinations of ChRM are negative, consistent with magnetization during a reversed-polarity interval in the northern hemisphere. Site-mean ChRM directions show consistent inclinations but distinct stratigraphic groupings of declinations. Inclination-only statistics indicate that the ChRM passes a tilt test within the Sylvester allochthon and regionally between the two localities. The ChRM was apparently acquired prior to structural imbrication within the Sylvester section and regional differential tilting. We interpret the ChRM to be a primary magnetization acquired at or soon after deposition during the Permo-Carboniferous reversed-polarity superchron. The mean ChRM inclination of −16.7° ± 6.0° from the Sylvester allochthon indicates a paleo-latitude of 8.8° ± 3.4°N, which is corroborated by a paleolatitude of 1.9° ± 1.5°N from the Sliding Mountain locality. When compared with expected Pennsylvanian–Permian paleolatitudes, a net poleward translation of 20.3 ± 3.7° is implied for at least the sampled lithotectonic component of the Sylvester allochthon.

Upper Pennsylvanian and Lower Permian Marine Condensed Sections of the Eastern Shelf of the Midland Basin

Upper Pennsylvanian and Lower Permian Marine Condensed Sections of the Eastern Shelf of the Midland Basin

The Occurrence of Freshwater Limestones in the Upper Pennsylvanian and Lower Permian of the Northern Appalachian Basin: ABSTRACT

Freshwater limestones comprise a significant portion of the Upper Pennsylvanian and Lower Permian strata of the northern Appalachian basin. In some areas, the Monogahela Group consists of as much as 50% freshwater limestones. These limestones are clayey to silty, iron-bearing, sparsely fossiliferous, micritic, and thinly bedded or nodular and are presumed to be lacustrine in origin. They are part of a recurring sequence of beds that include coal, sandstone, shale/clay, and marine limestone. The initial goals of this study are to develop a stratigraphic framework for these freshwater limestones and to determine, their lateral continuity, thickness variability, and relation to other beds in this section, in particular the coals, on a regional scale. The Pittsburgh coal and Ames limestone are very persistent regionally and are used as a datum. Regional correlations show that possibly 20 freshwater limestone beds are persistent and widespread; some cover at least 5,000 mi{sup 2} in eastern Ohio, western Pennsylvania, northern West Virginia and western Maryland. Cross sections and fence diagrams constructed from drill logs and measured sections indicate that the thickness of these limestone beds varies laterally and between beds, ranging from less than 1 to 150 ft thick. Correlations also show stratigraphic and paleogeographicmore » relationships between the coals and freshwater limestones. Many of the limestones underlie coal beds, directly in some places. The coals and limestones are better developed in the northern part of the Appalachian basin. These associations may hold significant clues to the depositional and the paleoclimatic setting of the freshwater limestones and the coals.« less