413 results on '"ORDOVICIAN"'
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52. Growth characteristics in co-occurring Upper Ordovician species of the tabulate Catenipora from southern Manitoba, Canada.
- Author
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BAE, BOO‐YOUNG, ELIAS, ROBERT J., and LEE, DONG‐JIN
- Subjects
- *
COLONIZATION , *RIVERS - Abstract
Four species of the tabulate coral Catenipora are present in the Selkirk Member of the Red River Formation at Garson, Manitoba. They provide an opportunity to compare the growth characteristics of multiple, co-occurring species that produced cateniform coralla. Corallite increase, cyclomorphism and other growth features show high variability within and/or among the species. A total of five types of lateral increase and two types of axial increase are recognized. Lateral increase accounts for over 80% of all occurrences of corallite increase in each species, with the four species differing significantly in the relative frequency of the various types of lateral increase. The type of axial increase, megacorallites and agglutinated patches of corallites that developed from normal, undamaged corallites in C. foerstei are species specific. In all species, cyclic fluctuations in the tabularial area of corallites are considered to be annual, and the variable growth rates within colonies and species are attributed to differences in astogenetic stages or environmental conditions. Average annual vertical growth was positively correlated with average tabularial area in C. foerstei, C. cf. robusta and C. rubra. Catenipora cf . agglomeratiformis, however, which had the lowest average tabularial area and greatest sensitivity to sediment influx, had a high average growth rate comparable to that of C. rubra, which had the largest average tabularial area. The formation of ranks or lacunae by certain types of lateral increase seems to have been the most effective strategy for maintaining and/or expanding the colony growth surface in all four species, and was most common in C. cf . agglomeratiformis. A reptant growth pattern, characterized by creeping ranks, permitted effective recovery of damaged parts as well as quick formation of new ranks or lacunae. The growth surface of these species was situated near the sediment-water interface. □ Growth characteristics, intraspecific variation, interspecific variation, palaeobiology, tabulate corals. [ABSTRACT FROM AUTHOR] more...
- Published
- 2013
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53. Geochemistry of late Ordovician Viola limestone, Oklahoma...
- Author
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Gao, G. and Dworkin, S.I.
- Subjects
- *
LIMESTONE - Abstract
Presents information which deals with Ordovician (Caradocian) age Viola limestones from the Arbuckle Mountains, Oklahama. Indication of the suffering of limestone; Variations in mineralogy and isotope compositions. more...
- Published
- 1996
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54. Dolomite-rock textures and secondary porosity development in Ellenburger Group carbonates (Lower Ordovician), west Texas and southeastern New Mexico.
- Author
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Amthor, Joachim E. and Friedman, Gerald M.
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ROCK texture , *POROSITY - Abstract
Pervasive early- to late-stage dolomitization of Lower Ordovician Ellenburger Group carbonates in the deep Permian Basin of west Texas and southeastern New Mexico is recorded in core samples having present-day burial depths of 1·5-7·0 km. Seven dolomite-rock textures are recognized and classified according to crystal-size distribution and crystal-boundary shape. Unimodal and polymodal planar-s (subhedral) mosaic dolomite is the most widespread type, and it replaced allochems and matrix or occurs as void-filling cement. Planar-e (euhedral) dolomite crystals line pore spaces and/or fractures, or form mosaics of medium to coarse euhedral crystals. This kind of occurrence relates to significant intercrystalline porosity. Non-planar-a (anhedral) dolomite replaced a precursor limestone/dolostone only in zones that are characterized by original high porosity and permeability. Non-planar dolomite cement (saddle dolomite) is the latest generation and is responsible for occlusion of fractures and pore space. Dolomitization is closely associated with the development of secondary porosity; dolomitization pre- and post-dates dissolution and corrosion and no secondary porosity generation is present in the associated limestones. The most common porosity types are non-fabric selective moldic and vuggy porosity and intercrystalline porosity. Up to 12% effective porosity is recorded in the deep (6477m) Delaware basin. These porous zones are characterized by late-digenetic coarse-crystalline dolomite, whereas the non-porous intervals are composed of dense mosaics of early-digenetic dolomites. The distribution of dolomite rock textures indicates that porous zones were preserved as limestone until late in the digenetic history, and were then subjected to late-stage dolomitization in a deep burial environment, resulting in coarse-crystalline porous dolomites. In addition to karst horizons at the top of the Ellenburger Group, exploration for Ellenburger Group reservoirs... [ABSTRACT FROM AUTHOR] more...
- Published
- 1991
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55. Sedimentology and evolution of the Martinsburg Formation (Upper Ordovician) fine-grained turbidite depositional system, central Appalachians.
- Author
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Lash, Gary G.
- Subjects
- *
SEDIMENTOLOGY , *EVOLUTIONARY theories ,MARTINSBURG Formation (Pa.) - Abstract
The Upper Ordovician Martinsburg Formation of eastern Pennsylvania consists of mudstone, siltstone, and sandstone turbidites that accumulated in a tectonically active foreland basin. The mudstone-rich Bushkill Member, the stratigraphically lowest unit of the Martinsburg in this area, grades upward into approximately equal proportions of mudstone, siltstone, and sandstone of the Ramseyburg Member. Many of the turbidites of these units are arranged in small-scale (1-9 m) fining-upward sequences that are interpreted as reflecting the influence of external or allocyclic controls such as variations in the local rate of sea-level rise and/or variations in the intensity of tectonic activity in shelf/nearshore or hinterland areas rather than more commonly cited autocyclic mechanisms. The thick (approximately 2000 m) Bushkill-Ramseyburg coarsening-upward sequence records progradation of a muddy turbidite depositional system along the axis of the foreland basin. Although this sequence accumulated during a Caradocian eustatic rise in sea-level, sedimentation rates landward of the shoreline were apparently great enough to allow for long-term seaward progradation of the shelf source. The paucity of depositional lobe-like facies (coarsening-upward sequences) in the Bushkill Member allows for tentative comparison of the progradational Bushkill-Ramseyburg system with the active fan lobe of the Mississippi Fan. Progradation of the Bushkill-Ramseyburg system ceased abruptly when mudstone turbidites and laminated black shale of the upper unit of the Martinsburg, the Pen Argyl Member, accumulated. The great thickness of some mudstone turbidite beds of the Pen Argyl Member is interpreted to record topographic confinement of the central Appalachian foreland basin, which may have helped to preclude continued progradation of the Bushkill-Ramseyburg turbidite system. [ABSTRACT FROM AUTHOR] more...
- Published
- 1988
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56. Rhythms in deep sea, fine-grained turbidite and debris-flow sequences, Middle Ordovician, eastern Tennessee.
- Author
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Shanmugam, Ganapathy
- Subjects
- *
TURBIDITES , *DEBRIS avalanches , *SEDIMENTATION & deposition , *DIAGENESIS , *OCEAN , *GEOLOGICAL basins - Abstract
Studies the rhythms in deep sea, fine-grained turbidite and debris-flow sequences in the Middle Ordovician, eastern Tennessee. Depositional cycles; Diagenetic changes; Progradation of a deep-sea fan system; Appearance of minor lobe cycles over the non-cyclic basin plain sequence. more...
- Published
- 1980
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57. Three-dimensional architecture of a coalesced, collapsed-paleocave system in the Lower Ordovician Ellenburger Group, central Texas.
- Author
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Loucks, Robert G., Mescher, Paul K., and McMechan, George A.
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GROUND penetrating radar ,OIL wells ,MINE roof control - Abstract
The three-dimensional, interwell-scale architecture of a Lower Ordovician Ellenburger coalesced, collapsed-paleocave system was constructed through the integration of ground-penetrating radar (GPR), shallow-core, and outcrop data. The data were collected near Marble Falls in central Texas over an area (∼800 x 1000 m [∼2600 x 3300 ft]) that could cover several oil-well locations (∼160 ac; 0.65 km²) typical of a region such as west Texas. Integration of core-based facies descriptions with GPR-reflection response identified several paleocave facies that can be recognized and mapped with GPR data alone: (1) continuous reflections image the undisturbed strata, (2) relatively continuous reflections (over tens of meters) characterized by faults and folds image the disturbed strata, and (3) chaotic reflections having little to no perceptible continuity image heterogeneous, cave-related brecciated facies recognized in core that cannot be individually resolved with the GPR data. These latter facies include the highly disturbed strata, coarse-clast chaotic breccia, fine-clast chaotic breccia, and sediment fill. The three-dimensional architecture of the coalesced, collapsed- paleocave system based on core and GPR data indicates that there are trends of brecciated bodies that are as much as 350 m (1100 ft) wide, greater than 1000 m (3300 ft) long, and tens of meters high. These brecciated bodies are coalesced, collapsed paleocaves. Between the brecciated bodies are areas of disturbed and undisturbed host rock that are jointly as much as 200 m (660 ft) wide. As a cave system is buried, many structural features form by mechanical compaction. These features include folds, sags, and faults. The folds and sags measure from a few meters to several hundred meters wide. The collapse-related faults are numerous and can have several meters of displacement. Most are normal faults, but reverse faults also occur. [ABSTRACT FROM AUTHOR] more...
- Published
- 2004
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58. CHANGES IN COLONIAL DEVELOPMENT, INTRASPECIFIC HETEROCHRONY, MORPHOLOGICAL INTEGRATION, AND CHARACTER HERITABILITIES IN TWO POPULATIONS OF THE BRYOZOAN SPECIES BATOSTOMA JAMESI FROM THE KOPE FORMATION (UPPER ORDOVICIAN, CINCINNATION).
- Author
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Pachut, Joseph F. and Fisherkeller, Margaret M.
- Subjects
- *
FOSSIL bryozoa , *ANIMAL morphology - Abstract
Examines the paleoenvironmental settings of the bryozoan Batostoma jamesi in Cincinnati, Ohio. Description of stenolaemate Bryozoans; Patterns of morphological integration of the fossil; Characterization of the colony growth of acanthostyles and interzooecial walls of fossils. more...
- Published
- 2002
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59. CUPULOCRINUS ANGUSTATUS (MEEK AND WORTHEN, 1870), A CLADID CRINOID FROM THE UPPER ORDOVICIAN...
- Author
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Brower, James C.
- Subjects
- *
FOSSIL crinoidea ,MAQUOKETA Group - Abstract
Analyzes Cupulocrinus angustatus, a common and widely distributed crinoid in the Maquoketa Formation of the northern midcontinent of the United States. Indication of cluster significance tests; Correlation coefficients for the number of brachs; Differences in basic geometry and developmental constraints. more...
- Published
- 2002
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60. COMPARISON OF FLATTENED BLASTOZOAN ECHINODERMS: INSIGHTS FROM THE NEW EARLY ORDOVICIAN EOCRINOID....
- Author
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Sumrall, Colin D., Sprinkle, James, and Guensburg, Thomas E.
- Subjects
- *
ECHINODERMATA , *SPECIES - Abstract
Focuses on the comparison between flattened, eocrinoid-grade, blastozoan echinoderm and Haimacystis rozhnovi new genus and species in Utah. Difference of Haimacystis from echinoderm; Presentation of the morphology and plane of thecal flattening of flattened blastozoans; Similarity between the morphology of rhipidocystids and Haimacystis. more...
- Published
- 2001
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61. Distal sedimentation in a peripheral foreland basin: Ordovician black shales and associated...
- Author
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Lehmann, David and Brett, Carlton E.
- Subjects
- *
GEOLOGY - Abstract
Presents a geological survey analysis of black shale found in the western Taconic foreland, New York State and Ontario. Geological and stratigraphic setting of Taconic orogeny; Migration of basin axis. more...
- Published
- 1995
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62. ADDITIONAL INFORMATION ON LOWEST ORDOVICIAN TRILOBITES FROM THE UPPERMOST DEADWOOD FORMATION....
- Author
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Stitt, James H.
- Subjects
- *
TRILOBITES , *FOSSIL brachiopoda , *STRATIGRAPHIC paleontology - Abstract
Reports trilobites and brachiopods from the uppermost deadwood formation in South Dakota and Wyoming. Identification of the lowest Ordovician trilobites; Occurrence of the species in the Missisquoia Zone; Similarities of the trilobites and brachiopods from coeval strata in the Rabbitkettle Formation in Canada. more...
- Published
- 2000
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63. Sea-level forcing of carbon isotope excursions in epeiric seas: implications for chemostratigraphy.
- Author
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Fanton, K. C. and Holmden, C.
- Subjects
- *
PHYSIOLOGICAL effects of water levels , *ORDOVICIAN stratigraphic geology , *ABSOLUTE sea level change , *OCEANOGRAPHIC research , *WATER masses , *FLOODS , *CARBON isotopes - Abstract
Five new δ13C excursions are reported from the Upper Ordovician Galena Group of Iowa. The δ13Ccarb and δ13Corg trends are compared to sea-level trends based on conventional sedimentological and novel chemostratigraphic (εNd) methods. It is found that rising δ13C values occur during rising sea level, peak-magnitude δ13C values are coincident with inferred peak flooding, and declining δ13C values occur with declining sea levels. The relationship to sea level is explained by a simple model of episodic flooding of the Galena platform by cool, oxygen-depleted, nutrient-rich, bottom waters originating from the Sebree Trough, which was itself connected to the nearby Iapetus Ocean. Flooding of the inner Galena shelf during sea-level transgressions caused local changes in the carbon isotope balance of inner shelf waters due to (1) locally increased primary productivity and organic carbon burial, (2) locally increased exchange of 13C-enriched dissolved inorganic carbon (DIC) with surrounding epeiric sea water masses and the surface ocean, and (3) locally decreased 12C-weathering fluxes from the Transcontinental Arch. A sea-level driver of local C-cycle perturbations complicates the use of carbon isotopes as a chemostratigraphic tool because local and eustatic controls on sea level may combine to create different secular records of relative sea-level change in stratigraphically equivalent deposits of epeiric seas. [ABSTRACT FROM AUTHOR] more...
- Published
- 2007
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64. Suture modification by pectinirhomb growth in Lepadocystis decorus, a new species of....
- Author
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Sumrall, Colin D. and Carlson, David T.
- Subjects
- *
FOSSIL echinodermata , *ORDOVICIAN paleontology , *ANIMAL classification - Abstract
Examines a species of Late Ordovician callocystitid rhombiferan, Lepadocystis decorus, from the Brainard Shale of north-central Illinois. Account on the characteristics of the species; Comparison between the functionality of an open and a closed plate circlets; Need for maturity of plate circlets when used for taxonomy. more...
- Published
- 2000
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65. Paleobiologic and taphonomic aspects of the `granulosa' Trilobite cluster, Kope Formation (Upper...
- Author
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Hughes, Nigel C. and Cooper, Dan L.
- Subjects
- *
TRILOBITES , *ORDOVICIAN stratigraphic geology - Abstract
Focuses on the `granulosa' trilobite cluster from the Upper Ordovician Kope Formation in Cincinnati, Ohio. Variety of flexure postures; Display of internal pyritization; Bedding attitudes; Pattern of grading and minor lamination of sediment beds; Size range and clustering behavior. more...
- Published
- 1999
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66. Ordovician/Cambrian strata of Central Tennessee--a new play in a mature area.
- Author
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Tedesco, Steven A.
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PETROLEUM prospecting - Abstract
Focuses on the discovery of a petroleum basin in central Tennessee that was formed during the Cambrian and Ordovician period. Geology of the area; Presence of clastic material for deposition in adjacent basin; Indication of a Upper Cambrian strata pinching along the Nashville dome. more...
- Published
- 1996
67. UPPERORDOVICIANBRYOZOA FROM THEMONTAGNE DENOIRE, SOUTHERNFRANCE.
- Author
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Andrej Ernst and Marcus Key
- Subjects
MOUNTAINS - Abstract
This study focuses on bryozoans from the Upper Ordovician rocks of the Montagne de Noire, southern France and additional material from contemporary rocks of the Carnic Alps. Based on museum collections, 68 bryozoan species were identified with 18 species being new: Ceramoporella grandissp. nov., Crassalina fungiformesp. nov., Lichenalia nodatasp. nov., Atactoporella magnoporasp. nov., Dekayia buttlerisp. nov., Stigmatella carnicasp. nov., Trematopora gracilesp. nov., Bythopora tenuissp. nov., Nicholsonella divulgatasp. nov., N. rectasp. nov., Matsutrypa elegantulasp. nov., M. rogerisp. nov., Nematotrypa punctatasp. nov., Stellatodictya valentinaesp. nov., Ptilodictya feistisp. nov., Pseudohornera dmitriisp. nov., Ralfinella elegantulasp. nov. and Moorephylloporina contiisp. nov. Trepostomes are the most abundant and diverse group with 40 of the total 68 species, but cyclostomes, cystoporates and cryptostomes are also present. The age of the fauna is Caradoc to Ashgill, according to the distribution of species and genera. The fauna has palaeogeographical connections to the Upper Ordovician of Wales, Estonia and North America. [ABSTRACT FROM AUTHOR] more...
- Published
- 2007
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68. SYSTEMATICS OF THE ORDOVICIAN TRILOBITES ISCHYROTOMA AND DIMEROPYGIELLA, WITH SPECIES FROM THE....
- Author
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Adrain, Jonathan M., Westrop, Stephen R., Landing, Ed, and Fortey, Richard A.
- Subjects
- *
TRILOBITES , *SPECIES - Abstract
Investigates the systematics of the Ordovician trilobites Ischyrotoma and Dimeropygiella with species from the type Ibexian area in western Utah. Reinvestigation of faunas; Reassessment of the dimeropygid genera Ischyrotoma and Dimeropygiella; Availability of morphological information for most part of the exoskeleton. more...
- Published
- 2001
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69. Detrital zircon ages from Proterozoic, Paleozoic, and Cretaceous clastic strata in southern New Mexico, U.S.A.
- Author
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Amato, Jeffrey M.
- Subjects
ZIRCON ,PROVENANCE (Geology) ,SEDIMENTARY rocks ,CLASTIC rocks ,AGE groups ,SANDSTONE - Abstract
U-Pb ages were obtained from detrital zircon grains from Proterozoic, Ordovician, Devonian, Pennsylvanian, and Cretaceous clastic sedimentary rocks in southern New Mexico and are compared to previously published data from Proterozoic, Cambrian, Permian, and other Cretaceous strata. This provides the first combined data set from most of the known pre-Cenozoic clastic formations in southern New Mexico, albeit in a reconnaissance fashion. Proterozoic quartzite, conglomerate, and lithic sandstone yield mostly 1.65-Ga zircon ages that were derived from the Mazatzal province, with minor 1.8-1.7-Ga zircon ages from the Yavapai province. The Cambrian-Ordovician Bliss Sandstone is dominated by Grenville-age grains and Cambrian grains inferred to be locally derived. Newly acquired ages from the Ordovician Cable Canyon Sandstone are dominated by 1.7-1.6-Ga Mazatzal province zircon grains, whereas new data from the Devonian Percha Shale indicate subequal contributions from 1.7-1.6-Ga and ~1.4-Ga sources, along with 1.8-1.7- Ga zircon ages. Both of these formations likely had mainly distal sources as the Precambrian basement in the region was largely buried by older Paleozoic strata. New data from a sandstone in the Pennsylvanian La Tuna Formation show mostly Yavapai grains and minor Paleozoic zircon grains, including Cambrian zircon grains sourced from the nearby Florida Mountains landmass postulated to have been exposed during Pennsylvanian time. The Permian 'Abo tongue'/Robledo Mountains Formation of the Hueco Group has mostly Neoproterozoic and Grenville-age zircon grains and was derived from Ancestral Rocky Mountain uplifts that did not have a large ~1.4-Ga component. The Aptian Hell-to-Finish Formation of the Bisbee Group has mostly Yavapai-aged zircon grains in the pre-1000-Ma age group, but younger Albian- and Campanian-age sandstones have mostly Grenville-age zircon grains. New data from the Albian Beartooth Quartzite indicate syndepositional volcanic grains at 102 Ma and support correlations with the Mojado Formation rather than the younger Dakota Sandstone. Archean zircon ages are rare overall in all of the strata in southern New Mexico, but zircon grains with ages of ~2.74 Ga are most abundant. These grains could have been derived from basement rocks in the Wyoming or Superior provinces, or recycled from sediment originally derived from those sources. [ABSTRACT FROM AUTHOR] more...
- Published
- 2019
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70. Distinguishing fault reactivation from flexural deformation in the distal stratigraphy of the Peripheral Blountian Foreland Basin, southern Appalachians, USA.
- Author
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Bayona, Germán and Thomas, William A.
- Subjects
GEOLOGIC faults ,EVENT stratigraphy ,GEOLOGICAL basins - Abstract
Reactivation of intraplate structures and weak zones within the foreland lithosphere disrupt the modelled geometry and pattern of migration of the flexural wave in foreland basins. In the southern Appalachians (USA), the Middle Ordovician unconformity, irregular Middle Ordovician distal foreland deposition and backstepping of Middle–lower Upper Ordovician carbonate strata have been related to migration of the flexural wave. However, integration of stratigraphy, tectonic subsidence history and composition of palinspastically restored distal foreland strata, using a map of subsurface basement structures as reference, allows us to distinguish an early event of inversion from two events of flexural migration. Sections restoring at very short distances outside the boundaries of a former basement graben have the youngest passive-margin strata preserved beneath Middle Ordovician (∼466 Ma) peritidal to deep lagoonal carbonates with gravel-size chert clasts. In contrast, sections restoring inside the graben record >470 m of truncation of pre-Middle Ordovician passive-margin strata, late onset of deposition (∼456 Ma), and subaerial features in carbonate and siliciclastic strata. The lacuna geometry and early patterns of distal foreland uplift and carbonate deposition indicate that inversion of a basement graben in response to Middle Ordovician convergence, rather than a migrating or semi-fixed forebulge, was the primary control on the early evolution of the distal foreland. Drowning of the carbonate platform in more proximal settings, northeastward onset of deposition on upthrown blocks, and thick accumulation of carbonates in downthrown blocks record northwestward and northeastward flexural wave migration at the Middle–Late Ordovician boundary. In early Late Ordovician, the overall shoaling of carbonate and siliciclastic depocentres and the rise of tectonic subsidence curves indicate hinterlandward migration of flexural uplift. Both events of flexural migration were accompanied by influx of volcanic ash and synorogenic sediments. [ABSTRACT FROM AUTHOR] more...
- Published
- 2003
- Full Text
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71. Missouri fossils.
- Author
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Stinchcomb, Bruce L.
- Subjects
FOSSILS ,GEOLOGICAL specimens - Abstract
Focuses on the fossils from rock strata in Missouri. Objects that are found in Precambrian rocks; Information on Paleozoic invertebrate fossils; Location of Cretaceous rocks and fossils.
- Published
- 1997
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72. Vermont's geologic history as told by its fossils.
- Author
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Schuele, Ethel M.
- Subjects
FOSSILS - Abstract
Describes Vermont's geology using fossil evidences. Clues from Cambrian fossils; Locations of Ordovician fossils; Devorian Silurian fossils; Tertiary and Pleistocene fossils.
- Published
- 1996
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73. Bedrock geology of the Paleozoic rocks of western New Haven quadrangle, Connecticut.
- Author
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Deasy, Ryan T., Wathen, Bryan, and Wintsch, Robert P.
- Subjects
BEDROCK ,PALEOZOIC stratigraphic geology ,PETROLOGY - Abstract
The Paleozoic rocks underlying the western third of the New Haven Quadrangle, Connecticut, are mapped at a scale of 1:24,000. This area of ∼41.5 km2, previously mapped only in reconnaissance, contains polymetamorphic argillites and mafic rocks. The northern portion of the mapped area contains the pelitic Wepawaug schist, whereas the southern portion is underlain by the pelitic Savin Schist. Between them lies the Maltby Lakes Complex (MLC) that contains newly identified fault slivers of variably metamorphosed mafic phyllites and amphibolites. Metamorphic foliations in both the MLC and the Savin Schist are truncated by a swarm of basalt dikes: the Allingtown porphyry, which is itself commonly schistose and locally mylonitic. Previous interpretations held that these rocks constitute a conformable, northwest-topping stratigraphic sequence. In contrast, we propose that Ordovician(?) oceanic rocks of the MLC were variably metamorphosed and faulted against the Ordovician(?) Savin Schist. These were intruded by a swarm of stitching Allingtown dikes. This package of rocks was then faulted against Siluro-Devonian(?) Wepawaug forearc sediments. Existing thermochronology indicates a Devonian age of the subsequent regional metamorphism, overprinted by low-grade Permian fabrics associated with dextral transpression and final terrane assembly. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2017
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74. Phosphate mineralogy and equilibria in two Kentucky alfisols derivedfrom ordovician limestones
- Author
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Karathanasis, A. D.
- Subjects
SOIL science ,MINERALOGY ,PHOSPHATES - Published
- 1991
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75. Impact of Lake Michigan Allocations on the Cambrian-Ordovician Aquifer System
- Author
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Visocky, Adrian P.
- Subjects
- ILLINOIS, LAKE Michigan, UNITED States
- Published
- 1982
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76. Spatial variability of produced-water quality and alternative-source water analysis applied to the Permian Basin, USA.
- Author
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Chaudhary, Binod K., Sabie, Robert, Engle, Mark A., Xu, Pei, Willman, Spencer, and Carroll, Kenneth C.
- Subjects
WATER quality ,OIL field brines ,WATER analysis ,ARID regions ,CONTOURS (Cartography) ,GEOLOGICAL surveys ,GRAYWATER (Domestic wastewater) - Abstract
Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) more...
- Published
- 2019
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77. Lithistid sponge-microbial reefs, Nevada, USA: Filling the late Cambrian 'reef gap'.
- Author
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Lee, Jeong-Hyun, Dattilo, Benjamin F., Mrozek, Stephanie, Miller, James F., and Riding, Robert
- Subjects
- *
REEFS , *REGIONAL disparities - Abstract
Abstract Cambrian–Ordovician sponge-microbial mounds in the Great Basin of the western USA reveal reef structure and composition immediately prior to the Great Ordovician Biodiversification Event (GOBE). Here we describe lithistid sponge-microbial reefs from the upper Cambrian (Furongian, Stage 10) strata of the Arrow Canyon Range, Nevada. The reefs are mound-like structures up to 1 to 2 m high and a few meters wide that consist of an unidentified thin-walled, bowl-shaped anthaspidellid sponge, columnar microstromatolite fabric, and the calcified microbe Angusticellularia. The reefs formed in low-energy, subtidal environments in which lime mud filled spongocoels and inter-reef spaces around undisturbed, in place, thin-walled sponges. The reefs colonized stable substrates provided by oolitic and bioclastic grainstone shoals. The mutually attached lithistid sponges form the main framework of the reefs. These thin-walled and bowl-shaped lithistids most likely were adapted to low-energy environments. Spaces beneath the overhanging sponge walls were filled by microbial carbonates. These include pendent micro-dendritic Angusticellularia attached to dermal sponge surfaces and upward-growing masses of microstromatolites. After death the lithistid spongocoels were mainly filled by micritic sediment that hosted soft-bodied burrowing organisms and keratose-like sponges. These lithistid sponge-microbial reefs, together with an earlier example of late Cambrian (Paibian) dendrolite-lithistid reefs in the same area, characterize skeletal-microbial reefs immediately prior to the GOBE. Highlights • Lithistid sponges formed reef frameworks in the upper Cambrian of Nevada, USA. • Reefs dominated by thin-walled sponges developed under low-energy conditions. • Spaces beneath the overhanging sponge walls were filled by microbial carbonates. • In the Great Basin, gradual reef transition occurred across Cambro-Ordovician boundary. • Regional disparities in reef evolution pattern during early stage of the GOBE are recognized. [ABSTRACT FROM AUTHOR] more...
- Published
- 2019
- Full Text
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78. Analysis of sample-level properties along a paleoenvironmental gradient: The behavior of evenness as a function of sample size
- Author
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Bulinski, Katherine V.
- Subjects
- *
BIODIVERSITY , *GEOLOGISTS , *PALEONTOLOGISTS - Abstract
Abstract: The assessment of fossil biodiversity is influenced by a range of sampling effects such as sample size, evenness and lithological character. Many paleontologists have worked to understand and mitigate for such biasing effects, generating standardized assessments of local, regional and global biodiversity. However, when assessing biodiversity among individual communities with small sample sizes, such as those from lithified Paleozoic samples, it is important to understand how these properties relate to one another qualitatively and quantitatively. Here, the properties of richness and evenness were investigated at the sample level along an ecological gradient within a stratigraphically and geographically constrained interval, the Fulton submember of the Kope Formation (Upper Ordovician) of Kentucky and Ohio. Using a replicate subsampling procedure analogous to rarefaction, evenness values were generated using four metrics (J, PIE, E ss and E ssmin). Simulations using real and simulated data revealed that the PIE metric generates the most stable assessments of evenness at very small sample sizes, and relative evenness can be assessed at any sample size, provided that replicate subsampling is performed. Comparisons of richness, evenness and lithology revealed no directional trend along the ecological gradient, but two distinct groups of samples were identified by differences in evenness as well as the number of sampled individuals. Such differences in abundance structure influence perceptions of biodiversity when samples from low-evenness and high-evenness assemblages are aggregated. Increasing the sampling intensity in low-evenness communities may help to mitigate for these differences and more thoroughly capture the richness contained within small samples. [Copyright &y& Elsevier] more...
- Published
- 2007
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79. Multimethod (K–Ar, Rb–Sr, Sm–Nd) dating of bentonite minerals from the eastern United States.
- Author
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Toulkeridis, Theofilos, Clauer, Norbert, Chaudhuri, Sam, and Goldstein, Steve L.
- Subjects
BIOTITE ,BENTONITE ,GEOCHRONOMETRY - Abstract
Isotopic determinations (K–Ar, Rb–Sr and Sm–Nd), and trace and rare-earth elemental analyses were made on a few biotite and clay fractions of Palaeozoic bentonite units from the eastern United States. The clay fractions were gently leached with dilute hydrochloric acid to study separately the acid-soluble minerals intimately associated with the extracted clay particles. The data highlight interesting potentials for this integrated approach to decipher complex tectonothermal evolutions of sedimentary basins. Biotite K–Ar ages are consistent with a Middle Ordovician stratigraphic age for the bentonite units with a mean age of 459±10 Ma. The clay residues give a Sm–Nd isochron age of 397±44 Ma, indicative of their crystallization during Acadian tectonothermal activity at about 200 °C. The clay leachates, which are considered to represent mineral phases different from clay material, yield a distinct Sm–Nd isochron age of 285±18 Ma which is indistinguishable from K–Ar ages obtained previously on the clays, suggesting a thermally induced diffusion of radiogenic
40 Ar from clay particles during Alleghenian–Ouachita orogenic activity. The Rb–Sr system of the clay material seems to have been variably disturbed, except for the sample taken near the Allegheny Front for which an age of 179±4 Ma suggests a further localized activity of the thrust system at about 130–150 °C. Clearly the limited number of samples does not allow us to perfectly constrain an evolutionary model. However, analysis of the soluble minerals for their contents in metal and rare-earth elements suggests that metal-carrying fluids migrated during the Alleghenian–Ouachita orogenic activity in the eastern North American continent. Consequently, they could have contributed to the concentration of ore deposits in the region, but this possibility needs to be tested with a larger data base. [ABSTRACT FROM AUTHOR] more...- Published
- 1998
- Full Text
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80. The life and scientific work of William R. Evitt (1923-2009).
- Author
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Riding, James B. and Lucas-Clark, Joyce
- Subjects
DINOFLAGELLATES ,DINOFLAGELLATE cysts ,TRILOBITES ,CYSTS (Pathology) ,PALEONTOLOGY ,ACRITARCHS - Abstract
Occasionally (and fortunately), circumstances and timing combine to allow an individual, almost singlehandedly, to generate a paradigm shift in his or her chosen field of inquiry. William R. ('Bill') Evitt (1923-2009) was such a person. During his career as a palaeontologist, Bill Evitt made lasting and profound contributions to the study of both dinoflagellates and trilobites. He had a distinguished, long and varied career, researching first trilobites and techniques in palaeontology before moving on to marine palynomorphs. Bill is undoubtedly best known for his work on dinoflagellates, especially their resting cysts. He worked at three major US universities and spent a highly significant period in the oil industry. Bill's early profound interest in the natural sciences was actively encouraged both by his parents and at school. His alma mater was Johns Hopkins University where, commencing in 1940, he studied chemistry and geology as an undergraduate. He quickly developed a strong vocation in the earth sciences, and became fascinated by the fossiliferous Lower Palaeozoic strata of the northwestern United States. Bill commenced a PhD project on silicified Middle Ordovician trilobites from Virginia in 1943. His doctoral research was interrupted by military service during World War II; Bill served as an aerial photograph interpreter in China in 1944 and 1945, and received the Bronze Star for his excellent work. Upon demobilisation from the US Army Air Force, he resumed work on his PhD and was given significant teaching duties at Johns Hopkins, which he thoroughly enjoyed. He accepted his first professional position, as an instructor in sedimentary geology, at the University of Rochester in late 1948. Here Bill supervised his first two graduate students, and shared a great cameraderie with a highly motivated student body which largely comprised World War II veterans. At Rochester, Bill continued his trilobite research, and was the editor of the Journal of Paleontology between 1953 and 1956. Seeking a new challenge, he joined the Carter Oil Company in Tulsa, Oklahoma, during 1956. This brought about an irrevocable realignment of his research interests from trilobites to marine palynology. He undertook basic research on aquatic palynomorphs in a very well-resourced laboratory under the direction of one of his most influential mentors, William S. 'Bill' Hoffmeister. Bill Evitt visited the influential European palynologists Georges Deflandre and Alfred Eisenack during late 1959 and, while in Tulsa, first developed several groundbreaking hypotheses. He soon realised that the distinctive morphology of certain fossil dinoflagellates, notably the archaeopyle, meant that they represent the resting cyst stage of the life cycle. The archaeopyle clearly allows the excystment of the cell contents, and comprises one or more plate areas. Bill also concluded that spine-bearing palynomorphs, then called hystrichospheres, could be divided into two groups. The largely Palaeozoic spine-bearing palynomorphs are of uncertain biological affinity, and these were termed acritarchs. Moreover, he determined that unequivocal dinoflagellate cysts are all Mesozoic or younger, and that the fossil record of dinoflagellates is highly selective. Bill was always an academic at heart and he joined Stanford University in 1962, where he remained until retiring in 1988. Bill enjoyed getting back into teaching after his six years in industry. During his 26-year tenure at Stanford, Bill continued to revolutionise our understanding of dinoflagellate cysts. He produced many highly influential papers and two major textbooks. The highlights include defining the acritarchs and comprehensively documenting the archaeopyle, together with highly detailed work on the morphology of Nannoceratopsis and Palaeoperidinium pyrophorum using the scanning electron microscope. Bill supervised 11 graduate students while at Stanford University. He organised the Penrose Conference on Modern and Fossil Dinoflagellates in 1978, which was so successful that similar meetings have been held about every four years since that inaugural symposium. Bill also taught many short courses on dinoflagellate cysts aimed at the professional community. Unlike many eminent geologists, Bill actually retired from actively working in the earth sciences. His full retirement was in 1988; after this he worked on only a small number of dinoflagellate cyst projects, including an extensive paper on the genus Palaeoperidinium. [ABSTRACT FROM AUTHOR] more...
- Published
- 2016
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81. Comparison between cryptospores from the Cambrian Log Cabin Member, Pioche Shale, Nevada, USA and similar specimens from the Cambrian Kaili Formation, Guizhou, China.
- Author
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Yin, LeiMing, Zhao, YuanLong, Bian, LiZeng, and Peng, Jin
- Subjects
COMPARATIVE studies ,CAMBRIAN Period ,SHALE gas reservoirs ,LOG cabins - Abstract
Abundant cryptospore-like microfossils have been collected from a sample of the 'Middle' Cambrian Log Cabin Member of the Pioche Shale in eastern Nevada, USA. Compared with organic-walled microfossils obtained from the Cambrian Kaili Formation in eastern Guizhou Province, China, some specimens of leiosphers may be inferred to be similar cryptospore-like microfossils. The new fossil record would be the oldest known specimens of cryptospore-like microfossils during the Cambrian Period. [ABSTRACT FROM AUTHOR] more...
- Published
- 2013
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82. Rings without a lord? Enigmatic fossils from the lower Palaeozoic of Bohemia and the Carnic Alps.
- Author
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Ferretti, Annalisa, Cardini, Andrea, Crampton, James S., Serpagli, Enrico, Sheets, H. David, and Štorch, Petr
- Subjects
- *
FOSSIL animals , *SILURIAN Period - Abstract
Fossilized ring-like structures with enigmatic function and taxonomic affiliation were recovered for the first time from the Upper Ordovician of the Carnic Alps and the Silurian of Bohemia. These rings, already mentioned as minor constituents in previous conodont studies (e.g. Webers 1966, p. 1; Bischoff 1973, p. 147), were reported from the Palaeozoic of several regions in Europe and North America. Originally considered as inwardly accreted adhering discs of a benthic hyolithelminth worm with a phosphatic tubular projection, they were later reinterpreted in relation to a putative crinoid epibiont or even as possible scyphozoans. Despite a long debate, neither the function of the enigmatic Palaeozoic rings nor their taxonomic affiliation has been fully clarified. The studied material, extracted by a standard technique in use for conodonts, consists of 235 elements from 16 stratigraphic levels in the Plöcken Formation ( Carnic Alps, Cellon Section; Amorphognathus ordovicicus Biozone, Hirnantian, Ordovician) and in the Kopanina Formation ( Bohemia, Mušlovka Quarry; Polygnathoides siluricus Biozone, Ludfordian, Silurian). To explore whether ring size and shape changed over time, we employed a novel combination of geometric morphometric approaches for outlines with no 'homologous' landmarks and showed that only size appreciably varied with an increase of ca. 20%. The emerging data from this study are consistent with the interpretation of the rings as an adhering structure of a benthic organism living on a relatively uniform hard substrate. [ABSTRACT FROM AUTHOR] more...
- Published
- 2013
- Full Text
- View/download PDF
83. Cover-collapse sinkholes in Kentucky, USA: geographic and temporal distribution.
- Author
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Currens, James
- Subjects
SINKHOLES ,GEOGRAPHY ,BUILDING failures ,AGRICULTURAL equipment ,GEOLOGICAL surveys ,MISSISSIPPIAN Period - Abstract
Sudden and unpredictable collapse of unconsolidated cover over soluble bedrock defines cover collapse. Cover collapse in Kentucky frequently damages buildings, roads, utility lines, and farm equipment. It has killed livestock, including thoroughbred horses, and has injured people at an estimated annual cost of $20 million. The Kentucky Geological Survey began developing a file of case histories of cover collapse in 1997 and now receives approximately 24 reports annually. The case history file contains 247 individual entries and spans some 30 years, yet is thought to represent only a fraction of the annual occurrences. The reported sites are distributed statewide but are concentrated in urban settings. The largest cover collapse recorded was in Logan County and was 15.5 m in diameter and 18 m deep. The Dishman Lane collapse in Bowling Green, KY, although larger, included some bedrock collapse. Collapse features have an average long axis length of 3.1 m and an average observable depth of 2.6 m. The ratio of the long and short axes of the collapse at ground level is 1.30. When plotted on a digitized topographic overlay showing outlines of mapped sinkholes, 11 % of the cover-collapse sites are inside a mapped sinkhole. Of a total of 124 observations that noted the presence or absence of buried trash, 10.7 % of sinkholes had trash present. Nearly 52 % of collapses are underlain by Mississippian rocks, whereas 39.7 % are underlain by Ordovician carbonates. The remaining percentage is underlain by Silurian and Devonian carbonates or lithology is undetermined. The most common months for cover collapse are April, May, and June. Continued accumulation of case histories of cover collapse in Kentucky will result in a better understanding of where, when, how, and why cover collapse occurs. [ABSTRACT FROM AUTHOR] more...
- Published
- 2012
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84. Researching candidate sites for a carbon storage complex in the Central Appalachian Basin, USA.
- Author
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Cumming, Lydia, Hawkins, Jared, Sminchak, Joel, Valluri, Manoj, and Gupta, Neeraj
- Subjects
CARBON sequestration ,ENHANCED oil recovery ,UNDERGROUND storage ,GAS fields ,OIL fields ,GAS power plants ,FOSSIL fuel power plants - Abstract
• Prefeasibility study for commercial-scale CCUS in the Appalachian Basin completed. • Assessment included an analysis of sources and sinks, economics, and other factors. • Project dimension and infrastructure requirements defined for two selected areas. The purpose of the Central Appalachian Basin-Carbon Storage Assurance Facility Enterprise Integrated Prefeasibility Project was to identify candidate sites in eastern Ohio for a storage complex capable of storing 50 million tonnes. Carbon capture and storage (CCS) will be essential in the Appalachian Basin, which includes coal-fired power plants, natural gas processing, refineries, chemical plants, and natural gas power. The project team investigated Cambrian-Ordovician Age sandstones and carbonates collocated near depleted oilfields, where enhanced oil recovery could provide a stepping stone for developing a storage hub. Feasible routes for linking sources to sinks via regional pipelines were assessed. The sub-basinal analysis demonstrated significant potential storage capacity in both deep saline reservoirs and depleted oil and gas fields. The project definition analysis revealed the project footprint would be reasonable and only two wells would be needed for injection of CO 2. Project economics illustrated a need for both government and private investment in the absence of a regulatory mandate. Ohio also lacks a comprehensive policy for long-term liability and subsurface storage rights, which could be addressed during pilot testing. Developing qualified sites within two selected areas for large-scale deployment of CCS appears feasible and the study helped to define future research needs. [ABSTRACT FROM AUTHOR] more...
- Published
- 2019
- Full Text
- View/download PDF
85. Revision of the unusual Carboniferous ophiuroid Cholaster (Echinodermata) and remarks on skeletal differentiation within the Asterozoa.
- Author
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Blake, Daniel B. and Nestell, Merlynd K.
- Subjects
- *
ECHINODERMATA , *ASTEROIDS , *ANTHROPOMETRY , *MILANKOVITCH cycles , *VERTEBRAE , *INSECT anatomy , *LIMESTONE - Abstract
Newly discovered, relatively well-preserved specimens of Cholaster whitei n. sp. (Ophiuroidea, Echinodermata) are described from a small area of extensive outcrop of the Bangor Limestone (Mississippian, Chesterian) exposed on the edge of Cedar Creek Reservoir in northern Alabama, USA. The only other known species of the genus, C. peculiaris Worthen and Miller, is based on a single specimen exposed in dorsal aspect and collected from strata of similar age from southwestern Illinois. Incomplete preservation of the single C. peculiaris specimen limits comparisons, but differences between the two occurrences support separation at the species level. Skeletal remains of both asteroids and ophiuroids are first recognized from Early Ordovician sediments, and representatives of the two classes have retained plesiomorphies or converged morphologically since that time, thereby suggesting important evolutionary potentials and limitations. Cholaster is asteroid-like and unusual among ophiuroids in that the arms are comparatively broad and strap-like, and lateral ossicles are similar to asteroid adambulacrals and marginals, whereas the "vertebrae" (i.e., fused axial pair) and oral frame configurations of C. whitei n. sp. are typical of the Ophiuroidea. The oral frame of C. peculiaris is unknown. A poorly preserved specimen of the asteroid Delicaster? also was recovered from nearby strata associated with the C. whitei n. sp. UUID: http://zoobank.org/e0eea445-58e5-4096-80c1-a65964832ef6 [ABSTRACT FROM AUTHOR] more...
- Published
- 2019
- Full Text
- View/download PDF
86. Paleomagnetic and mineral magnetic constraints on Zn–Pb ore genesis in the Pend Oreille Mine, Metaline district, Washington, USA.
- Author
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Pannalal, S. Johari, Leach, David L., and Symons, David T. A.
- Subjects
PALEOMAGNETISM ,GEOMAGNETISM ,LEAD ,ORES - Abstract
Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) more...
- Published
- 2007
- Full Text
- View/download PDF
87. Deep gas well encounters ultramafic kimberlite-like material in the Sauk Sequence of southeastern Ohio, USA.
- Author
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Baranoski, Mark T., Brown, V. M., and Watts, Doyle
- Subjects
- *
GAS wells , *GAS well drilling , *GEOLOGIC faults , *STRUCTURAL geology - Abstract
The first indication of a potential deep-subsurface kimberlite-like material in the Appalachian Basin, without surface expression, has been discovered in oil and gas well drilling samples from a deep well drilled near Zanesville, Ohio, USA. The well was drilled into the Cambrian Sauk Sequence within a localized fault-bounded graben, where a zone of ultramafic rocks was encountered. The zone of ultramafic rocks is within Sauk carbonates at 1720 m below sea level and is not highly anomalous on geophysical wire-line well logs. Petrographic analyses of grain-mounted samples show a 20 m zone of ultramafic rock material near the top of the Conasauga Group. Well cuttings from the ultramafic zone include relatively fresh phenocrysts of phlogopite with calcite, apatite, and titaniferous magnetite, in a secondary matrix of amphibole, chlorite, Fe-oxides, and possibly serpentine. The rocks have undergone deuteric alteration and probably later hydrothermal alteration. A 20-m-thick, localized, natural gas—bearing sandstone unconformably overlies (Knox unconformity) the Sauk Sequence above the ultramafic zone. Structural mapping indicates that the localized sandstone is confined to a small seismic-defined graben originating in the faulted Precambrian Grenville basement complex. Mapping of newly acquired gravity and magnetic data does not indicate the presence of an anomaly coincident with the graben, suggesting that the ultramafic material must be a very small, localized intrusive body (pipe or diatreme). Alternative interpretations include a thin intrusive sill, extrusive tuff deposits, Grenville-aged tectonic fault slice, or eroded igneous deposits. Subsurface mapping of units above the Sauk Sequence (Ordovician Black River Group-Trenton Limestone) shows no significant variation in structural contours above the feature. Although the igneous material has not been isotopically dated, the stratigraphic position suggests that it was intruded prior to Middle Ordovician time. [ABSTRACT FROM AUTHOR] more...
- Published
- 2007
- Full Text
- View/download PDF
88. Xeric Limestone Prairies of Eastern United States: Review and Synthesis.
- Author
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Lawless, Patrick J., Baskin, Jerry M., and Baskin, Carol C.
- Subjects
PLANT ecology ,XERIC ecology ,LIMESTONE ,PRAIRIES ,GRASSLANDS ,PLANT communities ,BIOTIC communities ,GEOLOGY - Abstract
Xeric limestone prairies (XLPs) are open, nonforested areas in which herbaceous plant communities occur on shallow. rocky soils derived from calcareous substrates. These grasslands are characterized by dominance of C
4 perennial grasses (particularly Schizachyrium scoparium) and are distributed in eastern United States from Missouri and Pennsylvania south to Arkansas and Georgia. XLPs occur in the Ozark Plateaus. Central Lowland. Interior Low Plateaus. Appalachian Plateaus. Ridge and Valley, and Coastal Plain physiographic provinces, and they are developed on Alfisols. Ultisols. Mollisols. Inceptisols, and Vertisols derived from Paleozoic limestones (also Eocene), dolomites, and calcareous shales. The C4 perennial prairie grass S. scoparium is the characteristic dominant taxon in XLPs of eastern United States. However, C, perennial forbs are dominant in some sites, and C, annual grasses (Sporobolus spp.) may be locally dominant in shallow-soil-zone microsites. Thirteen taxa apparently are endemic, or nearly so, to this vegetation type, including eight in the Ridge and Valley in Alabama (Cahaba River valley), four in the Ozark Plateaus in Missouri and Arkansas, and one in the Ridge and valley of West Virginia and Virginia. Various types of information are used to construct a conceptual model of the origin, maintenance, and successional dynamics of XLPs. Affinities of XLPs in eastern United States to other herbaceous vegetation types in eastern and western North America are discussed, and directions for future research are suggested. [ABSTRACT FROM AUTHOR] more...- Published
- 2006
- Full Text
- View/download PDF
89. A NEW NONCALCIFIED DASYCLADALEAN ALGA FROM THE SILURIAN OF WISCONSIN.
- Author
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LoDuca, Steven T., Kluessendorf, Joanne, and Mikulic, Donald G.
- Subjects
- *
ALGAE , *PALEONTOLOGY - Abstract
Noncalcified thalli, consisting of a narrow main axis with numerous branched hairlike laterals in whorls and a subapical array of undivided clavate laterals, from the Silurian (Llandovery) Brandon Bridge Formation of southeastern Wisconsin, constitute the basis for a new genus and species of dasycladalean alga, Heterocladus waukeshaensis. A relationship within the family Triploporellaceae is indicated by the whorled arrangement of the laterals and the absence of gametophores on mature specimens. A compilation of occurrence data suggests that noncalcified dasyclads, as a whole, were more abundant and diverse during the Ordovician and Silurian than at any other time in their history. The heterocladous thallus architecture of this alga adds to a wide range of morphological variation documented among Ordovician and Silurian dasyclads, the sum of which indicates that Dasycladales underwent a significant evolutionary radiation during the early Paleozoic. [ABSTRACT FROM AUTHOR] more...
- Published
- 2003
- Full Text
- View/download PDF
90. Nd Isotopes of Atoka Formation (Pennsylvanian) Turbidites Displaying Anomalous East-Flowing Paleocurrents in the Frontal Ouachita Belt of Oklahoma: Implications for Regional Sediment Dispersal.
- Author
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Dickinson, William R., Patchett, P. Jonathan, Ferguson, Charles A., Suneson, Neil H., and Gleason, James D.
- Subjects
NEODYMIUM ,ISOTOPES ,TURBIDITES ,GEOLOGICAL formations ,PALEOCURRENTS - Abstract
Focuses on the neodymium isotopes of Atoka Formation turbidites displaying anomalous east-flowing paleocurrents in the frontal Ouachita belt of Oklahoma. Implications of the formation on regional sediment disposal; Value yielded by the formation. more...
- Published
- 2003
- Full Text
- View/download PDF
91. NON-TRILOBITE ARTHROPODS FROM THE SILVER PEAK PEAK RANGE, NEVADA.
- Author
-
Waggoner, Ben
- Subjects
- *
ARTHROPODA ,SILVER Peak Range Wilderness (Nev.) - Abstract
Two non-trilobite arthropods are described from the Emigrant Formation (Lower Cambrian-Lower Ordovician) in the Silver Peak Range, Esmeralda County, Nevada. A Middle or Upper Cambrian "arachnomorph" arthropod with a phosphatic exoskeleton has been noted in previous faunal lists, but has not been previously described. This fossil is here named Quasimodaspis brentsae gen. et sp. nov. Q. brentsae belongs in the Aglaspidida, a close outgroup to the true chelicerates; this is the second report of an aglaspidid from the Great Basin. Esmeraldacaris richardsonae gen. et sp. nov. is a newly discovered arthropod from the lower Ordovician, from beds transitional between the Emigrant Formation and the overlying Palmetto Formation. It is a survivor of an early arthropod lineage that does not belong in any extant taxon, but which may also include the Ordovician Corcorania and the Cambrian Mollisonia. [ABSTRACT FROM AUTHOR] more...
- Published
- 2003
- Full Text
- View/download PDF
92. Structural sequences and styles of subsidence in the Michigan basin.
- Author
-
Howell, Paul D. and van der Pluijm, Ben A.
- Subjects
- *
STRUCTURAL geology , *LAND subsidence - Abstract
Studies the structural sequences and styles of subsidence in the Michigan basin. Cambrian-lower Ordovician; Lower middle Ordovician; Middle upper Ordovician; Uppermost Silurian-middle Devonian; Uppermost middle Devonian; Upper Devonian-Mississippian Strata; Methods for basin subsidence. more...
- Published
- 1999
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93. The Perkins Museum of Geology and the history of the Vermont State Collection.
- Author
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Howe, Jeffrey L.
- Subjects
GEOLOGICAL museums - Abstract
Describes the collection at Perkins Museum of Geology on the campus of the University of Vermont in Burlington. Background on sources of collection; Significant collections including Vermont minerals and stone products; Cambro-Ordovician fossils from the Champlain Valley; Braandon lignite. INSET: Visitor information.. more...
- Published
- 1996
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- View/download PDF
94. A novel method based on deep learning model for national-scale landslide hazard assessment.
- Author
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Yuan, Rui and Chen, Jing
- Subjects
LANDSLIDE hazard analysis ,NATURAL disaster warning systems ,DEEP learning ,MASS-wasting (Geology) ,LANDSLIDES ,RAINFALL - Abstract
Landslide hazard assessment is crucial for landslide monitoring and early warning. A novel method based on deep learning model for national-scale landslide hazard assessment was proposed in this study, which contains three stages: (1) landslide susceptibility analysis using three hybrid neural networks of convolutional neural network-simple recurrent unit (CNN-SRU), convolutional neural network-long short-term memory (CNN-LSTM), and convolutional neural network-gated recurrent unit (CNN-GRU); (2) landslide temporal probability prediction using the proposed spatiotemporal transformer (ST-transformer) to address the time uncertainty of rainfall threshold calculation in landslide temporal probability prediction and the matter without considering the geographical regional differences of landslide spatiotemporal probability weights; and (3) quantitative landslide hazard calculation with the preceding results using the improved landslide hazard formula. The validation of this method was conducted in conterminous United States, where the results of steps (1) and (2) demonstrated excellent performance compared with existing works. Consequently, the calculation derived from the previous two steps was effectively used for landslide hazard assessment using the improved landslide hazard formula, and its reliability was confirmed through the validation of actual landslide events. The proposed method is of practical significance for national-scale landslide hazard assessment. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
95. RADIOCARBON DATING AND FRESHWATER RESERVOIR EFFECTS OF AQUATIC MOLLUSKS WITHIN FLUVIAL CHANNEL DEPOSITS IN THE MIDWESTERN UNITED STATES.
- Author
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Rech, Jason A, Tenison, Christina N, Baldasare, Alexander, and Currie, Brian S
- Subjects
ALLUVIUM ,RADIOCARBON dating ,SEASHELLS ,BIVALVE shells ,MOLLUSKS ,FLUVIAL geomorphology - Abstract
Late Quaternary fluvial channel deposits are notoriously difficult to date. In the midwestern United States, shells of aquatic mollusks can be found within many fluvial channel sediments and therefore can be radiocarbon (
14 C) dated to determine the age of the deposits. However, carbonate platform rocks are abundant in this region, potentially causing freshwater14 C reservoir effects (FRE) in mollusk shells. We14 C dated 11 aquatic gastropod and bivalve shell samples from specimens collected live from a stream in southwestern Ohio during three different years to assess the modern14 C reservoir effect. Modern samples yielded an average14 C FREmodern of 518 ± 6514 C yrs for 2020 (n=5), 640 ± 3414 C yrs for 2021 (n=2), and 707 ± 7614 C yrs for 2022 (n=4). We also14 C dated matched pairs of organic wood or charcoal and aquatic mollusk shells from late Pleistocene and Holocene deposits in the Four Mile Creek floodplain to determine the FREfossil . These samples, free of any potential influence from nuclear bomb testing, yielded an overall weighted mean FREfossil of 1029 ± 34514 C yrs. We then assess the advantages and limitations of both the FREmodern and FREfossil methods for determining freshwater reservoir effects. Finally, we apply the FREfossil correction to a series of shell ages from fluvial terrace deposits as a case study. The results indicate that although there is a14 C FRE in streams from the midwestern United States, aquatic shells can provide robust age control on fluvial channel deposits. More research is needed to understand the spatial and temporal variability of FREs, as well as any species effects, among various watersheds across the midwestern United States. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
96. Microstegium vimineum Habitat Suitability Analysis in the Kentuckiana Region Using Geographic Information System (GIS) Modeling.
- Author
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Koenig, Kimberly and day, C. Andrew
- Subjects
GEOGRAPHIC information systems ,RIVER channels ,PLANT dispersal ,NATURE reserves ,HABITATS ,LAND management - Abstract
Microstegium vimineum or stiltgrass is a novel invader widely considered one of the most significant threats to oak-hickory woodlands in the eastern United States. Due to the insubstantial weight and buoyancy of seeds, Microstegium can disperse not only via overland dispersal routes but also via sheet flow, flooding, and stream channels, creating rapid progression of existing populations and greater likelihood of introduction to new areas. Using the knowledge of Microstegium habitat from previous research and field mapping of current populations, we identified and assessed environmental variables for use in habitat suitability modeling. We found canopy openness, distance from roads, and distance from streams to be the primary drivers of Microstegium presence. We then applied a GIS-based habitat suitability analysis across seven nature reserves in Kentuckiana as a potential tool for land management. Our pilot study developed a model which can potentially guide managers of natural areas to decide where best to focus mitigation and prevention of potential Microstegium invasion and population expansion when resources are limited. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
97. Dating slate belts using 40Ar/39Ar geochronology and zircon ages from crosscutting plutons: A case study from east-central Maine, USA.
- Author
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Ghanem, Hind, Kunk, Michael J., Ludman, Allan, Bish, David L., and Wintsch, Robert P.
- Subjects
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SLATE , *GEOLOGICAL time scales , *ZIRCON , *CRYSTALLIZATION - Abstract
We report the ages of cleavage development in a normally intractable lower greenschist facies slate belt, the Central Maine-Aroostook-Matapedia belt in east-central Maine. We have attacked this problem by identifying the minimum ages of muscovite in a regional Acadian cleavage (S 1 ) and in a local ductile fault zone cleavage (S 2 ) using 40 Ar/ 39 Ar geochronology and the ages of crosscutting plutons. Our success stems from the regional low-grade metamorphism of the rocks in which each crystallization event preserves a 40 Ar/ 39 Ar crystallization age and not a cooling age. Evidence for recrystallization via a pressure solution mechanism comes from truncations of detrital, authigenic, and in some rocks S 1 muscovite and chlorite grains by new cleavage-forming muscovite and chlorite grains. Low-blank furnace age spectra from meta-arkosic and slaty rocks climb from moderate temperature Devonian age-steps dominated by cleavage-forming muscovite to Ordovician age-steps dominated by a detrital muscovite component. S 1 - and S 2 -cleaved rocks were hornfelsed by granitoids of ∼407 and 377 Ma, respectively. The combination of these minimum ages with the maximum metamorphic crystallization ages establishes narrow constraints on the timing of these two cleavage-forming events, ∼410 Ma (S 1 ) and ∼380 Ma (S 2 ). These two events coincide in time with a change in the plate convergence kinematics from the arrival of the Avalon terrane (Acadian orogeny), to a right-lateral transpression arrival of the Meguma terrane in the Neoacadian orogeny. [ABSTRACT FROM AUTHOR] more...
- Published
- 2016
- Full Text
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98. Three new U.S. depth records set.
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OIL well drilling ,PETROLEUM industry ,HISTORY - Abstract
Provides information on oil drilling and producing depth records in the United States in 2000. List of true vertical depth records from 1993-2000; Chronological record of deepest producing zones in the country since 1938. more...
- Published
- 2001
99. Stress Features Inferred From Induced Earthquakes in the Weiyuan Shale Gas Block in Southwestern China.
- Author
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Chu, Risheng and Sheng, Minhan
- Subjects
INDUCED seismicity ,OIL shales ,SHALE gas ,HYDRAULIC fracturing ,FLUID injection ,EARTHQUAKE magnitude ,PORE fluids - Abstract
Stress features, particularly local stress field and earthquake stress drops, are important to understand mechanism of induced earthquakes. Since shale gas exploitations in 2015, the Weiyuan shale gas block has experienced frequent earthquakes. In this paper, we determine focal mechanisms of 257 events with ML > 1.5 by fitting three‐component waveforms, invert for direction of maximum horizontal stress for two dense earthquake clusters, and then calculate stress drops for 17 earthquakes with moment magnitudes between 2.2 and 2.75 through the spectral ratio method. The focal mechanisms of all earthquakes are reverse faulting. The orientation of local maximum horizontal compressive stress is in the ESE direction, consistent with crustal movement indicated by GPS measurements. Both the focal mechanisms and microseismicity locations suggest the existence of steeply dipping faults with dip angles of ∼70°, which are relatively rare and difficult to slip under usual conditions, unlike major induced earthquakes with strike‐slip or low‐angle thrusting faults in the midwestern United States and western Canada. However, the steeply dipping reverse events can be induced by large pore pressure from hydraulic fracturing. The stress drops range from 2.5 to 54.7 MPa, comparable to those of potentially induced earthquakes in the midwestern United States. Our results imply earthquakes in the Weiyuan area are controlled by local tectonic stress and induced by large pore pressure from hydraulic fracturing, which advances our knowledge of reactivation of steeply dipping reverse faults. Plain Language Summary: Earthquakes in the Weiyuan area in southwestern China are thought to be induced by hydraulic fracturing due to shale gas production. Local stress field and earthquake stress drops provide crucial information to understanding their physical mechanisms. Here we determine source parameters of 257 events with magnitude greater than 1.5, invert for direction of maximum horizontal stress, and calculate stress drops for 17 representative events. The results suggested that all the earthquakes occurred on reverse faults and the inferred maximum horizontal stress orientations agree with local GPS measurements. Surprisingly, we find some steeply dipping faults with dip angle of ∼70°, which are assumed to be stable under usual stress conditions. The stress drops range from 2.5 to 54.7 MPa, which are comparable to those of potentially induced earthquakes in the midwestern United States. We infer that the steeply dipping reverse events are induced by high pore pressure from hydraulic fracturing. Our results imply earthquakes in the Weiyuan area are controlled by local tectonic stress and induced by hydraulic fracturing with high‐pressure fluid injection. Key Points: Focal mechanisms of 257 ML > 1.5 earthquakes suggest consistent maximum horizontal stress with local tectonic settingsSteeply dipping reverse faults may be reactivated by high pore pressure fluid during hydraulic fracturingStress drops of the induced earthquakes range from 2.5 to 54.7 MPa [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
100. Uppermost Devonian (Famennian) to Lower Mississippian events of the western U.S.: Stratigraphy, sedimentology, chemostratigraphy, and detrital zircon geochronology.
- Author
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Cole, D., Myrow, P.M., Fike, D.A., Hakim, A., and Gehrels, G.E.
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DEVONIAN Period , *MISSISSIPPIAN Period , *STRATIGRAPHIC geology , *SEDIMENTOLOGY , *CHEMOSTRATIGRAPHY , *ZIRCON , *GEOLOGICAL time scales - Abstract
Upper Devonian to Lower Mississippian strata in Utah and Montana record global events through this important interval in Earth history. Late Famennian strata of the Beirdneau, Leatham, and Pilot Shale formations in Utah, and Three Forks and Sappington formations in Montana, record widespread deposition of generally fine-grained siliciclastic and carbonate strata. Integration of sedimentology, physical stratigraphy, chemostratigraphy, and published biostratigraphy allows for the recognition of important disconformities and regional stratigraphic patterns. These enable the reconstruction of uppermost Devonian to lowermost Mississippian depositional, tectonic, and eustatic history of the region. Carbon isotopic data allows for stratigraphic evaluation of the presence and absence of global bioevents of the Late Devonian, including the Annulata, Dasberg, and Hangenberg events, some of which are clearly recorded in hinterland deposits to the east in Colorado. While the Devonian–Mississippian boundary is also missing in our sections, a significant positive shift in δ 13 C carb in Lower Mississippian strata in Utah and Montana represents one of the largest positive δ 13 C carb isotope excursions of the Phanerozoic, linked to drawdown of atmospheric CO 2 and glaciation in the Kinderhookian. Detrital zircon spectra from latest Devonian to Early Mississippian strata of Utah and Colorado include populations representing derivation from the Mazatzal and Yavapai provinces, Middle Proterozoic anorogenic granite bodies, and a small influx of Grenville and presumed Appalachian–Caledonian grains. Minor Paleoproterozoic and Late Archean peaks in Utah are likely multiple generation grains originally derived from the Peace River Arch of northwestern Canada and recycled in Ordovician rocks of Nevada. These patterns in detrital zircon geochronological data reflect, in part, changes in sediment dispersal patterns due to tectonic and eustastic variability within the Antler foreland basin during the Devonian–Mississippian boundary interval. This variability also led to irregular spatial patterns of unconformity development, as well as complicated physical stratigraphic and chemostratigraphic architecture. [ABSTRACT FROM AUTHOR] more...
- Published
- 2015
- Full Text
- View/download PDF
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