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Hardgrounds from the Upper Ordovician strata of eastern Laurentia exhibit a wide range of morphologies, though the development of their complex surface topographies remains poorly understood. These early lithified seafloors, which can be laterally very extensive, may provide key information about basin dynamics and global ocean fluctuations. Based on spectacular exposures and newly-excavated material, we examined a suite of hardgrounds from the Upper Ordovician (Katian) of southern Ontario and the Cincinnati Arch region and documented the processes of genesis, development, and modification of simple, complex, and block hardgrounds. In this study, we used extensive field work, petrology, and cathodoluminescence to determine the evolution and shaping of hardgrounds as a result of intense submarine erosion and prolonged exposure of these surfaces and reveal a progression from simple to complex hardgrounds and ultimately to isolated cobble- to boulder-sized block hardgrounds. We survey the distribution of hardgrounds in a sequence stratigraphic framework to determine allocyclic controls on hardground development, highlight the important role that mixed siliciclastic-carbonate environments play in promoting the development of heterogeneous hardground topographies, and analyze the effects of high surface reliefs on local depositional and erosional regimes. In addition, we interpret the impact of increasingly abundant complex hardgrounds throughout the Ordovician on hard-substrate community diversification and their contribution to the Great Ordovician Biodiversification Event. We also discuss time-specific aspects of the Late Ordovician that made it a peak interval of hardground proliferation. • Upper Ordovician hardgrounds have been studied from the eastern U.S. and Canada. • Complex hardground morphologies are controlled by extended exposure and erosion. • Block hardgrounds may result from erosion of lenticular beds or complex hardgrounds. • Complex hardgrounds indicate periods of sediment starvation and negative sedimentation at key sequence stratigraphic surfaces. • Heterogeneous hardground habitats promote the recruitment of diverse encrusting communities. [ABSTRACT FROM AUTHOR]

Black gas shales are major parts of many foreland-basin sequences and comprise important components of unconformity-bound tectophase cycles, which reflect sedimentary/stratigraphic, flexural responses to deformational loading and relaxation in an orogen. Using as examples Upper Ordovician black gas shales, deposited during the Taconian orogeny in the Appalachian Basin of the eastern United States, black-shale origins and their importance in understanding the tectonic framework are discussed. Foreland-basin black shales are clearly the product of distinctive tectonic frameworks and histories, and aside from economic value, may provide important controls on the timing and location of tectonic events. [ABSTRACT FROM AUTHOR]

We present a systematic summary of the geological characteristics, exploration and development history and current state of shale oil and gas in the United States. The hydrocarbon-rich shales in the major shale basins of the United States are mainly developed in six geological periods: Middle Ordovician, Middle--Late Devonian, Early Carboniferous (Middle--Late Mississippi), Early Permian, Late Jurassic, and Late Cretaceous (Cenomanian--Turonian). Depositional environments for these shales include intra-cratonic basins, foreland basins, and passive continental margins. Paleozoic hydrocarbon-rich shales are mainly developed in six basins, including the Appalachian Basin (Utica and Marcellus shales), Anadarko Basin (Woodford Shale), Williston Basin (Bakken Shale), Arkoma Basin (Fayetteville Shale), Fort Worth Basin (Barnett Shale), and the Wolfcamp and Leonardian Spraberry/Bone Springs shale plays of the Permian Basin. The Mesozoic hydrocarbon-rich shales are mainly developed on the margins of the Gulf of Mexico Basin (Haynesville and Eagle Ford) or in various Rocky Mountain basins (Niobrara Formation, mainly in the Denver and Powder River basins). The detailed analysis of shale plays reveals that the shales are different in facies and mineral components, and "shale reservoirs" are often not shale at all. The United States is abundant in shale oil and gas, with the in-place resources exceeding 0.246x1012 t and 290x1012 m3, respectively. Before the emergence of horizontal well hydraulic fracturing technology to kick off the "shale revolution", the United States had experienced two decades of exploration and production practices, as well as theory and technology development. In 2007--2023, shale oil and gas production in the United States increased from approximately 11.2x104 tons of oil equivalent per day (toe/d) to over 300.0x104 toe/d. In 2017, the shale oil and gas production exceeded the conventional oil and gas production in the country. In 2023, the contribution from shale plays to the total U.S. oil and gas production remained above 60%. The development of shale oil and gas has largely been driven by improvements in drilling and completion technologies, with much of the recent effort focused on "cube development" or "co-development". Other efforts to improve productivity and efficiency include refracturing, enhanced oil recovery, and drilling of "U-shaped" wells. Given the significant resources base and continued technological improvements, shale oil and gas production will continue to contribute significant volumes to total U.S. hydrocarbon production. [ABSTRACT FROM AUTHOR]

Abstract: The Great Ordovician Biodiversification Event (GOBE) was a time of pronounced radiation within the Paleozoic and Modern evolutionary faunas. Despite increases in metazoan diversity during both the Cambrian and the Ordovician, recent geochemical evidence suggests that the Early Paleozoic may have experienced recurring deep ocean euxinia. The dynamic connections between deep ocean redox and fossil-rich shelf environments remain unclear, but one way to elucidate these relationships is to study rocks formed during the GOBE using both long-term global and short-term local redox proxies. Here we report geochemical results from the Middle Ordovician Juab Formation and Kanosh Formation at Fossil Mountain, Utah. The Kanosh Formation has been interpreted by different workers either as an anoxic restricted basin or as a well-oxygenated normal marine basin based on sedimentological and paleontological characteristics. Here we employ the sulfur isotopic composition of carbonate associated sulfate (CAS) as a proxy for long-term, whole-ocean redox changes during the Middle Ordovician. We use the abundances of organic carbon and total sulfur as proxies for short-term, localized changes in redox during the deposition of the Fossil Mountain sediments. Organic carbon abundances are low overall (average=0.7wt.%, maximum=1.2wt.% using the most conservative estimate), although some units may have had considerably higher organic content before burial. Total sulfur is uniformly low, with an average value of 0.02wt.% and a maximum value of 0.07wt.%. The total sulfur and organic carbon abundance results suggest that anoxia was not prevalent in the depositional environment of the Juab and Kanosh Formations. Similarly, the sulfur isotopic results correlate well with those reported from time-equivalent strata in Newfoundland, suggesting that the Fossil Mountain sediments were not deposited in a restricted basin. Even though the total sulfur and organic carbon data suggest that the local environment was not anoxic, our sulfur isotopic results support the hypothesis that the global ocean was likely euxinic during the Middle Ordovician. [Copyright &y& Elsevier]

It was recently discovered that the stems of extant crinoids may survive after detachment of the crown, presumably feeding by the absorption of nutrients through the ectoderm. Previously, only one analogous, albeit morphologically dissimilar, pattern of crownless survival has been recognized from the fossil record. Certain Upper Ordovician (Cincinnatian) crinoid pluricolumnals from Kentucky, Ohio and Indiana, derived from the disparids Cincinnaticrinus spp., have rounded terminations reminiscent of some modern bourgueticrinid overgrowths. Such specimens have hitherto been interpreted as distal terminations of mature individuals that have become detached from their attachment structures and taken to an eleutherozoic existence. However, it is considered more probable that they represent overgrowths of the column following predatory decapitation. If this new interpretation is correct, then post-decapitation survival of crinoid stems is now recognized for most of the history of the crinoids, 'lethal' predation on crinoid crowns occurred at least as early as the Late Ordovician and ancient crinoid populations can no longer be determined merely by counting crowns. [ABSTRACT FROM AUTHOR]

Abstract: δ 13C values of numerous limestone samples from Katian (Upper Ordovician) successions in Oklahoma and the Upper Mississippi Valley document the presence of at least three of the four positive excursions that have been recognized in the lower–middle Katian interval in the Cincinnati region in Ohio, Kentucky, and Indiana. A comparison with Estonia reveals that five out of the six positive excursions now recorded through the Katian succession in the Cincinnati region are present in the coeval stratigraphic intervals in Estonia, which suggests that these represent global perturbations in the carbon cycle. A study of the relations between flooding events and δ 13C excursions shows that only some of the excursions occur in transgressive intervals whereas other excursions are in regressive strata and hence, this is in conflict with the idea that positive carbon isotope excursions are forced by rises in sea level. Part of a previously published attempt to use Upper Ordovician sequence stratigraphy for trans-Atlantic correlation is shown to be seriously out of phase with the biostratigraphy and chemostratigraphy. Several of the sequences recognized in the Cincinnati region do not appear to have counterparts in Estonia, which suggests that they do not reflect eustatic, but local, conditions. [ABSTRACT FROM AUTHOR]

Two new kirkocystid mitrate stylophorans (Echinodermata, Homalozoa) and a new possible solute (Echinodermata, Homalozoa) are described from the Early Ordovician of the western United States. The mitrates are among the earliest members of their clade to appear near the beginning of the Ordovician Radiation. Anatifopsis ninemilensis new species comes from the Ninemile Shale in central Nevada and the McKelligon Canyon Formation in west Texas. Anatifopsis fillmorensis new species comes from the middle Fillmore Formation in western Utah and a Ninemile Shale equivalent limestone bed in southern Nevada. The possible solute Drepanocystis dubius new genus new species from the lower Wah Wah Limestone in western Utah, shows unusual morphology with an elongate theca and a long arm shaped like a sickle. [ABSTRACT FROM AUTHOR]

A formal Ordovician-Silurian chitinozoan biozonation for western Gondwana is proposed. This palaeogeographic province includes South America, and was located in medium to high latitudes during Ordovician and Silurian times. Ordovician chitinozoans are known from northern Argentina, southern Bolivia, and Brazil. Silurian chitinozoans occur in Brazil, northern Argentina, southern Bolivia and southern Peru. No published information is available about Ordovician-Silurian chitinozoans from Ecuador, Colombia or Venezuela. Altogether more than 150 localities (including wells and outcrops) are included in this study, and 154 species have been encountered. A biozonation based on the first occurrence of critical chitinozoan species is introduced. Five biozones are defined in the Ordovician (zones of Desmochitina sp. gr. minor, Conochitina decipiens, Eremochitina brevis, Lagenochitina obeligis and Tanuchitina anticostiensis), and nine in the Silurian (zones ofBelonechitina postrobusta, Spinachitina harringtoni, Pogonochitina djalmai, Margachitina margaritana-Salopochitina monterrosae, Angochitina echinata, Eisenackitina granulata, Fungochitina kosovensis and the subzones of Sphaerochitina solutidina and Desmochitina cf. D. densa). These biozones are compared with known graptolite, conodont, acritarch and spore zones from the same area, and chitinozoan zones on a global basis. [ABSTRACT FROM AUTHOR]

Throughout east–central United States, Lexington/Trenton limestones are largely Late Ordovician (Chatfieldian; mid-Caradoc), argillaceous, skeletal calcarenites, which are transgressive upward into Late Ordovician (late Chatfieldian–Edenian; mid-late Caradoc) shales and interbedded micrograined limestones. In central Kentucky, however, the same sequence is partially truncated by an unconformity and passes upward into a thicker, younger (Edenian; late Caradoc), regressive shoal complex of coarse calcarenites and calcirudites that is not generally typical of the Lexington/Trenton sequence elsewhere. The shoal complex is interpreted to have been a carbonate buildup and is partially bound by extant faults with basement precursors. Comparison of isopachous maps for pre- and postunconformity buildup units with basement structural lineaments suggests that the buildup is related to reactivation—and in one prominent case, inversion—of the basement structures. The coincidence of structural reactivation, inversion, and buildup development with other major regional, cratonic changes may reflect a reorganization of cratonic, far-field forces accompanying a nearly coeval reversal in the polarity of Taconic subduction. [Copyright &y& Elsevier]

Exceptional sub-micrometer details of shell microstructure are preserved in phosphatic micro-steinkerns representing several phyla from shell beds of the Upper Ordovician of the Cincinnati Arch region, USA. These fossils provide the most detailed record of Ordovician mollusk shell microstructures, as well as exceptional details on the earliest cases of undisputed nacre. The trend towards nacre in the Mollusca is one aspect of the surge in escalation between mollusks and their predators during the Great Ordovician Biodiversification Event. [ABSTRACT FROM AUTHOR]

Abstract The Evans Ferry section from the Appalachian Basin of eastern North America has been analyzed for chemostratigraphic trends to elucidate possible causal mechanisms facilitating the Great Ordovician Biodiversification Event (GOBE). Paired stable isotope (δ13C and δ34S) analyses were used in this carbonate-dominated locality from the Appalachian Basin to reconstruct the marine redox states during this key period of rapid biodiversification. This succession is one of the most expanded Sandbian Stage (Upper Ordovician) deposits known from North America, and it allows new high-resolution reconstructions of long-term, global carbon and sulfur cycle fluctuations. The integrated geochemical and sequence-stratigraphic investigation presented here from the Laurentian epeiric seaway allows for possible identification of the contraction and expansion of reducing water masses during the Middle–Late Ordovician that may have been linked to global-marine paleoredox dynamics. Utilizing new conodont-based 87Sr/86Sr isotope stratigraphy along with previous conodont biostratigraphy, we can confidently correlate our stable isotope profiles to other carbonate successions globally. Carbonate facies indicate that this area experienced partial restriction from open-marine conditions during certain intervals in the Sandbian. These semi-restricted environments record carbon (δ13C carb) isotope trends that are secular in nature, as they can be correlated to other successions across Laurentia and Baltica. We identify several intervals when δ13C carb and δ34S CAS (carbonate-associated sulfate) trends are decoupled. These inverse stratigraphic trends are, at times, followed by parallel positive shifts in δ13C carb and δ34S CAS. Causal mechanisms for the observed decoupled δ13C and δ34S trends may include a wide variety of factors such as more closed-system, local biogeochemical processes associated in part with diagenesis, or they could instead reflect variations in the global fluxes of organic matter and pyrite burial linked to changing marine paleoredox conditions. The positive covariation in trends presented here likely represents transient increases in organic carbon and pyrite burial in response to expansion of reducing marine environments. Highlights • Tracking oxygen dynamics through Middle to Upper Ordovician stratigraphy • Evidence of oxygenation pulses using carbon and sulfur stable isotope ratios • Linkages between increased biodiversity and marine ventilation events • Modeling indicates decreased pyrite burial as principle driver for isotope trends. [ABSTRACT FROM AUTHOR]

Numerous cemented and partially cemented K-bentonite beds occur in the long, complex succession of altered ash beds with the Middle to Late Ordovician Trenton Group and Utica Shale of New York State. Petrography and trace element geochemistry suggest a generally felsic-intermediate, calc-alkaline composition of the volcanic component. Cementation by carbonate is expressed as nodular concretionary masses within K-bentonite clay, or as a complete transformation of ash layers to hard, tabular ledges. Cementation typically imparts a sparry texture to K-bentonites, which is distinct from that of normal concretionary micrite layers observed at many levels. Cemented K-bentonites display remarkably well-developed glass shard textures, suggesting that carbonate cementation sometimes occurs prior to alteration of glass to clay minerals. The presence of cross-lamination in several cemented K-bentonites, dramatically shows that post-depositional hydraulic reworking or bioturbation of tuffaceous material was an important process on the Ordovician seafloor. Preliminary observations show the potential for detailed petrographic textural characterization of certain ash layers where cementation occurred soon after burial. Given that ashes are often associated with sedimentary condensation and frequently occur above submarine discontinuities, petrographic study of cemented ash should reveal if, and to what degree, ash layers record multiple depositional events.REE patterns show enrichments in light REE and moderate to pronounced Eu anomalies consistent with a felsic-intermediate igneous signature. Individual Calcareous ash bed trace element patterns and ratios – for example, REE and Hf/Zr, Th/U, K/Rb – may persist laterally in the Mohawk Valley, allowing their use as correlation tools. [ABSTRACT FROM AUTHOR]

Examines the use of sensitive high resolution ion microprobe for dating ordovician granites and tonalites in the central Appalachian Piedmont, U.S. Utilization of cathodoluminescence images of zoning in the zircons to select the areas for dating; Application of isotope dilution thermal ionization mass spectrometry; List of dated ares.

Provides evidence of a tectonically driven sequence succession in the middle Ordovician Taconic foredeep of the central Mohawk River Valley, New York. Implication of the developed facies mosaic for stacking patterns of the foreland basin; Differential and accommodation rate of subsidence across the region; Formation of the coeval Trenton Group succession.

Focuses and characterizes the earliest Whiterockian faunas during the Middle Ordovician period in Nevada. Prominence of trilobites as component of the Ordovician faunas; Meiklejohn Peak; Type species; Etymology; Holotype; Species variation.

Predation on ancient shelled prey is an often-studied topic in paleoecology, but the early Paleozoic and the brachiopods that dominated the seafloor at that time are relatively underrepresented in the predation literature. We assessed predatory repair scar frequencies among the brachiopod genera from the Early Richmondian (Late Ordovician) Oregonia Member (Arnheim Formation) near Flemingsburg, Kentucky. We found higher repair frequencies on the concavo-convex Rafinesquina and Leptaena relative to the bi-convex genera. There were no trends in repair frequency through the stratigraphic section and no relationships between repair frequency and community diversity metrics. It is possible that concavo-convex brachiopods' flat shape, thin shell profile, and free-lying (no pedicle attachment) lifestyle made them more likely or appealing targets of Ordovician crushing predators. It is also possible that concavo-convex brachiopods were better suited to survive crushing attacks than biconvex taxa. We also found differences in shell ornament that may influence the visibility of repair scars. [ABSTRACT FROM AUTHOR]

Analyzes the three stratigraphic sections in central Nevada in relation to the Late Ordovician mass extinction. Conduct of integrated sequence stratigraphic, biostratigraphic, and chemostratigraphic analyses; Formation of diachronous, stepwise faunal turnover in graptolites, conodonts, chitinozoans and radiolarians.

Examines acritarch assemblage from the upper Ordovician Maquoketa Shale of northeastern Missouri. Descriptions of the recovered acritarch species; Maquoketa Shale accumulation indicated by sedimentologic and paleontologic-palynologic finding; Comparison of Maquoketa Shale acritarch with that of Sylvan and Maquoketa Shales of Kansas.

Focuses on trilobite fossils from the lower third of the Middle Ordovician period from the Walcott-Rust Quarry in Trenton Falls, New York. Historical overview of the quarry; Species of trilobites found in the different layers; Explanation for presence of complete specimens; Systematic paleontology.

Reports on a study of a limestone-forming algae in upper Ordovician beds in southwestern Ohio. Discovery of a calcified reproductive layer in one of the specimens; Interpretation of the structures as either sporangia or sporangial chambers which occur in a sorus type of arrangement; Bearing of the find on the phylogenetic history of the Solenoporaceae.

Reports on the results of a study of Ordovician volcanic rocks in Maine showing that mafic rocks can be divided into three groups. Descriptions of Stacyville-Lobster Mountain group; Munsungun-Winterville group; Pinkham Road group; Correlation of within-plate basalt groups and coeval basalts; Recommendations.

This study, considering original detrital compositions and diagenetic alterations, relates sandstone and shale mineral and chemical composition to provenance and mass balance between the sedimentary assemblage and its provenance. Mature quartz-rich sandstones and siltstones with clay-rich shales in cores at depths of 60 m–5.2 km and burial temperatures of <50 to >150 °C from over 50 wells were utilized in this work. These provide the material for analysis of compositions and alterations in coastal and shallow marine clastic sedimentary rocks of the Middle Ordovician Simpson Group in Oklahoma and Kansas, U.S.A. Mineral and geochemical data were obtained by optical petrography, X-ray diffraction, scanning electron microscopy, electron microprobe, and whole rock X-ray fluorescence and ICP/MS analyses. Results of the study show significant progressive diagenetic changes with increased burial depth and temperature. Mineralogically and chemically, less altered rocks are comparable to modern quartz-rich sands and kaolinitic muds in siliciclastic sediments developed during humid tropical weathering in crystalline basement shield provenance in Africa and South America. By analogy to modern tropical cases, muds composed of major kaolinite with minor smectite and illite at deposition, were diagenetically transformed to illite-rich rocks by possible microbial action, at surface to shallow (<200 m, <40 °C) burial with influx of K, Rb and Mg from seawater. In sandstones, early open system diagenesis with calcite cementation and quartz overgrowths occurred at <1 km depth and < 40 °C. Further closed system silica diagenesis and K-metasomatism, occurred with deeper burial (to 3+ km and 100 °C) in the Pennsylvanian and Permian and later, during and following uplift of the Arbuckle and Wichita Mountains, with establishment of a new fold and thrust belt structural and hydrologic regime. Pressure solution of quartz and the illite to muscovite transformation in shales in the depth range 3–8 km, yielded silica for later generation quartz cement (10- >20%) in sandstone buried >3 km. During deep burial, high temperature (>110 °C) calcite cement from deep basin sources was precipitated in sandstones. Geochemical mass balance estimates, physical, and chemical evidence suggest quartz cement was sourced from within clastic rocks of the Simpson Group with minor external contribution of SiO 2. Na is in low abundance due to loss in solution during weathering in the provenance. Rare earth elements (REE) have typical abundances and distributions in shales with enrichment in light REE; littoral environment siltstones and matrix-rich sandstones display enrichment of heavy REE in phosphatic brachiopod shell fragments. [ABSTRACT FROM AUTHOR]

Presents an article in which ontogenies of three trilobites from the Garden City Formation are described. Classification of the three trilobites; Comparison of both larval and adult features of the trilobites; What members of the lineages show.

Ordovician metamorphic rocks of the Casco Bay Group are exposed in an approximately 170 km long NE-trending belt (Liberty-Orrington belt) in southern and south-central Maine. Geochemical analysis of rocks within the Spring Point Formation (469 ± 3 Ma) of the Casco Bay Group indicate that it is an assemblage of metamorphosed bimodal volcanic rocks. The mafic rocks (originally basalts) have trace element and Nd isotopic characteristics consistent with derivation from a mantle source enriched by a crustal and/or subduction component. The felsic rocks (originally rhyolites and dacites) were likely generated through partial melting of continental crust in response to intrusion of the mafic magma. Relatively low initial εNd values for both the mafic (-1.3 to + 0.6) and felsic (-4.1 to -3.8) rocks suggest interactions with Gander zone continental crust and support a correlation between the Casco Bay Group and the Bathurst Supergroup in the Miramichi belt of New Brunswick. This correlation suggests that elements of the Early to Middle Ordovician Tetagouche-Exploits back-arc basin can be traced well into southern Maine. A possible tectonic model for the evolution of the Casco Bay Group involves the initiation of arc volcanism in Early Ordovician time along the Gander continental margin on the eastern side of the Iapetus Ocean basin. Slab rollback and trenchward migration of arc magmatism initiated crustal thinning and rifling of the volcanic arc around 470 Ma and resulted in the eruption of the Spring Point volcanic rocks in a back-arc tectonic setting. [ABSTRACT FROM AUTHOR]

Studies late Ordovician jawed polychaete faunas of the type Cicinnatian Region in the United States. Collection of well-preserved scolecodonts; Polychaetes of the extant order Eunicida; Late Ordovician faunas of Laurentia with coeval ones of Baltica.

The Cambrian-Ordovician boundary is a type 1 depositional sequence boundary with dramatic local erosional incision in restricted marine facies on the easternmost New York Promontory. The systemic boundary is bracketed below by Late Cambrian, upper Cordylodus proavus Zone (s.s). conodonts from carbonates of the upper Little Falls Formation (=Whitehall Formation, abandoned). Presumed Lower Ordovician ellesmeraceratoid cephalopods from the upper Little Falls are uppermost Cambrian and among the oldest known in North America. The overlying deepening-shoaling cycle of the Tribes Hill Formation (=Cutting and Great Meadows Formations, abandoned) is the local expression of a lowermost Ordovician (Rossodus manitouensis Zone) depositional sequence recognizable across Laurentia. Complete replacement of conodonts takes place in the late Tremadocian or Tremadocian-Arenigian boundary interval with onlap of the "Fort Ann Formation" across the paleokarst cap of the Tribes Hill. The trilobites Hystricurus sp. and Symphysurina myopia Westrop new species occur in less restricted, thrombolitic facies of the middle Tribes Hill that have the highest conodont diversity. Ulrichodina Furnish, 1938, emend, is regarded as the senior synonym of the conodont Colaptoconus Kennedy, 1994 (=Glyptoconus Kennedy, 1980). [ABSTRACT FROM AUTHOR]

The Cane Run Bed is a prominent unit of micrograined limestone and shale of distal storm origin in the lower part of the Late Ordovician (late Chatfieldian; late Caradoc) Lexington Limestone (Trenton) in central Kentucky, USA. The unit''s prominence relates to presence of up to three horizons of penecontemporaneous, soft-sediment deformation that form a distinctive event bed; equivalent horizons of different lithology are also deformed. Concurrence of four lines of evidence, including deformation consistent with a seismogenic origin, widespread distribution in temporally and stratigraphically constrained horizons, a pattern of increasing frequency or deformation intensity toward likely epicentral areas, and the ability to exclude other likely causes, points strongly to a seismogenic origin for each horizon. This interpretation is bolstered by the facts that the deformation contains random fold axes, crosses facies boundaries, is associated with a periodically reactivated basement structural lineament, and crosscuts undeformed beds from both above and below. Moreover, mapping the distribution of deformation intensity allows for the interpretation of possible epicentral areas. The association of Cane Run deformation with other sedimentologic-stratigraphic anomalies related to reactivated basement faults, as well as their coincidence with the inception of a Taconian tectophase, suggest that Cane Run seismites are one of several responses to the distal transmission of far-field forces from the coeval Taconian orogeny into the foreland, largely via zones of basement structural weakness. Units like the Cane Run Bed and its equivalents, whose seismogenic origins can be confidently demonstrated, suggest that seismicity must have had a substantial influence at times on epicontinental sedimentation, even in seas far removed from orogenic sources of stress. [Copyright &y& Elsevier]

Abstract. Scoyenia beerboweri is a new ichnospecies of burrow from the late Ordovician (Ashgill) Juniata Formation in central Pennsylvania, USA. The burrows are abundant in red calcareous palaeosols, and were created by animals living at the time of soil formation, because they are filled with red sediment like that of the palaeosol matrix, and both cut across, and are cut by, nodules of pedogenic carbonate. The isotopically light carbon and oxygen of carbonate in the palaeosols indicate a terrestrial ecosystem of well-drained floodplains in a tropical seasonally-dry semi-arid palaeoclimate. Backfill layering within the burrows is evidence of a bilaterally symmetrical animal. Size distribution of the burrows reveals discontinuous growth, as found in arthropods. Ferruginized faecal pellets in the burrows indicate that they ingested sediment. For these reasons the burrows of Scoyenia beerboweri are most likely to be the work of millipedes. The nature of vegetation supporting them is unknown, although a single problematic plant-like fossil cast was found, and liverwort spores are widespread in rocks of this age. Vegetative biomass was limited judging from the degree of chemical weathering, extent of burial gleization and isotopic composition of carbon in the palaeosols. These distinctive respiration-dominated liverwort-millipede polsterlands lived at a time of global greenhouse climate, following Precambrian-Cambrian lichen-algal microbial earths and supplanted by Silurian brakelands of early vascular land plants. [ABSTRACT FROM AUTHOR]

Identifies conodonts representing several species and genera from the Upper Ordovician rocks in central Nevada. Geographic distribution; Amorphognathus ordovicicus; Gamachignathus ensifer; Oulodus ulrichi; Morphological features.

Documents the conodont biofacies distribution patterns in the Ordovician period in the United States. Morphology and features of Pseudobelodina manitoulinensis; Aphelognathus gigas; Baltobiodus alobatus; Besselodus arcticus.

Abstract: A paleomagnetic study of subsurface core samples from dolomitized carbonates of two producing reservoirs in the Upper Ordovician Trenton Formation, collected from four wells in southwestern Ontario yielded a paleomagnetic direction of D =152.3°, I =−12.3° (N =49, α 95 =8.7). This characteristic remanent magnetization (ChRM) direction was azimuth-corrected by aligning the viscous remanence magnetization (VRM) with the present Earth''s magnetic field direction. A drilling-induced magnetization (VRMdi) was present in less than half the specimens sampled in this study. In addition, where the VRM correction could not be made, a paleolatitudinal arc calculated from the inclination-only mean of I =−9.0° (N =34, α 95 =3.0°) intersected the apparent polar wander path in the Late Permian–Early Triassic. These paleodirections are similar to the paleomagnetic directions observed in Ordovician Trenton carbonates from the Michigan Basin and New York State, U.S.A., suggesting a related regional late Paleozoic remagnetization. [Copyright &y& Elsevier]

Well-preserved siliciclastic domal stromatolites, up to 2 m wide and 1·5 m high, are found in a 10 to 15 m thick interval within the Late Ordovician Eureka Quartzite of Southern Nevada and Eastern California, USA. These stromatolites appear as either isolated features or patchy clusters that contain more than 70% by volume quartz grains; their association with planar, trough and herringbone cross-bedding suggests that they were formed in an upper shoreface environment with high hydraulic energy. In this environment, sand bars or dunes may have provided localized shelter for initial microbial mat colonization. Biostabilization and early lithification of microbial mats effectively prevented erosion during tidal flushing and storm surges, and the prevalence of translucent quartz sand grains permitted light penetration into the sediment, leading to thick microbial mat accretion and the formation of domal stromatolites. Decimetre-scale to metre-scale stromatolite domes may have served as localized shelter and nucleation sites for further microbial mat colonization, forming patchy stromatolite clusters. Enrichment of iron minerals, including pyrite and hematite, within dark internal laminae of the stromatolites indicates anaerobic mineralization of microbial mats. The occurrence of stromatolites in the Eureka Quartzite provides an example of microbial growth in highly stressed, siliciclastic sedimentary environments, in which microbial communities may have been able to create microenvironments promoting early cementation/lithification essential for the growth and preservation of siliciclastic stromatolites. [ABSTRACT FROM AUTHOR]

Examines rare phosphatic microfossils of probable microvertebrates from Early and Middle Ordovician rocks of Wisconsin. Descriptions of ostracoderm Anatolepis types, vertebrate fragments and the palaeoscolecid worm; Significance of stratigraphic intervals to descriptive value; Role of fossil assemblages in identifying biologic affinities.

Cratonic quartz sandstones have presented several intractable problems. Besides their extreme textural and compositional maturity and paucity of shale, their sheet-like geometry is particularly notable. If the sandstones were entirely marine, as long supposed, such geometry is difficult to explain in terms of modern shelf sediments, which are generally held to be either relict or only slightly reworked by the Holocene transgression (palimpsest). Re-study of two quartz sandstones in the northern Mississippi Valley region reveals evidence for significant non-marine deposition followed by varying degrees of marine reworking during transgressions. Facies patterns are similar in the Cambrian Wonewoc and Ordovician St. Peter sandstones, both of which overlie unconformities. In both, a large-scale cross-stratified facies believed to represent aeolin ergs passes laterally into a planar-and-channelled facies inferred to represent sand plains composed of braided fluvial and aeolian sand sheet deposits. Criteria of Aeolian deposition in both facies include adhesion structures, large ripple index, fine climbing translatent lamination, grainfall and grainflow stratification. Criteria of braided fluvial deposition include shallow channels containing sequences of thinning-upward sets of trough cross-stratification, reactivation surfaces, low-index ripples, and polygonal cracks. Probable Aeolian sand sheets contain flat bedding punctuated by small channels, adhesion structures, and coarse-and ripples with large index. There is a conspicuous absence of trace and body fossils from these inferred non-marine deposits. In contrast is a burrowed and trough cross-stratified facies characterized by medium-scale cross-bedding alternating with bioturbated intervals and rare brachiopod or trilobite-mould coquinas, which is interpreted as shallow marine. In both formations, this last facies replaces laterally and overlaps the other two, reflecting transgression and variable reworking. The... [ABSTRACT FROM AUTHOR]

The fundamental biodiversity number, θ, as proposed by Hubbell, should be positively correlated with province area. Because θ can be calculated from preserved relative abundance distributions, this correlation can be tested in the fossil record for regions with known provinces. Late Ordovician (443-458 Ma) strata of Laurentia are divided into four geochemically and biologically distinct regions that reflect provinces in the epicontinental sea. We use existing and newly obtained bed-level census data to test whether Hubbell's θ is positively correlated with the area of these four regions, corresponding roughly to the Appalachian Basin, Cincinnati Arch, Upper Mississippi Valley, and western United States and Canada. Results indicate a positive relationship between province area and θ that suggests the influence of provincial area, among other factors, on diversity. This correlation highlights the inherent link between diversity and abundance structure at local and regional scales, such that changes at one scale will necessarily affect the other. Since diversity at these smaller spatial scales is an important component of global biodiversity, determining the nature of this relationship in the fossil record has implications for understanding how diversity is assembled globally throughout the Phanerozoic. [ABSTRACT FROM AUTHOR]

The lowermost Silurian Brassfield Formation of the Cincinnati Arch area records mid-continent deposition on a carbonate ramp that sloped gently into the Taconic foreland basin. The Brassfield is significant because it represents earliest Silurian deposition in the area resulting from sea-level rise following the late Ordovician glacial maximum, it records the faunal transition from the terminal Ordovician extinction, and its upper part contains tabulate coral-stromatoporoid reefs that are among the oldest Silurian reefs in North America. The lowermost unit of the Brassfield Formation, the Belfast Member, is the focus of this study. The Belfast previously has been interpreted as representing relatively shallow water deposition associated with the initial early Silurian transgression. Newly recognized sedimentological features, however, together with previous information, indicate that the Belfast was deposited in water deeper than previously recognized. The purpose of this paper is to evaluate previous studies of the Belfast that have lead to interpretations of shallow water deposition, present new sedimentological information indicative of deeper water deposition, and discuss the implications of those results. Previous interpretations of the Belfast as having been deposited in relatively shallow water, intertidal to shallow subtidal, including lagoonal, are equivocal. The Belfast exhibits 3D ripple marks and associated cross laminae, hummocks, hummocky and swaley cross stratification, and planar stratification, with thin interbeds of planar laminated mudstone, all consistent with deposition in an inner shelf-type setting, below fair-weather wave base, but above storm wave base (possibly on the order of 10-60 m deep). Trace fossils, including Chondrites, Rosselia, Teichichnus, Thalassinoides, and Palaeophycus, indicate that during rapid sedimentation associated with storms, organisms adjusted vertically. Under fair-weather conditions following storms, settling of suspended sediment formed planar laminae and organisms recolonized upper portions of some beds, while totally bioturbating others. Hence, the Belfast represents relatively deep-water deposition on the Ordovician-Silurian unconformity (which developed primarily under subaerial conditions) associated with a relatively rapid sea-level rise. The transition from the Belfast Member to the overlying part of the Brassfield Formation appears to record a sea-level fall. As such, the Belfast is a low-order sequence. The sea-level changes recorded by the Belfast and overlying part of the Brassfield are consistent with glacio-eustatic variations evident on published sea-level curves. An increase in subsidence also may have contributed to the rapid deepening recorded by the Belfast. Increased subsidence may have been associated with hydrostatic and/or sediment loading, Taconic orogenesis, dynamic subsidence (vis-à-vis dynamic topography) associated with northward directed subduction along the southern margin of Laurentia, or movement on regional structures, reflecting the influences of events at the southern plate margin or induced by hydrostatic loading. [ABSTRACT FROM AUTHOR]

As shallow aquifers become depleted or contaminated worldwide, use of deep aquifers will likely increase to meet growing water demands despite expensive drilling costs and well maintenance, and limited recharge to many of these deep systems. We discuss depletion of the Cambrian‐Ordovician sandstone aquifer, a deep bedrock aquifer that has been a major source of water in the Midwestern US for over 150 years. Using a participatory groundwater modeling approach with active stakeholder engagement, we developed a conceptual framework to assess risk to different sandstone units of the aquifer based on simulated heads and production well behavior (pumping levels and specific capacities). Over 320 m of static head decline has occurred since predevelopment in the deepest sandstone unit. Shallower units are actively being dewatered. Drawdown and head separation between sandstone units is even greater under pumping conditions and is most acute near a regional fault zone. Current depletion is prompting massive infrastructure changes to mitigate anticipated water supply shortages. Our results show that even with a substantial reduction in water use by 35% in 2030, many areas of the aquifer remain at High or Severe risk out to 2070. Head decline, as opposed to storage loss, is a critical metric for understanding depletion of deep bedrock aquifers. The participatory modeling process made clear that pumping levels at production wells should not be ignored in evaluations of aquifer sustainability and risk. Our conceptual risk framework could be applied to other deep bedrock aquifers undergoing depletion. Key Points: Over 320 m of head decline has occurred in the deep sandstone aquifer system underlying the United States' third largest metropolitan areaParticipatory modeling allows assessment of risk to groundwater supplies under pumping conditionsAssessment of deep aquifer sustainability requires understanding of multi‐aquifer wells, geologic barriers, and production well behavior [ABSTRACT FROM AUTHOR]

The glyptocystitoid rhombiferan Sprinkleocystis ektopios new genus and species is described from the Middle Ordovician (Caradoc) Benbolt Formation of Tennessee. This species is characterized by having four ambulacra bearing only terminal brachioles, the absence of lateral 5, and protuberant pectinirhombs and periproct. Many of its features are considered typical of the family Cheirocrinidae whereas others are more characteristic of the Glyptocystitidae. Its small size and simple ambulacral and pectinirhomb structures suggest a paedomorphic evolutionary origin, and its thecal morphology further suggests that the validity of a separate Cheirocrinidae and Glyptocystitidae may need reevaluation. [ABSTRACT FROM AUTHOR]

Fault-dismembered segments of a distinctive, extensive, highly allochthonous, and tectonically significant Ordovician (ca. 480-460 Ma) basin, which contains suites of bimodal metavolcanic rocks, associated base metal deposits, and thick immature deep-water (turbiditic) metasediments, occur in parts of the southern Appalachian Talladega belt, eastern Blue Ridge, and Inner Piedmont of Alabama, Georgia, and North and South Carolina. The basin's predominantly meta-sedimentary strata display geochemical and isotopic evidence of a mixed provenance, including an adjacent active volcanic arc and a provenance of mica (clay)-rich sedimentary and felsic plutonic rocks consistent with Laurentian (Grenvillian) upper-crustal continental rocks and their passive-margin cover sequences. Geochemical characteristics of the subordinate intercalated bimodal metavolcanic rocks indicate formation in a suprasub-duction environment, most likely a back-arc basin, whereas characteristics of metasedi-mentary units suggest deposition above Neoproterozoic rift and outer-margin lower Paleozoic slope and rise sediments within a marginal basin along Ordovician Laurentia's Iapetus margin. This tectonic setting indicates that southernmost Appalachian Ordovician orogenesis (Taconic orogeny) began as an extensional accretionary orogen along the outer margin of Laurentia, rather than in an exotic (non-Laurentian) arc collisional setting. B-type subduction polarity requires that the associated arc-trench system formed southeast of the palinspastic position of the back-arc basin. This scenario can explain several unique features of the southern Appalachian Taconic orogen, including: the palinspastic geographic ordering of key tectonic elements (i.e., back-arc, arc, etc.), and a lack of (1) an obducted arc sensu stricto on the Laurentian margin, (2) widespread Ordovician regional metamorphism, and (3) Taconic klippen to supply detritus to the Taconic foreland basin. [ABSTRACT FROM AUTHOR]

The Lower Ordovician middle Beekmantown Group is a very thin carbonate platform succession on the northern New York Promontory that thickens north into the Ottawa aulacogen near Montréal. The Tribes Hill Formation (Rossodus manitouensis Zone) records the earliest Ordovician (late Skullrockian, late early Tremadocian) eustatic high that submerged Laurentia, and produced the lowest Ordovician sequence along the New York Promontory. These dolostones are succeeded in the Beekmantown, New York, area by late Tulean?-Blackhillsian transgressive systems tract quartz arenites of the lower Fort Cassin Formation (Ward Member). The "Fort Ann Formation" (middle Stairsian, upper Tremadocian) of the southern Lake Champlain lowlands (=Theresa Formation sandstones in the Ottawa graben) is absent at Beekmantown, and moderate Stairsian (late Tremadocian) eustatic rise apparently did not inundate the Beekmantown area after Skullrockian-Stairsian boundary interval offlap. Highstand carbonates of the upper Fort Cassin Formation [Sciota Member = "Spellman Formation" and "Ogdensburg Member" of the "Beauharnois Formation" in the Montréal area; designations abandoned] at Beekmantown yield diverse conodonts seemingly characteristic of the Oepikodus communis-Fahraeu-sodus marathonensis Zone (new). However, associated trilobites, particularly Carolinites tasrnanensis (Etheridge, 19 19), show a cor- relation with the upper Trigonocerca lypica (trilobite) Zone of the Utah and the overlying Reutterodus andinus (conodont) Zone. This abrupt early Blackhillsian lithofacies change features the appearance of chitinozoans and conodonts known from marginal successions, and records the Laignet Point highstand (new). This highstand is recognized across Laurentia on the west Newfoundland and southern Midcontinent platforms. It is recorded on the east Laurentian continental slope by lower Oepikodus evae Zone dysoxic black mudstone in the Taconian allochthons. Taxonomic re-evaluations include Utrichodina Branson and MehI, 1933, with its genotype species U. abnormalis (Branson and MehI, 1933) emend., as the senior synonym of Colaptoconus Kennedy, 1994; Eucharodus Kennedy, 1980; and Glyptoconus Kennedy, 1980. Paraserratognathus An in An et at., 1983, emend. is the senior synonym of Wandelia Smith, 1991 and Stultodontus Ji and Barnes, 1994. Tropodus Kennedy, 1980 is the senior synonym of Chionoconus Smith, 1991. The trilobite fauna of the Sciota Member includes species of Isoteloides, Benthamaspis, Acidiphorus and Carolinites, of which I. fisheri is new. [ABSTRACT FROM AUTHOR]

Abundant silicified shell plates (valves) of some of the oldest-known chitons were recovered from the Late Cambrian Notch Peak Formation of Utah. The chiton fauna is dominated numerically by Matthevia wahwahensis new species, but also includes another mattheviid, Eukteanochiton milleri new genus and species, and a preacanthochitonid, Orthriochiton utahensis new genus and species. Robustum from the Early Ordovician Gasconade Formation of Missouri is herein reinterpreted as a septemchitonid chiton, and Hemithecella, from the Late Cambrian-Early Ordovician of the eastern United States, is once again considered a mattheviid chiton. Mattheviid valves are unique among chitons in that they are massive, elongate, and contain one or two tunnels; these characteristics have led some to exclude this family from the Polyplacophora. However, mattheviids and other chitons share many valve characters, including granules, an apical shelf, a thin anterior margin, bilateral symmetry, three valve types, and a shell layer perforated with canals. Furthermore, recently described chiton valves from the Silurian of Gotland, the Ordovician of Wisconsin, and the Cambrian-Ordovician of Missouri are gradational between the Notch Peak mattheviid valves and those of younger polyplacophorans. Also, Matthevia wahwahensis n. sp. has valves with a flat apical area, allowing for valve overlap, and so provides a link between the unusual chiton Matthevia variabilis, which had nonoverlapping, spiky valves, and Chelodes, a less disputed chiton. Known fossil assemblages reveal that, along the coastline of Laurentia during the Cambrian-Ordovician, chitons were diverse, consisting of at least four families and with much variation in valve shape. [ABSTRACT FROM AUTHOR]

Examines graptolites from near the Ordovician-Silurian boundary in Illinois and Iowa. Deposition of the strata yielding the graptolites during the initial transgression; Description of the Ordovician surface; Reflection of erosion in the transgressive sediments.

Describes flexible crinoids genera in the Upper Ordovician Maquoketa Formation of Illinois, Iowa and Minnesota. Systematic paleontology; Phylogeny of Ordovician and Lower Silurian flexible crinoids.

During the Late Ordovician, arborescent and frondose trepostome, and cystoporate Bryozoa were frequently bored in a manner distinctly different from Trypanites, Palaeosabella, and Vermiforichnus, domichnia that are commonly associated with these organisms. Maysvillian and Richmondian bryozoan taxa on the Cincinnati Arch were particularly infested by an unidentified organism that used the interior of bryozoan branches as its domicile. The domichnial trace Sanctum laurentiensis is newly described. Dwelling openings range in size from 1.1 mm to 3.2 mm and are located singly on surfaces of colony branches, commonly in a somewhat protected position. The circular opening leads through the exozone into an elongate or saccate chamber representing a variably shaped excavation of the bryozoan endozone. Traces ranging from 3.0 mm to 8.8 mm wide and 9.7 mm to 53 mm long are documented. Thin sections demonstrate that chambers were unlined and had irregular interior walls resulting from organismal mining of zooecial tubes. Cavity makers likely were multiple individuals of amphipod-like crustaceans (Arthropoda) that fed outside their domicile. Bryozoan colonies were occupied while upright, either entirely or partially live, or in some cases dead and overgrown by other bryozoans. Avoidance of predation and the ability to dwell and feed in a higher tier than that of infaunal tracemakers at the sediment-water interface were potential benefits of this domichnium. Presence of cavities reduced the strength of host branches, thus having a profound effect on colony morphology and growth over its lifetime. Unlike the many epizoans that used trepostomes as substrates with little long-term affect, Sanctum laurentiensis significantly impacted its bryozoan host. [ABSTRACT FROM AUTHOR]

Investigates the silurian deformation and metamorphism of Ordovician arc rocks of the Casco Bay Group in south-central Maine. Regional geological setting of the rocks; Stratigraphy of the upper Casco Bay Group; Structural geology of the rock; Conclusions.

Examines the presence of lingulate brachiopods in the Cambrian-Ordovician boundary beds in Utah. Phosphatic composition of brachiopoda; Affinities of the lingulate fauna; Chronostratigraphic framework of lingulate.

Selectivity patterns provide insights into the causes of ancient extinction events. The Late Ordovician mass extinction was related to Gondwanan glaciation; however, it is still unclear whether elevated extinction rates were attributable to record failure, habitat loss, or climatic cooling. We examined Middle Ordovician-Early Silurian North American fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per-taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk. Genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the Katian stage were particularly hard hit. The duration of the subsequent sampling gaps had little effect on extinction risk, suggesting that this extinction pulse cannot be entirely attributed to rock record failure; rather, it was caused, in part, by habitat loss. Extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled, a macroecological trait linked to thermal tolerance. A model trained on the relationship between 16 explanatory variables and extinction patterns during the early Katian interval substantially underestimates the extinction of exclusively tropical taxa during the late Katian interval. These results indicate that glacioeustatic sea-level fall and tropical ocean cooling played important roles in the first pulse of the Late Ordovician mass extinction in Laurentia.