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The well-preserved Llandovery (lower Silurian) succession of Anticosti Island (Quebec, eastern Canada) contains an expanded Aeronian–Telychian boundary interval when compared to other coeval basins. This boundary interval on Anticosti Island also includes two of the most important Llandovery biogeochemical events, the late Aeronian and Valgu events. These two events were previously documented in the Jupiter and Chicotte formations through the study of conodont, graptolite, and brachiopod biostratigraphy and δ13 C chemostratigraphy. Despite these multiple investigations, the exact position of the Aeronian–Telychian stage boundary on Anticosti Island has not been firmly established. Here we locally define and globally correlate chitinozoan biozones to refine the position of this stage boundary. The Ancyrochitina ramosaspina biozone, recognized in the Ferrum Member of the Jupiter Formation, correlates with the global Conochitina alargada biozone and indicates an Aeronian age. The Eisenackitina dolioliformis biozone suggests mostly a Telychian age for the Pavillon Member of the Jupiter Formation and the Chicotte Formation. Three new species are defined, namely Conochitina asselinae sp. nov., Spinachitina glooscapi sp. nov., and Ancyrochitina wilsonae sp. nov. (registration date: 4 December 2024, publication LSID: urn:lsid:zoobank.org:pub:11184506-F273-4D7A-BC28-A1BB4BC8FCD8, asselinae LSID: D282DA9D-6A9C-4B9E-AA6C-9ADC4473E95B, glooscapi LSID: 5801DC12-4EA1-439F-B7C8-FAF7C1B9D2C7, wilsonae LSID: 549EEF2F-7F19-4E6D-9F8E-384594B2FE65). Our new chitinozoan data, combined with previous studies, allow a comparison with the well-studied Baltic succession, confirming that limited unconformities mark the Aeronian–Telychian boundary interval on Anticosti Island, in contrast to the less complete coeval location. Our refined age model for the Aeronian to Telychian succession of Anticosti Island provides a solid baseline to study further Llandovery biochemical events in the aftermath of the Late Ordovician mass extinction. [ABSTRACT FROM AUTHOR]

Abstract: New high-resolution chemostratigraphy, in combination with updated biostratigraphy, refines the chronostrati-graphic resolution of the nearly 2 km thick Ordovician section below Anticosti Island. A total of 1414 horizons, spaced [...]

The resolution and fidelity of global chronostratigraphic correlation are direct functions of the time period under consideration. By virtue of deep-ocean cores and astrochronology, the Cenozoic and Mesozoic time scales carry error bars of a few thousand years (k.y.) to a few hundred k.y. In contrast, most of the Paleozoic time scale carries error bars of plus or minus a few million years (m.y.), and chronostratigraphic control better than [+ or -]1 m.y. is considered 'high resolution.' The general lack of Paleozoic abyssal sediments and paucity of orbitally tuned Paleozoic data series combined with the relative incompleteness of the Paleozoic stratigraphic record have proven historically to be such an obstacle to intercontinental chronostratigraphic correlation that resolving the Paleozoic time scale to the level achieved during the Mesozoic and Cenozoic was viewed as impractical, impossible, or both. Here, we utilize integrated graptolite, conodont, and carbonate carbon isotope ([delta][sup.13][C.sub.carb]) data from three paleocontinents (Baltica, Avalonia, and Laurentia) to demonstrate chronostratigraphic control for upper Llandovery through middle Wenlock (Telychian--Sheinwoodian, ~436-426 Ma) strata with a resolution of a few hundred k.y. The interval surrounding the base of the Wenlock Series can now be correlated globally with precision approaching 100 k.y., but some intervals (e.g., uppermost Telychian and upper Sheinwoodian) are either yet to be studied in sufficient detail or do not show sufficient biologic speciation and/or extinction or carbon isotopic features to delineate such small time slices. Although producing such resolution during the Paleozoic presents an array of challenges unique to the era, we have begun to demonstrate that erecting a Paleozoic time scale comparable to that of younger eras is achievable. doi: 10.1130/1326602.1

A new type of gold occurrence recently discovered in the Carlin trend, north-central Nevada, is clearly distinct from classic Carlin-type gold ore. These occurrences are interpreted to be of sedimentary exhalative (sedex) origin because they are stratiform and predate compaction and lithification of their unaltered Devonian host rocks. They contain barite that exhibits [[Delta].sup.34]S and [[Delta].sup.18]O values identical to sulfate in Late Devonian seawater and sedex-type barite deposits. Abrupt facies changes in the host rocks strongly suggest synsedimentary faulting and foundering of the carbonate shelf during mineralization, as is characteristic of sedex deposits. Gold occurs both as native inclusions in synsedimentary base-metal sulfides and barite, and as chemical enrichments in sulfide minerals. The absence of alteration and lack of [[Delta].sup.13]C and [[Delta].sup.18]O isotopic shift of primary carbonates in these rocks is strong evidence that this gold was not introduced with classic Carlin-type mineralization. Collectively, these features show that the Devonian strata were significantly enriched in gold some 300 m.y. prior to generation of the mid-Tertiary Carlin-type deposits. These strata may have been an important, perhaps even vital, source of gold for the latter. Although gold is typically low in most Zn-Pb-rich sedex deposits, our evidence suggests that transport of gold in basinal fluids, and its subsequent deposition in the sedex environment, can be significant.

New high-resolution chemostratigraphy, in combination with updated biostratigraphy, refines the chronostratigraphic resolution of the nearly 2 km thick Ordovician section below Anticosti Island. A total of 1414 horizons, spaced at 1.0-1.5 m intervals, were sampled from the New Associated Consolidated Paper (NACP) drill core and analyzed for major and trace elemental composition by portable X-ray fluorescence analyzer (pXRF). Select micrite and calcareous shale powders were then analyzed for δ13Ccarb (number of samples, N = 364) and 87Sr/86Sr ( N = 25). Our results indicate a Floian to early Darriwilian (F3-Dw1) age for the Romaine Formation, a middle Darriwilian to Sandbian (Dw2-Sa1) age for the Mingan Formation, a lower to mid-Katian (Ka1-Ka2) age for the Macasty Formation, an upper Katian (Ka3) age for the lower Vauréal Formation, an uppermost Katian (Ka4) age for the upper Vauréal, and a Hirnantian (H1) age for the Ellis Bay Formation. This integrated chemostratigraphic and biostratigraphic synthesis establishes the position of numerous unconformities, the duration of the intervening depositional sequences, and rates of sedimentation. [ABSTRACT FROM AUTHOR]

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Upper Ordovician hardgrounds display a spectrum of complexity reflecting a range of local to global-scale processes. Hardgrounds are cemented seafloor surfaces typically marked by the presence of encrusting taxa and borings. Many hardgrounds show evidence for successive episodes of colonization by hard substrate specialists and are associated with localized evidence of seafloor erosion such as overhangs and reworked concretions. They commonly show trace amounts of pyrite and dolomite cements indicating an association with sulfate reduction. The most widespread hardgrounds are highly complex and unravelling their history provides insights into global biogeochemical events. The Curdsville and Kirkfield hardgrounds in the Appalachian Basin (Kentucky and Ontario) represent relatively simple end members of the hardground spectrum. They covered 10s to 100s km2 and formed relatively quickly during the early Katian. They display both planar to subplanar and hummocky to topographically complex surfaces (cm-scale) and contain highly diverse encrusting echinoderm faunas. Study of these surfaces yields important insights into the evolutionary history of encrusting communities. By contrast, the slightly younger hardground at the top of the Galena Group (Ka1) is a surface that is present throughout most of the Midcontinent Basin (>7.5 × 105km²). It is an example of a highly complex surface that was repeatedly modified by erosion and mineralization. Near the eastern margin of the basin in Indiana, the capping Galena hardground is pinnacled with cavity-filling sharpstone clasts, phosphate grains and bored crusts, iron ooids, and pyritic impregnated surfaces. It is onlapped by graptolitic shales of the Kope Formation (Fm) (Ka1) indicating an unconformity of approximately 1 m.y. To the west, in Illinois, the Kope Fm is erosionally truncated and the hardground is directly overlain by graptolitic shales of the Waynesville Fm (Ka3), where the unconformity expands to nearly 4 m.y. Toward Iowa, the hardground is onlapped by meters of phosphorite. Taken together, these observations reveal that the capping Galena Group hardground reflects a complicated history of repeated subaerial exposure, karsting, and marine flooding by a dysoxic to anoxic water mass with fluctuating redox conditions, similar to the age equivalent hardground at the base of the Fjäcka Shale in the Baltic Basin. Thus, hardground studies provide important insights for resolving the temporal continuity of the Upper Ordovician rock record and unravelling processes that controlled carbonate precipitation and dissolution and the evolution of sea floor communities. Some simple hardgrounds may have formed through random exhumation of cemented sediments on the sea floor through the effects of storm scour. However, their clustering into certain portions of the Upper Ordovician suggests that processes that affected sea water chemistry may also be involved. The most complex surfaces reflect major environmental perturbations with large amplitude sea level oscillations and redox changes that in some cases generated rare-earth enriched phosphorites. [ABSTRACT FROM AUTHOR]

The late Katian Elkhorn event is a biogeochemical perturbation preceding the Late Ordovician mass extinction (LOME) with an exceptional record in the United States (U.S.). Results of our recent studies in this interval allow revised temporal ordering to strata across multiple basins providing insights into the magnitude of environmental disturbance and associated processes and feedbacks. The record of the Elkhorn event spans portions of the Appalachian and Midcontinent basins in the eastern U.S. and the Williston Basin and Cordilleran margin in the west. Our work focuses heavily on the Midcontinent Basin in particular, as it shares many characteristics of size, tectonic setting, and lithofacies with the Baltic Basin, providing the potential for resolving global signatures of the event. In its type-area, the Cincinnatian Series ends with the Elkhorn event. The succession is marked by shallowing from subtidal to marginal marine facies, capped by a karstic sequence boundary. Our new conodont data demonstrate that an overlying white to pink crinoidal grainstone package, previously assigned to the basal Silurian “white” Brassfield Formation near the Ohio-Indiana state line, is in fact Upper Ordovician. Further, δ13Ccarb values in this unit are elevated, in line with later phases of the Elkhorn event (2‰ more positive than reported Rhuddanian values). These findings support a correlation of the grainstone interval with the Fernvale Formation of central Tennessee. To the east, much of the northern Appalachian Basin was overfilled with widespread marginal marine to terrestrial red beds by the onset of the Elkhorn event, while the Midcontinent Basin to the west remained relatively sediment starved. In the southern Midcontinent, the mid-Elkhorn event sequence boundary was onlapped by ironstone deposition (lower Fernvale Formation). The ironstones are overlain by sparry and hematitic grainstones with localized bioherms. In Arkansas, where the Fernvale is thickest (>30 m), the sparry phase gives way upward to manganese carbonates and bioherms. Across the region, the Fernvale is, in turn, cut by a sequence boundary, suggesting a yet higher Katian sequence, and is perforated by paleokarst pockets that are filled and overlain by upper Katian (Ka4) sediments. This sequence boundary is onlapped by black shales and the thickest (>10 m) phosphorite of the Ordovician at the end of the Elkhorn event. Previous studies have suggested age equivalence of the Elkhorn and Paroveja δ13Ccarb excursions in Laurentia and Baltica. Despite the attraction of aligning the latest Richmondian and Pirgu regional stages, our data sets demonstrate that this is a miscorrelation. Critical to this revision are new integrated biostratigraphic and chemostratigraphic data sets in a transect from the margin of the Appalachian Basin into the Midcontinent Basin. The new data reveal that the Elkhorn Shale and Fernvale Formation are overlain by the Brainard and laterally equivalent Sylvan, and Mannie shales. These shale successions contain graptolites of the complanatusand pacificus zones. Thus, the Elkhorn event occurred in the latest manitoulinensis Zone, suggesting correlation with the Baltic Moe δ13Ccarb excursion. Our extensive new data sets provide regional chronostratigraphic correlation of strata deposited during the Elkhorn event. When temporally ordered, these records provide evidence for high amplitude sea level oscillations, major redox fluctuations, and reef pulses that demonstrate the waxing and waning of continental ice sheets on Gondwana and the spread of oceanic anoxia only a few million years before the LOME. These findings further call into question traditional models of rapid glaciation during a long-lived greenhouse state as the sole driver of the LOME and emphasize the need for new integrated Upper Ordovician research initiatives to better characterize Katian events. [ABSTRACT FROM AUTHOR]

Study of a subsurface core (named F688) from northern Indiana provides integrated data sets linking Katian chronostratigraphic records of the Appalachian and Midcontinent basins. The F688 core shows a variety of shallow- and deep-water facies containing numerous, well-preserved and zonally significant fossil species and diagnostic chemostratigraphic patterns. The succession belonging to the Cincinnatian Regional Stage in the F688 core is 210 m thick. Detailed benchtop examination of the succession revealed several phosphatic intervals, rich brachiopod faunas, multiple graptolitic horizons, and at least two tephras. Elemental analysis was conducted at 60 cm spacing quantifying lithofacies composition. Based on these results, the succession was assigned to six previously defined lithostratigraphic units (Kope, Waynesville, Liberty, Whitewater, Elkhorn, and Fort Atkinson formations). This lithostratigraphic succession shares components with both the Appalachian and Midcontinent basins, suggesting deposition near their shared margin. Twenty samples yielded abundant, well-preserved, low-diversity conodont assemblages with long-ranging taxa that clearly demarcate the position of the Ordovician–Silurian boundary at the top of the succession in the core. More than fifty palynologic samples, targeting graptolite-bearing intervals, were processed for chitinozoans and produced important new insights. The Kope Formation contains the chitinozoan species Belonechitina kjellstromi, Hercochitina downiei, and Clathrochitina sp. nov., co-occurring with a graptolite assemblage suggestive of the Geniculograptus pygmaeus Zone. Samples from the overlying Waynesville Formation produced graptolites indicative of the upper G. pygmaeus to Paraorthograptus manitoulinensis zones co-occurring with the long-ranging chitinozoan species Belonechitina micracantha and Plectochitina spongiosa as well as several new species of the genera Tanuchitina and Hercochitina. Higher in the core, the Liberty, Whitewater, Elkhorn, and Fort Atkinson formations yielded chitinozoan species characteristic of the upper Katian biozones of Anticosti Island and Nevada, such as Tanuchitina anticostiensis, Hercochitina longi, and Eisenackitina ripae. Results of δ13Ccarb analysis reveal partial preservation of the Kope, Waynesville, and Elkhorn excursions. A tephra in the rising limb of the Waynesville Excursion yielded needle-shaped clear zircons that will provide a high-precision U-Pb age. The Fort Atkinson Formation is overlain by the Brassfield Formation containing Silurian conodonts and δ13Ccarb values suggesting an Aeronian age. Chronostratigraphic data from our study of the F688 core resolves longstanding uncertainty about correlations between strata of Katian Age in the Appalachian and Midcontinent basins. Integration of core F688 with our other regional chronostratigraphic data in the Midcontinent Basin demonstrates that the Fort Atkinson Formation of the Indiana and Illinois subsurface is age equivalent to the Fernvale Formation of Tennessee, Arkansas, and Oklahoma. Across this area, the Fernvale is overlain by graptolitic shales of the uppermost P. manitoulinensis to basal Dicellograptus complanatus graptolite zones. By contrast, the type Fort Atkinson Formation of Iowa is interpreted to occur completely within the younger D. complanatus Zone. These regional correlations taken as a whole suggest that the uppermost Katian (all of Ka4) and all but the uppermost Hirnantian are missing throughout much of the Appalachian Basin. By contrast, the Midcontinent Basin contains a much more complete upper Katian and Hirnantian succession. Our comprehensive approach is correcting temporal miscorrelation and providing robust chronostratigraphic context for study of biogeochemical events, which will further enable us to disentangle proxy data and identify the processes that drove the Katian diversity peak and culminated in the Late Ordovician mass extinction. [ABSTRACT FROM AUTHOR]

Systematic collecting through the upper Wenlock (upper Homerian) and lower Ludlow (Gorstian and lowermost Ludfordian) Silurian rock succession of the Long Mountain, Powys, Wales, identifies some 48 chitinozoan species that distinguish four biozones, two subzones and an interregnum. Consideration of the chitinozoan biozones together with those of the graptolites enables a local three-fold subdivision of the late Homerian lundgreni graptolite Biozone, and the distinction of lower and upper intervals for the Gorstian incipiens graptolite Biozone. The base of the Ludlow Series in the Long Mountain more or less equates to the base of the Cingulochitina acme chitinozoan Biozone, although no key chitinozoan first or last appearance datums are associated with the series boundary itself. The new graptolite–chitinozoan biozonation allows enhanced correlation between upper Wenlock and lower Ludlow sedimentary deposits of the Lower Palaeozoic Welsh depositional basin and those of the palaeo-shelf in the stratotype Wenlock and Ludlow areas of Shropshire. Chitinozoans seem affected by the phenomena that caused the late Wenlock ‘Mulde extinction’ in graptolites but, with the final disappearance of 9 species and re-appearance of 11 species following an interval of overall low diversity, they seem to have suffered less severely than their macro-zooplanktonic contemporaries. [ABSTRACT FROM AUTHOR]

Fluid inclusions hosted by Mississippi Valley-type (MVT) ores in the Illinois-Kentucky district were analyzed using microthermometry, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and Raman spectroscopy to characterize the composition and temperature of mineralizing fluids in order to seek insights into the process of ore formation. Results from the present study support the interpretation of previous microthermometry studies that relate mineralization to mixing of two higher temperature brines and a cooler, dilute meteoric fluid. Fluid inclusions in the Illinois-Kentucky district have overall higher atomic ratios of Ba/Na, Ca/Mg, K/Na, Sr/Na, and lower atomic ratios of Mg/Na compared to inclusions in the Ozark MVT districts and are thus compositionally distinct. These differences may indicate that the Illinois-Kentucky and Ozark MVT ore fluids were derived largely from different source basins or may reflect input from igneous rocks in the Illinois-Kentucky district. Low Ca/Mg ratios of Illinois-Kentucky fluid inclusions indicate that mineralizing fluids were dolomitizing and therefore could not have traveled far through the limestone ore host formations, but instead traveled through deeper nonlimestone units before rising along faults and fractures in the district. Some fluid inclusions in Illinois-Kentucky MVT mineralization yielded strong LA-ICP-MS responses for ore metals. A single sphalerite-hosted fluid inclusion out of 18 analyzed contained detectable Pb, corresponding to a concentration of 420 ppm, whereas numerous fluorite-hosted fluid inclusions contained detectable Pb, Zn, and Cu, corresponding to maximum concentrations on the order of 1,000s of ppm. The high and similar concentrations of Cu, Pb, and Zn in some fluorite-hosted fluid inclusions in the Illinois-Kentucky district are problematic because Cu sulfide mineralization should be much more abundant than Pb and Zn sulfide mineralization owing to the lower solubility of Cu relative to Pb and Zn in the presence of reduced sulfur, which is not observed in the field. This raises the possibility that ore metals may exist as solid phases in suspension or adhering to fluid inclusion walls in some inclusions, rather than as dissolved species in aqueous solution. Raman microprobe analyses of fluid inclusions hosted by minerals occurring throughout the paragenetic sequence detected methane concentrations ranging from about 40 to 1,200 ppm, with most on the order of 100s ppm. Even for the lowest methane concentration determined, redox conditions would have been reducing, at a log of -55. 4 at a temperature of 100°C. At such reducing conditions, sulfide would predominate over sulfate; this is supported by high concentrations of Ba in the fluid inclusions. The overall reducing conditions throughout the paragenetic sequence and the possible presence of both metal-poor and -rich fluid inclusions would suggest that mixing between a metal-rich, sulfide-poor fluid and a metal-poor, sulfide-rich fluid were an important mechanism for sulfide mineral precipitation. Minimum depths of mineralization estimated from methane concentrations in fluid inclusions range to about 1,500 m and possibly 2,500 m, which would not have been reached until Late Pennsylvanian to Permian time, i. e., during the Alleghanian orogeny. [ABSTRACT FROM AUTHOR]