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The Middle Devonian (lower–middle Givetian) Hamilton Group of New York State is an iconic unit in North America, which has contributed many key concepts in stratigraphy, sedimentary geology, paleoecology, and evolution. This interval comprises a 100- to 1200-m-thick clastic wedge, shed westward from the Acadian Mountains, with thin but persistent carbonates. Despite the rich and diverse invertebrate fauna that consists of more than 300 species of corals, bryozoans, brachiopods, mollusks, echinoderms, and trilobites, the age of the Hamilton Group is rather poorly constrained in terms of chronostratigraphy owing to the rarity of biostratigraphically useful conodonts and goniatites. The upper part of the Hamilton Group that is the focus of this paper apparently belongs to the Polygnathus timorensis to middle Polygnathus ansatus Conodont chronozones. The middle to upper Hamilton Group in New York State comprises three formations—the Skaneateles, Ludlowville, and Moscow—each defined as an interval delimited with a sharply based fossiliferous limestone-calcareous siltstone; these formations are interpreted as containing condensed transgressive deposits overlain by thicker highstand to falling-stage shales, mudstones/siltstones, and sandstones. The eastern equivalents of these formations are dominated by fine-grained sandstones and siltstones and include two formations: the Panther Mountain Formation, equivalent to the Skaneateles and Ludlowville formations combined, and the Cooperstown Formation, equivalent to the Moscow Formation. In the present paper, we review, revise and update a hierarchical framework of lithostratigraphic subdivisions of these formations, including 24 members (four new), 50 submembers (more than half newly proposed or redefined; 14 informal at this time), and more than 80 named beds, both formal and informal. This refined lithostratigraphy provides an excellent framework for studying high-resolution sequence stratigraphy. As defined herein, members and most submembers represent high-frequency depositional sequences with basal shell-rich carbonates and abrupt flooding surfaces that mark the bases of highstand deposits. Not only are most of the members and submembers traceable across western and central New York, but also to a lesser extent into adjacent regions that include southern Ontario, Ohio, the Michigan Basin, and northeastern Pennsylvania. Nevertheless, much work on correlation remains to be done in eastern New York and central Pennsylvania, where local progradation of siliciclastics and expansion of successions obscures many of the finer scale features. [ABSTRACT FROM AUTHOR]

Silurian strata within the tristate area of Indiana, Ohio, and Kentucky have been thoroughly studied for well over a century. Due to rapid facies changes throughout the region numerous lithostratigraphic terminologies were established, many of which were difficult to correlate even over short distances. Recently these stratigraphic complexities have received renewed interest due to advancements in bio-, chemo-, and sequence stratigraphy that greatly improved our understanding of the tristate area. These improvements had significant implications for our ability to correlate Rhuddanian through lower Sheinwoodian strata between the Appalachian and Illinois basins and allowed unified nomenclatural and sequence stratigraphic hierarchies for this interval to be developed across the Cincinnati Arch. Recent advancements in regional chronostratigraphy of Silurian strata, however, highlight several discrepancies with regards to the 3rd- and 4th-order sequence stratigraphic hierarchies assigned within these basins. In an effort to alleviate these points of disagreement, we contribute new δ13Ccarb chemostratigraphic and sequence stratigraphic analyses of a basinward Appalachian section from Scioto County, Ohio, spanning upper Telychian through Gorstian strata assigned to the Estill through Tymochtee formations, complemented by gamma-ray core scans for localities traversing northwestward from the sampled core section into western Ohio. These new data allow unified nomenclatural and sequence stratigraphic hierarchies to be developed throughout the region for strata spanning the upper Telychian through Gorstian stages. Additionally, these findings highlight a significant shift in the primary sites of sediment accommodation during the studied depositional interval. [ABSTRACT FROM AUTHOR]

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]

Abstract: Delineation of stratigraphic sequences and their component systems tracts in mudrock-dominated facies is generally difficult due to the relatively homogenous, fine-grained nature of the strata. In this study, we apply a multi-proxy analytical approach to a thick Devonian mudrock-dominated succession through detailed analysis of sedimentologic, paleobiologic, and geochemical data through 600m of mudrock-rich facies. Varied combinations of proxies prove to be most useful in delineating sequence development in anoxic-, dysoxic-, and oxic-dominated mudrock settings, and in mixed mudrock–carbonate and mixed mudrock–sandstone successions. These interpretations are tested against an established sequence stratigraphic framework for 11 Middle to Upper Devonian (mid-Eifelian to lower Famennian) sequences in the Appalachian Basin. The sequences presented here further detail and refine global Devonian T–R cycles Id to IIe of the well known Johnson, Sandberg and Klapper sea-level curve. The usefulness of proxies in delineating depositional sequences and systems tracts varies dependent on depositional, paleoceanographic, paleoecologic, and early diagenetic conditions. Those proxies that show a range of variations in specific settings, such as grain size, degree of bioturbation, and concentrations of TOC and elements/elemental ratios (e.g., CaCO3, Al, Ti, Mg, Sc, Si, Mo, Ni, V; Si/Al and Ti/Al) may help delineate depositional dynamics related to redox conditions, condensation, dilution, and clastic, biologic, and/or authigenic sediment sources. In fine-grained, anoxic-dominated facies, interpreted to represent basinal settings, sequences and systems tracts are best delineated by anoxic-related proxies TOC and Mo. In intermediate, dysoxic-dominated settings, TOC, Mo, bioturbation, and Al remain effective indicators of sequence development. In relatively oxygenated, mudrock-rich and carbonate poor sequences, bioturbation may function as the most effective proxy for recognizing systems tracts. For mixed fine-grained siliciclastic–carbonate successions, concentration and type of CaCO3 (e.g., benthic macroskeletal, pelagic styliolinid/dacryoconarid, and micritic/calcisilt) are useful in identifying position within cycles. In more proximal, carbonate-poor successions, fine- and coarse-grained fractions become increasingly differentiated; these can be distinguished by relatively high Si/Al ratios (Si/Al≥ca. 5). Elemental ratios indicative of coarser clastic input (e.g., Si/Al, Zr/Al and Ti/Al) are applicable to identifying position with a sequence, but they may also be affected by input from eolian, volcanogenic, or biogenic sources. In addition, fluxes of siliciclastic, carbonate, and TOC sediment types may dilute the concentration of the others. Multiple lines of evidence should be examined in interpreting relative depth and position within a sequence. [Copyright &y& Elsevier]

Abstract: The well-exposed Middle Devonian rocks of the Appalachian foreland basin (Onondaga Formation; Hamilton Group, Tully Formation, and the Genesee Group of New York State) preserve one of the most detailed records of high-order sea-level oscillation cycles for this time period in the world. Detailed examination of coeval units in distal areas of the Appalachian Basin, as well as portions of the Michigan and Illinois basins, has revealed that the pattern of high-order sea-level oscillations documented in the New York–Pennsylvania section can be positively identified in all areas of eastern North America where coeval units are preserved. The persistence of the pattern of high-order sea-level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea-level oscillation, as opposed to autocylic controls, such as sediment supply, which would be more local in their manifestation. There is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to Milankovitch orbital variations, with the short and long-term eccentricity cycles (100kyr and 405kyr) being the dominant oscillations in many settings. Relative sea-level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism, given that the Middle Devonian appears to record a greenhouse phase of Phanerozoic history. These new correlations lend strong support to a revised high-resolution sea-level oscillation curve for the Middle Devonian for the eastern portion of North America. Recognized third-order sequences are: Eif-1 lower Onondaga Formation, Eif-2: upper Onondaga and Union Springs formations; Eif–Giv: Oatka Creek Formation; Giv-1: Skaneateles, Giv-2: Ludlowville, Giv-3: lower Moscow, Giv-4: upper Moscow–lower Tully, and Giv-5: middle Tully–Geneseo formations. Thus, in contrast with the widely cited eustatic curve of Johnson et al. (1985), which recognizes just one major transgressive–regressive (T–R) cycle in the early–mid Givetian (If) prior to the major late Givetian Taghanic unconformity (IIa, upper Tully–Geneseo Shale), we recognize four T–R cycles: If (restricted), Ig, Ih, and Ii. We surmise that third-order sequences record eustatic sea-level fluctuations of tens of meters with periodicities of 0.8–2myr, while their medial-scale (fourth-order) subdivisions record lesser variations primarily of 405kyr duration (long-term eccentricity). This high-resolution record of sea-level change provides strong evidence for high-order eustatic cycles with probable Milankovitch periodicities, despite the fact that no direct evidence for Middle Devonian glacial sediments has been found to date. [Copyright &y& Elsevier]

The late Wenlock Series (Homerian Stage) of the northern Midland Platform (central England) comprises silty mudstones and limestones of the upper part of the Coalbrookdale and overlying Much Wenlock Limestone formations. Based on outcrop studies and borehole data, the sequence stratigraphical interpretation developed for the inliers of the West Midlands is slightly revised, and extended to the stratotype sections along Wenlock Edge. A single third-order cycle of sea-level change is identified, punctuated by a regressive-transgressive episode associated with a higher-order glacioeustatic cycle, allowing the upper Wenlock Series of the area to be divided into two subsequences (A and B). Subsequence A and the early transgressive systems tract began with regression associated with the basal sequence boundary in late Cyrtograptus lundgreni Biozone times. This was followed by a period of slow transgression or still stand, allowing shallower water carbonate environments to prograde. A minor phase of regression followed, resulting in the generation of the shallowest water deposits of both the Lower Quarried Limestone and Farley members (of the MuchWenlock Limestone and Coalbrookdale formations, respectively). The overlying Subsequence B and the late transgressive systems tract are marked by transgression and a period of rapid sea-level fluctuation and are likely contained within the Gothograptus nassa Biozone. A minor highstand is widely recognizable at this time. The rest of Subsequence B consists of an initial phase of weak progradation (highstand systems tract), followed by a marked regression (falling stage systems tract) culminating in an erosive upper sequence boundary at or close to the top of the Monograptus ludensis Biozone, but within the uppermost Much Wenlock Limestone Formation. Above Subsequence B is a marked transgression into the Lower Elton Formation and the Ludlow Series. Both late Wenlock lowstands and the succeeding flooding events have been recognized on other palaeocontinents, reflecting the eustatic nature of sea-level changes reported here. [ABSTRACT FROM AUTHOR]

Abstract: Sequence stratigraphy provides an alternative approach to correlation that may also serve as a predictive framework for the interpretation of sea-level and sedimentological change. The main aim of this study is to apply sequence stratigraphic concepts to the biostratigraphically well constrained shallow to moderately deep shelf carbonates and basinal graptolitic shale facies of the Silurian successions in the Carnic Alps of Austria in order to correlate the sequence packages and sea-level changes established there with those identified in other areas of North America and Europe. Documenting local sea-level curves is essential for determining global eustasy. The sea-level curve for the Silurian of the Carnic Alps has been elaborated within a refined stratigraphic framework for the Silurian based on conodont and graptolite biozonation [Melchin, M.J., Cooper, R.A., Sadler, P.M., 2004. The Silurian Period. In: Gradstein, F.M., Ogg, J.G., Smith, A.G. (Eds), A Geologic Time Scale. Cambridge University Press, Cambridge, pp. 188–201.]. In particular, the minor and frequent sea-level changes within the Silurian of the Carnic Alps are of special interest as these stratigraphic intervals are poorly preserved and not well studied in other Silurian localities. The interpretation of the field and microfacies analysis indicates major sequence boundaries in the Llandovery (3), Wenlock (3), Ludlow (3) and Přídolí–Lochkovian (2) which may be correlated with coeval disconformities in the Appalachian Foreland Basin of eastern North America and/or in the Welsh Basin of the British Isles. The following times appear to represent relative sea-level highstand maxima in the Silurian of the Carnic Alps, as indicated by dark, graptolitic shales in deep shelf to basinal carbonate-dominated sections: a) early Aeronian, approximately the Coronograptus cyphus graptolite Zone/Demirastrites triangulatus graptolite Zone), b) the early Telychian (Oktavites spiralis graptolite Zone; Pterospathodus celloni conodont Superzone), c) late Telychian (lower Pterospathodus a. amorphognathoides conodont Zone); d) early to middle Sheinwoodian (Kockelella ranuliformis to Ozarkodina sagitta rhenana conodont Zones; Monograptus riccartonensis graptolite Zones); e) mid-Wenlock ((?upper Kockelella walliseri conodont Zone; Cyrtograptus rigidus graptolite Zone); f) mid Homerian (Ozarkodina bohemica conodont Zone; Gothograptus nassa graptolite Zone); g) near the Wenlock–Ludlow boundary (Neodiversograptus nilssoni graptolite Zone); h) Polygnathoides siluricus conodont Zone; i) near the Ludlow–Přídolí boundary (upper Ozarkodina snajdri Interval Zone); j) lower Přídolí (Monograptus parultimus graptolite Zone) and k) at the Silurian–Devonian boundary (earliest Lochkovian: Icriodus woschmidti woschmidti conodont Zone. Of these, the earlier (at least b–e) are well represented in the Appalachian Basin, as in Avalonian sections in Great Britain and in Baltica. Johnson [Johnson, M.E., 2006. Relationship of Silurian sea-level fluctuations to oceanic episodes and events. GFF 128, 115–121.] documented eight major highstands in global sea-level during the Silurian. The temporal resolution obtained in the Carnic Alps for local sea-level changes allows for refinement of the Telychian to Přídolí sea-level curve, as the stratigraphic successions are chronologically well-defined using both conodont and graptolite biostratigraphy and K-bentonite levels. Nearly all inferred deepenings in the Carnic Alps section, with the exception of that in the Polygnathoides siluricus conodont Zone, approximately match highstands recorded on the Silurian sea-level curves of Johnson [Johnson, M.E., 1996. Stable cratonic sequences and a standard for Silurian eustasy. In: Witzke, B.J., Ludvigson, G.A., Day, J. (Eds.), Paleozoic sequence stratigraphy – Views from the North American Craton. Geol. Soc. Am. Spec. Pap. vol. 306, Boulder, pp. 203–212., Johnson, M.E., 2006. Relationship of Silurian sea-level fluctuations to oceanic episodes and events. GFF 128, 115–121.]; however, the two Telychian highstands are not distinguished but rather are combined as highstand 4 on the Johnson curve, although they are recognized by Loydell [Loydell, D.K., 1998. Early Silurian sea-level changes. Geol. Mag. 135 (4), 447–471.], and the upper Kockelella walliseri conodont Zone deepening is not explicitly numbered by Johnson. These similarities suggest pervasive and probably eustatic events that are manifested in the Apulia Terrane [Cocks, L.R.M., Torsvik, T.H., 2002. Earth geography from 500 to 400 million years ago: a faunal and palaeomagnetic review. J. Geol. Soc. Lond. 159 (6), 631–644.], Laurentia and Avalonia during these time intervals. [Copyright &y& Elsevier]

Abstract: Recurrent taphofacies, including conservation lagerstätten, are identified within a spectrum of facies in fourth-order sequences in the Middle Cambrian Wheeler, and Marjum formations of the Drum Mountains and House Range, west-central Utah. These sequences are 3–20 m thick and commence with sharply-based compact, oncolitic, oolitic, or pelletal pack- and grainstones with sharply-defined, corroded and mineralized upper contacts that record drowning discontinuities and early transgressive systems tracts (TSTs). Overlying intervals of calcareous shale and thin-bedded wacke- to packstones with abundant, disarticulated polymerid and agnostoid trilobites represent late TSTs. These are commonly followed by lavender-gray mudstones rich in sponge spicules and comminuted fossil debris that reflect condensed maximum flooding zones. The overlying early highstand (HST) intervals of black, fissile shales are typically barren except for indistinct, circular carbonized algae, but in rare instances, include soft-bodied animal remains. A combination of lower dysoxic–anoxic conditions, with a fluctuating oxycline, and relatively rapid episodic influx of fine-grained detrital sediment favored repeated burial and preservation of abundant organic detritus and rarely soft-bodied animals. Interbedded dark gray, shales include abundant articulated agnostoid trilobites and diminutive polymerids (e.g., Jenkinsonia). Overlying platy, calcareous bedding planes covered with articulated bodies and molts of the polymerid Elrathia indicate rapid blanketing of undisturbed seafloors by calcareous mud layers. These beds grade upward successively into interbedded, sparsely fossiliferous platy to flaggy shale and thin, pale gray weathering calcisiltites, and burrow-mottled to nodular limestones, recording late HST to falling stage (FSST) carbonate shedding. Thin calcisiltites include fossil debris and articulated larger polymerid trilobites and the eocrinoid Gogia, preserved by obrutionary deposits. The repeated recurrence of these patterns provides the rudiments of a predictive model that not only explains the differing modes of preservation but may also aid in prospecting for new lagerstätten. [Copyright &y& Elsevier]

Comparison of the classic Upper Ordovician (Mohawkian to lower Cincinnatian; Caradoc to lower Ashgill) Black River and Trenton Groups in New York State/southern Ontario with the Tyrone–Lexington Formations exposed in the Jessamine Dome (southern Cincinnati Arch) in north-central Kentucky and southern Ohio reveals striking similarities. Previous emphasis on complex local facies mosaic has obscured widespread regional patterns. Biostratigraphy and K-bentonites provide broad constraints on inter-regional correlations; however, an allostratigraphic approach permits higher resolution correlations and a partial test of eustatic vs. strictly local tectonic models to explain stratigraphic patterns. Upper Mohawkian to lower Cincinnatian (∼455–449 Ma) depositional sequences, previously recognized for the Jessamine Dome and Nashville Dome areas, are correlated between the two main study areas and further refined; Chatfieldian (Rocklandian to Shermanian or Cobourgian of traditional terminology) sequences M5 and M6 of previous workers are interpreted to be composite sequences and are each subdivided into three smaller-scale sequences, which also have counterparts in the New York–Ontario strata. In turn, these correlations indicate at least partial allocyclic control on sedimentary cycles. Complex lateral variations within depositional sequences, especially in the late Shermanian to Edenian, indicate that tectonically controlled patterns of basinal subsidence and uplift of crustal blocks (perhaps reflecting forebulge migration) exerted a strong influence on the local facies and motif of depositional sequences. These tectonic features, however, did not obliterate the underlying allocyclic pattern. Indeed, high-resolution sequence stratigraphy enables detailed resolution of shifting patterns of minor uplift and subsidence. [Copyright &y& Elsevier]

Widespread zones of soft-sediment deformation are not ubiquitous throughout the rock record. Rather, they are associated with orogenic sediments and are concentrated in specific portions of depositional sequences characterized by deformation prone facies. Upper Ordovician soft-sediment deformation features exposed in Kentucky are here interpreted as the result of seismically induced thixotropic fluidization of muds resulting in foundering of denser silts and carbonate sands and corresponding diapiric injection of muds. Severity of soft-sediment deformation is associated with sediment density gradients, bed thicknesses, and varying magnitudes of triggering events. The widespread nature (>5000 km2) of multiple deformation horizons argues for a seismic trigger resulting from reactivation of multiple basement faults. Eight large-scale (3rd order) depositional sequences were examined for the presence of specific deformation features and stratigraphic position of those intervals. The regular distribution of deformation prone facies throughout the Upper Ordovician seems to have been regulated by eustatic fluctuations. Seismicity generated by far-field tectonics provided the triggering mechanism to disrupt deformation prone strata. The record of seismites and their co-occurrence with K-bentonites provides a meter of intensity and timing of tectophases of the Taconic Orogeny. [Copyright &y& Elsevier]

The Upper Ordovician Cincinnatian Series is a critical upper Katian reference succession. Previously, six 3rd-order depositional sequences (C1 to C6) have been recognized and frequently used as regional time slices. Recent research, however, indicates a need for revision and additions, including the recognition of additional 3rd- and 4th-order sequences. We propose amendments based upon high-resolution correlations using a combination of regional disconformities, cycle stacking patterns, bioevents, marker beds, and chemostratigraphy. Several disconformities, including a large regionally angular mid-Richmondian unconformity, are newly recognized or reinterpreted. In addition, distinctive depositional patterns aid in the recognition of systems tracts, with a) thick proximal laminated peritidal facies representing early transgressive systems tracts (TSTs) or lowstands, in part (LSTs), b) shell-rich limestone packages representing later TSTs and overlain by c) more shale-prone highstand systems tracts (HSTs), themselves overlain locally by d) siliciclastic dominated falling stage systems tract (FSST) deposits that are commonly removed beneath substantial unconformities (sequence boundaries). At present, we recognize eight 3rd-order Cincinnatian sequences, designated C1 through C8, and 16 4th-order subdivisions and their component systems tracts. A younger (Hirnantian?) sequence may be present at some localities as the enigmatic Centerville Formation and/or basal Belfast Member of the Brassfield Formation. The implications of these new correlations and sequence interpretations include a new standard for relative sea-level changes and insights into basin dynamics. This framework also permits a more nuanced history of biotic changes that include geologically brief pulses of immigration associated with the transgressions of the C1 (lower Kope Formation), C5C (Clarksville Member of Waynesville Formation), and C7A (basal Whitewater Formation). • Synthesis of Upper Ordovician (Cincinnatian) litho- and biofacies patterns • Revised model of cratonic, mixed siliciclastic‑carbonate sequences presented • Existing sequence stratigraphic framework for the Cincinnatian is strongly revised. • New framework recognizes 8 third-order and more than 16 fourth order sequences. • Provides new insights into temporal patterns of physical and biotic events [ABSTRACT FROM AUTHOR]

• First Silurian pinnacle reef tracts coincident with Manitowoc δ 13 C carb excursion. • Pinnacle reefs form above sequence boundaries during positive δ 13 C carb excursions. • Growth of pinnacle reefs driven by rapid sea level rise and calcification overshoot. • Reefs increasingly coincide with positive δ 13 C carb excursions in early Paleozoic. • Lockstep distribution of pinnacles and δ 13 C carb excursions: mid-Telychian onward. The first appearance of pinnacle reef tracts, composed of hundreds to thousands of localized biogenic structures protruding tens to hundreds of meters above the surrounding mid-Silurian seafloor, represents a step change in the evolution of the marine biosphere. This change in seafloor morphology opened a host of new ecological niches that served as "evolutionary cradles" for organism diversification. However, the exact timing and drivers of this event remain poorly understood. These uncertainties remain, in large part, due to a paucity of index fossils in the reef facies, the difficulty of correlating between the offshore pinnacle reefs and more temporally well-constrained shallow marine facies, and cryptic unconformities that separate amalgamated reefs. Here we use δ 13 C carb stratigraphy within a sequence stratigraphic framework to unravel these complex relationships and constrain the origination of Silurian pinnacle reef tracts in the North American midcontinent to near the Pt. celloni Superzone— Pt. am. amorphognathoides Zonal Group boundary of the mid-Telychian Stage. In addition, we identify a striking relationship between pulses of reef development and changes in global δ 13 C carb values and sea level. Viewed through this new perspective, we correlate prolific periods of reef development with short-lived carbon isotope (δ 13 C carb) excursions and eustatic sea level change that, ultimately, reflect perturbations to the global carbon cycle. From changes in the dominance of microbial reefs of the Cambrian to metazoan colonization of reefs in the Middle Ordovician, through the subsequent collapse of metazoan diversity with the Late Ordovician mass extinction, and the first appearance of early Silurian (Llandovery) pinnacle reef tracts and their proliferation during the late Silurian (Wenlock-Pridoli) and Devonian, major reef formation intervals increasingly coincide with δ 13 C carb excursions. These patterns suggest that Paleozoic reef evolution was the product of environmental forcing by perturbations of the global carbon cycle. [ABSTRACT FROM AUTHOR]

Abstract: The Late Wenlock Series (Homerian Stage) of the central Midland Platform occupies an area stretching from Ledbury to the Malvern, Suckley and Abberley Hills. Based upon the establishment of a sequence stratigraphic framework for the Much Wenlock Limestone Formation, and the immediately under- and over-lying Coalbrookdale and Lower Elton Formations, comparisons can now be made with key sections across the northern Midland Platform and beyond. These correlations have been strengthened by the determination of apatite rare earth element (REE) geochemical signatures obtained from four volcanic ash layers (bentonites) at Whitman's Hill Quarry (Herefordshire), which allow for comparisons with published coeval sections at Wren's Nest Hill (West Midlands) and Wenlock Edge (Shropshire), as well as with bentonites described from the Island of Gotland (Sweden). Across the study area fifteen parasequences associated with two pronounced regressive episodes, separated by a marked transgression, can be identified. The lithological responses to these relative sea-level changes are the same as those reported from the West Midlands, including the threefold division of the Much Wenlock Limestone Formation into Lower Quarried Limestone, Nodular Beds and Upper Quarried Limestone Members. Apatite REE geochemical signatures from Whitman's Hill Quarry identify three bentonites which probably originated from a granodiorite magmatic source, while a fourth bentonite has a distinctively mafic composition, more akin to that of a gabbro or syenite. This distinctively mafic bentonite is preserved on a marked flooding surface within the Nodular Beds Member and appears compositionally and stratigraphically equivalent to a bentonite at Wren's Nest Hill (West Midlands). Furthermore in both sections this bentonite is of notable thickness (120–200mm) allowing for its identification in other sections across the region. Comparisons with Gotland identify three closely spaced bentonites of a similar mafic composition to the bentonite described from the Midland Platform. While similarities in stratigraphic position and composition do not, at present, allow for the identification of a single ash fall event covering both the Midland Platform and Gotland, they are indicative of a shared source region, which may offer the possibility for future bentonite correlation between these regions. [Copyright &y& Elsevier]

Abstract: Episodes of instability in the global climato-oceanic system have become the hallmark of the Silurian Period. These events are marked by six large positive carbon isotope excursions associated with major extinctions. The widespread environmental consequences of these perturbations of the global carbon cycle remain poorly documented. A high-resolution chronostratigraphic reconstruction of the Appalachian foreland basin (AFB) provides a framework to evaluate environmental signatures of two of these carbon isotope excursions (Valgu and Ireviken events; Telychian–Sheinwoodian) at a regional scale. Integration of published biostratigraphic range data, mapping of sequence stratigraphic surfaces and facies, and generation of high-resolution carbon isotope profiles for several transects provides precise correlation of the basin stratigraphy yielding a high-resolution temporal framework. This chronostratigraphic reconstruction of the AFB highlights the importance of time-specific facies (TSF) during these intervals. For instance, packages of red, green, and gray marine rocks separately occupied discrete time intervals—cutting across “local” facies belts indicative of shallow to deep marine environments. Similarly, widespread iron mineralization occurred during discreet time slices as “bathtub rings” rimming the margins of the basin. Changes from one time-specific facies to the next are coincident with changes in carbon isotope values, indicating a genetic link between fractionation of the global carbon reservoir and redox changes from generally oxic to anoxic oceanic conditions in parts of the AFB. The basal part of the study interval was deposited during the Valgu Event. This first event begins with an unconformity marking global lowstand. This fall in sea level was coincident with rising carbon isotope values as recorded in adjacent basins. A slight sea level rise and flooding of the subaerial unconformity occurred near the peak in carbon isotope values. Oxidized iron minerals were deposited in a zone that extended from the lower shoreface into the basin center—pinching out into shallower parts of the basin. Thin pyrite–phosphorite–glauconite layers, associated with black shales in the basin center, were deposited over these ferruginous strata. As the event ended and carbon isotope values shifted negatively to a more stable baseline, temperatures warmed, sea level reached a Silurian high, and oxic conditions associated with very low rates of organic carbon (OC) burial were established. These conditions were relatively stable for nearly four million years. This long period of stasis was punctuated by the Ireviken Event, which displays a strikingly similar progression of TSF patterns, yet more intense and longer lived than the preceding Valgu Event. With the first positive shift in carbon isotopes at the onset of the Ireviken Event, the basin redox system changed from largely oxidizing to reducing, coincident with a rapid drop in sea level and an abrupt reappearance of iron mineralization on the basin margins. The sea level fall associated with the shift to peak values of the carbon isotope excursion is marked by the progradation of a significant body of sand well out into the basin. During this sea level drop, conditions in the basin center became highly reducing and periodically sulfidic. Widespread ironstones and ankeritic carbonates were deposited isochronously, rimming the shallow basin margins where they alternated with light gray pyritic shales, indicating fluctuating redox conditions. A large negative carbon isotope excursion of ~3‰ is coincident with a shift from regression to transgression, suggesting glacial melting via methane release. Continued deposition of ironstones through this time interval suggests a primary link to shallow marine redox processes rather than large-scale transgression or regression of the shoreline. The ironstones are overlain by gray to black pyritic shales deposited across all environments, revealing a final stage of redox progression into sustained sulfidic conditions as peak values of the carbon isotope excursion returned to a high stable baseline near +4‰. The similar expression of TSFs within the AFB of these two global events demonstrates that fractionation of the global atmospheric and oceanic carbon reservoirs had a predictable, cascading impact on shallow sea floor environments. The associated redox processes reveal the dynamic regional interactions of a shallow oxic epicontinental water mass with a broader anoxic oceanic water mass, providing valuable insight into the origin of some of the largest extinctions in the Silurian Period. [Copyright &y& Elsevier]

Abstract: The Wenlock Epoch of the Silurian Period has become one of the chronostratigraphically best-constrained intervals of the Paleozoic. The integration of multiple chronostratigraphic tools, such as conodont and graptolite biostratigraphy, sequence stratigraphy, and δ 13Ccarb chemostratigraphy, has greatly improved global chronostratigraphic correlation and portions of the Wenlock can now be correlated with precision better than ±100kyr. Additionally, such detailed and integrated chronostratigraphy provides an opportunity to evaluate the fidelity of individual chronostratigraphic tools. Here, we use conodont biostratigraphy, sequence stratigraphy and carbon isotope (δ 13Ccarb) chemostratigraphy to demonstrate that the conodont Kockelella walliseri, an important guide fossil for middle and upper Sheinwoodian strata (lower stage of the Wenlock Series), first appears at least one full stratigraphic sequence lower in Laurentia than in Baltica. Rather than serving as a demonstration of the unreliability of conodont biostratigraphy, this example serves to demonstrate the promise of high-resolution Paleozoic stratigraphy. The temporal difference between the two first occurrences was likely less than 1million years, and although it is conceptually understood that speciation and colonization must have been non-instantaneous events, Paleozoic paleobiogeographic variability on such short timescales (tens to hundreds of kyr) traditionally has been ignored or considered to be of little practical importance. The expansion of high-resolution Paleozoic stratigraphy in the future will require robust biostratigraphic zonations that embrace the integration of multiple chronostratigraphic tools as well as the paleobiogeographic variability in ranges that they will inevitably demonstrate. In addition, a better understanding of the paleobiogeographic migration histories of marine organisms will provide a unique tool for future Paleozoic paleoceanography and paleobiology research. [Copyright &y& Elsevier]

Carbonate fluorapatite-filled millimeter-scale microsteinkerns are a key element of the "Small Shelly Fossil" (SSF) fauna generally associated with the late Proterozoic–Cambrian. The purported disappearance of these fossils and this style of phosphatic preservation during the Cambrian Stage 2 "Botomian extinction" has been linked to changes in ocean chemistry and/or changes to the physical environment due to the evolution of metazoans, as well to the changing role of metazoans in the marine environment. Through a qualitative meta-analysis of existing literature, we document a broader temporal distribution for SSF-style preservation than previously recognized. We examine these occurrences for common patterns of depositional conditions, and we offer a conceptual model for both the origin of the phosphatic microsteinkerns and their eventual concentration in certain sediments, based on known biogeochemical diagenetic processes of authigenic calcium fluorapatite precipitation (phosphogenesis) and subsequent concentration of phosphatic sedimentary particles. This polycyclic phosphogenic condensation (PPC) model makes predictions as to how and where this form of preservation might occur in Cambrian and non-Cambrian marine strata alike. Unlabelled Image • "Small shelly fossil"-style preservation is found throughout the Phanerozoic. • Known sedimentary processes explain these fossil occurrences. • Phosphatic steinkerns are "time-rich". [ABSTRACT FROM AUTHOR]