Mississippian Succession Research Articles

Palynological assemblages from the Majaditas Formation (Carboniferous), Argentina: An example of reworking in glacial sediments

Reworked palynomorphs are commonly found in sedimentary deposits of glacial environments. However, instances of reworking were few times identified in the Carboniferous assemblages of central-western Argentina. In this study, two well-preserved palynological assemblages recovered from shales bearing dropstones of the Majaditas Formation in San Juan province are described for the first time. The palynoflora comprises spores, monosaccate pollen, acritarchs, and prasinophyte. Although in a low proportion (at least 2%), some palynomorphs correspond to reworked specimens of the underlying Devonian and Mississippian successions. The assemblages are indicative of the Subzone A of the Raistrickia densa/Convolutisporamuriornata Biozone that characterizes the late Serpukhovian-early Bashkirian in the country. Close similarities are evident with other palynofloras described for glaciogenic deposits of the same age in the region.

Far-field correlation of palaeokarstic surfaces in Mississippian successions using high-frequency foraminiferal diversity trends

The degree to which emergent surfaces are correlated in late Asbian carbonate successions in Britain and Ireland is assessed by the integration of detailed biostratigraphy and diversity trends in foraminifers. Data are related to the Trowbarrow Quarry section in northern England, which provides a reference section for the upper Asbian because of its rich assemblages and high sampling density. Diversity trends are shown to be non-random, possess cyclic behaviour, and can be quantitatively correlated between sections. The assemblages allow stratigraphic segmentation into 13 intervals of foraminiferal diversity trends, which sub-divide the coarser-resolution biozones and sub-biozones. Similar foraminiferal trends are recognised in sections hundreds of kilometres away from Trowbarrow, in South Wales, and southeastern and western Ireland, facilitating a more precise correlation of strata. These highlight the coeval nature of emergent surfaces and rhythms between these regions, thus, establishing a precise stratigraphy. This new assessment also enables better discrimination of ‘missing beats’ and large hiatuses in the successions. The establishment of this rhythmic stratigraphy permits recognition of the late occurrence of some biostratigraphical markers, enabling amendment of biostratigraphic mismatches.

Timing and evolution of the Mississippian sedimentary system on southeastern Laurussia: Evidence from the Appalachian area, U.S.A.

This paper is a synthesis of Mississippian sedimentation on the southeastern, Appalachian margin of Laurussia. The Mississippian stratigraphic framework in the Appalachian area shows a large-scale, three-part, wedge-like, clastic‑carbonate-clastic sequence, which has been interpreted to be a likely flexural response to coeval Neoacadian Orogeny. Using an already established flexural framework and biostratigraphy, we have interpreted the approximate timing of flexural events based on biostratigraphy. These flexural events begin with active deformational loading that initiated rapid subsidence in the Appalachian foreland basin, during which the deeper-water, black Sunbury Shale and equivalents were deposited throughout the basin. Subsequent relaxational loading contributed to basin infilling through the deposition of a deeper-water, clastic succession, manifest as the extensive Cuyahoga-Logan-Borden-Grainger-Price-Rockwell-Pocono deltaic clastic wedge. By the time this clastic wedge had filled the foreland basin, clastic source areas in the orogen had apparently been lowered to the point that shallow seas migrated far eastward across former source areas. This brief period of equilibrium between the basin and source areas resulted in reduced clastic influx at a time when the basin entered subtropical latitudes, setting the stage for widespread carbonate deposition, represented by units like the Newman, Greenbrier, and Slade Limestones. Ensuing, rebound-related uplift, perhaps abetted by incipient, subsurface, Alleghanian thrusting, generated new sediment source areas and accompanying wedges of prograding marginal-marine and terrestrial sediment represented by the Pennington, Mauch Chunk and equivalent units. Marginal-marine sedimentation continued into Early Pennsylvanian time, when a combination of Alleghanian uplift and LPIA lowstand conditions generated a period of widespread, deep erosion that in many places across the Appalachian Basin destroyed substantial parts of the underlying Mississippian succession along the sub-Absaroka or “Mississippian-Pennsylvanian” unconformity. Although the basic Mississippian stratigraphic framework described above for the Appalachian Basin largely appears to be a consequence of Neoacadian flexural responses, major details regarding processes, timing and lithology were apparently controlled by concomitant interactions involving paleoclimate, eustasy, coeval Ouachita tectonism, and possibly early Alleghanian tectonism.

Palaeoenvironment, palaeogeography, and palaeoclimatology of the Mississippian carbonate ramp in the Alborz tectonostratigraphic zone: Implications for deciphering the controlling factors on ramp evolution

The Mississippian successions of the Alborz tectonostratigraphic zone have been studied in several sections (Dozdehban, Naserabad, Shahmirzad, and Mighan) extending from north to southeast. The sedimentological data indicate three main facies associations (FA): (FA1) a basin to distal outer ramp of low‐energy, low‐oxygen environment with low bioturbation and less developed in situ fossils; (FA2) a middle ramp facies accompanied by storm‐induced sediments (tempestites), echinoderm‐dominated mud mounds, and high fragmentation of skeletal components; and (FA3) an inner ramp facies, represented by sand shoal, and lagoonal/back‐barrier, mainly characterized by the dominance of oolitic, bioclast, and intraclast grainstones. The sedimentary features imply the formation of the succession on a broad flat‐topped, high‐to‐moderate‐energy shelfal carbonate ramp which had been open to the N/NE, the downslope direction, as revealed by local palaeoenvironmental reconstructions. Analysis of several proxies indicates a subtropical palaeoclimate evidenced by (a) widespread tempestite facies and occurrence of storm‐depositional processes, (b) diverse and abundant pellet‐forming thalassinoideans and burrowing echinoids trace fossil assemblages, (c) geochemical proxy indicating a palaeotemperature of 23°–25°, and (d) a rich subtropical heterozoan fossil association. The data provided here imply the palaeolatitudinal position of the Alborz Mississippian ramp is 30–40°S along the southern margin of the Palaeotethys.

Early Carboniferous (Mississippian) intertwining sediment dispersal network across the Laurentian cratonic interior

Early Carboniferous (Mississippian) strata across the Laurentian cratonic interior record the transition from a stable carbonate platform, supporting a broad epicontinental sea, to a series of widespread, mixed carbonate-siliciclastic successions. As the southern terminal sink, the Mississippian succession preserved on the southern Midcontinent provides evidence and constraints for sediment dispersal patterns. This paper presents the first comprehensive U–Pb detrital-zircon geochronological record of all known Mississippian sandstones from the southern Ozark Dome of southern Missouri and northwestern Arkansas. This study identifies the provenance of these Mississippian sandstones and establishes their sediment dispersal networks across the cratonic interior. Results show that a major provenance shift occurred between Lower and Upper Mississippian strata. The Lower Mississippian Bachelor Sandstone was sourced from the Laurentian craton, while Upper Mississippian and basal Pennsylvanian sandstones were sourced through recycling of upper Proterozoic and lower Paleozoic sandstones within the Laurentian craton to the north, the unroofing of the Appalachian orogenic belt from the east-northeast, and potentially some direct contribution from uplifted Precambrian basement along the Transcontinental Arch to the northwest. By combining previously published detrital zircon data from Laurentia, we propose that the Mississippian sedimentation reflects an intertwining dispersal system associated with multiple sources. Sediments derived from all three potential sources were merged and transported southward across Laurentia.

New records of crinoids from Trearne Quarry SSSI (Mississippian, Lower Carboniferous), north Ayrshire

The Mississippian succession of Ayrshire, SW Scotland, is rich in fossil crinoids, albeit mainly preserved as fragments. Trearne Quarry is exceptional in yielding moderately common crinoid cups and thecae from certain horizons. To the two nominal taxa that have been documented hitherto, we add a further seven, all cladids with one exception. These species all come from the Blackhall Limestone of the Lower Limestone Formation (Visean, Mississippian). Nominal crinoid species identified from Trearne Quarry include Cladida: Rhabdocrinus scotocarbonarius (Wright), Ureocrinus bockschii (Geinitz), Ureocrinus globulus (de Koninck), Tyrieocrinus laxus Wright, Fifeocrinus tielensis (Wright), Hydreionocrinus formosus Wright, Parazeacrinites konincki (Bather) and Phanocrinus ardrossensis (Wright); and Diplobathrida, Camerata: Cribanocrinus baccatus (Wright). Species have distributions limited to one or a few mudrock beds. Identifiable crinoids are uncommon in massive, coral-rich reefal facies.

Carboniferous palynoevents in the circum-Arctic region

The Carboniferous of the present-day Arctic yields an abundant and diverse association of terrestrial palynomorphs, particularly from Mississippian successions. Relatively few sections have been studied. However, those published so far demonstrate considerable similarities in the palynofloras between Arctic regions. Based on the published record, we present a compilation of 31 last occurrences (LOs), first occurrences (FOs), and some abundance events that have correlation potential around the Arctic. The chronostratigraphic resolution is relatively low, and the lack of independent age control hampers exact age assignments. But for most of these successions, palynology is the only dating tool available.

Upper Paleozoic stratigraphy and detrital zircon geochronology along the northwest margin of the Sverdrup Basin, Arctic Canada: insight into the paleogeographic and tectonic evolution of Crockerland

The upper Paleozoic succession along the northwest margin of the Canadian Arctic Sverdrup Basin is little studied and poorly understood yet has the potential to yield insights into the paleogeographic and tectonic evolution of the Arctic regions including Crockerland. Carboniferous and Permian drill cuttings were collected from five exploration wells on Brock, Mackenzie King, and Ellef Ringnes islands. Seven unconformity-bounded sequences were identified and correlated. Reflection seismic interpreted on Ellef Ringnes Island indicates that a major syn-sedimentary fault offsets the Mississippian succession bounding a down-to-the-north half-graben. Late Pennsylvanian (Gzhelian) fault reactivation, associated with the Melvillian Disturbance, created a depression that extended northward and was bordered to the south by a structural high. Episodic minor fault reactivation occurred until the Early–Middle Permian boundary. During the latest Early Permian (Kungurian), sand derived from Crockerland prograded southward onto the Sverdrup Basin’s northwest margin and continued into the Roadian. After a lull during the Wordian, clastic progradation resumed in the Capitanian. Detrital zircon U–Pb ages recovered from Kungurian and Roadian samples on Brock and Ellef Ringnes islands display Devonian Clastic Wedge (DCW) signatures. A Moscovian–Artinskian carbonate blanket likely covered Crockerland and sheltered DCW material from erosion, implying it was a subsiding, carbonate bank throughout most of the Pennsylvanian – Early Permian. Base level fall in the Kungurian, associated with a transition to a more humid climate, breached these carbonate rocks to allow erosion and transportation of DCW material. Recycling of the DCW started earlier (Artinskian) and peaked later (Wordian) along the southern margin of the basin.

Source-rock reservoirs geochemistry of Devonian–Mississippian mudrocks in central Oklahoma

The Woodford Shale and the overlying Mississippian limestone constitute one of the prolific unconventional hydrocarbon targets in central and northern Oklahoma. With the advantage of horizontal drilling technology, Devonian and Mississippian mudrocks have become important topics for research to understand the petroleum system fundamentals, including sources of hydrocarbons for these unconventional reservoirs. In this study, organic geochemistry and petrography of Mississippian mudrocks and the Woodford Shale were examined. The key study core is from Lincoln County, Oklahoma, representing the Mississippian mudstone and Woodford Shale. Three additional cores in Payne County and one core from Logan County were studied. Core samples were assessed for hydrocarbon generation potential using Rock-Eval pyrolysis together with biomarker analysis using gas chromatography–mass spectrometry. Organic and thin-section petrography was performed to identify maceral composition and develop a sedimentary facies classification. Mudrocks within the Mississippian section exhibited adequate organic richness for petroleum generation, thereby augmenting the established generation potential of the Woodford Shale. Several unique Mississippian biomarkers were identified, including diterpenoids and extended tricyclic terpanes. Macerals of the Mississippian rocks exhibit dominance of lamalginite and bituminite, whereas Woodford macerals are high in telalginite. Based on the organic matter composition and sedimentology, six facies were identified within the Mississippian mudrocks. Furthermore, based on organic richness and key biomarker ratios, the Mississippian succession is divided into three units. Organic and sedimentological signatures suggest a shoaling-upward succession from the Woodford Shale to the Mississippian carbonate.

A revised Mississippian (Courceyan – Chadian) geology of the Clogher Valley, counties Fermanagh and Tyrone (Northern Ireland)

Following a geological research programme in 1998-2000, the Mississippian succession in the Clogher Valley has been revised and important new detail has been revealed. Immediately overlying the terrestrial Ballyness Formation, the interval originally ascribed to the Clogher Valley Formation has been subdivided into three new formations: the Clogher Valley Formation sensu stricto, the Fardross Sandstone Formation and the Moysnaght Limestone Formation. This sequence is overlain by the Ballyshannon Limestone Formation. The lithostratigraphy of these units is described and previous biostratigraphic work is reviewed and supplemented with new data. These indicate that the top of the clastic redbed Ballyness Formation is close to the Devonian-Carboniferous boundary, whilst the following marine succession ranges in age from the late Courceyan through to the Chadian. The thickness, nature and distribution of evaporite horizons in the succession is described. The provenance of various sandstones within the sequence has been assessed and lateral facies changes and thickness variations in the succession are attributed to syn-depositional tectonic activity.

Early Mississippian evaporites of coastal tropical wetlands

AbstractExtensive evaporites in Lower Mississippian successions from palaeoequatorial regions are commonly used as evidence for an arid to semi‐arid palaeoclimate. However, in this article, detailed studies of evaporites and their context refute this interpretation. Detailed sedimentological and petrographical analysis of the Lower Mississippian of northern Britain, is combined with archived log data from more than 40 boreholes across southern Scotland, northern England and Northern Ireland, and published literature from Canada. Two key cores from the Tweed Basin and the northern margin of the Northumberland – Solway Basin contain 178 evaporite intervals and reveal twelve distinct forms of gypsum and anhydrite across seven facies that are associated with planar laminated siltstone and intercalated thin beds of ferroan dolostone. Nodular gypsum and anhydrite, typically in intervals <1 to 2 m thick, are integral components of the succession. Nodular evaporite occurs within about 1 m of a palaeosurface, but most evaporite deposits represent ephemeral brine pans to semi‐permanent hypersaline lakes or salinas on a floodplain that was subjected periodically to storm surges introducing marine waters. Formation of evaporites under a strongly seasonal climate in a coastal wetland is supported by palaeosol types and geochemical proxies, and from palaeobotanical evidence published previously. Although 65% of modern equatorial areas experience a strongly seasonal climatic regime, salinas and sabkhas are a minor component today in comparison with the evidence from these Lower Mississippian successions. This implies that the earliest terrestrial environments were complex and dynamic, providing a diverse range of habitats in which the early tetrapods became terrestrialized and represent a setting that is rarely preserved in the geological record.

A new Mississippian biozonal scheme for the Finnmark Platform, Norway – Palynostratigraphic integration of exploration wells 7128/4-1 and 7128/6-1

Abstract A new biozonal scheme for the Mississippian succession in the Finnmark Platform, offshore Norway, is presented. Palynological analysis of exploration wells 7128/4-1 and 7128/6-1 that penetrated the Billefjorden Group, allow integration of all of the Mississippian palynological data from the region, providing better age constraint, and correlation of the sedimentary successions on the Finnmark Platform. Two new biozones and three subzones are described, in ascending stratigraphic order: the Granulatisporites granulatus Biozone (mid to late Visean), consisting of the Potoniespores delicatus Subzone (mid Visean), the Monilospora mutabilis Subzone (late Visean) and the Convolutispora vermiformis Subzone (late Visean), and the Tripartites vetustus Biozone (late Visean). The new biozones are correlated to the Carboniferous miospore biozones of Western Europe based on first and last occurrences of selected taxa.

Taphonomy of a Mississippian crinoid pluricolumnal, Newton Grange, Derbyshire, UK

The Mississippian (Lower Carboniferous) succession of Derbyshire contains numerous crinoid specimens, but they remain poorly documented. Although these well-lithified limestones may include abundant crinoids, they are difficult to study; better results can be obtained from weakly lithified mudrocks, as seen elsewhere. A moderately long pluricolumnal of 29 columnals has been collected from the mudrock of the Newton Grange crinoid bed of the Hopedale Limestone Formation, Peak Limestone Group; it most likely comes from high in the formation (=Brigantian) and was deposited in the deeper water of the Widmerpool Gulf. The pluricolumnal is part of the mesistele of either a cladid or a camerate crinoid. The pluricolumnal was originally circular in section, but has been deformed into an ellipse. A second elongate structure, probably a second pluricolumnal (not preserved), was adpressed into the surface, and calcite of the endoskeleton lost on this and the opposite side of the pluricolumnal to expose the axial canal. All these post-burial modifications were probably under the influence of the weight of overburden, but indicate a complex scenario for the preservation of a simple specimen.

LA-ICP-MS U-Pb dating of Carboniferous ash layers in the Cantabrian Zone (N Spain): stratigraphic implications

Seven centimetre-thick volcanic ash-fall layers interbedded within the thick Carboniferous successions of the Cantabrian Zone in northern Spain were dated by U–Pb zircon laser ablation inductively coupled plasma mass spectrometry across an interval ranging from Visean to Kasimovian, thus covering most of the Carboniferous period. All these ash layers occur in fossiliferous successions, allowing us to insert the radiometric data within a well-constrained biostratigraphic framework. Considering the analytical uncertainty, the obtained ages match the ages inferred from the conodont biostratigraphy established in the Mississippian succession (which hosts the oldest two ash layers, Visean in age), and the fusuline and mega- and microflora data from the strata hosting the Moscovian and Kasimovian (Westphalian–Stephanian) tonsteins. The age of a Langsettian tonstein along with data provided by several papers stating that in the Cantabrian Zone Langsettian floras were contemporaneous with lowermost Moscovian fusulines suggest that Langsettian floras could have been younger in Spain than in other areas. Our absolute ages provide new constraints not only for the correlation of the Carboniferous successions of the Cantabrian Zone with time-equivalent reference successions in other parts of the world but also for calibrating the Carboniferous global chronostratigraphic units based on marine fossils with the West European regional units. Supplementary material: Stratigraphic position and biostratigraphic information on the studied ash-fall layers, analytical methods and geochronological results are available at https://doi.org/10.6084/m9.figshare.c.3768701

The Mullaghmore Sandstone Formation of north-west Ireland: a regional Mississippian lowstand deposit

The Mullaghmore Sandstone Formation of north-west Ireland is a distinctive clastic unit of late Arundian age in an otherwise carbonate-dominant Mississippian succession. The distinctive base is erosive in the more proximal sections but is gradational in the successions deposited further offshore from the pre-Mullaghmore shoreline. The source area lay to the north-west and is interpreted to be dominated by felsic igneous and/or high grade metamorphic rocks due to the presence of large, first cycle feldspars that are common in all of the sandstones. The formation was deposited in the coastal zone with both fluvial and marginal marine deposits present in almost all sections. The fluvial channel deposits are most common in north-western sections and commonly show evidence for tidal currents in the coastal zone. Most of the coastal sediments are dominated by wave-generated structures. The formation is interpreted as the deposits of a deltaic coastal plain that was lobate in plan view. The top of the formation is interpreted as a regional transgressive surface. While there is local autocyclic repetition of facies, no higher-order sequences are detectable on a regional scale. The driving mechanisms for this regional lowstand are most likely regional tectonics rather than glacioeustasy, as the event is not readily correlated over any significant distance.

New insights on East Finnmark Platform palynostratigraphy and paleogeography — A study of three shallow cores from a Mississippian succession in the Barents Sea, Norway

Palynomorph assemblages from cores from three shallow stratigraphic boreholes (7029/3-U-1; 7127/10-U-2; 7127/10-U-3) drilled on the East Finnmark Platform have enabled the recognition of four miospore assemblages and two sub-assemblages from the Billefjorden Group in this area, rectifying earlier biozonations. The assemblages are correlated to the Western European biozonation and are based mainly on taxa abundance and the first and last appearances of selected species. All assemblages are Visean to possibly early Serpukhovian in age. Correlations with other biozonations from areas of similar paleolatitude are suggested. Our results suggest that strata assigned to the Billefjorden Group in the offshore may be slightly older than previously assumed. Even so, the Billefjorden Group succession in the offshore is younger than that recognized in the onshore. A mixed signature between the flora from the Arctic region and areas further south in the Euramerican Supercontinent has been observed which may be indicative that the Finnmark Platform was located in a microfloristic transitional region. Generically, the climate in this region was humid and warm during the Visean time which is reflected in the significant amount of neutral, humid and moderately humid floral elements represented by the miospore assemblages.

Microfacies and carbon isotope records of Mississippian carbonates from the isolated Bama Platform of Youjiang Basin, South China: Possible responses to climate-driven upwelling

Changes in Mississippian global paleogeography derived from the reconfiguration of the continents have been suggested to result in a change in oceanic circulation, carbon cycling, as well as in global cooling. Here, integrated δ13Ccarb chemostratigraphy and foraminiferal biostratigraphy across the Mississippian (late Tournaisian, Visean, early Serpukhovian; MFZ6–MFZ16 foraminiferal biozones) of the Gongchuan section located in the isolated Bama Platform in the Youjiang Basin, South China, are presented. The δ13Ccarb trend shows an abrupt decline during late Visean (Asbian-early Brigantian; MFZ13–14). This decline is also observed in subequatorial western Euramerica, whereas coeval sections in subequatorial eastern Euramerica show consistently elevated δ13C values across the entire Visean. The δ13C decline in western Euramerica and the South China Block (eastern Paleo-Tethys) coincides with a global regression with a suggested glacioeustatic origin, the onset of high-frequency climate and sea-level oscillations, and the closure of the Rheic seaway between Euramerica and Gondwana. We propose a model explaining the divergence of δ13C records resulting from the closure of the Rheic seaway and development of upwelling zones in the western margin of Euramerica and the eastern Paleo-Tethys realm. Quantitative microfacies analysis across the Mississippian succession in the Gongchuan section shows facies-independent disappearance of corals and increased proportion of cortoids and filter-feeding organisms at the onset of the Asbian δ13C decline, which may support an increase in nutrient level that can be expected as a result of upwelling.

Stratigraphic Framework and Depositional Controls on Reservoir Occurrence, Big Valley Formation, Southern Alberta

Abstract Within the past decade, the Big Valley and Exshaw formations in southern Alberta have received significant interest as a potential unconventional oil play because of the overwhelming exploration/exploitation success in the stratigraphically-equivalent Three Forks and Bakken formations in Saskatchewan, Manitoba and North Dakota. Because of continuous industry hype, this upper Devonian-lower Mississippian succession came to be known as the “Alberta Bakken”. Such a term suggests potentially prolific oil production from a reservoir similar to the Bakken in Saskatchewan. In fact the term “Alberta Bakken” is misleading since to date there has been only moderate oil production from localized carbonate reservoirs in the Big Valley Formation, and from very fine-grained sandstones and siltstones of the Mississippian Lower Banff Formation. Reservoir development in the Big Valley Formation is stratigraphically and areally restricted by both depositional facies controls and post-depositional early diagenetic, subaerial and structural-collapse processes. Detailed lithofacies analysis indicates that the Big Valley Formation is divisible into two units: an upper shallow marine limestone and a lower hydrocarbon-bearing, partially dolomitized, peritidal carbonate. The peritidal unit, in turn, is divisible into four lithofacies: peloidal packstone-grainstone (the primary oil-bearing lithofacies), microbial laminite, laminated dolomudstone and intraclastic breccia-laminite. Regionally, each lithofacies is discontinuous and in the order of 0.5 to 2.0 m thick. Locally, however, the peloidal packstone-grainstone attains thicknesses of up to 8 m, forming isolated oil-producing reservoirs. These over-thickened zones correspond to specific areas of Big Valley Formation ‘thicks’, which tend to align with a NNW-SSE trending ‘basement’ lineament that underlies the study area. It is equivocal whether this structural trend is basement-controlled, or reflects dissolution of salt beds along the margin of an underlying evaporite basin. Successful exploration in the Big Valley Formation appears to depend on whether the over-thickened areas can be located.

Upper Devonian–Mississippian stratigraphic framework of the Arkoma Basin and distribution of potential source-rock facies in the Woodford–Chattanooga and Fayetteville–Caney shale-gas systems

Wireline logs were used to document the stratigraphic framework of Upper Devonian–Mississippian strata in the Arkoma Basin, and maps of high-gamma ray (HGR) log response were used to analyze the spatial distribution of potential source rocks in the Woodford–Chattanooga and Fayetteville–Caney shale-gas systems. The Woodford–Chattanooga shale is a transgressive deposit that accumulated on an arid continental margin influenced by marine upwelling and minimal sediment influx. A broad HGR depocenter along the southwestern margin of the basin includes two areas of higher accommodation containing the thickest HGR concentrations. Basin-wide patterns of HGR likely reflect broad tectonic influence on accommodation. The proportion of chert in the formation increases eastward and southward, likely reflecting latitudinal and bathymetric influence on the accumulation of siliceous ooze. The Lower Mississippian Burlington sequence, which lies between the two shale-gas systems, comprises carbonate ramp and distal shale deposits. Proximal ramp facies form an apron around the southern flank of the Ozark uplift and grade radially basinward into distal facies. An Upper Mississippian succession in the east includes lowstand deposits of the Batesville delta, which onlap the relict Burlington ramp. Basinwide, the succession includes the transgressive Fayetteville–Caney shale overlain by regressive deposits of the proximal Pitkin Limestone and distal upper Fayetteville (Arkansas) and “false” Caney (Oklahoma) shale. The HGR shale is concentrated in an area of intermediate accommodation on the western margin of the Mississippi Embayment and just basinward of the Pitkin Limestone pinchout in Arkansas, and in an area of relatively high accommodation in Oklahoma.

The Carboniferous Archerbeck Borehole, near Canonbie (Dumfriesshire, southern Scotland): biostratigraphic revision of the late Asbian to early Pendleian succession using foraminiferans and regional correlations

ABSTRACTThe upper half of the Archerbeck Borehole contains a continuous Mississippian succession from the late Asbian (late Viséan) to the Pendleian (early Serpukhovian), with numerous limestone horizons. The borehole sequence lies within the Solway Basin (western end of the Northumberland Trough) and bridges the successions between the Midland Valley of Scotland and the Pennines (northern England). The rich foraminiferal and algal assemblages are compared to those described by previous authors, and genera as well as species are updated as far as is possible. In addition, some other overlooked or underestimated taxa have been identified and illustrated, which improve notably the biostratigraphic resolution of the Archerbeck Borehole succession. Within the abundant foraminiferal assemblages can be highlighted the richness and diversity of representatives of the family Archaediscidae. In general, the succession developed in the Archerbeck Borehole is closely comparable with that in the Alston Block of northern England. The Asbian/Brigantian transition mimics that observed in the Janny Wood boundary stratotype section, with clear late Asbian horizons (lower part of the Archerbeck Beds), transitional beds (middle and upper parts of the Archerbeck Beds), and Brigantian limestones (from the Cornet Limestone upwards). The base of the early Brigantian is placed at the base of the Cornet Limestone (equivalent to the Lower Peghorn Limestone in the Alston Block). The base of the late Brigantian is placed at the base of the Gastropod Limestone (equivalent to the Scar Limestone Member in northern England), and the base of the Pendleian is repositioned at the base of the Under Limestone (equivalent to the Four Fathom Limestone Member in northern England). Throughout, the borehole, protista and microfloral elements are abundant, which allows the recognition of Assemblages 4 to 10, previously recognised in northern England and the Midland Valley of Scotland. Furthermore, other local assemblages are recognised and related to palaeoecological controls, although they do not represent any improvement in biostratigraphical resolution.