Abstract The Late Pennsylvanian was a time of ice ages and climate dynamics that drove biotic changes in the marine and non-marine realms. The apex of late Paleozoic glaciation in southern Gondwana was during the Late Pennsylvanian, rather than the early Permian as inferred from more equatorial Pangaea. Waxing and waning of ice sheets drove cyclothemic sedimentation in the Pangaean tropics, providing an astrochronology tuned to Earth-orbital cycles, tied to climatic changes, reflected in aeolian loess and palaeosol archives. Vegetation change across the Middle–Late Pennsylvanian boundary was not a ‘Carboniferous rainforest collapse’, but instead a complex and drawn out step-wise change from one kind of rainforest to another. Changes in marine invertebrate and terrestrial vertebrate animals occurred across the Middle–Late Pennsylvanian boundary, but these did not lead to substantive changes in the organization of those communities. The base of the Upper Pennsylvanian is the base of the Kasimovian Stage, and this boundary needs a GSSP to standardize and stabilize chronostratigraphic usage. To avoid further chronostratigraphic confusion, the Cantabrian Substage should be abandoned, and the traditional Westphalian–Stephanian boundary should be returned to and recognized as the time of major floristic change, the lycospore extinction event.

Abstract For the west European regional chronostratigraphic framework, the Cantabrian substage was conceived as covering a widely apparent stratigraphic gap between the top of the Westphalian and the base of Stephanian A, the lowest unit of the Stephanian. A continuous depositional history covers this time gap in the Cantabrian region of Spain; the upper limit of this interval was defined by the succeeding Barruelian substage, equivalent to Stephanian A. Intense tectonic and magmatic activity characterizes this period; the Iberian orogenic belt was an essentially linear feature buckled through the Late Pennsylvanian into the tightly folded Cantabrian Orocline. This evidences an extensive southern foreland to the Variscides, in which the coal-swamp biome persisted through the Late Pennsylvanian, supporting biostratigraphical correlation with the Donbass. New high precision U–Pb CA-ID-TIMS radiometric dating of tonstein horizons supports a preliminary time-framework of regional substages: base of the Asturian (proposed, ex-Westphalian D) c. 310.7 Ma; base of the Cantabrian c. 307.5 Ma; base of the Barruelian (ex-Stephanian A) c. 304.9 Ma; base of the Saberian (proposed) c. 303.5 Ma. The Cantabrian and Barruelian embrace the entire Kasimovian of the global time-scale, and the top of the Barruelian is essentially coincident with the base of the Gzhelian.

Abstract In spite of numerous revisions from 1966 to present, the Cantabrian Substage of the Stephanian Stage (Pennsylvanian) was never properly defined as a chronostratigraphic unit. Defined and redefined at least three times, the Cantabrian lacks boundary stratotypes that correspond to clear and correlateable biochronological signals. Thus, instead of using a biochronological datum of well-established validity and utility, Cantabrian advocates have relied on ill-defined macrofloral assemblage zones and on lithostratigraphic boundaries to define the substage. As a result, the Cantabrian is demonstrably diachronous, even within Europe; indeed, the Cantabrian has proven to be unusable for correlations outside its type area in northern Spain. To resolve these problems, we recommend that the Cantabrian Substage be abandoned, and the Westphalian–Stephanian boundary be redefined at the major floral turnover that has been documented in the USA, western and central Europe, and in the Donets Basin. We further recommend that the bases of the Kasimovian Series, Stephanian Series, Missourian Series, and Upper Pennsylvanian Series all be aligned with this same floral turnover.

Abstract Upper Carboniferous stages in terrestrial strata are consistently recognizable throughout the Euramerican Realm based on the ranges of plant macrofossils rather than named biozones. Uniformitarianism is an invaluable principle used to understand much of Earth's history. However, it has been recognized that relatively short time intervals exist when major changes occurred in the biota and sedimentation style at a non-uniformitarian time scale. Many well-defined Upper Carboniferous stage boundaries are located at such events. The Cantabrian Stage was proposed in 1969 based on the assumption that the ‘Florensprung’ (‘floral jump’) of Gothan, a dramatic change in terrestrial floras at the traditional Westphalian–Stephanian boundary, indicated that strata were missing, and the postulated ‘gap’ had to be closed by finding strata representing this ‘missing’ time elsewhere. The suggestion of a ‘gap’ or hiatus at this level reflects uniformitarian thinking, but is incorrect. As recent work has shown that a drastic climatic change reached a threshold in the tropical palaeoequatorial parts of Pangaea at the Westphalian–Stephanian (approximately the Moscovian–Kasimovian) boundary as a consequence of a drying trend, floras changed rapidly, and the traditional Westphalian–Stephanian boundary is thus one of the most easily recognizable biostratigraphic boundaries in Pennsylvanian terrestrial beds. The Cantabrian Stage, proposed to fill the non-existent gap, does not exist and cannot be recognized, either in its type area or elsewhere.

Abstract This paper focuses on the southern part of the East Midlands oil province, in which most hydrocarbon reservoirs are in Carboniferous strata and are primarily oil producing. The oils are predominantly sourced from the Namurian interbedded shales in the Gainsborough Trough and are trapped within anticlinal structures. Oil and gas exploration and production in the UK was marked by the Hardstoft-1 discovery in 1919. Since this discovery, more than 33 fields have been discovered in the East Midlands oil province, including the fields studied in this paper: Egmanton (in 1955), Bothamsall and Corringham (in 1958), Gainsborough and Beckingham (in 1959), South Leverton (in 1960), Glentworth (in 1961), and, the UK's second largest onshore field, Welton (in 1981). All of these fields produce from a Carboniferous petroleum system, sourced from Pendleian-age shales, reservoired in Namurian- and Westphalian-age sands, and trapped predominantly via structural, anticlinal traps.

Abstract The Crosby Warren Field is located onshore the UK, south of the Humber Estuary. It was discovered by RTZ Oil & Gas with the CW-1 (L46/12-3) well in 1986. The oil reservoir is Carboniferous, Namurian, Beacon Hill Flags sandstone, with gas found in Namurian sandstones of the Rough Rock, and the discovery well originally flowed waxy 40° API oil at rates of 45 bopd, which increased to nearly 700 bopd following fracture stimulation. The Beacon Hill Flags are a 10 m-thick group of laminated sandstones within a substantial gross thickness of sandstones, silts, muds and occasional thin claystones. The expected ultimate recovery for the field will be about 0.9 MMbbl of oil and 0.7 bcf of gas. Almost all of the oil and gas have already been recovered, and end of life for the field is expected to be in 2022.

Abstract The Cavendish Field is located in UK Continental Shelf Block 43/19a on the northern margin of the Outer Silverpit Basin of the Southern North Sea, 87 miles (140 km) NE of the Lincolnshire coast in a water depth of 62 ft (18.9 m). The Cavendish Field is a gas field in the upper Carboniferous Namurian C (Millstone Grit Formation) and Westphalian A (Caister Coal Formation) strata. It was discovered in 1989 by Britoil-operated well 43/19-1. Production started in 2007 and ceased in 2018. Gas initially in place was 184 bcf and at end of field life 98 bcf had been produced. The field was developed by three wells drilled through the normally unmanned platform into fluvio-deltaic sandstone intervals that had sufficiently good reservoir quality to be effective reservoirs. The majority of the formation within closure comprises mudstones, siltstones and low permeability, non-reservoir-quality feldspathic sandstones. The quality of the reservoir is variable and is controlled by grain size, feldspar content and diagenesis. The field is a structural trap, sealed by a combination of intra-Carboniferous mudstones and a thick sequence of Permian mudstones and evaporites.

Abstract The Chiswick Field is a Carboniferous gas field located in UK Blocks 49/4a and 49/4b in the Southern North Sea, approximately 18 km NW of the Markham Field, close to the UK–Netherlands median line. The Kew Field is situated approximately 3 km NE of the Chiswick Field. The Kew structure is a NW–SE-trending horst separated from the Chiswick Field, a large anticlinal domal structure, by a major NW–SE fault and a structural low. The productive reservoir units are Carboniferous (Westphalian A and B) fluvial sandstones. Both fields are situated on the eastern edge of the Silverpit Basin (part of the Southern Permian Basin). The initial exploration drilling had Leman Sandstone Formation as the primary objective, but the first wells encountered a tight Permian reservoir with gas-bearing Carboniferous reservoirs, subsequently appraised and developed. The current estimate for the gas initially in place of Chiswick and Kew is respectively 687 bcf and 85 bcf in the Carboniferous reservoir. The fields to date (Q4 2018) have produced respectively 220 bcf and 33 bcf sales gas. Gas recovery is through natural depletion from hydraulically fractured, horizontal development wells.

Abstract The Ketch, Schooner and Topaz fields were discovered between 1984 and 1987 and produced from Upper Carboniferous, Westphalian C/D (Bolsovian/Asturian) reservoirs. Gas production began in 1996, 1999 and 2009 for Schooner, Ketch and Topaz respectively. The low net-to-gross reservoir consists of discrete, low sinuosity fluvio-deltaic channels evolving upwards into an aggradational, distal fluvial fan setting, dominated by braided channels. Fault compartmentalization and variable sandbody extent mean that reservoir connectivity was a key subsurface uncertainty. The Ketch and Schooner fields gas-in-place estimates at development approval of 956 and 1021 bcf are now modelled as 581 and 654 bcf respectively. This reduction is due mainly to remapping (Schooner) and revised reservoir modelling reflecting production experience. Generally poor reservoir connectivity is demonstrated by the lower connected gas-in-place volumes, estimated at 351 and 481 bcf respectively, based on production data. Field recovery to cessation of production in 2018 was 263 (Ketch) and 310 bcf (Schooner) or 75 and 64% of the in-place volume connected to production wells. Topaz has 139 bcf gas in place, with recovery of 10.4 bcf from a connected volume of 14 bcf, equating to 74% recovery of connected volumes or 7.5% full field recovery.

Abstract Classic fold-thrust structures within Carboniferous-age strata at Broadhaven, SW Wales are well-known for their excellent preservation of Variscan deformation. These sites have been important for conceptual model generation of the link between faulting and folding, and are often cited as exemplars of fault-propagation folds following work by Williams & Chapman. Here we employ the virtual outcrop method to digitally map and measure, in detail, the classic Den’s Door outcrop. 3D reconstruction of the site by digital photogrammetry allows us to extract high-density structural measurements, reassess the existing model of structural development for the outcrop, and re-evaluate the link between faulting and folding. We find that digital mapping highlights greater variability in fault displacement and bed thicknesses than previously documented. Fracture analysis shows that fracture intensity is closely linked to structural position and bed-thickness variability, and fracture orientations record the existence of discrete mechanical boundaries through the structure. These results record complex patterns of strain distribution and multi-phase deformation. Evidence for temporal and spatial variability in strain distribution suggests that multiple kinematic and non-kinematic models of deformation are required to faithfully describe even this apparently simple structure. This calls into question the applicability of end-member models of fault-related folding, particularly for multilayered stratigraphy.

Abstract The Namurian and Westphalian sequences from the onshore well Scaftworth-B2, located in the Gainsborough Trough, central England, have been analysed for whole-rock inorganic geochemical data via inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (MS). The changes within key elements, and elemental ratios, results in a chemostratigraphic zonation scheme consisting of eight chemostratigraphic sequences and 13 chemostratigraphic packages, providing the type zonation for the Bowland Shale and overlying formations. Mineralogical data are provided by whole rock X-ray diffraction (XRD) and are used to calibrate the mineral modelling in order to generate a modelled mineral log for the study well. Furthermore, the modelled mineralogy is then used to calculate a relative brittleness for the samples, which can then be collaborated with traditional rock properties data at a later date. Elemental data can also be used to model the relative abundance of detrital quartz and biogenic silica; while total silicon is detected by ICP, biogenic silica is not detected by XRD owing to its amorphous nature. Enrichment factors calculated from the inorganic elemental data suggest that the sediment was deposited in an unrestricted marine setting, which experienced periods of anoxia.