A critical investigation is made of the unconformities reportedly present in Oxford Clay Formation and Corallian Group (Jurassic, Oxfordian) strata in central and southern England. A revised cross-section through strata belonging to the coeval Coralline Oolite Group and Upper Calcareous Grit and Ampthill Clay formations of the Tabular Hills, North Yorkshire is used to show the lateral extent of unconformities within these strata. There is definite correlation of only two of these unconformities present in Yorkshire with similar erosive episodes in the equivalent strata in southern England. The extent to which the sequences of strata delimited by these unconformities can be correlated with sequences defined in the North Sea Basin is discussed. The tectonic nature of the unconformities is evident, as there was not a simple drop in relative sea-level causing erosion. Erosion occurred down to deeper levels in certain areas, this being caused by differential uplift. The reasons for this phenomenon are still to be determined.

The Middle Oxfordian Highworth Limestone of Wiltshire has long been renowned for the wide variety of fossils it contains. Though there are no longer available any exposures of this unit, field walking of the outcrop has enabled the collection of a large assemblage of fossils from this important part of the Corallian sequence of Wiltshire. The occurrence of these prolific bivalve, ammonite and coral faunas is set into the context of the Middle Oxfordian palaeogeography of southern England.

The Global Stratotype Section and Point (GSSP) for the base of the Kimmeridgian Stage (Jurassic System), at Flodigarry, Staffin Bay, Isle of Skye, Scotland, UK Journal Item How to cite: Wierzbowski, Andrzej; Barski, Marcin; Coe, Angela L.; Hounslow, Mark W.; Matyja, Bronisław A.; Price, Gregory D.; Wierzbowski, Hubert; Wright, John K.; Atrops, with contributions from Francois; Grabowski, Jacek; Mattioli, Emanuela; Morton, Nicol; Ogg, James G.; Olóriz, Federico; Page, Kevin; Parent, Horacio; Przybylski, Piotr; Schweigert, Guenter and Villaseñor, Anna Bertha (2023). The Global Stratotype Section and Point (GSSP) for the base of the Kimmeridgian Stage (Jurassic System), at Flodigarry, Staffin Bay, Isle of Skye, Scotland, UK. Episodes (Early Access).

The sequence of Jurassic and Cretaceous strata laid down in north Lincolnshire is traced northwards onto the Market Weighton High, and compared with the equivalent Cleveland Basin sequence as it is traced south onto the High. Understanding of the manner of operation of the High has long been hindered by the amount of erosion of strata over it, particularly in the Early Cretaceous. Facies analysis of the remaining strata present on either side of the High is used to estimate the thickness and the facies of strata originally deposited over it. Although there were periodic uplifts of the High, leading to increasing omissions of strata approaching it, there is little evidence that during the Jurassic the High was emergent for significant periods. Most strata were either originally present at Market Weighton in marginal marine facies, or continued across the High without interruption. The operation of the High in the light of modern understanding of crustal stresses during the Mesozoic is reviewed.

ABSTRACT This paper provides a record and analysis of a site in east‐midland England, at which organic and soil material are found between two Middle Pleistocene tills. This is the first discovery of its kind in the area, and demonstrates unequivocally that the region was glaciated on two separate occasions, something that has long been inferred and articulated, but not actually demonstrated. The landforms, sediments and soils are studied with respect to their geomorphological, lithological, pedological, palaeobotanical and structural properties. The organic and soil material along with soil structures indicate, sequentially, a periglacial climate, a long period of warm temperate weathering and a cool temperate climate. Evaluation of this evidence in terms of existing published work identifies a number of problems with existing models and suggests that the most likely model for the glacial history of this part of midland England is an early Middle Pleistocene glaciation which is represented only by trace erratics, a Marine Isotope Stage (MIS) 12 age glaciation which moved across the area from the NW and deposited a chalk‐free till, and an MIS 8 age glaciation that transported and deposited an upper chalky till from the NE. © 2021 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.

Detailed study of all the ammonite collections gathered by the authors in the Staffin Bay sections has resulted in minor changes in the distribution of ammonite taxa, and slight modification of the position of the Oxfordian/Kimmeridgian boundary. Most significant is the discovery of Pictonia (Triozites) cf. seminudata which results in the placing of the stage boundary 0.16 m below the level formerly proposed. This study discusses the evolution of the Subboreal family Aulacostephanidae, and the Boreal family Cardioceratidae, indicating changes in the patterns of individual development in the evolution of both families in terms of heterochrony. The Oxfordian/ Kimmeridgian boundary interval shows major morphological changes in both ammonite families which were released from phylogenetic constraints by heterochrony, closely related to changes in environmental conditions.

New information from boreholes at Lyneham and the construction of a relief road south of Royal Wootton Bassett has been combined with field mapping to produce the first synthesis of the transition between the Upper Jurassic shelf sediments of the Wessex Basin and the laterally equivalent clay facies sediments overlying the East Midlands Microcraton. Periodic uplifts of the Wootton Bassett High at the northern margin of the Wessex Basin saw the repeated attempts to spread clay facies sedimentation southwards into central and southern Wiltshire frustrated by uplifts of the high. This resulted in periods of erosion followed by new episodes of shallow water shelf sedimentation succeeded by deeper water strata, these beds resting upon the eroded edges of the older sediments.

New data are presented in relation to the worldwide definition of the Oxfordian/Kimmeridgian boundary, i.e. the base of the Kimmeridgian Stage. This data, mostly acquired in the past decade, supports the 2006 proposal to make the uniform boundary of the stages in the Flodigarry section at Staffin Bay on the Isle of Skye, northern Scotland. This boundary is based on the Subboreal-Boreal ammonite successions, and it is distinguished by the Pictonia flodigarriensis horizon at the base of the Subboreal Baylei Zone, and which corresponds precisely to the base of the Boreal Bauhini Zone. The boundary lies in the 0.16 m interval (1.24–1.08 m) below bed 36 in sections F6 at Flodigarry and it is thus proposed as the GSSP for the Oxfordian/Kimmeridgian boundary. This boundary is recognized also by other stratigraphical data – palaeontological, geochemical and palaeomagnetic (including its well documented position close to the boundary between magnetozones F3n, and F3r which is placed in the 0.20 m interval – 1.28 m to 1.48 m below bed 36 – the latter corresponding to marine magnetic anomaly M26r).The boundary is clearly recognizable also in other sections of the Subboreal and Boreal areas discussed in the study, including southern England, Pomerania and the Peri-Baltic Syneclise, Russian Platform, Northern Central Siberia, Franz-Josef Land, Barents Sea and Norwegian Sea. It can be recognized also in the Submediterranean-Mediterranean areas of Europe and Asia where it correlates with the boundary between the Hypselum and the Bimmamatum ammonite zones. The changes in ammonite faunas at the boundary of these ammonite zones – mostly of ammonites of the families Aspidoceratidae and Oppeliidae – also enables the recognition of the boundary in the Tethyan and Indo-Pacific areas – such as the central part of the Americas (Cuba, Mexico), southern America, and southern parts of Asia. The climatic and environmental changes near to the Oxfordian/Kimmeridgian boundary discussed in the study relate mostly to the European areas. They show that very unstable environments at the end of the Oxfordian were subsequently replaced by more stable conditions representing a generally warming trend during the earliest Kimmeridgian. The definition of the boundary between the Oxfordian and Kimmeridgian as given in this study results in its wide correlation potential and means that it can be recognized in the different marine successions of the World.

Study of a number of new exposures of strata belonging to the Oxfordian Corallian Group in the area around Steeple Ashton, Wiltshire, combined with geological mapping, has enabled the production of the first full synthesis of Oxfordian sedimentation in the area. Situated on the north-western margin of the Wessex Basin, the area experienced intermittent sedimentation, with episodes of subsidence leading to the accumulation of shallow marine shelf sediments, interspersed with episodes of uplift and erosion, with pebble beds and erosion surfaces. One of the most celebrated stratal units in the area is the Steeple Ashton Coral Bed. The extent of the outcrop of the Coral Bed has been established here for the first time. Apart from the very localised Ringstead Coral Bed of Dorset, this is the only coralliferous development in the Upper Oxfordian of Britain, and is remarkable for the wide variety of coral species present. Corals only developed substantially for one short period, during which there was the most varied and prolific coral growth. This study sets the Steeple Ashton Coral Bed into the context of Oxfordian sedimentation in Wiltshire, and of Late Oxfordian sedimentation in N. W. Europe.

Betton Farm quarries contain, within a small area, a remarkable range of facies associated with the development of a Jurassic coral reef. A NW-SE-trending barrier reef protected the whole area containing the two quarries. Betton Farm North Quarry displays Thamnasteria patch reefs. These consist of scattered, 1 m high masses of colonial coral surrounded by reef debris that were situated behind the barrier within a large reef platform area. In Betton Farm South Quarry, bioclastic sand, consisting largely of coral and bivalve debris, interdigitates with the development of a small ribbon reef made up of the massive colonial coral Thamnasteria. This ribbon reef, only 3 to 4 m wide, sheltered a lagoonal area that accumulated lime mud and was colonized by large gastropods and burrowing bivalves. A fauna of reef-specializing bivalves and echinoids occupied these areas of patch/ribbon reef development, which were periodically swept by nutrient-bearing currents. Competition between the growth of the ribbon of Thamnasteria and the accumulation of fringing sediments saw periods when the Thamnasteria expanded over the coral-shell sand, and periods when the encroaching sediment cut back the growth of the Thamnasteria considerably. Considered initially to represent the Coral Rag Member of the Coralline Oolite Formation, the Betton Farm Coral Bed is now seen to represent localized coral reef developments situated near the base of the Malton Oolite Member, and growing upon antecedent bedrock features such as hard-ground surfaces that formed during pauses in sedimentation of the Malton Oolite.

Summary Two hundred and sixty-six specimens of cardioceratid ammonites found in concretions from the Tenants’ Cliff Member of the Lower Calcareous Grit Formation (Upper Oxfordian, Upper Jurassic) at Tenants’ Cliff, near Scarborough, England, were analysed to determine the type of damage within the assemblage. Forty-five specimens were severely damaged. They consist largely of just a body chamber fragment, with small pieces of fractured shell scattered through the matrix. This type of damage is characteristic of predation by sharks or marine reptiles. Fourteen, almost complete but damaged specimens showed an indent that is either subcrescentic or V-shaped. Measurements of the position of this damage showed that the V-shaped indent was present on the body chamber of these specimens anterior to the final suture. Comparisons with other specimens from different localities and time periods, as well as sedimentological evidence and modern behavioural records, suggests that such damage was caused by squids.

Information obtained during the digging of a pipeline trench southwest of Calne, Wiltshire, has enabled the compilation of the first complete sequence through the strata of the Corallian Group (Oxfordian) in this area of west Wiltshire. A detailed description of this sequence of sands, clays, ooidal and coralliferous limestones which represent the Kingston and Stanford Formations is provided, and the information obtained used to provide a new synthesis of the stratigraphy of the Corallian Group in west Wiltshire. The existence of a previously unrecognized sedimentary sub-basin of the Wessex Basin is demonstrated. Previously unrecorded stratal sequences and faults have been discovered, and the existence established within the Wiltshire Corallian of a new coralliferous horizon, the Westbrook Coral Bed. The setting of this sedimentary sequence within the tectonic regime which existed in this part of the Wessex Basin in the Late Jurassic is reviewed.

Synopsis The Middle Callovian/Oxfordian/Early Kimmeridgian Staffin Shale Formation at Staffin Bay, Isle of Skye contains one of the most complete, fossiliferous successions through Oxfordian strata in Britain, with Cordatum Zone (Chronozone) strata very well developed. During several visits to Staffin over the last 40 years, the author has collected some eighty ammonites from the Cordatum Zone. Well-preserved cardioceratid ammonites are common in the Costicardia Subzone of the Cordatum Zone, and these are the subject of the present study. Cordatum Subzone ammonites are less common and less well preserved at Staffin and, consequently, more problematic for such detailed study. Detailed analysis of Cordatum Zone cardioceratids as a whole shows that it is likely that almost all these Costicardia Subzone cardioceratinids belonged to the one species Cardioceras costicardia biosp.; all other morphospecies of Cardioceras recognized by previous authors from this subzone are regarded here as varieties of C. costicardia biosp. Goliathiceras , however, is regarded here as a separate Lower Oxfordian cardioceratid genus.

A detailed study of the lithologies of each of the beds present in the Osmington Oolite Formation of south Dorset is used to allocate numerous loose-collected ammonites to their correct stratigraphic horizons. Much new material has been collected by the author in addition to the limited amount of material available in museum collections. The age of the faunas of the three constituent members of the Osmington Oolite Formation is each assessed and placed into the context of Middle Oxfordian ammonite sequences elsewhere in England and in Europe.

A magnetic polarity pattern for Boreal and Sub-Boreal ammonite zones of the Upper Oxfordian to Lower Kimmeridgian was established and confirmed in four British sections, including the proposed Global Boundary Stratotype Section and Point (GSSP) on the Isle of Skye (Scotland) to define the base of the international Kimmeridgian Stage. A coeval pattern for Sub-Mediterranean ammonite zones was compiled from seven sections in Poland, one German section and multi-section composites from France and Spain. The mean paleopole for the European Craton (excluding Spain) at the Oxfordian–Kimmeridgian boundary is 74.2°N, 181.3°E (Α95 = 3.8°). The common magnetic polarity scale enables inter-correlation of ammonite subzones among these three faunal provinces and to the marine magnetic-anomaly M-Sequence. The proposed GSSP at the base of the Pictonia baylei Zone is near the base of an extended interval dominated by reversed polarity, which is interpreted to be Chron M26r. This GSSP level projects to the lower to middle part of the Epipeltoceras bimammatum Subzone, which is the middle subzone of this E. bimammatum Zone in the Sub-Mediterranean standard zonation. In contrast, the traditional placement of the Oxfordian–Kimmeridgian boundary in that Sub-Mediterranean standard zonation (base of Sutneria platynota Zone) is at the base of Chron M25r, or nearly 1 million years younger.

A suite of 11 sections through the Oxfordian (Upper Jurassic) strata in the Dorset and Yorkshire regions of England and the Isle of Skye in Scotland yielded magnetic polarity patterns directly calibrated to the ammonite biostratigraphy of the Boreal and the Subboreal faunal provinces. The sections include the leading candidate for the global stratotype (GSSP) for the Callovian–Oxfordian stage boundary. The mean Oxfordian paleomagnetic pole derived from the Dorset and Yorkshire sections is 71.3°N, 172.6°E (δp=4.2°, δm=6.1°). The integrated magneto-biostratigraphic scale is consistent with results from the Sub-Mediterranean faunal province and extends the polarity pattern to the base of the Oxfordian. After adjusting for the estimated durations of ammonite subzones from cycle stratigraphy, the magnetostratigraphy confirms models for marine magnetic anomalies M30 through to M37, including some of the short-duration features recorded by deep-tow magnetic surveys in the western Pacific. The Callovian–Oxfordian boundary (base of Quenstedtoceras mariae Zone) occurs in a normal-polarity zone that is correlated to the youngest part of polarity chron M37n of this extension to the M-sequence.

Four areas in southern England centred on Swindon and Westbury (Wiltshire), Bourton (north Dorset) and the Dorset coast near Weymouth (south Dorset) have yielded well-preserved late Oxfordian and early Kimmeridgian (Upper Jurassic) ammonites in abundance. These ammonites belong principally to the aulacostephanid genera Ringsteadia and Pictonia, and their microconch equivalents Microbiplices and Prorasenia. Systematic descriptions of these genera are included herein. Within the zonal and subzonal sequence of the English Oxfordian/Kimmeridgian Stage boundary beds, the established subdivision of the Late Oxfordian Pseudocordata Zone into Pseudoyo, Pseudocordata and Evoluta Subzones is confirmed. In the Early Kimmeridgian Baylei Zone, however, the evidence is that the sequence throughout much of southern England is incomplete compared with more complete sequences such as that at Staffin in the Isle of Skye, with the presence of only one faunal biohorizon, the densicostata horizon.

The latest Callovian and Early Oxfordian are characterised by one of the highest levels of mixing of Boreal, Submediterranean and even Mediterranean faunas. In particular the massive expansion of Boreal Cardioceratidae from their original “home” in Arctic areas as far south as south-east France, brings them into contact with Mediterraneanstyle faunas rich in Phylloceratidae. This so-called “Boreal Spread” provides the framework within which highresolution inter-bioprovincial correlations are possible and hence the context for a successful GSSP designation for the base of the Oxfordian Stage within Europe (and hence the beginning of the Upper Jurassic). Associated with the Cardioceratidae, especially in more Tethyan areas is a great variety of Perisphinctoidea, including Aspidoceratidae, Periphinctinae, Grossouvrinae and rarer Pachyceratidae as well as frequent Hecticoceratinae and rarer Phylloceratidae. As several of these persist beyond Europe they therefore provide tantalising indications that a truly global correlation of any GSSP established in Europe will ultimately be possible. The stratigraphical, taxonomic and palaeobiogeographical context and significance of the trans Callovian-Oxfordian boundary faunas within Europe is here reviewed and the faunas of the candidate GSSP at Redcliff Point, Weymouth, SW England are described, including the basal Oxfordian species Cardioceras (Pavloviceras) redcliffense sp. nov.