Jurassic Kimmeridge Clay Research Articles

First occurrence of an acipenseriform (Chondrostei: Acipenseriformes) from the Upper Jurassic Kimmeridge Clay Formation of England

ABSTRACT Several fragmentary remains of an enigmatic acipenseriform, the order of fishes that includes living sturgeons and paddlefishes, are described from the Upper Jurassic Kimmeridge Clay Formation of southern England. These remains are significant because they represent the first definitive evidence of an acipenseriform from the Upper Jurassic described outside of Asia. In total, five associated dorsal caudal fulcra from the caudal fin and a paired pelvic fin from at least two separate individuals are identified as acipenseriform, although it is uncertain to which family they belong. Three families of Mesozoic acipenseriform are considered: the †Chondrostei (Lower Jurassic, Europe), the †Peipiaosteidae (Upper Jurassic to Lower Cretaceous, Asia), and the extant Acipenseroidei (Lower Cretaceous–recent, Laurasia). The new Kimmeridgian Clay acipenseriform fossils would significantly extend the temporal and spatial distribution of whichever family they are ascribed, but their affinities remain unclear. Regardless, the stratigraphic and paleobiogeographic occurrence of the new specimens holds novel implications for the poorly known evolutionary history of this primitive clade of extant non-Neopterygian fishes.

Unravelling the history of a complex hydrocarbon play through petroleum systems modelling – Catcher area development (CAD), UK Central North Sea region

Significant uncertainty exists with regards to the migration history of hydrocarbons in the Catcher Area Development (CAD) region, West Central Shelf, UK Central North Sea. In this study, petroleum system modelling is carried out to understand the pathways, timing and processes involved in hydrocarbons migration from the Jurassic Kimmeridge Clay to the injectite dominated sandstone reservoirs of the CAD region. The Cromarty sandstones are identified as the lateral carrier of hydrocarbons from the graben area to the CAD reservoirs. Out of the six CAD fields, five were charged along a fill spill chain. During the charging process, the CAD system was mostly seal limited, with significant hydrocarbon leakage into the overburden. Hydrocarbon migration and gas leakage in the region continues today. The present-day accumulations of the CAD region are spill limited suggesting the potential for more discoveries westward. This study provides an understanding of why gas chimneys are widespread in the CAD region and how the quality of hydrocarbons in the different fields relates to one another and those of the wider region. It also supports the presence of prospects further SW of the CAD region.

ORIGIN OF OIL IN UPPER PERMIAN (ZECHSTEIN) CARBONATE RESERVOIR ROCKS AT THE JARVIS STRUCTURE UNDERLYING THE ETTRICK FIELD, OUTER MORAY FIRTH, UK NORTH SEA

Oil in the Jarvis structure underlying the main Upper Jurassic reservoir at the Ettrick oilfield (Outer Moray Firth, UK northern North Sea) is present in Upper Permian (Zechstein) carbonates. The origin of this “Jarvis oil” is investigated in this paper using a multidisciplinary approach based on data from well‐logs and cores from wells 20/02‐2 and 20/02‐3. Reservoirs at the Jarvis structure consist of carbonates in the upper part of the Halibut Carbonate Formation (Ca2) and in the Carbonate Member of the Turbot Anhydrite Formation (Ca3). These carbonates are typical Zechstein dolomites composed of a range of facies from mudpackstones with storm beds deposited at moderate water depths to shoreface bioclastic‐oolitic packstones to shallow‐subtidal and intertidal microbial laminites. Interbedded anhydrites replace sabkha and lagoonal selenitic gypsum. Several shallowing‐upward units are recognised. Molecular analysis of the Jarvis oil, and comparisons with biomarker and other geochemical data from extracts of Zechstein cores and published data from different source rocks from the North Sea area, suggest that the oil was generated by marine, OM‐rich shales in the Upper Jurassic Kimmeridge Clay Formation. The oil was generated at peak oil window maturity and is characterised by high Pr/Ph, BNH/H and DBT/P ratios, and abundant C28 steranes and C28+29 monoaromatic and C26R + C27S triaromatic steroids. The molecular composition of organic material in extracts of core samples of Zechstein carbonates from wells in the Jarvis structure differs significantly from that of the Jarvis oil. Biomarkers such as BNH are absent in the core extracts, and there are different distributions and abundances of saturated and aromatic hydrocarbons, likely controlled by thermal maturity.

Facies variations in the Upper Jurassic source rocks of the Norwegian North Sea; from micro- to macro scale

In the northern North Sea, the Upper Jurassic Kimmeridge Clay (KC) and its equivalents in the Norwegian sector (i.e., Mandal, Tau, and Draupne) are the most prolific source rocks. These source rock units are known to record both lateral and vertical heterogeneity in organofacies with increasing terrigenous organic inputs near highs and basin flanks. Existing interpretations rely predominantly on Rock-Eval data, but only a few authors validate their geochemical interpretations with maceral assessments. In this study, Upper Jurassic source rocks from fourteen wells in the northern North Sea were analysed for both organic petrography and geochemistry. A potential correlation between the maceral compositions and Rock-Eval, total organic carbon (TOC), and stable carbon isotopes (saturate and aromatic fractions) of source rock extracts was established. This correlation suggests that carbon isotopes mirror the organofacies, and inferred redox conditions during sedimentation, described for the studied source rocks.Stable carbon isotopes of the saturate and aromatic fractions for 152 oils distributed across the Norwegian North Sea were compared to biomarker compounds sensitive to precursor organic material and oxygen abundance in the sedimentary environment. A correlation consistent with that observed between stable carbon isotopes and organofacies documented for the investigated source rocks is also observable in the oil dataset. Hence, the stable carbon isotope composition of the oils in the North Sea dataset appears to carry information related to the bulk organofacies and redox conditions prevailing during the sedimentation of their source. Oils often reflect the compositional attributes of their parental sources more efficiently than a single, or a set of rock extracts. Therefore, the stable carbon isotopes of migrated oils provide a means of inferring gross organofacies and redox conditions within different source rock kitchens in the study area.

Characterization of bituminite in Kimmeridge Clay by confocal laser scanning and atomic force microscopy

This work investigates bituminite (amorphous sedimentary organic matter) in Upper Jurassic Kimmeridge Clay source rock via confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). These petrographic tools were used to provide better understanding of the nature of bituminite, which has been historically difficult to identify and differentiate from similar organic matter types in source rocks. As part of an International Committee for Coal and Organic Petrology (ICCP) working group, an immature (0.42% vitrinite reflectance), organic-rich (44.1 wt% total organic carbon content) sample of Kimmeridge Clay was distributed to multiple laboratories for CLSM characterization. The primary observations from CLSM imaging and spectroscopy include: 1) the interpreted presence of Botryococcus algae as a contributor to bituminite precursors; 2) color red-shift of sulfide reflectance and bituminite auto-fluorescence from below the sample surface; 3) positive alteration of bituminite from laser-induced photo-oxidation of the sample surface, including fluorescence blue-shift; 4) fluorescence blue-shift associated to higher fluorescence intensity regions in bituminite indicative of compositional (fluorophore) differences; 5) the need for fluorescence spectroscopy standardization as applied via CLSM; and 6) the suitability of CLSM fluorescence spectroscopy to predict solid bitumen reflectance from bituminite spectral emission via calibration to an extant dataset. Secondary CLSM observations include detection of reflected laser light from highly reflective inclusions in bituminite, including sulfides and fusinite, and radiolytic alteration of bituminite caused by substitution of U for Fe in sulfides. Findings from AFM include the observation that surface roughening or surface flattening of bituminite are induced by differential broad ion beam (BIB) milling and are dependent on the location and scale of AFM topology measurement. This result highlights our still limited understanding of the effects of BIB milling on sedimentary organic matter and indicates the need for further research before this technique can be advanced as a standard practice in petrographic sample preparation. Collectively, the results of this study illustrate the general applicability and versatility of AFM and CLSM as tools for organic petrology research, specifically for better understanding of the nature and properties of the bituminite maceral.

3D petroleum systems modelling as an exploration tool in mature basins: A study from the Central North SeaUK.

In this paper we apply two different geoscience tools: 3D petroleum systems modelling and the findings of rock magnetic analysis to a reassessment of the hydrocarbon migration system from the Upper Jurassic Kimmeridge Clay source rock to the reservoirs in the Tertiary Tay sandstones in the Western Central Graben in the Central North Sea, UK. The Tay Sandstones provide an excellent laboratory to study vertical and lateral migration in an area where the subsurface geology is well constrained by both modern 3D seismic data and a high density of cored wells. Mature, super basins such as the North Sea are often characterised by a perception that most of the oil has been found and there is no reason to update models even if new data has become available. During the course of this study, two untested prospects in the Gannet and Guillemot complexes have been identified and are presented as examples of the value generated by this type of integrated approach which promotes new thinking and critical testing of conventional models.

The stratigraphy of the Kimmeridge Clay Formation (Jurassic) of the Vale of Pickering, Yorkshire, UK

The Upper Jurassic Kimmeridge Clay Formation (KCF) underlies much of the Vale of Pickering where it is almost wholly concealed by the Cretaceous Speeton Clay Formation and Quaternary deposits. There are few KCF inland or coastal exposures in Yorkshire with the result that the succession was stratigraphically poorly known until the 1970s oil crisis when the British Geological Survey drilled continuously cored boreholes at Marton and Reighton to examine the formation as a possible source of hydrocarbons. These were supplemented in 1987 by continuously cored boreholes drilled at Marton, Reighton, Ebberston and Flixborough by the Institut Français du Pétrole for hydrocarbons research. Taken together, the boreholes have enabled the lithological, palaeontological, geochemical and geophysical characters of the full thickness of the formation to be examined. Comparison of the KCF successions proved in Yorkshire with those in the adjacent North Sea, the East Midlands and the Dorset coast type area, shows marked variations in thickness related to penecontemporaneous faulting. However, there are only minor variations in the lithologies and faunas at any particular stratigraphical level. This appears to be due to a combination of Milankovitch-driven climatic fluctuations and pulsed variations in sea level which combined to produce similar depositional conditions throughout the English KCF at any one time. The chronostratigraphical classification of the KCF developed in southern England has therefore been shown to be applicable to the Yorkshire outcrop and the southern North Sea. The changes in sea level may be eustatic rather than regional events, but there is insufficient palaeontological evidence to enable them to be correlated with confidence with those of the standard Jurassic sea-level curve.

Durnonovariaodus maiseyi gen. et sp. nov., a new hybodontiform shark-like chondrichthyan from the Upper Jurassic Kimmeridge Clay Formation of England.

A partial skeleton of a hybodontiform shark-like chondrichthyan from the Upper Jurassic Kimmeridge Clay Formation of Dorset, England, is described and designated as a new genus and species, Durnonovariaodus maiseyi gen. et sp. nov. The holotype and only known specimen, which is represented by disarticulated splanchnocranial elements with associated teeth, a single dorsal fin spine, the pelvic girdle, as well as unidentifiable cartilage fragments, plus countless dermal denticles, exhibits a puzzling combination of dental and skeletal features, providing important new insights into the morphological and ecological diversity of hybodontiforms. Durnonovariaodus gen. nov. displays a unique set of dental characters, showing close morphological resemblance to Secarodus from the Middle Jurassic of England, which was erected for distinctive, strongly labio-lingually compressed multicuspid cutting teeth originally described as Hybodus polyprion. Skeletally, Durnonovariaodus gen. nov. resembles Hybodus and Egertonodus in having a palatoquadrate with a palatobasal process and an ethmoidal articular surface, combined with the possession of dorsal fin spines ornamented with costae. Therefore, and given the absence of any conclusive phylogenetic framework, Durnonovariaodus maiseyi gen. et sp. nov. is here tentatively referred to Hybodontidae until more complete material becomes available in order to enable a more reliable suprageneric identification. The holotype of Durnonovariaodus maiseyi gen. et sp. nov. contains two separate pelvic half-girdles, a feature previously considered as evolutionarily primitive among hybodontiforms. However, unfused pelvic half-girdles also occur in the supposedly closely related species Hybodus hauffianus and may in fact have been more widely distributed among hybodontiforms than previously thought, thus rendering the phylogenetic utility of separated pelvic half-girdles for inferring hybodontiform interrelationships difficult and unresolved.

A new ophthalmosaurid ichthyosaur from the Upper Jurassic (Early Tithonian) Kimmeridge Clay of Dorset, UK, with implications for Late Jurassic ichthyosaur diversity.

A new ophthalmosaurid ichthyosaur, Thalassodraco etchesi gen. et sp. nov., from the Upper Jurassic Kimmeridge Clay Formation of Dorset, UK is described. The specimen, a partial, articulated skull and anterior thorax in the Etches Collection of Kimmeridge, Dorset, is exceptionally well preserved on a slab of laminated coccolith limestone and has been expertly prepared. It comprises a near complete skull in articulation with associated anterior vertebral column and dorsal ribs, complete pectoral girdle, fully exposed left forelimb, and some elements of the right forelimb. Other elements present, including an ischiopubis are preserved on separate slabs. Presumed rapid burial of the anterior portion of the specimen in the coccolith substrate has preserved a number of ossified ligaments lying across the vertebral column and associated ribs as well as stomach contents and decayed internal organs. Aspects of the dentition, skull roof bones and the forelimb configuration distinguishes the new specimen from previously described Late Jurassic ichthyosaurs. Autopmorphies for T. etchesi include a large rounded protuberance on the supratemporal bone; a thin L-shaped lachrymal, with a steeply curved posterior border; ~ 70 teeth on the upper tooth row, and deep anterior dorsal ribs. A well resolved phylogenetic analysis shows T. etchesi as a member of a basal clade within Ophthalmosauridae comprising Nannopterygius, Gengasaurus, Paraophthalmosaurus and Thalassodraco. The new specimen adds to the diversity of the Ichthyopterygia of the Kimmeridge Clay Formation and emphasises the important contribution of amateur collectors in palaeontology.

Experimental Investigation of the Dependence of Accessible Porosity and Methane Sorption Capacity of Carbonaceous Shales on Particle Size

Crushing and grinding of carbonaceous shale samples is likely to enhance the accessibility of pores and embedded organic matter as compared to the intact rock. This may lead to an overestimation of the total (volume and sorptive) gas storage capacity. In order to investigate the importance of these effects we have measured unconfined apparent grain densities (helium pycnometry) and methane sorption capacities (high-pressure methane excess sorption) of four carbonaceous shales (Cambro-Ordovician Alum Shale, Jurassic Kimmeridge Clay, Jurassic/Cretaceous Bazhenov Shale, and Late Cretaceous Eagle Ford Shale) as a function of particle size. Measurements were first conducted on 38 mm diameter core plugs, which then were crushed and milled to successively smaller particle sizes (<10 mm, <2 mm, <64 μm, and <1 μm). Apparent grain densities of the smallest particle fractions of the Alum, Bazhenov and Kimmeridge samples were consistently higher by 0.5 to 1% than apparent grain densities of the original sample plugs. Methane excess sorption capacity increased significantly for particle sizes <64 μm for the Alum and <1 μm for the Bazhenov and Kimmeridge samples while no significant changes upon grinding were observed for the Eagle Ford Shale. For the Bazhenov Shale, the apparent grain density increased slightly from 2.446 g/cm3 to 2.450 g/cm3 upon particle size reduction from <64 μm to <1 μm while the maximum sorption capacity (“Langmuir volume”) increased substantially from 0.11 mmol/g to 0.19 mmol/g. Similarly, for the Kimmeridge Clay and Alum Shale, a slight increase of the apparent grain density from 1.546 g/cm3 to 1.552 g/cm3 and from 2.362 g/cm3 to 2.385 g/cm3, respectively, was accompanied by increases in sorption capacity from 0.37 mmol/g to 0.45 mmol/g and from 0.14 mmol/g to 0.185 mmol/g, respectively. The increase in sorption capacity indicates an opening of a considerable amount of micropores with large internal surface area upon physical disruption of the rock fabric and/or removal of included fluids. It may also be due to increased swelling abilities of clay minerals and organic matter upon destruction of the stabilizing rock fabric with decreasing particle size. Grain density and sorption isotherms measured on small particle sizes are likely to overestimate the gas storage capacities and the amounts of producible gas-in-place since under field conditions (largely undisrupted rock fabric), significant portions of this storage capacity are essentially inaccessible. Poor interconnectivity of the pore system and slow, diffusion-controlled transport will massively retard gas production. Based on these findings, particle sizes >64 μm should be used for porosity and sorption measurements because they are more likely to retain the properties of the rock fabric in terms of accessible pore volume and sorptive storage capacity.

The Maria Field, Block 16/29a, UK North Sea

Abstract The Maria oilfield is located on a fault-bounded terrace in Block 16/29a of the UK sector of the North Sea, at the intersection of the South Viking Graben and the eastern Witch Ground Graben. The field was discovered in December 1993 by the 16/29a-11Y well and was confirmed by two further appraisal wells. The reservoir consists of shoreface sandstones of the Jurassic Fulmar Formation. The Jurassic sandstones, ranging from 100 to 180 ft in thickness, have variable reservoir properties, with porosities ranging from 10 to 18% and permeabilities from 1 to 300 mD. Hydrocarbons are trapped in a truncated rotated fault block, striking NW–SE. The reservoir sequence is sealed by Kimmeridge Clay Formation and Heather Formation claystones. Geochemical analysis suggests that Middle Jurassic Pentland Formation and Upper Jurassic Kimmeridge Clay Formation mudstones have been the source of the Maria hydrocarbons. Estimated recoverable reserves are 10.6 MMbbl and 67 bcf (21.8 MMboe). Two further production wells were drilled in 2018 to access unexploited areas.

The Howe and Bardolino fields, Blocks 22/12a and 22/13a, UK North Sea

Abstract The Howe and Bardolino fields lie in UK Blocks 22/12a and 22/13a, respectively, on the eastern flank of the Forties–Montrose High. The Howe Field was discovered in 1987 by well 22/12a-1, and Bardolino in 1988 with well 22/13a-1ST. Both share common Jurassic reservoirs, have Upper Jurassic Kimmeridge Clay Formation top seals, require some form of lateral seal and have similar fluids. Howe has been producing relatively dry oil throughout its production life, indicating relatively good connectivity across the field area. In contrast, the Bardolino accumulation is proven to be compartmentalized. Bardolino is likely to be segmented through some fault-related mechanism. In place volumes at the Howe Field are 46.8 MMbbl, with 17 MMbbl produced thus far through a combination of natural aquifer and solution gas cap drive by subsea development well 22/12a-9Z. In place volumes at the Bardolino Field are 11.2 MMbbl, with 1.1 MMbbl produced to date through depletion drive by a subsea development well 22/13a-8. This represents recovery rates of 35% for Howe and 10% for Bardolino to date. In place volumes for the undeveloped Pentland Formation at Howe are 5 MMbbl. In place estimates for the undeveloped Kimmeridge Clay Formation sandstones at Bardolino are 8 MMbbl.

Macroevolutionary trends in the genus Torvoneustes (Crocodylomorpha: Metriorhynchidae) and discovery of a giant specimen from the Late Jurassic of Kimmeridge, UK

AbstractThe metriorhynchid crocodylomorph fauna of the Late Jurassic Kimmeridge Clay Formation (KCF) of the UK was highly diverse. One genus from this Formation, Torvoneustes, was unique in evolving dentition similar to known chelonivorous crocodylomorphs and enlarged attachment sites for the pterygoideus adductor musculature. Here we report the largest known Torvoneustes specimen, the occipital region of a large cranium that was discovered on the shore of Brandy Bay, Dorset, UK (KCF). We also report three tooth crowns discovered during the 19th century from Oxfordshire that can also be referred to Torvoneustes. The partial braincase is unique in having: verticalized basioccipital tuberosities that have thickened ventral margins, the notch between the basioccipital tuberosities is a narrow inverted ‘U’-shape and a subrectangular-shaped carotid canal foramina. The presence of ‘occipital fossae’ (deep concavities with the hypoglossal foramina in their dorsomedial corners) and carotid foramina with raised rims relative to the basioccipital posterior surface, allow us to refer it to Torvoneustes. Although incomplete, the exceptional size of the specimen demonstrates that Torvoneustes attained larger body lengths than previously supposed (3.7–4.7 m). Comparing the dimensions of this specimen to other metriorhynchids suggests that at least some Torvoneustes specimens rivalled Plesiosuchus manselii in body length.

Characterising the vertical separation of shale-gas source rocks and aquifers across England and Wales (UK)

Shale gas is considered by many to have the potential to provide the UK with greater energy security, economic growth and jobs. However, development of a shale gas industry is highly contentious due to environmental concerns including the risk of groundwater pollution. Evidence suggests that the vertical separation between exploited shale units and aquifers is an important factor in the risk to groundwater from shale gas exploitation. A methodology is presented to assess the vertical separation between different pairs of aquifers and shales that are present across England and Wales. The application of the method is then demonstrated for two of these pairs—the Cretaceous Chalk Group aquifer and the Upper Jurassic Kimmeridge Clay Formation, and the Triassic sandstone aquifer and the Carboniferous Bowland Shale Formation. Challenges in defining what might be considered criteria for ‘safe separation’ between a shale gas formation and an overlying aquifer are discussed, in particular with respect to uncertainties in geological properties, aquifer extents and determination of socially acceptable risk levels. Modelled vertical separations suggest that the risk of aquifer contamination from shale exploration will vary greatly between shale–aquifer pairs and between regions and this will need to be considered carefully as part of the risk assessment and management for any shale gas development.

Stalked barnacles (Cirripedia, Thoracica) from the Upper Jurassic (Tithonian) Kimmeridge Clay of Dorset, UK; palaeoecology and bearing on the evolution of living forms

New thoracican cirripede material from the Kimmeridge Clay (Upper Jurassic, Tithonian) is described. This includes a log, encrusted on the lower surface with hundreds of perfectly preserved, articulated specimens of Etcheslepas durotrigensis Gale, 2014, and fewer specimens of Concinnalepas costata (Withers, 1928). Some individuals are preserved in life position, hanging from the underside of the wood, and the material provides new morphological information on both species. It appears that Martillepas ovalis (Withers, 1928), which occurs at the same level (Freshwater Steps Stone Band, pectinatus Zone) attached preferentially to ammonites, whereas E. durotrigensis and C. costata used wood as a substrate for their epiplanktonic lifestyle. Two regurgitates containing abundant barnacle valves, mostly broken, and some bivalve fragments, have been found in the Kimmeridge Clay. These were produced by a fish grazing on epiplanktonic species, and are only the second example of regurgitates containing barnacle valves known from the fossil record. The evolution of modern barnacle groups is discussed in the light of the new Jurassic material as well as recently published molecular phylogenies. New clades defined herein are called the Phosphatothoracica, the Calamida and the Unilatera.

Establishing the Baseline in Groundwater Chemistry in Connection with Shale-gas Exploration: Vale of Pickering, UK

The baseline chemistry of groundwater from two aquifers in the Vale of Pickering, North Yorkshire, has been investigated ahead of a proposal to explore for shale gas, planning permission for which has recently been granted. Groundwater in a shallow aquifer including Quaternary and/or Jurassic Kimmeridge Clay deposits shows compositions distinct from a Corallian (Jurassic) Limestone aquifer, reflecting different lithologies and hydrogeological conditions. Corallian groundwaters along the margins of the vale are controlled by reaction with carbonate, with redox conditions varying according to degree of aquifer confinement. Superficial aquifer groundwaters are confined and strongly reducing, with some observed high concentrations of dissolved CH4 (up to 37 mg/L; Feb 2016 data). This appears to be of mixed biogenic-thermogenic origin but further work is needed to determine whether the source includes a deeper hydrocarbon reservoir contributing via fractures, or a shallower source in the Quaternary or Kimmeridge sediments. The data show a shallow aquifer with a high-CH4 baseline which pre-dates any shale-gas activity.

Reservoir geochemistry: Evaluation of thermal maturity from gasoline-range hydrocarbons

Oils and condensates with high concentrations of gasoline-range hydrocarbons typically lack adequate quantities of [Formula: see text] biomarkers used for thermal maturity and organic facies evaluations. I attempted a calibration of rock-based thermal maturity parameters between gasoline-range molecular parameters and nonmolecular maturity parameters such as Rock-Eval Tmax, vitrinite reflectance, and downhole temperatures. This enables maturity evaluation of volatile oils and condensates whose biomarker concentrations are at low or trace levels. The rock-based calibration data were used to assess thermal maturity of nonvolatile oils, volatile oils, and condensates from the Central Graben area of the UK North Sea and includes samples from high-pressure (gradients [Formula: see text]) and high-temperature ([Formula: see text]) hydrocarbon systems. Source rocks for theses North Sea oils and condensates are the Upper Jurassic Kimmeridge Clay and Heather shales, with a predominance of marine, algal type II organic matter.

Arthritic, scavenged and largely abandoned: the curious tale of a giant pliosaur from the Kimmeridge Clay at Stretham, Cambridgeshire, U.K.

A substantial part of an exceptionally large pliosaur skeleton was uncovered in Upper Jurassic Kimmeridge Clay at Stretham in 1952. Relatively few bones were collected without delay by palaeontologists before members of the public were permitted to take what they wanted. When the importance of the find became evident, attempts were made to recover the material that had been dispersed. Two further discoveries of pliosaur bones dating from 1960 are assumed to belong to the same animal. About one-quarter of the post-cranial skeleton, together with four teeth and a few possible jaw fragments, are held in a museum collection.The osteological maturity, length and pathology of the specimen have not been firmly established; and its scientific name has fallen victim to the mistaken identification of a crucial skeletal element, to a baseless association with the mandible of an unconnected fossil, to changing views on the bones that are taxonomically significant and to the frequent revision of Late Jurassic pliosaurid taxonomy. A fresh study of the rather limited material that is available might lead to a reconciliation of some of these issues. In the meantime, a comprehensive review of every significant published paper and of unpublished material relating to the discovery, collection and examination of the Stretham pliosaur is presented here.

Detailed stratigraphy of the uppermost Kimmeridge Clay Formation (Upper Jurassic) from the Swanworth Boreholes, Dorset, UK

The higher parts of the cores of the Swanworth Boreholes, Dorset, allow detailed investigation of parts of the Upper Jurassic Kimmeridge Clay Formation that are difficult to sample on the coastal type-section. The member-level divisions set up by Buckman and Arkell are confirmed as readily recognisable. Body-fossils have been found throughout the beds examined and are recorded and confirm the ammonite zonal boundaries as proposed by Cope (1978). The extensive bioturbation of the sediments in the highest beds was primarily caused by decapod crustaceans whose remains are preserved in the borehole cores. Detailed examination of the cores has failed to confirm the existence of the so-called Chapman's Pool Pebble Bed, nor can its existence at nearby Gad Cliff be confirmed.

New cirripedes (Crustacea, Thoracica) from the Jurassic and Cretaceous of the United Kingdom

Extensive new material of scalpelliform cirripedes, including articulated individuals, from the Late Jurassic (Tithonian) Kimmeridge Clay of Dorset, southern England, is described and used as a basis for taxonomic revision of the family Zeugmatolepadidae. Two subfamilies, the Zeugmatolepadinae and Martillepadinae nov., are established and two new genera (Martillepas, Concinnalepas) in the latter subfamily are described from the Upper Jurassic and one (Icenilepas) from the Upper Cretaceous Chalk. Material from the Kimmeridge Clay of Dorset also includes the oldest fossil representative of the family Pollicipedidae for which a new genus and species, Etcheslepas durotrigensis, are erected, and the oldest calanticid, Cretiscalpellum sp. nov. Jurassic taxa established by T.H. Withers in 1928, on the basis of sparse material, are redescribed, and referred to the new genera as Martillepas ovalis, M. costata, M. hollisi, Concinnalepas concinna and Etcheslepas fragilis.