Purbeck Beds Research Articles

Ostracod assemblages, palaeoenvironment and cyclicity of Purbeck-type sediments of the Münder Formation (Lower Cretaceous, Hils Syncline, N-Germany)

Berriasian marlstones in the upper part of the Münder Formation (“Purbeck”) of the Hils Syncline have been regarded as freshwater deposits with minor brackish influence. However, similar to some marlstones of the English Purbeck Limestone Group, it remained unclear whether these deposits rich in non-marine ostracods are lacustrine or marine-lagoonal in origin. Facies analysis of the sediments revealed strikingly symmetric cycles composed of (1) red-brown massive marlstones of distal alluvial plains, (2) greenish-grey bedded marlstones with microbial lamination of the supralittoral zone, (3) dark-grey charophyte marlstones and (4) light-grey charophyte limestones with scattered porostromate oncoids of the eulittoral zone, (5) poorly bedded light-grey micritic limestones and (6) clayey marlstones of the sublittoral zone. Ostracod associations revealed by cluster analysis and associated microfossils indicate cyclic salinity changes coincident with lithofacies alternations. A Theriosynoecum-association is restricted to eulittoral and shallow sublittoral lithofacies types and reflects freshwater to oligohaline conditions. This association is accompanied by the freshwater gastropods Gyraulus and Provalvata as well as charophytes of the genera Atopochara, Clavator and Globator. Supralittoral marlstones are characterized by a mixed Cypridea-association, composed of autochthonous Cypridea of ephemeral freshwater pools and transported faunal elements. Increased salinities of miohaline to mesohaline conditions are indicated for sublittoral lithofacies types by a Mantelliana-association. Maximum flooding is indicated by the appearance of small foraminifera. Variations of monospecific ostracod stable isotope ratios coincide with the cyclic salinity fluctuations interpreted from ostracod assemblages along the section. This correlation of lithofacies types and ostracod faunas implies that salinities increased with increasing water level and vice versa. Consequently, a coupling of the water level of the Hils Basin to short-term eustatic sea-level changes must be assumed. Therefore, the Hils Basin is interpreted as a marine embayment during the Berriasian with freshwater spreading out on top of marine-brackish water, but not a lake. A similar approach combining micropalaeontological and sedimentological evidence may help to distinguish between marginal-marine sediments affected by cyclic sea-level changes and lacustrine sediments displaying climatically-driven cyclicity in the Purbeck-type area and elsewhere in Europe.

Drawing the line: the history of the Jurassic—Cretaceous boundary

The first System boundaries were based on lithostratigraphical criteria — the junction between two formations. As biostratigraphy and chronostratigraphy developed, ammonite faunas were used in the Mesozoic to define stages and form the basis of most zonal schemes. In the uppermost Jurassic and lowermost Cretaceous, this process is complicated by extreme ammonite faunal provincialism; from this developed separate ammonite zonal schemes, separate stages and the recognition of different Jurassic-Cretaceous boundaries, dependent upon the ammonite faunal province. The acceptance of the Tithonian Stage as the Primary Standard for the terminal Jurassic means that the basal Cretaceous boundary will be drawn at the base of the Berriasian Stage. Selection of appropriate boundary stratotype sections is under consideration. Correlations of the southern English non-marine sections with the Tethyan marine limestones have been made using magnetostratigraphy and various microfossil groups; although the conclusions vary somewhat, it is apparent that the majority of the Purbeck Limestone Group of southern England is of Cretaceous age.

The Purbeck Limestone Group of Dorset, southern England

The late Jurassic to early Cretaceous Purbeck Limestone Group of Dorset has been a focus for media and academic attention for the last 150 years. For example, The Illustrated London News in 1857 carried an article by the Revd Charles Kingsley, (of The Water Babies fame), titled ‘Geological Discoveries at Swanage’. describing fossil‐hunting endeavours of Samuel Husband Beckles (1814–1890; Fig. 1). Beckles had been encouraged by Richard Owen (1804–1892) to go in search of the tiny fossilized mammalian remains in these strata. Beckles rose to the challenge and at his own expense employed a team of workmen to carry out the excavations; in the process they uncovered a thin layer containing the numerous remains of diminutive mammals along with the remains of other vertebrates, including turtles, crocodiles and ornithischian dinosaurs. Since then, dinosaur tracks and related discoveries from these same strata have often caught the imagination of the press, inspiring sensational headlines such as ‘Builder digs up giant lizard fight’ and ‘Dinosaur graveyard in Swanage Bay’!Contemporary illustration of Samuel Beckles’ excavation on the cliffs of Durlston Bay, from Charles Kingsley's account of the discoveries at Swanage which appeared in The Illustrated London News in 1857.image

BURNT KIMMERIDGIAN SHALE AT EARLY ROMAN SILCHESTER, SOUTH‐EAST ENGLAND, AND THE ROMAN POOLE–PURBECK COMPLEX‐AGGLOMERATED GEOMATERIALS INDUSTRY

Summary. A wide range of geomaterials were worked at industrial settlements scattered over an area of c.225 km2 in the Poole Harbour–Isle of Purbeck district of modern Dorset. These materials, more than one handled at some sites, included shale (‘coal’), burnt shales (yellow, red) and cementstones from the Kimmeridge Clay Formation (Upper Jurassic), Purbeck marble from the Purbeck Group (earliest Cretaceous), hard chalk from the Chalk Group (Upper Cretaceous), and potting clays and sands from the Bracklesham Group (Palaeogene), for South‐east Dorset Black‐burnished Pottery Category 1. There was also a salt industry, which could have used pottery for packaging. The industrial products are conterminously distributed in southern and central Britain and, in the case of pottery and shale items, reached as far as the northern frontiers. Raw material of red burnt shale was exported to Silchester (Calleva Atrebatum), where it was made into mosaic tesserae. Of proven Kimmeridgian age on the evidence of fossils, the mudstone used to make it had been collected and quarried on the coast of the Isle of Purbeck before being burnt. The decline in the demand for stone products, excepting shale, in the second century AD saw an expansion of the potting industry, which persisted into the fifth century. The term complex‐agglomerative is introduced to describe this diverse and dispersed enterprise at this highest hierarchical level, examples of which occur elsewhere in the Roman world.

Clay mineralogy of the Cretaceous strata of the British Isles

AbstractThe clay mineralogy of the Cretaceous strata of the British Isles is described and discussed within its lithostratigraphical and biostratigraphical framework using published and unpublished sources as well as 1400 new clay mineral analyses. The regional clay mineral variation is described systematically for the following strata:(1)Southern England — Purbeck Limestone Group (Berriasian/Ryazanian; Lulworth and Durlston formations), Wealden Group (Valanginian—Barremian/Aptian; Ashdown, Wadhurst Clay, Tunbridge Wells Sands, Grinstead Clay Member, Wealden Clay, Wessex and Vectis formations), Lower Greensand (Aptian—Lower Albian; Atherfield Clay, Hythe, Sandgate, Folkestone Sands, Ferruginous Sands, Woburn Sands and Faringdon Sponge Gravels formations), Selborne Group (Middle—Upper Albian; Gault Clay and Upper Greensand formations) and the Chalk Group (Cenomanian—Lower Maastrichtian).(2)Eastern England — Cromer Knoll Group (Ryazanian—Upper Albian; Speeton Clay, Spilsby Sandstone, Sandringham Sands, Claxby Ironstone, Tealby, Roach Ironstone, Dersingham, Carstone and Red Chalk (or Hunstanton Red Limestone) formations).(3)Scotland — Inner Hebrides Group (Cenomanian—Campanian; Morvern Greensand, Gribun Chalk, Coire Riabhach Phosphatic Hibernian Greensands formations).(4)Northern Ireland — Hibernian Greensands (Cenomanian—Santonian) and Ulster White Limestone formations (Santonian—Lower Maastrichtian).The stratigraphical patterns of clay mineral variation divide naturally into two types; firstly, the more complex pattern of the Lower Cretaceous strata and secondly, the simple pattern of the Upper Cretaceous. Clay mineral variations in the non-marine and marine Lower Cretaceous strata of England are best explained by the interplay of two main clay mineral assemblages between which all gradations occur. The assemblage which dominates the main clay formations consists of mica, kaolin and poorly defined mixed-layer smectite-mica-vermiculite minerals, and sometimes includes vermiculite and traces of chlorite. It is dominantly of detrital origin and detailed evidence indicates it is derived largely from the reworking of Mesozoic sediments although ultimately from weathered Palaeozoic sediments and metasediments. Although mainly of detrital origin, this assemblage contains a persistent component that formed coevally with the approximate depositional age of its host sediment. Whether this component is of soil origin or was neoformed in the sediment shortly after deposition is unclear. There is little firm evidence indicating the sources of this clay mineral detritus. However, in the strata of the Wealden Group of southern England, mineral trends suggest three sources; one of these was to the west (Cornubian Massif), another must have been the Anglo- Brabant landmass. In the Selborne Group (Middle—Upper Albian) and in the overlying Lower Chalk (Cenomanian) where this assemblage makes its last appearance in the Cretaceous of England, there is good evidence of easterly and south-easterly sources.The second main assemblage tends to be largely monominerallic, and usually dominated by smectite with or without small amounts of mica; less frequently, kaolin, berthierine or glauconite sensu lato is the sole or dominant component. It is considered to be of volcanogenic origin, derived from the argillization of volcanic ash under different conditions of deposition and diagenesis. The source of the ash in Berriasian—Aptian times seems to have been an extensive volcanic field in the southern part of the North Sea and in the Netherlands, whereas in the Albian (and extending into the Cenomanian) a westerly source dominated. The current controversy about the role of climate or pattern of volcanic activity controlling the clay mineral stratigraphy of the Lower Cretaceous is reviewed.In the lower part of the Upper Cretaceous strata of England, Scotland and Ireland, sand-grade glauconite is particularly abundant. Much of it represents the glauconitization of pene- contemporanous volcanic ash, possibly of basaltic origin, associated with continental breakup and the opening up of the Atlantic Ocean and the earliest stages in the development of the Hebridean Tertiary Igneous Province. The Upper Cretaceous Chalk facies of England and Ireland is dominated by a smectite-rich clay assemblage containing mica, and the various hypotheses for its origin (detrital, neoformation, volcanogenic) are reviewed in the light of available mineralogical, chemical and geological data.

Correlation between the basal part of the Lower Cretaceous Speeton Clay Formation, Yorkshire, and the Purbeck Limestone Group, Dorset: a bentonite tie line

SUMMARY Four beds in the middle and upper parts of the Upper Jurassic–Lower Cretaceous Purbeck Limestone Group at Durlston Bay, Dorset, contain acid insoluble residues that suggest a penecontemporaneous volcanogenic origin, probably as sub-aerial ashfalls. Their particle size distribution patterns, mineralogy, geochemistry and K–Ar signatures indicate post-depositional alteration of fine-grained volcanic glass by pore waters. Major and trace element chemistry indicates that: (1) two beds in the Cherty Freshwater Beds (Lulworth Formation) were derived from ashes of trachyandesite-andesite-rhyodacite/dacite composition that were argillized in saline pore waters enriched in Mg 2+ ; (2) a bed in the Unio Beds (Durlston Formation) developed from an ash of trachytic composition; and (3) a bed in the Viviparus Shales and Clays (Durlston Formation) originated from an ash of trachyandesite-andesite-rhyodacite/dacite composition within the suboxic zone of brackish pore waters. Comparison of the four Purbeck volcanogenic beds with bentonite beds in the lower part of the Speeton Clay on the Yorkshire coast and offshore in the North Sea suggests that those from the Unio Beds and Viviparus Shales and Clays are equivalent respectively to Beds D7D and D6J at Speeton.

New beetles (Insecta: Coleoptera) from the Berriasian Purbeck Limestone Group, Dorset, UK

Four new beetle species are described from the Lower Cretaceous Purbeck Limestone Group of southern England: Mesogyrus anglicus sp. nov. (Gyrinidae), Coptoclavella purbeckensis sp. nov. (Coptoclavidae), Palaeodytes incompleta sp. nov. (Dytiscidae) and Cretorabus sulcatus sp. nov. (Carabidae). The first three taxa were aquatic; the last is terrestrial but may have frequented the margins of water bodies.

The turtles of the Purbeck Limestone Group of Dorset, southern England

The turtles from the Purbeck Limestone are revised and it is concluded that there are four shell‐based cryptodire species present, namely Pleurosternon bullockii, ‘Glyptops’typocardium comb. nov., Helochelydra anglica comb. nov.,Hylaeochelys latiscutata. There is also one skull‐based species, Dorsetochelys delairi, which may prove to be the skull of ‘Glyptops’, Hylaeochelys or an unknown shell‐type. All other taxa are junior synonyms except ‘Chelone’obovata Owen, 1842 and Tretosternon punctatum Owen, 1842 which are nomina dubia, the material being unfigured and either lost or incorrectly associated. Other taxonomic conclusions are that (1) because Tretosternon is a nomen dubium, the next senior name for this Purbeck–Wealden genus is Helochelydra Nopcsa, 1928; (2) ‘Pleurosternon’typocardium and ‘Glyptops’ruetimeyeri are synonymous, the senior combination being ‘Glyptops’typocardium; (3) the Purbeck ‘Tretosternon’ material is combined with the holotype and only specimen of Platychelys? anglica as Helochelydra anglica comb. nov.; (4) Hylaeochelys emarginata and H. sollasi are junior synonyms of Hylaeochelys latiscutata; (5) one of Owen's ‘lost’ syntypes of ‘Tretosternon punctatum’ has been recognised and is a plastron of Hylaeochelys latiscutata.

Some Observations on the Dinosaur Tracks at Münchehagen (Lower Cretaceous), Germany

Dinosaur tracks at the Dinosaurier-Freilichtmuseum Münchehagen are well-known and are the reason the site is designated part of the German National Monument system. Although both sauropod and ornithopod tracks have been described in some detail, additional observations are presented herein. These include observations on the gauge and heteropody of sauropods and evidence for quadrupedal progression by ornithopods. Theropod tracks are also recorded in the region at this time and have proven to be taxonomically controversial. Most of the in situ tracks on the “main” surface are those of sauropods preserved on a single large ripple-marked sandstone bedding plane. The sauropod tracks are nearly parallel but the trackmakers were evidently going in two different directions and therefore not travelling together. The presence of ornithopod tracks in close stratigraphic proximity to the main sauropod track layer, (and perhaps on the same layer) is interesting and raises questions about the close spatial and temporal co-occurrence of two large, well-known herbivore groups that are often found in quite separate paleoenvironments. This co-occurrence may be explained in part as a regional paleogeographical phenomenon, but may also be associated with faunal turnover at the Jurassic-Cretaceous boundary. The local depositional environment is thought to have been a barrier sandstone complex beside a coastal lagoon: a similar palaeoenvironment but a different lithology to that of the English Purbeck. The Münchehagen ichnofaunas are comparable to those from contemporaneous sites in Europe such as the Purbeck Limestone Group and Wealden of England.

Palynostratigraphy of the classic Portland and Purbeck sequences of Dorset, southern England, and the correlation of Jurassic-Cretaceous boundary beds in the Tethyan and Boreal realms

Abstract Placement of the Jurassic-Cretaceous boundary and its correlation between the Tethyan and Boreal realms are still contentious. The distribution of stratigraphically significant dinoflagellate cysts in the Portland Stone and Purbeck formations of the Isle of Purbeck, Dorset, UK provides a basis for direct correlation between these sections and the type Berriasian in southeast France. The base of the Berriasian — and thus of the currently accepted Jurassic-Cretaceous boundary — most probably lies at the base of the Cypris Freestones in the Purbeck Formation. Miospore correlation between the Dorset sections and ammonite-bearing rocks in the Spilsby Province suggests that the base of the Cretaceous lies close to the base of the Subcraspidites preplicomphalus zone in the Boreal Realm.

Le gisement « Purbeckien » de vertébrés de Cherves-de-Cognac, Charente (SW France) : nouvelles données biostratigraphiques

‘Purbeckian’ vertebrate deposit from Cherves-de-Cognac (SW France): new biostratigraphical data. The Purbeckian facies of the Aquitaine Basin northern margin outcrop has a thickness of about 30 m in the gypsum quarry of Champblanc, Cherves-de-Cognac, located about 10 km northeast of Cognac (Charente, SW France). Two lithological units have been identified. The basal unit (U1) is an alternation of gypsum and finely bedded black marls sometimes stromatolitic. The upper unit (U2) is a limestone-marl alternation, more or less fossiliferous. In the upper part of the unit, a one meter thick level has yielded a rich vertebrate fauna. A micropaleontological analysis of these levels, until now considered as Uppermost Jurassic age, has provided rich and diversified associations of brackish and fresh-water ostracodes and charophytes allowing them to be dated as Berriasian and to be related with the lower part of the Middle Purbeck of southern England. To cite this article: J.-P. Colin et al., C. R. Palevol 3 (2003).

The first mayfly from the Lower Cretaceous of southern England (Insecta: Ephemerida= Ephemeroptera)

The first mayfly from the British Cretaceous, Durlophlebia radleyi gen. et sp. nov., is described on the basis of a subimaginal hind wing from the Berriasian Purbeck Limestone Group of Dorset, UK. Its presence in hypersaline deposits in the Lulworth Formation indicates that there were also fresher water bodies in the region at that time.

Biostratigraphy of Jurassic–Cretaceous boundary strata in the Terschelling Basin, The Netherlands

SUMMARY The Jurassic–Cretaceous boundary beds in the Scruff Greensand Formation from Dutch sector North Sea wells L06-2 (between 2245.36 m and 2262.76 m) and L06-3 (between 2028.90 m and 2037.80 m) have yielded both ammonite faunas and abundant marine and terrestrial palynomorphs. Ammonite endemism in Europe was intense at the Jurassic–Cretaceous boundary. This means that pan-European correlations of Jurassic–Cretaceous boundary beds based on macrofossils are problematical. The ammonite faunas of wells L06-2 and L06-3 provide the most extensive and complete marine macrofossil record so far across the Volgian–Ryazanian (Jurassic–Cretaceous) boundary in the Spilsby Province and the North Sea Basin. The Primitivus, Preplicomphalus, Lamplughi, Runctoni and Kochi Zones have been identified. In both wells, the occurrences of the dinoflagellate cyst Gochteodinia virgula mean that the successions are no older than latest mid-Volgian. The dinoflagellate cyst associations of L06-2 are indicative of the late Volgian/early Ryazanian. The range tops of Gochteodinia virgula and Amphorula expirata are revised as a result of correlations with the ammonite zonation. Dinoflagellate cyst floras in L06-3 are indicative of the latest Volgian–? earliest Ryazanian. In particular, the co-occurrence of Batioladinium? gochtii and Gochteodinia virgula at 2030.60 m in well L06-3, together with ammonite data, indicates that this horizon is of latest Volgian (Lamplughi Zone) age. Both wells contain reworked palynomorphs, including recycled older Late Jurassic dinoflagellate cysts. In addition, the palynological assemblages yield relatively diverse sporomorph associations. The sporomorph succession of both wells is used to establish an ammonite-calibrated sporomorph chronostratigraphy. Comparison with other studies suggests that the Jurassic/Cretaceous boundary occurs within the Cherty ‘Freshwater’ Beds of the Purbeck Limestone Group in Dorset, southern England, and within the Serpulite Member of Germany.

The oldest tribosphenic mammal from Laurasia (Purbeck Limestone Group, Berriasian, Cretaceous, UK) and its bearing on the ‘dual origin’ of Tribosphenida

We report the discovery of a tribosphenic molar in the Purbeck Limestone Group, Early Cretaceous, southern England, which we attribute to a new taxon, Tribactonodon bonfieldi gen.n. sp.n. In addition to the fact that it represents the oldest unequivocal tribosphenic mammal known from Laurasia, this tooth shows characters which have an important bearing on the distinction between the two infraclasses of Holotheria (Australosphenida and Boreosphenida) as defined by Luo et al., and which lead us to question the timing and place of their emergence.

STRUCTURES IN JURASSIC ROCKS OF THE WESSEX BASIN, SOUTHERN ENGLAND - II: DIAPIRISM IN EVAPORITE LAYERS

The Jurassic Purbeck Beds of the Fossil Forest cliff, Lulworth Cove (southern England) encloses a ~ 10 m-thick wedge in which four juxtaposed levels (L2-L5) of differential strain have been characterized, between two levels of non deformed rocks (LI and L6). Within the zone of strain, level L2 comprises basal calcareous marls displaying 1 cm-thick zones of bed-parallel foliation developed in an anastomosed pathway to form pillow-like features, and upper layers of evaporite where tens of mushrooms or diapirs are observed. They commonly display a ~ 1 m-sized circular geometry on bed-parallel sections, a ~ 0.5 m high central zone forming a generally bed-perpendicular tail, and are surrounded by rim synclines where the evaporite layers are entrapped together with chert and shale; level 3 consists of evaporite and shales displaying cmto dm-scale extension and contraction structures; level L4 comprises remnants of evaporite layers embedded in a shale matrix - a tectonic melange; and level L5 comprises blocks of evaporite and limestone involved in a shale / argillite matrix, a limestone breccia (the so-called Broken Beds) inside which some layers are still preserved and exhibit 1-10 m-scale contraction and extension structures. Level L5 results from the westwards displacement of a wedge above an extensional detachment (the interface L3 / L4) and below another detachment established on a layer of shale at the contact with level L6. The mushrooms clearly deform the L3 / L4 detachment and are interpreted as thermal convection structures formed by a progressive down-sucking of the layers back in the direction of an imaginary point at the center of the diapirs – a centripetal suction leading to contraction and coeval extension, soon after initial displacement of the wedge. The pillow-like features result from percolation of fluids across the marls simultaneously with the evolution of the mushrooms.

STRUCTURES IN JURASSIC ROCKS OF THE WESSEX BASIN, SOUTHERN ENGLAND - I: FIELD EXAMPLE OF DEFORMED CRUSTAL WEDGES

Detailed studies of the Purbeck Formation (Jurassic) in the Fossil Forest outcrop, Lulworth Cove (Dorset, southern England) allow to define a ~ 10 m-thick wedge of deformed layers comprising four juxtaposed structural levels (L2-L5) situated between two levels of non deformed layers (L1 and L6). L1 consists of limestone and L6 consists of limestone and intercalated shale / argillite. Within the wedge, the basal structural level (L2) consists of calcareous marls displaying pillow-like structures due to a layer-parallel anastomosed foliation, and evaporite, shale and chert displaying m-scale mushrooms; level L3 consists of evaporite and shale displaying cm- to dm-scale features like normal and thrust faults, folds, foliation and boudins; level L4 consists of evaporite and shale transformed into a tectonic melange; and level L5 consists of evaporite and limestone affected by m-scale folds, contraction and extension faults. Intensive fracturing of the layers around the hinges of the folds transformed L5 in a set of Broken Beds, The wedge deformed progressively, as it slided above a top-down to the west basal detachment along levels L3 and L4, and below a bottom-down to the west detachment established along a layer of calcareous shale (bottom of level L6). The structural analysis, together with other published data, all indicate that an event of extension affected regionally the area, earlier in the Alpine inversion of the Wessex Basin, during which the entire set of rocks tilted to the north and further slip occurred within the Broken Beds. The slide of a detachment-bounded wedge of rocks and the vertical partition of deformation styles and intensity of strain, all place the Fossil Forest outcrop as a key-field locality for direct observation of tectonic processes analogous to those currently recognized for deformation of the continental crust.

New symmetrodonts (Mammalia, Theria) from the Purbeck Limestone Group, Lower Cretaceous, southern England

Le genre Spalacotherium Owen fût initialement créé à partir de spécimens provenant du Groupe de Purbeck en 1854. Cet article décrit une nouvelle espèce, S. evansae, provenant d'un site purbeckien découvert en 1986; celle-ci est représentée non seulement par des molaires inférieures et supérieures mais peut-être aussi par des molaires de lait. Le genre Tinodon n'était, jusqu'à maintenant, connu que dans la Formation Morrison du Wyoming, USA, un peu plus ancienne que celle de Purbeck; quelques molaires inférieures et surtout une molaire supérieure du même gisement sont attribuées à une nouvelle espèce, T. micron, ce qui ajoute un genre à la liste des taxons communs aux deux formations. La molaire supérieure de T. micron est particulièrement intéressante en ce qu'elle fournit des indications sur un taxon occupant une position clé dans la phylogénie des symmétrodontes, tout en soulevant le problème d'homologie des tubercules.

New fossil flies (Insecta: Diptera) from the Purbeck Limestone Group (Lower Cretaceous, Berriasian) of Dorset, UK

Two new species from small, exclusively Mesozoic, families of nematoceran Diptera (true flies) from the Purbeck Limestone Group (Berriasian) of Dorset, UK are described, namely Procramptonomyia zigzagensis sp. nov. (Procramptonomyiidae) and Ellia purbeckensis sp. nov. (Elliidae). The fossil evidence suggests that these two families, along with the extant Cramptonomyiidae, are closely related.

The footprints of iguanodon: A history and taxonomic study

A historical survey of the discovery of footprints of iguanodont dinosaurs is presented, from the first reports in 1846 to the present. Reasons are given for considering the ichnogenera Iguanodonichnus and Camptosaurichnus to be problematical and respectively comprising the footprints of sauropods and theropods; consequently, no valid ichnogenus has been available to accommodate those of typical iguanodonts. The desirability of selecting a type series of Iguanodon footprints from the Early Cretaceous Purbeck Beds of southern England, rather than from the somewhat later Hastings Beds (Weal‐den), is explained. The new ichnogenus Iguanodon‐tipus is proposed; its type ichnospecies, I. burreyi, is illustrated and discussed.

Skeletal aragonite neomorphism — quantitative modelling of a two-water diagenetic system

The neomorphism of skeletal aragonite occurs by the simultaneous dissolution of aragonite and precipitation of calcite along thin solution films, which may have an associated zone of partly dissolved aragonite (chalky zone). It has been proposed that pore waters at neomorphic calcite–aragonite contact zones (neomorphic fronts) may be partly isolated from bulk pore waters and thus retain primary geochemical signatures to varying degrees. Iterative computer programs were developed that simulate aragonite neomorphism in two-water diagenetic systems using stable isotope and trace element data. Neomorphism of aragonitic mollusks from the Purbeck Group of southern England (Late Jurassic to Early Cretaceous) was associated with a decrease in strontium concentration from approximately 5100 ppm to 500 ppm. Modelling results indicate a high bulk water/rock ratio and minimal, if any, isolation of the neomorphic front waters for the Purbeck Group mollusks and also for some Pleistocene corals. Partial isolation of neomorphic front waters from bulk pore waters is uncommon, based on published data on the geochemistry of neomorphic calcites. However, partial isolation does occur in some thick, low porosity shells, such as the gastropod Strombus gigas (Pleistocene). Process-based modelling of fluid–rock interaction provides a means for better interpreting trace element and stable isotope data in diagenetic carbonates. Sensitivity analysis results indicate that water/rock ratios cannot be determined at much better than order of magnitude accuracies, because of uncertainties over initial pore water composition, fractionation factors and distribution coefficients.