Microvertebrates from the Rhaetian basal bone bed of Saltford,near Bath,SW England

The famous Rhaetian bone bed (Late Triassic, 205 Ma) is well known because it marks a major switch in depositional environment from terrestrial red beds to fully marine conditions throughout the UK and much of Europe. The bone bed is generally cemented and less than 10 cm thick. However, we report here an unusual case from Saltford, near Bath, S.W. England where the bone bed is unconsolidated and up to nearly 1 m thick. The exposure of the basal beds of the Westbury Formation, Penarth Group includes a bone bed containing a diverse Rhaetian marine microvertebrate fauna dominated by sharks, actinopterygian fishes and reptiles. Despite the unusual sedimentary character of the bone bed, we find similar proportions of taxa as in other basal Rhaetian bone beds (55–59 % Lissodus teeth, 13–16 % Rhomphaiodon teeth, 12–14 % Severnichthys teeth, 6–9% Gyrolepis teeth, 3–4% undetermined sharks’ teeth, 1–3% undetermined bony fish teeth, and < 1% of each of Hybodus, Parascylloides, and Sargodon), the only differences being in the proportions of Rhomphaiodon teeth, which can represent 30–40 % of specimens elsewhere. This suggests that taphonomic bias of varying Rhaetian bone beds may be comparable despite different sedimentary settings, and that the proportions of taxa say something about their original proportions in the ecosystem.     

Geology and microvertebrate faunas of the Rhaetian Westbury Formation of Doniford Bay,Somerset

The Rhaetian (latest Triassic) succession of Doniford Bay, North Somerset has been noted as a site of fossils for over 200 years, and yet has never been described in detail despite its importance for palaeontology, for knowledge of a classic Triassic-to-Jurassic transition sequence, for structural geology, and as a venue for field trips. There are two bone beds, which differ substantially in sedimentary and palaeontological characteristics. Fossils include the usual teeth, denticles, and scales of small hybodont sharks, bony fishes, and marine reptiles. The lower (basal) bone bed is in many ways like those from other localities around Bristol and in South Wales, whereas the upper bone bed shows rich organic matter and an absence of calcite, suggesting a deeper location of deposition. Further, the lower bone bed contains abundant abraded silica grains, suggesting transport of sediment and bone debris from a beach or river. The two bone beds differ in faunal composition, and the upper bone bed lacks the locally derived clasts, larger silica grains, and calcite seen in the lower bone bed. Bones and teeth are equally abraded in both bone beds, confirming long-distance transport of fish and reptile fossils and that the upper bone bed cannot be interpreted as having derived from the lower.     

Microvertebrates from the Wadhurst Clay Formation (Lower Cretaceous) of Ashdown Brickworks,East Sussex,UK

Ashdown Brickworks, near Bexhill, East Sussex, has produced a large number of vertebrate fossils from the Wadhurst Clay Formation, part of the Wealden Supergroup (Hastings Group; Valanginian; Lower Cretaceous). Here we describe the microvertebrate fauna of the ‘conglomerate bed’, representing a rich sample of taxa. While most of the recovered teeth and bones are abraded, some heavily, most can be identified to species level. The taxa include four species of hybodont sharks (Egertonodus basanus, Planohybodus ensis, Polyacrodus parvidens, P. brevicostatus), three taxa of bony fishes (an unidentified Lepidotes-like semionotiform, the pycnodontiform Ocloedus, and an albuliform), three taxa of crocodyliforms (the goniopholid Hulkepholis, a bernissartiid, and the atoposaurid Theriosuchus), and the theropod dinosaurs Baryonyx and an allosauroid. Sediments of the Wadhurst Clay Formation as a whole indicate freshwater to very slightly brackish-water environments of deposition, and the mainly aquatic time-averaged mixture of fishes and tetrapods recovered from the ‘conglomerate bed’, together with isolated terrestrial species, confirms this interpretation.     

The exposures of Ludlow rocks and associated beds at Tites Point and near Newnham,Gloucestershire

The Leintwardine and Whitcliffe Beds of the Ludlow Series outcropping at Tites Point and near Newnham, Gloucestershire, are described and compared with similar beds exposed at May Hill. Data from the Brookend Borehole, 1 ½ miles (2.41 km) south of Tites Point, reveal that southward thickening affects all subdivisions of the Ludlow Series. The occurrence of the Ludlow Bone Bed in the Tites Point outcrop is also recorded.     

Correlation of the Kimmeridgian-Tithonian (Jurassic) boundary beds exposed in the Boulonnais,France with those at Kimmeridge,Dorset, UK

Sediments of Kimmeridgian and Tithonian age are well exposed on the Boulonnais coast of northern France between Equihen and Cap Gris Nez and on the south coast of England at and adjacent to Kimmeridge Bay. Both successions were deposited on a marine shelf and lie within the Subboreal faunal province which enables detailed correlations to be made between them based on ammonite assemblages. They are, however, lithologically markedly different due to their environmental settings: close to a land area in the case of the Boulonnais and within a depositional basin in the case of Kimmeridge. The succession adjacent to the Kimmeridgian-Tithonian boundary exposed in the Boulonnais is highly condensed and laterally variable with more attenuated successions occurring close to the former Anglo-Brabant Massif land area. The boundary occurs at the end of a succession of up to six regressive-transgressive events that onlap the land area. This is in contrast to that at outcrop at Kimmeridge, where the Kimmeridgian-Tithonian boundary is marked by a correlative conformity in an unbroken basinal succession. The cliff and foreshore exposures in the Kimmeridge area provide the only unbroken succession in the Subboreal faunal province of the beds adjacent to the Kimmeridgian-Tithonian boundary.     

Integrated Rhaetian foraminiferal and conodont biostratigraphy from the Slovenian Basin, eastern Southern Alps

Conodonts and re-deposited shallow-water benthic foraminifera co-occur in the Upper Norian-Rhaetian Slatnik Formation of the Slovenian Basin (Southern Alps). The Mt. Kobla and Mt. Slatnik sections were investigated in order to give the first direct correlation between these two groups. The Norian-Rhaetian boundary (NRB) is placed at the First Appearance Datum of the conodont Misikella posthernsteini and is approached with the First Occurrence of the foraminifer Involutina turgida. An association of Trocholina turris with duostominids is a good marker for the Rhaetian. Careful revision of literature combined with our data culminated in reambulation of stratigraphical ranges for several foraminiferal species. The foraminiferal Triassic-Jurassic boundary (TJB) can be defined with the Last Occurrence of Galeanella tollmanni, ??Sigmoilina?? schaeferae or duostominids. The absence of the uppermost Rhaetian Misikella ultima conodont zone and the close coincidence of foraminiferal and conodont TJB could point to the presence of hiati in the upper part of the Slatnik Formation. Consequently, the exact pattern of disappearance of Late Triassic foraminifera at the boundary could not be observed. It is clear, however, that the foraminiferal assemblage was decimated for reef-dwelling foraminifera, duostominids and most of the platform-dwelling foraminifera. Biotic changes at the TJB are best explained as a result of a biocalcification crisis.     

Garnet clinopyroxenite inclusions from diatremes in the Gloucester area,New South Wales,Australia

The paper discusses the petrography, mineralogy, petrochemical affinities, P/T crystallization regimes and genetic aspects of four garnet clinopyroxenite inclusions from diatremes in the Gloucester area, New South Wales. Inclusion mineral assemblages (which generally display textural evidence of annealing) include garnet-plagioclase-(sulphur-rich scapolite)-clinopyroxene, garnet-hornblende-orthopyroxene-clinopyroxene and garnet-hornblende-clinopyroxene. The garnet-plagioclase clinopyroxenite inclusion possesses an essentially alkali basaltic chemistry. It probably represents a crystallized basaltic liquid whereas the petrochemical affinities of the two garnet pyroxenites carrying amphiboles are more appropriate to subcalcie clinopyroxenites with variable Mg/Fe ratios. Experimental and other data suggest that the Gloucester garnet clinopyroxenite suite crystallized at pressures of the order of 10–14 kb and temperatures in the vicinity of 1000° C. The chemical compositions of many garnet pyroxenites, occurring either as inclusions in alkali basaltic rocks or as localized facies within some alpine-type peridotites, such as those in the western Mediterranean region, suggest that they can be interpreted as lower temperature heteromorphs of “primitive” subcalcic clinopyroxenites, variable in Al contents and hy/di ratios, but retaining consistently low Ti, Na, K and P. It is suggested that many inclusions of garnet (-spinel) pyroxenite and subcalcie Clinopyroxenite, restricted to alkali basaltic rocks and their associates, originally may have been interleaved with upper mantle aluminous peridotites and that they represent partial melt products of their aluminous peridotitic hosts.     

An Aeronian (Middle Llandovery) graptolite from the Pentamerus Beds near Hillend Farm,Shropshire, UK

A specimen of Clinoclimacograptus retroversus is recorded from the Pentamerus Beds of the A489 road section near Hillend Farm, Shropshire, England. This specimen, combined with the presence of the brachiopod Eocoelia hemisphaerica, demonstrates that the beds here must be of mid to late Aeronian (Mid Llandovery) age. The fossiliferous horizons lie only a few metres above the Precambrian unconformity and thus help to constrain the timing of the transgression here. Copyright © 2002 John Wiley & Sons, Ltd.     

川东华蓥山二叠系/三叠系界线附近粘土层中粘土矿物的类型及成因

对川东华蓥山二叠系/三叠系界线附近粘土层中的粘土矿物进行野外采样和室内X射线衍射分析,结果表明,这些粘土矿物主要由规则混层伊利石-蒙脱石组成,其中1个样品可能含有少量不规则混层绿泥石-蒙脱石等粘土矿物。总地看来,该界线粘土层中的规则混层伊利石－蒙脱石中伊利石层的含量自下而上呈现减少的趋势,平均含量约83%,所经历的最大古地温在125～150℃之间。这些粘土矿物的构成和特征与前人在华南其他地区相同层位取得的成果总体上具有较好的一致性,显示了该粘土层成因的相同性及所具有的等时意义。不同地区粘土矿物构成的差异性（如高岭石的存在与含量）可能与二叠系/三叠系界线不整合的存在与否或间断时间有关,规则混层伊利石－蒙脱石的混层比则与埋藏历史和沉积—沉积期后的流体介质有关。     

A nautiloid with ventral bitemarks from the Charmouth Mudstone Formation (Lower Jurassic) near Lyme Regis,Dorset, UK

Locally within the Charmouth Mudstone Formation (Sinemurian, Lower Jurassic) of the Dorset coast fatally bitten ammonites with ventral bite marks are common. Ventral bite marks occur at the rear of the body-chamber. The predator probably severed attachment muscles, thus removing its prey more easily. We report the first ventrally bitten fossil nautiloid, which is unusual in that the large bite mark is entirely within the phragmocone. The nautiloid is juvenile with a very short body-chamber extending 46° back from the apparently undamaged aperture. The whorl cross-section is nearly circular, giving the predator little to grip when biting. Nautiloid shells are also thicker than ammonite shells. Despite these difficulties, the predator bit repeatedly and damaged both the shell and septa. Five rounded bites occur on the left side, separated by sharp points. This suggests the predator was probably another cephalopod with suckered arms and powerful jaws. The centre of the bite is 160.5° back from the aperture, close to the mean value for ammonites (184.5°), suggesting the predator located the position of the first bite opposite the victim's aperture. Thus, we think the predator attacked an incomplete nautiloid shell which explains why the damage affects only the phragmocone.     

Sulphate efflorescences at the geyser near Pinchollo,southern Peru

Sulphate mineralization precipitated around a geyser located above the village of Pinchollo, Chivay district and below Hualca Hualca volcano (6025 m a.s.l.) in the Western Cordillera of southern Peru is described. The geyser is one of many manifestations of thermal activity in the Arequipa department. Its age is estimated to be Upper Pleistocene–Holocene, as the discharge point lies at the intersection of a fault system with latitudinal dip-slip fault cutting a volcanic-debris avalanche of probably Pleistocene age. Thermal waters present in the Chivay district are mainly chloride-rich with a neutral pH. They are rich in Li, Sr, and B. The water erupting in the geyser boils at about 85 °C, as it lies at some 4353 m a.s.l.The minerals examined, of various habits and various yellow, orange and white colours were precipitated on the soil and on plants close to the geyser (location 1), on the walls of a 1 m diameter pothole filled with boiling water (location 1a) and at a distance of some 100 m to the west of the geyser (location 2). All are sulphates. Their chemical composition is fairly simple, consisting of Al, Fe, K, Mg, Ca, S, NH₄ and O, and all display chemical zoning. But the phase composition is more complex. In all locations, alunogene, copiapite, coquimbite, tschermigite and gypsum are present. Close to the geyser (location 1) magnesium-containing sulphates, namely, boussingaultite and pickeringite also occur. Iron sulphates such as mohrite and rozenite precipitate on the walls of the pothole (location 1a). Sulphates containing potassium such as jarosite, alunite and voltaite–voltaite (Mg) dominate among the efflorescences in location 2, where hematite was also noted. Any quartz and kaolinite or illite/mica admixture identified in some samples derives from adjacent soil.The present geothermal system does not involve the deposition of precious-metal deposits such as those associated with an earlier deep-going epithermal system that scavenged a large volume of rock. Most likely, as the present-day thermal waters do not involve a juvenile-water component, the geyser waters derive from a shallower source.     

Terrestrial environments during MIS 11: evidence from the Palaeolithic site at West Stow,Suffolk, UK

Multidisciplinary investigations of the sequence at Beeches Pit, West Stow (Suffolk, UK), have a direct bearing the age of the Hoxnian Interglacial and its correlation with the continental Holsteinian and with the global marine record. At this site, glacial deposits (till and outwash gravels) referable to the Anglian Lowestoft Formation fill a subglacial channel cut in Chalk bedrock. Above these glacial deposits a series of interglacial sediments occurs, consisting of limnic, tufaceous and colluvial silts, lacking pollen but rich in shells, ostracods and vertebrates. Lower Palaeolithic flint artefacts of Acheulian character have also been recovered, including refitting examples. Charred material is abundant at certain horizons and many of the bones have been burned. Several discrete areas of burnt sediment are interpreted as hearths. The molluscan fauna comprises some 78 taxa and includes species of considerable zoogeographical and biostratigraphical importance. The land snail assemblage from the tufa consists of woodland taxa with no modern analogue, including species that are either extinct (e.g. Zonitoides sepultus) or which no longer live in Britain (e.g. Platyla polita, P. similis, Neniatlanta pauli). This is also the type locality of Retinella (Lyrodiscus) skertchlyi, which belongs to a subgenus of zonitid land snail now living only on the Canary Islands. There are indications from this fauna (‘the Lyrodiscus biome’) that the climate was wetter and perhaps warmer than the present day. The vertebrate fauna is also noteworthy with species of open habitats, such as rabbit (Oryctolagus cf. cuniculus), and of closed forest, such as squirrel (Sciurus sp.) and garden dormouse (Eliomys quercinus) present at different times. The occurrence of southern thermophiles, such as Aesculapian snake (Zamenis longissimus), indicates temperatures warmer than those of eastern England today. The upper levels include much material reworked from the interglacial sediments, although there is clear faunal evidence for climatic deterioration. Both the molluscan and vertebrate faunas suggest correlation of the interglacial sediments with the Hoxnian. Uranium series dates from the tufa (∼455 ka BP), TL dates from burnt flints (414±30 ka BP) and a range of amino acid racemization data all support correlation of this interglacial with MIS 11. However, four OSL dates from sand beneath the interglacial sequence yield a mean age of 261±31 ka BP, far younger than all other age determinations and far younger than implied by the biostratigraphy. Archaeologically the site is unusual in showing prolonged human occupation within closed deciduous forest and evidence for controlled use of fire in a Lower Palaeolithic context. Biostratigraphical correlations with other Lower Palaeolithic sites support the suggestion that Acheulian and Clactonian industries both occurred in southern Britain during the same substage of the Hoxnian, although not necessarily at precisely the same time. The characteristics of the MIS 11 interglacial in Britain are discussed in the light of evidence from Beeches Pit and elsewhere.     

The Widdington Sands: High-level Kesgrave Sands and Gravels near the Cam-Stort interfluve,Northwest Essex,UK

A small but stratigraphically significant exposure of Quaternary sandy sediments (Widdington Sands) was observed and recorded in the early 1970s in northwest Essex. These data are here re-examined and re-evaluated, yielding new insights into early proto-Thames aggradation following the marine recession of the Norwich Crag Formation (MIS 74–71, about 2 Ma). As the proto-Thames trajectory shifted south eastwards, a period of landscape stability ensued in the early Middle Pleistocene (MIS 19–13) during which the Valley Farm Soil was formed. This and the succeeding Barham Soil can be recognised in the stratigraphy, the second palaeosol heralding the arrival of glaciation in the Anglian Stage (MIS 12, 480–420 ka). These pedogenic signatures are enclosed within palaeokarstic features in the form of infilled sinkhole pipes. A large doline has functioned as a sediment trap preserving pre-truncation structures including reverse ring faults. These confirm basal support removal leading to upward migration of a dissolution cavity and roof collapse within the sinkhole pipe. The process and timing of subsidence can thus be defined more clearly than for similar features found in comparable Kesgrave aggradations of the Middle Thames. The likely glacitectonic origin of the planar sub-till surface is examined and discussed. Dating of Early Pleistocene fluvial activity is constrained by estimating the height of a former terrace surface whose elevation points to a correlation with the higher Stoke Row Member (MIS 64, 1.8 Ma), suggesting the oldest known proto-Thames activity within southern East Anglia.