bluuebunny/crossref_metadata_2025 huggingface dataset:
Trace fossils from the Precambrian–Cambrian boundary candidate at Meishucun, Jinning, Yunnan, China
Authors: Crimes T. P. , Zhiwen Jiang
Published: May 2009

The Precambrian–Cambrian boundary candidate section at Meishucun, China, has yielded trace fossils which are abundant at some horizons. The earliest occur in Unit 3 of the Zhongyicun Member approximately 8 m above the lower selected stratotype reference point for the boundary and includeArenicolitessp.,Asteriacitessp.,Neonereites biserialis, N. uniserialisandSellaulichnus meishacunensis. The next trace-fossil-bearing horizon is in Unit 6 of the Zhongyicun Member whereCochlichnussp.,Monomorphichnussp.,Neonereites biserialisandN. uniserialisoccur. Immediately above, in Unit 7, areCruzianasp.,Didymaulichnus miettensis, Monomorphichnussp. andRusophycussp. In the Badaowan Member at the top of the section there areDidymaulichnussp. andTaphrhelminthopsis circularisin Unit 9,Arenicolitessp.,Diplocraterionsp.,Gordia molassica, Skolithossp. andT. circularisin Unit 11, andGordia meandria, ?Plagiogmussp.,Skolithossp. andT. circularisin Unit 12.

Comparison of this trace-fossil distribution with that in key Precambrian–Cambrian boundary sections in other countries indicates that the ranges of a few trace fossils cross the boundary (e.g.Didymaulichnus, Neonereites, Planolites) but most appear only in the Cambrian. Different ichnogenera seem to appear at various levels above the boundary.ArenicolitesandAsteriacitesare among the first, whileTaphrhelminthopsis circularisis only encountered higher in all sequences. Some have only been recorded at much higher levels and relatively close to the first appearance of trilobites (e.g.Cruziana, Diplocraterion, Rusophycus). This suggests that the first appearance of specific trace fossils or groups of trace fossils may be valuable for locating the boundary in some sections and for correlating late Precambrian and early Cambrian strata.
Mid-Palaeozoic metamorphism and polyphase deformation of the Forland Complex, Svalbard
Authors: Manby G. M.
Published: May 2009

The Forland Complex of Prins Karls Forland has been subjected to mid-Palaeozoic greenschist facies metamorphism and polyphase deformation. Metamorphism was initiated prior to D1 deformation and gave rise to a parallelism of stratigraphic and metamorphic reaction surfaces. D1 gave rise to imbricately thrust, southwest-directed fold nappes which have not noticeably disturbed the isograd surfaces. D2, interpreted as belonging to the mid-Cenozoic West Spitsbergen Orogeny (WSO) which was coaxial but not coplanar with D1, produced crenulation folds and pressure solution cleavages and some thrusting. D3 structures are related to the formation of the Prins Karls Forland–Forlandsundet–Oscar II horst and graben system which is a late expression of the WSO. The rejuvenation of the Prins Karls Forland horst along NNW–SSE faults, the large scale E–W flexures and ENE–WSW faults in the Forland Complex and Tertiary graben deposits are assigned to D3.
Carbonated melilitites and calcitized alkalicarbonatites from Homa Mountain, western Kenya: a reinterpretation
Authors: Clarke M. G. C. , Roberts B.
Published: May 2009

Homa Mountain is a well developed ijolite/carbonatite complex of Miocene to Quaternary age. Late stage olivine melilitite occurs as a satellite plug, parts of which show strong deuteric alteration to carbonate resulting in complete pseudomorphing of the melilite.

A second satellite centre exposes a grey carbonate tuff and accompanying dykes, all of which exhibit relic textures after an elongate, rectangular mineral also formerly believed to be melilite. Comparison with other recently described occurrences indicates however that the second centre erupted alkali-carbonatite and that the chief mineral originally present was nyerereite (Na2Ca(CO3)2). The field relationships and petrographic characters of both rock types are described and criteria are given which permit distinction between carbonated melilite and calcitized nyerereite. It is concluded that olivine melilitite and alkalicarbonatite are closely related in space and time.
A note on Lower Jurassic magmatism in the Coastal Cordillera of Atacama, Chile
Authors: Naranjo J. A. , Puig A. , Suárez M.
Published: May 2009

Radiometric dates on specimens of plutons of the Coastal Cordillera of Atacama span the period 300–110 Ma. A group of dates cluster around 190 Ma and evidence is presented which strongly suggests that they represent near crystallization ages. The geographic distribution of these plutons, adjacent to Liassic tuffs and lavas (Pan de Azúcar and Posada de los Hidalgo formations), suggests a genetic relationship between them, and that the plutons were the roots of the Lower Jurassic volcanic chain. The location of these granitoids to the west of the Liassic volcanic rocks, favours a previous idea that the Liassic basin extended eastwards as a back-arc or intra-arc basin. The host rocks to the Lower Jurassic plutons include Palaeozoic granitoids and metasedimentary rocks, indicating that the volcanic chain was founded on continental crust. The distance from the Liassic plutons to the present-day trench is less than 100 km, which indicates the possibility that part of the arc-trench system of that time is missing.
Cambrian and late Precambrian basaltic igneous activity in the Scottish Dalradian: a review
Authors: Graham C. M. , Bradbury H. J.
Published: May 2009

In the evolution of the Scottish Dalradian basin, the climax of widespread tholeiitic magmatism pre-dated or coincided with major basement faulting and the onset of deep marine sedimentation in Lower Cambrian times. Earlier basin-deepening and precursory igneous activity had already occurred. Major and trace element chemistry of low-grade metabasites indicates their affinity with basalts from ocean-spreading centres, or transition to ‘within-plate’ types. Geological evidence favours a tectonic setting for this igneous suite and the Highland Border Series on the NW margin of an actively evolving Lower Cambrian ocean basin, possibly a marginal basin to the Iapetus Ocean System.
Plagiogranites in the Coolac ophiolite suite, New South Wales, Australia
Authors: Ashley P. M. , Franklin B. J. , Ray A. S.
Published: May 2009

Plagiogranites occur mainly as intrusive bodies and tectonic inclusions within mafic and ultramafic members of the Coolac ophiolite suite. Quartz diorites and trondhjemites appear to represent localized late-stage felsic differentiates of subalkaline tholeiitic magma, with their formation dominantly controlled by fractionation of hornblende and plagioclase. Albitites are interpreted as altered equivalents of quartz diorites and trondhjemites. Chemical data, while emphasizing the similarity of these rocks to ‘oceanic plagiogranite', also indicate that variation in the latter may be broader than previously defined. The Coolac rocks show less marked Fe-enrichment, higher Ni and Cr, and lower Y and Zr than many ophiolitic plagiogranites. These data are consistent with weak calc-alkaline tendencies demonstrated in the Coolac ophiolite suite.
Surface and subsurface structural study of the Wadi El Rayan area, Southwest Fayoum, Egypt
Authors: Youssef M. M. , El Khashab H. M.
Published: May 2009

The surface geologic map of the Wadi El Rayan area, based on the study of aerial photographs and field observations, is correlated with seismic structural two-way time maps for the basement, the top of Cenomanian and the base of Tertiary horizons. Major structural features comprise a northeasterly faulted plunging anticlinal stretch traversing the NW-SE Wadi El Rayan depression. Three sets (ENE-WSW, NW-SE and NE-SW) of faults dissect the area. Folding movement was still active at least to the end of Middle Eocene epoch. ENE-WSW faults affecting the basement, and traced in higher levels, have the same trend as the fold axes. It is thus possible that compressional features appearing on the surface and subsurface horizons are in part due to thrusting in deeper levels that took place parallel to folding.
The Phanerozoic cover sequences preserved as xenoliths in the kimberlite of eastern Sierra Leone
Authors: Hubbard F. H.
Published: May 2009

Sedimentary and volcanic rocks, now unrepresented in surface exposure, occur as xenoliths in the kimberlite of the Koidu District of eastern Sierra Leone. The sedimentary rocks prove, on micropalaeontological evidence, to have Lower Palaeozoic stratigraphic age. An eastern extension of the Ordovician/Silurian marine transgression on to the Leo Uplift of the West African Craton of some 200 km is indicated. The volcanic rocks may belong to the same cycle of surface rock generation or relate to the younger, widespread, Triassic magmatic event.
Precambrian-Cambrian Boundary candidate, Aldan River, Yakutia, U.S.S.R.
Authors: Cowie J. W. , Rozanov A. Yu.
Published: May 2009

The current situation in 1982 regarding the status and validity of the Ulakhan-Sulugur section on the Aldan River as a candidate for the global stratotype section and point for the Precambrian-Cambrian (PC-C) Boundary is reviewed with details of new work since 1973 and consequent revisions of views on controversial topics on a regional, continental and intercontinental scale of stratigraphic correlations with a short note regarding accessibility.
The petrochemistry of the basic volcanic rocks of the South Connemara Group (Ordovician), western Ireland
Authors: Ryan P. D. , Max M. D. , Kelly T.
Published: May 2009

16 samples of Ordovician basic volcanic rocks of the South Connemara Group, which abut the southern side of the metamorphic rocks of the Connemara massif in western Ireland, have been analysed for both major and trace elements. Although subject to low grade regional metamorphism and subsequently hornfelsed by the Galway Granite (400 Ma), their immobile element contents do not appear to be significantly disturbed. These elements characterise the metabasites of the South Connemara Group as ocean floor basalts having their origins in a marginal basin. The Skird Rocks Fault, separating the South Connemara Group from high grade metamorphic rocks of the Connemara massif, is consequently regarded as the northern margin of the vestiges of the lapetus Ocean which can be traced into, and along, the Southern Uplands Fault.
The South Harris gravity anomaly
Authors: Durrance E. M. , Grainger P. , Kearey P.
Published: May 2009

The results of a gravity survey of South Harris show that a residual gravity anomaly of + 220 g.u. occurs towards the southeast of the anorthosite-gabbro-tonalite igneous suite, with a minor low of + 150 g.u. over the anorthosite outcrop and a minor high of + 170 g.u. over the main gabbro outcrop. The distribution of the maximum positive anomaly and the minor anomalies is interpreted as due to interbanding of gabbro and anorthosite. The tonalites do not produce a local anomaly and are interpreted as extending to only limited depth. North of the igneous suite the residual gravity anomaly falls to - 10 g.u. over a hidden granite within migmatitic gneisses. It is suggested that the igneous suite was formed when a large body of gabbroic-anorthositic magma was injected into older continental crust, causing melting and the formation of contemporaneous tonalites, with complex fractionation producing gabbro and anorthosite layering. The sequence of events is interpreted as relating to an igneous episode that was a prelude to continental rifting which predated later phases of metamorphic/orogenic activity.
The Portland-Purbeck junction (Portlandian-Berriasian) in the Weald, and correlation of latest Jurassic-early Cretaceous rocks in southern England
Authors: Wimbledon W. A. , Hunt C. O.
Published: May 2009

Ammonites and palynology are described at the Portland-Purbeck junction in the Weald. A major disconformity exists between glaucolithus Zone Portland Beds and the overlying basal Purbeck facies, the basal Purbeck Beds of the Weald are correlated with the Middle Purbeck strata of Dorset. The Cinder Bed of Dorset and Wiltshire is described as one of several marine incursions entering Wessex from further south in the Anglo-Paris basin, not from the Spilsby basin. The use of Cinder Bed as a convenient Jurassic-Cretaceous (Portlandian-Ryazanian) boundary is critically reviewed, as is the placing of the base of the Berriasian Stage in the type Purbeck section. The rival biostratigrahic schemes based on ostracods and palynology are discussed and the discrepancies between the two schemes in southern England are examined.
The distribution of metamorphic temperatures around the Strontian Granodiorite
Authors: Ashworth J. R. , Tyler I. M.
Published: May 2009

The Strontian Granodiorite, a ‘Newer Granite’ emplaced late in the Caledonian orogenic cycle, has an aureole which is strongly asymmetrical: the metamorphic zones are broader to the east of the intrusion than to the west. The asymmetry is attributed to a gradient in the background, regional temperatures. The muscovite-out isograd, marking completion of dehydration of muscovite + quartz to sillimanite + K feldspar (estimated temperature 645 °C), lies within 2 km of the contact on the west, whereas the cordierite isograd, due to the onset of dehydration of biotite+sillimanite+quartz (estimated temperature 690 °C) is at least 2.5 km from the contact on the east. This temperature interval of 45 °C, which is rather insensitive to small errors in the estimated pressure (preferred value 4.1 kbar), is used in a simple geometrical treatment to estimate the regional gradient in the plane of present exposure: approximately 5 °C/km in a direction 30° S of E. Because the intrusion does not appear to have been tilted, this result is regarded as an estimate of the horizontal component of the temperature gradient on the west flank of a regional thermal dome, inherited from the regional metamorphic climax and decaying on a timescale which is suggested, by radiometric data in the literature, to be ˜ 10 Ma. A tectonic origin for the perturbed regional temperature distribution (uplift of hot rocks in the east relative to colder rocks further west) is suggested by the metamorphic petrology of the region, and supported by literature data on structural movements, notably of the Sgurr Beag Slide.
The age and palaeoecology of the St Erth Beds, southern England, based on planktonic foraminifera
Authors: Graham Jenkins D.
Published: May 2009

Planktonic foraminifera are recorded for the first time from the St Erth Beds but they are small and very rare. A late Pliocene G. inflaia Zone age is postulated on the presence of Globorotalia inflata and dextrally coiled Neogloboquadrina pachyderma. It is suggested that the depth of water at the time of deposition was much less than 100 m, possibly in the photic zone, and the palaeotemperature was in the range of 10–18 °C.
A new K—Ar age from uppermost Tremadoc rocks of north Wales
Authors: Kokelaar B. P. , Fitch F. J. , Hooker P. J.
Published: May 2009

New conventional K–Ar dating of virtually unaltered pargasite phenocrysts extracted from a metabasalt of the uppermost Tremadocian Rhobell Volcanic Group, cropping out near Dolgellau, Gwynedd, north Wales, yields an age of 508 ± 11 Ma. This result provides a valuable new time-scale calibration point although incompatible with some other versions of the radiometric time-scale for the Lower Palaeozoic which have indicated ages of less than 508 ± 11 Ma for the Tremadoc/Arenig boundary.
Chlorite-mica stacks in low-strain rocks from central Wales
Authors: Craig J. , Fitches W. R. , Maltman A. J.
Published: May 2009

Weakly deformed, low grade, Lower Palaeozoic metasediments from central Wales contain abundant stack-like intergrowths of chlorite and white mica that closely resemble stacks described from the Devonian Hunsruckschiefer of West Germany; the Ordovician Martinsburg Slate, New Jersey, U.S.A.; and elsewhere. Several theories have been proposed to explain the origin of such stacks, including a detrital origin; strain-controlled growth of chlorite on a detrital mica nucleus; and strain-controlled intergrowth during metamorphism. None of these satisfactorily explains the central Wales stacks. A detrital origin is precluded by the presence of many stacks with shapes too delicate to have survived transportation, and a lack of hydrodynamic equivalence between the stacks and the clastic host grains. Features inconsistent with strain-controlled growth are constant alignment parallel to bedding but non-systematic orientation with respect to tectonic cleavage, their common occurrence in undeformed rocks, and petrographic evidence that they precede the tectonic cleavage. It is proposed that the stacks formed during diagenesis and low-grade metamorphism, and before the onset of deformation, through mimetic growth on a primary bedding fabric composed of clay minerals.
FabianaSilvestri (Foraminiferida) from India, with notes on its global distribution
Authors: Samanta Bimal K.
Published: May 2009

FabianiaSilvestri, a morphologically distinctive larger foraminifer, is circum-global in distribution and is reported to be almost equally abundant in the three marine Tertiary provinces, Tethyan, Indo-Pacific and Caribbean-American. The genus is reported to range from Upper Palaeocene to the top of the Eocene. During the mid-late EoceneFabianiaseems to have been represented by three species,F. cassis(Oppenheim),F. cubensis(Cole & Bermudez) andF. saipanensisCole. In the Indian subcontinent it is known only from eastern India, where it is represented byF. cassisandF. saipanensis. F. indicaNagappa is here regarded as a junior synonym ofF. saipanensisCole.F. cassisis reported for the first time from India. In eastern India,Fabianiais found to be restricted to the middle to upper part of the Middle Eocene.
Microfossil-based biostratigraphy of the Precambrian Hecla Hoek sequence, Nordaustlandet, Svalbard
Authors: Knoll A. H.
Published: May 2009

The Precambrian Murchisonfjorden Supergroup of Nordaustlandet, Svalbard, contains approximately 6000 m of folded, but essentially unmetamorphosed, shallow marine sedimentary rocks. The abundant microfossils found through much of the section allow confident biostratigraphic subdivision of the succession and correlation with contemporaneous sequences in East Greenland and Scandinavia.

Diamictite-bearing rocks of the Gotia Group (uppermost in the sequence) contain a depauperate assemblage of acritarchs dominated byBavlinella Javeolata. A Vendian age of deposition is indicated. Carbonates of the immediately underlying Ryssö Formation contain a wide variety of microfossils including stromatolitic associations of several types, planktonic acritarchs, and, near the top of the formation, vase-shaped heterotrophic protists. The acritarchs, includingChuaria circularis, Kildinella hyperboreica, K. sinica, Trachysphaeridiumspp., and others, and the protistan remains indicate a latest Riphean age. The underlying Hunnberg Formation is similarly fossiliferous. A typically Late Riphean acritarch suite is present, and in addition double-walled forms and large (500 μm), thick-walled spheroids bearing club-shaped 10 μm diameter spines are found. Thus, it appears that the entire carbonate sequence of the Roaldtoppen Group was deposited late in Late Riphean time.

The thick detrital succession comprising the lowermost part of the unmetamorphosed Nordaustlandet sequence, the Celsiusberget and Franklinsundet groups, contains fossils at various levels. Although microfossils are often somewhat coalified, identifiable Late Riphean taxa such asChuaria circularisandKildinellaspp. are present in rocks as low as the middle Westmanbukta Formation. The presence of the distinctive carbonaceous macrofossilTawuia dalensisin the Kapp Lord Formation permits an age estimate of 850–900 Ma for this formation.

All told, the entire Murchisonfjorden Supergroup of Nordaustlandet appears to have been deposited during the Late Riphean and Vendian intervals. The long-recognized lithostratigraphic parallels between this sequence and the Eleonore Bay and Tillite Groups of East Greenland are complemented by strong biostratigraphic similarities.
Diapiric deformations in the Quaternary deposits of the central Ebro Basin, Spain
Authors: Simón J. L. , Soriano A.
Published: May 2009

From a study of 24 outcrops in Neogene and Quaternary deposits of the central Ebro Basin, a number of diapiric deformations have been recognized, two principal types being differentiated: domal or pillow structures, and piercement or intrusive structures. The former are incipient diapirs of gypsum. Piercing structures have reverse faulted contacts not caused by halokinesis; here Neogene marls are the active plastic material, contrasting with the competent behaviour of gypsum. These intrusive structures are viscous diapirs which easily pierce the non-consolidated, low strength Quaternary gravel overburden and submit it to a horizontal compressive stress. As a consequence, reverse faults and flexures develop in it. Generally normal faults and tension cracks do not appear. Underlying gypsum beds are frequently pulled up into diapirs and they constitute the structural core.

Density contrast and conditions for plastic flow exist at the marl–gravel boundary. It seems to have been specially common at the time of Quaternary fluvial sedimentation, so that much deformation is synsedimentary. Diapiric phenomena have been very active during early to middle Pleistocene time, becoming weaker afterwards.
Formation of olivine pseudo-crescumulates by syntectonic axial planar growth during mantle deformation
Authors: Christiansen F. G. , Roberts S.
Published: May 2009

Large elongated euhedral olivines, resembling olivines appearing in crescumulates, from dunite bodies of ophiolite mantle sequences have been subjected to a detailed structural and fabric study. Localities from the Semail Ophiolite, Oman and the Vourinos Complex, Greece are described. The studies indicate that the regional mantle flow structures control the shape and crystallographic orientation of the large euhedral olivines, which are elongated parallel to [001] and flattened parallel to (100) due to syntectonic high temperature metamorphic growth. The growth is controlled by the deformation such that grains oriented unsuitable for slip are growing whereas grains with other orientations are selectively deformed. This being so there may be more than one interpretation of crescumulate textures developed in environments that have suffered a penetrative deformation.
Heavy minerals of Hampshire Basin Palaeogene strata
Authors: Morton A. C.
Published: May 2009

Three heavy mineral associations have been recognized in Palaeogene sands from the Hampshire Basin: one typical of the Scottish Highlands to the north, one of the Armorican massif to the south, and one characteristic of the Cornubian massif to the west. These associations interplay throughout the sequence to produce 10 heavy mineral units correlatable over the basin. The bases of several of the units correspond to commonly accepted time-surfaces and encourage correlation between areas showing strong facies variation. Transgressive units are dominated by Scottish-type material, regressive units by Armorican or Cornubian detritus. There is a relationship between local source area uplift and regression, the main reason for which is that the widespread transgressions submerged or otherwise cut off more local sediment sources, allowing input from the Scottish Highlands, a positive feature throughout much of Tertiary time, to dominate.
Modern carbonate marine-sands in estuaries of southwest England
Authors: Merefield J. R.
Published: May 2009

Large deposits of marine-sand occur in the Taw, Camel and Hayle estuaries of north Devon and Cornwall. Total carbonate concentrations reach 67% in the Hayle, 62% in the Camel, and 40% in the Taw. Well mixed, the sands contain modern skeletal debris of consistent composition, which persists up to 18 km and 12 km landward from the mouths of the Taw and Camel estuaries. Although primarily a molluscan sand, remains of barnacles, bryozoans, echinoids, foraminifera, sponge spicules, decapods and coralline algae are common. Carbonate mineralogy provided by these components (on a 100% carbonate basis) consists of 45% aragonite, 38% low Mg-calcite and 17% high Mg-calcite. Two estuaries of the southeast coast of Devon (the Exe and Teign) contain smaller carbonate concentrations of up to 9 and 14%. Values are low there owing to dilution by readily eroded cliff-talus from local exposures of New Red Sandstone. These Permo-Triassic sediments provide carbonate lithoclasts, however, which supplement the modern biogenic supply. Strontium values have been used to estimate the extent of carbonate lithoclasts supplied to the Exe and Teign. The present source of marine-sand of estuaries in southwest England is considered to be mostly near-shore detritus supplemented by eroded cliff-talus, derived largely from local outcrops. Once this material enters the estuarine regime it is available as a supply of sediment for further up-estuary transport.
Indirect dating of tectonic events by Rb—Sr analysis of syntectonic garnets: an example from schists of the Seve Nappe, central Scandinavian Caledomdes
Authors: Reymer A. P. S.
Published: May 2009

Rb-Sr analyses of syntectonic single-crystal garnets from the Svartsobacken and Dikanas schist units of the Seve Nappe, Scandinavian Caledonides, show systematic differences. One group yields a Precambrian age spectrum consistent with that given by whole-rock analyses; the other group gives Caledonian ages similar to those given by mica analyses. It follows that the tectonic events reflected in the garnet inclusion patterns are also of different ages and, subject to certain limitations, the method can be used to provide a clearer interpretation of the deformational and metamorphic history of the rock.
Geochemistry of Upper Riphean-Vendian basalts associated with the ‘sparagmites’ of southern Norway
Authors: Furnes H. , Nystuen J. P. , Brunfelt A. O. , Solheim S.
Published: May 2009

Summary. Upper Riphean/Vendian basalt lavas within the Hedmark Group of the Osen-Røa Nappe Complex, the lowest tectonostratigraphic unit within the Scandinavian Caledonides, are typical continental tholeiites. Differences in their REE patterns may reflect source heterogeneities, while the general lack of correlation between incompatible trace element ratios may be due to contamination of the basalts by continental crust. Their association with fluvial deposits in NNW-trending graben, and some geochemical disparities with time-equivalent basalt dykes of MORB-like character in tectonically higher units, may indicate their formation in an aulacogen related to the central rift zone of the lapetus Ocean.
K-Ar age of the East Peripheral kimberlite at De Beers Mine, Kimberley, R.S.A.
Authors: Fitch F. J. , Miller J. A.
Published: May 2009

Summary. The kimberlite pipe at De Beers Mine, Kimberley is a complex, multiple structure. Three concordant argon-40/argon-39 age spectra have been obtained from samples from the 720 m level in the East Peripheral kimberlite. Each spectrum is dominated by a major plateau-feature between 84 and 89 Ma and none shows significant evidence of either excess argon or argon loss discrepancy. The available evidence suggests that the K-Ar age of normal magmatic emplacement-cooling of the East Peripheral kimberlite at De Beers Mine was close to 86 ± 2 Ma.
Record of the stromatolite Plicatina from India
Authors: Bhattacharya A. R.
Published: May 2009

Summary. A rare and typically Lower Riphean stromatolite Plicatina is reported from the Indian subcontinent for the first time. Elsewhere, its only well-known report is from the Lower Riphean rocks of Morocco. The present form has been identified as Plicatina misrai, a new form-species. It occurs in the thick calcareous Kapkot Formation, which is a practically unfossiliferous and widespread rock unit of the Lesser Himalaya. The present report has wider implications in many aspects, especially in raising the level of confidence in assigning a definite age to the rock unit in which it occurs.
A revision of the Ordovician olenid trilobiteTriarthrusGreen
Authors: Ludvigsen R. , Tuffnell P. A.
Published: May 2009

Summary. The large number of species assigned toTriarthrusGreen are here allocated to three genera - ten species to a revisedTriarthrusGreen (late Caradoc-Ashgill), thirteen species to a revisedPorterfieldiaCooper (Arenig-Llandeilo), and five species toBienvilliaClark (Tremadoc-Arenig).Triarthruslacks an anterior border furrow on the cranidium; this furrow is confined to the yoked cheeks. BothPorterfieldiaandBienvilliahave an anterior border furrow on the cranidium; these genera are distinguished primarily on the length of the preglabellar field.
An earthquake origin for synsedimentary deformation in a late Triassic (Rhaetian) lagoonal sequence, southwest Britain
Authors: Mayall M. J.
Published: May 2009

Summary. The late Triassic (Rhaetian) Cotham Member in southwest Britain was deposited in a shallow, dominantly freshwater lagoon and contains a bed of synsedimentary deformation which can be traced for at least 25 km. The bed includes microfaults and plastically deformed slump-folds. In south Wales and north Somerset the top of the bed is slightly eroded and desiccation cracks up to I m deep are present. The deformation was probably caused by earthquake activity and associated uplift in the north Somerset-south Wales area. Earthquake activity is inferred to have been part of the early Cimmerian tectonic phase in northern Europe. The bed of synsedimentary deformation is a stratigraphic 'event' which can be used for correlation in this area.
A Late Pleistocene interglacial flora and molluscan fauna from Thatcham, Berkshire, with notes on Mollusca from the interglacial deposits at Aveley, Essex
Authors: Holyoak D. T.
Published: May 2009

Summary. Pollen, plant macrofossils and Mollusca suggesting a mid-Ipswichian age are described from a clast of detritus mud found in gravels underlying the floodplain of the River Kennet at Thatcham, Berkshire. The clast of fluvial mud contained rich fossil assemblages giving evidence of deciduous forest habitats and fens, besides conditions within the river. Non-marine Mollusca from a sample of clay-silt from the interglacial site at Sandy Lane, Aveley are described. Thirteen species are added to the published list of Mollusca. Among these additions,Pseudamnicola confusais important in providing the first evidence from the site of slightly brackish conditions. The fauna as a whole is similar to fluvial faunas of Ipswichian Interglacial age.
Definition of the Tremadoc Series and the series of the Ordovician System in Britain
Authors: Whittington H. B. , Dean W. T. , Fortey R. A. , Rickards R. B. , Rushton A. W. A. , Wright A. D.
Published: May 2009

The Tremadoc Series and series of the Ordovician System are widely used in international correlations, and this review explains and summarizes how the base of each of these series is recognized in Britain. No type section in which the base of any one of them is displayed has ever been selected and formally designated, hence the basal horizon of each series is a matter of general understanding rather than precise definition. This general understanding is of particular biozones, or of assemblages of fossils and their relative ages. The geographical separation between type sections of series, and differences in facies, complicate the understanding of relative ages of biozones. Brachiopod and trilobite faunas of the Llandeilo, Caradoc and Ashgill Series have been studied in detail in recent years, and biozones proposed. These biozones have proved difficult or impossible to recognize outside their type areas in Britain, and brachiopod–trilobite faunas of the Tremadoc, Arenig and Llanvirn Series are likewise highly provincial. Thus for correlation within and outside Britain attention has been focused on the ‘standard’ graptolite biozones, particularly since such conodont faunas as have been found have not proved useful. Yet there are problems associated with these ‘standard’ biozones; for example, theTetragraptus approximatusBiozone is unknown in Wales or England, the relationship between the base of theGlyptograptus teretiusculusBiozone and the earliest Llandeilo shelly faunas requires clarification, and at what level the base of the Caradoc Series may lie in theNemagraptus gracilisBiozone is unknown.

Thus to bring precision to definitions of Ordovician Series in Britain the identification of continuous, fossiliferous sequences that will serve as stratotypes, is required. Such a section for the basal portion of the Tremadoc Series has recently been proposed. Systematic studies related to particular biozones are needed, for example early Caradoc and early Ashgill brachiopods, and graptolites of theDidymograptus bifidusandGlyptograptus teretiusculusBiozones. The stratigraphical ranges and abundances of species in particular sections require documentation, so that the type of biozone (assemblage, acme, concurrent-range, etc.) may be recognized. Such work could lead towards chronostratigraphy, the provision of a standard stratigraphical scale in Britain for the Tremadoc Series and Ordovician series.
The British Caledonides: interpretations from Cenozoic analogues
Authors: Mitchell A. H. G.
Published: May 2009

Recent interpretations of Cenozoic arc systems and collision belts facilitate reinterpretation of some aspects of British Caledonide evolution. End-Cambrian ‘Grampian’ collision of the passive ‘Dalradian’ foreland following southeastwards subduction beneath an island arc was accompanied by initiation of the Highland Boundary Fault as a high-angle south-directed oblique-slip thrust. Mid-Ordovician to early Devonian northwestward oblique subduction of the Iapetus Ocean beneath the Grampian orogen resulted in a continental margin magmatic arc, back-arc thrusting and development of an accretionary prism, while southeastward subduction led to arc magmatism and back-arc extension followed by initiation of the Rheic Ocean as a back-arc marginal basin; this syn-subduction N–S asymmetry of the Iapetus Ocean margins was analogous to the E–W asymmetry of the modern Pacific. Closure of Iapetus was diachronous, earlier in the northeast: during end-Silurian collision the southern Caledonides behaved as a passive foreland; post-collision foreland thrusting resulted in deposition and deformation of Lower Old Red Sandstone foreland basin deposits in Wales, and probably in northwest-directed back-thrusting in the region of the Longford-Down accretionary prism. Subsequent dextral movement in the suture zone juxtaposed the southern Caledonides with Scotland and northern Ireland, beneath which northwestward subduction had continued into the early Devonian.
On the mechanism of formation of reduction spots in the carboniferous/permian red beds of Warwickshire
Authors: Mykura H. , Hampton B. P.
Published: May 2009

Measurements of the size and shape of the grey reduction spots and of the variation of iron content across the spot–host rock interface have been made on samples from the Enville Group. The red coloration due to Fe3+is thought to reside mainly in the matrix material cementing the mineral grains of the rock. The reduction to Fe2+is ascribed to carbonaceous particles included in the sediment. To account for the sharp boundary of the spots it is suggested that the outward movement of the boundary is due to concentration dependent inward diffusion of oxygen which converts the carbonaceous material to carbonate.
Lower pleistocene dinoflagellate cyst, foraminiferal and pollen assemblages in four boreholes in the Southern North Sea
Authors: Cameron T.D.J. , Bonny A.P. , Gregory D.M. , Harland R.
Published: May 2009

Neogene and Lower Pleistocene stratigraphy in the Southern North Sea has been investigated in four I.G.S. boreholes between East Anglia and the Netherlands. The foraminifera of the Red Crag Formation in Borehole 81/51 are closely similar to Upper Pliocene assemblages in Holland. The overlying succession is clearly punctuated by unconformities in seismic profiles, separating four early Pleistocene formations in the boreholes, and indicating intervals of significant stratigraphic hiatus offshore. The Westkapelle Ground and Smith's Knoll Formations correlate with Thurnian and Antian Stage deposits in East Anglia. Pollen spectra in the Winterton Shoal and Yarmouth Roads Formations are similar to Baventian and Bramertonian assemblages in Britain. The autochthonous marine and allochthonous terrestrial microfauna and flora provide conflicting evidence of early Pleistocene palaeoclimate. The dinoflagellate cysts and foraminifera indicate that each formation was deposited in a warm temperate neritic environment. The pollen record, containing evidence of fluctuation between boreal and mixed coniferous–deciduous regional forest cover, suggests alternation between cool and warm temperate palaeoclimate.
The recognition of the base of the Westphalian D Stage in Britain
Authors: Cleal C. J.
Published: May 2009

The I.U.G.S. Subcommission on Carboniferous Stratigraphy recommends that the base of the Westphalian D is best recognized using plant macrofossils. In Britain, however, South Wales is the only coalfield where the distribution of the plants is sufficiently well known for them to be used to locate this boundary. Elsewhere in Britain other criteria have been used, particularly non-marine bivalves and plant microfossils, but these must be regarded with considerable caution.
The Sinian–Cambrian boundary of China and its related problems
Authors: Yusheng Xing , Qixiu Ding , Huilin Luo , Tinggui He , Yangeng Wang
Published: May 2009

The Sinian and Cambrian systems within the Yangtze stratigraphic province represent continuous deposits, and the strata above and below the Sinian–Cambrian boundary are rich in fossils. From all the relevant boundary sections, the Meishucun section in Jinning County, Yunnan Province serves as the stratotype section for the Sinian–Cambrian boundary and is the Chinese candidate for the global stratotype section and point for the Precambrian–Cambrian boundary. The present paper, with the various charts and tables, elaborates on several typical Sinian–Cambrian boundary sections and the distribution of fossils in them.

In accordance with the characteristics of biological evolution, three biotas can be recognized for the period from the Late Sinian to the Early Cambrian. The first biota appeared in the Late Sinian, characterized by the presence of the soft-bodied metazoans; the second biota occurred during the Meishucun Stage of the early Cambrian, and is characterized by the appearance and prevalence of small shelly fossils from many different phyla; and the third biota came into existence during the Qiongzhusi Stage of the Early Cambrian; it is characterized by the first appearance and prevalence of trilobites.

The Meishucun Stage of the Lower Cambrian can be divided into three fossil zones. The Sinian–Cambrian boundary is placed at the base of the first Anabarites–Circotheca–Protohertzina zone. According to isotopic dating by the Rb–Sr whole-rock isochron technique, the age of the Sinian–Cambrian boundary is inferred to be 610±10 Ma.
Magnetostratigraphy of lower Cambrian strata from the Siberian Platform: a palaeomagnetic pole and a preliminary polarity time-scale
Authors: Kirschvink Joseph L. , Rozanov A. Yu.
Published: May 2009

Four sedimentary sections seen in continuous exposures along the Lena River on the Siberian Platform in Yakutia contain a record of the geomagnetic field during the Tommotian and Atdabanian stages of Early Cambrian time. The direction of the stable remanent magnetization indicates that the Siberian platform was located on the equator, and the corresponding palaeomagnetic pole provides a well-dated extension of the Siberian apparent polar wander path. A belt of archaeocyathid bioherms which separates two major facies zones in the lower Cambrian was positioned on and aligned more or less parallel with the palaeoequator. The geographical position of this belt appears to have tracked the southward motion of the Siberian platform during post-Tommotian time. These palaeomagnetic results combined with the extensive biostratigraphy of the Siberian Platform provide a provisional geomagnetic polarity time scale for this part of Early Cambrian time. Comparison of these results with data of similar age from Central Australia suggests that strata of Tommotian and lower Atdabanian age are not present in the Amadeus Basin of Australia.
Precambrian—Cambrian boundary and correlation from southwestern and central part of Spain
Authors: Liñán E. , Palacios T. , Perejón A.
Published: May 2009

This paper comprises the first palaeontological correlation between the Upper Proterozoic–Lower Cambrian Series of Ossa-Morena, Luso-Oriental-Alcúdica and Galaico-Castellana Zones of the Iberian Peninsula.

The authors show the palaeontological events on acritarchs, stromatolites, cyanophyta, soft-bodied metazoa, trilobites, archaeocyathans and skeletal microfossils from three representative sequences of the above mentioned zones and discuss the position of the Precambrian–Cambrian boundary in the sequences. The Sierra de Córdoba general Series (Ossa-Morena Zone) has an erosive discontinuity between the rocks with the first record of Cambrian metazoan activity (Skolithossp.,Monomorphichnussp.,Phycodes pedumandRusophycussp.) and the rocks with a palynological association (Bavlinella faveolata, Protosphaeridium flexosum, Trachisphaeridiumsp., aff.Octoedryxium truncatum, Phycomicetes? sp. and cf.Ooidiumsp.) which suggests a Lower–Middle Vendian age. For this reason we suggest that the Precambrian–Cambrian boundary be placed at this unconformity.

The upper part of the Sierra de Guadalupe Series (Luso-Oriental-Alcúdica Zone) includes detrital beds withPhycodes pedum, Planolitessp. andTreptichnussp. which are also the first record of Cambrian metazoan activity. In the middle part of the sequences, acritarchs attributed to the genusMicrhystridiumare found at the top of the Calcareous Beds. This is taken to indicate an early Cambrian age. Vendotaenids andBavlinella faveolataare found in abundance, thus indicating a Late Vendian age for the middle part of this unit. Thus, we propose the Precambrian–Cambrian boundary be located in the upper part of the Calcareous Beds.

In the Rio Uso Series (Galaico-Castellana Zone), the Azorejo Sandstones containRusophycusgr.radwanskii, Planolitessp. andGordiasp. Trace fossils produced by trilobite-like arthropoda (Monomorphichnus) have been cited in the upper part of the underlying Pusa Shales. Moreover,Octoedryxium truncatumandBavlinella faveolataare found in the lower part of this unit which suggest that the Precambrian–Cambrian boundary could be situated in the Pusa Shales.

Calcareous microfossils related to annelid polychaetes are found associated with Upper Vendian acritarchs in the Calcareous Beds of Sierra de Guadalupe. They are the oldest record of skeletal metazoa in the Spanish Series.

The medusoids found are associated with a Vendian flora and they are also the oldest non-skeletal metazoa record known in the Iberian Peninsula.
Microfossils and small shelly fossils from the Lower CambrianHyolithesLimestone at Nuneaton, English Midlands
Authors: Brasier M. D.
Published: May 2009

The Lower Cambrian sequence at Nuneaton is outlined, paying particular attention to the 2 m thick Home Farm Member (including theHyolithesLimestone) and its faunal succession at the type locality, Woodlands Quarry, Hartshill. There follows the first modern description and illustration of microfossils and small shelly fossils from this member. Of thirty-two species covered here, twenty are described and illustrated from Nuneaton for the first time and eight of these are new records. The varied fauna includes phosphatic and calcareous microproblematica (especiallyColeoloides typicalis), protoconodonts, agglutinated foraminifera, cap-shaped molluscs, primitive bivalves, hyoliths, inarticulate brachiopods and sponges. The fauna has affinity with fossils in the top Tommotian to lower Atdabanian rocks from Siberia and China, from the Baltic area and the belt from southeast Newfoundland to Massachusetts.
A revised age and correlation for the topmost Sholeshook Limestone Formation (Ashgill) of South Wales
Authors: Price D.
Published: May 2009

The age of the youngest part of the Sholeshook Limestone Formation is reconsidered in the light of recent advances in knowledge of Ashgill trilobite faunas. A low Rawtheyan (Zone 5) age is suggested and correlations are proposed with Ashgill rocks in the SW Berwyns and with part of the Swindale Limestone Formation of Cross Fell. The Cautleyan/Rawtheyan boundary is a level at which faunal changes are sufficiently pronounced to permit reliable and precise correlation.
New evidence on the vertebrate fauna, stratigraphy and palaeobotany of the interglacial deposits at Swanton Morley, Norfolk
Authors: Coxon P. , Hall A. R. , Lister A. , Stuart A. J.
Published: May 2009

The stratigraphy and palaeobotany of new in situ exposures of interglacial deposits at Swanton Morley, Norfolk are described. These organic sediments, which probably accumulated in a river back channel, are shown to cover pollen zones Ib to IIb of the Ipswichian interglacial. Macroscopic plant fossils include a new record for Trapa natans from subzone Ip IIb. Vertebrate remains from the new excavations, and from previous finds, have been pollen-dated. The Ip IIa fauna, the first recorded from this subzone, includes Emys orbicularis, small mammals including Microtus oeconomus, and some large mammals. Hippopotamus amphibies is recorded from early zone Ip III. Of particular interest are hazelnuts gnawed by Apodemus, and large mammal bones damaged by Crocuta.
Resolution of the age structure of the detrital zircon populations of two Lower Cretaceous sandstones from the Weald of England by fission track dating
Authors: Hurford A. J. , Fitch F. J. , Clarke A.
Published: May 2009

Modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies, supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography. A computer program has been written and used to identify modes in the zircon fission track age distribution within two Lower Cretaceous sandstone samples from the Weald of southern England. Pronounced modes appear in one rock around 119 Ma, 160 Ma, 243 Ma and 309 Ma and in the other around 141 Ma, 175 Ma, 257 to 277 Ma and 394 to 453 Ma. The geological implications of these quite dissimilar zircon age spectra are discussed. It is concluded that they support the palaeogeographical models of Allen (1981) and indicate that the provenance of the first sample, from the Top Ashdown Sandstone member at Dallington in East Sussex, was almost entirely southerly, while that of the second, from the Netherside Sand member at Northchapel in West Sussex, was more varied, but predominantly westerly and northerly.
The genusBiplanispiraUmbgrove (Foraminiferida) and its occurrence in India
Authors: Samanta Bimal K.
Published: May 2009

BiplanispiraUmbgrove is closely related toPellatispiraBoussac, from which it probably arose by the subdivision of the median chambers by the rapidly expanding marginal crest and the development of planispirally arranged secondary chambers on both sides of the peripheral flange. The genus appears to be polyphyletic, its species having been derived from different representatives ofPellatispira. Illustrated records ofBiplanispiraare confined to the region between eastern India and Eua, Tonga, and the genus appears to be restricted to the middle and upper parts of the Upper Eocene. In the Upper Eocene of the Garo Hills, eastern India, it is represented byB. hoffmeisteri(Whipple) and in the Andaman Islands byB. mirabilis(Umbgrove). This is the first record of the genus from mainland India.