bluuebunny/crossref_metadata_2025 huggingface dataset:
Upper Triassic to Lower Cretaceous continental and coastal saline lake evaporites inthe Atacama region of northern Chile
Authors: Suarez M. , Bell C. M.
Published: May 2009

Evaporites within Upper Triassic to Lower Cretaceous sequences in the Atacama region of northern Chile are interpreted as the deposits of continental and coastal saline lakes. Halite casts and finely laminated calcareous evaporites, intercalated with alluvial and fluvial sediments, are probably playa lake deposits. These continental evaporites have been recognized in Upper Triassic alluvial sediments (Cifuncho Formation), in Upper Triassic–Lower Jurassic braided river deposits (basal unit of the Pan de Azúcar Formation), and within a sequence of Lower Cretaceous aeolian, alluvial and playa lake mudflat sediments (Quebrada Monardes Formation). Lower Cretaceous evaporites between marine limestones (Lautaro Formation) and continental redbeds (Quebrada Monardes Formation) were probably deposited in coastal saline lagoons, produced during a regionally extensive marine regression.

These sequences, and other similar successions in northern Chile, provide a record of almost continuous evaporite deposition, and hence of arid to semi-arid conditions, since Upper Triassic times. These conditions were primarily the result of a constant latitudinal position within the subtropical zone. A contributary factor was the geographical position of the area, initially on the west coast of Gondwanaland and subsequently on the coast of South America, with cold, northward-flowing ocean currents and offshore winds.
Stratigraphy and age of the ammonoid Durvilleoceras woodmani from the Greville Subgroup, New Zealand
Authors: Waterhouse J. B.
Published: May 2009

Durvilleoceras woodmani of debated Late Permian or Early Triassic age is accompanied by other ammonoids, deemed to belong to Araxoceratidae, Xenodiscidae, and Goniatitida, of chiefly Late Permian age. The ammonoids are found principally in the Deserter Bay and especially Tongue Point Members (new names) of the newly named South Arm and Wells Arm formations of the Greville Subgroup, which are overlain, apparently in normal stratigraphic succession, by the Waiua Formation and newly named formations of the Te Mokai Group, with three successive faunas of Permian appearance.
Origin and emplacement of an inferred late Jurassic subduction-accretion complex, Euboea, eastern Greece
Authors: Robertson A. H. F.
Published: May 2009

In northern Euboea, central eastern Greece, an up to 3 km-thick polygenetic melange (Pagondas complex) is structurally interleaved between a Triassic–Jurassic carbonate platform (Pelagonian Zone) and an overriding harzburgitic ophiolite. The melange mainly comprises late Triassic shallow-water limestone and calciturbidites, radiolarites, Triassic–Jurassic tholeiites, alkaline basalts and minor andesites. The units concerned range from kilometre-sized thrust sheets, and detached blocks, to broken formation and structureless, or bedded matrix-supported conglomerates (diamictite). The melange includes remnants of Neotethyan oceanic lithosphere, overlain by radiolarites, hemipelagic carbonates and distal calciturbidites derived from a Mesozoic carbonate platform. Tholeiites were erupted at a Triassic–Jurassic spreading axis, whilst within-plate-type alkali basalts are interpreted mainly as seamounts. Kilometre-scale detached blocks of shallow-water coralline limestone are identified as collapsed atolls, formed within an ocean and/or along the rifted continental margin. Volcaniclastic sediments are locally interbedded with radiolarite, and reflect post-volcanic erosion of the ocean floor. Intra-oceanic convergence began, apparently in late early Jurassic time, giving rise to the Euboea ophiolite above an inferred westwards-dipping subduction zone. The Pagondas Complex then developed as an accretionary prism. The subduction trench later collided with the Pelagonian passive margin, driving the hot Euobea ophiolite over the accretionary complex, to produce amphibolites and greenschists of the metamorphic sole. Trench–margin collision then drove the entire supra-subduction zone complex, apparently eastwards, downflexing the Pelagonian carbonate platform to form a foredeep in which late Jurassic (Kimmeridgian–Tithonian) radiolarian sediments accumulated. During emplacement, the accretionary complex was disrupted and partly resedimented as debris flows, turbiditic volcaniclastic sandstone and shale in a foredeep, or foreland basin setting.
An ankylosaurid dinosaur from the Upper Cretaceous of Shandong (China)
Authors: Buffetaut Eric
Published: May 2009

In 1923, H. C. T’an and O. Zdansky collected remains of an ankylosaurid dinosaur in the Late Cretaceous Wangshi Group of the Laiyang region, in eastern Shandong (China). Apart from a few caudal vertebrae, this material, which is kept at the Palaeontological Institution of the University of Uppsala (Sweden), was never described or figured. It includes a well-preserved sacrum with the attached right ilium and part of the presacral rod, caudal vertebrae, a left femur and a dermal scute. This material is referred to an ankylosaurid of the genus Pinacosaurus Gilmore, 1933, on the basis of the widely divergent ilium bearing a strong ventral ridge and of the slenderness of the femur. In the absence of cranial material, a specific attribution is difficult and the Uppsala material is referred to as Pinacosaurus cf. grangeri (P. grangeri being the only generally accepted species of Pinacosaurus). This is the first record of Pinacosaurus outside the Gobi Basin of Mongolia and northwestern China. In the Gobi Basin, Pinacosaurus has been reported only from the Djadokhta Formation or its equivalents, of supposed Campanian age, and it is suggested that at least the part of the Wangshi Group which yielded the Shandong Pinacosaurus may be of roughly the same age as the Djadokhta Formation.
An atheloptic trilobite assemblage from the Carboniferous of North Devon
Authors: Owens R. M. , Tilsley J. W.
Published: May 2009

New collections of trilobites have been made from Dinantian rocks in North Devon, distributed among seven genera. Of these,Wagnerispina, Archegonus (Phillibole), Liobole, Aprathia, and probablyLichanocoryphegen. nov., are primitive phillipsiids belonging to the subfamily Archegoninae. Reasons are given here for the others,TawstockiaandSpatulina, previously considered to be primitive phillipsiids of the subfamily Cystispininae, to belong to the higher phillipsiids, as effaced, blind members respectively of the Linguaphillipsiinae and Cummingellinae. The species of these genera from North Devon discussed here, three of which are new, are either small-eyed or blind, and form an atheloptic assemblage; they occur in hemipelagic sediments of the Codden Hill Chert Group in the Barnstaple district, and the Kersdown Chert Formation in the Bampton district. Ammonoids associated with the trilobites indicate an early Viséan, late Chadian age for the fauna, and the same or similar trilobite species and subspecies occur in the Březina Shales of Moravia, suggesting that they are approximately coeval.
The oldest known dinosaur from southeast Asia: a prosauropod from the Nam Phong Formation (late Triassic) of northeastern Thailand
Authors: Buffetaut Eric , Martin Valérie , Sattayarak Nares , Suteethorn Varavudh
Published: May 2009

The distal part of the fused ischia of a prosauropod from the Nam Phong Formation (late Triassic) of Phetchabun Province, in northeastern Thailand, is described. Comparisons with various prosauropods, as well as with an early sauropod, show that the Thai specimen is especially robust. However, the available material is too incomplete to warrant a precise identification. It is the first vertebrate fossil found in the Nam Phong Formation, the oldest known dinosaur from southeast Asia, and the first prosauropod to be reported from that region.
Denudation chronology from cave and river terrace levels: the case of the Buchan Karst, southeastern Australia
Authors: Webb J. A. , Fabel D. , Finlayson B. L. , Ellaway M. , Shu Li , Spiertz H.-P.
Published: May 2009

Detailed mapping of surface and underground karst features at Buchan, in eastern Victoria, has shown that the three river terraces along the Buchan River can be correlated with three levels of epiphreatic development in the nearby caves. Each level represents a stillstand in the denudational history of the area. Uranium series dating of speleothems and palaeomagnetic studies of cave sediments indicate that all three stilistands are more than 730 ka old. The periods of incision separating the stillstands were probably the result of active tectonic uplift. This contrasts with some northern parts of the Southeastern Highlands, which have been stable since the Eocene. The overall amount of incision and uplift at Buchan is small, indicating that the majority of scarp retreat in this section of the highlands must have occurred earlier. The denudation history of the Buchan area over the last 730 ka has seen only 2–3 m of incision, despite the major climatic and sea-level changes that have occurred in that time. Whereas most karst landscapes in the Northern Hemisphere have been extensively modified during the late Pleistocene, the Buchan karst was little affected, and its geomorphology has an older origin.
Azolla tegeliensis Florschütz from the early Pleistocene of the British Isles
Authors: Field Michael H.
Published: May 2009

Fossil megaspores of the aquatic fern Azolla tegeliensis Florschütz have been recovered from sediments of early Pleistocene age at Great Blakenham, Suffolk, England. This discovery is the first record for this taxon in the British Isles. The find reinforces a recently suggested correlation of the British early Pleistocene sediments with those from con tinental northwest Europe. In the long continuous Pleistocene sequences in The Netherlands the megaspores of A. tegeliensis have been recovered from early Pleistocene sediments, where they are restricted to the Tiglian Stage. Sediments at Great Blakenham can now be correlated with the Tiglian sediments of The Netherlands.
Evidence for extensive post-Caledonian karst development in southwestern Spitsbergen
Authors: Bjørnerud M.
Published: May 2009

Proterozoic limestones at several localities in southwestern Spitsbergen contain karst-related features (layered clastic infillings, collapse breccias, deeply weathered depressions) which overprint the Caledonian deformational fabric in the rocks. These features apparently developedbetween middle Devonian and mid-Carboniferous time when the Precambrian basement complex stood high above sea level. Recognition of these karst features may shed light on depositional and tectonic events in post-Caledonian Spitsbergen.
Crystallization of solid solutions from aqueous solutions in a porous medium: zoning in (Ba, Sr)SO4
Authors: Prieto Manuel , Putnis Andrew , Fernandez-Diaz Lurdes
Published: May 2009

Barite-celestite solid solutions have been synthesized under controlled conditions by the counter-diffusion of Ba2+, Sr2+and SO42–ions through a porous transport medium (silica gel), to investigate the factors which control compositionalzoning. The equilibrium compositions of solid solution and aqueous solutionhave been determined from the relative solubilities of barite and celestite, predicting that virtually pure barite should precipitate from Sr-rich solutions. However, nucleation and growth in a porous medium, where mass transport is by diffusion, takes place at very high supersaturations. The threshold supersaturation for nucleation is inversely related to the solubility and is therefore much higher for barite than celestite. The balance between the thermodynamics and kinetics of nucleation and growth at high supersaturations leads to zoning patterns the reverse of those predicted at equilibrium. At high supersaturations the zoning is periodic and sector-controlled with many of the general features observed in natural minerals. Oscillatory zoning with compositional gaps can take place without the need to invoke miscibility gaps or periodic variations in externally controlled intensive parameters.
A preliminary petrographic study of the Chilean nitrates
Authors: Searl Alison , Rankin Sharon
Published: May 2009

The nitrate deposits of the northern Atacama Desert occurin a narrow zone between the low-lying Pampa del Tamarugal to the east and the hills of the Coastal Range to the west. High purity nitrate ore occurs as stratiform seams about 20 cm thick, present at depths of 3–7 m below thedesert surface. The ore is hosted by a variety of lithologies and overlain by salt-cemented regolith. The ore is largely composed of nitratite (= sodanitre or Chilean salt peter) and halite with locally abundant humberstonite, polyhalite and mirabilite. Other salts present include Ca iodates and a variety of sulphate, borate and chromate minerals. Textural relationships can be used to deduce paragenetic sequences for individual salt samples and these combined to produce a generalized paragenetic web for the nitrate ore.These textural data can be combined with published solubility data to investigate the course of fluid evolution during ore genesis. The multiplicity of paragenetic relationships within the ore reflects the derivation of precipitating fluids from a variety of sources: westwards flowing Andean groundwater, coastal fogs, occasional rainfall and Andean-derived surface floodwaters. The unusual mineralogy of the nitrate ore reflects the extreme chemical evolution of the precipitating brines through multiple episodes of salt precipitation and remobilization during transport to the nitrate horizons. The formation of high purity nitrate ore appears to be the result of multiple phases of dissolution, reprecipitation and recrystallization, that have separated the highly soluble nitrate salts from less soluble salts in the overlying profile. Salts have largely accumulated through displacive growth, but some of the host silicate and carbonate lithologies have also undergonea small degree of salt replacement.
Carbon isotope and magnetic polarity evidence for non-depositional events within the Cambrian-Ordovician Boundary section near Dayangcha, Jilin Province, China
Authors: Ripperdan R. L. , Magaritz M. , Kirschvink J. L.
Published: May 2009

Carbon isotope and magnetic polarity stratigraphic results from the Cambrian-Ordovician Boundary section at Xiaoyangqiao, near Dayangcha, Jilin Province, China, in comparison to a contemporaneous section at Black Mountain, Australia, indicate strata equivalent to major portions of the Australian sequence are either absent or are restricted to highly condensed intervals. These intervals are correlative with regressive sea level events identified in Australia and western North America, suggesting regional or eustatic sea level changes strongly influenced deposition of the Xiaoyangqiao sequence. These results also suggest the Xiaoyangqiao section is unfavourable as the site of the Cambrian-Ordovician Boundary Global Stratotype Section and Point.
Sidewall differentiation in an alkalic magma chamber: evidence from syenite xenoliths in tuffs of the Latera caldera, Italy
Authors: Turbeville B. N.
Published: May 2009

Feldspathoidal and quartz-bearing syenite xenoliths in c. 235 to 155 ka tuffs surrounding the Latera caldera have textures and mineral assemblages that indicate an origin from the crystalline margins of a shallow magma chamber. This lithic suite exhibits a diversity of plutonic fabrics; unaltered, glass-bearing nodules with undeformed sanidine frameworks coexist with completely crystallized clasts, many of which show evidence of subsolidus modification. The syenites comprise eutectic mineral assemblages with high percentages of titanite, apatite, and melanite garnet as accessory minerals. Ubiquitous reaction textures in syenite accompany progressive changes in mineral assemblages, and they show the decreasing influence of limestone contamination with distance from the contact of syenite and skarn wallrock. Diagnostic mineral assemblages include nepheline rich in calcite inclusions, coexisting titanite and metamorphic perovskite, zircon with baddeleyite inclusions, fluorapatite mantled by a possible carbonate-bearing apatite (francolite), melanite garnet intergrown with clinopyroxene, and interstitial haüyne rich in pyrrhotite inclusions.

At Latera, pumice fragments in the same deposit can exhibit up to ten-fold differences in vesicularity and crystal content (from < 5 to > 50 vol. % phenocrysts). These clasts, in conjunction with glass-bearing syenite and skarn xenoliths, may represent a range of progressively crystallized magmas that were quenched at the instant of their eruptive entrainment. The major element abundances of pumices and syenite reflect the fractionation of plagioclase and sanidine, with lesser amounts of fassaitic diopside, leucite, biotite, apatite, and alkali amphibole. Trace element ratios (e.g. Rb/Sr, Nb/Ta, Zr/Hf, LREE/HREE), on the other hand, are highly variable for crystalline and pumiceous ejecta, and some element variations (e.g. Li, Ta, Nb, Th) cannot be entirely reconciled with simple crystal-liquid fractionation. The syenite clasts span a range of compositions from strongly fractionated assemblages rich in accessory minerals to compositions that more closely approximate quenched reservoir liquids. These features reflect processes that range from pure fractional crystallization to in situ crystallization where fractionated liquid was trapped in the pores of sidewall cumulates along the chamber roof and walls.
A basement culmination in the Scandinavian Caledonides formed by antiformal stacking (Bångonåive, northern Sweden)
Authors: Greiling R. O. , Gayer R. A. , Stephens M. B.
Published: May 2009

The Bångonåive basement culmination, a doubly plunging antiform trending SW-NE in its southern part and SSW-NNE in the north, is part of a major Caledonian antiform in north-central Scandinavia. Crystalline, Proterozoic basement rocks (mainly syenite) are unconformably overlain by a sedimentary cover including tillites at the base, passing up into arkoses, quartzites and shales, capped by black phyllites. This sequence is correlated with the Varangian to Cambrian succession of the Baltoscandian platform farther east. Detailed mapping revealed a succession of five basement-cover horses, which represent the accessible part of an antiformal stack exposed beneath the Middle and Upper Allochthons and taken here as the Lower Allochthon structural level.

Caledonian deformation varies in intensity from penetrative near thrusts and in pelitic rocks to very weak in the more internal parts of the horses. A penetrative foliation is associated with the growth of white mica and rare biotite. This early fabric is overprinted by a mylonitic foliation related to localized shear zones, which separate the structural units within the Lower Allochthon. Stretching and mineral lineations trend WNW-ESE and related shear-sense criteria indicate transport (top) towards the ESE. Structural units (horses) are thrust into an antiformal stack and folded around the lowermost horse exposed, which is itself folded into an anticlinal lift-off fold. Towards the northeast, the antiformal stack is overprinted by a pop-up and an out-of-sequence thrust. The latter breached the roof of the Lower Allochthon and transported part of it over the Middle and Upper Allochthons. Further folds are associated with lateral and oblique ramps in the Lower Allochthon. These structures relate very well with the complex fold pattern previously observed in the higher structural units and thrust tectonics provides a straightforward genetic explanation for these folds. Therefore, earlier genetic models of the Bångonåive basement culmination as a simple imbrication of basement into higher units, as a buckling structure or as a gravitational dome structure are rejected here. The structural information, supported by gravimetric data, is consistent with an essentially flat regional detachment surface (2° dip) extending from the present external Caledonian margin to the base of the Bångonåive antiformal stack.
Crustal structure of the London–Brabant Massif, southern North Sea
Authors: Rijkers Richard , Duin Ed , Dusar Michiel , Langenaeker Vital
Published: May 2009

In 1991 a deep seismic line, MPNI-9101, was acquired in the southern North Sea. The line runs from the Mesozoic Broad Fourteens Basin in the north, across the West Netherlands Basin, onto the London–Brabant Massif in the south. The London–Brabant Massif is a WNW–ESE trending stable structure located beneath southeastern England, the southern North Sea and Belgium. The London–Brabant Massif represents the most easterly part of the Anglo-Brabant Massif. At the northern margin of the London-Brabant Massif, Devonian and Carboniferous siliciclastic and carbonate rocks onlap the massif. Farther south, shallow parts of the seismic line in the vicinity of the axial zone of the London–Brabant Massif are almost completely devoid of primary reflections. This zone is composed of strongly folded Lower Palaeozoic sedimentary units which have been mapped in the onshore part of Belgium. Numerous seismic reflection multiples from the base of the Cretaceous are observed on this part of the section. The southern limit of the zone is very abrupt and may correspond to a fault belt delimiting an area of magmatic rocks known in the onshore part of Belgium. Unusually the deeper parts of the seismic line show a strongly reflective lower crust beneath the London-Brabant, a phenomenon which has not been observed on other deep seismic sections across the massif. Two-way travel times to the base of the lower crustal reflective zone (corresponding to the Moho), increase from 10 seconds beneath the West Netherlands Basin in the north to 12 seconds beneath the London–Brabant Massif, suggesting a thickening of the crust.
Post-Palaeozoic cooling and uplift of the Brabant Massif as revealed by apatite fission track analysis
Authors: Vercoutere C. , Van Den Haute P.
Published: May 2009

A fission track study has been carried out on apatite from the igneous rock belt running along the southern border of the Brabant Massif. The study includes age determinations and a length analysis of both surface tracks and confined tracks. Apatite fission track ages vary between 146 Ma and 209 Ma. Confined track length distributions and the projected length age spectra indicate that the rocks cooled relatively rapidly from above 100 °C to ambient temperatures. The fission track ages therefore date a cooling phase of the Brabant Massif which is interpreted as reflecting an important uplift during the major part of the Jurassic, related to the Cimmerian tectonism which affected the North Sea basin and adjacent areas. Two apatite samples from the southerly Dinant Basin yield fission track ages around 200 Ma, similar to the oldest ages observed in the Brabant Massif, and with comparable track length characteristics. This indicates that the uplift was not limited to the Brabant region but also affected the Hercynian basement to the south.
Latest Middle Cambrian metazoan reef from northern Iran
Authors: Hamdi B. , Rozanov A. Yu. , Zhuravle A. Yu.
Published: May 2009

Middle and Late Cambrian reefs were built mainly by cyanobacterial communities. A few reefs with a metazoan as well as an algal component, however, are known from this interval. A Middle Cambrian reef formed primarily by spicular demosponges is described here from the Mila Formation in the Elburz Mountains, northern Iran. The reef is enclosed within calcareous grainstones which contain terminal Middle Cambrian (late Mayan) trilobites. The Mila Formation reef was constructed by sponges of the family Anthaspidellidae and bacterial (algal?) sheaths, and is the earliest metazoan reef to be documented from the interval after the demise of archaeocyath sponges. The reefal community is typical of subsequent reefal communities of Early–Middle Ordovician age. The Ordovician examples differ only by the incorporation of additional metazoan elements.
Bahamian giant stromatolites: microbial composition of surface mats
Authors: Riding Robert , Awramik Stanley M. , Winsborough Barbara M. , Griffin Karen M. , Dill Robert F.
Published: May 2009

Subtidal columnar stromatolites up to 2.5 m high near Lee Stocking Island in the Exuma Cays, Bahamas, have surface mats approximately equally composed of algae and cyanobacteria. The stromatolites are composed of fine–medium oöid and peloid sand. This sediment is supplied to the growing stromatolite surfaces by strong tidal currents which lift grains into suspension and sweep migrating dunes over the columns. The algae include an unidentified filamentous chlorophyte, and numerous diatom species mostly belonging to Mastogloia, Nitzschia and Navicula. The dominant cyanobacteria are two oscillatoriacean species, both probably belonging to Schizothrix. Trapping of sediment is mainly effected by the unidentified chlorophyte which is veneered by epiphytic diatoms. Grains are bound into a mucilaginous mat composed of diatoms and cyanobacteria. Cyanobacteria alone would not be able to trap and bind coarse sediment so effectively in this environment. In being coarse-grained and having a significant eualgal component to their mats, these stromatolites are similar to subtidal columnar stromatolites at Shark Bay, Western Australia. The Lee Stocking stromatolites are physically stressed by high velocity tidal currents and mobile sediment. The Shark Bay stromatolites are stressed by hypersalinity. In both cases stress deters grazers, encrusters and bioeroders. These coarse-grained eualgal stromatolites contrast with micritic and predominantly prokaryotic stromatolites of most Recent marine environments, and are not analogues for most pre-Phanerozoic stromatolites. They appear to be a response to changing stromatolitic mat components in the Cenozoic.
The Wedza–Mimosa platinum deposit, Great Dyke, Zimbabwe: layering and stratiform PGE mineralization in a narrow mafic magma chamber
Authors: Prendergast M. D.
Published: May 2009

The Wedza–Mimosa platinum deposit is a loosely stratiform PGE-rich sulphide zone (MSZ) set within a complexly layered, shallow synclinal sequence of pyroxenites and gabbros. Both the MSZ and its host rocks display systematic stratigraphic, lithological and compositional variations between the margins and the axis of the deposit. A well preserved marginal facies is characterized by discordant layering, stratigraphic complexity, evidence of non-equilibrium crystallization, magmatic erosion and extensive pegmatoids, as well as by irregular MSZ development and metal contents. The principal transverse variations and marginal phenomena are interpreted in terms of the high transverse heat flux and heat gradient caused by the narrow trumpet-like cross-sectional structure of the original magma chamber, the magma replenishment process, the angular relationship between the chamber floor and the stratified magma, and the increase in magma density caused by the onset of plagioclase crystallization.
On the origin of Grunty Fen and other landforms in southern Fenland, Cambridgeshire
Authors: West R. G.
Published: May 2009

Depressions and embayments of the southern Fenland margin and islands are ascribed to periglacial processes in the Devensian Stage (last cold stage) of the Pleistocene. The processes, which may be included in the general term thermokarst, include thermal erosion as an important element. The age of the active landscape evolution appears to be Late Devensian. The Crowland Bed of the Fenland Pleistocene succession is a product of these processes.
Proterozoic Mn-oxide precipitation by planktonic plant protists (acritarchs)
Authors: Morad S. , Vidal G.
Published: May 2009

Microfossils of plant protists called acritarchs occur embedded in, mostly, authigenic chlorite cement in sandstones of the Visingsö Group (Upper Proterozoic; southern Sweden). These microfossils are commonly encrusted by a Mn-oxide layer. Similar Mn-oxide was not observed elsewhere in the sandstones, thus suggesting that certain acritarchs have played a role in the transfer and precipitation of Mn in ancient sedimentary environments. In the light of available information on the role of extant protists in biomineralization, possible mechanisms for the precipitation of Mnoxide in the Visingsö Group are discussed.
Fe-enrichment in tholeiitic pyroxenes: complex two-pyroxene assemblages in Mesozoic dolerites, southern Tasmania
Authors: Hall R. P. , Hughes D. J. , Joyner L.
Published: May 2009

The pyroxene assemblages of four samples of ferrodolerite from the Mesozoic Mount Wellington sill of southern Tasmania are described. The pyroxenes of each sample define an Fe-enrichment trend equivalent to almost half of a Skaergaard-type pyroxene evolution trend. The calcic pyroxenes range from augite to ferroaugite (Ca30–40Mg40–17Fe15–45) and late-stage hedenbergite (Ca45 Mg5Fe50), and the pigeonites from intermediate to ferriferous types (Ca13Mg55–15Fe32–70). XMg numbers (Mg/(Mg + Fe)) of the calcic pyroxenes vary from 0.8 to 0.1, and of the calcium-poor pyroxenes (pigeonites) from 0.62 to 0.17. The chemical variation in the pyroxenes within individual samples is far greater than between the different samples. One sample contains an extremely wide range of pyroxenes which include some of the most ferriferous pigeonites ever recorded (Ca14Mg15 Fe71). Ti and Al contents are also highly varied, Ti:Al ionic ratios ranging from 1:15 to 1:2 with decreasing XMg. The augites have higher Ti and Al contents than pigeonites with corresponding XMg. The hedenbergites have erratic but generally low Ti contents, due to their late precipitation together with ulvospinel. The presence of such highly variable pyroxenes within individual samples and in some cases as single, complex grains makes the recognition of coexisting pyroxene pairs in such dolerites very difficult, but graphical pyroxene thermometers suggest a crystallization temperature range of 1100 to 850 °C.

The range of pyroxene compositions in such dolerites is strongly influenced by the oxygen fugacity (fO2) of the liquid from which they derive. The primary Fe-Ti oxide phase in these Tasmanian dolerites is ulvospinel (now oxidized to ilmenite ‘oxidation-exsolution’ lamellae in titanomagnetite hosts) clearly demonstrating the originally low fO2 of the parental tholeiitic magma of the Mount Wellington sill.
Inter-related plutonism and deformation in South Victoria Land, Antarctica
Authors: Cox Simon C.
Published: May 2009

The Lower Palaeozoic Bonney Pluton is a regionally extensive coarse-grained, variably megacrystic, monzodioritic to granitic body that crops out over 1000 km2 in South Victoria Land. It intruded upper amphibolite facies Koettlitz Group metasediments and interlayered orthogneisses. Magmatic fabrics are developed in the centre of the pluton by flow alignment of K-feldspars before the majority of phases had crystallized, whereas solid-state fabrics developed in the pluton margins by ductile–plastic deformation. Structures developed in the host-rocks vary around this elongate northwest–southeast-trending pluton. Upright, tight northwest–southeast-trending macroscopic folds are developed at the sides of the pluton, with axis-parallel stretching lineations and boudinage indicating strong northwest–southeast extension. Broad warps of tight macroscopic folds, and mesoscopic refolded folds, sheath folds and complicated interference patterns characterize areas at the ends of the pluton. Emplacement of the pluton involved radial expansion in a regional northeast–southwest compression, and growth predominantly in the northwest–southeast direction. Superposition of the radial expansion and regional compression resulted in an inhomogeneous strain field at a regional scale, with coaxial strain at the sides of the pluton and non-coaxial strain at the ends. Upright folds developed at the pluton's sides, and became tighter with continued coaxial deformation. Non-coaxial structures developed at the ends of the pluton and were pushed aside by the growing pluton into areas of coaxial deformation, resulting in complex folding, re-folding and sheath folds. Metamorphism of the host-rocks and migmatite development was more intense at the sides of the pluton than near the ends, possibly due to different P-T-t paths of host-rocks around syntectonic plutons.
Geochemistry and eruptive environment of metavolcanic rocks from the Mona Complex of Anglesey, North Wales, U.K
Authors: Thorpe R. S.
Published: May 2009

The late Precambrian–early Palaeozoic Monian Supergroup of the Mona Complex is a thick sequence of flysch-type sediments and metavolcanic rocks which were deposited during the late Precambrian–early Palaeozoic and deformed during the late Precambrian and Caledonian (Ordovician/Silurian) orogenies. The Monian Supergroup includes tectonically emplaced, geographically separated outcrops of metabasalt/andesite, gabbro and serpentinized ultramafic rocks all of ophiolite affinity. The major units of the Mona Complex are separated by important faults/fault zones which may represent terrane boundaries. New chemical analyses, together with existing ones, show that the metabasalts and meta-andesites from the older New Harbour Group of north Anglesey have characteristics of suprasubduction zone arc eruptives whereas the metabasalts from the younger Gwna Group of south Anglesey and Lleyn have MORB geochemistry. It is suggested that these volcanic rocks were produced during the late Precambrian–early Palaeozoic development of the lapetus Ocean and emplaced as separate terranes during its closure.
Evidence for temperate soil development during the Early Devensian in Gower, South Wales
Authors: Case D. J.
Published: May 2009

Investigations into the micromorphology of the Pwll Du Red Beds in Gower, South Wales, have revealed pedo-features in the form of compound void coatings. Overlying marine deposits dated to the Ipswichian (Oxygen Isotope Substage 5e), the Red Beds are interpreted as the product of sedimentation and pedogenesis during Early Devensian time.
Chemical correlation of Moinian rocks in the northern Highlands of Scotland
Authors: Winchester J. A. , Lambert R. St J. , Holland J. G.
Published: May 2009

Comparison is made between the semipelitic and psammitic schists of the Morar and Glenfinnan Division in their type areas and the succession in the Fannich district of Northern Ross-shire. The tentative lithological correlation of the Morar Pelite with the Sgurr Mor Pelite is confirmed, while the Meall an t-Sithe Pelite and the semipelites of the Glenfinnan Division likewise have a similar geochemistry. In establishing these similarities, ratios involving Sr, Nb, Y, Zr and P2O5 have been found to be most useful, particularly Sr/Y. Other ratios (Ca/Y, K/Rb, K2O/(Na2O+CaO) and K/Ba) can also yield useful information regarding correlation and sedimentary history. Sr/Y decreases stratigraphically upwards in these successions and also towards the north east, suggesting a palaeogeography for the Morar Division involving increasing remoteness from the source area with time and in a northeasterly direction.
Occurrence of the ophiolitic complexes along the Indoburman orogenic belt
Authors: Duarah R. , Saikia M. M. , Bhattacharjee C. C.
Published: May 2009

The ophiolitic complexes within the Indoburman orogenic belt form a conspicuous N-S line along the eastern margins of Manipur and Nagaland. The rock assemblages consisting of mafic-ultramafics are associated with deep sea pelagic sediments of the Disang Group (Lower Cretaceous-Eocene). The ultramafics in part, represent the oceanic crust and upper mantle material that formed the basement on which the radiolarites and other pelagic sediments were deposited. The fossil radiolaria present in the cherts suggest that the orogen took its foundation during late Jurassic-Lower Cretaceous time. The westward obduction of the flysch ophiolites in the form of large thrust sheets was possible during underthrusting of the Indian plate beneath the Burmese. The position of the ophiolitic belt defines the Indoburman suture zone.
The (?) mid Triassic volcanic rocks of Lakonia, Greece
Authors: Pe-Piper G. , Panagos A. G. , Piper D. J. W. , Kotopouli C. N.
Published: May 2009

Thick subaerial volcanic sequences of probable mid Triassic age rest unconformably on Permo-Carboniferous limestones in the ‘Phyllite Series’ within the Gavrovo-Tripolitsa zone of the external Hellenide nappes. The volcanic rocks are varied in character. Pyroclastic rocks (often reddened) predominate, but minor basalt or andesite and rhyolitic hypabyssal intrusions and flows are also found. The rocks have experienced low-grade metamorphism and the only relict primary minerals are pyroxene and rare plagioclase in basic rocks and potash feldspar in acid rocks. The most important metamorphic phases are albite, chlorite, potassium mica, epidote, hematite, quartz and pumpellyite. Twenty-seven whole-rock major-element analyses suggest that there has been some exchange of Na2O and K2O for CaO during metamorphism, but that other elements have been relatively stable. A genetic interpretation of the rocks is attempted using published geochemical discriminator diagrams. The basic rocks are tholeiitic in major element chemistry and pyroxene composition. Trace element (Hf, Ta, Th, Ce, Yb) distribution suggests magma generation at a destructive plate margin.
A late Caledonian breccia dyke swarm in Glen Creran, near Glen Coe in the Grampian Highlands
Authors: Platten I. M.
Published: May 2009

A series of late Caledonian breccia dykes composed of Dalradian schist fragments are emplaced in the Leven Schists. The form and extent of the breccia dykes are described, and dilational and nondilational components identified as contributing to the space occupied by individual breccias. Fabrics and textures of the breccia material are related to transport mechanisms and later compaction. The breccias are considered to have evolved as fluidized systems.
A Miocene submarine volcano at Low Layton, Jamaica
Authors: Wadge G.
Published: May 2009

A submarine fissure eruption of Upper Miocene age produced a modest volume of alkaline basalt at Low Layton, on the north coast of Jamaica. The eruption occurred in no more than a few hundred metres of water and produced a series of hyaloclastites, pillow breccias and pillow lavas, massive lavas, and dikes with an ENE en échelon structure. The volcano lies on the trend of one of the island's major E–W strike-slip fault zones: the Dunavale Fault Zone. The K–Ar age of the eruption of 9.5 ± 0.5 Ma. B.P. corresponds to an extension of the Mid-Cayman Rise spreading centre inferred from magnetic anomalies and bathymetry of the Cayman Trough to the north and west of Jamaica. The Low Layton eruption was part of the response of the strike-slip fault systems adjacent to this spreading centre during this brief episode of tectonic readjustment.
Development of the Thames drainage system in Early and Middle Pleistocene times
Authors: Green C. P. , McGregor D. F. M. , Evans A. H.
Published: May 2009

Pre-Anglian terrace stages of the proto-Thames system are traced from the present middle Thames area into Essex and south East Anglia. Gravel composition indicates that each of the main terrace stages is associated with an influx of far-travelled material, probably signifying at least three phases of pre-Anglian glaciation in the south Midlands. Gravel composition also indicates the occurrence of major changes during Early and Middle Pleistocene times in the extent of the Thames catchment, and in the disposition of the main drainage lines. The important role of the Goring Gap in the development of the drainage system is noted, and the nature and distribution of Anglian fluvioglacial gravels are described.
The tectonic significance of Triassic dolomite and cargneule in the Gran Paradiso region, Western Alps
Authors: Vearncombe J. R.
Published: May 2009

The interrelationships of dolomite, anhydrite, gypsum and cargneule (a yellow-brown dedolomitised breccia), are discussed with specific reference to the Gran Paradiso region, Western Alps. The dolomite is a highly deformed rock which occurs along the soles of both early and late-Alpine thrusts. Evidence suggests that cargneule formed late in the geological history of the region. It is suggested that dolomite + anhydrite + water acted as an important decollement horizon. Recent exposure to the surface, hydration of anhydrite to gypsum and dedolomitisation resulted in cargneule formation.
Calcareous algae and Middle Jurassic facies of southern England
Authors: Elliott G. F.
Published: May 2009

The rarity of calcareous green algae (Order Dasycladales, and family Udoteaceae) in apparently suitable Middle Jurassic facies of southern England is summarized. They are well known from Tethyan areas to the south and opportunities for migration and establishment existed then. It is concluded that tolerance for warm but extra-tropical conditions, which exists in some but not all modern representatives of these algae, has developed gradually since Triassic time and was not well established until Cenozoic time. In Middle Jurassic time few species showed this tolerance, hence the very limited occurrences north of the Tethys.
Geochemical prospecting for Cu in Hamash area, Southeastern Desert, Egypt
Authors: Soliman M. M.
Published: May 2009

Stream sediment surveys were carried out on an area of about 200 km2 in the Hamash area. Results indicated that Cu anomalies are concentrated near the intersection of deep-seated tectonic zones and a block fault in the northeastern and southwestern parts of the district. Geophysical techniques, drilling and bedrock sampling show that the Cu mineralization is at the surface, and encrustations of secondary Cu minerals correspond mainly to sulphide-bearing quartz veins and hydrothermally altered granitic and volcanic rocks. No deposits of commercial interest have been found. Under arid conditions reconusissance survey along secondary dispersion trains proved to be a successful method of delineating small zones of Cu mineralization.
Origin of fine-grained granular rocks in layered intrusions
Authors: Thy P. , Esbensen K. H.
Published: May 2009

Extremely fine-grained granular rocks are found interleaved with cumulates in some layered differentiated intrusions. The question arises as to whether these can be interpreted as chilled magmas. If this were so it would allow the liquid line of descent to be determined directly. A study of extremely fine-grained granular rocks in the differentiated, layered basic Fongen–Hyllingen complex, Norway, however, showed rocks of this type to be cumulates. Fluctuations in volatile pressure due to crystallization of a hydrous phase may give rise to modal and grain-size variation in layered intrusions.
Interference fold patterns of the early Precambrian Rock Groups in the Songshan area, China
Authors: Suo Shutian , Liu Ruqi , Ma Xingyuan
Published: May 2009

The Songshan area is located in the southern part of the North China platform, which is one of the most completely cratonized tectonic units of China. Its basement has experienced a complex evolutionary history and was eventually consolidated at the end of early Proterozoic time about 1.7 Ga ago.

A systematic study has been made of the deformation history of the lower Proterozoic Songshan Group and the Archean Dengfeng Group. At least two widespread episodes of deformation can be recognised in the early Proterozoic Zhongyue tectonic cycle and three in the Archean Songyang cycle. Large scale and small scale interference patterns of the superimposed folding are investigated with the aim of recognizing possible regularities in their occurrence and of gaining an insight into the regional deformation history. Two important aspects of superimposition relationships are illustrated: the control of earlier structures upon later ones and the reform of the former by thelatter; their geometrical regularities are also dealt with respectively.
Smectite, zeolite, biotite and apatite in the Corallian (Oxfordian) sediments of the Baulking area in Berkshire, England
Authors: Chowdhury A. N.
Published: May 2009

Significant quantities of clinoptilolite-heulandite, lesser amounts of low tridymite-cristobalite, sparse euhedral biotite, apatite and fresh plagioclase accompany the abundant smectite in the mudrocks from the Corallian sequence in the Baulking and Uffington boreholes. The association is thought to be genetically related, of volcanic origin and formed from the in situ decomposition of volcanic ash. Smectite concentrations fluctuate, showing five maxima, but are unrelated to lithology and hence to environment. This suggests repeated ash-falls during the Corallian sedimentation in the Berkshire area. The initial volcanic episode appears to have been contemporaneous with the shoaling which initiated Corallian sedimentation in southern England, suggesting a common tectonic control.
Conodont faunas, age and correlation of the Alas Formation (Carboniferous), Sumatra
Authors: Metcalfe I.
Published: May 2009

Summary. The Alas Formation (shelf limestones) of Sumatra is reinterpreted to be of late Visean age, on the basis of conodonts and brachiopods, rather than of Permian age as previously thought. It is, therefore, the oldest dated formation in Sumatra. The Alas Formation probably underlies or is equivalent to the lower part of the Kluet Formation within the Tapanuli Group.
Orbicular rhythmic layering in the palabora carbonatite, South Africa
Authors: Moore Alan C.
Published: May 2009

The earliest stage of magmatic activity within the Palabora carbonatite was marked by the intrusion of phosphate-bearing pyroxenite. In good exposures in the north, large-scale (2m diameter) orbicular structures are found. These consist of regularly-spaced alternating dark layers (phlogopite-rich) and light layers (diopside-plus apatite-rich) which, in hand specimen, are very similar to the ‘inch-scale’ planar layering which has been described in layered mafic instrusions. One of the purposes of this paper is to describe these unique features which are currently being destroyed by mining, as they form economic phosphate concentrations.

The resemblance of the Palabora orbicules to Liesegang rings has led to the development of a qualitative model whereby the orbicules are regarded as having been formed by concentric periodic precipitation around central cores within dynamically quiet, isolated pockets of largely liquid magma. The controlling parameters are interpreted as being the rates of growth of the constituent minerals and the rates of diffusion of the elements crucial to their growth, i.e. K+, Al3+ and (OH)- for dark layers, and Ca2+ and P5+ for light layers.

The presence of these spectacular structures with their delicate layering indicates that at the time of crystallization of the pyroxenites relatively non-turbulent conditions prevailed, and diopside, phlogopite and apatite crystallized essentially coevally. Hence, the vertical large-scale banding in the pyroxenite may also be a function of diffusion controlled processes rather than being caused by separate magma pulses.
Late cretaceous quartz geodes after anhydrite from Burgos, Spain
Authors: Elorza J. J. , Rodriguez-Lazaro J.
Published: May 2009

The present work describes the quartz geodes (cauliflower-like) that appear in a specific level of the Late Cretaceous (north of Burgos). Due to their special characteristics, principally anhydrite relicts and spherulitic quartz (length-slow chalcedony), they are considered as pseudomorphs of anhydrite nodules, formed during early diagenesis. At the same level compact chert nodules sporadically appear, presenting a considerable amount of sponge spicules with fibrous texture (length-fast chalcedony). The silicification of the anhydrite nodules took place before total compaction and cementation of the sediment. The source of silica is principally biogenic (sponge spicules). We offer a hypothesis to explain the formation of the anhydrite nodules since there is no link between the depositional environment and the existence in itself of anhydrite nodules. Indirectly it is possible to see the effects of an arid climate, which have not been recorded in the lithologic column here described.