Plant fossils are described from the Cuche Formation, Eastern Cordillera, Colombia in the area of Floresta. Those identified as Colpodexylon cf. deatsii Banks and cf. Archaeopteris sp. suggest an earliest Late Devonian (Frasnian) age for the formation. These or similar taxa are also found in contemporaneous deposits in western Venezuela, and other elements of the Venezuelan flora are found in a geographically intermediate locality. All three Devonian plant localities in the northwest of South America are within the Colombian Eastern Cordillera and its northern extension, the Venezuelan Perijá Range, an area that has been integrated as a part of the so-called ‘Eastern Andean Terrane’ or ‘Central Andean Province’, supposedly accreted to the autochthonous block of the Guyana Shield during the early Jurassic or before. Although both invertebrates and plants from this terrane have strong affinities to North American and European assemblages, and might be interpreted as implying a Laurussian origin for the Eastern Andean Terrane, the evidence is not yet unequivocal, with some authors postulating an in situ development of this province.

The Neogene extensional province of southern Tuscany in central Italy provides an outstanding example of fossil and active structurally controlled fluid flow and epithermal ore mineralization associated with post-orogenic silicic magmatism. Characterization of the hydrodynamic regime leading to the genesis of the polysulphide deposit (known as Filone di Boccheggiano) hosted within the damage zone of the Boccheggiano Fault is a key target to assess modes of fossil hydrothermal fluid circulation in the region and, more generally, to provide inferences on fault-controlled hydrothermal fluid flow in extensional settings. We provide a detailed description of the fault zone architecture and alteration/mineralization associated with the Boccheggiano ore deposit and report the results of fluid inclusion and stable oxygen isotope studies. This investigation shows that the Boccheggiano ore consists of an adularia/illite-type epithermal deposit and that sulphide ore deposition was controlled by channelling of hydrothermal fluids of dominantly meteoric origin within the highly anisotropic permeability structure of the Boccheggiano Fault. The low permeability structure of the fault core compartmentalized the fluid outflow preventing substantial cross-fault flow, with focused fluid flow occurring at the hangingwall of the fault controlled by fracture permeability. Fluid inclusion characteristics indicate that ore minerals were deposited between 280° and 350°C in the upper levels of the brittle extending crust (lithostatic pressure in the order of 0.1 GPa). Abundant vapour-rich inclusions in ore-stage quartz are consistent with fluid immiscibility and boiling, and quartz ore vein textures suggest that mineralization in the Boccheggiano ore deposit occurred during cyclic fluid flow in a deformation regime regulated by transient and fluctuating fluid pressure conditions. Results from this study (i) predict a strongly anisotropic permeability structure of the fault damage zone during crustal extension, and (ii) indicate the rate of secondary (structural) permeability creation and maintenance by active deformation in the hangingwall of extensional faults as the major factor leading to effective hydraulic transmissivity in extensional terranes. These features intimately link ore-grade mineralization in extensional settings to telescoping of hydrothermal flow along the hangingwall block(s) of major extensional fault zones.

A newly investigated travertine deposit in southern Tibet provides a window into Holocene hydrological, geomorphic and climatic processes near the boundary of the Tibetan Plateau and High Himalaya. Travertine, deposited as a result of the degassing of CO2-rich groundwater as it emerges on the Earth's surface, is in many cases formed along the trace of major crustal-scale faults in primarily extensional tectonic regimes. A travertine platform measuring roughly 1 km by 0.5 km exists near the town of Nyalam in southern Tibet along a major Himalayan down-to-the-N normal fault, the South Tibetan Fault System. A wide variety of travertine depositional textures and features are recorded in the platform on a series of terraces. Active travertine deposition was observed from spring mounds and seeps along the base of the platform at the modern river level. Palaeotemperatures of spring water, calculated from δ18O of the travertine, range from 9 to 25 °C, which closely matches the temperatures recorded from modern springs in the area. A complex geomorphological landscape records interaction between growing alluvial fans, travertine accumulation, and a rapidly down-cutting river with associated fluvial terraces. River incision was contemporaneous with travertine deposition, as indicated by cemented fluvial river gravel layers interbedded with travertine. High 87Sr/86Sr ratios in the travertine (mean of 0.7168) indicate subsurface fluid interaction with radiogenic crystalline rocks of the underlying Greater Himalaya. Uranium-series ages of the travertine platform range from 5400 a (±950 a) to 11600 a (±1000 a), and indicate a younging progression from higher terraces near the valley wall to lower terraces at present-day river level. Travertine that overlies a river gravel terrace 18 m above river level formed at 11600 a. This date yields a local incision rate of 1.6 mm a−1, consistent with estimated fluvial incision rates in the High Himalaya. The range of our U-series ages coincides with an interval of higher precipitation associated with greater intensity of the Indian monsoon, which led to elevated spring discharge and carbonate precipitation in this part of the High Himalayas.

New geological mapping has revealed further details of the tectonic and stratigraphic effects of Devonian and later reactivations of the Billefjorden Fault Zone, one of a number of important north—south trending lineaments in Svalbard. Analysis of offsets along the many steeply-dipping faults within the zone, and effects on the subsidence and deformation of the adjacent crustal blocks, is presented as a series of tectonic maps from the Late Devonian through to the Tertiary. Late Devonian sinistral transpression, suggested previously, cannot be ruled out, and Carboniferous reactivation was dominated by extension, with possibly a slight dextral strike-slip component. After Late Carboniferous to Early Cretaceous platform subsidence, during which the fault zone had little effect on sedimentation, development of the Tertiary West Spitsbergen Fold Belt (related to the opening of the Arctic Ocean) involved compressive (and transpressive?) reactivation of basement-seated structures further east, including the Billefjorden Fault Zone. In the Billefjorden—Austfjorden area this produced a large monoclinal fold across the fault zone, which was later cross-cut by extensional structures to produce the present day Billefjorden syncline. This localized late extension is related to a slight variation in the trend of the Billefjorden Fault Zone through this area.

ONE of the objectives of the East African Archaeological Expedition of 1934–5 was the examination of the plateau north of Lake Eyasi—the Vogel River area—where, it was hoped, a continuation of the richly fossiliferous Oldowaya Middle Pleistocene lake beds would be found. This hope was essentially realized ; deposits with an interesting Middle Pleistocene fauna a little earlier than that of Oldoway were found, with the difference that they were entirely terrestrial. The development of precisely datable beds resting upon a main Rift Valley Scarp made possible a study of physiographical changes associated with the faulting.

Recent finds of tetrapod ichnites in the red-bed and volcaniclastic succession of the Iberian Pyrenean Basin permits an assessment of the faunal diversity and palaeoenvironment of a late early Permian setting. The tetrapod ichnoassemblage is inferred with the aid of photogrammetry and constituted by Batrachichnus salamandroides, Limnopus isp., cf. Amphisauropus (these three ichnotaxa present associated swimming traces, assigned to Characichnos), cf. Ichniotherium, Dromopus isp., cf. Varanopus, Hyloidichnus isp. and Dimetropus leisnerianus. These ichnotaxa suggest the presence of temnospondyls, seymouriamorphs, diadectomorphs, araeoscelids, captorhinids and synapsid pelycosaurs as potential trackmakers. These faunas correlate to the late early Permian. Two ichnoassociations correspond to two different palaeoenvironments that were permanently or occasionally aquatic (meandering fluvial systems and unconfined runoff surfaces, respectively). Ichnotaxa in the fluvial system is more diverse and abundant than in the runoff surfaces system. The Iberian Pyrenean ichnoassemblage reveals the faunistic connection and similarities among nearing basins (Spain, southern France and Morocco) differing from the Central European basins (i.e. German Tambach Formation). Based on the palaeogeography and the climate models of the early Permian, we suggest the correlation of ichnofaunal composition with different palaeoclimate biomes. This results in a diffuse boundary of Gondwana–Laurasia land masses, indicating no geographic barriers but a possible climate control on the faunal distribution. Further studies, integrating data from distant tracksites, should refine these biome boundaries.

Arrested-type charnockite formation occurs in an assemblage of high-grade gneisses at several localities of the Chilka Lake area that belongs to the Proterozoic Eastern Ghats Belt of India. The isolated ellipsoidal domains are found exclusively in leucogranite (leptynite) bands that intruded lit-par- lit interbanded granulite-grade supracrustal and intermediate igneous rocks (khondalite–enderbite). Macrostructures and microfabrics document a multiple deformation of the rock assemblage under high-grade conditions. The intrusion of the leucogranitic melts separates a first episode of deformation, D1, from a younger progressive deformation, D2–D4. A transpressive regime and inhomogeneous deformation is indicated for D2–D4 by the associated structures and fabrics. But quartz c-axis patterns show that pure shear prevailed during the closing stages of deformation. The spatial distribution and orientation of the ellipsoidal charnockite domains within the host leptynite and the orientation pattern of orthopyroxene c-axes inside the domains provide evidence for a synkinematic in situ formation of the domains during D3, through partial breakdown of the leptynite assemblage (Bt+Grt+Qtz+Fl1[rlhar ]Opx+Fsp+Ilm+Fl2/L). Local fluid migration along steep foliation planes associated with large-scale D3 folds triggered the reaction. Orthopyroxene blastesis was confined to the centre of the domains, and an envelope formed in which the residing fluid caused secondary intergranular formation of chlorite, ore and carbonate, imparting the domains' typical greenish-brown charnockite colour. The shape of the envelope, which varies from prolate in limbs to oblate in hinges of D3 folds, is responsive to the local stress field. Comparison of chemical rock compositions supports the in situ formation of charnockite in leptynite. Subtle compositional differences are controlled by the changing mineralogy. Compared to the host leptynite, the charnockite domains are enriched in K2O, Ba, Rb and Sr, but depleted in FeO*, MnO, Y and Zr. The data obtained in this study provide conclusive evidence that the ellipsoidal charnockite domains do not represent remnants of stretched enderbite layers as proposed by Bhattacharya, Sen & Acharyya, but formed in situ in the leptynite as a result of localized synkinematic fluid migration late in the deformation history.

New data implying crustal activation of Eastern Avalonia along the Anglo-Brabant fold belt are presented. Late Ordovician subduction-related magmatism in East Anglia and the Brabant Massif, coupled with accelerated subsidence in the Anglia Basin and in the Brabant Massif during Silurian time, indicate a foreland basin development. Final collision resulted in folding, cleavage development and thrusting during the mid-Lochkovian to mid-Eifelian. In the southeast of the Anglo-Brabant fold belt, Acadian deformation produced basin inversion and the regional antiformal structure of the Brabant Massif. The uplift, inferred from the sedimentology, petrography and reworked palynomorphs in the Lower Devonian of the Dinant Synclinorium is confirmed by illite crystallinity studies. The tectonic model discussed implies the presence of two subduction zones in the eastern part of Eastern Avalonia, one along the Anglo-Brabant fold belt and another under the North Sea in the prolongation of the North German–Polish Caledonides.

A description is given of a nearly complete specimen of a new Ordovician eurypterid genus belonging to the family Stylonuridae. The classification of the Eurypterida is discussed; two super-families and two new families are proposed and three new names substituted for pre-occupied generic names.

Since writing the letter quoted in the foregoing communication by my friend Prof. Liversidge, I have had the opportunity of examining a larger fragment of the calcareous rock to which it refers, and am thereby enabled to add somewhat, not merely to the list of Foraminifera which it contains, but also to the general conclusions to be drawn from it. The lithological characters of the rock are, as Prof. Liversidge has stated, precisely those of many specimens of white chalk, but it is seldom that a Cretaceous mineral is so entirely composed of the recognizable remains of microzoa, and it is still more rarely that a geological deposit occurs, for which so exact a counterpart in process of formation can be indicated. Under these circumstances some further remarks on the subject may not be without interest.

The subsidence history of the Aquitaine basin has been determined from deep exploratory well data. The contribution of sediment loading to the subsidence has been evaluated and removed, including corrections for effects of compaction, water depth and changes of sea-level but not of flexural rigidity of the lithosphere. The tectonic subsidence curves obtained indicate that the basin underwent two periods of subsidence acceleration in the Trias–Early Lias and Late Jurassic–Early Cretaceous. They are interpreted in relation to the displacements of Iberia with respect to Europe as two periods of extension followed by periods of passive subsidence due to conductive cooling of the lithosphere; the formation of the ‘flysch trough’ in the southern part of the basin is then discussed.

Geochemical and Sr–Nd–Pb isotopic data are presented for volcanic rocks from Zougouyouchaco (30.5 Ma) and Dogai Coring (39.7 Ma) of the southern and middle Qiangtang block in northern Tibet. The volcanic rocks are high-K calc-alkaline trachyandesites and dacites, with SiO2 contents ranging from 58.5 to 67.1 wt % The rocks are enriched in light REE (LREE) and contain high Sr (649 to 986 ppm) and relatively low Yb (0.8 to 1.2 ppm) and Y (9.5 to 16.6 ppm) contents, resulting in high La/Yb (29–58) and Sr/Y (43–92) ratios, as well as relatively high MgO contents and Mg no., similar to the compositions of adakites formed by slab melting in subduction zones. However, the adakitic rocks in the Qiangtang block are characterized by relatively low εNd(t) values (−3.8 to −5.0) and highly radiogenic Sr ((87Sr/86Sr)i=0.706–0.708), which are inconsistent with an origin by slab melting. The geochemistry and tectonics indicate that the adakitic volcanic rocks were most likely derived from partial melting of delaminated lower continental crust. As the pristine adakitic melts rose, they interacted with the surrounding mantle peridotite, elevating their MgO values and Mg numbers.

The earliest nematophorid (planktic) dendroid graptolites (Family Anisograptidae) are described and revised from several heterofacial facies sections of the Broom Point Formation, Cow Head Group, western Newfoundland (Broom Point North and St Paul's represent medial to upper continental slope, Martin Point and Green Point distal slope environments). Noting potential conodont recycling in the palaeoslope environments of the proximal Cow Head Group sections, graptolites are the only group of fossils that could not have been subject to post-burial transport. The graptolites belong to an informal group of quadriradiate form-species principally representing two originally related but then diverging phyletic groups: pendent Rhabdinopora Eichwald, 1855 and horizontal to sub-horizontal Staurograptus Emmons, 1855; both being stratigraphically within Assemblage Zone I (emended after Cooper, 1979) of earliest Tremadoc or early Ibexian age (top of Cordylodus intermedius to base of C. lindstromi conodont zones). Assemblage I graptolites offer a higher resolution than coeval conodonts and are a better tool for inter-facies correlations both within the Broom Point Formation and with other graptolitic sequences on a global scale. Form-species of quadriradiate Rhabdinopora rustica (such as ?R. praeparabola and R. parabola) and of Staurograptus dichotomus (e.g. ‘Radiograptus’ or ‘Heterograptus’ flexibilis or ‘Aletograptus’) are interpreted as astogenetic morphs, or as phylogenetically descendant variants of these forms. Upon evidence of late astogenetic insertion of dissepiments in Staurograptus and Anisograptus the names ‘Heterograptus’ and ‘Radiograptus’ are placed into junior synonymy, and ‘Aletograptus’ is regarded a junior synonym of Staurograptus because its post-primary dichotomies are merely delayed distally (or omitted) to be observed exclusively in very mature specimens. The Cow Head Group fauna is compared with earliest nematophorids from Oslo, Norway (Naersnes) and Dayangcha, Jilin, China (Xiaoyangqiao), and a new comprehensive ecostratigraphic zonation for early Tremadoc graptolites is proposed.

Details of the Infra-Cambrian Polarisbreen Series are given, arising partly out of observations made since they were defined in outline by the authors in 1956. The Polarisbreen Series includes the distinctive Polarisbreen Tillite Formation, which correlated with the neighbouring Sveanor Formation of Nordaustlandet and with other tillites in Vestspitsbergen. They are regarded as a product of the great infra-Cambrian ice age and are correlated with world-wide tillite horizons of this age.

The SW–NE-striking Porongos belt, located between juvenile Neoproterozoic rocks in the west and the Dom Feliciano belt, characterized by intense reworking of older crust, in the east, comprises a greenschist to amphibolite-facies metavolcano-metasedimentary succession (Porongos sequence) of unknown age with some exposures of Palaeoproterozoic gneisses (Encantadas gneisses). High-temperature ductile deformation of the basement gneisses comprises at least two magmatic events followed by three deformational phases including folding and shearing (DT1–DT3) and can be attributed to the Palaeoproterozoic Trans-Amazonian orogeny. The deformation of the Porongos sequence occurred during the Neoproterozoic Brasiliano orogeny and comprises four ductile deformation phases (DB1–DB4), including two phases of isoclinal folding associated with shearing recorded in mylonitic layers, followed by closed NW-vergent folding and thrusting leading to formation of a thrust stack. Uplift of the basement and formation of late tectonic sedimentary basins occurred as a result of semi-ductile to brittle block faulting in a sinistral strike-slip regime. The Porongos sequence can be subdivided into a southeastern and a northwestern part. Trace element analyses as well as Sm–Nd and Rb–Sr geochemical data indicate partial melting and significant contamination by old continental crust for the metavolcanic rocks. The metavolcanic rocks show εNd(t=780 Ma) values of −20.64 and −21.72 (northwestern units) and −6.87 (southeastern sequence). The metasedimentary rocks were derived from late Palaeoproterozoic to Archaean sources, and the data indicate different sources for the northwestern and southeastern rock units of the Porongos sequence. εNd(t=780 Ma) are −6.25 and −6.85 in the southeastern units, with TDM model ages between 1734 and 1954 Ma, and vary between −14.72 and −17.96 in the northwestern parts, which have TDM model ages between 2346 and 2710 Ma. High 87Sr/86Sr(t) values between 0.7064 and 0.7286 confirm reworking of older crust. Isotopic signatures of the Porongos sequence do not show indications for a significant contribution from a Neoproterozoic juvenile source. A passive margin or continental rift environment is suggested for the tectonic setting of the Porongos belt, which is compatible with both deposition of shallow marine to deep marine sediments and stretching of continental crust leading to volcanism which is characterized by significant contamination by old continental crust.

A conodont-graptolite biostratigraphic study was carried out on the top strata of the San Juan, Las Chacritas and Las Aguaditas formations in the La Trampa Range, Precordillera of San Juan in western Argentina. Significant conodont records in the San Juan and Las Chacritas formations allow for the recognition of the Yangtzeplacognathus crassus, Eoplacognathus pseudoplanus (Microzarkodina hagetiana and M. ozarkodella subzones) and Eoplacognathus suecicus zones of Darriwilian age. Index species and co-occurrences of graptolites and conodonts were recorded in the Las Aguaditas Formation allowing the identification of the Nemagraptus gracilis and the Pygodus anserinus zones, which represent the Sandbian Stage. These data indicate a hiatus between the Las Chacritas and the Las Aguaditas formations, corresponding to the Pygodus serra Zone and the Pterograptus elegans and Hustedograptus teretiusculus zones (upper Darriwilian). A total of 7287 identifiable conodont elements were recorded from the study section. The species frequency registered for each zone shows that Periodon and Paroistodus are the most abundant taxa, which are indicative of open marine environments. The records of particular conodont taxa, such as Histiodella, Periodon, Microzarkodina, Eoplacognathus and Baltoniodus, allow a precise global correlation with other regions such as south-central China, Baltoscandia, North America, Great Britain, Southern Australia and New Zealand. The graptolite fauna identified here are recognized worldwide in equivalent strata in the Baltic region, Great Britain, North America, China, southern Australia and New Zealand. The presence of graptolites in the ribbon limestones of the Las Chacritas Formation is documented for the first time.

A 425 ka long record from piston core GIK17925-3 taken in the northeastern South China Sea was used to study the environmental conditions controlling the distribution of the Zoophycos trace fossil. The 12 m long core offers a unique opportunity to study the response of the Zoophycos-producing animal to environmental variations over four glacial–interglacial cycles. The trace fossils show a strong glacial to interglacial variation in their abundance with a special preference for intervals with low sedimentation rates. Additional X-ray radiograph studies of piston cores from the Southeast Asian Marginal Seas show that the trace fossil Zoophycos is widespread in slope and deep-marine sediments, with the highest abundances encountered in low sedimentation rate settings. The preference of the Zoophycos producer for low sedimentation rates in a setting with strong seasonal fluctuations in food supply due to the shift between winter and summer monsoons, is interpreted to be the result of a cache-model behaviour, where food is collected during rich times and squirrelled away for poor times. Core GIK17925-3 also offers an opportunity to assess the impact of Zoophycos bioturbation on various palaeoenvironmental proxies. In this core, more than 30 % of the measured data points were more or less strongly affected by Zoophycos bioturbation. Together with the widespread occurrence this percentage indicates that Zoophycos may pose a serious threat to palaeoclimatic reconstructions in cores from low to moderate sedimentation rate sites.

The Lake Ambrose volcanic belt (LAVB) outcrops as a 45 km long northeast-trending belt of mafic and felsic volcanic rocks along the eastern side of the Victoria Lake Group in south-central Newfoundland. It comprises roughly equal proportions of mafic pillow basalt and high silica rhyolite, locally interbedded with epiclastic turbidites. Volcanic rocks have been metamorphosed in the greenschist facies and are extensively carbonatized.

U-Pb (zircon) dates from rhyolite at two, widely separated localities give identical ages of 513 ± 2 Ma (Upper Cambrian), and this is interpreted as the eruptive age of the volcanic sequence. Primitive arc and low-K tholeiites can be recognized on the basis of major and trace element geochemistry, ranging from LREE-depleted to LREE-enriched. Geochemical variation between mafic volcanic types is interpreted predominantly to reflect contrasts in source characteristics and degree of partial melting; some variation within each geochemical type attributable to fractional crystallization can be recognized. Detailed examination of some samples indicates that the heavy REE and related elements have locally been mobile, probably as a result of carbonate complexing.

The LAVB is the oldest well-dated island arc sequence in Newfoundland, and perhaps in the Appalachian–Caledonian Orogen. Its age requires modification of widely held models for the tectonic history of central Newfoundland. It is older than the oldest known ophiolite, demonstrating that arc volcanism was extant before the generation of the oldest known oceanic crust in this part of Iapetus. It further demonstrates that there was a maximum of approximately 30 Ma between the rift-drift transition which initiated Iapetus, and the initiation of subduction. This suggests that the oceanic sequences preserved in Newfoundland represent a series of arcs and back arc basins marginal to the main Iapetus Ocean, and brings into question whether the Appalachian accreted terranes contain any remnants of normal mid-ocean ridge type Iapetan crust.

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.

The Trans-European Suture Zone (TESZ) is the boundary between ancient Precambrian lithosphere of the East European Craton (EEC) and the younger lithosphere beneath the latest Neoproterozoic–Palaeozoic mobile belts of western Europe. The former is characterized by a thick crust (c. 45 km), low heat flow and a tectono-thermal age of about 3000 to 800 Ma, the latter by a thinner crust (c. 30 km), higher heat flow and a tectonothermal age of 560 to 290 Ma. These contrasting types of crust were juxtaposed during the Caledonian and Variscan orogenic episodes. The crystalline basement of the TESZ is largely concealed by sedimentary basins controlled by the reactivation of structures within the suture zone during Permian–Mesozoic extension and Cenozoic inversion. The pre-Permian evolution of the craton and the mobile belts, and the location of the sutures, is inferred from isolated outcrops, hundreds of boreholes and geophysical evidence. Existing seismic data demonstrates that the TESZ is rather narrow and has an expression at all levels of the lithosphere and deep into the asthenosphere. Teleseismic studies have demonstrated that the differences in the velocity structure of the asthenospheric and lithospheric mantle across the TESZ persist to depths of c. 400 km (Zielhus & Nolet, 1994).