Zone Sensu Research Articles

The deformation and mechanisms of the Zhangbaling tectonic belt during Indosinian to early Yanshanian: Implications for the relationship with the Tan-Lu Fault Zone

The Zhangbaling tectonic belt is located in the middle segment of Dabie-Sulu Orogenic Belt and in the eastern part of the main segment of the Tan-Lu Fault Zone (TLFZ). Based on detailed field work and comprehensive analysis, this study discussed the tectonic evolution mechanics of the Zhangbaling tectonic belt and the Tan-Lu Fault Zone as well as the relationship between them during Indosinian to early Yanshanian period. Three stages of tectonic deformation have been determined in the period from Indosinian to early Yanshanian in Zhangbaling area, i.e., a series of WNW and nearly EW trending tight congruous nearly recumbent folds formed in the early stage; a flatly ductile shearing zone formed mainly between Beijiangjun lithofm. and Xileng lithofm. in the middle stage and the demonstrate NNE trending wide flat folds and strong thrusting or napping from NW to SE formed in the last stage. The superimposition of these three deformation stages formed the basic tectonic framework of this area. The folding and thrusting (sliding in the front margin) was developed in the mid-upper crust (include sedimentary cover) during the period of subduction and collision processes between South China Block and North China Block, shows a progress deformation of the three stages during the period of Indosinian and early Yanshannian due to the conversion of the Tethyan to the Circle Pacific Ocean tectonic regimes. The Tan-Lu Fault Zone can be divided into two big development phases since Hercynian. The first phase is a fault zone sensu lato, as a boundary of a rifted cratonic margin (or basin) that shows a wide arc-shaped along the northeastern margin of the South China Block during Indosinian. The TLFZ of this period is a collision suture between South China Block and North China Block during Indosinian period, a thrust-napping fault zone belong to the Tethyan regimes sensu lato, as well as the southeast margin of the Zhangbaling tectonic belt. This big phase corresponds to the three stages deformation activities in Zhangbaling area. The second phase is a wrench fault system usually mentioned by most researchers, which belongs to the Pacific Ocean Cycle Regime sensu stricto since early Yanshanian to Himalayan periods.

Upper Tithonian Himalayitidae Spath, 1925 (Perisphinctoidea, Ammonitina) from Le Chouet (Drôme, France): implications for the systematics

Abstract This contribution focuses on the late Tithonian ammonite faunas belonging to the Family Himalayitidae Spath in the key-section of Le Chouet (Drôme, France). The great majority of specimens from the Mediterranean Tethys, previously referred to Durangites Burckhardt, are now interpreted as juveniles and/or microconchs of the highly variable species Protacanthodiscus andreaei (Kilian). Moreover, comparison between specimens from France, Spain and Bulgaria formerly assigned to Durangites astillerensis Imlay and the type material of this species, supports the introduction of Boughdiriella chouetensis gen. nov. et sp. nov. Further, the revision of the type specimens of D. astillerensis and Durangites of the D. vulgaris group shows that the former species deserves a new generic status, for which Parrasiella gen. nov. is erected. Toucasiella, previously only known from Spain and Tunisia, is also reported for the first time from south east France. The revision of the “Mediterranean Durangites” supports the rejection of a Durangites spp. Zone as part of the standard zonation for the upper Tithonian, and its replacement by the P. andreaei Zone ( = D. vulgaris Zone sensu Sarti, 1988).

Dinoflagellate cyst biostratigraphy of Upper Cretaceous strata from two wells in the Norwegian Sea

Rich assemblages of dinoflagellate cysts from two sections in the Norwegian Sea provide a solid basis for a palynostratigraphic framework for the upper Albian to upper Maastrichtian succession in this area. The framework is based on a unique composite section combining samples from the shallow stratigraphic core 6711/4-U-1 and core-samples from well 6707/10-1, the latter filling in data from the intervals represented by hiatuses in core 6711/4-U-1. Seven previously described, and one new palynostratigraphic zone, are recognised. These are based on the relative abundances of prominent taxa together with top and base occurrences of selected age-diagnostic dinoflagellate cyst taxa. The zones and their ages in ascending order from the oldest to youngest comprise: the intra late Albian to intra early Cenomanian Subtilisphaera kalaalliti Interval Zone sensu Nøhr-Hansen (1993a); the intra early Cenomanian to intra late Cenomanian Palaeohystrichophora infusorioides–Palaeohystrichophora palaeoinfusa Interval Zone sensu Radmacher et al. (2014b); the Turonian to ?intra early Coniacian Heterosphaeridium difficile Interval Zone sensu Nøhr-Hansen (2012); the ?intra early Coniacian to late Santonian Dinopterygium alatum Interval Zone sensu Radmacher et al. (2014b); the early Campanian Palaeoglenodinium cretaceum Interval Zone sensu Radmacher et al. (2014b); the new intra Campanian Hystrichosphaeridium dowlingii–Heterosphaeridium spp. Interval Zone; the intra late Campanian Chatangiella bondarenkoi Interval Zone sensu Radmacher et al. (2014b) and the intra late Maastrichtian Wodehouseia spinata Range Zone sensu Nøhr-Hansen (1996). Comparison of the palynological events with records in adjacent regions enables correlation across similar paleolatitudes in the Northern Hemisphere.

Discovery of a microcontinent (Gulden Draak Knoll) offshore Western Australia: Implications for East Gondwana reconstructions

Analysis of dredged samples from the Gulden Draak Knoll demonstrates that it is a submarine rifted continental fragment that lies at the boundary between the western Perth Abyssal Plain and Wharton Basin, Indian Ocean. The Knoll comprises a granulite facies basement, including pelitic paragneiss and mafic orthogneiss, with a Cambrian granite inferred to intrude the other rocks. Boulders and cobbles of felsic gneiss with Mesoproterozoic and Cambrian protolith ages were also sampled likely reflecting a complex basement to variable sedimentary and volcanic rocks. The U–Pb isotopic system in the Archean and Mesoproterozoic zircon is significantly disturbed, reflecting Cambrian orogenesis that affected all samples. The protolith to garnet–sillimanite–biotite paragneiss has a maximum deposition age of 1163±24Ma and includes older detrital zircon grains with populations at c. 2.65Ga and between 1.4 and 1.1Ga. A younger population in this sample is interpreted as a mix of newly grown metamorphic zircon and isotopically reset zircon, implying that the granulite facies metamorphism occurred at c. 511±5Ma. Protracted Cambrian orogenesis is indicated by a metamorphic age in the mafic orthogneiss of 530±6Ma and isotopic disturbance shortly following emplacement of granite (c. 540Ma with zircon ages disturbed to 509±7Ma) and the protolith to the felsic orthogneiss (c. 528Ma with zircon ages disturbed to 510±3Ma). Xenocrystic zircon grains in the Cambrian rocks include Archean (c. 2839±9Ma) and Mesoproterozoic (1230–1370Ma) populations also isotopically disturbed during Cambrian orogenesis. Igneous Cambrian zircon grains have less radiogenic Hf-isotope compositions (Hfi=0.281821–0.281367) than Mesoproterozoic xenocrysts (Hfi=0.282267–0.281993), indicating limited involvement of the Mesoproterozoic crust in granite production. A more likely source includes Archean crust represented by xenocrysts with Hfi=0.281399–0.280863. The Gulden Draak Knoll is reconstructed in Gondwana (‘Leeuwin’ full-fit model) along strike of a major structure termed the Indo–Australo–Antarctic Suture (IAAS), recently mapped from geophysical interpretations in Wilkes Land, Antarctica. New isotopic data suggest that basement rocks from the Gulden Draak Knoll have affinity to crust exposed either side of the IAAS. Determining if this structure is a suture zone sensu stricto remains to be tested.

Imaging the upper mantle transition zone with a generalized Radon transform of SS precursors

We demonstrate the feasibility of using inverse scattering for high-resolution imaging of discontinuities in the upper mantle beneath oceanic regions (far from sources and receivers) using broadband wavefield observations consisting of SS and its precursors. The generalized Radon transform (GRT) that we developed for this purpose detects (in the broadband data) signals due to scattering from elasticity contrasts in Earth's mantle. Synthetic tests with realistic source–receiver distributions demonstrate that the GRT is able to detect and image deep mantle interfaces, even in the presence of noise, depth phases (‘ghosts’), phase conversions, and multiples generated by reverberation within the transition zone. As a proof of concept, we apply the GRT to ∼50,000 broadband seismograms to delineate interfaces in the depth range from 300 to 1000 km beneath the northwest Pacific. We account for smooth 3D mantle heterogeneity using first-order perturbation theory and independently obtained global tomography models. The preliminary results reveal laterally continuous (but undulating) scatter zones near 410 and 660 km depth and a weaker, broader, and more complex structure near 520 km depth. The images also suggest the presence of multiple, laterally intermittent interfaces near 350 km and between 800 and 1000 km depth, that is, above and below the transition zone sensu stricto. Filtering of the data (we consider four pass-bands: 20–50 s, 10–50 s, 5–50 s, and 2–50 s) reveals a prominent frequency dependence of the magnitude, width, and complexity of the interfaces, in particular of the scatter zone near 520 km depth; such dependencies may put important constraints on the mineralogy and phase chemistry of the transition zone.

Radiolarians from the upper Guadalupian (Middle Permian) Reef Trail Member of the Bell Canyon Formation, West Texas and their biostratigraphic implications

Moderately well-preserved radiolarians are described from two measured sections of the Reef Trail Member of the Bell Canyon Formation (Middle Permian), exposed in the Patterson Hills, Guadalupe Mountains National Park, West Texas. The Reef Trail Member is the youngest member of a series of basinal marine carbonates deposited in the Delaware basin prior to the deposition of the Castile Formation evaporites, and represents the uppermost Guadalupian (upper Capitanian). The Guadalupian-Lopingian boundary is presumed to occur at or just above the top of the Reef Trail-Castile contact because of the presence of C. postbitteri hongshuiensis ~ 2m below the top of the Reef Trail Member in sections in the Patterson Hills. A total of 30 genera containing 51 species were recovered from the Reef Trail Member, belonging to the orders Albaillellaria, Latentifistularia, Spumellaria, and Entactinaria. The following new taxa are described: Raphidociclicus scutum, Camptoalatus volaticus, Pseudoalbaillella delawarensis, Astroentactinia porosa, Stigmosphaerostylus favusa, Polyedroentactinia quadrata, Praedeflandrella firmata, P. prolata, Copicyntra spinosa, Copicyntra irregulata, and Paracopicyntra puncta, and Copicyntroides nazarovi. The following taxa are emended: Raciditor scalae (Caridroit and De Wever 1986), and Klaengspongus Sashida 2000b. Near the top of the Reef Trail Member, there are marked fluctuations in the relative abundances of albaillellarian and latentifistularian species. Fluctuations are possibly controlled by paleoenvironmental changes associated with the onset of the end-Guadalupian extinction event. Biostratigraphically, the fauna most closely correlates with the widely recognized F. bipartitus – F. charveti Zone sensu Caridroit, which we now consider to be uppermost Guadalupian, not Lopingian, and to the Guadalupian F. charveti Zone of Sun and Xia 2006 from oceanic facies in China. Both older and younger biostratigraphic markers also occur in the Reef Trail fauna, including Pseudoalbaillella longtanensis and A. yamakitai, requiring a reevaluation of the reliability of these albaillellarian taxa in biostratigraphy.

The AMMA-CATCH Gourma observatory site in Mali: Relating climatic variations to changes in vegetation, surface hydrology, fluxes and natural resources

The Gourma site in Mali is one of the three instrumented meso-scale sites deployed in West-Africa as part of the African Monsoon Multi-disciplinary Analysis (AMMA) project. Located both in the Sahelian zone sensu stricto, and in the Saharo–Sahelian transition zone, the Gourma meso-scale window is the northernmost site of the AMMA-CATCH observatory reached by the West African Monsoon. The experimental strategy includes deployment of a variety of instruments, from local to meso-scale, dedicated to monitoring and documentation of the major variables characterizing the climate forcing, and the spatio-temporal variability of surface processes and state variables such as vegetation mass, leaf area index (LAI), soil moisture and surface fluxes. This paper describes the Gourma site, its associated instrumental network and the research activities that have been carried out since 1984. In the AMMA project, emphasis is put on the relations between climate, vegetation and surface fluxes. However, the Gourma site is also important for development and validation of satellite products, mainly due to the existence of large and relatively homogeneous surfaces. The social dimension of the water resource uses and governance is also briefly analyzed, relying on field enquiry and interviews. The climate of the Gourma region is semi-arid, daytime air temperatures are always high and annual rainfall amounts exhibit strong inter-annual and seasonal variations. Measurements sites organized along a north–south transect reveal sharp gradients in surface albedo, net radiation, vegetation production, and distribution of plant functional types. However, at any point along the gradient, surface energy budget, soil moisture and vegetation growth contrast between two main types of soil surfaces and hydrologic systems. On the one hand, sandy soils with high water infiltration rates and limited run-off support almost continuous herbaceous vegetation with scattered woody plants. On the other hand, water infiltration is poor on shallow soils, and vegetation is sparse and discontinuous, with more concentrated run-off that ends in pools or low lands within structured endorheic watersheds. Land surface in the Gourma is characterized by rapid response to climate variability, strong intra-seasonal, seasonal and inter-annual variations in vegetation growth, soil moisture and energy balance. Despite the multi-decadal drought, which still persists, ponds and lakes have increased, the grass cover has largely recovered, and there are signs of increased tree cover at least in the low lands.

THE MIDDLE CAMBRIAN EODISCOID TRILOBITE DAWSONIA OELANDICA (WESTERGÅRD, 1936)

The eodiscina comprises small, isopygous trilobites with either two or three thoracic segments. Small eyes may be present, but several genera and species lack visual organs. Eodiscoids are characteristic elements of many Cambrian faunas and are important for correlations of upper Lower Cambrian and lower Middle Cambrian strata (e.g., Robison et al., 1977; Ahlberg and Bergstrom, 1993; Geyer and Shergold, 2000; Fletcher, 2003). Only five eodiscoid species are known from the Middle Cambrian of Sweden; Eodiscus scanicus (Linnarsson, 1883), E. borealis Westergard, 1946, E. punctatus (Salter, 1864), Dawsonia oelandica (Westergard, 1936), and Opsidiscus bilobatus (Westergard, 1946). The last-mentioned species is from the upper Middle Cambrian Lejopyge laevigata Zone (sensu Westergard, 1946) in Sweden, and is one of the latest known occurrences of an eodiscoid hitherto known (Rasetti, 1952). The purpose of this paper is to refine and augment the concept of the Middle Cambrian eodiscoid trilobite D. oelandica . Insufficient work has been published on the species and the most recent thorough descriptions of the genus date back to the nineteenth and early to middle twentieth century (e.g., Matthew, 1896; Westergard, 1936, 1946; Rasetti, 1952). The specimens in this study were collected on the island of Oland, southeastern Sweden, and briefly discussed by Westergard (1936, 1946), supplemented with new, well-preserved material from the province of Jamtland, central Sweden. The material discussed in this paper was collected from three localities in Sweden (Fig. 1). Five cephala (Fig. 2.1–2.12) and two pygidia (Fig. 3.1–3.6) were collected by T. Weidner from a block of dark gray limestone found at a road section near the small community of Mon (Fig. 1.1, 1.2), located c. 30 km south of Ostersund, Jamtland, central Sweden. The road section, c. 100 m long and at most c. 8 …

UPPER OLENEKIAN (SPATHIAN) AMMONOIDS FROM CHIOS (LOWER TRIASSIC, GREECE): TAXONOMY AND STRATIGRAPHIC POSITIONS

On the Greek island of Chios, Lower Triassic sections bave delivered rich ammonoid faunas from red limestones of the Hallstatt facies. Here, we present a palaeontological description of Spathian ammonoids, which have been collected during two field campaigns by Italian-German teams (Assereto et al. 1980; Gaetani et al. 1992). The ammonoid associations are composed of Ceratitida and Phylloceratida, each order containing species of the Noritaceae, Hedenstroemiaceae, Xenodiscaceae, Dinaritaceae, Pinacocerataceae, Phyllocerataceae, Ptychitaceae, Ussuritaceae and Megaphyllitaceae. Long ranging genera, e.g. Procarnites and Leiophyllites, are present as well as endemic ones, e.g. Chiotites, which occurs exclusively in the Lower Triassic of Chios. The ammonoid association is indicative of the Prohungarites-Subcolumbites zone sensu Kummel (1973a). The haugi zone, installed as uppermost Olenekian in North America, is not represented by ammonoids on Chios.

Protopteraspis Gosseleti (Vertebrata: Pteraspidomorphi: Heterostraci) from the Lower Devonian of Shropshire, England

New Protopteraspis material from Shropshire is sufficiently similar to Protopteraspis leathensis from the Welsh Borderland, and the type‐species Protopteraspis gosseleti from France, to justify transfering P. leathensis to P. gosseleti. The Anglo‐Welsh, biostratigraphic leathensis Zone is changed to the Protopteraspis Zone (sensu Blieck and Janvier 1989). Possible lifestyles are discussed for Protopteraspis gosseleti.

Les faunes d'Ammonites du Barrémien supérieur / Aptien inférieur (Bédoulien) dans la région stratotypique de Cassis-La Bédoule (SE France) : état des connaissances et propositions pour une zonation par Ammonites du Bédoulien-type

Upper Barremian/lower Aptian (Bedoulian) ammonite faunas in the stratotypic area of Cassis-La Bédoule (SE France). Present knowledge status and proposal for an Ammonite zonation of the type-Bedoulian. On the basis of recent investigations, the ammonite inventory of the upper Barremian/lower Aptian beds in the historical stratotype area of La Bédoule leads to confirm that the Bedoulian substage (and thus the Aptian stage) lower boundary is determined by the first appearance of the genus Deshayesites. The Bedoulian/Gargasian boundary is drawn at the top of the Dufrenoya furcata zone (= Dufrenoya spp./Tropaeum bowerbancki zone sensu Conte, 1994). The ammonitic content of the stratotype leads also to a subdivision which conforms better to most of the recently proposed Mediterranean zones and permits to partly correlate the standard zonation with that of the Boreal realm.

The Evolution of High-T-Low-P Granulites in the Northern Marginal Zone Sensu-Stricto, Limpopo Belt, Zimbabwe - The Case for Petrography

The Limpopo Belt of southern Africa is generally believed to represent the root of a late Archaean continental collision zone, and has been used to demonstrate the validity of the uniformitarian concept in tectonics Large scale tectonic models have been applied in spite of the fact that large portions of the belt yet await the most basic investigations. Here we report the first detailed field and petrographic study of the northernmost part of the Limpopo Belt, the Northern Marginal Zone sensu stricto (NMZ s.s) and conclude, on the basis of relative age relation, nature of PT evolution and deformation, that none of the current models can correctly explain the evolution of the study area. The evolution of NMZ s.s, is complex and includes four metamorphic stages, two major plutonic episodes and at least three deformation events. The oldest rocks, mafic granulites, record all four stages of metamorphic mineral growth. The first two stages predate deposition of sediments and the intrusion of voluminous enderbite and charnockite between 2.72 and 2.62 Ga. The bulk of our observations relate to the late Archaean (stage 3) granulite facies event. Abundant reaction textures are preserved in mafic granulite, metasediments, metamorphosed charnockite and enderbite and allow us to qualitatively reconstruct the PT evolution. Prograde heating occurred in the sillimanite stability held. During peak temperature conditions vapour-absent melting is observed in most felsic lithologies,Temperatures between 800 and 850 degrees C at pressures as low as 0.4-0.5 GPa are indicated by various mineral assemblages. The thermal peak was followed by an increase in pressure. Typical reactions of anti-clockwise PT evolution, like breakdown of cordierite + spinel to sapphirine and orthopyroxene + plagioclase to garnet + quartz, are frequently found. Maximum pressure is constraint to ca. 0.85 GPa by the complete absence of garnet in mafic granulites. Initial cooling was rapid, and is indicated by the back reaction of melt + orthopyroxene to biotite + quartz symplectites preserved in migmatites. This metamorphic event was accompanied by intrusion of porphyritic charnockite and granite, and by coeval compressional deformation. The observed evolution, especially the combination of an anti-clockwise PT loop and compressional tectonics, requires a strong, transient heat-source affecting the base of the crust. Neither the thermal evolution nor the relative timing is correctly predicted by existing collision models. The NMZ s.s. granulites were finally exhumed in a separate event along upper greenschist-facies thrusts, in response to a transpressive orogeny affecting the units further south at 2.0 Ga. In spite of potential ambiguities inherent to a qualitative approach, our observations show that petrography and field work, if used in conjunction with dating of a few key age relations and structural interpretation, are a pre-requisite to the erection of realistic tectonic models. The example of the NMZ s.s. may encourage geoscientists with limited access to analytical facilities to reassess the geological evolution of terrains which lack basic description.

A revision of the classical Aalenian succession in the Middle Jurassic of San Vigilio, Lake Garda, Northern Italy

The outcrops around Capo San Vigilio include the type horizons of many Aalenian ammonite species created by Benecke (1865) and Vacek (1886), important in interregional and interbioprovincial correlations. Their biostratigraphy at the type locality remains however highly uncertain. A reinvestigation has begun, based on three sources of information: (a) detailed lithostratigraphy at Capitello quarry and on Monte Pomo; (b) new collections made in situ; and (c) a careful re-examination of the types in the Vacek collection in Vienna. All the ammonites came from an interval 0.9 m thick, divisible into four units (the Scissum Bed, 2a-d) at the top of the San Vigilio Oolite, and a fifth (3) at the base of the overlying “Calcari a Skirroceras” in the Rosso Ammonitico Veronese. Three faunal horizons can sofar be distinguished: 2b, topmost Lower Aalenian (with Leioceras comptum and Erycites fallifax)), upper Scissum Zone sensu anglico; 2d, lowest Middle Aalenian (with Ancolioceras opalinoides)), basal Murchisonae Zone; and 3, condensed, the source of the majority of Vacek's species, ranging from middle Murchisonae Zone to Concavum Zone, near the top of the Aalenian, but no higher. A closer time-resolution within this interval should be attainable but will need detailed taphonomic analysis and further collecting. The faunal horizons of many of Vacek's species are listed, as deduced from the lithologies of his types and from newly collected topotypes.

Geodynamic evolution of Korea: A view

Abstract Evidence for South Korean Palaeozoic geodynamic evolution is restricted to the Ogcheon Belt, which is a complex polycyclic domain forming the boundary between the Precambrian Gyeonggi Block to the northwest and the Ryeongnam Block to the southeast. Two independent sub-zones can be distinguished: the Taebaeksan Zone to the northeast and the Ogcheon Zone sensu stricto. The Taebaeksan Zone and Ryeongnam Block display characteristic features of the North China palaeocontinent. This domain remained relatively stable during the Palaeozoic. In contrast, the Ogcheon Belt s. s. is a highly mobile zone that belongs to the South China palaeocontinent and corresponds to a rift that opened during the Early Palaeozoic. In lowermost Devonian times, the rift basin was closed and the Ogcheon Belt was structured in a pile of nappes. From the lack of suture in the Ogcheon Belt it can be inferred that the Gyeonggi Block belongs to the South China palaeocontinent. Thus, the boundary between the North China and South China blocks should be located to the north of Gyeonggi Block, that is, in the Palaeozoic Imjingang Belt. From the Middle Carboniferous, sedimentation started again on a weakly subsiding paralic platform located in the hinterland of the Late Palaeozoic orogen of southwest Japan. In the Late Carboniferous, increasing subsidence recorded extensional tectonics related to the opening of the Yakuno Oceanic Basin (southwest Japan). In the Middle Permian, the end of marine influences in the platform and emplacement of terrestrial coal measures, may be correlated with the closure of the oceanic area and subsequent ophiolite obduction. In Late Permian to Early Triassic times, the Honshu Block (the eastern palaeomargin of the Yakuno Basin) collided with Sino-Korea. Post-collisional intracontinental tectonics reached the Ogcheon Belt in the Middle Triassic (Songnim tectonism). Ductile dextral shear zones associated with synkinematic granitoids were emplaced in the southwest of the belt. In the Upper Triassic, the late stages of the intracontinental transcurrent tectonics generated narrow intramontane troughs (Daedong Supergroup). The Daedong basins were deformed during two tectonic events, in the Middle (?) and Late Jurassic. The Upper Jurassic to Lower Cretaceous basins (Gyeongsang Supergroup), that are controlled by left-lateral faults, may have resulted from the same tectonic event.

Auriferous mineralization in some shear-zones: A three-stage model of metallogenesis

Studies of numerous shear zones hosting auriferous quartz veins suggest a three-stage model of formation for such veins. These stages are indicative of the progressive increase of the gold concentration with the evolution of the shear zone and comprise an early stage with “invisible” gold, an intermediate stage with finegrained gold, and a late stage with gold nuggets. The early stage, consisting of two consecutive episodes, comprises the development of the shear zone sensu stricto which results in the formation of a structure characterized by mylonite. This structure subsequently acts as a drain for hydrothermal fluids. Under the combined action of deformation and hydrothermal circulation, the rocks in this structure undergo mineralogical transformations that depend on the initial composition of the rock. These phenomena occur with increasing intensity towards the cores of the structures, the sites of substantial silicification and sulfidation. Gold is first fixed in the crystal lattice of pyrrhotite (up to 30 ppm of gold), disseminated throughout the structure as a whole. In the core, it is destabilized to pyrite-marcasite during the second episode of this early stage and the gold thus freed is trapped in the lattice of locally abundant ferriferous sulfides: pyrite, arsenopyrite (up to 1.6 wt% gold), and berthierite. At the intermediate stage, again consisting of two consecutive episodes, the shear zone can generate openings, allowing the emplacement of lenses and veins of milky white quartz. When these various veins are in turn crushed by continuing tectonic activity, microsaccharoidal quartz forms by cataclasis, and acts as a “receptacle” for the gold mineralization. Therefore textbook “auriferous quartz veins” are only one particular aspect of this stage, characterized by the appearance of visible native gold caused by destabilization of the auriferous sulfides of the early stage. This gold is generally very fine-grained (several micrometres) and relatively silverfree. The late stage, i.e. the fifth episode, in a brittle domain, can occur within a structure of the early or intermediate stage. It corresponds to a stage of opening, during which stockworks of quartz or of quartz and carbonate form, causing in situ remobilization of the auriferous mineralization from the earlier stages. This phenomenon is accompanied by the appearance of gold nuggets several millimetres in size, very often rich in silver (electrum).

High-pressure metamorphism in metabasites from the Betic Cordilleras (S.E. Spain) and its evolution during the Alpine orogeny

The Nevado-Filabride complex is the lowest tectonic unit of the Betic Zone sensu stricto (ss) of the Betic Cordilleras (S.E. Spain). The upper series of this complex consists of a metamorphosed sequence intruded by basic and ultrabasic igneous rocks. High-pressure metamorphism in the eclogite and blueschist facies is recorded in the metabasites, but this was partially obliterated by further successive metamorphic stages in the almandine-amphibolite and greenschist facies.

Foraminifera of a Joli Fou Shale equivalent in the Lower Cretaceous (Albian) Hasler Formation, northeastern British Columbia

The discovery of the arenaceous foraminifer Haplophragmoides gigas Cushman in the Hudson Hope area of northeastern British Columbia indicates that the Early Cretaceous (Albian) Joli Fou Sea flooded around the north side of the Peace River Arch, making an embayment that penetrated as far west as the Rocky Mountain Foothills. The microfauna of 25 genera and 46 species of arenaceous foraminifers is illustrated carrying Bathysiphon spp., Hippocrepina sp., Hyperammina spp., Lituotuba? sp., Psammosphaera spp., Reophax spp., Ammodiscus spp., Glomospira sp., Miliammina spp., Psamminopelta spp., Trochamminoides sp., Haplophragmoides spp., Ammomarginulina sp., Ammobaculites spp., Haplophragmium spp., Trochammina spp., Textulariopsis sp., Pseudobolivina spp., Plectorecurvoides sp., Verneuilina sp., Gaudryina sp., Uvigerinammina sp., Gravellina sp., and Eggerella sp.The suite occurs in the lower part of the Hasler Shale of the Fort St. John Group about 10–20 m above beds carrying a microfauna of the Ammobaculites wenonahae Subzone (= Stelckiceras liardense ammonite Zone) present in the basal portion of the Hasler Shale. The Haplophragmoides gigas Zone sensu stricto is overlain by a sequence of silty beds (Viking equivalent?), which in turn is succeeded by the Miliammina manitobensis Zone microfauna. The H. gigas assemblage has both boreal and southern aspects, suggesting a mixing of the waters from north and south as the first expression of the Colorado Sea in earliest late Albian time. The assemblage is a deep neritic one and lacks any calcareous component. Diagnostic megafauna are lacking.

Distribution of the marine littoral Foraminifera in Argentina, Uruguay and Southern Brazil

Benthic foraminifers collected in the marine littoral zone (sensu lato) of Argentina, Uruguay and Southern Brazil have been studied and compared with the Foraminifera collections from the same area studied previously. Two figures have been prepared, which show the geographical range and relative abundance of the most important species (cosmopolitan and non-cosmopolitan). The following biogeographical conclusions were drawn on the basis of an analysis of these figures. The whole area, from a latitude of about 32° S up to the southern coast of Tierra del Fuego, should be considered as one biogeographical unit (a “kingdom” of Buccella peruviana, sensu lato). This unit has 2 internal boundaries, which are located approximately at latitudes 41° and 52° S. They divide the whole area into 3 sub-areas which can be called (from North to South): North Patagonian (32° to 41° S), South Patagonian (41° to 52° S) and Malvinian (52° S—southern coast of Tierra del Fuego). With the exception of Buccella peruviana, sensu lato, which is typical of all 3 sub-areas, these sub-areas are characterized by the following faunal features. The North Patagonian sub-area contains abundant numbers of Elphidium discoidale. The South Patagonian sub-area is characterized by abundant numbers of Elphidium macellum. The Malvinian sub-area contains abundant numbers of Elphidium macellum, and also several very typical representatives of the Malvin current water, for instance, Cassidulina crassa, sensu stricto, Angulogerina angulosa, Uvigerina bifurcata, Cassidulinoides parkerianus, Ehrenbergina pupa and others. It is a matter of opinion whether the sub-areas cited be considered biogeographical sub-provinces, or even smaller units. They cannot be interpreted as biogeographical provinces.