Marine carbonate reservoirs, as a focus of petroleum exploration and development in China, are involved with high exploration risk and prediction difficulty owing to high heterogeneity and diversity of reservoir beds. In the Tarim Basin, NW China, carbonate reservoirs host about 38% of the whole basin's hydrocarbon resources in a large prospecting area mainly distributed in the Cambrian and Ordovician rocks in central (Tazhong) and northern (Tabei) Tarim. Recently, a better understanding has been made of the karsted weathering crust at the top of the Lower Ordovician Yingshan Formation in the northern slope area of the Tazhong Low Rise, Central Uplift, Tarim Basin. As a new frontier of exploration, oil/gas distribution and controlling factors of carbonate reservoirs in the Yingshan Formation are not clearly understood. In this work, we investigated the reservoir beds and oil/gas properties in 13 wells in Well block ZG-43 on the No. 10 structural belt in the Tazhong Low Rise, and studied hydrocarbon accumulation characteristics with seismic and geochemical data. The Yingshan Formation in Well block ZG-43 is mainly composed of calcarenite, dolomitic limestone, dolomite, cryptite, as low porosity and low permeability reservoir beds, with fracture-void porosity constituting the main reservoir pore space. Oil/gas is quasi-layer distributed beneath the unconformity between the Yingshan and Lianglitag formations to a depth of 140 m. The oil in Well block ZG-43 is condensate with low density, low viscosity, low sulphur, low resin, low asphaltene, and high wax. The gas is 87.3% methane, generally containing H₂S. The oil/gas distribution pattern is oil in the east and gas in the west, and H₂S content in the west is lower than that in the east. The controlling factors for hydrocarbon are multi-source supply and multi-phase charging, interstratal karstification, hydrothermal activity, structural location and sealing condition. A structural–lithological trap is the main type of oil/gas accumulation. Oil/gas distribution was clearly affected by strike–slip faults. Oil/gas with multi-source supply and multi-phase charging was controlled by favourable local palaeo-highs, and affected by later karsting and hydrothermal activity, as well as gas invasion in the Himalayan (Cenozoic) period. Under the caprock of compact limestone in the third to fifth members of the Lianglitag Formation, oil/gas migrated up along the strike–slip fault planes, and moved laterally to both sides in a ‘T’ shape, and formed large-scale quasi-layer condensate gas reservoirs controlled by reservoir bed quality. Copyright © 2013 John Wiley & Sons, Ltd.

The c. 700 m thick succession of continental–brackish-marine deposits forming the Lourinhã Formation, cropping out along the coast of western Portugal between Baleal and Santa Cruz, has been correlated using laterally persistent shelly marker beds. Three shelly units record the episodic establishment of relatively short-lived, brackish-marine embayments, transgressing from the southwest, onto a low-lying coastal plain. The succession displays systematic changes in facies types and stacking patterns reflecting differences in fluvial style, bedload character and palaeontological content. Based on these observations, four new members for the Lourinhã Formation are proposed: the Sáo Bernardino, Porto de Barças, Areia Branca and Ferrel members. New biostratigraphical data indicate that the Lourinhã Formation is Late Kimmeridgian to earliest Early Tithonian in age. This age has also been obtained from the underlying mixed carbonate and clastic deposits of the Abadia Formation at Consolação. As a result, these latter sediments are now re-assigned to the Alcobaça Formation, a lithostratigraphical term currently in use in other areas of the Lusitanian Basin. Improved regional mapping of the Lourinhã Formation has established a new sub-basin within the western parts of the Lusitanian Basin. This sub-basin, now named the Consolação Sub-basin, is bounded to the east by the Lourinhã–Caldas de Rainha (L–C) fault zone and to the west by the Berlengas Horst. Copyright © 2013 John Wiley & Sons, Ltd.

The Middle Jurassic Khatatba Formation acts as a hydrocarbon reservoir in the subsurface in the Western Desert, Egypt. This study, which is based on core samples from two exploration boreholes, describes the lithological and diagenetic characteristics of the Khatatba Formation sandstones. The sandstones are fine- to coarse-grained, moderately to well-sorted quartz arenites, deposited in fluvial channels and in a shallow-marine setting. Diagenetic components include mechanical and chemical compaction, cementation (calcite, clay minerals, quartz overgrowths, and a minor amount of pyrite), and dissolution of calcite cements and feldspar grains. The widespread occurrence of an early calcite cement suggests that the Khatatba sandstones lost a significant amount of primary porosity at an early stage of its diagenetic history. In addition to calcite, several different cements including kaolinite and syntaxial quartz overgrowth occur as pore-filling and pore-lining cements. Kaolinite (largely vermicular) fills pore spaces and causes reduction in the permeability of the reservoir. Based on framework grain–cement relationships, precipitation of the early calcite cement was either accompanied by or followed the development of part of the pore-lining and pore-filling cements. Secondary porosity development occurred due to partial to complete dissolution of early calcite cements and feldspar. Late kaolinite clay cement occurs due to dissolved feldspar and has an impact on the reservoir quality of the Khatatba sandstones. Open hydraulic fractures also generated significant secondary porosity in sandstone reservoirs, where both fractures and dissolution took place in multiple phases during late diagenetic stages.

The Aínsa Basin of northern Spain contains a deep-marine succession comprising up to 24 sandstone bodies separated by thick marl-rich units. A detailed analysis of nine outcrops (>900 m of sediment profiles) from the Morillo Formation of the San Vicente Group, from the upper part of the basin succession, has enabled a reappraisal of the unit. Within the Morillo Formation, sediment transport was to the NW, and a range of environments are recognized including channels, lobes and pelagic deposits. The overlying Coscojuela Formation, which partly cuts into the Morillo Formation, shows W-directed palaeocurrents in its proximal reaches, with flows being deflected to the N along an adjacent slope. Destabilization of the adjacent carbonate platform resulted in a significant input of carbonate material into the flow. The final phases of sedimentation within the Aínsa Basin were more complex than previously suspected, probably as a result of a combination of factors, including tectonic activity, resulting in basin narrowing due to anticlinal growth, as well as encroachment and/or destabilization of the adjacent regional carbonate platforms. Copyright © 2013 John Wiley & Sons, Ltd.

Carbonate factories on insular oceanic islands in active volcanic settings are poorly explored. This case study illuminates marginal limestone deposits on a steep volcanic flank and their recurring interruption by deposits linked to volcaniclastic processes. Historically known as Ilhéu da Cal (Lime Island), Ilhéu de Baixo was separated from Porto Santo, in the Madeira Archipelago, during the course of the Quaternary. Here, extensive mines were tunnelled in the Miocene carbonate strata for the production of slaked lime. Approximately 10 000 m³ of calcarenite (−1 to 1ø) was removed by hand labour from the Blandy Brothers mine at the south end of the islet. Investigations of two stratigraphic sections at opposite ends of the mine reveal that the quarried material represents an incipient carbonate ramp developed from east to west and embanked against the flank of a volcanic island. A petrographic analysis of limestones from the mine shows that coralline red algae from crushed rhodoliths account for 51% of all identifiable bioclasts. This material was transported shoreward and deposited on the ramp between normal wave base and storm wave base at moderate depths. The mine's roof rocks are formed by Surtseyan deposits from a subsequent volcanic eruption. Volcaniclastic density flows also are a prevalent factor interrupting renewed carbonate deposition. These flows arrived downslope from the north and gradually steepened the debris apron westwards. Slope instability is further shown by a coral rudstone density flow that followed from growth of a coral reef dominated by Pocillopora madreporacea (Lamarck), partial reef collapse, and transport from a more easterly direction into a fore-reef setting. The uppermost facies represents a soft bottom at moderate depths in a quiet, but shore-proximal setting. Application of this study to a broader understanding of the relationship between carbonate and volcaniclastic deposition on oceanic islands emphasizes the susceptibility of carbonates to dilution and complete removal by density flows of various kinds, in contrast to the potential for preservation beneath less-disruptive Surtseyan deposits. Copyright © 2013 John Wiley & Sons, Ltd.

A Lower Devonian (Emsian) tempestite in the western Yangtze plate, China, was studied based on ichnological and stratigraphical features. The results indicated that the local tempestite can be grouped into clastic constituent types, which include bottom erosion structures, graded beds, swaley cross-stratification (SCS), parallel lamination, bioturbation and the new composition Zoophycos ichnofabrics. Five storm sequences and three Zoophycos ichnofabrics (Zoophycos–Chondrites ichnofabric, Zoophycos–Chondrites–Thalassinoides ichnofabric and Zoophycos–Thalassinoides–Palaeophycus ichnofabric) were discerned. It is demonstrated that the Zoophycos-producers from the complex types of Zoophycos in storm sequences were opportunistic organisms (r-strategists). This study reveals storm-generated physical and biogenic structures and textures and provides a good ichnological method to identify storm deposits. Copyright © 2013 John Wiley & Sons, Ltd.

Abundant scratching traces are described from the Early Triassic Kockatea Shale Formation in the Northampton area of the northern Perth Basin, Western Australia. Except for the Radichnus trace that represents grazing of a possible decapod mecochirids, Scalpoichnus minchinensis igen. and isp. nov. is established to accommodate other scratching sculptures, which might have been produced by arthropods that share similar feeding behaviours to those of decapods. These arthropod traces occurred on a mat-bound substratum defined by wrinkle structures. Microbial mats may have served as food resources for trace-makers feeding on the substratum. Furthermore, microbial envelopes functioning as a sole veneer in early diagenesis acted as a crucial role for the preservation of those shallow-tiered engraving traces. Abundant arthropod traces indicate frequent grazing activities probably by decapods or organisms having similar feeding habits upon microbial mat-bound substratum, implying that the deposit-feeders or omnivores survived on the matgrounds in the aftermath of the end-Permian mass extinction in Gondwanaland. Copyright © 2013 John Wiley & Sons, Ltd.

The peltasperm foliage Autunia naumannii (Gutbier) Kerp and possible peltasperm fructifications are for the first time described from the uppermost Taiyuan Formation of earliest Permian age near Wuda, Inner Mongolia. This is the oldest record of this group on the North China Block (Sino-Korean Platform), indicating an early migration into this area. Data of other occurrences in China demonstrate independent radiations of the group in Cathaysia. All known records indicate that peltasperms probably originated in the tropical extrabasinal areas of Euramerica, and subsequently migrated within the tropical belt and experienced independent regional radiations in Europe, the southwestern United States and on the North China Block. The present discovery of Autunia naumannii (Gutbier) Kerp in China adds a common floral component between the Euramerican and Cathaysian floras, providing more evidence indicating mutual migration of floral elements between Cathaysia and Euramerica. Copyright © 2013 John Wiley & Sons, Ltd.

The present article describes, for the first time, petrological and geochemical details of the Mawpyut differentiated complex which is related to the Sylhet trap located at Jaintia Hills district, Meghalaya, northeastern India. The Mawpyut complex occurs as an arcuate body that intrudes into the surrounding Shillong Group rocks. The complex in general contains ‘ultramafic’ and ‘mafic’ rocks, as well as minor syenitic veins that postdate the main units. The lithotypes correspond to cumulate and noncumulate units. The cumulate unit is represented by olivine clinopyroxenite, clinopyroxenite, plagioclase-bearing ultramafic, olivine gabbronorite, mela-gabbronorite, melagabbro, orthopyroxene gabbro, and gabbro, all with a pronounced cumulus texture. The noncumulate unit is marked by gabbro, monzonite, monzodiorite, and quartzsyenite.

We report new petrological data on the sapphirine granulite from Tuguiwula in the Inner Mongolia Suture Zone in the North China Craton which further confirm extreme crustal metamorphism associated with collisional orogeny. The peak metamorphic conditions of the rock have been estimated by sapphirine + quartz assemblage at T > 950 °C and P > 7.5 kbar (M1) based on mineral equilibrium modelling in the NCKFMASHTO system. These conditions are slightly lower than those reported in previous studies (~1050 °C and 10.5 kbar) due to the consideration of Fe₂O₃ content in the sapphirine granulite in this study, although we confirm a peak ultrahigh-temperature metamorphism in this region. The peak event was followed by a cordierite-forming retrograde event (M2), and biotite-forming retrograde stage (M3) which are constrained in the P–T pseudosection by the stability of cordierite (<7.5 kbar) and biotite + sillimanite + K-feldspar (<890 °C). Combining the results of this study and the petrological observations of spinel + quartz assemblage formed prior to sapphirine + quartz, and orthopyroxene + sillimanite + quartz assemblage after sapphirine + quartz reported in previous studies, a counterclockwise P–T history for these rocks is further confirmed, reflecting heat input into the lower crust from asthenospheric upwelling and underplating associated with the Palaeoproterozoic collisional orogeny in the North China Craton. Copyright © 2013 John Wiley & Sons, Ltd.

Ten well-preserved, earthquake-triggered liquefaction mounds and a carbonate sand volcano have been found in the Mesoproterozoic Wumishan Formation (1550–1400 Ma) in the Beijing area, North China. These features crop out in a roadcut near Zhuanghuwa Village. All ten mounds occur in the same sedimentary layer and have rounded shapes with some concentric and radial fissures arising from the centre. They range from 1.5 to 4 m in diameter and from 10 cm to 30 cm in height. The carbonate sand volcano has a diameter of 110 cm and the ‘crater’ at the top has a depth of about 30 cm. Associated with these mounds and the sand volcano are many ‘normal’ sedimentary structures and numerous soft-sediment deformation structures. The former include ripple marks, cross-bedding, stromatolites and desiccation cracks, indicating deposition in a stable shallow-water peritidal platform environment. The latter include intrastratal faults and folds, seismically formed breccias and carbonate clastic dykes. The morphological features and the genesis of these liquefaction mounds are very similar to mounds formed recently by the great Wenchuan Earthquake of China (2008). Detailed thin-section study of the mounds found no signs of any kind of biological constructional process; instead it reveals some obvious fluidification and liquefaction characteristics. Comparative studies have shown that these features are probably the products of Mesoproterozoic earthquake activity. Copyright © 2013 John Wiley & Sons, Ltd.

The Jilongshan skarn Cu–Au deposit is located at the Jiurui ore cluster region in the southwestern part of the Middle–Lower Yangtze River valley metallogenic belt. The region is characterized by NW-, NNW- and EW-trending faults and the mineralization occurs at the contact of lower Triassic carbonate rocks and Jurassic granodiorite porphyry intrusions. The intrusives are characterized by SiO₂, K₂O, and Na₂O concentrations ranging from 61.66 to 67.8 wt.%, 3.29 to 5.65 wt.%, and 2.83 to 3.9 wt.%, respectively. Their A/CNK (A/CNK = n(Al₂O₃)/[n(CaO) + n(Na₂O) + n(K₂O)]) ratio, δEu, and δCe vary from 0.77 to 1.17, 0.86 to 1, and 0.88 to 0.96, respectively. The rocks show enrichment in light rare earth elements ((La/Yb)_N = 7.61–12.94) and large ion lithophile elements (LILE), and depletion in high field strength elements (HFSE), such as Zr, Ti. They also display a peraluminous, high-K calc-alkaline signature typical of intrusives associated with skarn and porphyry Cu–Au–Mo polymetallic deposits. Laser ablation inductively coupled plasma spectrometry (LA-ICP-MS) zircon U–Pb age indicates that the granodiorite porphyry formed at 151.75 ± 0.70 Ma. A few inherited zircons with older ages (677 ± 10 Ma, 848 ± 11 Ma, 2645 ± 38 Ma, and 3411 ± 36 Ma) suggest the existence of an Archaean basement beneath the Middle–Lower Yangtze River region. The temperature of crystallization of the porphyry estimated from zircon thermometer ranges from 744.3 °C to 751.5 °C, and 634.04 °C to 823.8 °C. Molybdenite Re–Os dating shows that the Jilongshan deposit formed at 150.79 ± 0.82 Ma. The metallogeny and magmatism are correlated to mantle–crust interaction, associated with the subduction of the Pacific Plate from the east. Copyright © 2013 John Wiley & Sons, Ltd.

The western Shandong Province (WSP) is one of the typical Neoarchaean granite–greenstone belts in the Eastern Block of the North China Craton (NCC) and is an important region to investigate the early Precambrian evolutionary history of the NCC. The Taishan association, consisting of a ~2.7 Ga komatiite–tholeiite sequence and a ~2.5 Ga felsic volcano-sedimentary sequence, is the major lithological assemblage in the WSP. In the Qixingtai area, the felsic volcano-sedimentary sequence, partly subjected to anatexis, is composed of hornblende gneiss, voluminous fine-grained biotite gneiss and biotite plagioclase gneiss. SHRIMP zircon dating shows that the protolith of the biotite plagioclase gneiss formed after ca. 2.53 Ga. The tonalite intrusion into the volcanic protoliths of the fine-grained biotite gneiss and biotite plagioclase gneiss occurred at 2.52 Ga. Our age data constrain the time of formation of the felsic volcano-sedimentary sequence in the Taishan area as 2.53–2.52 Ga. The majority of zircons from the felsic volcano-sedimentary rocks have intermediate ε_Hf(t) values (−1.2 to +2.1). The whole rock Nd isotopes of the Taishan felsic volcano-sedimentary rocks yield the ε_Nd(t = 2522 Ma) values of +2.6 to −1.8 and T_DM2 ages 3.03–2.68 Ga. These values indicate the pre-existing crust was reworked at the end of the Neoarchaean (~2.5 Ga).

The Higher Himalayan Leucogranites (HHLG) intruded into the high grade rocks of the Higher Himalayan Crystallines (HHC) in Arunachal Himalaya of the Eastern Himalaya, yield distinctive field data, petrography, microstructures, geochemical and mineral chemistry data. The Arunachal HHLG are characterized by the presence of two micas; normative corundum; high contents of SiO₂ (67–78 wt.%), Al₂O₃ (13–18 wt.%), A/CNK (0.98–1.44) and Rb (154–412 ppm); low contents of CaO (0.33–1.91 wt.%) and Sr (19–171 ppm), and a high ratio of FeO_(tot)/MgO in biotite (2.54–4.82). These distinctive features, along with their strong depletion in high field strength elements (HFSE), suggest their affinity to peraluminous S-type granite generated by the partial melting of crustal material. Geothermobarometric estimations and mineral assemblages of the HHC metapelites confirm that the HHLG were probably generated in the middle crust (~20 km) and the produced melts intruded the HHC in the form of sills/dykes. Microstructurally, the HHLG shows high temperature deformation features including chessboard extinction in quartz and cuspate/lobate grain boundaries between quartz and feldspars (plagioclase and K-feldspar). The deformation microstructures suggest that the HHLG was deformed under early high temperature ductile deformation conditions. These fabrics were subsequently superimposed by later brittle deformation features associated with decreasing temperatures during the exhumation of the HHLG towards shallow structural levels at the time of Himalayan orogeny. Copyright © 2013 John Wiley & Sons, Ltd.

Ages of Cenozoic sedimentary basins yield information that can be used to infer detailed spatial and temporal evolution in the Alpine foreland. The Tertiary deposits of the NW Iberian Peninsula comprise the remains of a broken foreland basin (the West Duero Basin). This work constrains the timing of tectonic fragmentation and the evolution of the western termination of the Alpine Pyrenean–Cantabrian Orogen (NW Iberian Peninsula). The discovery of Issiodoromys cf. minor 1 and Pseudocricetodon in the lower formation of the Tertiary depression of Sarria (the Toral Formation) constrains its age to the late Early Oligocene (MP23–MP25), similar to its age in the El Bierzo depression (MP24–MP25). Sedimentation initiated in the NE of the study area at Oviedo during the Middle Eocene (Bartonian–Early Priabonian MP16–MP17) and migrated towards the west and south during the Early Oligocene. The Toral Formation was deposited in a foreland basin that connected the present day outcrops of the El Bierzo, Sarria and As Pontes Tertiary depressions. The basin was segmented during the westward migration of structural deformation associated with the Orogen, and the subsequent uplift of the Galaico–Leoneses Mountains. The present-day height above reference level of the base of the Toral Formation has been used to quantify Alpine segmentation that took place after Early Oligocene times. Minimum tectonic uplift assessed is 960 m in the Cantabrian Mountains and 1050 m in the Galaico–Leoneses Mountains. Copyright © 2013 John Wiley & Sons, Ltd.

The Yangchang granite-hosted Mo deposit is typical of the Xilamulun metallogenic belt, which is one of the important Mo–Pb–Zn–Ag producers in China. A combination of major and trace element, Sr, Nd and Pb isotope, and zircon U–Pb age data are reported for the Yangchang batholith to constrain its petrogenesis and Mo mineralization. Zircon LA-ICPMS U–Pb dating yields mean ages of 138 ± 2 and 132 ± 2 Ma for monzogranite and granite porphyry, respectively. The monzogranites and granite porphyries are calc-alkaline with K₂O/Na₂O ratios of 0.75–0.92 and 1.75–4.42, respectively. They are all enriched in large-ion lithophile elements (LILEs) and depleted in high-field-strength elements (HFSEs) with negative Nb and Ta anomalies in primitive-mantle-normalized trace element diagrams. The monzogranites have relatively high Sr (380–499 ppm) and Y (14–18 ppm) concentrations, and the granite porphyries have lower Sr (31–71 ppm) and Y (5–11 ppm) concentrations than those of monzogranites. The monzogranites and granite porphyries have relatively low initial Sr isotope ratios of 0.704573–0.705627 and 0.704281, respectively, and similar ²⁰⁶Pb/²⁰⁴Pb ratios of 18.75–18.98 and 18.48–18.71, respectively. In contrast, the ε_Nd(t) value (−3.7) of granite porphyry is lower than those of monzogranites (−1.5 to −2.7) with Nd model ages of about 1.0 Ga. These geochemical features suggest that the monzogranite and granite porphyries were derived from juvenile crustal rocks related to subduction of the Paleo-Pacific plate under east China. Copyright © 2013 John Wiley & Sons, Ltd.

The Red Hills Road Cave, Jamaica, is the most important site for terrestrial arthropods in the post-Miocene of the Greater Antilles. Its fauna includes millipedes, isopods, crabs and insects, in addition to land snails and vertebrates. Arthropods are preserved in three dimensions and delicate structures such as limbs can be recognized. This unusual preservation was favoured by acidic groundwater rich in dissolved calcium carbonate; periods of high rainfall during which the bottle-shaped cave was filled with water; and any arthropod washed in would have drowned. The absence of spiders, centipedes and most insects is due to the absence of carbonate in their exoskeletons. Millipedes and isopods possess a potential for preservation by carbonate mineralization that does not occur in other groups; they secrete calcium carbonate in the exoskeleton which hardens the cuticle and is water permeable, bringing about mineral replacement of the original structures.

Using teleseismic waveform records from 363 broadband stations, we applied H–κ stacking of receiver functions to estimate crustal thickness (H) and average Vp/Vs ratio (κ) in the central and western North China Craton (NCC) and adjacent regions. Our results show that, except for thinning in the Cenozoic rifts and southern edge of the central NCC, H gradually thickens westward from ~30 km at the easternmost edge of the central NCC to >60 km near the northeastern margin of the Tibetan Plateau. κ exhibits complex variations, with locally high or low anomalies in the rifts, at the southern edge of the central NCC and at tectonic boundary zones. Low-density uppermost mantle and distinct N–S differences are observed in the Ordos, suggesting typical cratonic crust. Thickened crust and complex variations in κ at the southwestern boundary of the Ordos may be related to the formation of the Palaeozoic Qilian Block and late uplift of the Tibetan Plateau. Thinned crust and locally high κ are observed in and near the Cenozoic rifts, suggesting complex crustal modifications that may have been caused by repeated reactivation at pre-existing weak zones by successive thermal-tectonic events. Thin crust and low κ are found at the southern edge of the central NCC, suggesting crustal modifications such as delamination, especially in the lower crust, which may be related to collision of the NCC and Yangtze Block. Copyright © 2012 John Wiley & Sons, Ltd.

Stable isotope data (δ¹⁸O, δ¹³C) were obtained for magnesite (MgCO₃) from Holocene salt lake deposits of the Taoudenni–Agorgott basin, Mali, in which it is the only carbonate mineral present. The deposits have a high glauberite content (Na₂Ca(SO₄)₂), representing a type of continental evaporite formation that is commonly magnesite-bearing. Samples from seven different levels in a 5 m long sequence were analysed. δ¹⁸O_V-PDB values are between +3.17 and +5.91‰, which is lower than might be expected for evaporitic environments, recording reduced ¹⁸O enrichment at high salinity. δ¹³C_V-PDB values are between −1.32‰ and −4.79‰, showing an influence of carbon derived from the decomposition of organic matter rather than from exchange with atmospheric CO₂. Covariance between δ¹⁸O and δ¹³C is strong for the lower part of the sequence, recording coupled ¹⁸O and ¹³C enrichment as commonly observed for closed basins. Covariance is lacking for the upper part of the sequence, with only periodic massive magnesite deposition in a more shallow lake. Copyright © 2012 John Wiley & Sons, Ltd.

Cretaceous dyke swarms are widespread in the Guocheng fault belt, Jiaodong Peninsula, eastern North China Craton (NCC). Elemental analyses show that these dykes are classified as high-K calc-alkaline to shoshonitic series, and are characterized by high MgO (up to 10.33 wt%; Mg^# < 69.8), Cr (<571 ppm) and Ni (<235 ppm) at low silica contents. They are enriched in LILEs (e.g. Sr, Ba, K and Pb) and LREEs, depleted in HFSEs (e.g. Nb–Ta, Zr–Hf, Ti and P), and possess relatively radiogenic Sr (initial ⁸⁷Sr/⁸⁶Sr = 0.7078 to 0.7116) and Nd [ε_Nd(t) = −20.8 to −13.5] and much less radiogenic Pb (²⁰⁶Pb/²⁰⁴Pb = 17.13 to 17.56) isotope signatures. These data, combined with inversely zoned amphibole and pyroxene phenocrysts, suggest a hybrid origin for the Guocheng dykes. The inferred magma evolution is dominated by repeated injection of basic magma from metasomatized subcontinental lithospheric mantle (SCLM) into a lower crustal reservoir of intermediate-felsic composition. This refertilized lithospheric mantle source, probably together with its overlying enriched lower crust, was formed by subduction-related fluid metasomatism in the Palaeoproterozoic, which resulted from final cratonization of the NCC at ca. 1.8 Ga during assembly of Columbia supercontinent. Our observations also imply that similar mixed magma system with oxidized and sulphur-rich signatures may be the key to the formation of hydrothermal polymetal deposits and the potential target for mineral exploration in some undiscovered areas. Copyright © 2012 John Wiley & Sons, Ltd.

Limestone horizons of Upper Ordovician (Katian) age in southwest Wales contain diverse fossil faunas including rugose corals. The existence of Ordovician Rugosa in Wales was first reported by Murchison in the 1830s, but since then hardly any specimens have been documented systematically until this present study. Newly collected material from the area around Llanddowror (Carmarthenshire) has now confirmed the diversity of rugose corals in the Sholeshook Limestone (Katian age), an arenaceous limestone originating from the shelf edge of the palaeocontinent Avalonia. The majority of the specimens are preserved as moulds. This means that in many instances preservation of the fossils was insufficient for specific identification; nevertheless, it was possible to document a diverse rugose coral fauna, including Helicelasma, probable Grewingkia and Kenophyllum, and a potential early mucophyllid. While associated with considerable difficulties, as some diagnostic features of Rugosa are not visible in moulds, it is demonstrated here that the work with such specimens can result in faunal information which would otherwise be unobtainable. An assemblage of rugose and tabulate corals in the Sholeshook Limestone can be differentiated from a similar assemblage in the neighbouring Robeston Wathen Limestone which has a slightly different lithology. The fauna has strong similarities with other Avalonian (Irish, English, Belgian) as well as Baltic (Estonian and Norwegian) rugose coral faunas. Copyright © 2012 John Wiley & Sons, Ltd.

Mineralogical, textural, geochemical, and weathering characteristics of loess deposits in Golestan province of Iran suggest that they are mostly derived from felsic igneous rocks and are related to Quaternary palaeoclimate. Whole-rock analyses indicate heavy minerals such as zircon, tourmaline and phyllosillicate minerals (e.g. muscovite, chlorite, illite) exert a significant control on the chemical composition. The loess samples display uniform chemical composition, indicative of similar alteration history. Chemical index of alteration suggests a weak to moderate degree of weathering in a felsic source area. Scanning electron micrographs of quartz grains reveal abundant silt-sized quartz particles, a result of glacial grinding during the Late Pleistocene in Central Asia. Subsequently, these silt particles were transported from Central Asia to their depositional site by wind and paraglacial processes. Local topography of northeast Iran (Alborz Mountains) acted as a major barrier, entrapping the airborne particles on the plains of Golestan province. Copyright © 2012 John Wiley & Sons, Ltd.

The Haji-Abad ophiolite in SW Iran (Outer Zagros Ophiolite Belt) is a remnant of the Late Cretaceous supra-subduction zone ophiolites along the Bitlis–Zagros suture zone of southern Tethys. These ophiolites are coeval in age with the Late Cretaceous peri-Arabian ophiolite belt including the Troodos (Cyprus), Kizildag (Turkey), Baer-Bassit (Syria) and Semail (Oman) in the eastern Mediterranean region, as well as other Late Cretaceous Zagros ophiolites. Mantle tectonites constitute the main lithology of the Haji-Abad ophiolite and are mostly lherzolites, depleted harzburgite with widespread residual and foliated/discordant dunite lenses. Podiform chromitites are common and are typically enveloped by thin dunitic haloes. Harzburgitic spinels are geochemically characterized by low and/or high Cr number, showing tendency to plot both in depleted abyssal and fore-arc peridotites fields. Lherzolites are less refractory with slightly higher bulk REE contents and characterized by 7–12% partial melting of a spinel lherzolitic source whereas depleted harzburgites have very low abundances of REE and represented by more than 17% partial melting. The Haji-Abad ophiolite crustal sequences are characterized by ultramafic cumulates and volcanic rocks. The volcanic rocks comprise pillow lavas and massive lava flows with basaltic to more-evolved dacitic composition. The geochemistry and petrology of the Haji-Abad volcanic rocks show a magmatic progression from early-erupted E-MORB-type pillow lavas to late-stages boninitic lavas. The E-MORB-type lavas have LREE-enriched patterns without (or with slight) depletion in Nb–Ta. Boninitic lavas are highly depleted in bulk REEs and are represented by strong LREE-depleted patterns and Nb–Ta negative anomalies. Tonalitic and plagiogranitic intrusions of small size, with calc-alkaline signature, are common in the ophiolite complex. The Late Cretaceous Tethyan ophiolites like those at the Troodos, eastern Mediterranean, Oman and Zagros show similar ages and geochemical signatures, suggesting widespread supra-subduction zone magmatism in all Neotethyan ophiolites during the Late Cretaceous. The geochemical patterns of the Haji-Abad ophiolites as well as those of other Late Cretaceous Tethyan ophiolites, reflect a fore-arc tectonic setting for the generation of the magmatic rocks in the southern branch of Neotethys during the Late Cretaceous. Copyright © 2012 John Wiley & Sons, Ltd.

The Daqingshan area in the North China Craton (NCC) incorporates several suites of magmatic intrusives including gabbros, granodiorites, charnockites and syenogranites, which were overprinted by subsequent metamorphic events. In this study, we report detailed morphological and textural characteristics as well as sensitive high resolution ion microprobe (SHRIMP) U–Pb ages of zircons from ten representative samples of the magmatic suites including syenogranites, charnockites and granodiorites. The zircons in these rocks are characterized by typical magmatic crystallization features including elongate prismatic grains with angular to sub-angular faces which are overprinted by a variety of reworked textures indicating strong recrystallization. These structures are terminated by thin and variable metamorphic overgrowths. U–Pb analyses of the zircons reveal multiple tectono-thermal events including magmatic crystallization at 2.30–2.00, 1.96–1.94 and 1.85–1.82 Ga and metamorphic overprint at 1.97–1.94 and 1.87–1.82 Ga. The episodic magmatism and regional metamorphism recorded in our study show a complex sequence of tectonic processes during the early to late Palaeoproterozoic associated with the amalgamation of crustal blocks within the NCC, with the youngest episode of the syenogranites representing regional extension at the end of the final cratonization of the NCC. Copyright © 2012 John Wiley & Sons, Ltd.

The latest Carboniferous–Early Permian Dorud Group in the Chaman-Saver area of eastern Alborz, Iran is more than 222 m thick and includes thick sequences of oncolitic limestone, sandy limestone, sandstones and shales. The Emarat and Ghosnavi formations of this Group are dated here as latest Gzhelian to early Sakmarian Stages. During the Asselian Stage, the sea level fell abruptly and epeirogenic episodes occurred. These events generated a broad, shallow carbonate platform suitable for the growth and diversity of smaller foraminifers in the Chaman-Saver area which, consequently, displays faunal differences with the rest of the Alborz Mountains. Three foraminiferal biozones are proposed: Nodosinelloides potievskayae–Vervilleina bradyi Zone (latest Gzhelian), Calcitornella heathi–Nodosinelloides sp. Zone (latest Gzhelian–Asselian), and Rectogordius iranicus n. gen. n. sp.–Hemigordius schlumbergeri Zone (early Sakmarian). The new taxa described herein include: Pseudovidalina iranica n. sp., P. damghanica n. sp., Rectogordius iranicus n. gen. n. sp. and Tezaquina sp. 1. Copyright © 2012 John Wiley & Sons, Ltd.

The different hydrodynamic behaviour of detrital clay minerals in the marine depositional environment allows assessment of relative sea-level variations in the sedimentary record. Comparison of smectite and kaolinite:illite (S+K:I) changes with the global sea-level curves and with the third-order cycles of the eustatic curve for European basins allows assessment of the influence of global eustasy and local tectonics on sequence stratigraphy. In the South Iberian Margin, sedimentation took place both on open-marine platforms and in deeper water areas. On this margin during the Late Oligocene to Early Aquitanian, the variations in sedimentation were caused not only by global eustasy but also by compressive tectonics. Correlations were made between the S+K:I cycles and the third-order cycles for European basins, enabling the definition of four third-order sedimentary sequences (here called C1, C2, C3, and A1) and two lower-order sequences within C3 and A1 (here called C3a, C3b, A1a, and A1b) related to tectonic movements. High S+K:I values were observed during episodes of maximum flooding in each sequence and lower-order sequence and in each succession, enabling changes in palaeocoastal morphology to be considered. Copyright © 2012 John Wiley & Sons, Ltd.

The palynological contents as well as macroscopic charcoal fragments from a calcareous sandstone pebble from Quaternary glacial deposits of the North Sea (80 km SW of the Dogger Bank) are described. The taxonomic composition of the palynoflora points to a Late Jurassic (or Late Jurassic/Early Cretaceous) age of the sandstone. The charcoal is interpreted as direct evidence of palaeo-wildfire occurring during this period in the source area of the sediments of this particular sandstone. This finding, together with already published data on Mesozoic deposits, allows to conclude that wildfires were obviously widespread during this period in the area of the modern day North Sea and adjacent areas. Copyright © 2012 John Wiley & Sons, Ltd.

Turbidite facies distribution and palaeocurrent analysis of submarine fan evolution in the Pindos foreland basin of west Peloponnesus peninsula (SW Greece) indicate that this part of the foreland was developed during Late Eocene to Early Oligocene in three linear sub-basins (Tritea, Hrisovitsi and Finikounda). The basin fill conditions, with a multiple feeder system, which is characterized by axial transport of sediments and asymmetric stratigraphic thickness of the studied sediments, indicate that the Pindos Foreland Basin in this area was an underfilled foreland basin. Sediments are dominated by conglomerates, sandstones and mudstones. The flow types that controlled the depositional processes of the submarine fans were grain flows, debris flows and low- and high-density turbidity currents. The sedimentary model that we propose for the depositional mechanisms and geometrical distribution of the turbidite units in the Tritea sub-basin is a mixed sand-mud submarine fan with a sequential interaction of progradation and retrogradation for the submarine fan development and shows a WNW main palaeocurrent direction. The Hrisovitsi sub-basin turbidite system characterized by small-scale channels was sediment starved, and the erosion during deposition was greater than the two other studied areas, indicating a more restricted basin topography with a NW main palaeocurrent direction. The Finikounda sub-basin exhibits sand-rich submarine fans, is characterized by the presence of distinct, small-scale, thickening-upward cycles and by the covering of a distal fan by a proximal fan. It was constructed under the simultaneous interaction of progradation and aggradation, where the main palaeocurrent direction was from NNW to SSE. Copyright © 2012 John Wiley & Sons, Ltd.

The Zhongchuan district is an important component of the metallogenic belt in the Western Qinling. The Zhongchuan granite pluton occurring in the centre of the Zhongchuan metallogenic area has been poorly constrained, though the Triassic granite in Western Qinling has been well documented. In-situ zircon U–Pb ages, Hf isotopic compositions and whole-rock geochemical data are presented for host granite and mafic microgranular enclaves (MMES) from the Zhongchuan pluton, in order to constrain its sources, petrogenesis and tectonic setting of the pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMES and the host granitic rocks mainly due to interactions between coeval felsic host magma and mafic magma. The zircon U–Pb age of host granite (231.6 ± 1.5 to 235.8 ± 2.3 Ma) has overlapping uncertainty with that of the MMES (236.6 ± 1.3 Ma), establishing that the mafic and felsic magmas were coeval. The Hf isotopic composition of the MMES (ε_Hf(t) = −13.4 to 4.0) is distinct from the host granite (ε_Hf(t) = −15.7 to 0.0), indicating that both enriched subcontinental lithosphere mantle (SCLM) and crustal sources contributed to their origin. The zircons have two-stage Hf model ages of 1064 to 1798 Ma for the host granite and 858 to 1747 Ma for the MMES. This suggests that the granitic pluton was likely derived from partial melting of a Late Mesoproterozoic crust, with subsequent interaction with the SCLM-derived mafic magmas in tectonic affinity to the South China Block. Copyright © 2012 John Wiley & Sons, Ltd.

Palaeoproterozoic intermediate to potassic felsic volcanism in volcano-sedimentary sequences could either have occurred in continental rift or at convergent magmatic arc tectonic settings. The Vinjamuru domain of the Krishna Province in Andhra Pradesh, SE India, contains such felsic and intermediate metavolcanic rocks, whose geochemistry constrains their probable tectonic setting and which were dated by the zircon Pb evaporation method in order to constrain their time of formation. These rocks consist of interlayered quartz–garnet–biotite schist, quartz–hematite–baryte–sericite schist as well as cherty quartzite, and represent a calc-alkaline volcanic sequence of andesitic to rhyolitic rocks that underwent amphibolite-facies metamorphism at ~1.61 Ga.

In South America, autochthonous archaeocyathan faunas preserved in Early Cambrian limestones have not been found yet. Nevertheless, a few well-documented occurrences of these fossils in clasts contained in coarse-grained rocks of a wide age range have been discovered in recent years. Erratic limestone blocks from the Late Carboniferous–Early Permian Fitzroy Tillite Formation in the Falkland/Malvinas Islands yielded three archaeocyath taxa. Also, seven taxa were reported from archaeocyathan limestone clasts in a metaconglomerate of the Cambro-Ordovician El Jagüelito Formation in northern Patagonia. In addition, a new record from the Late Carboniferous–Early Permian Sauce Grande Formation diamictites in Sierras Australes, Buenos Aires Province, Argentina, is presented herein. Preservation of this scarce new material is poor, but at least three different taxa can be distinguished. The most likely source of all archaeocyathan limestone clasts found in southern South America is the Shackleton Limestone from the Transantarctic Mountains in East Antarctica. The new record from the Sauce Grande Formation and the inferred clast provenance reinforce the correlation between this unit, the Dwyka Tillite (South Africa) and the Fitzroy Tillite Formation (Falklands/Malvinas), suggesting a very wide distribution of these Antarctic occurrences during the Late Carboniferous–Early Permian Gondwana glaciation (Episode III). Thus, even though being allochthonous, archaeocyaths are emerging as a new key biological feature for Gondwana palaeogeographic reconstructions. Copyright © 2012 John Wiley & Sons, Ltd.

The ptychoparioid trilobite Blainia gregaria Walcott, 1916 is described for the first time from the late middle Cambrian (Series 3) of the Argentine Precordillera. It occurs commonly in the upper part of La Laja Formation, a carbonate platform succession that crops out in the Precordillera Oriental of San Juan where it reaches a thickness of some 600 m. Sections were sampled on cerro Tres Marías in Sierra de Marquesado and in quebrada de Zonda at the northern termination of Sierra Chica de Zonda. More than 1200 specimens were recovered from 22 stratigraphic levels over a thickness of 155 m, located in the uppermost 15 m of the Soldano Member, the approximately 100 m thick Rivadavia Member, and in the lower 40 m of the Juan Pobre Member. Our biometric study dealt with 205 cranidia and 365 pygidia from cerro Tres Marías. Measured dimensions of a subset of this collection provide bivariate datasets that in some characters show broad scatter plots and relatively low linear correlation coefficients, indicative of rather wide intraspecific morphological variation. Six morphotypes (three cranidial and three pygidial), recognized mainly on the basis of shape, occur together in the same collections. This evidence for an unusually high degree of variability leads to a proposed synonymy of some 30 previously named species in North America belonging to two genera, Blainia Walcott, 1916 and Glyphaspis Poulsen, 1927, the latter considered a junior synonym. The biogeographic distribution of B. gregaria, as redefined here, shows that it was an endemic Laurentian species that inhabited the inner parts of the carbonate platform that rimmed the craton and mantled portions of its interior. Its presence in western Argentina is further evidence for the very close faunal relationship between the Precordilleran terrane, known as Cuyania, and Laurentia during the Cambrian. Copyright © 2012 John Wiley & Sons, Ltd.

The classical lower-middle Cambrian boundary is approximately equivalent with the boundary of the Cambrian Series 2 and 3, which is now in the process of definition by the International Subcommission on Cambrian Stratigraphy. Currently, there are two oryctocephalid trilobite species first appearance data (FAD) that are suggested as possible markers of this level: Ovatoryctocara granulata Tchernysheva, 1962 and Oryctocephalus indicus (Reed, 1910), respectively. Until now neither of these two species has been recorded in the Mediterranean subprovince or Baltica. As a result, in these regions a level potentially correlating with either the FAD of Ovatoryctocara granulata or Oryctocephalus indicus has to be located using the available bio-, isotope-, and event-stratigraphy data.

Phylogenetic relationships among species of the family Olenidae (Trilobita, Ptychopariida) were traditionally established by the direct comparison of morphological features and the evaluation of stratigraphic placement. In this study, a cladistic analysis of Parabolinella Brøgger is conducted in order to test the supposed monophyly of the genus and to determine the relationships of its species. Twenty-one taxa (sixteen of this genus) from the late Cambrian and Tremadocian of Baltica, Avalonia, Laurentia, South China and the western margin of Gondwana were revised. Forty non-ordered characters were considered in the analysis, 34 belonging to the cephalon, four to the pygidium, and two to the thorax. Some of these characters were specially defined for this study. The phylogenetic analysis was performed under unweighted parsimony. The obtained tree is partially consistent with the stratigraphic record of the studied species and shows correspondence with global late Cambrian and early Ordovician palaeogeography. Parabolinella may have originated in deep water sites of the Oaxaca region, Mexico and then migrated to other regions. The genus diversified in outer shelf facies of the Baltica Province during the late Cambrian and Tremadocian, whereas it would have dispersed to the South China Province in early Tremadocian times. Copyright © 2012 John Wiley & Sons, Ltd.

A new conodont collection from the Alfarcito area of the Tilcara Range, Cordillera Oriental of northwestern Argentina, has been studied. The Santa Rosita Formation exposed in this area consists of the Tilcara, Casa Colorada, Pico de Halcón, Alfarcito, Rupasca and Humacha members, which have a combined total thickness of ca. 1100 m. The sequence is composed of interbedded shales and sandstones, including calcarenites and coquinas, mostly appearing in the upper parts of the units. An abundant fauna of conodonts (ca. 11 000 elements), associated with graptolites and trilobites, was recorded. The biostratigraphic analysis allows for the identification of the Cordylodus intermedius and C. lindstromi sensu lato zones at the base of the Alfarcito Member. The C. angulatus Zone spans the upper part of the latter unit, and the Paltodus deltifer Zone (Paltodus deltifer pristinus and P. deltifer deltifer subzones) is identified in the Rupasca and Humacha members. The new species Acanthodus raqueli, A. humachensis, Utahconus tortibasis, U. scandodiformis, U. purmamarcensis, Variabiloconus crassus, Kallidontus gondwanicus and Acodus primitivus are recorded from the two latter biozones and they are described herein. The genera Acanthodus and Variabiloconus are emended, and a new genus Tilcarodus is created to include T. humahuacensis (Albanesi and Aceñolaza). Copyright © 2012 John Wiley & Sons, Ltd.

The taxa frequencies and cluster analysis of 10 837 conodonts recovered from the Santa Rosita Formation on the eastern flank of the Quebrada de Humahuaca, Cordillera Oriental of Argentina, were carried out for palaeoenvironmental interpretations. The first type of analysis allowed us to identify three conodont biofacies: Variabiloconus-Teridontus, Utahconus-Acanthodus and Tilcarodus-Drepanoistodus, and the cluster analysis helps define respective sub-biofacies. The first biofacies is not constrained to a particular environment, the second biofacies, which is characterized by typical Laurentian genera, is related to sandstones from shallow-water environments, while the third one is better represented in deeper water siliciclastic lithofacies. A nektobenthic mode of life is suggested for Utahconus and Acanthodus, but a pelagic behaviour is apparent for the rest of the taxa, well adapted to off-shore biotopes in particular cases (proto- and paraconodonts). The faunal composition reveals a mixture of Baltic and Laurentian taxa, as well as endemic forms that define the Southwestern Gondwana Province from the Cold Domain in the Shallow-Sea Realm. The presence of typical species from low latitudes (e.g. Australia) confirms the installation of an oceanic perigondwanian corridor, which was open to faunal migration during the late Cambrian–early Ordovician. Copyright © 2012 John Wiley & Sons, Ltd.

The machaeridians are marine Palaeozoic annelids, which developed a dorsal skeleton composed of calcite sclerites, achieving a world-wide distribution from the Early Ordovician to the Middle Permian. The absence of records from this group is notable in Argentina in spite of intense studies of Palaeozoic rocks. This fact can be explained by biases in sampling or because of preservation problems. Machaeridian sclerites of the families Plumulitidae and Turrilepadidae collected in Middle and Upper Ordovician rocks from the San Juan Precordillera, Argentina, are described here for the first time. Plumulites sp. is recorded in early Darriwilian strata from the Gualcamayo Formation exposed in the western flank of the Cerro La Chilca locality, and from the Las Aguaditas Formation in the Quebrada de Las Aguaditas section. Plumulitid and turrilepadid sclerites are described from the upper member of the Los Azules Formation (late Sandbian) in the Cerro Viejo de Huaco area. The material of the Los Azules Formation is the first record of turrilepadids in Sandbian rocks, which are scarce in Ordovician successions. The referred strata bear pelagic, benthic and nektobenthic faunal assemblages, constituting a similar taphocoenosis preserved in shales and calcareous silty shales related to transgressive events. The record of machaeridians expands our knowledge of the Ordovician biotas from Argentina and provides new information on the palaeobiogeographical distribution of this Palaeozoic annelid group. Copyright © 2012 John Wiley & Sons, Ltd.

The discovery of magnetic spherules in acid-insoluble residues from conodont samples encouraged a systematic search for Ordovician micrometeorites from northwestern Argentina. Some 220 melted micrometeorites were recovered from the magnetic fraction of six samples (total rock weight: 23 kg) from the Cordillera Oriental (Santa Rosita Formation) and 17 from five samples (total rock weight: 8.9 kg) from the Argentine Precordillera (Las Aguaditas, Gualcamayo and Las Vacas formations). The specimens resemble I-type cosmic spherules, in their chemistry and distinct dendritic and polygonal crystalline structures. They represent a flux of micrometeorites several orders of magnitude greater than present. The wide differences in spherule abundance between the Precordillera and the Cordillera Oriental samples could reflect uncertainties in the sedimentary rates or temporal variations in the flux of extraterrestrial matter to Earth. The micrometeorite-bearing formations span the late Tremadocian to the late Darriliwian (~480–460 Ma), which is consistent with a period of elevated flux of extraterrestrial material, as recorded several thousand kilometres away from coeval horizons in Scotland, Sweden and central China. Copyright © 2012 John Wiley & Sons, Ltd.

A low-diversity graptolite fauna from the upper part of the Eusebio Ayala Formation exposed in the intracratonic Paraná Basin of eastern Paraguay is reported herein. The sections studied are composed dominantly of red micaceous mudstones with intercalations of purple sandstones from a series of clay quarries (Santa Elena; Galeano; Western Itauguá) around Itauguá city. The graptolites Metaclimacograptus sp., Normalograptus cf. ajjeri (Legrand), and Normalograptus cf. medius (Törnquist) indicate an early Llandovery age for the upper Eusebio Ayala unit. Compared to coeval, postglacial successions in southwestern Gondwana, the graptolites studied have their closest affinities with those from the Rhuddanian lower Lipeón (Subandean Ranges, northwestern Argentina) and La Chilca (Precordillera) formations. In addition, a trilobite assemblage dominated by the genus Mucronaspis was collected from the Eusebio Ayala Formation type locality near Eusebio Ayala city. The latter represents an isolated small outcrop which seems to be latest Ordovician (Hirnantian) in age. Copyright © 2012 John Wiley & Sons, Ltd.

An association of silicified spicules of hexactinellid sponges was collected from Silurian sandstones at the top of the La Chilca Formation, cropping out at Cerro del Fuerte, 20 km east of Jáchal, in the San Juan Precordillera of west-central Argentina. This is the first occurrence of a Silurian spicule fauna recorded at higher palaeolatitudes from Argentina and the entire South American part of Gondwana. The spicules were extracted by means of formic acid treatment from sandstones of the uppermost part of the La Chilca Formation, which ranges in age from the late Hirnantian to Llandovery, based on graptolites, brachiopods and conodonts. The spicule association is composed only of scarce siliceous hexactine-based spicules which cannot be attributed to any specific hexactinellid taxon. The fragmentary preservation of this allochthonous sponge assemblage points toward preburial transport. These spicules represent the only microfauna found in the uppermost sandstones. Macrofossils are absent. No conodonts have been recovered in these levels. Two interpretations on the spicules of the Precordillera can be argued: (a) that those early Silurian hexactinellids could have occurred in quartz sandstones of the shore-facies to off-shore transitional associations, in the upper La Chilca Formation, or (b) that these sponges flourished in mainly calcareous shales in quiet deep-water conditions, and that their fragile spicules were removed and deposited by oceanic currents, on the top of the outer-shelf sand bars.

Silurian and Devonian corals occur abundantly in siliciclastic rocks of the Argentine Precordillera. They are distributed along a Silurian storm-dominated shallow-water platform, a transitional restricted nearshore environment, and a Devonian muddy platform setting. Four main associations of rugose and tabulate corals have been recorded: a Silurian association, a lowermost Devonian and two associations in Lower Devonian rocks. The Silurian shallow-water platform coral association shows abundant colonies of a tabulate pleurodictyform coral. The type and the domical form of corals indicate high-energy environments. The lowermost Devonian coral association shows the abundance of the tabulate coral Argentinella argentina, which could have formed patches in protected low-energy environments. The Lower Devonian coral associations correspond to a muddy platform environment. The first one includes rugose and hemispherical tabulate corals and the second is composed of tabulate corals assigned to Parastriatopora sanjuanina, and Parastriatopora sp. They are long stick-like, fasciculate forms, grouped in apparently life position. Rugose and tabulate corals in the Upper Silurian and Lower Devonian of Argentina constitute low-diversity associations of western Gondwana, developed in mid- to high-latitudes. The morphologies acquired by corals are related to water energy. Laminar or encrusting forms were more competitive in the Silurian shallow-water, high-energy environments. Slender branching forms with a high profile typically inhabited Devonian relatively deeper water or protected settings. The stratigraphic distribution observed partially followed the well- known pattern in which shallow-water faunas disappeared during regressive events and are replaced by new forms in the subsequent transgressive sequence. The turnover pattern detected across the Silurian-Devonian transitional interval is in agreement with that previously recognized on the basis of the accompanying fauna. Copyright © 2011 John Wiley & Sons, Ltd.

The distribution and diversity of marine palynomorphs, such as acritarchs and chlorophytes, and terrestrial palynomorphs, such as miospores, are controlled mainly by palaeoenvironmental and palaeogeographical conditions. Recently, global patterns of organic-walled phytoplankton were illustrated for the Late Silurian to earliest Devonian based on data from different stratigraphic sections and palaeocontinents. Here, we analyze the Silurian and the Early Devonian diversity in the Argentinean Precordillera, Central Andean, and Chacoparanense basins. The evolution of the diversity is evaluated in a well-constrained biostratigraphic framework, bearing in mind local palaeoenvironmental conditions and changes within each basin. Taking into account recently published and unpublished data from well-dated sections, the biodiversity of Silurian phytoplankton seemingly increases upwards, reaching its maximum peak during the Ludlovian. However, palynomorphs are rarely recorded in Wenlockian strata, and the supposed Pridolian layers are not confidently well constrained. The first record of trilete spores in Argentina is Ludlovian, approximately 30 million years after their first appearance in the Late Ordovician. Palynomorph diversity increases in the Early Devonian, with a higher diversity of miospores than that of the marine phytoplankton. We interpret possible discrepancies in biodiversity trends of organic-walled phytoplankton between Argentina and other regions, as related to the quantitatively and qualitatively disparity of data, as well as the lack of rigorous biostratigraphic and palaeoenvironmental assessments of the Argentinean basins. Copyright © 2011 John Wiley & Sons, Ltd.