Tuff Beds Research Articles

New geochronological constraints for the Lower Cretaceous Jiufotang Formation in Jianchang Basin, NE China, and their implications for the late Jehol Biota

The Lower Cretaceous Jiufotang Formation in western Liaoning Province, northeastern China contains important vertebrate fossils of the late Jehol Biota, e.g., the four-winged non-avian dinosaur Microraptor . This formation documents the late phase of the Jehol Biota, producing the most abundant fossil records of the Mesozoic birds. However, the precise age constraints on the fossiliferous layers of this formation remain scarce and chronological consensus of this formation has not been reached, limiting our understanding of the evolutionary history of the Jehol Biota and its time-spatial distribution. Here we present secondary ion mass spectrometry (SIMS) U-Pb zircon analysis results of four tuff samples interbedded within the Jehol fossil-bearing layers from the Jiufotang Formation outcrops at the Sanmendian and Xiaotaizi sections in the Jianchang Basin, western Liaoning. Stratigraphic correlation between two outcrop sections is achieved by combining lithostratigraphic, biostratigraphic, and SIMS U-Pb zircon dating results. One tuff bed SMD17-1 closed to the boundary of the Yixian/Jiufotang formations from the Sanmendian section yielded an age of 122.0 ± 0.9 Ma, and three tuff beds XTZ17-1, XTZ17-2, and XTZ17-3 from the Xiaotaizi section dated to 118.9 ± 0.8 Ma, 118.8 ± 0.6 Ma, and 118.6 ± 1.1 Ma, respectively. These ages suggest that the Jiufotang Formation in Jianchang Basin was deposited at ca. 122.0–118.9 Ma, the latest Barremian–Aptian stage of the Lower Cretaceous and provides stringent constraints on the Mesozoic vertebrates discovered in the Jianchang Basin. Furthermore, the late Jehol Biota documents in the Jiufotang Formation has been placed between ~123 and ~119 Ma based on our new chronology and previous radiometric dates. It is critical to evaluate the evolutionary history of various important Mesozoic taxa discovered from the Jehol Biota and explore the patterns and modes of major vertebrate lineages documented in this interval. • • We report a new chronology from the Jiufotang Formation in Jianchang Basin, NE China. • • The fossiliferous horizons have precisely constrained to 122.0–118.9 Ma. • • Age calibration for the diversification of mammals and birds of late Jehol Biota. • • Updated age of the Jiufortang Formation for Palaeobiology Database ( paleodb.org /).

New insights on the age and stratigraphy of the Cisuralian succession in the Cooper Basin, Australia, based on U–Pb CA-TIMS dating of volcanic air-fall tuffs

Absolute age constraints for Cisuralian units in the Cooper Basin have been hampered by poorly calibrated palynostratigraphic schemes, with implications for pan-Australian and global correlations. New U–Pb CA-TIMS (uranium–lead chemical abrasion-thermal ionisation mass spectrometry) dates acquired from volcanic air-fall tuff beds from the Patchawarra Formation combined with legacy palynological data offer new insights on the age, stratigraphy and tectonic history of the basin. Six tuffs from different regions of the Cooper Basin give dates from 284.87 to 277.36 Ma, which suggest that the Patchawarra Formation was deposited between the Artinskian and Kungurian rather than from the Sakmarian to Kungurian, as previously thought. The new dates indicate a possible unconformity at the base of the Patchawarra Formation and the underlying Tirrawarra Sandstone. They also suggest that the overlying REM succession (Roseneath Shale, Epsilon Formation and Murteree Shale) is entirely Guadalupian age rather than ranging from the Cisuralian to the Guadalupian. Consequently, existing Cisuralian and Guadalupian high-resolution spore-pollen zonations should be used with care when applied in conjunction with U–Pb CA-TIMS dates. The tuff dates in the thin Patchawarra Formation over the prominent Gidgealpa–Merrimelia–Innamincka Ridge within the Cooper Basin support the interpretation that the ridge was an area of relatively slow subsidence rather than being a positive feature during deposition. Compacted sediment accumulation rates of between 25 and ∼40 m/My for this unit are faster than for most cratonic basins, which raise questions on the tectonic setting of the Cooper Basin. The use and further acquisition of tuff dates will enhance correlations and facilitate improved paleogeographic reconstructions and our understanding of the late Paleozoic ice age. KEY POINTS Six volcanic air-fall tuff beds dated from the Cisuralian Patchawarra Formation, Cooper Basin. U–Pb CA-TIMS dates range from 284.87 to 277.36 Ma. Dates suggest deposition occurred between the Artinskian and Kungurian. New insights on basin tectonics, sedimentation rates and basin stratigraphy.

Výsledky geologického průzkumu kladenského souvrství severně od Nýřan v letech 2007–2021

Coal-bearing sediments of the Radnice and Nýřany members (Kladno Formation) were explored in the SW part of the Plzeň Basin in an area between the villages Pankrác and Rochlov during field seasons of 2007–2021. The goal of the research was to find sites where the Whetstone Horizon (Radnice Member) and the Main Nýřany Coal Seam with fauna-bearing sapropel coal occur close to the surface. Both horizons bear record of the Fossil- Lagerstätte-type, which makes such areas promising for their future exploration as paleontological localities. Based on the combined information from old mining maps, boreholes and geological maps, we suggested sites suitable for future shallow excavations and paleontological research of the fossil-bearing horizons. We tested and further refined our assumptions based on evaluation of archival data from 51 shallow pits and 3 shallow boreholes. The Whetstone Horizon has been found in six different sites at depths between 2 and 7 m. Besides the typical architecture of the Whetstone Horizon composed of the coarse-grained light-coloured tuff at the base (so-called “bělka”) and overlain by laminated tuffitic mudstone (so-called Whetstone) tuffite – tuff – coal seam, also tuffite – tuff – mudstone, tuff – mudstone, tuffite – coal seam and tuffite – arkosic sandstone sequences have been documented. The pits demonstrated that the Whetstone Horizon features variable thicknesses over a short distance. Flora and fauna found in the bělka tuff bed is documented. The Main Nýřany Coal Seam with bands of sapropel coal has been found in two pits.

Did the Boreal Realm extend into the equatorial region? New paleomagnetic evidence from the Tuva–Mongol and Amuria blocks

Fossil organisms of the Boreal Realm in the Tuva–Mongol Block (TMB) and Amuria Block (AMB) are commonly thought to have lived at mid to high latitudes during the Carboniferous Period; however, reliable paleomagnetic constraints have not been available previously to test this hypothesis. Here we report newly obtained combined paleomagnetic and geochronological results from the Upper Mississippian Gunbayan Formation in the AMB and the Lower Pennsylvanian Altan-Ovoo Formation in the TMB. Zircon U–Pb dating of tuff beds from the Gunbayan and Altan-Ovoo formations yield ages of 331.0 ± 2.7 and 315.5 ± 2.4 Ma, respectively. A total of 263 paleomagnetic specimens underwent stepwise thermal demagnetization. After removing the viscous remanent magnetizations of the recent geomagnetic field, stable high-temperature components (HTCs), carried by magnetite, were successfully acquired from 240 specimens. The HTCs of the Gunbayan Formation passed a fold test and a reversal test, and those of the Altan-Ovoo Formation passed a fold test, suggesting that they represent primary remanence magnetizations. We used the elongation/inclination method to test and correct for all the HTC directions of the clastic rocks of the studied formations. Their corresponding paleomagnetic poles are 46.0°N/320.0°E (A=952.0°) at ca. 330 Ma for the AMB and 43.5°N/355.9°E (A=952.9°) at ca. 315 Ma for the TMB. The updated paleomagnetic database indicates with certainty that both the TMB and the AMB were located in northern hemisphere low-latitude regions and close to the equator at ca. 330 Ma, suggesting that the Boreal Realm might have extended into the equatorial region at the onset of the large ice age of the Carboniferous. The paleobiogeographic characteristics and distribution of climate-sensitive lithologies indicate that this realm occupied a wide northern temperate belt during 330–315 Ma.

Geochronology and geochemistry of Middle Permian tuff in Chaohu region, China: Implications for their origin and geological significance

Tuff of Middle Permian as a record of volcanic activity are widely distributed in the northern hemisphere, such as South China, but origin of the tuff bed remains unclear. Stratigraphy, geochronology, geochemistry, and zircon Hf isotopic composition of the tuff layers from Gufeng Formation in Chaohu region, South China, are systemically investigated to reveal the origin of the tuff. The stratigraphical investigation and geochronological dating reveal that zircon U–Pb age of 271.6 ± 3.1 Ma for lower tuff layer is identical to the formation age (272 Ma) of the bottom boundary in the Gufeng Formation, while the zircon U–Pb age of 263.6 ± 3.8 Ma for upper tuff layer represents the boundary age between the lower and upper Gufeng Formation. The tuff with a lot of clastic materials has high Th/Ce (0.18–0.84) and Th/La (0.29–1.23) ratios, enrichment in LREE, Th, U and Hf, and depletion in Ba, Nb and Sr, with obviously negative Eu anomalies (δEu = 0.41–0.58). Compared with the lower tuff layer, the upper tuff layer has higher zircon εHf (t) values (−5.65 to 10.2) and lg fO2 values (−14.6 to −7.42). The distinctly chemical and isotopic results indicate that the intermediate-felsic tuff in the Chaohu region were originated from more crustal materials in early stage of the Gufeng Formation and increased juvenile crustal materials and higher oxygen fugacity in late stage of the Gufeng Formation.

Volcano–air–sea interactions in a coastal tuff ring, Jeju Island, Korea

Abstract The Holocene tuff ring of Songaksan, Jeju Island, Korea, is intercalated with wave-worked deposits at the base and in the middle parts of the tuff sequence. They are interpreted to have resulted from fair-weather wave action at the beginning of the eruption and storm wave action during a storm surge event in the middle of the eruption, respectively. The tuff ring is overlain by another marine volcaniclastic formation, suggesting erosion and reworking by marine processes because of post-eruption changes in sea-level. Dramatic changes in the chemistry, accidental componentry and ash-accretion texture of the pyroclasts are also observed between the tuff beds deposited before and after the storm invasion. The ascent of a new magma batch, related to the chemical change, could not be linked with either the Earth and ocean tides or the meteorological event. However, the changes in the texture of the pyroclasts suggest a sudden change in the diatreme fill from water-undersaturated to supersaturated because of an increased supply of external water into the diatreme. Heavy rainfall associated with the storm is inferred to have changed the water saturation in the diatreme. Songaksan demonstrates that there was intimate interaction between the volcano and the environment.

New data about three sphenophylls and their spores from the volcanic tuff of Wuda, Taiyuan Formation, earliest Permian, China

A new species Sphenophyllum parvifolium sp. nov. is proposed for a whole plant based on organically connected leafy shoots and cones from the Wuda locality, Inner Mongolia, North China. The most characteristic feature is the sporangiophore with lanceolate expansions bearing sporangia. Cones were studied morphologically, including cuticles and in situ spores. Cones yielded monolete spores of the Laevigatosporites or Latosporites type. Other sphenophylls from this locality include Sphenophyllum cf. oblongifolium and Sphenophyllum cf. angustifolium, both with associated cones yielding in situ spores of the same type as Sphenophyllum parvifolium, and sterile specimens of Sphenophyllum kawasakii. Some foliated axes of this type bear cones, but without in situ spores. Hook-like structures at the ends of leaf lobes of these Sphenophyllum species could have enabled the plants to climb. All species are from a volcanic tuff bed, between coal seams Nos. 6. and 7 in the Wuda Coalfield. The age of the plant-bearing tuff in the Taiyuan Formation is 298.34 ± 0.09 Ma (Asselian, earliest Permian).

A revised Permian–Triassic stratigraphic framework for the northeastern Galilee Basin, Queensland, Australia, and definition of a new Middle–Upper Triassic sedimentary unit

The upper Paleozoic–lower Mesozoic strata in the northeastern Galilee Basin are important for their hydrocarbon and groundwater potential; however, despite numerous previous investigations, the nature of this stratigraphic interval remains enigmatic. This study integrates lithostratigraphy, palynology and U–Pb zircon geochronology of well-exposed Permian and Triassic sedimentary rocks and nearby stratigraphic cores from the Hughenden district to determine their maximum depositional ages and then revises the stratigraphy where necessary. The newly defined Galah Tuff Bed was discovered at the top of the Betts Creek beds in Porcupine Gorge and was dated at 251.9 ± 3 Ma. This provides an important age constraint for the Betts Creek beds and is a tie-point for correlations with coeval units in the adjacent Bowen Basin and the Sydney and Gunnedah basins to the southeast. The Galah Tuff Bed is interpreted to correlate with the Yarrabee Tuff in the Bowen Basin. Unconformably overlying the Betts Creek beds is a newly recognised stratigraphic unit, defined herein as the Porcupine Gorge Formation. Detrital zircon maximum depositional ages and palynology indicate a significant depositional hiatus of up to 20 million years between the Betts Creek beds and Porcupine Gorge Formation. The hiatus indicates that the lower part of the Porcupine Gorge Formation is at least upper Middle Triassic, whereas the upper part of the unit extends into the Late Triassic. This age also constrains the overlying Warang Sandstone, which is considerably younger locally than previously reported and is likely diachronous across the northeastern Galilee Basin. KEY POINTS An integrated lithostratigraphy, palynology and U–Pb detrital zircon geochronology methodology is applied to the Permian–Triassic succession the northeastern Galilee Basin. Two new stratigraphic units were recognised: the upper Permian Galah Tuff Bed (251.9 ± 3 Ma) and the late Middle–Late Triassic Porcupine Gorge Formation (238.7 ± 3 Ma). The Galah Tuff Bed, correlative of the Yarrabee Tuff in the Bowen Basin, is evidence for widespread volcanism in the late Permian. The age of the Porcupine Gorge Formation indicates diachroneity of the Triassic succession in the Galilee Basin, warranting further examination.

Late Oligocene\u2014Early Miocene shortening in the Thrace Basin, northern Aegean

Late Cenozoic was a period of large-scale extension in the Aegean. The extension is mainly recorded in the metamorphic core complexes with little data from the sedimentary sequences. The exception is the Thrace Basin in the northern Aegean, which has a continuous record of Middle Eocene to Oligocene marine sedimentation. In the Thrace Basin, the Late Oligocene–Early Miocene was characterized by north-northwest (N25°W) shortening leading to the termination of sedimentation and formation of large-scale folds. We studied the stratigraphy and structure of one of these folds, the Korudağ anticline. The Korudağ anticline has formed in the uppermost Eocene–Lower Oligocene siliciclastic turbidites with Early Oligocene (31.6 Ma zircon U–Pb age) acidic tuff beds. The turbidites are underlain by a thin sequence of Upper Eocene pelagic limestone. The Korudağ anticline is an east-northeast (N65°E) trending fault-propagation fold, 9 km wide and 22 km long and with a subhorizontal fold axis. It is asymmetric with shallowly-dipping northern and steeply-dipping southern limbs. Its geometry indicates about 1 km of shortening in a N25°W direction. The folded strata are unconformably overlain by Middle Miocene continental sandstones, which constrain the age of folding. The Korudağ anticline and other large folds in the Thrace Basin predate the inception of the North Anatolian Fault (NAF) by at least 12 myr. The Late Oligocene–Early Miocene (28–17 Ma) shortening in the Thrace Basin and elsewhere in the Balkans forms an interlude between two extensional periods, and is probably linked to changes in the subduction dynamics along the Hellenic trench.

Self-Organizing Maps for identification of zeolitic diagenesis patterns in closed hydrologic systems on the Earth and its implications for Mars

We have conducted a survey of zeolite occurrences in saline-alkaline paleolake deposits on Earth to identify the most prominent zeolite alteration patterns and to characterize the most common authigenic minerals and their paragenetic relationships. We collected the bulk mineral assemblages (from previous and our studies) as identified by X-ray diffraction from zeolitic tuff beds and associated sedimentary beds from thirteen paleolake deposits from the USA, Mexico, Greece, and Tanzania. We applied the Kohonen Self-Organizing Maps (SOM) to look for interesting patterns in the tuff bed mineral assemblages without prescribing any specific interpretation, and for information reduction and classification. Decision Tree (DT) method was applied to characterize these clusters. We were able to define clear class boundaries between fresh glass, non-analcime zeolites, analcime, and K feldspar. The non-analcime zeolites were further grouped into several classes based on mineral type. We also discuss the potential implications for Mars, showing that the mineral assemblages of diagenetic facies identified by SOM and DT can be used to test or validate the orbital, in situ, or modeling results, while the trained SOM provides a robust generalized ability to classify the new mineral assemblage data into the most common diagenetic facies identified in saline-alkaline paleoenvironments that contain zeolites. The study concludes that generalizing the complex geochemical behaviors using unsupervised statistical learning methods can help to identify the most prominent geochemical behaviors.

Triassic coal measures, Tasmania: new U–Pb CA-TIMS ash bed dates and numerical calibration of palynostratigraphy

Four new high-precision U–Pb ash bed dates constrain the timing and rate of coal measures deposition in Tasmania and, combined with new palynological data, allow improved numerical age calibration of eastern Australian Late Triassic spore-pollen biozones. Felsic ashfall tuff beds are numerous in the middle and upper parts of the 400 m-thick Mount Nicholas Coal Measures of northeast Tasmania. Our four U–Pb CA-TIMS dates on zircon span 99 m of section and range from 222.52 to 217.84 Ma. All four dates are closely associated with palynomorph assemblages belonging to the Craterisporites rotundus Assemblage Zone. Our data indicate an age of at least 223 Ma, and likely several million years older, for our earliest observed C. rotundus Zone assemblages, whereas the base of the Polycingulatisporites crenulatus Zone may be ca 217 Ma (and no older than 217.84 Ma). KEY POINTS Felsic ash beds are common in the middle and upper parts of the Upper Triassic Mount Nicholas Coal Measures. The ash beds have yielded four new U–Pb CA-TIMS dates on zircon that span 99 m of section and range from 222.52 to 217.84 Ma. The new dates all lie within the upper part of the Craterisporites rotundus Assemblage Zone.

Petrography, mineralogy, and geochemistry of the Hemrin Basalt, Northern Iraq: Implications for petrogenesis and geotectonics

The studied Hemrin Basalt (HB) was previously mis-identified and called burnt hills. The HB is studied petrographically and geochemically as constraints for its provenance and geotectonics. The immobile trace element plot of Zr/TiO2–Nb/Y as well as mineralogy, textures and hand specimen appearance indicate that the studied rocks are basalts. This basalt occurs as surficial thin layer capping few hills along a NW/SE oriented direction within the Injana Formation in the Low-Folded Tectonic Zone, which is not related and far from the ophiolites of northeastern Iraq. It consists dominantly of diopside, labradorite and volcanic glass, and many accessory and secondary vesicle-filling minerals (amygdules). The basalt is very fine-grained with a massive and vesicular/amygdaloidal structures, and sub-ophitic as well as very rare and unusual textures, called firework and feathery in this study which are very similar to those of lunar basalts. The large ion lithophile elements (LILE) are enriched 4.8 times relative to the high field strength elements (HFSE), indicated from the MORB-normalized diagram for major and trace elements. The average content of rare earth elements (REE) in HB is 140 ppm with 10.6 times enrichment of LREE relative to HREE which is reflected in their chondrite-normalized diagram having a negative slope of 7.6 and a small Eu-anomaly of 0.7. The (La/Yb)n–La plot showed that the source magma was fractionally crystallized; whereas, the immobile trace element ratios and elemental values such as Nb/U, Ce/Pb, Nb/La, LREE/HREE, LILE/HFSE, Zr, Hf, Nb, and Ta indicated that source magma for HB was contaminated while rising through the Arabian continental crust. Many major, immobile trace and REE element discriminating diagrams showed that the studied rocks are high-K calc-alkaline basalts formed as a continental volcanic arc under orogenic convergent tectonic conditions because of the continent-continent collision between the Arabian and Turkish/Iranian plates. The surficial HB and the surrounding calc-alkaline tuffs are probably related and formed by the same volcanic eruption during Quaternary period, <0.5 Ma ago. The source of HB is most probably a hot spot volcano erupted in the area close to the studied hills, ejecting large amounts of volcanic ash which deposited the tuff beds and the associated bentonites in the surroundings, and culminated by a basaltic flow which formed the HB.

A tuffaceous volcaniclastic turbidite bed of Early Miocene age in the Temburong Formation of Labuan, North‐West Borneo and its implications for the Proto‐South China Sea subduction in the Burdigalian

AbstractA 2 m thick bed of smectite‐rich clay within a sequence of distal deep water turbidites and marine mudstones of the Temburong Formation on the island of Labuan, Sabah, North‐West Borneo, is an altered, re‐sedimented pyroclastic tuff which is geochemically of rhyolite‐dacite composition. The tuff bed was deposited in deep water, although probably &lt;1,000 m, by traction currents and retains relic siliceous shards, feldspar phenocrysts and biotite crystals but was dominated by ash‐grade material. The tuff is interpreted as a turbidite deposit and most probably records long distance sub‐marine transport down the depositional slope from an active volcanic system in the hinterland. It has a zircon U–Pb weighted mean age of 19.6 ± 0.1 Ma whilst combined forminiferal and nannofossil ages from the enclosing marine mudstones range from 21.5 to 19.4 Ma; together these indicate an early Miocene age for the Temburong Formation. The tuff is the result of a very short‐lived volcanic arc magmatic episode and was either related to similar aged volcanics of the Sintang Suite in central Borneo or a product of the Proto‐South China Sea subduction beneath the Cagayan arc north‐east of Borneo. The age indicates that deep water sedimentation in North‐West Borneo continued into the Burdigalian suggesting the subduction trench of the Proto‐South China Sea was active into the early Miocene, beneath the depocentre of the Temburong turbidite fan. By contrast, sandstones representative of the typical marine Temburong Formation yield abundant zircons which are dominately Cretaceous in age indicating an important switch in source provenance during the Early Miocene from the Crocker Formation that is dominated by Permian‐Triassic zircons. This difference in zircon populations likely reflects an important tectonic event in the early Miocene that resulted in uplift of central Borneo to supply sediment to the Sabah Trough whilst the input of material derived from the western terrains diminished. The Temburong Formation was sourced by reworking of uplifted Rajang Group, Sapulut or Trusmadi formations.

Chapter 2.1a Ferrar Large Igneous Province: volcanology

Abstract Preserved rocks in the Jurassic Ferrar Large Igneous Province consist mainly of intrusions, and extrusive rocks, the topic of this chapter, comprise the remaining small component. They crop out in a limited number of areas in the Transantarctic Mountains and southeastern Australia. They consist of thick sequences of lavas and sporadic occurrences of volcaniclastic rocks. The latter occur mainly beneath the lavas and represent the initial eruptive activity, but also are present within the lava sequence. The majority are basaltic phreatomagmatic deposits and in at least two locations form immense phreatocauldrons filled with structureless tuff breccias and lapilli tuffs with thicknesses of as much as 400 m. Stratified sequences of tuff breccias, lapilli tuffs and tuffs are up to 200 m thick. Thin tuff beds are sparsely distributed in the lava sequences. Lava successions are mainly 400–500 m thick, and comprise individual lavas ranging from 1 to 230 m thick, although most are in the range of 10–100 m. Well-defined colonnade and entablature are seldom displayed. Lava sequences were confined topographically and locally ponded. Water played a prominent role in eruptive activity, as exhibited by phreatomagmatism, hyaloclastites, pillow lava and quenching of lavas. Vents for lavas have yet to be identified.

Carajás Mineral Province - Example of metallogeny of a rift above a cratonic lithospheric keel

The Carajás Mineral Province (CMP) is located on the southeastern margin of the Amazonian Craton, in northern Brazil. It is the largest producer of high-grade iron ore and a major world supplier of copper, nickel, manganese and gold. This article presents the CMP as a product of oblique rift evolution (2.76–2.06 Ga) controlled by the Canaã and Cinzento strike slip system. The Carajás rift is hosted in the tonalite-trondhjemite-granodiorite (TTG)-greenstone Rio Maria terrains (3.0–2.85 Ga). It overlies a subcratonic lithospheric mantle (SCLM) keel as indicated by seismic tomography and is filled by the Carajás plutonic-volcanic sedimentary sequences (CPVSS) that host the CMP. The rifting stage (Grão Pará Group) began with intense tholeiitic fissure volcanism with basalt and rhyolite flows, coeval intrusions of alkali granites and mafic-ultramafic bodies, BIFs, shales and restricted tuff beds. The Azul and Águas Claras Formations consist mainly of shales and sandstones deposited during the sag stage. The calc-alkaline signature of the Grão Pará metavolcanic rocks was demonstrated to reflect the composition of the melted TTG basement. The high magnesium and platinum-group elements (PGE) contents of Puma and Onça mafic-ultramafic complexes indicate extensive partial fusion, conditions that are indicative of a plume origin. We are proposing that CMP's IOCG deposits were formed from saline carbonate fluids exsolved from deep-seated metasomatic mantellic magmas (MMM), channelled and concentrated along jogs and step-overs in strike-slip fault systems in the Carajás rift.The CMP comprises three main ore-forming stages: (1) a plume stage, ca. 2.76–2.73 Ga, creating supergiant exhalative sedimentary biogenic Fe deposits (Serra Norte, Serra sul and Serra Leste), syngenetic exhalative Cu–Au–Zn (Pojuca deposit), exhalative Mn (Antonio Vicente), Ni-PGE-reef deposits in a magma mixing zone of layered intrusions (e.g. Luanga deposit), and Siqueirinho IOCG deposit; (2) a metasome stage including crustal extension and mantle flash melting (60–100 km depth), ca. 2.68–2.50 Ga, forming the most important IOCG deposits like Salobo, Alemão and Igarapé Bahia. and (3) a sag stage, ca. 2.68–2.06 Ga, with sedimentary Mn deposited in a redox-controlled stratified oceanic environment. The deposits related to granitic intrusion, ca. 1.88 Ga, with Cu-(Au–Mo–W–Sn) greisen (Breves deposit) and Cu-(Au–Mo–F) veins (Gameleira and Alvo 118 deposits) are associated with the A-type magmatism that affected the entire central Amazonian Craton. These deposits are, in contrast, related to an intracratonic silicic large igneous province (SLIP) and have no relation to the Archean Carajás cratonic lithosphere keel rift evolution. The CMP is directly related to the thinning of the lithosphere above a mantle plume, beneath a sub-continental lithospheric mantle (SCLM) keel.

T0 Early Permian coal-forest preserved in situ in volcanic ash bed in the Wuda Coalfield, Inner Mongolia, China

An early Permian tuff bed between Coal 7 and Coal 6 of the Wuda Coalfield in Inner Mongolia bears T0 peat-forming vegetation preserved in situ. Documentation of the fossil record uncovered in an area of about 80 m2 shows 14 morphotaxa representing 11 whole-plant species with a wide variety of growth forms. The uncovered phytocoenosis is interpreted as a forest dominated by cordaites as the tallest trees, the remains of which covered over 50% of the excavated area. Marattialean tree ferns represent the lower canopy that was not taller than about 3 m. This storey fills gaps between cordaites and covers over 20% of the area. A rare element of lower canopy taxa was the cycadophyte genus Pterophyllum represented by a single plant. Poorly developed herbaceous groundcover includes Sphenophyllum oblongifolium, and four small fern species mostly with sphenopteroid type of foliage. Although members of the herbaceous layer covered only 7% of the excavated area, it was the most diverse storey of the peat-forming forest. Considering the small area excavated, along with the higher diversity known from the same tuff bed in the adjacent, former opencast mine, it appears that species richness in the forest was comparable to some of the less diverse Westphalian peat-forming floras in Euramerica.

Sedimentological analysis and radioisotopic age of the Las Cañas Formation in Dulce river outcrops, Río Hondo, Santiago del Estero (Northwestern Argentina)

In northwestern Argentina (NWA), particularly at ~27° S, the best known Neogene depocenters are intermountain tectonic valleys located in the Sierras Pampeanas geological province. Conversely, basins located to the east from the Aconquija and Ambato ranges, toward the Chaco-Pampean Plain, have been scarcely studied due to the extensive vegetal coverage. In the last decade, despite some contributions were focused in these areas and reported valuable data concerning tectonic and lithological interpretations, chronostratigraphic data are scarce, even absent so far. Herein we present a sedimentological analysis and an 40Ar/39Ar age of the Dulce River outcrops related to the Neogene Guasayán Range deposits, at the transition between NW Sierras Pampeanas and Chaco-Pampean Plain basin (~27° S). The study area includes Neogene fossiliferous sediments of the Las Cañas Formation; particularly, we focused in a section located between Cañada de la Costa and Sotelo localities (Río Hondo Department, Santiago del Estero Province). The chronostratigraphic study allowed us to assign an early Pliocene age to the studied section of the unit; the first absolute dating obtained for this formation is 3.73 ± 0.07 Ma. The measured stratigraphic logs are ~540 m thick of relatively well-preserved light to reddish-brown clastic deposits. The paleoenvironmental analysis of partial stratigraphic sections suggests the presence of a braided sandy river with well-developed muddy floodplains. We identified two fossiliferous beds below the dated tuff bed, separated by a tuffaceous-sandstone deposit. The new chronostratigraphic datum indicates that the Guasayán Range began to rise during the late Pliocene. Based on the stratigraphy, absolute age, and geographical location of the studied area, a correlation among the Las Cañas Formation, India Muerta Formation (NW Sierras Pampeanas), and the Pozo del Tigre Member, Chaco Formation (Chaco-Pampean Plain) is suggested. This study represents a significant contribution in the context of the scarcely, isolated, and fossiliferous Neogene outcrops of the Tucumán Basin.

Occurrence of a Likely Tuff Bed between the Middle and Upper Siwaliks, Taunsa area, Dera Ghazi Khan, Eastern Sulaiman Range, Pakistan

A likely tuff bed lies along the gradational contact of the Middle and Upper Siwaliks in eastern Sulaiman Range, Taunsa area of Dera Ghazi Khan district, Pakistan. This tuffaceous unit is 0.5–3 m thick and extends for 10 km along the north-south strike in the eastern limb of the Zindapir anticline. It is greyish white to white on fresh surface, fine-grained to silty at the bottom and clayey at the top and thus shows a fining upward grain-size grading. The lower part of the ash bed shows a prominent lamination defined by megascopically visible abundant biotite, while the central and upper parts are so fine-grained that the individual minerals cannot be seen in hand sample. Unlike the lower well-laminated part, the central and upper parts are crudely laminated to apparently massive. The bulk samples analysed with X-ray diffraction consist of quartz, feldspar (plagioclase), biotite, clays, calcite and some ore mineral likely spinel, while the clay-size fractions contain illite, chlorite, biotite and probably their mixed-layered varieties. The colour, texture, presence of abundant biotite and stratigraphic position of the Taunsa tuff correlate with those reported from Potwar plateau and from Kashmir basin. However, the apparent absence of smectite from the XRD pattern makes the Taunsa ash bed different from both Potwar and Kashmir tuffs. The present stratigraphic position of the tuff bed corresponds to shallow diagenetic zone, while the absence of smectite in the tuff and crystallinity of illite suggest that the tuff is probably derived upon reworking from a deeper diagenetic zone belonging to a lower stratigraphic level. The Eocene or other older pre-Siwalik units in Pakistan may have or had some primary ashfall deposits as reported in the northwestern Himalayas of India. This older volcanic ash may have been reworked to its present site of occurrence along the gradational contact of the Middle and the Upper Siwaliks in Taunsa area of Dera Ghazi Khan. However, the primary source of the Taunsa tuff may belong more likely to Chagai arc in Pakistan than to Dacht-e-Nawar volcanic complex in Afghanistan.

Occurrence of a Likely Tuff Bed between the Middle and Upper Siwaliks, Taunsa area, Dera Ghazi Khan, Eastern Sulaiman Range, Pakistan

A likely tuff bed lies along the gradational contact of the Middle and Upper Siwaliks in eastern Sulaiman Range, Taunsa area of Dera Ghazi Khan district, Pakistan. This tuffaceous unit is 0.5–3 m thick and extends for 10 km along the north-south strike in the eastern limb of the Zindapir anticline. It is greyish white to white on fresh surface, fine-grained to silty at the bottom and clayey at the top and thus shows a fining upward grain-size grading. The lower part of the ash bed shows a prominent lamination defined by megascopically visible abundant biotite, while the central and upper parts are so fine-grained that the individual minerals cannot be seen in hand sample. Unlike the lower well-laminated part, the central and upper parts are crudely laminated to apparently massive. The bulk samples analysed with X-ray diffraction consist of quartz, feldspar (plagioclase), biotite, clays, calcite and some ore mineral likely spinel, while the clay-size fractions contain illite, chlorite, biotite and probably their mixed-layered varieties. The colour, texture, presence of abundant biotite and stratigraphic position of the Taunsa tuff correlate with those reported from Potwar plateau and from Kashmir basin. However, the apparent absence of smectite from the XRD pattern makes the Taunsa ash bed different from both Potwar and Kashmir tuffs. The present stratigraphic position of the tuff bed corresponds to shallow diagenetic zone, while the absence of smectite in the tuff and crystallinity of illite suggest that the tuff is probably derived upon reworking from a deeper diagenetic zone belonging to a lower stratigraphic level. The Eocene or other older pre-Siwalik units in Pakistan may have or had some primary ashfall deposits as reported in the northwestern Himalayas of India. This older volcanic ash may have been reworked to its present site of occurrence along the gradational contact of the Middle and the Upper Siwaliks in Taunsa area of Dera Ghazi Khan. However, the primary source of the Taunsa tuff may belong more likely to Chagai arc in Pakistan than to Dacht-e-Nawar volcanic complex in Afghanistan.

Geological implications of gamma ray (GR) anomalies in marine shales: A case study of the Ordovician-Silurian Wufeng-Longmaxi succession in the Sichuan Basin and its periphery, Southwest China

Conventionally, high gamma ray (GR) values usually indicate high argillaceous contents in sedimentary rocks, while high-GR sections in marine shales have more siliceous minerals and fewer clay minerals. However, the origin of the anomalously high-GR peaks in marine shales has been less well studied. In addition, high-GR marine shale intervals are usually important sections for horizontal drilling and fracturing. The Wufeng-Longmaxi shales in the Sichuan Basin and its periphery were investigated to study the sedimentary characteristics and genesis of anomalously high-GR peaks based on elemental and natural GR spectral logging data, sedimentary observations and geochemical analysis. Uranium enrichment is concluded to control the GR peak occurrences in the Wufeng-Longmaxi shales, and uranium enrichment is affected by a hypoxic reducing environment, high organic matter content, well-developed tuff beds, and the adsorption of phosphorus-bearing minerals and iron-bearing minerals. The anomalously high-GR peaks are manifestations of volcanic activity and rapid transgression. Rutile, uranium-bearing minerals, apatite, barium feldspar and tuff beds are petrological evidence of volcanic activity, and Fe, K and U/Th ratio anomalies also show geochemical evidence of volcanic activity. The degree of water stagnation, disorderly mineral distribution, and reducing environment are evidences of rapid transgression. The uranium enrichment indicates that volcanic eruptions provided large numbers of uranium ions for the seawater uranium pool, forming a material basis for uranium shale deposition. De-glaciation transgression provided a sedimentary environment and pathways for uranium enrichment. Two uranium enrichment events are identified in the Wufeng-Longmaxi shales. The high-GR shale section controlled by notable uranium enrichment is characterized by an anoxic reducing environment, high TOC content, good pore structure and high brittleness. High-GR segment identification contributes to shale gas sweet spot detection. This study demonstrates that high-GR anomalies in marine shales are related to geological events and also provide certain time references for marine shales.