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The oldest known specimens of the enigmatic mollusc Jinonicella kolebabai Pokorný, 1978 are redescribed from Middle Ordovician strata of Ukraine and Belarus. The phosphatic internal moulds preserve imprints of growth lines, hitherto only documented in Silurian specimens. The persistent distribution of Jinonicella in the Baltoscandian basin of the Russian Platform suggests that this was the centre of origin of this taxon. During the Silurian, Jinonicella inhabited Siberia and Laurentia, and the smaller European terranes of Bohemia and the Carnic Alps. In the Devonian, Jinonicella is reported from Laurentia, Bohemia and the Rhenish Massif. [ABSTRACT FROM AUTHOR]

The Paleozoic evolution of Patagonia was the focus of controversies between its allochthonous or autochthonous origin. The arrival of plate tectonics supported new allochthonous alternatives and from an initial fixist resistance, different mobilistic hypotheses have made their way. There is currently some consensus about its allochthony, but there is no agreement on collision times or in the configuration of the continental blocks involved. Based on the present data an alternative is developed that fits better with existing information. The northeast-vergent deformation in Ventania System, the Hespérides Basin, its wide longitudinal and transverse distribution, show that collision occurred in the northern sector of Northern Patagonian Massif, and extended through the southern African Gondwanides. Their similar metamorphic and tectonic patterns identified a previous southward subduction with a Permian climax, characteristic of a continent-continent collision. The associated magmatic arc has been partially obliterated by slab-breakoff and delamination in the Late Permian-Triassic. The western magmatic belt along the Pacific margin is older, spanning from Devonian to mid-Carboniferous. The Chaitenia island arc collision in Upper Devonian produced an episode of exhumation and uplift. This western belt extends into Tierra del Fuego island and its contour allows tentatively to recognize a Southern Patagonian terrane. It is speculated that this block may have included the Antarctic Peninsula, although more data is needed to characterize its composition and areal development. However, it is concluded that the dimensions of this southern terrane cannot justify the broad regional deformation of the Gondwanides. [ABSTRACT FROM AUTHOR]

The paleogeographic evolution of the Moroccan Variscides has been a matter of discussion for several decades, with current theories mostly based on classical geological correlations. In this regard, the scarce number of studies devoted to U-Pb geochronological analyses of detrital zircon populations is particularly limiting when trying to ascribe the different domains to a single continental piece either derived from the West African Craton or to different sources, with some located in the Nubian Shield or the Saharan Metacraton. In this work, detrital zircon grains from 10 samples of sandstones from the Paleozoic (Ordovician to Devonian) sequence of the Eastern Meseta and Middle Atlas were dated in order to identify possible sediment sources and elucidate the paleogeography of this easternmost portion of the Moroccan Variscides. The main detrital zircon populations have Ediacaran-Cryogenian ages (610–670 Ma, related to the Cadomian and/or Pan-African orogeny) and middle Paleoproterozoic ages (1980–2080 Ma, related to the Eburnean orogeny), which are in agreement with previous data from the Western Meseta, suggesting similarity between both Mesetas, and strong West African Craton affinity. Such an affinity verifies the most accepted paleogeographic interpretation considering that the Moroccan Mesetas remained attached to northern Gondwana during the entire Paleozoic period. The main differences between our samples and those from the Western Meseta concern the minor detrital zircon populations, such as the Cambro-Ordovician and the Tonian-Stenian ones. In particular, Eastern Meseta and Middle Atlas samples lack a Cambro-Ordovician detrital zircon population, usually interpreted as related to the rifting that opened the Rheic Ocean. This population is locally reported in the Western Meseta and widely described in southwestern Europe, where magmatism of this age is well known. Furthermore, the most northeastern samples are also characterized by a Tonian-Stenian detrital zircon population (up to 30% of the data), which might imply northeastern African sources (Saharan Metacraton and/or Arabian-Nubian Shield). Unlabelled Image • Ordovician-Devonian samples from Eastern Meseta and Middle Atlas were studied. • The main detrital zircon populations are Ediacaran-Cryogenian and Paleoproterozoic. • These detrital zircon populations suggest WAC affinity for the studied area. • The minor Tonian-Stenian population might be sourced in north-eastern Africa. • There is no evidence of the Cambro-Ordovician rifting in the studied region. [ABSTRACT FROM AUTHOR]

Abstract In this paper we present a method to integrate core-log data when a full set of good quality velocity measurements on core samples is not available. We used some simple and justified assumption along with additional information that came from static triaxial tests. Large number of used core data significantly reduces uncertainty of obtained results. We started from evaluating five components of the stiffness tensor, and then calculated the static and dynamic moduli and Thomsen's parameters. The proposed method is based on data from three wells located in the Early Paleozoic Baltic Basin in Poland. The parameters were calculated based on data from one reference well-denoted in this paper as A-1. For this well, around 300 m of core was retrieved from the lower Silurian and Ordovician interval and a significant number of tests were performed on core samples. Results were then validated for the next two wells denoted as B-1 and C-1. The obtained model fits quite well with core data, which shows that chosen method proved to be efficient. Highlights • Core-log data integration for mechanical modeling of a transversely isotropic rock. • The method for integration in case of poor quality or missing mechanical core data. • Special case for Silurian and Ordovician shales from the Baltic Basin, Poland. [ABSTRACT FROM AUTHOR]

Abstract Overall petrologic and geochemical data indicate that the early Paleozoic magmatism in the Olkhon area of the Baikal Region exhibits diverse types of granitoids, whose time of formation is estimated at a narrow age interval of 500-465 Ma. This magmatism was responsible for the formation of both autochthonous gneiss-migmatite-granitoid suites (Sharanur complex) and multiphase intrusions (Aya complex) emplaced into the upper horizons of the continental crust. In major-element chemistry, K 2 O/Na 2 O values, and rare-element composition the migmatite-plagiogranites and calc-alkaline and subalkaline granitoids of the Sharanur complex are similar to the host gneisses and schists, as they were likely derived from melting of the ancient metamorphic substratum of the Olkhon series. In new isotope-geochemical characteristics (ICP MS method) the Sharanur granitoids are close to the first-phase biotite granites of the Aya massif, whose further geochemical evolution was governed mainly by intrachamber magmatic differentiation leading to the production of second-phase leucogranites enriched in HREE and HFSE (in particular, Ta and Nb) and depleted in Sr, Ba, Eu, Li, and LREE. The origin of the autochthonous and intrusive granitoids is related to early Paleozoic collision events within the Olkhon metamorphic terrane, while the formation of syncollisional granitoids is best explained by both melting of the crust protolith (Sharanur complex) and magmatic differentiation (multiphase Aya intrusion). All mineralogical and geochemical characteristics indicate that these granitoids are distinguished from rare-metal pegmatoid granites and Li-F and Rb-Be-Nb pegmatites, whose vein bodies crosscut the granitoids, and are regarded as middle Paleozoic rocks, which mark the transition to within-plate magmatism in the Baikal Region. [ABSTRACT FROM AUTHOR]

Abstract The Dunhuang Tectonic Belt (DTB) is located about 100 km south of the Beishan–Tianshan orogen in the Central Asian Orogenic Belt in NW China. It was previously considered as a part of the Tarim or North China craton. Detailed structural analyses reveal two episodes of deformation in the central DTB, D1 and D2. D1 is a north-side-up reverse shear, and D2 a dextral strike slip. Mineral assemblages, microstructures and quartz C-axis patterns indicate that D1 deformation took place under amphibolite facies conditions (500 to 600 °C) and D2 mostly under greenschist-facies conditions (300–450 °C). U–Pb zircon dating of eight granitoid/intermediate intrusions (mostly dikes, with well constrained cross-cutting relationships with the D1 and D2 structures) and an amphibolite gneiss indicates that D1 deformation took place before ca. 349 Ma and most likely at ca. 406 Ma, and D2 between ca. 249 Ma and ca. 241 Ma. The DTB has a structural, metamorphic and magmatic signature in the Paleozoic–Mesozoic that is typical of an orogenic belt. It shares a similar geological history with the Beishan–Tianshan orogen and is likely a part of the Central Asian Orogenic Belt. The DTB and the Beishan-Tianshan orogen might represent two separate Paleozoic mountain belts that developed more or less synchronously on the south and north sides, respectively, of the last vestige of the Paleo-Asian Ocean before its terminal closure in the Permian. The D1 reverse shearing in the DTB is interpreted to be related to a Silurian–Devonian terrane accretion/collision and the D2 dextral strike slip to post-accretional/collisional movement among terranes in Late Permian–Middle Triassic time. Highlights • Two episodes of deformation are recognized in the Dunhuang Tectonic Belt (DTB): D1, a N-side-up reverse shear, and D2, a dextral strike slip. • U–Pb zircon dating indicates that D1 took place before ca. 349 Ma and most likely at ca. 406 Ma, and D2 at ca. 249–241 Ma. • The DTB has characteristics in the Paleozoic–Mesozoic that are typical of an orogenic belt and is likely a part of the Central Asian Orogenic Belt. • The DTB might represent a Paleozoic mountain belt that developed on the south side of the last vestige of the Paleo-Asian Ocean. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Three Upper Paleozoic megasequences are proposed in the Beishan Region, NW China. • They are interpreted to have formed in response to three respective tectonic stages. • The southern Paleo-Asian Ocean is considered to have closed before the Carboniferous. Abstract The Upper Paleozoic sedimentary sequence in the Beishan Region, northwest China, provides a complete record of the complex amalgamation and extension history of the Central Asian Orogenic Belt (CAOB) for this part of China. Integrating newly obtained stratigraphic, paleontological and radiometric data, this paper reviews the Upper Paleozoic stratigraphic sequences of the Beishan Region. The Upper Paleozoic strata here are divided into three megasequences (MS). They are, in ascending order: Devonian, Mississippian–Guadalupian and Lopingian megasequences (MS1, MS2, and MS3), separated by two major unconformities each indicative of a huge sedimentary hiatus. MS1 is made up of continental and epicontinental marine deposits in the pre-rift stage; MS2 of transgressive marine and volcanic strata in the syn-rift stage; and MS3 of continental sediments in the inversion stage. The major unconformity between MS1 and MS2 is interpreted to represent the regional uplift and erosion caused by the final amalgamation of CAOB in the Beishan Region. The syn-rift MS2 represented by transgressive marine and volcanic strata in the Beishan Region can be well-correlated with Pennsylvanian–Guadalupian megasequences in Inner Mongolia, where they rest on a major interregional unconformity. This correlation suggests the closure of the Paleo-Asian Ocean in Beishan and Inner Mongolia before the Carboniferous, followed by the development of a synchronous marine rift megasequence in the southern part of the CAOB. [ABSTRACT FROM AUTHOR]

The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells, or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The Reggane, Ahnet, Mouydir and Illizi basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches. Through the analysis of new unpublished geological data (i.e., satellite images, well logs, seismic lines), the deposits associated with these arches and syncline basins exhibit thickness variations and facies changes ranging from continental to marine environments. The arches are characterized by thin amalgamated deposits with condensed and erosional surfaces, whereas the syncline basins exhibit thicker and well-preserved successions. In addition, the vertical facies succession evolves from thin Silurian to Givetian deposits into thick Upper Devonian sediments. Synsedimentary structures and major unconformities are related to several tectonic events such as the Cambrian–Ordovician extension, the Ordovician–Silurian glacial rebound, the Silurian–Devonian "Caledonian" extension/compression, the late Devonian extension/compression, and the "Hercynian" compression. Locally, deformation is characterized by near-vertical planar normal faults responsible for horst and graben structuring associated with folding during the Cambrian–Ordovician–Silurian period. These structures may have been inverted or reactivated during the Devonian (i.e., Caledonian, Mid–Late Devonian) compression and the Carboniferous (i.e., pre-Hercynian to Hercynian). Additionally, basement characterization from geological and geophysics data (aeromagnetic and gravity maps), shows an interesting age-dependent zonation of the terranes which are bounded by mega-shear zones within the arches–basins framework. The "old" terranes are situated under arches while the "young" terranes are located under the basins depocenter. This structural framework results from the accretion of Archean and Proterozoic terranes inherited from former orogeny (e.g., Pan-African orogeny 900–520 Ma). Therefore, the sedimentary infilling pattern and the nature of deformation result from the repeated slow Paleozoic reactivation of Precambrian terranes bounded by subvertical lithospheric fault systems. Alternating periods of tectonic quiescence and low-rate subsidence acceleration associated with extension and local inversion tectonics correspond to a succession of Paleozoic geodynamic events (i.e., far-field orogenic belt, glaciation). [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The Kon Tum massif is an Early to Middle Triassic Metamorphic Core Complex (MCC). • A top-to-the NW ductile shearing accommodated the exhumation. • The MCC superimposes on an Early Paleozoic collision belt between N. and S. Vietnam. • The collision was the driver of the Early Paleozoic intracontinental belt of S. China. • The interaction between Emeishan mantle plume and continental subduction is proposed. Abstract In Central Vietnam, the Kontum massif is subdivided from North to South into: (i) Kham Duc, (ii) Ngoc Linh, (iii) Kan Nack complexes. The Kham Duc complex consists of metapelite, metapsammite, paragneiss, metagabbro, amphibolite, serpentinized ultramafic, and orthogneiss blocks. The southern part of this complex experienced an Early Paleozoic crustal melting event responsible for migmatites and anatectic granites. The Ngoc Linh complex, the largest one, is formed by metatexite and granitoid enclosing blocks of eclogite, high pressure (HP) granulite, orthogneiss, metagabbro, amphibolite, granodiorite, and migmatite. The Kan Nack complex is formed by migmatites with (ultra) high temperature (U)HT granulite, charnockites and enderbites. The three metamorphic complexes are intruded by per-aluminous granite, and subordinate mafic plutons. In spite of local variations, the foliation of the Ngoc Linh complex defines a bulk domal structure, and the stretching lineation consistently trends NW-SE. The NW-SE lineation is also observed in the tectonically overlying the Kan Nack complex. The Ngoc Linh and Kan Nack complexes are interpreted here as parts of a metamorphic core complex (MCC), or “Ngoc Linh MCC”, exhumed by a top-to-the-NW detachment fault. Along the northern margin of the Ngoc Linh MCC, upright folds with E-W striking axes, and E-W stretching lineation deform the foliation. These structures are developed in a transpressive regime coeval with the activity of plurikilometer-scale dextral strike-slip faults. Zircon and monazite U/Pb radiometric datings document a 250–240 Ma age for the crustal melting, and the top-to-the-NW ductile shearing coeval with the formation of the Ngoc Linh MCC. This extensional tectonics is followed by a dextral strike-slip faulting, at ca 240–230 Ma, before the emplacement of the two-mica granitic plutons at ca 240–224 Ma. Furthermore in the Ngoc Linh and Kan Nack complexes, zircon and monazite yield U-Pb Early Paleozoic ages. In the Kham Duc complex, a ca 460 Ma MP/MT, garnet-biotite-staurolite-kyanite metamorphism, followed by migmatites at ca 450 Ma, is also recognized. The 420–400 Ma age of the Dai Loc plutonic suite, and the 450–425 Ma age of the Dien Binh calc-alkaline granodiorite document an Early Paleozoic event. The Early Paleozoic mafic and ultramafic masses of the Hiep Duc complex are ophiolites included into a metasedimentary matrix. Thus, the Kham Duc complex is interpreted as a tectonic mélange formed during a collisional orogeny that subsequently underwent crustal melting giving rise to the migmatites. A part of the Early Paleozoic rocks are enclosed as xenoliths in the Triassic migmatite of the Ngoc Linh MCC. These petrologic, structural, and chronological features allow us to propose the following geodynamic evolution for the Kontum massif. During the Early Paleozoic, a continental collision, which was accommodated by a north-directed subduction of a southern block (S. Vietnam, or Viet-Cambodia block) below a northern block (N. Vietnam or Viet-Lao block), occurred along the Tam Ky-Phuoc Son suture. During the Early Triassic, at ca 250–245 Ma, the S. Vietnam block experienced a crustal melting giving rise to the Ngoc Linh MCC that reworked the Early Paleozoic orogen. Lastly, during the Middle Triassic, the dextral faulting superimposed upon the Ngoc Linh migmatite. The geodynamic significance of the Kontum massif is discussed in the general framework of Indochina- South China relationships. The Early Paleozoic collision in Vietnam is viewed as the driving force responsible for the development of the intracontinental orogeny of S. China. In order to account for the important heat flow required for the formation of UHT metamorphic rocks, a possible interaction between the SCB-Indochina collision, and the Emeishan mantle plume is proposed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Paleozoic magmatism occurred in the Central-East Iranian Microcontinent. • It preserves a continental collision along the northern frontier of Gondwana. • U-Pb dating of three generations of zircons shows 518 Ma, 483 Ma, 382 Ma of ages. Abstract This paper presents petrographic and U-Pb LA-ICP-MS isotopic data of a single peraluminous intrusion (alkali-feldspar granite of Airekan) with partial gneissic foliation on the north western margin of the Yazd Block in the west of the Central-East Iranian Microcontinent (CEIM) to discuss the evolution of this terrain. This intrusion typically suggests a continental collision orogenesis along the northern frontier of Gondwana in the CEIM. The U-Pb dating of zircons indicates that Airekan granite has a distinctive inherited magmatic component at ∼518.2 ± 4.9 Ma but zircons with 892, 679, 614 and 554 Ma ages. These zircons were likely to be ultimately sourced from neighboring Neoproterozoic – Cambrian leucogranite terrains, similar to the other localities in the northern margin of Gondwana, along the Alpine-Himalayan belt from Europe, Turkey, NE Iran, CEIM, Pakistan, India to southern Tibet. The zircons and overgrowths around the inherited components with igneous morphology indicate a plutonism at Lower Ordovician (∼483 ± 2.9 Ma). Petrographic features and morphology of zircon crystals indicate that partial resetting of the U-Pb system in zircons have occurred at ∼382.6 ± 3.2 Ma in Devonian, during the Paleo-Tethys evolutions in Khur region (Anarak-Jandaq terrane) in the southern active margin of Laurasia. [ABSTRACT FROM AUTHOR]

U–Pb and Lu–Hf isotope analyses of detrital zircons collected from the Devonian–Permian strata of Kotel’ny Island (New Siberian Islands, Eastern Russian Arctic) provide vital information about provenance areas and history of the poorly studied Paleozoic basement of the Laptev and East Siberian shelves. Based on detrital zircon signatures, our study reveals that the studied succession can be divided into two distinct groups: Devonian–Lower Carboniferous and uppermost Carboniferous–Permian. U–Pb and Lu–Hf isotope signatures of detrital zircons from the Devonian–Lower Carboniferous deposits correspond to well-known Precambrian–Early Paleozoic magmatic and metamorphic events within the northern part of Baltica, indicative of a peri-Baltican affinity of the New Siberian Islands during this time. A lack of zircon ages close to the depositional age of the formation, along with a mature composition of the sandstones, suggest that the Devonian–Lower Carboniferous succession formed as a result of extensive sediment reworking from a distal provenance. By contrast, uppermost Carboniferous–Permian sandstones have an immature composition, with numerous young detrital zircons close to the age of sedimentation and Hf signatures typical of a continental arc environment. We therefore suggest that the provenance for these younger deposits was located within a coeval orogeny and based on previous studies, we conclude that these deposits were sourced from the north-western part of the Uralian Orogen. [ABSTRACT FROM AUTHOR]

Combined (U-Th)/He and U-Pb detrital zircon geochronological data are reported from Ordovician to Devonian strata of the Severnaya Zemlya archipelago to address the paleogeography of the Kara Terrane in the Russian High Arctic. (U-Th)/He ages from all six samples analyzed were not reset after sediment deposition, indicating that detrital zircons carry information on the exhumation history in the source region of the clastic material. In Ordovician-Silurian strata, (U-Th)/He ages range from 583.8 ± 46.7 to 429.0 ± 34.3 Ma. These ages nicely coincide with significant regional exhumation during the Caledonian and Timanian orogenies. In addition, combined U-Pb and (U-Th)/He dating show that within the source region, zircons that were crystalized during the Timanian Orogeny (U-Pb ages 680–560 Ma) were likely exhumed during younger Caledonian events ((U-Th)/He ages of 455–495 Ma), suggesting potential overlap of these orogens within the source region. In Devonian strata, detrital zircon (U-Th)/He ages range from 517.2 ± 41.38 to 332.9 ± 26.6 Ma, with a peak age of ca. 375 Ma. This 375 Ma event may be correlated with either the Ellesmerian Orogeny or the terminal Solundian/Svalbardian stages of the Caledonian Orogeny. [ABSTRACT FROM AUTHOR]

The Barluk arc, situated in West Junggar, is an important component of the Kazakhstan domain in the Central Asian Orogenic Belt (CAOB). However, the nature of the Barluk arc (active continental margin or oceanic island arc) is in debate. The igneous rocks in the Shiwu area, Barluk arc, have diagnostic petrologic, geochronologic and geochemical signatures that uncover the attributes of the Barluk arc. In this paper, we report detailed petrology, whole rock geochemistry and Sr–Nd isotopic, zircon U–Pb dating and Hf isotopic data of igneous rocks in the Shiwu area. Our results reveal that: (1) except for 302.2 Ma gabbro, igneous rocks from Barluk arc in the Shiwu area are dioritic and granitic, have ages ranging from 323.8 to 310.5 Ma, and they have geochemical signatures originated from typical continental arcs, including calc-alkaline series rocks, enrichment of LILE, depletion of HFSE, and higher Th/Yb and Ta/Yb values; (2) the granitic porphyry and rhyolite in Barluk arc have old T DM2 (Hf) ages, up to 1091 Ma, suggesting the existence of Precambrian crust or similar materials as their sources; and (3) The 302.2 Ma gabbro dike has high values of εNd(t) (+7.54) and εHf(t) (+12.8 to +15.5), and a young T 2DM (Nd) age (455 Ma), and therefore it was possibly related to upwelling of asthenosphere mantle in a post-subduction extensional tectonic setting. Based on these parameters, we suggest that the Barluk arc is defined as a Late Paleozoic continental margin arc along the margin of the Kazakhstan Continent. Westward subduction of the Junggar Oceanic plate in the Barluk area started in Early Devonian and continued to the Late Carboniferous (310 Ma). Subsequent post-collisional tectonic processes between the Junggar Oceanic plate and Kazakhstan Continent continued to the Late Carboniferous (302 Ma). [ABSTRACT FROM AUTHOR]

Geological redox proxies increasingly point towards low atmospheric oxygen concentrations during the early Paleozoic Era, with a subsequent protracted rise towards present-day levels. However, these proxies currently only provide qualitative estimates of atmospheric O2 levels. Global biogeochemical models, in contrast, are commonly employed to generate quantitative estimates for atmospheric O2 levels through Earth's history. Estimates for Paleozoic pO2 generated by GEOCARBSULF, one of the most widely implemented carbon and sulfur cycle models, have historically suggested high atmosphericO2 levels throughout the Paleozoic, in direct contradiction to competing models. In this study, we evaluate whether GEOCARBSULF can predict relatively low Paleozoic O2 levels. We first update GEOCARBSULF by adopting the recent compilation of the δ13C value of marine buried carbonate and replacing the old formulation of the sulfur isotope fractionation factor with empirical sulfur isotope records. Following this we construct various O2 evolution scenarios (with low O2 levels in the early Paleozoic) and examine whether GEOCARBSULF can reproduce these scenarios by varying the weathering/degassing fluxes of carbon and sulfur, or carbonate δ13C. We show that GEOCARBSULF can, in fact, maintain low-O2 (even 1-5% atm) levels through the early Paleozoic by only varying the carbonate δ13C within 2 standard deviation (SD) bounds permitted by the geological record. In addition, it can generate a middle-late Paleozoic rise in O2 concentration, coincident with the diversification of land plants. However, we also argue that tracking atmospheric O2 levels with GEOCARBSULF is highly dependent on carbonate carbon isotope evolution, and more accurate predictions will come from an improved C isotope record. [ABSTRACT FROM AUTHOR]

With proven gas potential, the gas charging and accumulation mechanisms for the Upper Paleozoic tight gas reservoir in the Longdong District of the Ordos Basin remain controversial. Pore structure is the most direct and critical factor that affects gas charging and accumulation in the reservoir. However, the pore structure characterization of tight sandstone is far more difficult than that for conventional reservoir rocks due to significant heterogeneity. The present work aims to introduce a new quantitative method for pore structure characterization that integrates multi-fractal distribution analysis, an effective and profitable method for quantitative heterogeneity analysis, and high-pressure mercury intrusion porosimetry (HPMIP). Twenty-one samples from targeted tight formations with different gas-bearing status were obtained for analysis. The results show that the best formations for gas charging and accumulation in the Upper Paleozoic tight sandstone formations in the Longdong District are the formations with more large pores, more homogeneous small pores, and well-developed micro-fractures. The existence of micro-fractures is the key factor that affects gas charging and accumulation. Tight sandstone samples were categorized into three types in accordance with the HPMIP curve configuration. Due to the high heterogeneity of pore structures, analyses based solely on HPMIP curve configuration has its shortcomings, which can be compensated by multi-fractal distribution analysis. The multi-fractal distribution of target tight formations could be interpreted as two linear segments, representing large pores and small pores. The separating points of the two segments vary from 0.1 μm to 0.5 μm in different samples due to different pore structures. Large pores are not ideal fractals in gas-bearing formations due to the existence of micro-fractures, whereas they are fractals in dry formations where micro-fractures are not developed. Small pores are all ideal fractals, with the highest heterogeneity in type γ samples and the lowest heterogeneity in type α samples. A conclusion was made in this work: if the slope of segment one in the multi-fractal distribution of mercury saturation ( S Hg ) versus capillary pressure ( P C ) is larger than 1, this measure could be accepted as an empirical indicator for the existence of micro-fractures. [ABSTRACT FROM AUTHOR]

The Ediacaran-Ordovician Meguma Supergroup was thrust over Avalonia basement prior to the intrusion of post-Acadian, ca. 370 Ma, S-type granitic batholiths. This has led to two main hypotheses regarding the original location of the Meguma terrane, a continental rise prism bordering either NW Africa or Avalonia. On the other hand, the pre-Acadian, ca. 440 Ma Brenton pluton has yielded the following U/Pb LA-ICP-MS zircon data: (1) 448 ± 3 Ma population peak inferred to be the intrusive age and (2) ca. 550 and 700 Ma inherited ages common to both Avalonia and NW Africa. In contrast, Hf isotopic analyses of zircon yielded model ages ranging from 814 to 1127 Ma with most between 940 and 1040 Ma: such ages are typical of Avalonia and not NW Africa. The ages of the inherited zircons found within the Brenton pluton suggest that it was probably derived by partial melting of sub-Meguma, mid-crustal Avalonian rocks, upon which the Meguma Supergroup was deposited. Although Avalonia is commonly included in the peri-Gondwanan terranes off NW Africa or Amazonia, paleomagnetic data, faunal provinciality, and Hf data suggest that, during the Ediacaran-Early Cambrian, it was an island chain lying near the tropics (ca. 20-30 °S) and was possibly a continuation of the Bolshezemel volcanic arc accreted to northern Baltica during the Ediacaran Timanide orogenesis. This is consistent with the similar derital zircon population in the Ediacaran-Cambrian Meguma Supergroup and the Dividal Group in northeastern Baltica. [ABSTRACT FROM AUTHOR]

The source of the Lower Paleozoic natural gas in the Ordos Basin has been a highly controversial issue. Using data obtained from newly drilled wells, we present the geochemical characteristics of Lower Paleozoic natural gas in various regions of the Ordos Basin. The Lower Paleozoic natural gas is dominated by hydrocarbons, of which methane accounts for 40.17%–97.24%, and the heavier gaseous hydrocarbon (C 2+ ) ranges from 0.01% to 9.72%. Non-hydrocarbon gases in the Lower Paleozoic gas reservoir are mainly CO 2 and N 2 , 2%–10% for CO 2 and 0.04%–48.56% for N 2 , higher than those in the Upper Paleozoic gas reservoir. This observation showed that the high CO 2 and N 2 content was related to the Ordovician marine carbonate rock deposits. The carbon and hydrogen isotopes of the methane, ethane, and propane in the Lower Paleozoic natural gas of the Ordos Basin showed various degrees of reversal, indicating the mixing origin of natural gas. In the central–eastern Ordos Basin, coal-derived gas from the Carboniferous–Permian (C-P) coal measure and oil-associated from the Lower Ordovician Majiagou Formation marine source rocks gas coexist, as well as mixtures of these two gases. For the Lower Paleozoic natural gas from the western margin of the basin, coal-derived gas coexist with oil-associated gas, but no mixing gas, in which coal-derived gas originated mainly from the C–P source rocks and oil-associated gas from the Lower Ordovician Kelimoli Formation and Middle Ordovician Wulalike Formation source rocks in the western margin of the basin. The Lower Paleozoic natural gas in the southern part of the Ordos Basin was mixing gas, and the oil-associated gas is the dominant one. The natural gas was originated from the Lower Ordovician Majiagou Formation source rocks in the central–eastern Ordos Basin and the Pingliang Formation mudstone and argillaceous limestone at the southern margin of the basin. [ABSTRACT FROM AUTHOR]

A structural-geological study has been performed on the northern slope of the Kyrgyz Ala-Too Range. Deformations of the peneplaned Paleozoic basement surface, structures of granite disintegration, and morphostructural manifestation of Late Cenozoic tectonic movements have been investigated. Based on the location of pre-Paleocene peneplain remnants with the retained weathering mantle partly overlapped by Paleocene-Miocene sedimentary complexes, we have reconstructed the morphology of the folded surface of the Chunkurchak Trough separated from the Chu Basin at the early Miocene. The dome-fold forms, the morphology and arrangement of which are controlled by disintegration of the basement, have been described for the basement surface. It has been established that granites are broken by systems of steeply dipping, fanshaped, and gently dipping faults and fractures. Variously oriented insignificant offsets along slickensides, as well as displacements deduced from the geometry of fracture intersections, are a result of volumetric cataclastic flow of rocks. The tectonic mobility of disintegrated granites, which are abundant in the Paleozoic-Precambrian basement, explains the complexity and scale of tectonic processes initiated by Cenozoic activation. In paleotectonic reconstructions, which take into consideration tectonic flow and the redistribution of basement masses, the estimates of Cenozoic relative rapprochement of the Chu Basin and the Kyrgyz Ala-Too Range decrease substantially to 4-6 km. [ABSTRACT FROM AUTHOR]

The Eocene Heart Mountain slide of northwest Wyoming covers an area of as much as 5000 km2 and includes allochthonous Paleozoic carbonate and Eocene volcanic rocks with a run-out distance of as much as 85 km. Recent geochronologic data indicated that the emplacement of the slide event occurred at ~48.9 Ma, using laser ablation inductively coupled plasmamass spectrometry (LA-ICPMS) extracted fromU-Pb zircon ages frombasal layer and injectite carbonate ultracataclasite (CUC). We now refine that age with U-Pb results from a lamprophyre diatreme that is temporally and spatially related to the CUC injectites. The ages for the lamprophyre zircons are 48.97 ± 0.36 Ma (LA-ICPMS) and 49.19 ±0.02 Ma (chemical abrasion isotope dilution thermal ionization mass spectrometry). Thus, the lamprophyre and CUC zircons are identical in age, and we interpret that the zircons in the CUC were derived from the lamprophyre during slide emplacement. Moreover, the intrusion of the lamprophyre diatreme provided the trigger mechanism for the Heart Mountain slide. Additional structural data are presented for a variety of calcite twinning strains, results from anisotropy of magnetic susceptibility for the lamprophyre and CUC injectites and alternating-field demagnetization on the lamprophyre, to help constrain slide dynamics. These data indicate that White Mountain experienced a rotation about a vertical axis and minimum of 35° of counterclockwise motion during emplacement. [ABSTRACT FROM AUTHOR]

Fossil brachiopods are of major importance for the reconstruction of palaeoenvironmental conditions, particularly of the Paleozoic. In order to better understand signals of ancient shell materials, modern analogue studies have to be conducted. Here we present C and O isotope data in conjunction with Mg/Ca, Sr/Ca, Mn/Ca and Fe/Ca data for nine modern rhynchonellid and terebratulid brachiopod species from tropical to intermediate latitudes and shallow to very deep marine settings. C and O isotope signals of most species suggest formation of secondary shell layers near or in isotopic equilibrium with ambient seawater. Some species – especially in the suborder Terebratellidina – show partly distinct disequilibrium signals, suggesting some degree of phylogenetic control on the expression of vital effects. Mn/Ca and Fe/Ca ratios measured in the modern species form a baseline to assess fossil preservation, but also yield environmental information. Mg/Ca and Sr/Ca ratios follow previously observed patterns, with all studied brachiopod species comprising low-Mg calcite. Strong covariation of Sr/Ca ratios with Mg/Ca ratios is only observed in rhynchonellids and possibly one terebratulid species, potentially linking the incorporation behaviour of alkaline earth metals to phylogeny. Sr/Ca show a strong negative correlation with δ 13 C values in terebratellidinid species which exhibit major isotopic disequilibrium and also combined data from three localities for which two species were studied indicate such a negative relation. The observed covariation of Sr/Ca ratios with δ 13 C values may therefore become a useful tool to detect δ 13 C disequilibrium and to robustly estimate δ 13 C values of ambient DIC in deep time. [ABSTRACT FROM AUTHOR]

In placing Japanese tectonics in an Asian context, variation in the Paleozoic geological environment is a significant issue. This paper investigates the geochemistry of the lower Paleozoic basalt formation (Iwatsubodani Formation) in the Hida Gaien belt, Japan, to consider its tectonic setting. This formation includes the following two types of rock in ascending order: basalt A with sub-ophitic texture and basalt B with porphyritic texture. Basalt A has a high and uniform FeO*/MgO ratio, moderate TiO, high V, and low Ti/V. The HFSE and REE are nearly the same as those in MORB, and all the data points to basalt A being the 'MORB-like fore-arc tholeiitic basalt (FAB)' reported, for example, from the Izu-Bonin-Mariana arc. By contrast, basalt B has a low FeO*/MgO ratio, low TiO, and low V and Ti/V. It has an LREE-enriched trend and a distinct negative Nb anomaly in the MORB-normalized multi-element pattern and a moderately high LREE/HREE. All these factors suggest that basalt B is calc-alkaline basalt. It is known that FAB is erupted at the earliest stage of arc formation-namely, subduction initiation-and that boninitic/tholeiitic/calc-alkaline volcanism follows at the supra-subduction zone (SSZ). Thus, the occurrence of basalts A (FAB) and B (calc-alkaline rock) is strong evidence of early Paleozoic arc-formation initiation at an SSZ. Evidence for an early Paleozoic SSZ arc is also recognized from the Oeyama, Hayachine-Miyamori, and Sergeevka ophiolites. Hence, both these ophiolites and the Iwatsubodani Formation probably coexisted in a primitive SSZ system in the early Paleozoic. [ABSTRACT FROM AUTHOR]

A mosaic of terranes or blocks and associated Late Paleozoic to Mesozoic sutures are characteristics of the north Sanjiang orogenic belt (NSOB). A detailed field study and sampling across the three magmatic belts in north Sanjiang orogenic belt, which are the Jomda-Weixi magmatic belt, the Yidun magmatic belt and the Northeast Lhasa magmatic belt, yield abundant data that demonstrate multiphase magmatism took place during the late Paleozoic to early Mesozoic. 9 new zircon LA-ICP-MS U-Pb ages and 160 published geochronological data have identified five continuous episodes of magma activities in the NSOB from the Late Paleozoic to Mesozoic: the Late Permian to Early Triassic (c. 261-230 Ma); the Middle to Late Triassic (c. 229-210 Ma); the Early to Middle Jurassic (c. 206-165 Ma); the Early Cretaceous (c. 138-110 Ma) and the Late Cretaceous (c. 103-75 Ma). 105 new and 830 published geochemical data reveal that the intrusive rocks in different episodes have distinct geochemical compositions. The Late Permian to Early Triassic intrusive rocks are all distributed in the Jomda-Weixi magmatic belt, showing arc-like characteristics; the Middle to Late Triassic intrusive rocks widely distributed in both Jomda-Weixi and Yidun magmatic belts, also demonstrating volcanic-arc granite features; the Early to Middle Jurassic intrusive rocks are mostly exposed in the easternmost Yidun magmatic belt and scattered in the westernmost Yangtza Block along the Garzê-Litang suture, showing the properties of syn-collisional granite; nearly all the Early Cretaceous intrusive rocks distributed in the NE Lhasa magmatic belt along Bangong suture, exhibiting both arc-like and syn-collision-like characteristics; and the Late Cretaceous intrusive rocks mainly exposed in the westernmost Yidun magmatic belt, with A-type granite features. These suggest that the co-collision related magmatism in Indosinian period developed in the central and eastern parts of NSOB while the Yanshan period co-collision related magmatism mainly occurred in the west area. In detail, the earliest magmatism developed in late Permian to Triassic and formed the Jomda-Wei magmatic belt, then magmatic activity migrated eastwards and westwards, forming the Yidun magmatic bellt, the magmatism weakend at the end of late Triassic, until the explosure of the magmatic activity occurred in early Cretaceous in the west NSOB, forming the NE Lhasa magmatic belt. Then the magmatism migrated eastwards and made an impact on the within-plate magmatism in Yidun magmatic belt in late Cretaceous. [ABSTRACT FROM AUTHOR]

We present results of lithological and geochemical studies of Paleozoic deposits stripped by drilling within the Ledyanskaya area in the north of the Tunguska syneclise. The studied section has a terrigenous sulfate-carbonate composition and is complicated by trap intrusions. We have established that the Ordovician-Devonian sedimentation proceeded within an epicontinental basin, with its depth varying from supralittoral to lower sublittoral zones. In the Carboniferous and Permian, coastal-continental sedimentation was predominant; in the Late Permian it was accompanied by volcanic activity. Analysis of the poroperm properties of rocks has distinguished three potential oil reservoirs: Silurian reef carbonate deposits and Ordovician and Carboniferous sand horizons. The Lower Silurian argillaceous-carbonate rocks and Devonian carbonate-sulfate-clay members, halite beds, dolerite bodies, and tuffaceous rocks are probably confining beds of these reservoirs. Geochemical study of organic matter has shown several possible sources of hydrocarbons: Upper Proterozoic deposits, Lower and Middle Cambrian Kuonamka complex, Middle Devonian Yukta Formation, and Upper Paleozoic coal-bearing deposits. [ABSTRACT FROM AUTHOR]

The W Au, Pb Zn Ag, and Sb Ba mineralizations of the polymetallic Tighza-Jbel Aouam district (central Meseta, Morocco), are hosted in Paleozoic rocks surrounding late-Carboniferous granitic stocks. The Pb Zn Ag Tighza deposit formed at 254 ± 16 Ma, and is clearly disconnected from the late-Variscan W Au deposit (295-280 Ma). The Pb Zn Ag mineralization precipitated from a complex hydrothermal fluid. It displays air-normalized 3 He/ 4 He ratio (0.018–0.103) typical of the upper crust. This crustal component is confirmed by the oxygen and carbon isotope compositions (δ 18 O = +19 to +25‰; δ 13 C = −3.6 to −11.2‰) and the ɛ Nd values (−4.84 to −9.01) of gangue carbonates, which show mixing of (i) fluids that have interacted with late-Carboniferous magmatic rocks, and (ii) fluids in equilibrium with the Paleozoic metasediments. In addition, the Pb Zn Ag mineralization has 40 Ar/ 36 Ar values in the range 284–315 typical of a meteoric fluid. The radiogenic Pb isotopic compositions ( 207 Pb/ 204 Pb = 15.70–15.80 and 206 Pb/ 204 Pb = 18.30–18.50) suggest leaching of Pb from the surrounding Paleozoic metasediments and late-Variscan granites, whereas the low radiogenic signatures ( 207 Pb/ 204 Pb = 15.40 and 206 Pb/ 204 Pb = 18.05) provide evidence of a deeper source attributed to the lower crust. Crustal thinning related to extensional tectonics in late-Permian and Early-Triassic lead to high-K calc-alkaline to alkaline magmatic activity, which is evidenced by a dense SW-NE-trending dike network that pre-dated the Atlantic Ocean opening (early Liassic times). This magmatic event induced a regional heat flux increase that triggered the circulation of a complex hydrothermal fluid, which has a strong crustal component, but also a meteoric and a lower crustal components. The polymetallic district of Tighza-Jbel Aouam thus results from superposition of an intrusion related porphyry-gold mineralization (W Au, 286 Ma) followed by a Pb Zn Ag epithermal mineralization (254 Ma), during two distinct magmatic-hydrothermal events. The proposed metallogenic model for the Pb Zn Ag Tighza-Jbel Aouam deposit provides new constraints for the Pb Zn Ag exploration in the Moroccan Meseta. Exploration targets must take into account the following geological features: (i) Permo-triassic high-K calk-alkaline to alkaline dikes, (ii) extensional tectonics and reactivation of ancient crust-scale faults and shear zones, and (iii) Paleozoic series containing organic matter (e.g., black shales) subjected to low grade metamorphism (e.g., greenschist facies). [ABSTRACT FROM AUTHOR]

Zircon U–Pb ages, geochemical data and Sr–Nd isotopic data are presented for volcanic rocks from the lower Permian Dashizhai Formation. These rocks are widely distributed in the south-eastern Central Asian Orogenic Belt in central Inner Mongolia, China. The volcanic rocks mainly consist of basaltic andesite and rhyolite, subordinate dacite and local andesite, and exhibit bimodal geochemical features. The results of zircon U–Pb dating indicate that the volcanic rocks formed during the early Permian (292–279 Ma). The mafic volcanic rocks belong to low-K tholeiitic to medium-K calc-alkaline series. These mafic volcanic rocks are also characterised by moderately enriched light rare earth element (LREE) patterns; high abundances of Th, U, Zr and Hf; negative Nb, Ta and Ti anomalies; initial 87 Sr/ 86 Sr ratios of 0.70514–0.70623; and positive ε Nd (t) values (+1.9 to +3.8). These features indicate that the mafic volcanic rocks were likely derived from the high-percentage partial melting of subduction-related metasomatised asthenospheric mantle. The felsic rocks show an A-type affinity, with enrichments in alkalis, Th, U and LREEs. The felsic rocks are depleted in Ba, Sr, Nb, Ta and Ti and exhibit moderately LREE-enriched patterns (La N /Yb N = 2.09–6.45) and strongly negative Eu anomalies (Eu/Eu ∗ = 0.04–0.25). These features, along with the positive ε Nd ( t ) values (+2.6 to +7.7) and young T DM2 ages (T DM2 = 435–916 Ma), indicate that the felsic rocks were likely derived from a juvenile crustal source that mainly consisted of juvenile mid-ocean ridge basalt -related rocks. The volcanic association in this study and in previously published work widely distributed in central Inner Mongolia. The observations in this study suggest that the lower Permian volcanic rocks formed in an identical tectonic environment. The regional geological data indicate that the bimodal volcanic rocks from the lower Permian Dashizhai Formation in the study area formed in an extensional setting that was likely related to post-collisional delamination. [ABSTRACT FROM AUTHOR]

In this paper, some potassic and ultrapotassic rocks in the South China Block (SCB) have been recognized, according to a set of new geochronological, geochemical and Sr-Nd isotopic data. Zircon U-Pb dating from six plutons yield consistent crystallization ages of 445–424 Ma. These potassic and ultrapotassic rocks can be geochemically subdivided into three groups. Group 1, represented by the Longchuan gabbro, longmu diabase, Tangshang and Danqian diorite (445–433 Ma), have low silica contents (SiO 2 = 47.38–54.16 wt.%), and high MgO (4.21–9.51 wt.%) and total alkalis (Na 2 O + K 2 O = 3.08–5.57 wt.%), with K 2 O/Na 2 O ratios of 0.62–1.82. They are enriched in LREE and depleted in Ba, Sr and Ta-Nb-Ti, and exhibit relatively high initial 87Sr/86Sr ratios (0.70561–0.71128), low ε Nd (430 Ma) values (−8.4 to −3.2), suggesting that they were most plausibly generated by the partial metling of enriched mantle source (EMI). Group 2, from the Huwei diorite (424 Ma), have 45.68–52.87 wt.% of SiO 2 , 5.79–9.25 wt.% of MgO and 52–65 of mg-number. They have significantly higher Th (9.92 ppm), Ce (88.0–115 ppm) concentration and Ce/Yb (27.6–46.8), Th/Yb ratios (2.58–7.99), and relatively low initial 87Sr/86Sr ratios (0.70501–0.70599), and high ε Nd (430 Ma) values (−2.1 to −1.5). We propose that they originated from the partial melting of the depleted mantle source with subsequent contamination by crustal materials. Group 3, represented by the Daning lamprophyre (∼445 Ma), has SiO 2 contents ranging from 41.73 wt.% to 45.22 wt.%, MgO from 13.74 wt.% to 15.16 wt.%, and mg-muber from 73 to 77, with high K 2 O/Na 2 O ratios (>2.0). They have 87Sr/86Sr ratios of 0.62912–0.70384 and ε Nd (t = 430 Ma) values of −6.4 to −6.3, indicating that the source components are close to the EMI source, with significant sediments involved. These Silurian potassic and ultrapotassic rocks in the SCB can be responsible for post-orogenic delamination and intra-plate extension. And the delamination had a small size and a long duration, and a negligible impact. [ABSTRACT FROM AUTHOR]

Two Gondwana-derived Paleozoic belts rim the Archean/Paleoproterozoic nucleus of the East European Platform in the Black Sea region. In the north is a belt of Paleozoic passive-margin-type sedimentary rocks, which extends from Moesia to the Istanbul Zone and to parts of the Scythian Platform (the MOIS Block). This belt constituted the south-facing continental margin of the Laurussia during the Late Paleozoic. This margin was deformed during the Carboniferous by folding and thrusting and forms the Variscan foreland. In the south is a belt of metamorphic and granitic rocks, which extends from the Balkanides through Strandja, Sakarya to the Caucasus (BASSAC Block). The protoliths of the metamorphic rocks are predominantly late Neoproterozoic granites and Paleozoic sedimentary and igneous rocks, which were deformed and metamorphosed during the Early Carboniferous. There are also minor eclogites and serpentinites, mostly confined to the northern margin of the BASSAC Block. Typical metamorphism is of low pressure-high temperature type and occurred during the Early Carboniferous (Visean, 340-330 Ma) coevally with that observed in the Central Europe. Volumetrically, more than half of the crystalline belt is made up of Carboniferous-earliest Permian (335-294 Ma) granites. The type of metamorphism, its concurrent nature over 1800 km length of the BASSAC Block and voluminous acidic magmatism suggest that the thermal event probably occurred in the deep levels of a continental magmatic arc. The BASSAC arc collided with Laurussia in the mid-Carboniferous leading to the foreland deformation. The ensuing uplift in the Permian resulted in the deposition of continental red beds, which are associated with acidic magmatic rocks observed over the foreland as well as over the BASSAC Block. In the Black Sea region, there was no terminal collision of Laurussia with Gondwana during the Late Paleozoic and the Laurussia margin continued to face the Paleo-Tethyan ocean in the south. [ABSTRACT FROM AUTHOR]

Continuing palaeofloristic studies in the Northern Tocantins Fossil Forest, we describe two new calamitalean species from the Permian of the Parnaíba Basin (central-north Brazil). The fossils comprise axes of various sizes, preserved anatomically as siliceous petrifactions, and found in highly mature sandy fluvial deposits of the Motuca Formation. Based on anatomical and morphological characteristics, Arthropitys tocantinensis sp. nov. and Arthropitys barthelii sp. nov. are described. They share a small central pith cavity (extremely reduced in the latter), scalariform tracheid pitting, and prominent pitting of the ray parenchyma. However, they differ markedly in their branching system: the former having 3–12 branches per node either with or lacking secondary growth, the latter showing 2–17 branches without any secondary growth. However, in A . tocantinensis sp. nov., the presence of large woody branches supports a more complex architecture with at least three successive orders of branches. The extensive secondary tissue in both species is homogeneous; clear segmentation is only visible in the proximal wood of A . tocantinensis sp. nov., but completely absent in A . barthelii sp. nov. The growth architecture of these upright growing, self-supporting trunks are reconstructed based on sizable transverse and longitudinal preparations. Our results confirm that thick woody calamitaleans were elements of disturbed riparian vegetation and much more diverse in terms of anatomy and branching patterns than previously thought. They were well adapted to seasonally dry conditions and formed major plant constituents of Permian low-latitude Southern Hemisphere communities. Additionally, we report the first evidence of colonisation on arborescent calamitaleans by herbaceous sphenophyte axes from the Permian. One of the Arthropitys stems hosts at least 30 Sphenophyllum shoots of various ontogenetic stages, growing inside the destroyed pith, which was previously excavated by arthropod boring. Based on the distribution of key genera within late Paleozoic floras of Euramerica, Gondwana and Cathaysia floral realms cluster analysis and Jaccard Coefficient highlight the distribution of a “Mid-North Brazilian” phytogeographic Region during the early Permian. [ABSTRACT FROM AUTHOR]

The Paleozoic accretionary orogenesis and continental crustal growth in Central Asia are thought to have close relationship with the evolution of the Paleo-Asian Ocean (PAO). The well-exposed plutons in the northern Barleik Mountains of the West Junggar region, NW China, may provide essential insights into the evolution of the Junggar Ocean, a branch of the PAO, and mechanism of continental crustal growth. Our work on the Barleik plutons indicates an early suite of 324–320 Ma diorite and a late suite of 314–259 Ma quartz syenite and granitic porphyry. All the plutons are characterized by high-K calc-alkaline to shoshonitic signatures, varying depletion in Nb, Ta, Sr, P, Eu, and Ti, low initial 87 Sr/ 86 Sr ratios (0.70241–0.70585), strongly positive ε Nd (t) values (+ 5.7–+7.7), and young one-stage Nd model ages (390–761 Ma), suggesting that they resulted from different batches of magma that were produced by fractional crystallization of a metasomatized mantle source with minor crustal contamination. The diorite is coeval with the youngest arc magmatic rocks, indicating a subduction-related origin. By contrast, the quartz syenite and granitic porphyry are geochemically similar to A 2 -type granites, with high Zr, Ga, and FeO T /[FeO T + MgO], and are coeval with the widespread plutons in the West Junggar. This, together with the occurrence of Late Carboniferous fluvial deposits and the lack of < 320 Ma ophiolitic and subduction-related metamorphic lithologies, definitively indicates a post-collisional setting after the closure of the Junggar Ocean. Slab breakoff accompanied by asthenospheric upwelling and basaltic underplating is a possible geodynamic process that is responsible for the post-collisional magmatism and vertical crustal growth in the region. Thus a tectonic switch from subduction to post-collision started at the end of the Early Carboniferous (~ 320 Ma), probably as a result of the final closure of the Junggar Ocean. [ABSTRACT FROM AUTHOR]

Tight sandstone gas is regarded as a significant unconventional resource. One intriguing problem for tight sandstone gas accumulation is how gas was trapped in the tight-sandstone reservoirs. In this paper, we attempted to look for a reasonable explanation for this, which has attached great theoretical and practical significances. In this study, a dynamic equilibrium equation characterizing the critical buoyancy threshold (CBT) was established based on physical experiments, and the formation mechanism of tight gas and CBT were discussed. The explanations were further testified through the tight-gas reservoirs of the Upper Paleozoic Ordos Basin. A dynamical CBT occurs during the charge process in tight-gas reservoirs, and water- gas inversion with separating phases is dominated before natural gas reaches the CBT. At this stage, the driving force for gas movement is abnormal gas pressure, and almost no buoyancy exists. The pore throats, smaller than those corresponding to the CBT, enable the formation water to resist the gas to move upward. As a result, with no water-gas displacements, the gas migrates upward in a piston-like style forming continuous gas reservoir. The corresponding pore throat and depth of the CBT are geologically significant, which indicates a critical condition. However, the CBT condition is not constant and varies significantly according to the geologic setting. The case study of the tight-gas reservoirs of the Upper Paleozoic Ordos Basin indicates that the critical pore-throat radius was 1.77 µm by the end of the Early Cretaceous, with the corresponding critical permeability and porosity value of 0.686 mD and 10.6%, respectively. In contrast, its current counterparts are 1.33 µm, 0.39 mD, and 8.6%, respectively, which indicates that the original tight sandstone gas reservoir has shrunk during the geologic history. [ABSTRACT FROM AUTHOR]

An extended description of the implementation of the deep geothermal wells GRT-1 and GRT-2 respectively drilled in 2012 and 2014 in the framework of the ECOGI project is given. These wells located in Rittershoffen (France) offer a unique opportunity to gather high quality datasets on a deep geothermal system in the Upper Rhine Graben at the transition between the Buntsandstein sandstone and the Palaeozoic granite basement. We present the extensive logging and well testing program that was applied and focus on hydraulic and thermal characterization of the targeted deep reservoir. Well architectures of GRT-1 and GRT-2 are described. Temperature logs in both wells are discussed in details. In particular, temperature in the production well GRT-2 is shown to reach 177 °C at 3196 m MD at thermal equilibrium. Production tests of both wells, reservoir development strategy applied in well GRT-1 and circulation test realised between wells are analysed. Productivity and injectivity indexes of GRT-1 and GRT-2 are estimated: Post-stimulation injectivity of GRT-1 and productivity of GRT-2 are respectively estimated to 2.5 l/s/bar and 3.5 l/s/bar. Hydraulic properties of the reservoir are inferred from production tests. Implications for the characterization of the large scale natural hydro-thermal system are discussed. [ABSTRACT FROM AUTHOR]

Both reservoir engineers and petrophysicists have been concerned about dividing a reservoir into zones for engineering and petrophysics purposes. Through decades, several techniques and approaches were introduced. Out of them, statistical reservoir zonation, stratigraphic modified Lorenz (SML) plot and the principal component and clustering analyses techniques were chosen to apply on the Nubian sandstone reservoir of Palaeozoic – Lower Cretaceous age, Gulf of Suez, Egypt, by using five adjacent wells. The studied reservoir consists mainly of sandstone with some intercalation of shale layers with varying thickness from one well to another. The permeability ranged from less than 1 md to more than 1000 md. The statistical reservoir zonation technique, depending on core permeability, indicated that the cored interval of the studied reservoir can be divided into two zones. Using reservoir properties such as porosity, bulk density, acoustic impedance and interval transit time indicated also two zones with an obvious variation in separation depth and zones continuity. The stratigraphic modified Lorenz (SML) plot indicated the presence of more than 9 flow units in the cored interval as well as a high degree of microscopic heterogeneity. On the other hand, principal component and cluster analyses, depending on well logging data (gamma ray, sonic, density and neutron), indicated that the whole reservoir can be divided at least into four electrofacies having a noticeable variation in reservoir quality, as correlated with the measured permeability. Furthermore, continuity or discontinuity of the reservoir zones can be determined using this analysis. [ABSTRACT FROM AUTHOR]

In Korea, trilobites are among the most intensively studied fossil groups in the past century and provide invaluable information about lower Paleozoic stratigraphy, paleogeography, and tectonics of the Korean Peninsula. Trilobites occur in the lower Paleozoic Joseon Supergroup of the Taebaeksan Basin which was part of the Sino-Korean Craton in the Paleozoic. The Joseon Supergroup is divided into the Taebaek, Yeongwol, and Mungyeong groups. The Taebaek and Yeongwol groups are richly fossiliferous, while the Mungyeong Group is poorly fossiliferous. Contrasting trilobite faunal contents of the Taebaek and Yeongwol groups resulted in two separate biostratigraphic schemes for the Cambrian-Ordovician of the Taebaeksan Basin. A total of 22 biozones or fossiliferous horizons were recognized in the Taebaek Group; 19 zones were established in the Yeongwol Group; and four biozones were known from the Mungyeong Group. These trilobite biozones of the Taebaeksan Basin indicate the Joseon Supergroup ranges in age from the Cambrian Series 2 to Middle Ordovician and can be correlated well with the formations of North China, South China, and Australia. [ABSTRACT FROM AUTHOR]

An Early Paleozoic acid volcanic sequence has been recently detected southeast of Sonid Zuoqi in central Inner Mongolia to constrain the tectonic evolution of the Central Asian Orogenic Belt in this area. First, the volcanic rocks have zircon U–Pb ages of 439–445 Ma. They are characterized by (a) a high silica content, moderate alkali content and low iron content; (b) enrichment in light rare earth elements, depletion of heavy rare earth elements, and negative Eu anomalies; and (c) negative Nb, Ta, and Ti anomalies. Finally, the volcanic samples yield ε Hf (t) values of − 4.7 to + 9.2 with T DM2 ages of 835–1724 Ma. For petrogenesis, they were possibly arc derived, from predominant juvenile materials with subordinate ancient continental crust. Combined with previous studies, the Early Paleozoic Sonid Zuoqi arc magmatism can be divided into three stages: a primitive arc stage represented by 464–490 Ma low-K, calcic granitoids; a normal continental arc stage represented by 439–445 Ma medium-K, calcic to calcic-alkalic plutons and volcanic rocks and a syn-collisional stage represented by 423–424 Ma high-K granites. Furthermore, the timing and tectonic settings of the above magmatic rocks show similarities to those in Xilinhot and other areas of the northern Early to Mid-Paleozoic orogenic belt (NOB), although the rock assemblies and their proportions vary more or less in different areas. Accordingly, the NOB that formed on this arc was probably attributed to the northward subduction of the Paleo-Asian Ocean beginning at ~ 500 Ma, which experienced this type of arc development and was terminated by a soft collision before the Late Devonian. [ABSTRACT FROM AUTHOR]

The appinite–granite association has been found in various tectonic regimes related to recent subduction, arc-continent or continent–continent collision and post-collision (orogen), and appinites generally originate from recently subduction-modified lithospheric mantle. We conducted a study on a rarely reported appinite–granite association formed in an intracontinental regime, the Zhangjiafang–Qinglongshan complex (ZQC), in which the appinites were derived from an ancient sub-continental lithospheric mantle (SCLM). The ZQC is located in the western Wugongshan domain, and consists of basaltic to intermediate appinites and granitoids. Ten dated samples (including massive and gneissoid granitoids, hornblende gabbro, and diorite) give zircon 206 Pb/ 238 U ages ranging from 444 ± 3 Ma to 452 ± 4 Ma, indicating that these various lithologies were emplaced synchronously. The basaltic appinites show radiogenic 87 Sr/ 86 Sr i (0.71016–0.71431) and negative ε Nd (t) (− 6.1 to − 8.9) and zircon ε Hf (t) (− 4.2 to − 7.5) values. Combined with regional geological background, an origin from the Neoproterozoic metasomatised SCLM can be inferred for the appinites in the Wugongshan domain. The granitoids are peraluminous and almost high-K calc–alkaline to shoshonitic. They exhibit a wide range of isotopic compositions ( 87 Sr/ 86 Sr i = 0.70828–0.71857, ε Nd (t) = − 6.2 to − 10.5, zircon ε Hf (t) = − 9.5 to − 26.6). Some of the granitoids display the most evolved Sr–Nd isotopic signatures among all the studied lithologies, which are consistent with those of the middle to upper crust, suggesting a pure crustal origin. Other granitoids show relatively mafic composition and less evolved isotopic signature. The intermediate appinites have intermediate chemical compositions between those of the basaltic appinites and granitoids, and similar Sr–Nd isotopic compositions to those of the basaltic appinites that have relatively evolved composition and isotopic signature. The petrographical and the geochemical studies, as well as magma mixing and mingling between mafic magma and felsic magma observed in field work, indicate that the ZQC was formed by several complex magmatic processes including assimilation and fractional crystallization (AFC) of a basaltic magma derived from an enriched mantle, magma mixing and mingling, fractional crystallization of a crust-derived felsic magma. The contribution of the Neopreoterozoic subduction-modified lithospheric mantle to the early Paleozoic granitoids in South China has been poorly constrained due to its evolved isotopic signatures (such as negative ε Nd (t) and ε Hf (t) values, high initial ratio of 87 Sr/ 86 Sr) and few studies on the early Paleozoic basaltic–felsic rock association. Our work here suggests that the Wugongshan appinite–granite association was formed in an intracontinental orogen, and the ancient enriched mantle may have had a significant chemical contribution to the formation of some of the Paleozoic peraluminous granites in South China. [ABSTRACT FROM AUTHOR]

NW Iberia includes a rather complete section of a Variscan suture, where different terranes with continental or oceanic affinities appear with clear structural relationships. Three groups of terranes, namely Upper, Ophiolitic and Basal units and a frontal tectonic mélange appear in Galicia, in Cabo Ortegal, Órdenes and Malpica-Tui complexes. They constitute a huge allochthonous pile thrust over the Iberian parautochthonous and autochthonous domains, which represent the section of the Gondwanan margin that escaped continental subduction during the Variscan cycle. Considering the allochthonous character of the nappe pile and the strong deformation associated to the Variscan collision, there are problems to identify the original tectonic setting of the terranes and thence, it is difficult to reconstruct the paleogeographic context during the Variscan and pre-Variscan times in detail. Key features to perform any model for the Variscan convergence should consider the existence of two different high-P metamorphic events (dated at c. 400 and 370 Ma, respectively), separated in time for the generation of mafic-ultramafic sequences at c. 395 Ma which constitute the most common ophiolites described in the Variscan suture. Some dynamic models developed in NW Iberia have important problems to explain the observed tectonothermal evolution, especially the older high-P metamorphic event and the exhumation of deeply subducted transitional-type sections. On the other hand, the recently discovered participation of an older continental crust in the generation of different protoliths of the Middle Devonian ophiolites, makes difficult the interpretation of these ophiolites in relation to open wide oceanic domains. This paper describes the distribution, structure, lithologies, geochronology and chemical composition of the terranes involved in the Variscan suture of NW Spain. The scope of this description ranges from detailed regional aspects to the discussion of the development of the Variscan Orogen in the context of the assembly of Pangea. A two-stage collisional model affecting a wide Gondwanan platform may explain most of the evidences in NW Iberia. The generation of a long pull-apart basin probably occurred after the first collision, where the Devonian ophiolites were formed. These ophiolites have been in general described in the context of the Rheic Ocean, but according to the new existing data they do not seem related to this ocean, but rather they were formed after its closure. [ABSTRACT FROM AUTHOR]

Several generations of Paleozoic granitic rocks are studied with Sm-Nd isotopic methods in the northwestern part of the Aktau-Dzhungar microcontinent of Central Kazakhstan (Atasu-Mointy divide). The initial Nd isotopic composition of the granitic rocks varies in a relatively narrow range from-0.1 to-3.5ε; the Nd model ages are also similar (1.11-1.46 Ga). These results indicate that the crustal source of all the Paleozoic granitic rocks of the region had similar composition and, probably, age. It is shown that the t (DM) values of the Paleozoic granites reflect different proportions between ancient and juvenile material in the crustal source. [ABSTRACT FROM AUTHOR]

The Alxa Terrane is situated in a key area between the North China and Tarim cratons. Paleozoic magmatic records in this terrane place important constraints on the subduction processes of the southern Paleo-Asian Ocean. New data of zircon U-Pb ages and whole-rock elemental and isotopic data reveal two groups of intermediate to felsic plutons in the Alxa Terrane. One group consists of diorites and granitoids that were emplaced at ca. 460–440 Ma and characterized by lower Al 2 O 3 /TiO 2 ratios and higher TiO 2 contents, implying high temperature–low pressure crystallization conditions and a shallow source region. The second group is dominated by granitoids aged at ca. 420–407 Ma and displays high Sr and Ba, low Y and high rare earth elements, with very high Sr/Y ratios and mostly positive Eu anomalies. These characteristics imply low temperature–high pressure crystallization conditions and source regions at deep crustal levels where garnet is stable in the residual phase. Both of the two groups are mostly calc-alkaline to high-K calc-alkaline, depleted in Nb, Ta and Ti and enriched in Ba, K and Sr, indicative of an arc affinity most likely related to the southward subduction of the Paleo-Asian Ocean. Zircon ε Hf (t) and whole-rock ε Nd (t) values of these magmatic rocks decrease from 458 Ma to 440 Ma and increase from 417 Ma to 407 Ma, whereas whole-rock initial 87 Sr/ 86 Sr ratios display an opposite trend. Such an isotopic change suggests a tectonic switch from an advancing to a retreating subduction regime at ~ 407 Ma. Synthesized data from this and previous studies suggest that the 460–400 Ma magmatic arc in the Alxa Terrane represented the western extension of the Paleozoic arc belt on the northern margin of the North China Craton. [ABSTRACT FROM AUTHOR]

Upper Paleozoic (~ 365 Ma) mafic and intermediate volcanic rocks of the Piskahegan Group constitute a subordinate part of the Mount Pleasant caldera, which is associated with a significant polymetallic deposit (tungsten–molybdenum–bismuth zones ~ 33 Mt ore with 0.21% W, 0.1% Mo and 0.08% Bi and tin–indium zones ~ 4.8 Mt with 0.82% Sn and 129 g/t In) in southwestern New Brunswick (Canada). The epicontinental caldera complex formed during the opening of the late Paleozoic Maritimes Basin in the northern Appalachians. The mafic and intermediate rocks make up two compositionally distinct associations. The first association includes evolved rift-related continental tholeiitic basalts, and the second association comprises calc-alkaline andesites, although both associations were emplaced penecontemporaneously. The basalts have low Mg# ~ 0.34–0.40, smooth chondrite-normalized REE patterns with (La/Yb) n ~ 5–6, primitive mantle-normalized trace element patterns without noticeable negative Nb–Ta anomalies, and their ɛ Nd(T) ranges from + 2.5 to + 2.2. The basalts were generated by partial melting of a transition zone between spinel and garnet mantle peridotite at a depth of ~ 70–90 km. The calc-alkaline andesites of the second association have chondrite-normalized REE patterns that are more fractionated, with (La/Yb) n ~ 7–8.5, but without significant negative Eu anomalies. Compared to the basaltic rocks, they have lower ɛ Nd(T) values, ranging from + 0.5 to + 1.9, and their mantle-normalized trace element plots show negative Nb–Ta anomalies. The ɛ Nd(T) values display negative correlations with indicators of crustal contamination, such as Th/La, Th/Nb and SiO 2 . The andesitic rocks are interpreted to have formed by assimilation–fractional crystallization processes, which resulted in the contamination of a precursor basaltic magma with crustal material. The parent basaltic magma for both suites underwent a different evolution. The tholeiitic basalts experienced shallow-seated fractional crystallization and evolved along a tholeiitic trend of “early iron” enrichment (non-oxic conditions). The contaminated magma of the second association followed a calc-alkaline fractionation trend of “no iron” enrichment (oxidizing conditions) characterized by a high P H2O and P O2 environment at the mid-crust levels. The Piskahegan Group, which is associated with an important polymetallic mineral deposit, differs from the numerous non-mineralized rift-related volcanic suites of the regional Upper Devonian to Lower Carboniferous successions in the Maritimes Basin by the presence of a significant amount of coeval calc-alkaline andesite, which may be an indicator of potential mineralization. [ABSTRACT FROM AUTHOR]

This study uses illite crystallinity, chlorite crystallinity, illite polytypes, the b0 cell-dimension of K-white mica, clay mineral assemblages and mineral geothermo-geobarometers to investigate the overprint of diagenesis and metamorphism on the Meso-Neoproterozoic and the Lower Paleozoic along the profile Yueyang-Linxiang in northeastern Hunan Province, China. Illite crystallinity Kübler index (KI) of the <2µm fractions ranges from 0.225 to 0.485°Δ2θ while chlorite crystallinity Árkai index (AI) ranges from 0.244 to 1.500°Δ2θ. This indicates that the Meso-Neoproterozoic and the Lower Paleozoic along the profile Yueyang-Linxiang were overprinted with diagenesis and anchi- to epimetamorphism. Peak metamorphic temperature is estimated with the IV site chlorite geothermometer roughly at 360°C. The b0 cell dimension values of illites (K-mica) range from 0.9002 to 0.9054 nm and, on average, at 0.9030 nm for the Meso-Neoproterozoic. Based on cumulative frequency curves of illite (K-mica) b0 cell dimension, the peak metamorphic pressure of the Meso-Neoproterozoic along the profile Yueyang-Linxiang is derived of an intermediate pressure type. Most illites occur in the 2M1 polytype and some of them in a mixture of 2M1+1M types especially those in the Paleozoic. This result partly agrees with the conclusion of the lower greenschist and greenschist facies of the Lengjiaxi and Banxi Groups. However, it is not agreed with the sedimentary cover from the Sinian to the Lower Paleozoic or from the Banxi Group to the Lower Paleozoic. Crustal thickening due to 'collision' between the Yangtze and Cathaysia blocks led to an increase in the thickness of the Meso-Neoproterozoic to ca. 14 km and resulted in a temperature increase in those rocks due to burial. The very low grade to low grade metamorphism overprinting the Meso-Neoproterozoic implies that the so called 'Chiangnania or Jiangnan orogen' was no relative with the 'Grenvillian orogeney; instead, it might be a continuous amalgamation product between the Yangtze and Cathaysia blocks. [ABSTRACT FROM AUTHOR]

The Ulaan Tolgoi massif of rare-metal (Ta, Nb, and Zr) granites was formed at approximately 300Ma in the Eastern Sayan zone of rare-metal alkaline magmatism. The massif consists of alkaline salic rocks of various composition (listed in chronologic order of their emplacement): alkaline syenite → alkaline syenite pegmatite → pantellerite → alkaline granite, including ore-bearing alkaline granite, whose Ta and Nb concentrations reach significant values. The evolution of the massif ended with the emplacement of trachybasaltic andesite. The rocks of the massif show systematic enrichment in incompatible elements in the final differentiation products of the alkaline salic magmas. The differentiation processes during the early evolution of the massif occurred in an open system, with influx of melts that contained various proportions of incompatible elements. The magma system was closed during the origin of the ore-bearing granites. Rare-metal granitoids in the Eastern Sayan zone were produced by magmas formed by interaction between mantle melts (which formed the mafic dikes) with crustal material. The mantle melts likely affected the lower parts of the crust and either induced its melting, with later mixing the anatectic and mantle magmas, or assimilated crustal material and generated melts with crustal-mantle characteristics. The origin of the Eastern Sayan zone of rare-metal alkaline magmatism was related to rifting, which was triggered by interaction between the Tarim and Barguzin mantle plumes. The Eastern Sayan zone was formed in the marginal part of the Barguzin magmatic province, and rare-metal magmas in it were likely generated in relation with the activity of the Barguzin plume. [ABSTRACT FROM AUTHOR]

The geochemical and lithological analysis of sections in the Sablya Range (Subpolar Urals) made it possible to substantiate a model of spatial-temporal and genetic interrelations of processes responsible for rock formation during the Vendian-Early Paleozoic evolution stage in the northeastern margin of the East European continent. Different lithological types are defined among rocks at the transition between the basement and sedimentary cover with their description and discussion of the role of synchronous magmatism in the formation of the latter. The succession of geological events and unusual features in the evolution of the composition, stratigraphy, and genetic affinity of deposits constituting the section of the transitional interformation zone are established. [ABSTRACT FROM AUTHOR]

The multi-stage geological evolution and extensive continental deformations during the course of its history make the Central Asian metallogenic region (CAMR) a unique and complicated large-scale metal domain. New geological observations and precise age-data allow an improved reconstruction of the geological evolution of the CAMR. This paper summarizes the Paleozoic orogenic evolution and related ore formation in the core part of the CAMR based on the geological data published both during the Soviet period and the last decades. Four ore-formation provinces (Altay, Balkhash-Junggar, Chu-Yili-Tianshan, and Southwest Tianshan) could be classified. The Balkhash-Junggar and Chu-Yili-Tianshan provinces are the major topics of this paper. The Balkhash-Junggar province consists of 4 huge ore-forming belts (Zharma-Saur, Tarbahtay-Xiemistay, Aktogay-Baerluke, Balkhashwestern Junggar) with 11 large ore-college areas. The Chu-Yili-Tianshan province consists of 4 huge ore-forming belts (Alatau-Sairimu, Chu-Yili-Bolehuole, Issyk-Awulale, Kazharman-Nalaty) with 22 large ore-college areas. Formation of large ore-college area corresponds to a specific stage of continental crust growth. Comparison of geology and ore deposits in the CAMR provides rich information for future exploration and understanding of ore-forming processes. The Paleo-Junggar Ocean closed at Early Devonian in the Balkhash-western Junggar ore-forming belt. Afterwards, widespread volcanicsedimentary rocks formed at extensional stage due to delamination of the thick lower crust formed during previous accretionary processes. Felsic magma intrusion caused formation of porphyry Cu-Au deposit at ∼310 Ma and related hydrothermal gold deposits about 10 Ma later. For example, in the Hatu-Baobei-Sartohay Au-Cr ore-college area in the Balkhash-western Junggar ore-forming belt, small granitic to diorite plutons and various dykes (312-277 Ma) and large granite bodies (∼300 Ma) intruded into the Devonian to Early Carboniferous volcano-sedimentary basin. These magmatic activities and fault systems mainly controlled ore-forming processes. [ABSTRACT FROM AUTHOR]

During thermochemical sulfate reduction (TSR), H 2 S generated by reactions between hydrocarbons and aqueous sulfate back-reacts with remaining oil-phase compounds forming new organosulfur compounds (OSCs) that have similar δ 34 S values to the original sulfate. Using Compound Specific Sulfur Isotope Analysis (CSSIA) of alkylthiaadamantanes (TAs), alkyldibenzothiophenes (DBTs), alkylbenzothiophenes (BTs) and alkylthiolanes (TLs), we have here attempted to differentiate OSCs due to primary generation and those due to TSR in oils from the Tarim Basin, China. These oils were generated from Cambrian source rocks and accumulated in Cambrian and Ordovician reservoirs. Based on compound specific sulfur isotope and carbon isotope data, TAs concentrations and DBT/phenanthrene ratios, the oils fall into four groups, reflecting different extents of source rock signal, alteration by TSR, mixing events, and secondary generation of H 2 S. Thermally stable TAs, that were produced following TSR, rapidly dominate kerogen-derived TAs at low to moderate degrees of TSR. Less thermally stable TLs and BTs were created as soon as TSR commenced, rapidly adopted TSR-δ 34 S values, but they do not survive at high concentrations unless TSR is advanced and ongoing. The presence of TLs and BTs shows that TSR is still active. Secondary DBTs were produced in significant amounts, sufficient to dominate kerogen-derived DBTs, only when TSR was at an advanced extent. The difference in sulfur isotopes between (i) TLs and DBTs and (ii) BTs and DBTs and (iii) TAs and DBTs, represents the extent of TSR while the presence of TAs at greater than 20 μg/g represents the occurrence of TSR. The output of this study shows that compound specific sulfur isotopes of different organosulfur compounds, with different thermal stabilities and formation pathways, not only differentiate between oils of TSR and non-TSR origin, but can also reveal information about relative timing of secondary charge events and migration pathways. [ABSTRACT FROM AUTHOR]

Disseminated Mississippi Valley-type (MVT) mineralization occurs throughout northeastern Wisconsin, USA, and is recognized as the source of regionally extensive natural groundwater contamination in the form of dissolved arsenic, nickel, and other related metals. Although considerable attention has been given to arsenic contamination of groundwater in the region, limited attention has been focused on characterizing the bedrock sources of these and other metals. A better understanding of the potential sources of groundwater contamination is needed, especially in areas where groundwater is the dominant source of drinking water. This article describes the regional, stratigraphic, and petrographic distribution of MVT mineralization in Paleozoic rocks of northeastern Wisconsin, with a focus on sulfide minerals. Whole-rock geochemical analysis performed on 310 samples of dolomite, sandstone, and shale show detectable levels of arsenic, nickel, cobalt, copper, lead, zinc, and other metals related to various sulfide mineral phases identified using scanning electron microscopy. MVT minerals include pyrite, marcasite, sphalerite, galena, chalcopyrite, fluorite, celestine, barite, and others. We describe the first nickel- and cobalt-bearing sulfide mineral phases known from Paleozoic strata in the region. Arsenic, nickel, and cobalt are sometimes present as isomorphous substitutions in pyrite and marcasite, but discrete mineral phases containing nickel and cobalt elements are also observed, including bravoite and vaesite. Locally abundant stratigraphic zones of sulfide minerals occur across the region, especially in the highly enriched Sulfide Cement Horizon at the top of the Ordovician St. Peter Sandstone. Abundant quantities of sulfides also appear near the contact between the Silurian Mayville Formation and the underlying Maquoketa and Neda formations in certain areas along and east of the Niagara escarpment. This article illustrates how a detailed geochemical and mineralogical investigation can yield a better understanding of groundwater quality problems. [ABSTRACT FROM AUTHOR]