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1. Interpreting detrital modes and geochemistry of sandstones from the late Paleozoic Tepuel-Genoa Basin: Paleogeographic implications (Patagonia, Argentina)

   https://doi.org/https://doi.org/10.1016/j.jsames.2020.102858  

   Ciccioli, P. L.; Limarino, C. O.; Isbell, J.L.; Taboada, A. C.; Pagani, M. A.; Gulbranson, E.L. (September 2020, Journal of South American earth sciences)

   null (Ed.)

   The provenance of sandstones deposited in the late Paleozoic Tepuel-Genoa Basin is analyzed in this paper. Five sections were sampled in Esquel, Sierra de Tepuel, Sierra de Tecka, El Molle, and Río Genoa areas for petrographic and geochemical studies. The sandstones in the Tepuel-Genoa Basin are dominated by feldspathic litharenites and litharenites, showing lithic fragments of volcanic and sedimentary rocks in the Valle Chico Formation and medium-to high-grade metamorphic rock clasts in the rest of the units. Detrital modes of seventy-five sandstones samples from the Valle Chico, Pampa de Tepuel, Moj´on de Hierro, and Río Genoa formations were counted and analyzed. Seven modal components have discriminant value for identifying provenance areas (Qm, Qi, Lv, Lmm-h, Lm-Lp, Lm, Qpm). These modal components allow identification of three petrofacies: 1. Quartzose-lithic (Qm69Lv2Lm29), 2. Quartzose (Qm89Lv4Lm7) and 3. Volcanic-sedimentary (Qm60Lv38Lm1). The quartzose-lithic petrofacies is mainly composed of monocrystalline quartz, medium- and high-grade metamorphic clasts and polycrystalline quartz with cataclastic texture, this assemblage is interpreted as being derived from the crystalline rocks that form the Deseado Massif. The quartzose petrofacies is composed of monocrystalline quartz with scarce contributions of metamorphic clasts and traces of volcanic fragments; the provenance area is ascribed to sedimentary terrains, which most likely covered part of the Deseado Massif. The volcanic-sedimentary petrofacies is comprised of volcanic (acidic and intermediate rocks) and sedimentary (sandstone and mudstone) clasts, with discrete amounts of quartz grains with idiomorph shapes and embayments. This assemblage may correspond to material supply from the Devonian-Early Carboniferous accretionary complex developed in Chile or the unroofing of the western volcanic arc located in the central part of Patagonia. The validity of the three defined petrofacies was evaluated using Principal Component Analysis and triangular compositional diagrams; both methods show good separation and lack of overlap between the three petrofacies. Major (Si, Al, Fe, Na, K) and trace-REE elements (Zr, Th, Sc, Hf) were used to improve the petrographic information. The relation SiO2 against K2O/Na2O indicates that the Pampa de Tepuel and the Moj´on de Hierro formations correspond to a passive margin, while the Valle Chico and Río Genoa formations represent different types of active continental margins. The Th/Sc and Zr/Sc ratios and the Th-Hf-Co distributions indicate that the sandstones of the Tepuel Group were formed from rocks compatibles with the average composition of the upper continental crust. 

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2. A waning Saxothuringian Ocean evidenced in the Famennian tephra-bearing siliceous succession of the Bardo Unit (Central Sudetes, SW Poland)

   https://doi.org/10.1130/B35971.1  

   Racki, Grzegorz; Mazur, Stanisław; Narkiewicz, Katarzyna; Pisarzowska, Agnieszka; Bardziński, Waldemar; Kołtonik, Katarzyna; Szymanowski, Dawid; Filipiak, Paweł; Kremer, Barbara (February 2022, GSA Bulletin)

   Abstract A tephra-rich cherty-clayey Famennian succession within the major Brzeźnica olistostrome in the Bardo Mountains, Central Sudetes, SW Poland, preserves a record of the lost ocean later incorporated into the Variscan orogenic belt. Fluctuating but mostly oligotrophic regimes and low primary production levels were influenced by weak up-welling below the perennial oxygen minimum zone, which controlled the interplay between biosiliceous and siliciclastic deposition in the oceanic basin, with episodic oxygen deficiency. The Hangenberg Black Shale has been identified in this oceanic setting based on its characteristics described worldwide (including mercury enrichments). A tectonic uplift of the sediment source area near the Devonian-Carboniferous boundary, recorded in the distinguishing provenance signal of old continental crust, was paired with a global transgression, anoxia, and volcanic episode in an interglacial interval. Assuming paleogeographic affinity with the Bavarian facies of the Saxothuringian terrane, we interpret the allochthonous sediments as part of an accretionary prism that was gravitationally redeposited into the late orogenic basin in front of advancing Variscan nappes. The oceanic basin parental to the Bardo pelagic succession is therefore thought to represent a tract of the waning Saxothuringian Ocean in the Peri-Gondwanan paleogeographic domain that was eventually subducted beneath the Brunovistulian margin of Laurussia. The sediments of the Bardo Ocean basin also include a distal record of Famennian explosive volcanic activity that was likely related to a continental magmatic arc whose remnants are preserved as the Vrbno Group of the East Sudetes. 

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3. Episodic evolution of a protracted convergent margin revealed by detrital zircon geochronology in the Greater Caucasus

   https://doi.org/10.1111/bre.12825  

   Vasey, Dylan A; Garcia, Leslie; Cowgill, Eric; Trexler, Charles C; Godoladze, Tea (January 2024, Basin Research)

   Abstract Convergent margins play a fundamental role in the construction and modification of Earth's lithosphere and are characterized by poorly understood episodic processes that occur during the progression from subduction to terminal collision. On the northern margin of the active Arabia‐Eurasia collision zone, the Greater Caucasus Mountains provide an opportunity to study a protracted convergent margin that spanned most of the Phanerozoic and culminated in Cenozoic continental collision. However, the main episodes of lithosphere formation and deformation along this margin remain enigmatic. Here, we use detrital zircon U–Pb geochronology from Paleozoic and Mesozoic (meta)sedimentary rocks in the Greater Caucasus, along with select zircon U–Pb and Hf isotopic data from coeval igneous rocks, to link key magmatic and depositional episodes along the Caucasus convergent margin. Devonian to Early Carboniferous rocks were deposited prior to Late Carboniferous accretion of the Greater Caucasus crystalline core onto the Laurussian margin. Permian to Triassic rocks document a period of northward subduction and forearc deposition south of a continental margin volcanic arc in the Northern Caucasus and Scythian Platform. Jurassic rocks record the opening of the Caucasus Basin as a back‐arc rift during southward migration of the arc front into the Lesser Caucasus. Cretaceous rocks have few Jurassic‐Cretaceous zircons, indicating a period of relative magmatic quiescence and minimal exhumation within this basin. Late Cenozoic closure of the Caucasus Basin juxtaposed the Lesser Caucasus arc to the south against the crystalline core of the Greater Caucasus to the north and led to the formation of a hypothesized terminal suture. We expect this suture to be within ~20 km of the southern range front of the Greater Caucasus because all analysed rocks to the north exhibit a provenance affinity with the crystalline core of the Greater Caucasus. 

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4. Origin of paleovalleys on the Rio Grande do Sul Shield (Brazil): Implications for the extent of late Paleozoic glaciation in west-central Gondwana

   Fedorchuk, N.D.; Isbell, J.L.; Griffis, N.P.; Montañez, I.P.; Vesely, F.F.; Iannuzzi, R.; Mundil, R.; Yin, Q.-Z.; Pauls, K.N.; Rosa, E.L.M (April 2018, Palaeogeography, palaeoclimatology, palaeoecology)

   The location, longevity, and geographic extent of late Paleozoic ice centers in west-central Gondwana remain ambiguous. Paleovalleys on the Rio Grande do Sul Shield of southernmost Brazil have previously been interpreted as fjords carved by outlet glaciers that originated in Africa and emptied into the Paraná Basin (Brazil). In this study, the sedimentology, stratigraphy, and provenance of sediments infilling two such paleovalleys (the Mariana Pimentel and Leão paleovalleys) were examined in order to test the hypothesis that an ice center over present day Namibia drained across southernmost Brazil during the Carboniferous and Permian. Contrary to previous findings, the facies assemblage from within the paleovalleys is inconsistent with a fjord setting and no clear evidence for glaciation was observed. The facies show a transition from a non-glacial lacustrine/estuarine environment, to a fluvial-dominated setting, and finally to a restricted marine/estuarine environment. Detrital zircon results present a single population of Neoproterozoic ages (c. 800–550 Ma) from the paleovalley fill that matches the ages of underlying igneous and metamorphic basement (Dom Feliciano Belt) and is incongruent with African sources that contain abundant older (Mesoproterozoic, Paleoproterozoic, and Archean) zircons. Furthermore, results suggest that the formation of the paleovalleys and the deposition of their fill were controlled by the reactivation of Neoproterozoic basement structures during the Carboniferous and Permian. The lack of evidence for glaciation in these paleovalleys highlights the need for detailed studies of supposed late Paleozoic glacial deposits. These results are supportive of the hypothesis that well-established glacial sediments on the Rio Grande do Sul Shield (southern margin of the Paraná Basin) may be the product of a separate lobe extending north across Uruguay, rather than a single, massive ice sheet draining west from Africa. 

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5. Provenance of uppermost Carboniferous–Lower Triassic sandstones, Bogda Mountains, NW China: implication on late Paleozoic tectonic history of southern Central Asian Orogenic Belt

   Wu, S X; Yang, W (August 2025, International Meeting for Applied Geoscience and Energy)

   Provenance of uppermost Carboniferous–Lower Triassic sandstones, Bogda Mountains, NW China: implication on late Paleozoic tectonic history of southern Central Asian Orogenic Belt The Permian-Triassic time is a critical stage in the Paleozoic continental amalgamation and Cenozoic orogenic reactivation of southern Central Asian Orogenic Belt (CAOB). Field, petrographic and detrital zircon U-Pb geochronological data of the uppermost Carboniferous– Lower Triassic sandstones from 3 sections in Bogda Mountains, greater Turpan-Junggar basin, NW China, are used to decipher the tectonic history. They are Tarlong- Taodonggou (TT) and Zhaobishan (ZBS) in the south and Dalongkou (DLK) in the north, 100 km apart and ~7,000 m in total thickness. Four petrofacies of 229 sandstones are defined using the abundance of volcanic, sedimentary, and metamorphic (with polycrystalline quartz) lithics. Petrofacies A (Lv73Ls21(Qp+Lm)6) contains mainly volcanic lithics, indicating a volcanic arc as the main source. Petrofacies B (Lv14Ls41(Qp+Lm)45) and Petrofacies C (Lv38Ls14(Qp+Lm)48) contain mixed sedimentary, metamorphic, and volcanic lithics, indicating multiple sources. Petrofacies D (Lv11Ls82(Qp+Lm)7) contains mainly sedimentary lithics with a trace amount of volcanic and metamorphic lithics, indicating local rift-shoulder sedimentary sources. Additionally, the U-Pb dates of 3505 detrital zircon grains of 35 sandstones were analyzed. The predominant Paleozoic zircon grains yield major age populations at ca. 360–280 Ma and 485–385 Ma. Precambrian dates are present, ranging from 542 Ma to 3329 Ma. During Gzhelian–Asselian, andesite and basalt are the major source lithologies in TT. Zircon ages peak at ~300 Ma. During Sakmarian–Kungurian, basalt and andesite are the main source rocks in TT and ZBS; and zircon ages of both areas peak at ~300 Ma. The Roadian–Wordian is probably represented by a regional unconformity. The Guadalupian source lithology and zircon date show a major change. Andesite is the common and rhyolite and basalt minor source lithologies for TT and DLK; but rhyolite significant for ZBS. A unimodal peak at ~305 Ma occurs in TT; two peaks at 305 and 455 Ma with common Precambrian dates in ZBS; and peaks of 310–295 Ma in DLK. During Wuchiapingian–mid Olenekian, andesite and rhyolite are the common source lithologies for TT and DLK, and rhyolite as the primary volcanic lithology for ZBS. In TT, Wuchiapingian-Induan samples have a major age peak at ~300 Ma, and an Olenekian sample has two peaks at ~300 and ~450 Ma. In ZBS, the age pattern is similar to that of the Guadalupian sample. In DLK, samples have a major age peak at ~310 Ma and a minor peak at ~450 Ma. The comparable age clusters identified by multi-dimensional scaling indicate that North Tianshan is the source for TT and ZBS during the latest Carboniferous–early Permian. But south Central Tianshan became the main source solely to ZBS. During late Permian–Early Triassic, both north and central Tianshan became the common sources to the three areas due to enhanced denudation. The source change in mid-Permian across a regional unconformity is synchronous with Paleo-Asian Ocean closure and arc-continent and continent-continent collisions, which occurred no later than Guadalupian. 

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