Palaeogeographic Implications Research Articles

Depositional environments of complex lake systems – palaeogeographical evolution and main controls: A case study of the Lower to Middle Permian Roseneath–Epsilon–Murteree strata, Cooper Basin, Australia

ABSTRACTLake systems are among the largest integrated depositional complexes in the continental realm. Their interplay with tectonics and climate often complicates the interpretation of depositional processes, usually resulting in a complex facies architecture that is challenging to correlate regionally. The Lower to Middle Permian Roseneath–Epsilon–Murteree strata of the Cooper Basin in Australia represent a glacially influenced fluvial–deltaic lake system, which hosts substantial petroleum resources. Despite their potential, the Roseneath–Epsilon–Murteree strata are inadequately understood in terms of regional facies architecture and their palaeogeographical implications. Using a multidisciplinary approach with robust data, including cores, petrology, wireline logs and geochemistry, the sedimentary evolution of the Roseneath–Epsilon–Murteree strata is described within a new basin‐wide sequence stratigraphic framework defined by key surfaces identified from cores and wireline logs. Detailed facies analysis of over 1400 m of cores and wireline logs from nine wells identified twelve lithofacies and eight facies associations, revealing various depositional processes and environments. The Roseneath–Epsilon–Murteree strata are interpreted as having formed in a fluvial–deltaic–lacustrine system influenced by a cold climate. First‐order and second‐order maximum flooding surfaces define a regional sequence stratigraphic framework, subdividing the Roseneath–Epsilon–Murteree strata into four sequence units (SU1, SU2, SU3 and SU4), deposited during four phases (I, II, III and IV). Cyclic stacking patterns observed in both cores and wireline logs reveal two transgressive–regressive cycles. Palaeogeographical maps of the four depositional phases suggest that the Roseneath–Epsilon–Murteree strata were dominated by a lacustrine system with some delta and mire deposits. Rivers primarily drained towards the south/south‐west from the Gidgealpa, Merrimelia, Packsaddle and Innamincka ridges (‘GMI Trend’) as indicated by decreasing sandstone percentages and increasing gross unit isopach maps. The deposition of the Roseneath–Epsilon–Murteree strata was primarily controlled by basin subsidence. Additionally, palaeoclimate trends and extensive glaciation in the Permian played important roles in providing sediments and affecting lake level changes. The lake system recorded by the Roseneath–Epsilon–Murteree strata serves as an analogue for other fluvial–deltaic–lacustrine systems in basins worldwide. A multidisciplinary approach, similar to the one utilized in this study, can help to elucidate their evolution and aid in resource prediction.

New insight on upper Silurian-lowermost Devonian conodont biostratigraphy of the Argentine Precordillera and its palaeogeographic implications for the SW Gondwana margin

ABSTRACT The Cerro del Fuerte section, located in the Central Precordillera of San Juan Province, is considered a reference section to the study of Silurian-Devonian conodont biostratigraphy from Argentina and South America. The conodont association recovered in this section comprises twenty-five conodont taxa (species and sub-species) belonging to ten genera which allowed to record six conodont biozones from the Ludlow, Pridoli, and the Early Devonian (Lochkovian). Based on this new conodont biostratigraphy we propose constraining the brachiopod biostratigraphy reported in the same section. The Lau Event is probably recorded in the middle levels of the Los Espejos Formation where a change in the conodont fauna is verified. Despite that during the late Silurian and Early Devonian, the Argentina Precordillera was located at high southern latitudes in southwest Gondwana, the conodont fauna studied are composed of geographically widespread taxa supporting that the late Silurian – early Devonian was a time interval with minimal conodont provincialism.

Watermass architecture of the Ordovician–Silurian Yangtze Sea (South China) and its palaeogeographical implications

The South China Craton experienced large changes in climate, eustasy and environmental conditions during the Late Ordovician Hirnantian Ice Age, but their impact on the watermass architecture of the Yangtze Sea has not yet been thoroughly evaluated. Here, we reconstruct the salinity–redox structure of the Yangtze Sea based on five Upper Ordovician–Lower Silurian shale successions representing a lateral transect from a deep-water area of the Inner Yangtze Sea (IYS; Shuanghe section) across the shallow Hunan–Hubei Arch (Pengye, Jiaoye and Qiliao sections) to the relatively deep-water Outer Yangtze Sea (OYS; Wangjiawan section). Carbon isotope ( δ 13 C org ) profiles show that the Guanyinqiao Bed (recording the peak Hirnantian glaciation) thins and is less completely preserved at sites on the flanks of the Hunan–Hubei Arch than in deeper water areas to the SW and NE, reflecting bathymetric influences. Watermass salinities were mainly marine at Shuanghe and brackish at the other four study sites, with little variation among Interval I (pre-glaciation), Interval II (Hirnantian glaciation) and Interval III (post-glaciation). Redox proxies document mainly euxinia at Shuanghe and Wangjiawan and suboxia at the other sites during Interval I, with shifts towards more reducing (mostly euxinic) conditions at most sites during Intervals II and III, which shows that all the study sections were deep enough to remain below the redoxcline during the glacio-eustatic lowstand. Two features of the Shuanghe section mark it as being unusual: it alone exhibits fully marine salinities, implying greater proximity to the open ocean than the other four sites, and it exhibits an especially large shift towards more reducing conditions during Interval III (i.e. the post-Hirnantian transgression), implying greater water depths. These features are difficult to reconcile with the standard palaeogeographical model for the Ordovician–Silurian South China Craton, which is characterized by a geographically enclosed and restricted IYS and a more open OYS, arguing instead for the SW end of the IYS to have been connected to the global ocean and the OYS to have been a restricted oceanic cul-de-sac. A review of sedimentological and facies data for the IYS region suggests that our re-interpretation of the Ordovician–Silurian palaeogeography of the South China Craton is viable, although further vetting of this hypothesis is needed. Supplementary material: The dataset and the full crossplot of Sr/Ba v. CaO for this study are available at https://doi.org/10.6084/m9.figshare.c.7170648 Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system

The Barremian–lower Aptian of NE Arabia: The Kharaib and Shu'aiba formations in Wadi Rahabah and Wadi Kebdah, Ras Al Khaimah, U.A.E.

We present a high-resolution record of carbonate depositional facies, biostratigraphy, stable-isotope and elemental geochemistry of the Kharaib and Shu'aiba formations exposed in Ras Al Khaimah, northern UAE. This is the first comprehensive study of these deposits in the northeastern Arabian Peninsula, which have previously been studied extensively in Abu Dhabi, Oman, NE Saudi Arabia, and southwestern Iran, and represents the most detailed biostratigraphic and chemostratigraphic record currently available from a continuous outcrop section of the Arabian Plate. The Barremian–Aptian boundary was approximated based on orbitolinid biostratigraphy, while a subdivision of the Barremain was not possible. There is no biostratigraphic evidence that the Shu'aiba Formation in the section studied ranges into the upper Aptian. Previously well-established depositional sequences of the Barremian–lower Aptian of the Arabian Plate are discussed in the context of carbonate textures, siliciclastic influx, and biotic assemblages. There is a general trend of decreasing siliciclastic components during the Barremian and earliest Aptian, and peaks in siliciclastic influx indicate episodes of maximum accommodation. Palaeogeographic implications of our data for the distribution of intrashelf basins and their connection to Neotethys are discussed. The negative carbon-isotope excursion that globally marks the onset of OAE1a is not evident in our dataset, while the positive excursion at the end of OAE1a is present in the late early Aptian. A comparison of carbon-isotope records across the early Aptian of the Arabian Plate highlights issues of correlations that are predominantly based on chemostratography in diagenetically altered platform carbonates.

Early Permian crinoids (Echinodermata) from Laurasia and their palaeogeographic implications

Early Permian crinoids (Echinodermata) from Laurasia and their palaeogeographic implications

Mid-Carboniferous rugose corals from Xinjiang, Northwest China: Evolutionary and palaeogeographical implications

The mid-Carboniferous represents a key transition in the evolution of rugose corals, but the evolutionary pattern has been scarcely studied due to the lack of consecutive carbonate succession caused by Hercynian orogeny and Gondwana glaciation. In this study, seventeen rugose coral species belonging to fourteen genera are described from the late Visean to Bashkirian strata in the Suguersu section, northern Xinjiang, Northwest China. The late Visean is distinguished by large dissepimented solitary coral species, such as Haplolasma sp., Palaeosmilia murchisoni, and colonial coral Lithostrotion decipiens. Coral diversity dramatically decreased during the Serpukhovian, with only one species present. During the Bashkirian, rugose corals gradually recovered with the increased diversity and abundance, as evidenced by the occurrence of colonial coral Petalaxis kitakamiensis. This evolutionary pattern is consistent with that from South China and Russia, represented by the replacement of the Mississippian large solitary corals by the Pennsylvanian colonial corals. The Suguersu coral assemblage is composed of endemic taxa in Xinjiang and Qinghai regions of Northwest China, South China and Japan in northeastern Palaeotethys, as well as a few cosmopolitan elements across the Palaeotethys. This suggests that the Suguersu coral assemblage is biogeographically endemic, with occasional exchanges with other palaeo-oceans during the mid-Carboniferous period.

Katian (Late Ordovician) trilobites of the North Qilian Mountains and their palaeogeographical implications for the Proto‐Tethys Archipelagic Ocean

AbstractTrilobites from the middle Koumenzi Formation (Katian, Upper Ordovician) of the North Qilian Mountains, Menyuan, northeastern Qinghai Province are systematically documented for the first time. The fauna consists of five families, seven genera and seven species, one of which is new (Remopleurides zhangi), showing a close relationship to those of the Kazakh terranes (such as the Chu‐Ili terrane, Chingiz‐Tarbagatai area and the Karatau‐Naryn and North‐Tien Shan microcontinents), and the North China and Laurentia palaeoplates during the Katian (Late Ordovician). The cluster and non‐metric multidimensional scaling analyses of the Middle–Late Ordovician (late Darriwilian–Katian) trilobite faunas with 299 genera or subgenera from 46 horizons of 37 areas, provide valuable information for the palaeogeographical reconstruction of the Proto‐Tethys Archipelagic Ocean (PTAO) of this interval. The Qilian terrane and adjacent areas are essential components of the PTAO, some of which include the Qilian terrane, the North Qilian Mountains area, the Altun faulted terrane, the Hexi Corridor area and the East Qinling terrane. Their relative positions in the PTAO are inferred by the palaeobiogeography of trilobite faunas. Furthermore, based on discussions of the spatiotemporal distribution of those faunas, the Pliomerina and/or Sinocybele Province of the Middle–Late Ordovician (late Darriwilian–Katian) age is defined as a trilobite faunal province of the PTAO. Moreover, a distinct faunal subprovince, essentially comprising the South China Palaeoplate and its neighbours (e.g. Tarim, Annamia, Sibuma, East Qinling, Turkestan‐Alai and probably Talesh), might be surrounded by the equatorial cold‐water tongue.

Insular aurochs (Mammalia, Bovidae) from the Pleistocene of Kythera Island, Greece

Islands are renowned for their remarkable biotas and have been widely recognised as natural laboratories for the study of evolution, speciation, and extinction. Large mammals in insular environments typically evolve to dwarfs and small ones to giants, a trend known as the island rule. Despite their dominance in the continental European mammal faunas of Middle-Late Pleistocene, Bison and Bos are usually lacking from the neighbouring endemic insular assemblages. Here, we report the first insular bovin from the Late Pleistocene of Kythera Island, Greece and we carry out a detailed morphometrical analysis with emphasis on its adaptations and palaeogeographic implications. Based on both dental and postcranial qualitative and quantitative comparisons, we attribute the studied material from Kythera to Bos primigenius. Significant differences from both its continental Pleistocene relative and the endemic bovins from Mediterranean islands, allow us to recognize it as a new subspecies, Bos primigenius thrinacius n. ssp., the third known insular dwarf of this taxon in Europe. Our main hypothesis is that the gradual disconnection of Kythera Island from the neighbouring Peloponnese peninsula just after MIS 6 (late Middle Pleistocene, ∼180 ka) resulted in the isolation of a mainland Bos primigenius population in the rocky and predator free environment of palaeo-Kythera Island. Under these particular conditions the population underwent some remarkable changes and gained some peculiar features, especially on metapodials. The timing and reasons of Bos primigenius thrinacius extinction remain unknown.

First complete Niobe yangtzeensis Lu, 1975 (Asaphidae, Trilobita) from the Middle Ordovician of South China, and its systematic and palaeogeographic implications

Since Niobe yangtzeensis was erected in 1975, due to no complete or even cephalic specimens, the generic assignment of Niobe yangtzeensis remains controversial. Based on the new discovery of a complete specimen of Niobe yangtzeensis in Yichang of South China, this species is redescribed and its generic position assignment is clarified and confirmed. A phylogenetic analysis of Niobinae shows that each of the four genera of this subfamily (Niobe, Niobella, Proxiniobe and Gog) forms a monophyletic group, and that among which Niobe yangtzeensis belongs to the genus Niobe. The palaeogeographical distribution and environmental analysis of Niobinae, suggest that Niobella, Proxiniobe and Gog lived in a relatively deeper-water (the outer-shelf or slope) environment, while Niobe preferred a shallower water environment, such as the inner shelf.

Peri-Gondwanan acritarchs and chitinozoans from the Lower–Middle Ordovician Lashkarak Formation in the Alborz Mountain Ranges, northern Iran: regional stratigraphical significance and palaeogeographical implications

The Lashkarak Formation (Lower–Middle Ordovician) in the Gerdkuh locality, 10 km west of Damghan city, northern Iran, has been found to contain acritarchs and chitinozoans. This study aimed to understand these chitinozoan and acritarch successions as well as brachiopods in this part of the Alborz Mountains, in a novel manner. Ninety-seven surface samples from this succession were collected and analysed. Thirty samples yielded well-preserved palynomorph taxa such as acritarchs, chitinozoans, and scolecodonts, as well as graptolite remains. In total, 53 taxa were identified among the acritarchs (38 species belonging to 21 genera) and chitinozoans (15 species belonging to 10 genera). Although scolecodonts and graptolite remains were also observed, they were not studied in detail. The palynological analyses revealed the presence of several diagnostic acritarchs in the Lashkarak Formation, including Vulcanisphaera simplex, Arbusculidium filamentosum, Coryphidium bohemicum, Dactylofusa velifera, Striatotheca mutua, Arkonia virgata, and Orthosphaeridium ternatum. These acritarchs allowed the recognition of five acritarch assemblage zones. Similarly, seven chitinozoan biozones were recognised: Eremochitina brevis, Desmochitina ornensis, Belonechitina henryi, Cyathochitina protocalix, Cyathochitina calix, Siphonochitina formosa, and Laufeldochitina clavata. These findings confirm the inclusion of the Alborz Mountains in the peri-Gondwana palaeoprovince during the Early–Middle Ordovician. The co-occurrence of the acritarch and chitinozoan taxa with previously identified brachiopods allowed for the establishment of a more detailed Early–Middle Ordovician biozonation, demonstrating their potential usefulness for global chronostratigraphy. Based on palynological and brachiopod assemblages, a shallow marine inner shelf setting is suggested for the Early–Middle Ordovician at the Gerdkuh locality. Moreover, in this study, four new morphotype species were erected, consisting of one new chitinozoan (Cyathochitina gerdkuhensis sp. nov.) and three new acritarchs (Baltisphaeridium razii sp. nov., Navifusa alborzensis sp. nov., and Orthosphaeridium iranense sp. nov.). However, Othosphaeridium cf. ternatum was left in open nomenclature.

Heterogeneity of the Ailaoshan–Song Ma ophiolitic mélange and its palaeogeographic implications for the evolution of Eastern Palaeo-Tethys

In comparison with ophiolite, ophiolitic mélange, especially its matrix, contains more information about the evolution of the relevant ocean. The evolution of the eastern Palaeo-Tethys recorded a whole Wilson cycle of numerous continental blocks such as the South China Block and Indochina Block, including rifting away from the Gondwana continent, subsequent northward migration and final collage with the Laurasia continent. Based on structural geology, detrital zircon, and related geochemical analyses, the Ailaoshan–Song Ma ophiolitic mélange can be divided into M1, M2, and M3 units with distinct detrital zircon age spectra and εHf(t) values suggesting for different provenances. These units are in faults-contact along the orogenic belt, indicating a strike–parallel heterogeneity of the ophiolitic mélange. To further understand the heterogeneity of these ophiolitic mélanges, five samples from the matrix of the Ailaoshan ophiolitic mélange were collected to be conducted detrital zircon UPb dating and LuHf isotope analyses. All samples share the same zircon age spectrum, with two obvious age peaks at 430 and 960 Ma, which is comparable with the M1 unit. These results imply that the northwestern Ailaoshan ophiolitic mélange segment can be subdivided into M1 in the interior and M2 in the exterior rather than the previous division, indicating a strike–perpendicular heterogeneity. Based on their geometries (NE-dipping) and depositional ages (M1, 310–270 Ma; M2, 260–240 Ma), the elder M1 unit was thrusted upon the younger M2 unit, indicating a tectonic inversion. This inversion, which is associated with the whole geometry of the Ailaoshan belt, is ascribed to the transpressive deformation of the Cenozoic Red River Fault. These spatial heterogeneities well match the different evolutionary stages of the eastern Palaeo-Tethys.

First record of tempestites from Quaternary lacustrine deposits in the Ağrı Basin (Eastern Anatolia, Türkiye): palaeoclimatological and palaeogeographic implications

Several event layers have been identified in lacustrine deposits in the AErI Basin of Anatolia (E Türkiye). Sedimentological and palaeontological data newly indicate a storm-induced origin for some of them. The sedimentary structures in three sections, a few tens of metres apart from each other laterally, such as hummocky cross-stratification, wave-generated cross-bedding, parallel bedding, erosional surfaces, and graded bedding, which are considered characteristic of tempestites, are clearly present. Additionally, fining-upwards units and biogenic escape structures located at different levels of these sections indicate a similar origin. The vertical variations in layer thickness, grain size, and sedimentary structures in these sedimentary sections indicate fluctuating hydrodynamic conditions during deposition, while lateral decrease in the size and wavelength of the structures reflects deepening. This interpretation of storm-induced deposition is compatible with regional palaeoclimatological and palaeogeographical data, and is supported by evidence of Quaternary storm-induced sedimentation in adjacent lacustrine basins in the region

The Bothriolepis (Placodermi, Antiarcha) material from the Valentia Slate Formation of the Iveragh Peninsula (middle Givetian, Ireland): Morphology, evolutionary and systematic considerations, phylogenetic and palaeogeographic implications.

Material of the antiarch placoderm Bothriolepis from the middle Givetian of the Valentia Slate Formation in Iveragh Peninsula, Ireland, is described and attributed to a new species, B. dairbhrensis sp. nov. A revision of the genus Bothriolepis is proposed, and its taxonomic content and previous phylogenetic analyses are reviewed, as well as the validity of morphologic characteristics considered important for the establishment of the genus, such as the shape of the preorbital recess of the neurocranium. A series of computerised phylogenetic analyses was performed, which reveals that our new species is the sister taxon to the Frasnian Scottish form B. gigantea. New phylogenetic and biogeographic analyses of the genus Bothriolepis together with comparisons between faunal assemblages reveal a first northward dispersal wave from Gondwana to Euramerica at the latest in the mid Givetian. Other Euramerican species of Bothriolepis seem to belong to later dispersal waves from Gondwana, non-excluding southward waves from Euramerica. Questions remain open such as the taxonomic validity and stratigraphic constraints for the most ancient forms of Bothriolepis in China, and around the highly speciose nature of the genus.

Middle Devonian (Givetian) coral-stromatoporoid patch reefs from the Lazhuglung Formation, Xizang (Tibet) and their palaeoecological and palaeogeographical implications

We carried out, for the first time, detailed studies on the coral-stromatoporoid patch reefs from the Lazhuglung Formation near Shouxinghu in the Lazhuglung-Badangco area, Ngari Prefecture of Xizang (Tibet) Autonomous Region, China. On the basis of 1085 thin sections prepared from three patch reefs, the fossil components and reef structures are depicted. The patch reefs are found to encompass diverse fossil organisms, including tabulate and rugose corals, stromatoporoids, brachiopods, gastropods, ostracods, nautiloids, calcified cyanobacteria, and tubeworms. Tabulate corals and stromatoporoids are the predominant reef-builder, particularly Alveolites obtortus and Gerronostromaria gromotuchense. The patch reefs are Middle Devonian Givetian in age based on the tabulate coral and stromatoporoid assemblage. Extensive biotic interactions between the reef organisms are found in all three patch reefs, which are beneficial for the reef formation and development. The ecological features of the corals and stromatoporoids indicate a mesophotic ecosystem that is widespread in the Givetian. In addition, the common species and similar characteristics between the faunas in the Lazhuglung Formation, North Qiangtang Block and those in South China suggest a close palaeobiogeographic relationship. This study enhances our understanding on fossil components, reef structure and tectonic affiliation of the Palaeozoic strata in the Lazhuglung-Badangcuo area.

Norian conodonts of the South Qiangtang Terrane, North Tibet, and their palaeogeographic implications

Prior to their extinction at the Triassic-Jurassic boundary, conodonts were relatively diverse and abundant during Norian time. The great faunal turnovers at the base of the Norian and the base of the Alaunian (Middle Norian) confirm that the end-Triassic mass extinction was protracted through Late Triassic time rather than a single event. Norian conodonts also display obvious geographic distribution. Thus, investigation of Norian conodonts is not only of biostratigraphic significance, but it will elucidate the end Triassic mass extinction event as well as Late Triassic palaeobiogeography. Lacian (Early Norian) and Alaunian faunas appear to have spread extensively through Tibetan terranes of the Eastern Tethys, yet evidence of a continuous Lacian to Alaunian conodont succession as well as faunal turnover at the base of the Alaunian is sparse. Our biostratigraphic investigation of carbonate deposits of the Mopanshan area of the South Qiangtang Terrane has yielded abundant Norian conodonts. The Lacian Ancyrogondolella uniformis-Norigondolella hallstattensis Fauna and the Alaunian Mockina postera-Norigondolella steinbergensis Fauna are well-represented in the study region. The Norian conodont succession of the Eastern Tethys may be correlative with that of the Western Tethys and Eastern Pacific. The obvious geographic distribution provides evidence that the Indus-YarluZangbo Suture Zone (IYZSZ) separated Eastern Tethys into northern Tethys and southern Tethys realms. Norian conodonts are less abundant and diverse in the southern Tethys realm relative to the northern (or peri-Gondwana) Tethys. The Himalaya Terrane in the south belonged to southern Tethys whereas the Lhasa and the South Qiangtang terranes were part of the northern Tethys. Moreover, the absence of Norigondolella steinbergensis from the southern Tethys seemed to differentiate this realm from the northern Tethys.

Dispersed spore assemblages from the Lower Devonian Rañeces - La Vid groups of Northern Spain: Palaeogeographical implications

Dispersed spore assemblages are described from the Early Devonian (late Lochkovian-late Emsian) Rañeces Group (Asturias) and equivalent La Vid Group (Leon) of Northern Spain. The lower part of both groups consists predominantly of limestone and yields only impoverished palynological assemblages. However, the upper parts contain more clastic sediments and yield rich assemblages of well preserved palynomorphs. These are dominated by marine forms but also include abundant spores. Sixty-two spore taxa are reported from the Valporquero Formation (Leon). These all belong to a single assemblage that can be equated with the lindlarensis-sextantii Assemblage Zone (mid-early late Emsian age) erected in northern Gondwana. The sequences are independently age constrained by conodont and invertebrate macrofossil evidence and the ages derived from these studies are concordant with the assigned spore zones. The Spanish spore assemblages are from deposits that accumulated around the Armorican Terrane Assemblage (ATA), a group of islands that lay between the continents of Laurussia and Gondwana. Jacaard Index analysis indicates that the Valporquero Formation spore assemblage is endemic, and not closely related to those previously described from Laurussia or Gondwana, although it has more in common with the latter. This suggests that the Armorican Terrane Assemblage was widely separated from both Laurussia and Gondwana, but was located closer to and had more connectivity with Northern Gondwana.

Rudists (Bivalvia: Hippuritida) from the Lower Cretaceous Khalsi Formation, Ladakh, India, and their palaeogeographic implications

Rudist fauna composed of the Radiolitidae and the Polyconitidae is reported from the Aptian–Albian Khalsi Formation, southern Ladakh, India. The rudists are identified as Auroradiolites gilgitensis, A. biconvexus, Magallanesia rutogensis, and Shajia tibetica. Among them, A. biconvexus and M. rutogensis are described first time in Ladakh. Additionally, two radiolitid specimens reported from the Saltoro Formation of the SSZ in northern Ladakh by Upadhyay (2014), are assigned to A. biconvexus, and one single specimen from Saltoro Formation which was assigned to Horiopleura sp. by Upadhyay (2014), is questionably transferred to S. tibetica in this study. The occurrence of A. gilgitensis in the early Aptian of Ladakh provides evidence for the eastern dispersal pattern of A. gilgitensis during early Aptian. The finding of M. rutogensis in Ladakh fills the geographical gap between the first plagioptychid, early Turonian Plagioptychus haueri in the Mediterranean and the previous westernmost record of M. rutogensis in Lhasa Block, and further strengthens the hypothesis that Plagioptychidae was evolved from Magallanesia or related form. The association of A. biconvexus, A. gilgitensis, and M. canaliculata support the hypothesis of southwest Asian- Pacific province for the palaeobiogeographic linkage of Auroradiolites and Horiopleura haydeni–Praecaprotina–Magallanesia. This study provides additional evidence in favour of the relatively close geographical connection and tectonic equivalence between the Ladakh and Lhasa blocks during the mid-Cretaceous. Meanwhile, it highlights the need for detailed biostratigraphic studies in other microcontinents along the northern margin of the East Tethys, which may provide critical information for their tectonic and palaeogeographic evolution.

Biostratigraphy and palaeogeographic implications of Ordovician and Silurian chitinozoa from the High Zagros Mountains, Northern Persian Gulf, Iran

A siliciclastic succession is exposed at the Faraghan mountain, northern Persian Gulf, southeastern Iran. A detailed, high-resolution palynological analysis was performed on the Zardkuh, Seyahou, Dargaz, and Sarchahan formations to verify the exact age and palaeogeographic position of the High Zagros Mountains. Two hundred surface samples from this succession were collected and analysed. Most samples yielded abundant and well-preserved chitinozoans, acritarchs, scolecodonts, and cryptospores. Fifty-three chitinozoan species (21 genera) were identified that permitted to establish the Eremochitina brevis, Desmochitina ornensis, Belonechitina henryi, Siphonochitina formosa, Belonechitina robusta, Tanuchitina fistulosa, Acanthochitina barbata, Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata, Spinachitina oulebsiri, and Spinachitina fragilis biozones in ascending stratigraphic order as was previously established for the North Gondwana Domain. These results indicate that the Zagros Mountain Belt of Iran was part of the North Gondwana palaeo-province during the Ordovician-Silurian. On the other hand, these chitinozoan biozones and other associated fauna (e.g. graptolites, trilobites, brachiopods, and conodonts) suggest a late Early Ordovician (Floian) to Early Silurian (Rhuddanian) age range, with unconformities, for this succession. Based on chitinozoan biozones, a distinctive hiatus is present between the Zardkuh and Seyahou formations at Faraghan mountain, which corresponds to the absence of jenkinsi-tanvillensis chitinozoan biozones, encompassing the latest Middle Ordovician (latest Darriwilian: stage slice Dw3) and the early Late Ordovician (Sandbian: the stage slices Sa1 to Sa2 and time slices 5a to 5b). Two chitinozoan species were erected: Belonechitina bifurcaspina sp. nov., Angochitina persianense sp. nov., and Eremochitina cf. brevis was left in open nomenclature.

S and Sr Isotope Compositions and Trace Element Compositions of the Middle Jurassic Evaporites in Eastern Tibet: Provenance and Palaeogeographic Implications

The origin of Middle Jurassic evaporites in the Qamdo Basin is still controversial because palaeontological studies have reported that they have both marine and continental characteristics. The 87Sr/86Sr ratios of the gypsum in the Middle Jurassic Dongdaqiao Formation in the Qamdo Basin range from 0.707602 to 0.708163, which are higher than that of contemporaneous seawater. Model calculations suggest that continental water prevailed over seawater during the precipitation of these evaporites. However, the majority of the gypsum samples have δ34S values of 15.3‰ to 16.3‰, which are consistent with that of contemporaneous seawater. This range of values (15.3‰ vs. 16.3‰) was likely caused by S isotope fractionation during evaporation because the δ34S values and Sr contents are negatively correlated. The δ34S values of the other three gypsum samples are 20.0‰, 20.5‰, and 20.8‰, which are significantly higher than that of Middle Jurassic seawater. The trace element compositions and scanning electron microscopy (SEM) observations indicate that these elevated δ34S values were caused by bacterial sulphate reduction (BSR). The Sr and S isotope systematics of the gypsums from the Dongdaqiao Formation demonstrate that the parent brines from which the evaporites precipitated were marine based with a large quantity of continental input. A comparison of the lithologies and Sr isotope compositions of the Middle Jurassic sequences in the Qamdo and Qiangtang Basins revealed that the Qiangtang Basin was mainly recharged by Jurassic seawater, while the Qamdo Basin was primarily recharged by continental water with some seawater-derived overflow from the Qiangtang Basin.

U–Pb age constraints on the protolith, cooling and exhumation of a Variscan middle crust migmatite complex from the Central Iberian Zone: insights into the Variscan metamorphic evolution and Ediacaran palaeogeographic implications

The Figueira de Castelo Rodrigo–Lumbrales Anatectic Complex (FCR-LAC) located in the Central Iberian Zone of the European Variscan Belt is delimited by two shear zones, which have been interpreted as constraining its exhumation. New U–Pb zircon and apatite ages for the migmatites allowed us to obtain a peak metamorphic age of the anatectic complex (316.8 ± 2.0 Ma), and to estimate fast cooling (7–54°C Ma –1 ) and fast exhumation (0.2–1.3 mm a −1 ) after a vertical displacement of c. 6–9 km. Our results show a similar zircon age distribution between migmatites and the Excomungada Formation from the host Ediacaran–Cambrian Douro–Beiras Supergroup. Although the existence of an inherited zircon population lasting c. 500 Ma, absent in the metasedimentary units, suggests the contribution of Ollo de Sapo magmatic rocks during the Lower–Middle Pennsylvanian melting events. Detrital zircon ages of the Pinhão Formation (Douro Group) have contrasting sources to units from the Beiras Group, which may indicate the presence of a barrier that prevented older detrital components from reaching the Douro basin. However, at odds with what has been postulated before, such a barrier must have been placed farther south of the FRC-LAC, and thus not coincident with the Juzbado–Penalva do Castelo shear zone. Supplementary material: A full description of the stratigraphy and lithologies (Supplementary 1 and 2, respectively); the analytical conditons of the LA-ICP-MS analyses (Supplementary Material 3); the U–Pb zircon and apatite data of the FCR-LAC migmatites and the U–Pb detrital zircon data of the DBSG (Supplementary Material 4) are available at https://doi.org/10.6084/m9.figshare.c.6002006