Tethyan Domain Research Articles

Cenomanian and lower Turonian relative chronology and palaeoenvironmental framework of the Nouader site (Aures Basin, Northeastern Algeria)

AbstractThe lower–upper Cenomanian boundaries interval of the Nouader site in the Aures Basin (NE Algeria) has been studied for the first time using the association of two particularly effective taxonomic groups, one macrofossil (ammonites), and the other microfossil (foraminifera). The study section is divided into two formations (Fahdene and Bahloul) and one member (Annaba). Biostratigraphicaly, six ammonite biozones and five foraminiferan biozones were identified and calibrated. The ammonite fauna allows recognition of the lower CenomanianMantelliceras mantelliZone, the upper lower CenomanianMantelliceras dixoniZone, the succeeding lower middle CenomanianCunningtoniceras inermeZone, theAcanthoceras rhotomagenseZone and its subzones ofTurrilites costatusandTurrilites acutus, followed by the upper middle CenomanianAcanthoceras amphibolumZone, the lower upper CenomanianEucalycoceras pentagonumZone and finally the lower TuronianPseudaspidoceras flexuosumZone. The foraminiferan biozones are respectively:Thalmanninella brotzeniZone,Thalmanninella reicheliZone,Rotalipora cushmaniZone,Whiteinella archaeocretaceaZone andHelvetoglobotruncana helveticaZone. Among 14 ammonite zones in the Tethyan domain versus 11 in the Boreal domain, seven are common to both domains. For the planktonic foraminifera the Tethyan domain has five zones, the Boreal domain also has five, with five in common. The succession of index species occurs in the same order in both Tethyan (NE Algeria and Central Tunisia) and Boreal realms (East and NW Europe). Furthermore, the supposed depositional setting is interpreted as a calm and relatively deep environment which can be located around the middle to the external platform.

Early Cambrian Muli arc–ophiolite complex: a relic of the Proto-Tethys oceanic lithosphere in the Qilian Orogen, NW China

The Qilian Orogen in the northern margin of the Tibetan Plateau is the northernmost of the Tethyan domain. Abundant ophiolites record the closure of an early Tethyan ocean and amalgamations between micro-continents of North China, Qaidam, and Tarim. The Muli arc–ophiolite complex in the western segment of the South Qilian belt represents remnants of the Proto-Tethyan oceanic lithosphere. It comprises serpentinite, dunite, cumulate gabbro, basalt, plagiogranite, and chert, which are in tectonic contact with Upper Ordovician turbidites. Basalts have typical subduction-related calc-alkaline geochemical affinity, representing portions of an island arc. Geochemical results for plagiogranites and spinels from serpentinite indicate that the Muli arc–ophiolite complex represents a super-subduction zone (SSZ)-type ophiolite. U–Pb zircon data indicate formation associated with southward subduction of the Proto-Tethys Ocean during a short interval between 539 and 522 Ma. Results of petrology, geochemistry, and zircon U–Pb dating demonstrate that granitoids intruded into this complex are Middle to Late Ordovician (470–450 Ma) products of subduction-related arc magmatism. Voluminous Late Ordovician–Early Silurian rocks include deep-water marine siliciclastic and volcaniclastic turbidites and abundant volcanic arc rocks located to the south of the Muli arc–ophiolite complex, whereas fluvial coarse-grained sandstones and conglomerates unconformably overlie the Cambrian–Middle Ordovician ophiolite–arc systems in the eastern South Qilian belt. This indicates that closure of the Proto-Tethys Ocean was diachronous during the early Paleozoic.

The coprolite Lumbricaria Münster in the Early Tithonian of the Neuquén Basin, Argentina: new evidence for a holothurian producer

Lumbricaria Munster is described for the first time outside the Tethys domain from distal facies of the Tithonian Vaca Muerta Formation, Neuquen Basin, Argentina. The studied material consists of elongate, convolute, cylindrical coprolites, showing an overlapping pattern, and commonly exhibiting constrictions. Internally, coprolites show a densely packed fabric, where the particles show the distinctive morphology of saccocomid ossicles. These specimens are assigned to Lumbricaria intestinum Munster and three morphotypes are defined: (a) morphotype 1 shows a disordered convolute structure; (b) morphotype 2 is shorter and has a non-convolute arrangement; and (c) morphotype 3 has a spiral arrangement. Coprolites are preserved within microbial laminites, as well as concretions in calcareous mudstones. In this paper we discuss the possible producers of these coprolites, where evidence from the studied material would support a holothurian producer.

Multistage Remobilization of the Southwestern Margin of the South China Plate: Insights From Zircon U‐Pb Geochronology and Hf Isotope of Granitic Rocks From the Yao Shan Complex, Southeastern Tibet Plateau

AbstractThe Yao Shan complex, located at the southwestern margin of the South China plate, to the east of the Sanjiang‐Southeast Asia Tethyan domain, and at the northern extension of the Day Nui Con Voi massif of the Ailao Shan‐Red River shear zone, provides a reasonable example to study the multistage tectonic remobilization of continental plates. In this paper, we present new zircon LA‐ICP‐MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) U‐Pb dating results and Hf isotopic data of the granitic plutons and dikes from the Yao Shan complex. Zircon U‐Pb ages of the granitic intrusions mainly concentrate on three periods: 825–780, 82–69, and 31–29 Ma. The zircons are characterized by mainly negative εHf(t) values with TDMC ages of 2637–1645, 1964–1610, and 2077–1400 Ma, respectively. The results show that the Yao Shan complex record evidences for three episodes of extensive partial melting of middle and lower crustal Precambrian crystalline basement rocks. They contributed to the granitic magmatism in relation to tectonic processes and structural deformation from Neoproterozoic, Late Cretaceous to Oligo‐Miocene. Therefore, we argue that the southwestern margin of the South China plate is the weakness for multistage remobilization throughout the tectonic evolution of the plate after its primary cratonization. Remobilization of the plate margin is related to oceanic plate subduction, triggered by rifting in a passive continental margin setting, induced by extension at back‐arc setting, or resulted from continental extrusion.

Aptian-Lower Albian Serdj carbonate platform of the Tunisian Atlas: Development, demise and petroleum implication

Abstract In this paper, we present an updated biostratigraphic evaluation of the Serdj Formation of the Tunisian Atlas. Newly collected ammonites, combined with available biostratigraphic data, allowed the establishment of a new and robust stratigraphic framework for this well-known formation. For the first time the characterization of the Mellegueiceras chihaouiae Zone has permitted the specification of the Aptian-Albian transition. This study reveals an early Albian age for the top of the Serdj Formation that includes the main reservoir flow unit which is producing oil in both onshore and offshore Tunisia. Outcrop data analysis has revealed nine transgressive-regressive cycles within the Aptian - early Albian carbonates. During early Aptian the carbonate deposition occurred in deep-marine settings that gave way to shallow, open shelf carbonates deposition during the late Aptian - early Albian. These successions provide evidences enabling their correlation with the third-order global depositional sequences detected in the sedimentary basins of the Tethyan domains. Regional surface to subsurface stratigraphic correlation, based on seismic and wire-line logs, enabled: (1) a reliable correlation between the stratigraphic elements of the buried successions with those of the Serdj Formation, (2) the characterization of the platform-basin transition domain and (3) the verification of the hypothesis that the Serdj Formation carbonates constitute the surface analogue of the subsurface oil field reservoirs. The detailed conceptual stratigraphic model suggests that the Serdj platform developed diachronous. Its demise occurred in the early Albian and not during the Aptian-Albian transition as previously believed. The hydrocarbon-productive reservoirs developed during the regressive phases especially in the up-dip settings of the platform where dolomitization greatly enhanced the reservoir quality.

Pyrite Re-Os age constraints on the Irankuh Zn-Pb deposit, Iran, and regional implications

The investigation of epigenetic carbonate-hosted Pb-Zn deposits from China and Europe in the Eastern and Western orogens of the Tethyan Domain, have provided a new perspective on the range of processes operating in this deposit class globally. However, improved metallogenic models require new constraints on the timing of mineralization throughout the Domain. To address this need, we applied Re-Os pyrite dating to the world class Irankuh Zn-Pb deposit, Iran. The Irankah deposit is located in the thrust belt of the Malayer-Esfahan Pb-Zn Metallogenic Belt (MEMB) in the Zagros Orogen, Iran. Mineralization is hosted by the Goushfil Main Fault and adjacent dolomitized limestones. The hydrothermal mineral assemblage comprises sphalerite, galena, pyrite, minor chalcopyrite and sulfosalt minerals, together with dolomite, barite and abundant quartz. Pyrite associated with main-stage sphalerite mineralization has low concentrations of 3 to 37 ng/g Re and 6 to 49 pg/g Os that are typical of low-level highly radiogenic (LLHR) sulfides. Nonetheless, vein and replacement pyrites from the Goushfil orebody yielded a 5-point isochron age of 66.5 ± 1.6 Ma that is interpreted as the main Zn-Pb mineralization age. The new mineralization age confirms an epigenetic origin for the Irankuh Zn-Pb deposit and supports an early onset for compressional deformation in the Zagros Orogen. The geochronological data support textural evidence that mineralization in veins occurred during regional compression in an active tectonic environment. Therefore the possibility that magmatic fluids and/or heat contributed to the mineralizing system should be incorporated into regional exploration models. Further work is required to test the extent to which epigenetic carbonate-hosted Pb-Zn deposits in the thrust and fold belt settings of the Central and Eastern Tethys differ from those in the Western Tethys and classic Mississippi Valley Type ore deposits.

A Barremian-?Aptian Tethyan precursor of the Cretaceous marine flooding of Morocco: Evidence from the red-bed series within the “Marginal Folds” of the eastern High Atlas

Stratigraphic, sedimentologic, and micropaleontologic studies have been undertaken on the “Infra-Cenomanian” continental red beds (= Dekkar Group) located on the northern side of the Moroccan eastern High Atlas. Rich charophyte assemblages containing Sphaerochara magna, Ascidiella stellata, Hemiclavator sp. A, Globator trochiliscoides, Atopochara trivolvis, At. triquetra, and Flabellochara harrisii indicate a late Barremian age for the lower part of the series. Within the continental deposits we have discovered in the Middle Member of the Dekkar 2 Formation limestones and marls containing echinoderms, dasycladacean algae and foraminifera (miliolids, Ammobaculites sp., Choffatella decipiens). The existence of two littoral to lagoonal-marine intercalations within the continental sedimentation reveals marine transgressive events during the late Barremian–?early Aptian. The lateral extension of these marine sediments allows the erection of paleogeographic boundaries that define a « Marginal Folds Gulf » characterized mainly by restricted marine paleoenvironments. This E-W directed gulf is a relatively long depression, a few tens of kilometers wide and one hundred kilometers long, developed in an area which is now at the foot of the eastern High Atlas. The infilling deposits is dominantly controlled by the distance from the North High Atlas Fault. The gulf terminated westward and probably opened northeastward into the Tethyan domain. This narrow gulf was separated from both the Tethyan Gulf known in the Central Middle Atlas during the Aptian and the coeval Atlantic Gulf located on the northern side of the Marrakech and Central High Atlas. Thus, the « Marginal Folds Gulf » is a new paleogeographic feature that documents marine incursions within the Jurassic–Early Cretaceous continental areas of the NW Africa.

Hot-house climate during the Triassic/Jurassic transition: The evidence of climate change from the southern hemisphere (Salt Range, Pakistan)

Abstract The Triassic–Jurassic boundary interval was characterised by the change from warm, semiarid–arid to a hot and humid climate in the Tethyan domain linked to input of greenhouse gases from the Central Atlantic Magmatic Province (CAMP) activity and Pangaea breakup. This study provides the very first outcrop evidences of palaeoclimatic evolution during the Triassic–Jurassic boundary interval in the then southern hemisphere, along the eastern margin of Gondwana facing the western Tethys. In the Tethyan Salt Range of Pakistan a succession of Upper Triassic dolomites, green-black shales (Kingriali Formation) to overlying Lower Jurassic quartzose sandstones, shales, laterites and conglomerates (Datta Formation) represents the sedimentary archives of this critical time interval. Bulk and clay mineralogy of the Upper Triassic shales indicate the presence of mainly illite while kaolinite is a minor component. The kaolinite content, a reflection of the mature stage of chemical weathering and hence hot–humid conditions, increases up-section in the overlying shales and sandstone–shale succession. The following laterite–bauxite horizons lack illite and are entirely composed of kaolinite, boehmite and haematite. The bulk rock geochemistry of the succession confirms a similar trend. The Chemical Index of Alteration (CIAmolar) displays an increasing trend from the Upper Triassic (CIA 68–80) to the overlying Lower Jurassic strata (CIA 90–97). The overall results for the succession reveal an increasing chemical maturity trend from Rhaetian to Hettangian thereby supporting a change from warm-arid to a hot and humid palaeoclimate, probably extreme greenhouse conditions. Similar changes in the clay mineralogy and sediment geochemistry across the Triassic–Jurassic boundary have been reported from basins across Europe. Thus the Salt Range provides sections from the southern hemisphere for correlations across the Triassic–Jurassic boundary.

Euxinic conditions and high sulfur burial near the European shelf margin (Pieniny Klippen Belt, Slovakia) during the Toarcian oceanic anoxic event

Abstract The Toarcian oceanic anoxic event (T-OAE; 183 Ma) was accompanied by severe biotic and geochemical perturbations that are considered as some of the most severe of the Mesozoic era. Nevertheless, paleoceanographic conditions during the T-OAE in the Tethyan domain remain poorly understood owing to the relatively low number of marine successions from this area investigated so far. In this study, we report new geochemical, palynological and pyrite framboid size data from Zazriva, northwestern Slovakia, a Lower Toarcian marine succession recording organic-rich sedimentation at the margin of the NW-European shelf. The lowermost Serpentinum ammonite Zone records high total organic carbon (TOC) contents (2 to 5 wt%) and very low organic carbon isotope values (from −30 to −32‰) characteristic of the T-OAE negative carbon isotope excursion in coeval sites. The size of the pyrite framboids, the high S contents independent on TOC, low sulfur isotope values (δ34S

Response of larger benthic foraminifera to the Paleocene-Eocene thermal maximum and the position of the Paleocene/Eocene boundary in the Tethyan shallow benthic zones: Evidence from south Tibet

Research Article| August 01, 2018 Response of larger benthic foraminifera to the Paleocene-Eocene thermal maximum and the position of the Paleocene/Eocene boundary in the Tethyan shallow benthic zones: Evidence from south Tibet Qinghai Zhang; Qinghai Zhang † 1Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, and CAS Centre for Excellence in Tibetan Plateau Earth Sciences, Lincui Road 16-3, 100101 Beijing, China2Department of Geosciences, University of Bremen, Klagenfurter Straße 4, 28359 Bremen, Germany †zhang@itpcas.ac.cn Search for other works by this author on: GSW Google Scholar Helmut Willems; Helmut Willems 2Department of Geosciences, University of Bremen, Klagenfurter Straße 4, 28359 Bremen, Germany3Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, East Beijing Road 39, 210008 Nanjing, China Search for other works by this author on: GSW Google Scholar Lin Ding; Lin Ding 1Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, and CAS Centre for Excellence in Tibetan Plateau Earth Sciences, Lincui Road 16-3, 100101 Beijing, China Search for other works by this author on: GSW Google Scholar Xiaoxia Xu Xiaoxia Xu 2Department of Geosciences, University of Bremen, Klagenfurter Straße 4, 28359 Bremen, Germany Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (1-2): 84–98. https://doi.org/10.1130/B31813.1 Article history received: 24 Mar 2017 rev-recd: 21 May 2018 accepted: 19 Jun 2018 first online: 01 Aug 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation Qinghai Zhang, Helmut Willems, Lin Ding, Xiaoxia Xu; Response of larger benthic foraminifera to the Paleocene-Eocene thermal maximum and the position of the Paleocene/Eocene boundary in the Tethyan shallow benthic zones: Evidence from south Tibet. GSA Bulletin 2018;; 131 (1-2): 84–98. doi: https://doi.org/10.1130/B31813.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Paleocene-Eocene thermal maximum (PETM) is one of the most pronounced global warming events in the Cenozoic. This event was associated with a large negative carbon isotope excursion (CIE) and with major changes in the atmosphere, hydrosphere, and biosphere. However, how the larger benthic foraminifera (LBFs) in the shallow Tethyan Ocean responded to the PETM remains controversial. In this study, we investigate two shallow-marine, LBF-rich carbonate sections from south Tibet, aiming to locate the position of the Paleocene/Eocene (P/E) boundary in the Tethyan shallow benthic zones (SBZs) and to examine the response of the LBFs to the PETM. Carbon isotope compositions of bulk carbonate were measured to constrain the stratigraphic position of the CIE onset marking the P/E boundary in the sections, and the LBFs were studied in rock thin sections in order to assess their biostratigraphy and to construct the SBZs. The combination of the carbon isotope data and constructed SBZs shows that the P/E boundary is located within SBZ5, not at the SBZ4/SBZ5 transition as proposed in the Western Tethyan domain. At the P/E boundary, no evident compositional change in LBF assemblages can be observed. However, a major compositional change in LBF assemblages occurs in the CIE recovery, characterized by the sudden disappearance of Miscellanea, Ranikothalia, Setia, Orbitosiphon, and the initial dominance of porcellaneous-walled Alveolina and Orbitolites together with small miliolids and rotaliids. We tentatively speculate that this compositional change in LBF assemblages may be related to a eutrophication event, likely resulting from intensified continental weathering during the CIE recovery of the PETM. You do not currently have access to this article.

Early Palaeozoic accretionary tectonics of West Kunlun Orogen: Insights from Datong granitoids, mafic–ultramafic complexes, and Silurian–Devonian sandstones, Xinjiang, NW China

The Datong area is located in the western part of the Western Kunlun Orogen (WKO), occupying a key area of the Tethyan domain. Our new SHRIMP U–Pb zircon ages from the Datong area provide new information about the Palaeozoic evolution of the Western Kunlun Orogen. A 473.0 ± 2.8 Ma granite with 493.6 ± 4.8 Ma inherited zircons from the Kusilafu extrusive rocks is interpretation as an A‐type granite formed in a fore‐arc tectonic setting. The 485.5 ± 1.9 Ma granitoid of the Datongdong pluton combined with the 452.7 ± 7 Ma granitoid of the Datong pluton indicate that the Datong pluton is an intra‐oceanic arc complex formed by the southern subduction of the Proto‐Tethyan ocean crust. Zircons from gabbros of the Datong mafic–ultramafic complex have a 499.2 ± 2.1 Ma U–Pb crystallization age. Combined with its complicated whole‐rock geochemistry, we propose that there may have existed a Datong seamount in the early Palaeozoic. The detrital zircon results of Silurian–Devonian sandstones reveal that the Late Silurian sandstones have the characteristic zircons both from the Tarim Block and Datong Arc, suggesting that the Datong arc collided with the Tarim Block in the Late Silurian. The tectonic history of the WKO was characterized by a southern subduction of Proto‐Tethys terminated in the Late Silurian.

Foraminiferal response to the PETM recorded in the SW Tarim Basin, central Asia

The Paleocene/Eocene (P/E) boundary interval is the most significant climatic transition during the Cenozoic, when the PETM (Paleocene Eocene Thermal Maximum) caused rapid warming and severe fluctuation of the Earth system, especially in marine settings. The SW Tarim Basin represents a distal branch of the NE Tethys, exposing Paleocene to Eocene successions that include the Qimugen Formation and provide optimal section for investigating the P/E boundary transition. By detail field-based lithological records and the planktonic and benthic foraminiferal assemblage analysis, the P/E boundary was redefined within the black mudstone bed of the Qimugen Formation. The planktonic foraminiferal assemblages recorded in the Qimugen Formation may be subdivided into four biozones, including bioevents of Globanomalina pseudomenardii, Globanomalina luxorensis and Pseudohastigerina wilcoxensis. Planktonic foraminiferal turnover is marked by the cool water subbotinids disappearance, give way to warm water muricate taxa, co-varying with the gradual disappearance of benthic foraminifera. The foraminiferal assemblages together with other identified microfossils suggest a shallow marine environment in which transgressions related to the sea level fluctuation of the Tethyan Domain took place in the Paleocene to Eocene boundary interval.

Biostratigraphy of upper Cretaceous through Paleocene successions in Grombalia, Tunisia (southern Tethyan domain)—reworking processes and interpretations

Revision of Late Cretaceous through Paleocene planktic foraminiferal zonal schemes for northeastern Tunisia (Khanguet El Hajjej and Sidi Rhilaine section) has provided new insights into the biostratigraphic framework of the Abiod Formation. A late Paleocene age is endowed with this unit based on the occurrence of late Cretaceous reworked microfauna associated with Morozovella velascoensis planktic foraminifera. The biostratigraphic equivalent, between the mayaroensis and velascoensis Zones near J. Barka, includes an occasional submarine reworking of sediments induced by mass flow transport, indicated by the presence of microfaunal content and heterogeneous extraclasts. The internal organization of sediment (olistoliths, mass flow deposits) reflects tectonic activity and clear evidence of redeposition during the late Paleocene.

Genetic implications for the Damajianshan W‐Cu‐As polymetallic deposit in Lvchun, Southwest China: Constraints from H–O, He–Ar, S, and Pb isotopes

The Sanjiang Tethyan domain in SE Asia is one of the most important mineral belts in China. The Damajianshan (DMJS) W‐Cu‐As polymetallic deposit is located in the southern part of Sanjiang Tethyan domain, related to Triassic quartz porphyry. Detailed exploration thereafter shows that the reserves of W, Cu, and As are 0.09, 0.42, and 0.12 Mt, respectively. The W is a typical oxyphile element and always coexisted with Sn–Li–Be–Nb–Ta. The Cu–As are typical sulphophile elements and always coexisted with Au–Ag–Pb–Zn–Sb–Hg. It is rarely reported that a deposit preserves tungsten and copper–arsenic simultaneously in the southern Sanjiang region. In this study, the S–Pb isotopic ratios of sulphides, the H–O isotopic compositions of fluid inclusions in hydrothermal quartz, and the He–Ar isotopic ratios of fluid inclusions in sulphides were analysed to constrain the origin of the DMJS deposit. Studies have shown that the δ34S values of sulphides from ores are mainly between −6.17‰ and +0.02‰; the sulphur isotope compositions indicate that the ore‐forming materials might originate from deep sources. The Pb isotope characteristics indicate that the ore metals might originate from deep sources and be closely related to the quartz porphyry. The δ18Ofluid values of ore‐forming fluids calculated from hydrothermal quartz range from −5.5‰ to +7.5‰, and the δD values of the fluid inclusions in quartz are from −81.7‰ to −50.2‰. The H–O isotope systematics indicate that the ore fluids in the DMJS deposit were probably initially sourced from magmatic water and later gradually mixed with Mesozoic meteoric water. Fluid inclusions in pyrite, chalcopyrite, arsenopyrite, and pyrrhotite possess 3He/4He ratios of 0.02–0.05 Ra, and their 40Ar/36Ar ratios range from 562.47 to 4159.15, indicating a complete crustal fluids and with higher radiogenic 40Ar. The noble gas isotopic data, along with the stable isotopic data, suggest that the ore‐forming fluids have a deep source. The unique geologic structure of the Sanjiang Tethys tectonic metallogenic region and the evolution of ore‐forming fluids both promoted the formation of this rare DMJS deposit.

Isotope records (C-O-Sr) of late Pliensbachian-early Toarcian environmental perturbations in the westernmost Tethys (Majorca Island, Spain)

The late Pliensbachian–early Toarcian (Early Jurassic) was a time of major environmental changes that culminated with the Early Toarcian Oceanic Anoxic Event (T-OAE, ca. ~183 Ma). This period is marked by significant disturbances in the carbon cycle and rapid climatic changes. To improve the understanding of the expression of these events in westernmost Tethyan domains, this study provides new belemnite and bulk carbonate C and O stable isotope records of a ~5 Myr upper Pliensbachian to middle Toarcian marine succession of the Balearic Basin (Es Cosconar section, Majorca). Time resolution has been improved by combination of biostratigraphic (ammonoids and brachiopods) and geochronologic (87Sr/86Sr) methods. Seawater paleotemperatures derived from δ18O belemnite records reveal cooler paleotemperatures in the upper part of the Spinatum Zone. The uppermost Spinatum Zone is characterized by the onset of a warming event that crosses the Pliensbachian-Toarcian boundary, culminating with the warmer temperatures (up to ~10 °C of warming) for the Serpentinum Zone of the lower Toarcian. This warming event has been detected contemporaneously in many other European and Tethyan basins and is interpreted to represent generalized raised seawater temperatures linked to the T-OAE. Four significant δ13C events have been recorded in belemnite and bulk carbonate records. The first is a negative carbon isotope excursion (CIE) around the Pliensbachian-Toarcian boundary, which is best represented in the belemnite record. Soon after, the bulk‑carbonate record shows a positive shift in the lower Tenuicostatum Zone concomitant with a return to background values in the belemnite record, suggesting strong water stratification or decoupling probably related with export of neritic carbonate to the basin. The third is a negative CIE represented in bulk carbonate across the Tenuicostatum-Serpentinum zonal transition, which could be correlated with the negative excursion characterizing the onset of the T-OAE in other sections. The position of this excursion corresponds with a gap in the belemnite record. Finally, in the lower Toarcian, both the bulk carbonate and belemnite carbon isotope records show pronounced positive CIEs in the lower-middle part of the Serpentinum Zone. These CIEs testify the impact of the T-OAE in the Balearic basin.

Late Cretaceous foraminiferids from sections in the Zabratówka area (Skole Nappe, Outer Carpathians, Poland)

Well preserved Late Cretaceous–Palaeogene planktonic and benthic foraminiferal assemblages were studied in the Zabratowka section of the Ropianka Formation in the Skole Nappe. The Racemiguembelina fructicosa and Abathomphalus mayaroensis standard foraminiferal biozones were distinguished. The K-T boundary was recognized within the interval between samples ZB10B–ZB9A, mainly composed of marly mudstones, interlayered with thin-bedded sandstones, and is characterized by the disappearance of planktonic taxa and an abundance of agglutinated species. Foraminiferal assemblages, collected from the turbiditic flysch-type sediments, indicate a primary depositional environment on the outer shelf to the upper part of the continental slope, with shallowing during the Maastrichtian in the part of the Skole Basin studied. The foraminiferids correspond to the assemblages of a palaeobiogeographical “transition” zone, located between the Boreal and Tethyan domains.

Paleozoic subduction-related magmatism in the Duobagou area, Dunhuang block: Constrained by zircon U-Pb geochronology and Lu-Hf isotopes and whole-rock geochemistry of metaigneous rocks

The Dunhuang block, situated at the junction of the Tethyan domain, Tarim craton, North China craton and the Central Asian Orogenic Belt (CAOB), consists mainly of Archean–early Mesoproterozoic basement rocks and Paleozoic metamorphic and magmatic rocks. In this study we performed systematic analyses on the Duobagou metaigneous rocks, including zircon U-Pb ages and Hf isotopes and whole-rock geochemistry, to discuss the evolutionary history of the Dunhuang block and the surrounding continental fragments during the Paleozoic.

Neoproterozoic granitoids along the Ailao Shan-Red River belt: Zircon U-Pb geochronology, Hf isotope analysis and tectonic implications

The Ailao Shan-Red River belt (ASRRB) is a complex tectonic collage of Archean to Miocene geological units, located between two major tectonic domains, i.e., the South China domain to the east and the Tethys domain to the west. Although general agreements have been reached on that the Ailao Shan suture zone along the ASRRB represents a Silurian to middle Triassic subsidiary ocean in the eastern Paleo-Tethyan system and the Ailao Shan-Red River shear zone within the belt occurred as the northeastern boundary of the Cenozoic extrusion of the Indochina block during the Indian-Eurasian collision, the Precambrian tectonic attributes of the belt remain controversial. This study presents new zircon U–Pb ages, whole-rock geochemical and Hf isotopic data of Neoproterozoic granitoids along the ASRRB.Neoproterozoic granitoids along the ASRRB are located to the east of the Jinshajiang-Ailao Shan suture zone. Samples from the granitoids have zircon 206U/238Pb ages between 799Ma and 724Ma, implying the existence of extensive Neoproterozoic granitic magmatism along the ASRRB. Their basement rocks share similar characteristics (e.g. Paleo- to meso-Proterozoic protolith ages) to those of the western Yangtze block. Evidences suggest that the Neoproterozoic intrusions and their metamorphic basement rocks along the ASRRB were derived from the southwest margin of the Yangtze block.Zircon εHf (t) values of the granitoid samples range from −10.22 to 0.64, with Hf crustal model ages of 1632.2–2335.9Ma. It is suggested, combining the present results and regional geology data, that the Neoproterozoic granitic magmatism along the ASRRB is dominantly of crustal origin, and contributions from mantle sources are common. They are possibly attributed to partial melting of ancient lower crust and addition of mantle fluids related to oceanic subduction. The results support a scenario that arc magmas were generated by continued oceanic subduction beneath the southwestern margin of the Yangtze block, instead of the northeastern margin of the Indochina block, lasted from 799Ma to 724Ma.

Microfacies analysis of larger benthic foraminifera-dominated Middle Eocene carbonates: a palaeoenvironmental case study from Meghalaya, N-E India (Eastern Tethys)

Larger benthic foraminifera (LBF) show significant abundance and diversity in the Palaeogene carbonate sediments of Meghalaya, N-E India, but have previously received less attention from the palaeoenvironmental perspective. LBF are important contributors to recent as well as fossil shallow marine, tropical carbonate settings. They find wide application in biostratigraphy and palaeoenvironmental reconstructions. The larger foraminiferal turnover (LFT) during the Palaeocene-Eocene transition is very important with respect to their evolution in several parts of the world including the Eastern Tethys. The present microfacies analysis documents the status of LBF in the Middle Eocene sediments from the Prang Formation of the Sylhet Limestone Group in Meghalaya, N-E India. Five major facies types (MFTs)—miliolid grainstone-packstones, alveolinid-rotaliid grainstone-packstones, nummulitid-alveolinid grainstone-packstones, coralline algal-nummulitid packstone-wackestones and coralline algal wackestones have been recorded in the current study. Evaluation of the palaeoenvironmental parameters aids in understanding the seascape of this Eastern Tethyan domain. It is suggested that an oligotrophic nutrient regime supported the rapid evolution and dominance of the LBF. Most notable is the prolific augmentation in Alveolina and Nummulites populations. High surface water temperatures during the Late Palaeocene-Early Eocene global warming episode possibly persisted to a certain level during the Middle Eocene and continued to favour the larger foraminifera as the major carbonate producers instead of the vulnerable corals.

Tectonostratigraphic framework and depositional history of the Cretaceous–Danian succession of the Danish Central Graben (North Sea) – new light on a mature area

Abstract An integrated tectonic and sequence stratigraphic analysis of the Cretaceous and Danian of the Danish Central Graben has led to significant new insights critical for our understanding of the chalk facies as a unique cool-water carbonate system, as well as for the evaluation of its potential remaining economic significance. A major regional unconformity in the middle of the Upper Cretaceous chalk has been dated as being of early Campanian age. It separates two distinctly different basin types: a thermal contraction early post-rift basin (Valanginian–Santonian), which was succeeded by an inversion tectonics-affected basin (Campanian–Danian). The infill patterns for these two basin types are dramatically different as a result of the changing influence of the tectonic, palaeoceanographic and eustatic controlling factors. Several new insights are reported for the Lower Cretaceous: a new depositional model for chalk deposition along the basin margins on shallow shelves, which impacts reservoir quality trends; recognition of a late Aptian long-lasting sea-level lowstand (which hosts lowstand sandstone reservoirs in other parts of the North Sea Basin); and, finally, the observation that Barremian–Aptian sequences can be correlated from the Boreal to the Tethyan domain. In contrast, the Late Cretaceous sedimentation patterns have a strong synsedimentary local tectonic overprint (inversion) that influenced palaeoceanography through the intensification of bottom currents and, as a result, the depositional facies. In this context, four different chalk depositional systems are distinguished in the Chalk Group, with specific palaeogeography, depositional features and sediment composition. The first formalization of the lithostratigraphic subdivision of the Chalk Group in the Danish Central Graben is proposed, as well as an addition to the Cromer Knoll Group.