Journal articles: 'Upper Pliensbachian – lower Toarcian' – Grafiati (2024)

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Abstract. Temporary road sections for the A303 bypass at Ilminster, Somerset, revealed Upper Pliensbachian and Toarcian sediments from an alternating limestone–marl facies, in marked contrast to the limestone-dominated Dorset coast succession. The lithostratigraphy is described, with the standard ammonite zonation providing chronostratigraphical correlation. The uppermost Pliensbachian (Spinatum Chronozone) and much of the Toarcian (Serpentinum, Bifrons, Variabilis, Thouarsense and Pseudoradiosa chronozones) of the classic Dorset coast Lower Jurassic sequence are represented by the Beacon Limestone Formation, formerly the ‘Junction Bed’ (a highly condensed carbonate deposit). The Tenuicostatum Chronozone is largely missing from the sequence. Elsewhere in southern and eastern England this interval is poorly or rarely exposed. The argillaceous units have yielded rich microfaunas and -floras (foraminifera, ostracods, calcareous nannofossils and palynomorphs), the biostratigraphical distributions of which are analysed and discussed in relation to contemporary evolutionary patterns and other UK records. This study provides an insight into the micro-biostratigraphy of the Late Pliensbachian to Toarcian interval for onshore southern England.

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Abstract. One of the main controversial items in palaeoclimatology is to elucidate if climate during the Jurassic was warmer than present day, with no ice caps, or if ice caps were present in some specific intervals. The Pliensbachian Cooling event (Lower Jurassic) has been pointed out as one of the main candidates to have developed ice caps on the poles. To constrain the timing of this cooling event, including the palaeoclimatic evolution before and after cooling, as well as the calculation of the seawater palaeotemperatures are of primary importance to find arguments on this subject. For this purpose, the Rodiles section of the Asturian Basin (Northern Spain), a well exposed succession of the uppermost Sinemurian, Pliensbachian and Lower Toarcian deposits, has been studied. A total of 562 beds were measured and sampled for ammonites, for biostratigraphical purposes and for belemnites, to determine the palaeoclimatic evolution through stable isotope studies. Comparison of the recorded uppermost Sinemurian, Pliensbachian and Lower Toarcian changes in seawater palaeotemperature with other European sections allows characterization of several climatic changes of probable global extent. A warming interval which partly coincides with a negative δ13Cbel excursion was recorded at the Upper Sinemurian. After a "normal" temperature interval, a new warming interval that contains a short lived positive δ13Cbel peak, was developed at the Lower-Upper Pliensbachian transition. The Upper Pliensbachian represents an outstanding cooling interval containing a positive δ13Cbel excursion interrupted by a small negative δ13Cbel peak. Finally, the Lower Toarcian represented an exceptional warming period pointed as the main responsible for the prominent Lower Toarcian mass extinction.

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AbstractAlthough the Mesozoic rocks of the Transdanubian Range have been the subject of a multitude of different studies, mineralogical research is largely underrepresented. The clay mineralogy of Lower Jurassic (especially the Pliensbachian and Toarcian) strata was broadly investigated earlier; however, systematic high-resolution clay mineralogical studies remain scarce. Here we present a mineralogical study focusing on the Upper Pliensbachian strata of the Lókút-Hosszúárok section, located near the Eplény Manganese Ore Field. We identified dioctahedral smectite, randomly interstratified illite/smectite, illite as 10 Å phyllosilicate, quartz and cristobalite. Based on our new results we propose that the smectite was formed by aging of Mg or Fe hydroxide-silica precipitates. The smectite and cristobalite were presumably formed from the siliceous tests of radiolarians, whose abundance was controlled by a local upwelling system. The occurrence of Pliensbachian smectite in the Lókút outcrop shows similarities with the Úrkút smectites known from both Pliensbachian and Toarcian strata, which implies that similar processes controlled the sedimentation during the Pliensbachian as well as during the black (gray) shale-hosted ore accumulation in the Eplény and Úrkút basins.

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The marl-limestone succession that encompasses the Pliensbachian–Toarcian Stage Boundary (Lower Jurassic) and crops out at Peniche (Lusitanian Basin, Portugal), was chosen as one of the candidates for the establishment of Toarcian GSSP. Chemostratigraphy analyses, of the Upper Pliensbachian (spinatum Zone)-Lower Toarcian (levisoni p.p. Zone) portion, were based on total organic carbon (TOC) (68 samples), the isotope carbon (δ13C) and oxygen (δ18O) (38 samples) on the whole rock sample. Presenting an absolute variation of around -2.0‰, the δ13C and δ18O values decrease from the middle part up to the uppermost part of spinatum Zone, with smaller values in the lowermost part of the polymorphum Zone. In the Lower Toarcian the δ13C data shows a positive trend (spread of + 2.0‰) with a maximum value in the middle-upper portion of the polymorphum Zone and a minimum in the lowermost part of the levisoni Zone. The δ18O values show a general tendency to decrease within the polymorphum Zone, with the smallest values observed in the lower portion of the levisoni Zone. In general the TOC values are low, around 0.2%, in the spinatum Zone, upwards they increase to 0.5% in the polymorphum Zone, whilst they decrease again to 0.2% in the lowermost levisoni Zone. Calcareous nannofossils assemblages were investigated in 12 slides of marly samples collected around the Pliensbachian – Toarcian Stage Boundary that, according to the adopted zonation, proposed for NW European, lies in the NJ5b biozone. Abundant and well preserved nannofossils assemblages comprise 12 genera and 18 species. The genera Schizosphaerella and Lotharingius are dominant. Calcivascularis jansae, a characteristic taxon of the Lower Jurassic tethyan nannofossils assemblages, is abundant in the whole investigated interval. Biscutum grande is the other tethyan taxon present in studied succession. The occurrences of C. jansae and B. grande support the tethyan affinity of the calcareous nannofossils assemblages recovered from the Pliensbachian – Toarcian transition sampled at Peniche section.

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The Lower Jurassic Sub-system comprises four stages, in chronological order, the Hettangian, Sinemurian, Pliensbachian and Toarcian. Each stage is subdivided into a sequence of ‘standard zones’ (= chronozones) and subzones – each correlated primarily on the basis of its ammonite fauna. A further increase in stratigraphical resolution is available by the use of intra-subzonal units known collectively as ‘horizons’. The close link between ammonites and chronostratigraphy means that faunal provincialism may determine which zonal framework, and therefore which subdivision of the Lower Jurassic, applies in different regions of Europe. Such provincialism is of minor importance in the early Jurassic (Hettangian – Lower Pliensbachian) but increases significantly in the Upper Pliensbachian and into the Toarcian where at least three ammonoid faunal provinces are distinguishable. The standard zonal schemes for each relevant faunal area are discussed here, with greatest emphasis being placed on the Northwest European Province, which is characteristic of much of northern Europe throughout most of the Early Jurassic. Intra-subzonal units have only been described in certain regions for parts of the Lower Jurassic but where recognisable these are introduced.

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The accuracy of published Jurassic time scales is compromised by a paucity of sufficiently accurate and stratigraphically well-constrained isotopic dates. U–Pb dating of volcaniclastic rocks within fossiliferous marine successions is a method suitable of providing additional useful calibration points. Stikinia and Wrangellia, two of the major accreted terranes of the Canadian Cordillera, comprise volcanosedimentary assemblages of magmatic arc origin. Within them we selected sections from which we report 14 new U–Pb zircon ages that are integrated with ammonite biochronology at the zonal level. Poor zircon recovery and complex U–Pb systematics made it difficult to obtain precise ages for many of the samples. The following ages were determined (with 2σ errors): 194.0+9.1–1.8 Ma from the Plesechioceras? harbledownense Assemblage (upper Sinemurian), 191.5 ± 0.8 Ma from the Plesechioceras? harbledownense Assemblage (upper Sinemurian) to the Whiteavesi Zone (lower Pliensbachian), 185.6+6.1–0.6 Ma from the Freboldi Zone (lower Pliensbachian), 184.7 ± 0.9 Ma from the Kunae Zone (upper Pliensbachian), 180.4+8.0–0.4 Ma from the Kanense to Planulata zones (lower to middle Toarcian), 179.8 ± 6.3 Ma from the Yakounensis Zone (upper Toarcian) to the lower Bajocian, 167.2+10.5–0.4 Ma from the Rotundum Zone (upper Bajocian), 158.2+1.9–0.4 Ma from the upper Bathonian, and 162.6+2.9–7.0 from the upper Bathonian to lower Callovian. Five other dates are inferior in precision, but still provide some constraints for time-scale calibration. The U–Pb dates reported here together with a wealth of other recently obtained Cordilleran isotopic dates will be used for a significant revision of the Jurassic time scale.

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Abstract. Palynomorph and foraminiferal assemblages have been studied from the Upper Pliensbachian to Bathonian of a borehole section on the island of Anholt in the Kattegat, situated near the eastern margin of the Norwegian-Danish Basin. Palynomorphs were recorded throughout the succession and have been used for both biostratigraphical and palaeoenvironmental assessments. Foraminifera were recorded from only the lower part of the succession, where they proved useful for interpreting palaeoenvironments. Four palynomorph and three foraminiferal zones have been established.The interval encompasses a palaeoenvironmental transition from a marine, inner shelf setting to mainly terrestrial conditions. The Upper Pliensbachian-Toarcian boundary marks the beginning of a major regression, which continued through the Toarcian and Aalenian. Hence, it took place significantly earlier at Anholt than in the centre of the Norwegian-Danish Basin, where a lowering of sea level did not occur until the late Toarcian.The Jurassic succession on Anholt spans the Fjerritslev and Haldager Sand formations; biostratigraphical data indicate that the Lower-Middle Jurassic boundary is here located within the uppermost part of the Fjerritslev Formation. The Fjerritslev and Haldager Sand formational transition was previously considered to coincide with the Lower-Middle Jurassic boundary.

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New ammonite faunas are described from sections along Bighorn and Scalp creeks in central-western Alberta where Lower Jurassic parts of the Fernie Formation are exposed. The first record of the upper Sinemurian Obtusum Zone from the Fernie is based on the occurrence of Asteroceras cf. stellare and Epophioceras cf. breoni in the basal pebbly coquina on Bighorn Creek. The overlying Red Deer Member has yielded Amaltheus cf. stokesi, representing the upper Pliensbachian Margaritatus Zone; in immediately superjacent strata the first North American examples of ?Amauroceras occur together with Protogrammoceras and ?Aveyroniceras. In the basal parts of the overlying Poker Chip Shale a fauna including Harpoceras cf. falciferum, Harpoceratoides, Polyplectus cf. subplanatus, Hildaites cf. serpentiniformis, and Dactylioceras cf. athleticum is correlated with the lower Toarcian Falciferum Zone.The upper parts of the Poker Chip Shale on Fording River in southeastern British Columbia contain a fauna representing some part of the upper Toarcian, but owing to poor preservation, generic identifications are only tentatively made.

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Flat clams represent a loosely defined group of thin-shelled, flat-valved bivalves. Their distribution and high concentration in some, especially Mesozoic, rocks have attracted interest, and several contrasting paleoecologic interpretations have been proposed to explain their occurrence. We present a comprehensive study of Posidonotis semiplicata (Hyatt), an Early Jurassic flat clam common in western North and South America. Posidonotis symmetrica (Hyatt), Posidonotis balteata (Crickmay), and Posidonotis cancellata (Leanza) are interpreted as subjective junior synonyms. In North America, P. semiplicata occurs in the upper Sinemurian to lower Toarcian of several Cordilleran allochthonous terranes. The South American record is restricted to upper Pliensbachian to lower Toarcian occurrences, suggesting that the species originated in the northeast Pacific in late Sinemurian time and spread to the southeast Pacific by the late Pliensbachian. The closely related Posidonotis dainellii (Losacco), sporadically known from the Tethys, is likely derived from P. semiplicata via migration through the Hispanic Corridor and subsequent geographic isolation. The functional morphology of P. semiplicata suggests an early ontogenic byssal attachment followed by a reclining mode of life with adaptation to soft substrates. The species is commonly found forming shell pavements in dark mudrocks with no, or very few, other benthic organisms. It provides an example of an epibenthic bivalve that favoured low-energy, dysaerobic environments, a niche preferentially exploited by flat clams.

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Extensive construction work at the canal cutting of the Ludwigskanal near Dörlbach, Franconian Alb, provided the opportunity to re-investigate a scientific-historical and biostratigraphically important reference section of the South-German Toarcian. The 16 m thick section, described bed by bed with respect to lithology and macrofossils, starts within the Upper Pliensbachian Amaltheenton Formation, covers the Toarcian Posidonienschiefer and Jurensismergel Formation, and ends in basal parts of the Opalinuston Formation. Carbonate contents are high in the Posidonienschiefer and successively decline within the Jurensismergel to basal parts of the Opalinuston. The high carbonate contents in the Posidonienschiefer are associated with comparatively low organic carbon contents. However, organic carbon contents normalized to the silicate fraction are similarily high if compared to other regions in Germany. Only the persistence of high organic carbon levels into middle parts of the Upper Toarcian differs from those of most regions in central Europe. Ammonite biostratigraphy indicates a thickness of >9 m for the Upper Pliensbachian, 1.15–1.20 m for the Lower Toarcian, 5.04 m for the Upper Toarcian, and >0.5 m for the Lower Aalenian. Despite the low sediment thickness, all Toarcian ammonite zones and almost all subzones are present, except for major parts of the Tenuicostatum Zone and the Fallaciosum Subzone. On the basis of discontinuities, condensed beds, and correlations with neighbouring sections in Southern Germany, a sequence stratigraphic interpretation is proposed for the Toarcian of this region: (i) The Posidonienschiefer Formation corresponds to one 3rd order T-R sequence, from the top of the Hawskerense Subzone to a fucoid bed at the top of the Variabilis Subzone, with a maximum flooding surface at the top of the Falciferum Zone. (ii) The Jurensismergel Formation exhibits two 3rd order T-R sequences: The first ranges from the basis of the Illustris Subzone (i.e., the Intra-Variabilis-Discontinuity) to the top of the Thouarsense Zone, with a maximum flooding surface within the Thouarsense Zone. The “belemnite battlefield” reflects a transgressive “ravinement surface” within the first Jurensismergel Sequence, not a maximum regression surface at its basis. The second sequence extents from the erosive basis of the Dispansum Zone to the top of the Aalensis Subzone, with a maximum flooding surface at the Pseudoradiosa-Aalensis Zone boundary. Finally, the Opalinuston starts with a new sequence at the basis of the Torulosum Subzone. Transgressive system tracts of these 3rd order T-R sequences are commonly phosphoritic, while some regressive system tracts show pyrite preservation of ammonites. The maximum regression surfaces at the basis of the Toarcian and within the Variabilis Zone reflect a significant submarine erosion and relief formation by seawater currents, while this effect is less pronounced at the basis of the Dispansum Zone and basis of the Torulosum Subzone (i.e., the boundary Jurensismergel-Opalinuston Formation).

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AbstractA gastropod fauna has been studied from upper Pliensbachian – upper Toarcian deposits of two sections of the Causses Basin (southern France) in order to investigate the mode of recovery after the early Toarcian anoxic event. The fauna consists of 15 species, one of which is new (Bathrotomaria kronzwilmesorumsp. nov.). Their stratigraphical distribution shows two peaks of diversity – in the Bifrons Zone (Bifrons Subzone) and in the Aalensis Zone (Mactra Subzone) – which reflect brief times during which the oxygen content and bottom consistency favoured the settlement of a relatively diversified fauna. In the Variabilis–Pseudoradiosa zones, gastropods are only represented by two species. This probably indicates more severe and unstable environmental conditions, only allowing the survival of gastropod taxa with wide adaptive capacities. The very low species diversity and the discontinuous and slow faunal recovery were probably determined by physiographic factors. The Causses area was a small basin confined by exposed lands and open towards the central part of western Tethys. Gastropods described here occur exclusively in the Toarcian – early Aalenian communities of the European epicontinental seas, whereas species from the central region of western Tethys are absent. Geographic isolation and marginal location of the Causses Basin restricted faunal exchange with the western European epicontinental seas, preventing fast recovery after the anoxic event. Gastropods of the central region of the western Tethys were probably unable to settle and colonize that area due to the strongly different environment.

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AbstractThe Toarcian Oceanic Anoxic Event (T-OAE, c. 182 Ma) represents a major perturbation of the carbon cycle marked by widespread black shale deposition. Consequently, the onset of the T-OAE has been linked to the combined effects of global warming, high productivity, basin restriction and salinity stratification. However, the processes that led to termination of the event remain elusive. Here, we present palynological data from Arctic Siberia (Russia), the Viking Corridor (offshore Norway) and the Yorkshire Coast (UK), all spanning the upper Pliensbachian – upper Toarcian stages. Rather than a ‘dinoflagellate cyst black-out’, as recorded in T-OAE strata of NW Europe, both the Arctic and Viking Corridor records show high abundance and dinoflagellate diversity throughout the T-OAE interval as calibrated by C-isotope records. Significantly, in the Arctic Sea and Viking Corridor, numerous species of the Parvocysta and Phallocysta suites make their first appearance in the lower Toarcian Falciferum Zone much earlier than in Europe, where these key dinoflagellate species appeared suddenly during the Bifrons Zone. Our results indicate migrations of Arctic dinoflagellate species, driven by relative sea-level rise in the Viking Corridor and the establishment of a S-directed circulation from the Arctic Sea into the Tethys Ocean. The results support oceanographic models, but are at odds with some interpretations based on geochemical proxies. The migration of Arctic dinoflagellate species coincides with the end of the T-OAE and marks the arrival of oxygenated, low-salinity Arctic waters, triggering a regime change from persistent euxinia to more dynamic oxygen conditions.

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New U–Pb zircon ages are reported from western Stikinia. Devonian and Pennsylvanian ages of volcanic rocks at Oweegee dome confirm the presence of pre-Permian strata, and with Paleozoic and Triassic detrital zircons from Lower Jurassic sandstone, they help to demonstrate pre-Lower Jurassic deformation and uplift. The absence of pre-Paleozoic inherited zircon from all samples is consistent with Nd–Sr isotopic data which suggest that Stikinia consists mainly of juvenile crust. U–Pb ages for posttectonic intrusions suggest that structures in Skeena Fold Belt in the Kinskuch area formed prior to Eocene time. Five ages for felsic volcanic rocks from stratigraphically well-constrained upper parts of the Hazelton arc are approximately 196–199 Ma and suggest near-contemporaneity for cessation of volcanism in the areas studied. The Sinemurian or late Sinemurian – early Pliensbachian ages are older than previously reported U–Pb and biostratigraphic ages for presumed correlative rocks to the west, and westward-migrating volcanism is implied. Together with Toarcian fossils from overlying sandstone, the new ages suggest that a hiatus of moderate duration preceded regionally extensive sedimentation.

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This study of Upper Pliensbachian – Bajocian/Bathonian deposits in a borehole drilled on the island of Anholt, Denmark incorporates sedimentology, biostratigraphy (palynomorphs and foraminifera), palaeomagnetism and coal petrology. The studied succession records a gradual change from marine inner shelf storm-influenced clays to mainly terrestrial sands, clays, and lignite containing a flora of mainly freshwater algae and pollen. The regression was initiated at the Pliensbachian–Toarcian boundary and marine influence ceased during Bajocian–Bathonian times; the regression thus took place earlier at Anholt than in the centre of the Danish Basin. The sediments in the Anholt borehole are referred to the Fjerritslev and Haldager Sand Formations. Although the Lower–Middle Jurassic boundary is commonly placed at the boundary between the two formations, our data indicate that at Anholt the upper Fjerritslev Formation (member F-IV) is of Aalenian age. The Lower–Middle Jurassic boundary occurs close to the boundary between members F-III and F-IV of the Fjerritslev Formation. In contrast to other Lower–Middle Jurassic successions in the North Sea region, smectites of inferred volcanic origin are preserved in the Anholt section, suggesting limited burial and hence less intense diagenetic illitisation or chloritisation of smectites. A down-hole increase in diagenetic influence is reflected by the increase down-section both in the thermal stability of kaolinite and in the vitrinite reflectance. Kaolinite of inferred authigenic origin forms a white powder in the quartz-dominated sands of the Haldager Sand Formation; this kaolinite is thermally very unstable and is interpreted to be of late diagenetic, post-uplift origin. The vitrinite reflectance data indicate that the Jurassic formations have been exposed to thermal maturation corresponding to burial to a depth of 1000–1200 m below their present depth. Post-maturation uplift of the order of 1 km probably occurred partly during Late Cretaceous – Paleocene inversion in the Kattegat area and partly during Oligocene–Recent regional uplift, the latter being the most important of the two uplift phases. Palaeomagnetic data indicate that the main carrier of magnetic remanence is fine-grained magnetite. The stable remanence shows a pronounced inclination shallowing, which is attributed to post-depositional compaction.

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The plicatulid bivalve Harpax spinosus is a common element of Pliensbachian to Lower Toarcian benthic community relicts occurring preferredly in fine- grained siliciclastic and mixed carbonate-siliciclastic sediments. There is general agreement that the bivalve was a secondary soft substrate dweller, being cemented with its flat to slightly concave right valve to small shells and bioclasts during early stages of growth and turning into a free recliner during later growth stages. Disagreement exists with respect to the life orientation of the bivalve, whether as free recliner it rested with its convex left valve or with its slightly concave right valve on the substrate. The former growth position would have required the bivalve to flip over when turning into a free recliner. Moreover, most authors assume that the bivalve discarded its host substrate during its reclining stage. The analysis of approximately 1500 specimens from the Upper Pliensbachian Amaltheenton Formation of southern Germany and time-equivalent horizons of southern France and Portugal shows that the bivalve remained cemented to the host substrate throughout its life time, even when the latter no longer supported the shell. The bivalve most likely rested with its concave valve on the soft substrate. The radially protruding spines served to keep the commissure above the sediment-water interface, to stabilize the shell and to prevent the shell from sinking into the sediment (snow-shoe strategy). Differences in the size of individuals at the localities investigated are thought to reflect differences in the degree of environmental stress, most likely caused by fluctuations in the oxygen content of the bottom water masses or by increasing soupiness of the substrate.

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The microfloras of the marine Neill Klinter, Vardekl0ft, and lower Hareelv Formations have been in­vestigated from exposures in the Vardekl0ft ravine at Hurry Inlet, eastern Jameson Land. The samples have yielded abundant spores and pollen as well as dinoflagellate cysts. Based on the occurrence of spores and pollen four microfloral assemblages (A-D) have been established. Biostratigraphic correlations based on the dinoflagellate occurrences as well, have been proposed by comparison with microfloras of Europe. Assemblage A and B of the Neill Klinter Formation have been correlated to (Late) Pliensbachian to Early Toarcian. The typical assemblage C microfloras are restricted to the Vardekl0ft Formation and is correlated to the Middle-Late Bajocian at the base of the formation and to the (Early) Callovian at the top. The assemblage D has been recovered from the lower Hareelv Formation. Based on the dinoflagel­late cysts the deepest samples available from this formation may be correlated to the Oxfordian corda­tum(-plicatilis) Zone while the upper part of the section in Vardekl0ft is referred to the Early Kimmerid­gian. The composition of the microfloras indicates marine to brackish palaeoenvironments with considerable variations in the terrestrial derived palynomorph groups. Comparison with age equivalent microfloras of Svalbard and And0ya, Northern Norway, and the Middle Europe indicates the stratigraphical distribution of some spores to be palaeolatitudinally control­led.

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ABSTRACT This Note presents a formal update to the Middle East Geologic Time Scale 2008 (ME GTS) for the Late Triassic and Jurassic rock units of Saudi Arabia. It reviews their lithostratigraphic nomenclature, ranks and stage assignments, and proposes names for third-order chrono-sequences as compiled and/or interpreted from the published literature. The review starts with the Late Triassic (Late Norian – Rhaetian) Minjur Sandstone of the Buraydah Group, with the Triassic – Jurassic (TrJ) boundary positioned at its top. The Minjur Sandstone consists of two units, here ranked as members, which are interpreted as the Late Norian – ?Early Rhaetian Lower Minjur Sequence (Lower Minjur Member) and ?Late Norian – Rhaetian Upper Minjur Sequence (Upper Minjur Member). The Early Jurassic Unconformity - Hiatus (Hettangian, Sinemurian and Pliensbachian stages) separates the Minjur Sandstone from the Toarcian Marrat Formation of the Jurassic Shaqra’ Group. The Shaqra’ Group consists of seven formations, from base-up: (1) Marrat Formation consisting of the Lower, Middle and Upper units, here ranked as members. (2) Dhruma Formation consisting of eight units (D1–D5, Wadi ad Dawasir “delta”, D6 and D7). The Dhruma units have been named in the literature as Balum Member (D1 and lower part of D2 units), Dhibi Limestone Member (upper part of D2 unit), Uwaynid Member (D3), Barrah Member (D4), Mishraq Member (D5), ‘Atash and Hisyan members (D7); the D6 and Wadi ad Dawasir “delta” units are not formally named as members. (3) Tuwaiq Mountain Limestone consisting of the Baladiyah (T1 unit), Mysiyah (T2 unit) and Daddiyah (T3 unit) members. (4) Hanifa Formation consisting of the Hawtah and Ulayyah members. (5) Jubaila Limestone with J1 and J2 units. (6) Arab Formation consisting of D to A members. (7) Hith Anhydrite consisting of Main Hith Anhydrite Member and Manifa Reservoir/Member. The seven formations of the Jurassic Shaqra’ Group are interpreted as 11 third-order chrono-sequences: (1) Early Toarcian Marrat Sequence B (Lower and Middle Marrat members) and Mid- to ?Late Toarcian Marrat Sequence A (Upper Marrat Member), the latter containing Arabian Plate maximum flooding surface MFS J10. (2) Bajocian Lower Dhruma Sequence (Balum Member and Dhibi Limestone), formed by the Balum and Dhibi subsequences, the former containing MFS J20. (3) Late Bajocian – Mid-Bathonian Dhruma Sequence B (Uwaynid, Barrah, Mishraq members, and Wadi ad Dawasir “delta” unit), with the Mishraq containing MFS J30. (4) Late Bathonian – early Mid-Callovian Dhruma Sequence A (unit D6, ‘Atash and Hisyan members), with the Hisyan containing MFS J40. (5) Mid- to Late Callovian Tuwaiq Sequence (Tuwaiq Mountain Limestone) containing an undesignated MFS at the base the Daddiyah Member (T3 unit). (6) Early and Mid-Oxfordian Hawtah Sequence (Hawtah Member of Hanifa Formation) containing MFS J50. (7) Late Oxfordian – ?Early Kimmeridgian Ulayyah Sequence (Ulayyah Member of Hanifa Formation) containing MFS J60. (8) Kimmeridgian Jubaila Sequence (Jubaila Limestone) containing MFS J70. (9) Arab-D Sequence (Arab-D Member inclusive of the Arab-D Anhydrite) containing an undesignated MFS in the Arab-D carbonate. (10) ?Kimmeridgian – ?Tithonian Arab-C and B Sequence (Arab C and B members) containing fourth-order MFS J80 and J90 in the lower carbonates of the members; and (11) ?Kimmeridgian – Tithonian Arab-A - Main Hith Sequence (Arab-A Member and Main Hith Anhydrite below the Manifa Reservoir/Member) containing fourth-order MFS J100 in the Arab-A Member. The Tithonian Manifa Member (upper part of the Hith Anhydrite Formation) is interpreted as heralding a transgression (fourth-order MFS J110), which deposited the Late Jurassic – Early Cretaceous Sulaiy Formation of the Thamama Group. The Jurassic – Cretaceous (JK) boundary is placed in the Sulaiy Formation by stratigraphic position. Based on the Geologic Time Scale GTS 2004 and Arabian Orbital Stratigraphy (AROS), the ages in million years before present of the sequence boundaries and maximum flooding surfaces are estimated for these chrono-sequences.

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A complete updated and revised lithostratigraphic scheme for the Jurassic succession of the onshore and offshore Danish areas is presented together with an overview of the geological evolution. The lithostratigraphies of Bornholm, the Danish Basin and the Danish Central Graben are described in ascending order, and a number of new units are defined. On Bornholm, the Lower–Middle Jurassic coal-bearing clays and sands that overlie the Lower Pliensbachian Hasle Formation are referred to the new Sorthat Formation (Lower Jurassic) and the revised Bagå Formation (Middle Jurassic). In the southern Danish Central Graben, the Middle Jurassic succession formerly referred to the Lower Graben Sand Formation is now included in the revised Bryne Formation. The Lulu Formation is erected to include the uppermost part of the Middle Jurassic succession, previously referred to the Bryne Formation in the northern Danish Central Graben. The Upper Jurassic Heno Formation is subdivided into two new members, the Gert Member (lower) and the Ravn Member (upper). The organic-rich part of the upper Farsund Formation, the former informal ‘hot unit’, is established formally as the Bo Member. Dominantly shallow marine and paralic deposition in the Late Triassic was succeeded by widespread deposition of offshore marine clays in the Early Jurassic. On Bornholm, coastal and paralic sedimentation prevailed. During maximum transgression in the Early Toarcian, sedimentation of organic-rich offshore clays took place in the Danish area. This depositional phase was terminated by a regional erosional event in early Middle Jurassic time, caused by uplift of the central North Sea area, including the Ringkøbing–Fyn High. In the Sorgenfrei–Tornquist Zone to the east, where slow subsidence continued, marine sandy sediments were deposited in response to the uplift. Uplift of the central North Sea area was followed by fault-controlled subsidence accompanied by fluvial and floodplain deposition during Middle Jurassic time. On Bornholm, deposition of lacustrine muds, fluvial sands and peats dominated. The late Middle Jurassic saw a gradual shift to shallow marine deposition in the Danish Central Graben, the Danish Basin and Skåne, southern Sweden. During the Late Jurassic, open marine shelf conditions prevailed with deposition of clay-dominated sediments while shallow marine sands were deposited on platform areas. The Central Graben received sand by means of sediment gravity flows. The clay sediments in the Central Graben became increasingly rich in organic matter at the Jurassic–Cretaceous transition, whilst shallow marine coarse-grained deposits prograded basinwards in the Sorgenfrei– Tornquist Zone.

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A sequence stratigraphic framework is established for the Jurassic of the Danish Central Graben based primarily on petrophysical log data, core sedimentology and biostratigraphic data from about 50 wells. Regional seismic lines are used to assist in the correlation of some wells and in the construction of isochore maps. In the Lower Jurassic (Hettangian–Pliensbachian) succession, five sequences have been identified. The Middle Jurassic is subdivided into four sequences that together span the uppermost Aalenian/lowermost Bajocian to the Callovian. In the Upper Jurassic, better well coverage permits greater stratigraphic resolution, and 11 sequences are identified and mapped. On the basis of the sequence stratigraphic correlation and the construction of isochore maps for individual sequences, the Jurassic basin history of the Danish Central Graben can be subdivided into seven discrete phases: (1) Shallow marine and offshore sediments deposited in a prerift basin extending from the North Sea to the Fennoscandian Border Zone (Hettangian–Pliensbachian). (2) Uplift and erosion in association with a Toarcian–Aalenian North Sea doming event. A major hiatus represents this phase in the study area. (3) Terrestrial and marginal marine sedimentation during initial rifting (latest Aalenian/earliest Bajocian – Late Callovian). (4) Early Oxfordian – Early Kimmeridgian transgression during and after a rift pulse. The sedimentary environment changed from coastal plain and marginal marine to fully marine. (5) Regression associated with a cessation or slowing of subsidence during a structural rearrangement that took place in the Late Kimmeridgian during a break in the main rift climax. Shallow to marginal marine sandstones were deposited above an erosion surface of regional extent. (6) Deep-water mudstones deposited in a composite graben with high subsidence rates related to rift pulses (latest Late Kimmeridgian – middle Middle Volgian). (7) Deposition of organic-rich mudstones and turbidite sandstones during the late Middle Volgian – Early Ryazanian. The main basin shallowed, became more symmetrical and experienced a decreasing rate of subsidence, recording the onset of the post-rift stage. A relative sea-level curve is constructed for the Middle–Late Jurassic. It shows close similarity to published eustatic (global) and relative (North Atlantic area) sea-level curves in the latest Bathonian – late Early Kimmeridgian, but differs in the Late Kimmeridgian – Middle Volgian interval, probably due to the high rate of subsidence in the study area.

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The article summarizes the results of the study of paleontology and biostratigraphy of the Jurassic of the Piennine Zone of the Ukrainian Carpathians by domestic and foreign researchers. For the first time, a summary paleontological description of these sediments is presented, taking into account numerous published data on identified macro- and mictofossils. A correlation biozonal scale has been created, as well as complex biostratigraphic schemes for each Jurassic series of its region in accordance with the International Stratigraphic Scale (2020). Because the stratigraphic sequence was disturbed by disjunctive dislocations, these schemes were developed by analysis of fragmentary sections. At present, three series of the Jurassic are determined by ammonites, belemnites, pelecypods, brachiopods, the Lower and Upper series are also dated by dinocysts, the Upper also by foraminifera and tintinnids. The stages and standard zones of the modern international scale are determined by ammonites: Liasicus of the Gettangian; Bucklandi, Obtusum, Raricostatum of the Sinemurian; Jamesoni, Emaciatum of the Pliensbachian; Tenuicostatum, Serpentinum, Bifrons, Thouarcense of the Toarcien; Opalinum, Murchisonae, Bradfordensis, Concavum of the Aalenian; Propinquans, Humpriesianum, Parkinsoni of the Bajocian; Zigzag, Aurigerus, Subcontractus, Bremeri, Retrocostatum of the Bathonian; Athletа of the Callovian; Plicatilis і Bifurcates of the Oxfordian; Divisum, Acanticum і Cavouri of the Kimmeridgian. Continuous dinocyst zonation is traced in the Upper Jurassic – Fibrata Аcme (Upper Oxfordian), Parvula Acme, Moluccana і Borzai (Kimmerigian), Pulla, Tithonica, Malmica, Semiradiata (Lower Tithonian) and all standard tintinnide zones of Tithonian — Chitinoidella (підзони Dobeni і Boneti), Praetintinnopsella, Crassicollaria. The boundaries of the stages from the Gettangiean to the Oxfordian are not determined. The boundaries between the Lower and Upper Oxfordian as well as between the Kimmeridgian substages are determined by ammonites as well as the boundary between the Kimmeridgian and Tithonian is determined by dinocysts, and the boundary between the Jurassic and Cretaceous is determined by tintinnids (corresponds to the boundary between the zones Crassicollaria of Tithonian and Calpionella of Berriassian). Stratigraphic unconformities were revealed by the macro- and mictofossils: the regional erosion on the boundary between the Aalenian and Bajocian as well as in Early Callovian, and short gap on the boundary between the Lower and Upper Bajocian.

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The Late Palaeozoic – Mesozoic extensional basin complex of East Greenland contains a record of deposition during a period of Rhaetian – Early Bajocian thermal subsidence, the onset of rifting in the Late Bajocian, its growth during the Bathonian–Kimmeridgian, culmination of rifting in the Volgian – Early Ryazanian, and waning in the Late Ryazanian – Hauterivian. The area was centred over a palaeolatitude of about 45°N in the Rhaetian and drifted northwards to about 50°N in the Hauterivian. A major climate change from arid to humid subtropical conditions took place at the Norian–Rhaetian transition. Deposition was in addition governed by a long-term sea-level rise with highstands in the Toarcian–Aalenian, latest Callovian and Kimmeridgian, and lowstands in the latest Bajocian – earliest Bathonian, Middle Oxfordian and Volgian. The Rhaetian – Lower Bajocian succession is considered the upper part of a megasequence, termed J1, with its base in the upper Lower Triassic, whereas the Upper Bajocian – Hauterivian succession forms a complete, syn-rift megasequence, termed J2. The southern part of the basin complex in Jameson Land contains a relatively complete Rhaetian–Ryazanian succession and underwent only minor tilting during Middle Jurassic – earliest Cretaceous rifting. Rhaetian – Lower Jurassic deposits are absent north of Jameson Land and this region was fragmented into strongly tilted fault blocks during the protracted rift event. The syn-rift successions of the two areas accordingly show different long-term trends in sedimentary facies. In the southern area, the J2 syn-rift megasequence forms a symmetrical regressive–transgressive–regressive cycle, whereas the J2 megasequence in the northern area shows an asymmetrical, stepwise deepening trend. A total of eight tectonostratigraphic sequences are recognised in the Rhaetian–Hauterivian interval. They reflect major changes in basin configuration, drainage systems, sediment transport and distribution patterns, and in facies and depositional environments. The sequences are bounded by regional unconformities or flooding surfaces and have average durations in the order of 10 Ma. They are subdivided into conventional unconformity-bounded depositional sequences with durations ranging from tens of thousands of years, in the Milankovitch frequency band, up to several million years. Deposition was alluvial and lacustrine in the Rhaetian–Sinemurian, but almost exclusively marine during the Pliensbachian–Hauterivian time interval when a marine strait, up to 500 km wide and more than 2000 km long, developed between Greenland and Norway, connecting the Arctic Sea and the North Sea. Coal-bearing fluvial and paralic deposits occur, however, at the base of the onlapping Middle Jurassic succession in the central and northern part of the basin complex. The sedimentary development is similar to that in the Northern North Sea and on the Norwegian shelf, and East Greenland offers important onshore analogues for virtually all of the types of deeply buried Jurassic depositional systems of these areas and especially their hydrocarbon reservoirs.

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Abstract In the Peloritani Mountains an Alpine nappe stack, involving an Hercynian or older basem*nt, is present. Some nappes involve a Meso-Cenozoic sedimentary cover, which starts with Upper Triassic-Hettangian continental redbeds (Verrucano), followed by Sinemurian neritic limestones and, up to the Oligocene, by marly-calcareous pelagic strata. Locally, Upper Triassic evaporites have been recognised. In the Sant’Angelo di Brolo valley, a peculiar sedimentary succession characterised by about 80 m of graded sandstones overlies the Verrucano redbeds. It has been described by Duée [1969] who ascribed it to the Alì Unit. Later on, Thery et al. [1985] interpreted the sandstones as fluvial deposits, Norian-Rhetian in age on the basis of pollens, and correlated them with the Sardinian « Keuper ». The finding of some ammonites and few nannofloras in the siliciclastic succession allow us to reach quite different conclusions. One ammonite specimen, collected in the uppermost part, shows morphological affinities with Spinammatoceras (M) tenax (Vacek), reported from the Middle Aalenian L. murchisonae Zone. Within the calcareous nannofossils, the presence of Lotharingius umbriensis in the lower part of the succession indicates an age not older than late Pliensbachian. However, the upper part of the same succession is characterised by the occurrence of Hexalithus magharensis, Triscutum tiziense, Watznaueria contracta, whose FO is early Aalenian. The petrographic study evidences that sandstones have two compositional groupings : a quartzose (quartzarenite to sub-litharenite) petrofacies of the continental redbeds (Verrucano), and a quartzo-feldspathic (feldspathic quartz-arenite to sub-arkose) petrofacies of the marine sandstones. The redbeds represent deposition by low gradient rivers and are similar to the composition of the Torrente Duno Fm in the Longobucco Group of the Sila Unit sedimentary cover. Their sources include abundant reworked quartz, felsitic volcanic, and low-grade metamorphic terrains. The overlying Middle Liassic-Aalenian marine sandstones testify an abrupt change in composition, reflecting changing source terrains. Its composition, including oversized feldspar grains, suggests gneissic/plutonic source terrains, added to the quartzose and metamorphic sources of the underlying fluvial sandstone. Identical changing detrital modes is testified in the Liassic formations of the Longobucco Group. These sandstone detrital modes mark the evolving early Jurassic rifted-continental margin of the Neotethys ocean. The studied succession shows characteristics unknown elsewhere in the Peloritanian Units, such as the presence of Mesozoic siliciclastic sediments younger than the « Verrucano » redbeds and the lack of terrains in carbonate platform facies above them. It has been deposited in a basin close to emerged areas, in which a clastic supply persists at least until Aalenian. Therefore, the Jurassic palaeogeography of the Peloritanian domain was more articulated than previously thought: pelagic areas were close to continental regions which supplied with siliciclastic detritus narrow basins, confined in grabens or half-grabens between emerged lands and sea-mounts. In the whole Jurassic of the Calabria-Peloritani Arc, siliciclastic marine terrains are known only in the Sila Unit. Here, Middle Carixian-Lower Domerian marls and sandstones in slope facies and an arenaceous turbiditic succession – late Domerian-early Toarcian in age (Longobucco Group) - have been described [Teale et Young, 1987]. There are close similarities in lithologies, tectono-sedimentary evolution, age and petrographic characters between these two sequences. The studied succession cannot be ascribed either to the Mandanici Unit, or to the Alì Unit. In fact, these units are affected by Alpine metamorphism and their Alpine cover is characterised by Upper Triassic evaporites followed by Jurassic and Cretaceous pelagic limestones and radiolarites. Its original bedrock is probably represented by the phyllites and marbles of the Piraino Unit, recently identified in the same region. In conclusion, the Sant’Angelo di Brolo succession was deposited in a marine environment between Pliensbachian (or Sinemurian) and Aalenian. Thus, both the late Triassic age and the fluviatile environment proposed for these terrains must be abandoned, as well as their correlation with the Sardinian « Keuper ».

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ABSTRACT A Stratigraphic model is proposed for the Jurassic sequence in Interior Oman. The model is based on regional well-log correlations, outcrop analysis and integration of Biostratigraphy. Large-scale architectures are restored using a well-to-well correlation technique, after the well-log markers of the relevant surfaces of sequence stratigraphy are identified. This identification is achieved by comparing well-log signatures to lithological and sedimentological columns of nearby exposed sections. The subsurface dataset consists of 19 wells arranged in two east-west profiles, 341 km and 332 km long. The Jurassic sequence in Interior Oman shows a general easterly thinning wedge and includes two hiatuses with marked age-gaps. Three major depositional episodes are identified: (1) a Pliensbachian-Toarcian coastal encroachment in a southward direction, represented by the dominantly clastic deposition of the Lower Mafraq Formation upon the Permian carbonates; (2) a general late Bajocian marine flooding (hybrid facies of marginal-marine environments of the Upper Mafraq Formation), followed through the Bathonian-Callovian by the carbonate Dhruma-Tuwaiq System which evolved through time from a low-angle, hom*oclinal ramp dipping in a (north) westwards direction, to a purely aggradational, flat-topped platform (upper Dhruma and Tuwaiq Mountain formations); (3) a Kimmeridgian-Tithonian onlap in an eastwards direction of finegrained limestones (Jubaila-Rayda) upon the post-Tuwaiq unconformity. Depositional hiatuses in the early Liassic and at the Early-Middle Jurassic transition are likely to reflect major eustatic sea-level lowstands. In contrast, subsurface correlations of the MFSs through the Dhruma-Tuwaiq indicate that the post-Tuwaiq unconformity is a low-angle (0.001 degrees) angular unconformity associated with tilting and truncation of the underlying sequences. Oxfordian sequences were probably never deposited in Interior Oman because of a lack of accommodation space and prolonged subaerial exposure. It is here proposed that the Upper/Middle Jurassic angular unconformity in Interior Oman was planed-off by subaerial carbonate dissolution during a steady, tectonically-driven uplift of the whole eastern Arabian shelf edge. The proposed geological model has several implications for the petroleum systems of Interior Oman. The geometric model predicts the distribution of the sedimentary facies, including source rocks, clastic and carbonate reservoirs, and seal facies. The occurrence of isolated Upper Mafraq-producing reservoir sands (i.e. Sayh Rawl field) are believed to be restricted to central and eastern Interior Oman. There are two other reservoir/seal combinations, both related to the Upper/Middle Jurassic unconformity: (1) truncation traps of the Dhruma-Tuwaiq below the unconformity (i.e. Hadriya and Uwainat reservoirs); (2) updip pinch-out trap of the Hanifa above the unconformity. Finally, it is believed that the early Late Jurassic general uplift and truncation of eastern Oman may have caused local remobilisation, updip migration, and loss to the surface of oil in reservoirs, initially generated from the prolific Al Huqf source rocks of Late Precambrian-Early Cambrian age.

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The extinction and recovery of Ostracoda at the Pliensbachian–Toarcian (P–T) boundary are analyzed based on a database of taxonomically revised Pliensbachian to Toarcian transition ostracod assemblages. In contrast to earlier assertions, the results of this study indicate that ostracod extinction rates were significant in comparison with other marine invertebrates. An extinction rate of 54% has been calculated for upper Pliensbachian ostracod species occurring in more than one section. Diversification took place in the latest Pliensbachian (Spinatum Zone) and early Toarcian (Tenuicostatum Zone), whereas diversity decrease occurred in the middle early Toarcian (Strangewaysi Subzone, Serpentinus Zone). This notable diversity decline in the early Toarcian corresponds to a global mass extinction time, whose peak has been documented in the Tenuicostatum Zone. Meanwhile, the ostracod mass extinction occurred within the Serpentinus Zone and was followed by radiation and recovery in the succeeding Bifrons Zone. Similar diversity changes of ostracods are observed in other European areas, although in the Cordillera Ibérica, the demise began later. Many aspects of this event are still debated, and there is no common cause or single set of climatic or environmental changes common to this event. The supposed extinction-causing environmental changes resulting from anoxia episodes are unclear and are unlikely to have been of sufficient intensity or geographic extent to cause this global extinction. In this paper, the decrease in marine species diversity is explained by a new palaeoceanographic scenario, in which a rapid global cooling episode is regarded as the ultimate cause.

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Abstract. One of the main controversial themes in palaeoclimatology involves elucidating whether climate during the Jurassic was warmer than the present day and if it was the same over Pangaea, with no major latitudinal gradients. There has been an abundance of evidence of oscillations in seawater temperature throughout the Jurassic. The Pliensbachian (Early Jurassic) constitutes a distinctive time interval for which several seawater temperature oscillations, including an exceptional cooling event, have been documented. To constrain the timing and magnitude of these climate changes, the Rodiles section of the Asturian Basin (Northern Spain), a well exposed succession of the uppermost Sinemurian, Pliensbachian and Lower Toarcian deposits, has been studied. A total of 562 beds were measured and sampled for ammonites, for biochronostratigraphical purposes, and for belemnites, to determine the palaeoclimatic evolution through stable isotope studies. Comparison of the recorded latest Sinemurian, Pliensbachian and Early Toarcian changes in seawater palaeotemperature with other European sections allows characterization of several climatic changes that are likely of a global extent. A warming interval partly coinciding with a δ13Cbel negative excursion was recorded at the Late Sinemurian. After a “normal” temperature interval, with temperatures close to average values of the Late Sinemurian–Early Toarcian period, a new warming interval containing a short-lived positive δ13Cbel peak, developed during the Early–Late Pliensbachian transition. The Late Pliensbachian represents an outstanding cooling interval containing a δ13Cbel positive excursion interrupted by a small negative δ13Cbel peak. Finally, the Early Toarcian represented an exceptional warming period, which has been pointed out as being responsible for the prominent Early Toarcian mass extinction.

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Belemnites collected in the 1920s from the Lower Jurassic Neill Klinter Formation of East Greenland are described for the first time. Two belemnite faunas are recognised. The Rrevekl0ft Member yielded Nannobelus, Pseudohastites, Passaloteuthis?, Gastrobelus? and a hastitid, giving an age of the Lower Pliensbachian Uptonia jamesoni to Prodacty/ioceras davoei zones for the molluscan-rich lower fauna! division. The Ostreaelv Member yielded Parapassaloteuthis, Acrocoelites (Toarcibelus), A. (Odontobe­/us), Simpsonibelus and "Parabrachybeus" representative of a Toarcian Hildoceras bifrons to Haugia variabilis Zone age as previously determined. However, the presence of Parapassaloteuthis gives a oldest age of at least Dactylioceras commune Subzone, with a loose specimen of a possible juvenile Acrocoe/ites trisulcu!osus suggesting that the Ostreaelv Member may range into the Harpoceras falciferum Zone. The Pliensbachian species are identical to those from western Europe and are the most northerly repre­sentatives of their taxa. The Toarcian species have closest affinity to those of northwest Europe rather than the distinct and endemic Siberian Toarcian belemnite fauna which arose at this time.

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Global perturbations to the Early Jurassic environment (∼201 to ∼174 Ma), notably during the Triassic–Jurassic transition and Toarcian Oceanic Anoxic Event, are well studied and largely associated with volcanogenic greenhouse gas emissions released by large igneous provinces. The long-term secular evolution, timing, and pacing of changes in the Early Jurassic carbon cycle that provide context for these events are thus far poorly understood due to a lack of continuous high-resolution δ13C data. Here we present a δ13CTOC record for the uppermost Rhaetian (Triassic) to Pliensbachian (Lower Jurassic), derived from a calcareous mudstone succession of the exceptionally expanded Llanbedr (Mochras Farm) borehole, Cardigan Bay Basin, Wales, United Kingdom. Combined with existing δ13CTOC data from the Toarcian, the compilation covers the entire Lower Jurassic. The dataset reproduces large-amplitude δ13CTOC excursions (>3‰) recognized elsewhere, at the Sinemurian–Pliensbachian transition and in the lower Toarcian serpentinum zone, as well as several previously identified medium-amplitude (∼0.5 to 2‰) shifts in the Hettangian to Pliensbachian interval. In addition, multiple hitherto undiscovered isotope shifts of comparable amplitude and stratigraphic extent are recorded, demonstrating that those similar features described earlier from stratigraphically more limited sections are nonunique in a long-term context. These shifts are identified as long-eccentricity (∼405-ky) orbital cycles. Orbital tuning of the δ13CTOC record provides the basis for an astrochronological duration estimate for the Pliensbachian and Sinemurian, giving implications for the duration of the Hettangian Stage. Overall the chemostratigraphy illustrates particular sensitivity of the marine carbon cycle to long-eccentricity orbital forcing.

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Abstract From the upper Pliensbachian–Toarcian interval of the Neotethys, this is the first record of isolated foraminiferal assemblages obtained from the Ammonitico Rosso limestone successions. The studied sections of Bakonycsernye (Hungary) had been dated by ammonites. The foraminiferal fauna extracted by glacial acetic acid yielded 86 benthic foraminiferal taxa. Most specimens belonged to the suborders Spirillinina and Lagenina followed by the Ammodiscina. The representatives of suborders Astrorhizina, Komokioidea, Verneuilinina, Robertinina, and Rotaliina were subordinated; miliolids were absent. Paralingulina csernyensis n. sp. was described from the upper Pliensbachian. The majority of species have wide stratigraphic ranges, however the previously known distributions of seven species changed based on their appearances in these sections. Nevertheless, the stratigraphic distributions of the foraminiferal species enabled accurate dating to stage-level. Based on the comparison of the taxonomic composition with other coeval foraminiferal faunas of the Neotethys, foraminiferal biozones and bioevents are discussed in this paper.

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Abstract. The Upper Pliensbachian–Toarcian (Jurassic) sedimentological, palaeontological and geochemical (belemnite 87Sr/86Sr, δ13C and δ18O) record is examined in two Eastern Tethyan (Bulgarian) locations. This interval contains the well-known Early Toarcian ocean anoxic event (T-OAE) and its manifestation and temporal context is examined in Bulgaria. Many of the features characteristic for the SW European sections were identified: collapse of carbonate platform productivity at the Pliensbachian/Toarcian boundary, the T-OAE (a short pulse of anoxic deposition in the Falciferum ammonite Zone), an Early Toarcian rapid warming event seen in the belemnite δ18O record that peaked around the Falciferum/Bifrons ammonite zonal boundary. The long-recognized positive δ13C excursion in the late Falciferum ammonite Zone is also seen but a precursor, sharp δ13C negative excursion seen around the Tenuicostatum/Falciferum ammonite zonal boundary in many organic carbon records is not evident in the belemnite data, a curious absence noted from other belemnite records. Subsequent fluctuations of the 87Sr/86Sr, δ13C and δ18O suggest there may be a further perturbation of the global isotopic systems. On the other hand, belemnite Sr isotope values from Bulgaria are in accord with those seen in Western Europe and hence its value for chronostratigraphy.

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Abstract. Pliensbachian and Toarcian ostracods are described from an interbedded marlstone/carbonate-mud •sequence in South-West England. Sediments of this age in other parts of Britain rarely offer a lithology favourable to the examination of calcareous microfossils. The fauna possesses similarities with other European sequences, particularly to the south. The presence of one species, Ektyphocythere dharennsourensis Boutakiout, Donze & Oulmalch, 1982 suggests possible links with North-West Africa at this time.

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Abstract. Five crises affecting ammonite evolution occurred during the Late Pliensbachian to Late Toarcian stages (Early Jurassic). The first two (Gibbosus and end-Spinatum zones) occurred during highly cold and regressive conditions which were followed by a global anoxic event generated during a supergreenhouse warm event (Levisoni subzone) concomitant with a worldwide transgressive event. The last two (Late Variabilis and Late Insigne zones) are related to regressive events. We present new carbon isotope data from Southern Peru that demonstrate that most of the major Toarcian crises affecting ammonite evolution can be correlated with the variations affecting the δ13C during that unstable period. The morphogenetic reactions of the ammonites during the five different upper Liassic critical episodes are analysed, showing how this group can be used as stress indicators.

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The Jurassic succession of the island of Bornholm in the Baltic Sea includes the Hettangian – lowermost Pliensbachian Rønne Formation, the Lower Pliensbachian Hasle Formation, the Upper Pliensbachian – (?)Lower Aalenian Sorthat Formation and the (?)Upper Aalenian – Bathonian Bagå Formation. Ammonites are only known from the Hasle Formation, and all available ammonite specimens from this formation are described and figured. Material reported by previous authors has been re-examined, together with previously undescribed specimens. Nine genera and eleven species are recognised. The ammonites show that the rocks from which they were collected fall into the Lower Pliensbachian (Carixian) Substage. The lowermost subzone proved in the Hasle Formation is the basal Taylori Subzone of the Jamesoni Zone of the Northwest European Subboreal standard zonation, which marks a marine transgression over underlying marginal marine beds without ammonites belonging to the Rønne Formation. All subzones of the Jamesoni Zone are proved together with the Valdani Subzone of the Ibex Zone. The Upper Pliensbachian (Domerian) Substage, previously reported, is now thought to be unproved by ammonite evidence. The underlying and overlying Rønne and Sorthat Formations are dated by dinoflagellate cysts and terrestrial palynomorphs, and the ammonite occurrences provide important control points for palynostratigraphic dating of the succession.

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Calcareous nannofossils are used here for the first time in order to establish a precise biostratigraphic framework for the Kermanshah Radiolarite Formation, an outcropping in Western Iran. The new data presented here challenge the previous tentative age interpretations (Pliensbachian to early Toarcian) based upon radiolarians. Calcareous nannofossil assemblages and events unequivocally indicated that the pelagic limestones and marls are late Sinemurian in age (NJT 3b nannofossil subzone), and that these are thrusted over shales and cherts dated as uppermost Sinemurian (NJT 3b-c nannofossil subzone) and lowermost Pliensbachian (NJT 4 nannofossil zone). This result leads not only to reconsideration of the age of the radiolarite formations, which are widespread in the Zagros orogenic system, but also a better understanding of the stratigraphic relationships between the various lithological units known in the area. Besides these new stratigraphic inferences, the calcareous nannofossil assemblages of the uppermost Sinemurian–lowermost Pliensbachian successions revealed the common presence of new morphologies of the Mitrolithus genus, never described before. These findings allow for the description of three new species, M. montgolfieri, M. pseudonannoconus, and M. tethysiensis, and reveal the existence of homeomorphy between the spine structure of conical Lower Jurassic coccoliths and the widespread Cretaceous nannoconids.

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Abstract. Pliensbachian and Toarcian Ostracoda first described by Exton (Geological Paper, Carleton University, Ottawa, 79: 1–104 1979) from the Lusitanian Basin, west-central Portugal have been re-examined. As a result, a greater diversity in the Ostracoda (80 species) is now recognized. Two species are newly described (Eucytherura zambujalensis sp. nov., Ektyphocythere mediodepressa sp. nov.) from the marls and calcareous shales of the Maria Pares Hill section near the village of Zambujal. Poor preservation precludes a complete taxonomic review of the present material. Five ostracod zones are proposed; Gammacythere ubiquita–Ogmoconchella gruendeli Zone, Poly cope cerasia–Polycope cincinnata Zone, Liasina lanceolata–Ogmoconcha convexa Zone, Bairdiacypris rectangularis–Kinkelinella sermoisensis Zone, and Cytherella toarcensis-Kinkelinella costata Zone. Although the ostracod assemblages possess strong similarities to those described from Northwest Europe, some of the Zambujal assemblages are dominated by the genus Polycope. A marked faunal turnover, in association with the extinction of the Metacopina occurs in the lower Subzone of the tenuicostatum Zone of Lower Toarcian age. These faunal events are discussed in relation to changing environmental conditions.

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The Cheremkhovo formation (Pliensbachian) is the primary coal-bearing formation of the Irkutsk basin, Eastern Siberia. Still, few geochemical studies of the Jurassic sediments of the Irkutsk coal-bearing basin have been conducted, and there are no data on the geochemistry of the coal-bearing formation itself. This study presents geochemical data for 68 samples from the Cheremkhovo formation and the overlying Lower Prisayan formation. The age of the former has been estimated by U-Pb dating of zircon from a tonstein (altered volcanic ash) layer as Pliensbachian, whereas the age of the latter is estimated as Pliensbachian–Toarcian according to regional stratigraphy. Major oxide and trace element concentrations were obtained using X-ray fluorescence spectrometry. Geochemical indicators showed diversity between the two studied formations. The indicators used show the change in climate conditions, from warm and humid in the Cheremkhovo formation, to hot and arid during the deposition of the lower Prisayan formation. The provenance of the Irkutsk coal-bearing basin was mainly influenced by the source composition, not recycling, and sediments were mainly derived from felsic to intermediate igneous rocks with a mixture of other rock types.

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Abstract. The integrated use of calcareous nannofossil and dinoflagellate cyst events in a study of the late Pliensbachian–early Toarcian interval in central Italy has yielded a high resolution biostratigraphy. The use of both the first and last occurrences of selected taxa belonging to the two phytoplankton groups allows the dating of the sediments with a very refined detail, even when lithologies are unfavourable to the preservation of one fossil group. The evolutionary history of calcareous nannofossils and dinoflagellate cysts during the early Jurassic and its links with global events are responsible for the high potential of this integrated biostratigraphy.

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Understanding of the evolutionary history of the ophiuroids, or brittle stars, is hampered by a patchy knowledge of the fossil record. Especially, the stem members of the living clades are poorly known, resulting in blurry concepts of the early clade evolution and imprecise estimates of divergence ages. Here, we describe new ophiuroid fossil from the Lower Jurassic of France, Luxembourg and Austria and introduce the new taxa Ophiogojira labadiei gen. et sp. nov. from lower Pliensbachian shallow sublittoral deposits, Ophiogojira andreui gen. et sp. nov. from lower Toarcian shallow sublittoral deposits and Ophioduplantiera noctiluca gen. et sp. nov. from late Sinemurian to lower Pliensbachian bathyal deposits. A Bayesian morphological phylogenetic analysis shows that Ophiogojira holds a basal position within the order Ophiurida, whereas Ophioduplantiera has a more crownward position within the ophiurid family Ophiuridae. The position of Ophioduplantiera in the evolutionary tree suggests that family-level divergences within the Ophiurida must have occurred before the late Sinemurian, and that ancient slope environments played an important role in fostering early clade evolution.

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Abstract. Oceanic anoxic events were time intervals in the Mesozoic characterized by widespread distribution of marine organic matter-rich sediments (black shales) and significant perturbations in the global carbon cycle. These perturbations are globally recorded in sediments as carbon isotope excursions irrespective of lithology and depositional environment. During the early Toarcian, black shales were deposited on the epi- and pericontinental shelves of Pangaea, and these sedimentary rocks are associated with a pronounced (ca. 7 ‰) negative (organic) carbon isotope excursion (CIE) which is thought to be the result of a major perturbation in the global carbon cycle. For this reason, the lower Toarcian is thought to represent an oceanic anoxic event (the T-OAE). If the T-OAE was indeed a global event, an isotopic expression of this event should be found beyond the epi- and pericontinental Pangaean localities. To address this issue, the carbon isotope composition of organic matter (δ13Corg of lower Toarcian organic matter-rich cherts from Japan, deposited in the open Panthalassa Ocean, was analysed. The results show the presence of a major (>6 ‰) negative excursion in δ13Corg that, based on radiolarian biostratigraphy, is a correlative of the lower Toarcian negative CIE known from Pangaean epi- and pericontinental strata. A smaller negative excursion in δ13Corg (ca. 2 ‰) is recognized lower in the studied succession. This excursion may, within the current biostratigraphic resolution, represent the excursion recorded in European epicontinental successions close to the Pliensbachian/Toarcian boundary. These results from the open ocean realm suggest, in conjunction with other previously published datasets, that these Early Jurassic carbon cycle perturbations affected the active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric).

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AbstractTwo fallen blocks of the Marlstone and stratigraphically overlying Junction Bed sampled on the beach below Doghouse Cliff in Dorset, UK (Wessex Basin) have been examined for carbon and oxygen isotopes of bulk carbonate as well as for strontium, carbon and oxygen isotopes and Mg:Ca ratios in the contained belemnites. The sequence, which contains most of the Toarcian zones and subzones within a metre or less of grey to yellow to pink, red and brown fossil-rich nodular limestone, is extremely condensed and lithologically similar to pelagic red limestones of the Tethyan Jurassic that are locally mineralized with Fe-Mn oxyhydroxides (e.g., Rosso Ammonitico). Strontium-isotope ratios of the contained belemnites are compatible with existing reference curves and both blocks show a rise to more radiogenic values post-dating the Pliensbachian–Toarcian boundary. The high degree of correlation between the relatively negative carbon and oxygen isotopes of the bulk carbonate is compatible with significant diagenetic overprint, and contrasts with higher carbon-isotope values in coeval condensed coccolith-rich limestones elsewhere. Evidence for the characteristic signature of the Toarcian Oceanic Anoxic Event, as represented by organic-rich sediment, is absent, possibly owing to a stratigraphic gap. Both blocks exhibit abrupt carbon-isotope shifts to lower values, one of which could represent the limbs of an incompletely recorded negative excursion associated with the Toarcian Oceanic Anoxic Event. That the Toarcian Oceanic Anoxic Event was also a significant hyperthermal is illustrated in both blocks by a drop in oxygen-isotope values and rise in Mg:Ca ratios of belemnites close to the base of the Junction Bed in the lowest part of the serpentinum zone.

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Feldman, Radulović, Hegab, and Radulović (2012) established the genus Cooperithyris for an upper Bathonian terebratulid brachiopod from Gebel Engabashi, northern Sinai, based on the type species C. circularis Feldman, Radulović, Hegab, and Radulović, 2012. Recently, Professor Fernando Alvarez, (Departamento de Geologia, Universidad de Oviedo, Oviedo, Spain) informed us of the existence of the hom*onym Cooperithyris Tchorszevsky, 1988, from the Pliensbachian–Toarcian of the Transcaucasus. In accordance with the International Code of Zoological Nomenclature (ICZN 1999, articles 53 and 60), we herein propose the replacement name, Sinaithyris, for the junior hom*onym. The new name is in reference to the Sinai Peninsula on which Gebel Engabashi is located and from which the specimens were collected.

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This is the second in a series of papers intended to establish a Lower Jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the North American succession. In North America the lower boundary of the Toarcian is drawn at the first appearance of Dactylioceras above the last occurrence of Amaltheus and Fanninoceras. The lower Toarcian is represented by the Kanense Zone; the middle Toarcian by the Planulata and Crassicosta zones; and the upper Toarcian by the Hillebrandti and Yakounensis zones. Section 5 on the Yakoun River in the Queen Charlotte Islands is designated the stratotype for the Planulata, Crassicosta, and Hillebrandti zones; section 3 on the Yakoun River is designated the stratotype for the Yakounensis Zone; an ideal stratotype for the Kanense Zone is not presently known. Reference sections further illustrating the faunal associations that characterize the zones are designated in eastern Oregon (Snowshoe Formation) and northern British Columbia (Spatsizi Group). The Dactylioceratidae, Harpoceratinae, and Hildoceratinae provide the most important zonal indicators for the lower Toarcian; Dactylioceratidae, Phymatoceratinae, and Bouleiceratinae for the middle Toarcian; and Phymatoceratinae, Grammoceratinae, and Hammatoceratinae for the upper Toarcian. Phymatoceras hillebrandti is described as a new species.

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This is the first in a series of papers intended to establish a Lower Jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the North American succession. Its development has been spurred by the need for high-resolution correlation between allochthonous terranes and the need for a standard to which microfossil sequences may be coupled.In North America the lower boundary of the Pliensbachian is drawn above the last echioceratids. The lower Pliensbachian is divided into, in ascending order, the Imlayi, Whiteavesi, and Freboldi zones; the upper Pliensbachian, into the Kunae and Carlottense zones. The Fannin Bay section in the Queen Charlotte Islands is designated the stratotype for the Whiteavesi, Freboldi, and Kunae zones; ideal stratotypes for the Imlayi and Carlottense zones are not presently known. Reference sections former illustrating the faunal associations that characterize all the zones are designated in western Nevada (the Sunrise Formation), northeastern Oregon (the Hurwal Formation), and northern British Columbia (the Spatsizi Group and Takwahoni Formation).The Polymorphitidae and Eoderoceratidae furnish the most important zonal indicators for the lower Pliensbachian; Oxynoticeratidae (Fanninoceras) and Hildoceratidae, for the upper Pliensbachian. Pseudoskirroceras imlayi and Acanthopleuroceras whiteavesi are described as new species. The presence of amaltheids in the northern parts of the allochthonous terranes permits a comparison with the northwest European succession at this level. Furthermore, the association in North America of typically east Pacific, Mediterranean, and northeast Asian species, as well as northwest European forms, emphasizes the critical importance of the North American Pliensbachian in achieving global correlations.

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A diversity and turnover analysis has been undertaken for a number of invertebrate groups in the Liassic of northwest Europe. There is a more or less steady rise in diversity from the early Hettangian through to the Pliensbachian, followed by a marked decline into the early Toarcian, after which it tends once more to increase. Ammonites stand out from the other invertebrates as having had an exceptionally high rate of turnover, with very short species durations.Increase of neritic habitat area due to rise of sea level, and recolonization following the end-Triassic mass extinction event appear to be the promoters of diversity increase or radiation. Severe reductions of neritic habitat area with associated environmental deterioration, related either to episodic marine regressions or spreads of anoxic bottom waters, and bound up respectively with sea-level fall and rise, are seen as the prime factors responsible for increase of extinction rate. While the environmentally sensitive ammonites were affected by even minor regressions, the other, more eurytopic groups were evidently more resistant to these. The only event that warrants the term mass extinction, affecting nearly all the benthos and nekton but not the plankton, correlates precisely with the early Toarcian anoxic event. Several episodes can be recognized of migrations of organisms into Europe following extinctions.

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A detailed study of the palynology and palynofacies of the Fjerritslev Formation (Lower Jurassic - basal Middle Jurassic) has resulted in the definition of four spore/pollen zones and four dinoflagellate cyst zones. The spore/pollen zones are the Corollina - Ricciisporites Zone (Late Rhaetian), the Cerebropollenites macroverrucosus Zone (Sinemurian - Pliensbachian), the Spheripollenites - Leptolepidites Zone (Toarcian), and the Perinopollenites elatoides Zone (Middle Jurassic). The dinoflagellate cyst zones are the Rhaetogonyaulax rhaetica Zone (Rhaetian), the Dapcodinium priscum Zone (latest Rhaetian - earliest Sinemurian), the Liasidium variabile Zone (Sinemurian), and the Nannoceratopsis gracilis Zone (Late Pliensbachian - ?Bajocian/Bathonian). These zones, and the Pinuspollenites - Trachysporites Zone Lund 1977 (Hettangian), are proposed for use in the Danish Subbasin. The combined spore/pollen and dinoflagellate cyst zonation has resulted in a detailed biostratigraphical subdivision of the sequences studied. A new combination, Manumia delcourtii (Poco*ck 1970) nov. comb. et emend., is proposed here, and the species description emended. New photographs of the holotypes of some of the species erected by Nilsson (1958) are included in the plates. The kerogen assemblages recorded from the Fjerritslev Formation, indicate a marine depositional environment, with a high but variable influence of terrestrially-derived organic particles. Stratigraphic variation in the kerogen assemblages generally correlate with the lithostratigraphical subdivision, and support previous environmental interpretations of the Fjerritslev Formation. Indications of strongly reducing conditions in the bottom waters were found in the Stenlille-2 borehole, in samples here referred to the Early Toarcian. The variations in the kerogen assemblages in the sequence investigated from the Gassum-1 borehole are not correlatable with the other boreholes, but seem primarily to reflect a distinct decrease in bioturbation in the Late Sinemurian. The Fjerritslev Formation does not generally represent a potential source rock for oil. Some levels (parts of the F-111 member) show, however, the characteristics of a fair to good source rock. The organic matter is generally immature or only at the earliest stage of maturity.