Stratigraphy of the Koobi Fora Formation (Pliocene and Pleistocene) in the Loiyangalani region of northern Kenya

Tuffaceous marker beds in the Loiyangalani region were previously identified as correlative with similar beds in the Shungura and Koobi Fora Formations of southwestern Ethiopia and northwestern Kenya. Associated sedimentary strata correlate with the Koobi Fora Formation, and include intercalated basalt flows. In the Loiyangalani region the Koobi Fora Formation has a composite thickness of at least 257 m, and records one time interval for which no strata are known in the Koobi Fora region. Four members of the Koobi Fora Formation (Lonyumun, Tulu Bor, Burgi, and KBS) are recognized in the region, and a composite member (Moiti–Lokochot) proposed because the Lokochot Tuff, the formal boundary between the Moiti and Lokochot Members has not been identified. This extends the known geographic area of the Koobi Fora Formation 100 km southward. These strata, together with others, were previously termed ‘Loiyangalani formation (or Formation)’. Deposition in the Loiyangalani region began at about the same time as in the Koobi Fora and Nachukui Formations. Newly named basalts are Kankam (3.2–3.3 Ma), Lenderit (2.02 to 2.18 ± 0.02 Ma), and Balo (1.79 ± 0.02 Ma). We also report K/Ar ages on basalts from Mt. Kulal (2.04 ± 0.02 to 2.40 ± 0.03 Ma) east of the region and from Serima Gorge (0.77 ± 0.01 Ma) south of the study area.     

The status and local stratigraphical context of the Hampen Formation type section (Bathonian,Middle Jurassic)

The type section of the Hampen Formation, as currently defined, is located near Salperton (Gloucestershire); it comprises beds of Middle Jurassic (Bathonian) age. Its validity as a type section is questioned; only the uppermost 2.3 m are herein considered truly to represent the Hampen Formation. The underlying 7.4 m are re-defined as a facies variant of the Througham Formation, for which the name Daglingworth Member is proposed. A review of the local stratigraphical context clarifies the relationship of the Hampen Formation, as newly defined, and of the Daglingworth Member, to contiguous stratigraphical units.     

Quechua II contraction in the Ayacucho intermontane basin: Evidence for rapid and episodic Neogene deformation in the Andes of central Perú

In the Ayacucho basin of central Perú the regional Quechua II contractional deformation is bracketed by ⁴⁰Ar/³⁹Ar isotopic age determinations to a maximum duration of about 300,000 years, and probably less than 150,000 years, centered on 8.7 Ma. The strongly deformed Huanta Formation beneath the Quechua II angular unconformity was deposited during a period of extension that began before 9.05 ± 0.05 Ma. Deposition of a thick succession of alluvial fan deposits interbedded with flows of basaltic andesite in the Tingrayoc Member continued up to about 8.76 ± 0.05 Ma with the later part of the sedimentary record reflected by lacustrine deposits of the Mayocc Member. The upper limit on contractional deformation is constrained by an age of 8.64 ± 0.05 Ma on a unit of tuff near the base of the Puchcas volcanics, which in places was deposited upon near-vertical beds of the Huanta Formation. The Ayacucho Formation was deposited, locally unconformably, upon the Puchcas volcanics beginning slightly before 7.65 ± 0.10 Ma.Extended periods of neutral to tensional stress interrupted by rapid well-developed pulses of contractional deformation demonstrate the episodic behavior of Andean orogeny in Perú. The very short duration for the Quechua II event implies that driving forces for episodic deformation may be related to coupling along the orogen boundaries and strain accumulation and release mechanisms in the continental crust instead of much longer-term variations in the configuration of converging plates.     

Changes in the depositional system of the Paleo-Kathmandu Lake caused by uplift of the Nepal Lesser Himalayas

Sedimentological and palynological studies on a series of slimes taken from a drill-well in the central part of the Kathmandu Basin and the Lukundol Formation at the southern margin of the basin indicate that the depositional environments of the Paleo-Kathmandu Lake changed at around 1 Ma. In the central part of the basin, the abrupt appearance of a fossiliferous 4 m thick sand bed, containing abundant fish teeth and gastropod opercula, and shell fragments, in an otherwise open-lacustrine mud sequence, suggests that a lowering of the water level occurred at about 1 Ma. The common occurrence of the green alga Pediastrum in the overlying mud beds implies that the lake remained shallow after the deposition of the sand bed. Changes in the depositional system of the Paleo-Kathmandu Lake at about 1 Ma are also recorded in the Lukundol Formation. Granitic gravel and detrital muscovite flakes, which are common in the Lower and Middle Members, disappear from the Upper Member. Paleocurrent directions in the Lower and Middle Members show flow from the north and east, whilst in the Upper Member they change to flow from the south. Sedimentary facies change from marginal lacustrine in the Middle Member, to a braided river facies in the Upper Member. These changes occurred at around 1 Ma, at the base of the Upper Member. They seem to have been caused by the initiation of rapid uplift of the Mahabharat Lekh, which was due to faulting and underthrusting along the Main Boundary Thrust System.     

Permo-Triassic volcanics of the Koltogory-Urengoi rift of the West Siberian geosyneclise

The lithologic composition of basalts from the most complex sections of the Koltogory-Urengoi Rift is considered, and their ⁴⁰Ar/³⁹Ar ages are given: basalts from the lower section of Nikol'skaya BH-1 (Bergamak Formation) — 272.9 ± 10.5 and 249.5 ± 3.0 Ma, basalts from the uppermost section (Voinov Formation) — 247.5 ± 2.9 Ma, and basalts from the lower section of Tyumenskaya SDB-6 (Korotchaevo Formation) — 251.2 ± 2.0 Ma. According to these and the paleomagnetic data, trap magmatism began in the Koltogory-Urengoi Rift in the Permian and ended in the Early Triassic, whereas the paleontological data suggest its beginning in the Early Triassic and its termination in the late Middle Triassic.In Tyumenskaya SDB-6 we have recognized both low-K tholeiitic and medium- to high-K subalkalic and calc-alkalic basalts, which form large alternating packets up to 480 m thick. This section is juxtaposed to the anomalous sections of the Siberian Platform trap formation near the margins of the Tunguska syneclise. The section of Nikol'skaya BH-1 is composed mainly of medium- and high-K subalkaline basalts with scarce flows of low-K ones. The low-K basalts differ from the medium- and high-K varieties in having lower contents of TiO₂, P₂O₅, Ba, Rb, Th, and ΣLREE.The Tyumenskaya SDB-6 basalts are characterized by paleohypergene alterations, up to the development of more than five levels of alumina-ferruginous cuirasses, as well as superposed chloritization, sericitization (hydromication), carbonatization, zeolitization, silicification, and epidotization, whereas the Nikol'skaya BH-1 basalts are subjected mainly to carbonatization, chloritization, and hydromication. We have concluded that the existence of a vast mega-arch above the superplume within the West Siberian geosyneclise in the Permo-Triassic was complicated by the Koltogory-Urengoi Rift. The Triassic rift deposits are both continental and marine sediments (sandstones and siltstones with glauconite, coccolith oozes, spherulitic lavas, and hyaloclastites). The basic volcanism within the rift showed the features of both rift and flood basalts as well as E-MORB.     

30 million years of Permian volcanism recorded in the Choiyoi igneous province (W Argentina) and their source for younger ash fall deposits in the Paraná Basin: SHRIMP U–Pb zircon geochronology evidence

We present four SHRIMP U–Pb zircon ages for the Choiyoi igneous province from the San Rafael Block, central–western Argentina. Dated samples come from the Yacimiento Los Reyunos Formation (281.4 ± 2.5 Ma) of the Cochicó Group (Lower Choiyoi section: andesitic breccias, dacitic to rhyolitic ignimbrites and continental conglomerates), Agua de los Burros Formation (264.8 ± 2.3 Ma and 264.5 ± 3.0 Ma) and Cerro Carrizalito Formation (251.9 ± 2.7 Ma Upper Choiyoi section: rhyolitic ignimbrites and pyroclastic flows) spanning the entire Permian succession of the Choiyoi igneous province. A single zircon from the El Imperial Formation, that is overlain unconformably by the Choiyoi succession, yielded an early Permian age (297.2 ± 5.3 Ma), while the main detrital zircon population indicated an Ordovician age (453.7 ± 8.1 Ma). The new data establishes a more precise Permian age (Artinskian–Lopingian) for the section studied spanning 30 Ma of volcanic activity. Volcanological observations for the Choiyoi succession support the occurrence of explosive eruptions of plinian to ultraplinian magnitudes, capable of injecting enormous volumes of tephra in the troposphere–stratosphere. The new SHRIMP ages indicate contemporaneity between the Choyoi succession and the upper part of the Paraná Basin late Paleozoic section, from the Irati up to the Rio do Rasto formations, encompassing about 24 Ma. Geochemical data show a general congruence in compositional and tectonic settings between the volcanics and Paraná Basin Permian ash fall derived layers of bentonites. Thickness and granulometry of ash fall layers broadly fit into the depletion curve versus distance from the remote source vent of ultraplinian eruptions. Thus, we consider that the Choiyoi igneous province was the source of ash fall deposits in the upper Permian section of the Paraná Basin. Data presented here allow a more consistent correlation between tectono-volcanic Permian events along the paleo-Pacific margin of southwestern Gondwana and the geological evolution of neighboring Paleozoic foreland basins in South America and Africa.     

Modelling the petroleum generation and migration of the third member of the Shahejie Formation (Es3) in the Banqiao Depression of Bohai Bay Basin,Eastern China

The mudstones in the third member of the Shahejie Formation (Es3) are the primary source rocks in the Banqiao Depression of Bohai Bay Basin. They are rich in organic matter with Total Organic Carbon (TOC) content up to 3.5%. The sandstones in the Es3 member are the deepest proven hydrocarbon reservoir rocks with measured porosity and permeability values ranging from 3.6% to 32.4% and from 0.01 md to 3283.7 md, respectively. One, two and three-dimensional basin modelling studies were performed to analyse the petroleum generation and migration history of the Es3 member in the Banqiao Depression based on the reconstruction of the burial, thermal and maturity history in order to evaluate the remaining potential of this petroleum province. The modelling results are calibrated with measured vitrinite reflectance (R_o), borehole temperatures and some drilling results of 63 wells in the study area. Calibration of the model with thermal maturity and borehole temperature data indicates that the present-day heat flow in the Banqiao Depression varies from 59.8 mW/m² to 61.7 mW/m² and the paleo-heat flow increased from 65 Ma to 50.4 Ma, reached a peak heat-flow values of approximately 75 mW/m² at 50.4 Ma and then decreased exponentially from 50.4 Ma to present-day. The source rocks of the Es3 member are presently in a stage of oil and condensate generation with maturity from 0.5% to 1.8% R_o and had maturity from 0.5% to 1.25% R_o at the end of the Dongying Formation (Ed) deposition (26 Ma). Oil generation (0.5% R_o) in the Es3 member began from about 37 Ma to 34 Ma and the peak hydrocarbon generation (1.0% R_o) occurred approximately from 30 Ma to 15 Ma. The modelled hydrocarbon expulsion evolution suggested that the timing of hydrocarbon expulsion from the Es3 member source rocks began from 31 Ma to 10 Ma with the peak hydrocarbon expulsion shortly after 26 Ma. Secondary petroleum migration pathways in the Es3 member of the Banqiao Depression are modelled based on the structure surfaces at 26 Ma and present-day, respectively. The migration history modelling results have accurately predicted the petroleum occurrences within the Es3 member of the Banqiao Depression based on the calibration with drilling results of 10 oil-producing wells, one well with oil shows and 52 dry holes. Six favorable zones of oil accumulations in the Es3 member of the Banqiao Depression are identified especially oil accumulation zones I and II due to their proximity to the generative kitchens, short oil migration distances and the presence of a powerful drive force.     

Stratigraphy and facies development of the marine Late Devonian near the Boulongour Reservoir,northwest Xinjiang,China

Late Devonian to Early Carboniferous stratigraphic units within the ‘Zhulumute’ Formation, Hongguleleng Formation (stratotype), ‘Hebukehe’ Formation and the Heishantou Formation near the Boulongour Reservoir in northwestern Xinjiang are fossil-rich. The Hongguleleng and ‘Hebukehe’ formations are biostratigraphically well constrained by microfossils from the latest Frasnian linguiformis to mid-Famennian trachytera conodont biozones. The Hongguleleng Formation (96.8 m) is characterized by bioclastic argillaceous limestones and marls (the dominant facies) intercalated with green spiculitic calcareous shales. It yields abundant and highly diverse faunas of bryozoans, brachiopods and crinoids with subordinate solitary rugose corals, ostracods, trilobites, conodonts and other fish teeth. The succeeding ‘Hebukehe’ Formation (95.7 m) consists of siltstones, mudstones, arenites and intervals of bioclastic limestone (e.g. ‘Blastoid Hill’) and cherts with radiolarians. A diverse ichnofauna, phacopid trilobites, echinoderms (crinoids and blastoids) together with brachiopods, ostracods, bryozoans and rare cephalopods have been collected from this interval. Analysis of geochemical data, microfacies and especially the distribution of marine organisms, which are not described in detail here, but used for facies analysis, indicate a deepening of the depositional environment at the Boulongour Reservoir section. Results presented here concern mainly the sedimentological and stratigraphical context of the investigated section. Additionally, one Late Devonian palaeo-oceanic and biotic event, the Upper Kellwasser Event is recognized near the section base.     

Paleomagnetism of the late Cryogenian Nantuo Formation and paleogeographic implications for the South China Block

A new paleomagnetic pole position is obtained from the well-dated (636.3 ± 4.9 Ma) Nantuo Formation in the Guzhang section, western Hunan Province, and the correlative Long’e section in eastern Guizhou Province, South China. Remagnetization of the recent geomagnetic field was identified and removed for both sections. The hard dual-polarity, interpreted as primary, component of the Nantuo Formation, directs east–westward with medium inclinations, yielding an average pole of 9.3°N, 165°E, A₉₅ = 4.3° that, for the first time, passed a strata-bound reversals test. The new data are consistent with previously published paleomagnetic data of the Nantuo Formation from Malong county, central Yunnan Province, which passed a positive syn-sedimentary fold test. Together, these sites represent shallow- to deep-water sections across a shelf-to-basin transect centered at ∼33° paleolatitude. The sedimentary basin may have faced an expansive ocean toward the paleo-East. In the ∼750 Ma and ∼635 Ma global reconstructions, the South China Block (SCB) was best fitted in the northern hemisphere close to northwestern Australia. However, a direct SCB-northwestern Australia connection, inferred to have existed during the Early Cambrian–Early Devonian, had not formed by the time of ∼635 Ma.     

Chronologic implications of new Miocene mammals from the Cura-Mallín and Trapa Trapa formations,Laguna del Laja area,south central Chile

Recent work in the central Andean Main Range of Chile near Laguna del Laja (∼37.5°S, 71°W) has produced the first mammal fossils for the region. Fossils, locally abundant and well preserved, occur patchily across a wide area southeast of the lake. Mammalian remains are derived from generally strongly folded (kilometer-scale) exposures of the locally ∼1.8 km thick, early to middle Miocene Cura-Mallín Formation; two identifiable specimens have been recovered from the overlying Trapa Trapa Formation as well. Both formations consist primarily of well-stratified (1–5 m thick layers) volcaniclastic and volcanic strata, deposited predominantly in fluviatile systems. The Cura-Mallín Formation is possibly the southern continuation of (or lateral equivalent to) the richly fossiliferous Abanico Formation mapped between ∼32°S and 36°S. Intensive sampling in a series of localities east and south of Laguna del Laja has yielded diverse faunas, in addition to radioisotopically dateable horizons. The new fossil mammal faunas represent as many as six South American Land Mammal “Ages” (SALMAs). Fossils, together with preliminary ⁴⁰Ar/³⁹Ar radioisotopic dates, ranging from ∼9 to 20 Ma across the exposed thickness of the Cura-Mallín Formation and into the overlying Trapa Trapa Formation, provide a robust geochronological framework for middle Cenozoic strata in the Laguna del Laja region. The sequence of directly superposed mammalian assemblages at Laguna del Laja is one of the longest in all of South America, rivaled only by the classic Gran Barranca section of Patagonian Argentina. These data illuminate the geological history of the area and its record of mammalian evolution. The potential to isotopically date these diverse faunas with high precision (error ± 0.5 Ma) presents a rare opportunity to calibrate related portions of the SALMA sequence.     

A Late-Eocene palynological record from the Hoh Xil Basin,northern Tibetan Plateau,and its implications for stratigraphic age,paleoclimate and paleoelevation

The Hoh Xil Basin, lying in the central Tibetan Plateau, is key to understanding the Cenozoic tectonics, paleoelevation and paleoclimate changes that have occurred in the Tibetan Plateau since the collision of the Indian and Asian tectonic plates. However, the stratigraphic age and paleoelevation indicated by the sediments of the Hoh Xil Basin remain hotly debated. Here we report on one palynological record from the TTH-C section, extracted from the Yaxicuo Group (the stratigraphic unit between the Fenghuoshan and Wudaoliang groups), and analyze its implications for stratigraphic age, paleoclimate and paleoelevation in the Hoh Xil Basin. The record shows that palynological taxa are mainly dominated by xerophytic Ephedripites, Nitrariadites (Nitrariapollis) and Chenopodipollis, with few ferns and conifers. Rich morphologies correspond well with those in the Xia Ganchaigou Formation (Fm) of the Qaidam Basin to the north. Palynological percentages are well correlated with the middle member of the Xia Ganchaigou Fm in the Qaidam Basin as well as the lower member of the Mahalagou Fm in the Xining Basin to the northeast. The ages of the middle member of the Xia Ganchaigou and lower member of the Mahalagou Fms from these two basins are both identical to the Bartonian Stage (~ 40–37 Ma) of the Late Eocene, according to their respective high-resolution magnetostratigraphic dating. This means that the age of the Yaxicuo Group at least covers the Bartonian Stage. Besides the Qaidam and Xining basins, the palynological assemblages of the TTH-C section are also similar to those of three other sites (the Jiuquan, Tu-ha and Hetao basins), indicating similarly arid climates dominated by a northwestern Chinese subtropical high, and a relatively low paleoelevation in the Hoh Xil Basin (mostly < 2000 m a.s.l.) in the Late Eocene.     

Precise dating of the Middle Permian: Zircon U–Pb geochronology from volcanic ash beds in the basal Gufeng Formation,Yangtze region,South China

Direct radiometric dating of the Lower/Middle Permian epochs has not been well accomplished. Shales and bedded cherts of the geologically well-documented Middle Permian Gufeng Formation are exposed in the Chaohu area, Anhui province, South China. Through detailed field examination and mapping of the Gufeng stratigraphic section, we found at least four volcanic ash beds within the basal shale strata. This new discovery indicates the existence of prominent volcanic activity during Gufeng sedimentation and provides the opportunity to precisely date the age of the Middle Permian. Zircon grains separated from two near-basal horizon yield LA‐ICP‐MS U–Pb ages of 272.0 ± 5.5 Ma (MSWD = 2.6) and 271.5 ± 3.3 Ma (MSWD = 1.7). As the first precise isotopic age (272 Ma) of the Middle Permian Gufeng Formation in South China, our data offer precise geochronological constraints for the division and correlation of Middle Permian not only in South China but also worldwide.     

Ion microprobe U–Pb dating and Sr isotope measurement of a protoconodont

This report describes in situ ion microprobe U–Pb dating of a protoconodont, an early Cambrian phosphate microfossil, using laterally high-resolution secondary ion mass spectrometry (NanoSIMS). On a single fragment of a fossil (approximately 850 μm × 250 μm) derived from a sedimentary layer in the Meishucunian Yuhucun Formation, Yunnan Province, southern China, 23 spots provide a ²³⁸U/²⁰⁶Pb isochron age of 547 ± 43 Ma (2σ, MSWD = 1.9), which is consistent with the depositional age, 536.5 ± 2.5 Ma estimated using zircon U–Pb dating of interbedded tuffs. However, five spots on a small region (approximately 250 μm × 100 μm) in the same protoconodont yield an isochron age of 417 ± 74 Ma (2σ, MSWD = 0.31), apparently younger than the formation age. The younger age might be attributable to a later hydrothermal event, perhaps associated with Caledonian orogenic activity recorded in younger zircon with an age of 420–440 Ma. We also measured ⁸⁷Sr/⁸⁶Sr ratios of the protoconodont by NanoSIMS. In the older domain, 19 spots give the ⁸⁷Sr/⁸⁶Sr ratio of 0.71032 ± 0.00023 (2σ), although seven spots on the younger region provide the ratio of 0.70862 ± 0.00045; this is significantly less radiogenic than the older domain. This is the first report of U–Pb age and Sr isotope heterogeneity within a single fragment of micro-fossil (215).     

Pliocene volcano-tectonics and paleogeography of the Turkana Basin,Kenya and Ethiopia

The distribution of hominin fossil sites in the Turkana Basin, Kenya is intimately linked to the history of the Omo River, which affected the paleogeography and ecology of the basin since the dawn of the Pliocene. We report new geological data concerning the outlet channel of the Omo River between earliest Pliocene and final closure of the Turkana Basin drainage system in the latest Pliocene to earliest Quaternary. Throughout most of the Pliocene the Omo River entered the Turkana Basin from its source in the highlands of Ethiopia and exited the eastern margin of the basin to discharge into the Lamu embayment along the coast of the Indian Ocean. During the earliest Pliocene the river’s outlet was located in the northern part of the basin, where a remnant outlet channel is preserved in basalts that pre-date eruption of the Gombe flood basalt between 4.05 and 3.95 Ma. The outlet channel was faulted down to the west prior to 4.05 Ma, forming a natural dam behind which Lake Lonyumun developed. Lake Lonyumun was drained between 3.95 and 3.9 Ma when a new outlet channel formed north of Loiyangalani in the southeastern margin of the Turkana Basin. That outlet was blocked by Lenderit Basalt lava flows between 2.2 and 2.0 Ma. Faulting that initiated either during or shortly after eruption of the Lenderit Basalt closed the depression that is occupied by modern Lake Turkana to sediment and water.Several large shield volcanoes formed east of the Turkana Basin beginning by 2.5–3.0 Ma, volcanism overlapping in time, but probably migrating eastward from Mount Kulal on the eastern edge of the basin to Mount Marsabit located at the eastern edge of the Chalbi Desert. The mass of the volcanic rocks loaded and depressed the lithosphere, enhancing subsidence in a shallow southeast trending depression that overlay the Cretaceous and Paleogene (?) Anza Rift. Subsidence in this flexural depression guided the course of the Omo River towards the Indian Ocean, and also localized accumulations of lava along the margins of the shield volcanoes. Lava flows at Mount Marsabit extended across the Omo River Valley after 1.8–2.0 Ma based on estimated ages of fossils in lacustrine and terrestrial deposits, and possibly by as early as 2.5 ± 0.3 Ma based on dating of a lava flow. During the enhanced precipitation in latest Pleistocene and earliest Holocene (11–9.5 ka) this flexural depression became the site of Lake Chalbi, which was separated from Lake Turkana by a tectonically controlled drainage divide.     

Magnetostratigraphy across the Triassic-Jurassic boundary in the main Karoo Basin

The end-Triassic mass extinction and the transition and explosive diversification of fauna over the Triassic-Jurassic boundary is poorly understood and poorly represented in the rock record of the Southern Hemisphere. This is despite the rich diversity in both body and trace fossils of Triassic-Jurassic age in southern Africa, which is not found in coeval Northern Hemisphere localities. We report here the first palaeomagnetic polarity zonation of the Upper Triassic-Lower Jurassic continental red bed succession (Elliot Formation; Stormberg Group) in southern Africa. The results from 10 partially overlapping sections, with a composite thickness of ~ 280 m, provide a magnetic polarity chronology of the main Karoo Basin in South Africa and Lesotho. Palaeomagnetic analyses reveal that heating samples to between 150 °C and ~ 300 °C removes the secondary, moderately inclined (~ 48°) normal-polarity component of remanent magnetization. This component overlaps with the present-day field and is comparable to the overprint direction expected from Lower Jurassic Karoo dolerite intrusions. In contrast, a likely primary, high unblocking temperature component, of dual polarity, consistently is of steeper inclination (~ 63°). This characteristic remanence passes the reversals test, except where means are based on small sample populations. There are only two resulting polarity zones for the ~ 200 m thick lower Elliot Formation (LEF) with potential for a thin 3rd magnetozone in the uppermost part. The upper Elliot Formation (UEF), in contrast, which was sampled over a thickness of ~ 80 m, has five polarity zones. The failure of the reversal test for the UEF and combined Elliot Formation (LEF + UEF) indicates that the normal polarity samples may be biased by a younger overprint of either the Jurassic normal polarity of the Karoo Large Igneous Province or present day field. The separate poles calculated for the four sites in the LEF and ten sites in the UEF overlap with the Late Triassic and Early to Middle Jurassic Gondwana poles, respectively. The combined Elliot Formation and UEF pole positions are better constrained than the LEF and therefore considered more reliable. Overall the LEF shows considerable overlap with the Late Triassic Apparent Polar Wander Paths (APWP) poles.     

Glacial diamictites of Serra Azul Formation (Ediacaran,Paraguay belt): Evidence of the Gaskiers glacial event in Brazil

Discontinuous outcrops of diamictites and siltstones are found above post-Marinoan carbonates from the Araras Formation and represent the record of a second glaciation in the northern Paraguay belt, Brazil. This new stratigraphic unit, named the Serra Azul Formation, varies in thickness between 250 and 300 m; it lies on top of dolomites of the Araras Group and is overlain by sandstones of the Raizama Formation. Massive diamictite, approximately 70 m thick, composes the basal unit (Unit A), followed by 200 m thick laminated siltstones (Unit B), which contain sparse intercalations of very fine-grained sandstone lenses. This new diamictite level is probably related to the Gaskiers Glaciation, with an age of approximately 580 Ma, and represents the youngest Neoproterozoic glacial event recorded in South America.     

Triassic volcanism in eastern Heilongjiang and Jilin provinces,NE China: Chronology,geochemistry, and tectonic implications

With the aim of constraining the Early Mesozoic tectonic evolution of the eastern section of the Central Asian Orogenic Belt (CAOB), we undertook zircon U–Pb dating and geochemical analyses (major and trace elements, Sr–Nd isotopes) of volcanic rocks of the Luoquanzhan Formation and Daxinggou Group in eastern Heilongjiang and Jilin provinces, China. The analyzed rocks consist mainly of dacite and rhyolite, with SiO₂ contents of 68.52–76.65 wt%. Three samples from the Luoquanzhan Formation and one from the Daxinggou Group were analyzed using laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb zircon techniques. Three zircons with well-defined oscillatory zoning yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 217 ± 1, 214 ± 2, and 208 ± 1 Ma, and one zircon with oscillatory zoning yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 201 ± 1 Ma. These ages are interpreted to represent the timing of eruption of the volcanic rocks. The Triassic volcanic rocks are characterized by high SiO₂ and low MgO concentrations, enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs) and heavy rare earth elements (HREEs), (⁸⁷Sr/⁸⁶Sr)_i = 0.7040–0.7050 (Luoquanzhan Formation) and 0.7163–0.7381 (Daxinggou Group), and ε_Nd (t) = 1.89–3.94 (Luoquanzhan Formation) and 3.42–3.68 (Daxinggou Group). These geochemical features indicate an origin involving the partial melting of juvenile lower crust (Nd model ages (T_DM2) of 651–821 Ma) and that compositional variation among the volcanic rocks arose from mineral fractionation and minor assimilation. These volcanic rocks formed within an extensional environment following collision of the NCC and Jiamusi-Khanka Massif during the Late Paleozoic–Early Triassic.     

Use of comprehensive two-dimensional gas chromatography for the characterization of ultra-deep condensate from the Bohai Bay Basin,China

A gas condensate from well ND1 in the Jizhong Depression of the Bohai Bay Basin, China is characterized by two-dimensional gas chromatography with flame ionization detector (GC × GC–FID) and time-of-flight mass spectrometry (GC × GC–TOFMS). This condensate is sourced from the fourth member of the Shahejie Formation (Es4) but reservoired in the Mesoproterozoic Wumishan Formation carbonate at a depth of 5641–6027 m and the reservoir temperature is 190–201 °C. It is the deepest and the highest temperature discovery in the basin to date. The API gravity of the condensate is 51° and the sulfur content is < 0.04%. A total of 4955 compounds were detected and quantified. Saturated hydrocarbons, aromatic hydrocarbons and non-hydrocarbon account for 94.8%, 5.1% and 0.02% of the condensate mass, respectively. Some long chain alkylated cyclic alkanes, decahydronaphthalenes and diamondoids are tentatively identified in this condensate. The C₆–C₉ light hydrocarbon parameters show that the gas condensate was generated at relatively high maturity but its generation temperature derived from the dimethylpentane isomer ratio seems far lower than the current reservoir temperature. Some light hydrocarbon parameters indicate evaporative fractionation may also be involved due to multiple-charging and mixing. The diamondoid concentrations and gas oil ratio (GOR) suggest that the ND1 condensate results from 53.3–55% cracking. Since significant liquids remain, the exploration potential of ultra-deep buried hill fields in the Bohai Bay Basin remains high.     

Late Paleozoic peperites in West Junggar,China, and how they constrain regional tectonic and palaeoenvironmental setting

Late Paleozoic peperites have been identified for the first time at the bottom of Tailegula Formation in West Junggar, China. This finding is significant for the reconstruction of Late Paleozoic evolution in the Junggar region. The peperites form successions up to 500 m thick interbedded with basaltic lava and sedimentary rocks. Four types of peperites are described and interpreted as resulting from basaltic lava bulldozed into wet, unconsolidated sediments at their basal contacts. Zircon LA-ICP-MS U–Pb dating of a tuff lens enclosed by lava showed that the peperites formed in the Late Devonian (ca. 364 Ma). The peperite-bearing units probably formed at a water depth of less than 3 km and are generally undeformed, occurring in continuous stratigraphic sections distributed regionally over a distance of 100 km on either side of the Darbut and Baijiantan ophiolitic belts, in contrast to the highly deformed slices of ophiolite. They demonstrate that the Darbut and Baijiantan ophiolitic belts should not be interpreted as significant plate boundaries and represent the underlying ocean crust uplifted along tectonic lineaments within a continuous shallow remnant ocean basin. The peperites formed during the spreading phase of the remnant ocean basin and represent the final stages of creation of oceanic crust.     

Chemostratigraphy and detrital zircon geochronology of the Neoproterozoic Khorbusuonka Group,Olenek Uplift,Northeastern Siberian platform

This study provides ⁸⁷Sr/⁸⁶Sr, δ¹³C and δ¹⁸O data from the best-preserved limestone and dolomite of the Ediacaran carbonate-dominated Khorbusuonka Group of the Olenek Uplift, NE Siberian Craton, as well as detrital zircon geochronological data from both underlying and overlying sandstones. The Maastakh Formation is characterized by ⁸⁷Sr/⁸⁶Sr ratios of ca. 0.70822 and δ¹³C values between + 4.8 and + 6.0‰. ⁸⁷Sr/⁸⁶Sr ratios in limestones of the Khatyspyt Formation are fairly uniform, ranging from 0.70783 to 0.70806. The carbon isotopic composition slowly decreases from bottom (+ 3.7‰) to top (− 0.2‰) of section. The Sr isotopic composition of the Turkut Formation varies from 0.70824 to 0.70914, value of δ¹³C is about zero: − 0.7…+0.7 ‰. The youngest population of detrital zircons from Maastakh Formation indicates that these rocks were formed not later than 630 Ma. U–Pb detrital zircons data of Kessyusa Group has a single peak at about 543 Ma, which is almost identical to the earlier dating. Based on biostratigraphy and isotopic data, the Sr isotopic compositions from the Khatyspyt Formation (⁸⁷Sr/⁸⁶Sr = 0.70783–0.70806) represent the composition of seawater at 560–550 Ma. Such low values of ⁸⁷Sr/⁸⁶Sr ratio in Ediacaran water were probably caused by the quick opening of Iapetus Ocean.