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High-resolution geochronology is essential for determining the growth rate of volcanoes, which is one of the key factors for establishing the periodicity of volcanic eruptions. However, there are less high-resolution eruptive histories ( > 10 6 years) determined for long-lived submarine arc volcanic complexes than for subaerial complexes, since submarine volcanoes are far more difficult to observe than subaerial ones. In this study, high-resolution geochronology and major-element data are presented for the Milos volcanic field (VF) in the South Aegean Volcanic Arc, Greece. The Milos VF has been active for over 3 Myr , and the first 2 × 10 6 years of its eruptive history occurred in a submarine setting that has been emerged above sea level. The long submarine volcanic history of the Milos VF makes it an excellent natural laboratory to study the growth rate of a long-lived submarine arc volcanic complex. This study reports 21 new high-precision 40 Ar / 39 Ar ages and major-element compositions for 11 volcanic units of the Milos VF. This allows us to divide the Milos volcanic history into at least three periods of different long-term volumetric volcanic output rate ( Qe ). Periods I (submarine, ∼ 3.3–2.13 Ma ) and III (subaerial, 1.48 Ma –present) have a low Qe of 0.9 ± 0.5 × 10 −5 and 0.25 ± 0.05 × 10 −5 km3 yr−1 , respectively. Period II (submarine, 2.13–1.48 Ma ) has a 3–12 times higher Qe of 3.0 ± 1.7 × 10 −5 km3 yr−1 . The Qe of the Milos VF is 2–3 orders of magnitude lower than the average for rhyolitic systems and continental arcs.

Geological records indicate that the hyper-aridity in the Atacama Desert has prevailed since at least the mid-Miocene, with shorter periods of increased humidity punctuating long-term aridity. The 7-m-high accumulation of colluvial sediments at the Salar Grande (21°S/70°W) studied here provides a key palaeoclimate record to understand hillslope dynamics and its relation to humid periods. While 10Be surface exposure ages point to long-term surface stability of the flat upslope surface, a combination of humidity-driven soil creep, overland flow and soil creep related to seismic shaking, caused denudation of the hillslope and accumulation of several metres of colluvium over much shorter timescales during the last 130 ka. A robust chronology for the hillslope sediments has been established by using Infrared Stimulated luminescence (pIR-IR225 protocol) on K-feldspar extracts from nine samples collected within the accumulation. A series of tests has been carried out to confirm the suitability of the method. The estimated ages indicate accelerated sedimentation at 35–80 ka, and 100–130 ka, which are interpreted as periods with more humid climate conditions than present. These findings agree with climate variations in the hyper-arid Atacama indicated by the activity of coastal alluvial fans and river catchments.

The observation that individual volcanic centres have their own eruption frequencies has been known for a long time but is as yet poorly understood. The key to a better understanding of the mechani...

High-resolution geochronology is essential for determining the growth rate of volcanoes, which is one of the key factors for establishing the periodicity of volcanic eruptions. However, there are less high-resolution eruptive histories (> 106 years) determined for long-lived submarine arc volcanic complexes than for subaerial complexes, since submarine volcanoes are far more difficult to observe than subaerial ones. In this study, high-resolution geochronology and major-element data are presented for the Milos volcanic field (VF) in the South Aegean Volcanic Arc, Greece. The Milos VF has been active for over 3 Myr, and the first 2 × 106 years of its eruptive history occurred in a submarine setting that has been emerged above sea level. The long submarine volcanic history of the Milos VF makes it an excellent natural laboratory to study the growth rate of a long-lived submarine arc volcanic complex. This study reports 21 new high-precision 40Ar/39Ar ages and major-element compositions for 11 volcanic units of the Milos VF. This allows us to divide the Milos volcanic history into at least three periods of different long-term volumetric volcanic output rate (Qe). Periods I (submarine, ∼ 3.3–2.13 Ma) and III (subaerial, 1.48 Ma–present) have a low Qe of 0.9 ± 0.5 × 10−5 and 0.25 ± 0.05 × 10−5 km3 yr−1, respectively. Period II (submarine, 2.13–1.48 Ma) has a 3–12 times higher Qe of 3.0 ± 1.7 × 10−5 km3 yr−1. The Qe of the Milos VF is 2–3 orders of magnitude lower than the average for rhyolitic systems and continental arcs.

The geometry and evolution of rivers originating from the Tibetan plateau are influenced by topography and climate change during the India-Asia collision. The Yangtze River is the longest among these rivers and formed due to capturing many rivers on the eastern Tibetan Plateau by the middle Yangtze. The timing of these capture events is still controversial. Here, we use detrital muscovite 40Ar/39Ar and zircon U–Pb ages to constrain the provenance of late Cenozoic sediments in the Jianghan Basin in the middle reaches of the Yangtze River. The combined data suggest that late Pliocene sediments were mainly derived from a local source in the Jianghan Basin including the Dabie Shan. The middle Pleistocene sediments were derived from the Min River west of the Three Gorges. This implies that at least one river, perhaps the palaeo-Han River, originating from the Dabie Shan region, flowed through the centre of the Jianghan Basin during the late Pliocene. The appearance of sediment from the Min River in the Jianghan Basin somewhere between late Pliocene and middle Pleistocene suggests that the Three Gorges section of the Yangtze River was formed somewhere between late Pliocene and middle Pleistocene (N2– Q2).

The new generation of multi-collector mass spectrometers (e.g. ARGUSVI) permit ultra-high precision (40Ar/39Ar geochronology of rocks and minerals. At the same time, the 40Ar/39Ar method is limited by relatively large uncertainties (>1%) in 40K decay constants and the ages of natural reference minerals that form the basis of the technique. For example, reported ages for widely used 40Ar/39Ar reference materials, such as the ca. 28 Ma Fish Canyon Tuff sanidine (FCTs) and the ca. 1.2 Ma Alder Creek Rhyolite sanidine (ACRs), vary by >1%. Recent attempts to independently calibrate these reference minerals have focused on K–Ar analyses of the same minerals and inter-comparisons with astronomically tuned tephras in sedimentary sequences and U–Pb zircon ages from volcanic rocks. Most of these studies used older generation (effectively single-collector) mass spectrometers that employed peak-jumping analytical methods to acquire 40Ar/39Ar data. In this study, we reassess the inter-calibration and ages of commonly used 40Ar/39Ar reference minerals Fish Canyon Tuff sanidine (FCTs), Alder Creek Rhyolite sanidine (ACRs) and Mount Dromedary biotite (MD2b; equivalent to GA-1550 biotite), relative to the astronomically tuned age of A1 Tephra sanidine (A1Ts), Faneromeni section, Crete (Rivera et al., 2011), using a multi-collector ARGUSVI mass spectrometer. These analyses confirm the exceptional precision capability (40Ar/39Ar step-heating spectra, with generally monotonically increasing ages (∼1% gradients). The similarity in these patterns, mass-dependent fractionation modeling, and results from step-crushing experiments on FCTs, which yield younger apparent ages, suggest that the discordance may be due to a combination of recoil loss and redistribution of 39ArK and isotope mass fractionation. In contrast to our previous inferences, these results imply that the sanidine samples are suitable 40Ar/39Ar reference materials, provided appropriate corrections are included for differential recoil loss of 39ArK and contributions from xenocrysts/antecrysts can be resolved. Relative to an age of 6.943 ± 0.005 Ma for A1Ts, we calculate astronomically tuned ages for FCTs, ACRs and MD2b of 28.126 ± 0.019 (0.066%) Ma, 1.18144 ± 0.00068 (0.058%) Ma and 99.125 ± 0.076 (0.077%) Ma, respectively (95% internal errors). These results are consistent with recent 238U/206Pb age data from these localities, but are marginally younger (∼0.2%) than previous 40Ar/39Ar ages inter-calibrated with astronomically tuned tephra from the Mediterranean, and distinctly younger (0.6%) than results optimized against a broad array of 238U/206Pb zircon ages. Consideration of published and assumed recoil loss 39ArK proportions (0.18–0.40%), yields recoil-corrected age estimates of 28.187 ± 0.019 Ma, 1.18404 ± 0.00068 Ma and 99.204 ± 0.076 Ma, respectively. This comparison indicates inherent uncertainties of >0.1% in the 40Ar/39Ar ages of reference minerals without consideration of recoil artefacts, thus limiting the benefits of high precision multi-collector analyses. Significant improvement to the accuracy of the 40Ar/39Ar method (40Ar/39Ar studies utilizing multi-collector mass spectrometry, additional constraints on recoil 39ArK loss from reference minerals, further resolution of discrepancies between astronomically tuned sedimentary successions and refinement of the 238U/206Pb zircon age cross-calibration approach.

International audience; The Maikop Series forms an important source rock in the former Paratethys. Deposition is often interpreted as anoxic, linked to restriction of the Paratethys. The Pirembel formation in the Talysh Mountains (Azerbaijan) is attributed to the Maikop Series and was deposited above the Eocene volcanic Peshtasar formation. Dating the onset of anoxia could help to distinguish glacio-eustatic from tectonic causes of restriction. We integrated magnetostratigraphy and biostratigraphy to date the onset of Pirembel sedimentation and used geochemistry to characterize the tectonic setting of the Peshtasar volcanic rocks. The onset of Maikop sedimentation in the Talysh was determined to be 37.7 Ma, ruling out a link with the major sea-level drop at the Eocene–Oligocene Transition (33.9 Ma) and favouring a tectonic cause. Extrapolating the average sedimentation rate (34 cm kyr) suggests that the entire Pirembel formation belongs to the Late Eocene. We hypothesize that the end of volcanism is important in the transition to Pirembel sedimentation. The palaeomagnetic and geochemistry results for the volcanic rocks cluster in three groups, suggesting three distinct episodes of volcanism. Volcanic sills within the Eocene Arkevan formation plot exactly on these groups, confirming the relationship between the Arkevan and Peshtasar formations. Volcanic rocks of the Talysh show continental-arc signatures and may be related to an Eocene volcanic belt extending towards southeastern Iran.

Sediment load in rivers is an indicator of erosional processes in the upstream river catchments. Understanding the origin and composition of the sediment load can help to assess the influence of natural processes and human activities on erosion. Tectonic uplift, precipitation and run-off, hill slopes and vegetation can influence erosion in natural systems. Agriculture and deforestation are expected to increase the sediment yield, but dams and reservoirs can trap much of this sediment before it reaches the ocean. Here, we use major element composition and 40Ar/39Ar ages of detrital muscovites to constrain the sediment contribution of various tributaries to sedimentation in the Yangtze delta. The sediment contribution calculated from muscovite data was compared with that estimated from current sediment load data from gauging stations. Muscovite data show that the main contributor to the Yangtze delta sands is the Min River, while the current sediment load suggests that the Jinsha and Jialing rivers are the most important current contributors to delta sediments. We suggest that this difference reflects an "old" and "young" erosion pattern, respectively as medium grained muscovite could be transported much slower than suspended sediment load in the complex river-lake systems of the Yangtze River basin. These two different erosion patterns likely reflect enhanced human activity (deforestation, cultivation, and mining) that increasingly overwhelmed long-time natural factors controls on erosion since ~1900 cal years B.P.

Cenozoic convergence between the Eurasian and African plates and concurrent slab roll-back processes have produced a progressive extension in back-arc areas, such as the Aegean region and western Anatolia. There is still a long-standing controversy as to whether this was a continuous or stepwise process. To shed light on this controversy and on the driving mechanism of regional extension, we present palaeomagnetic and geochronological results from the Soke Basin located at the southeastern rim of the Izmir–Balikesir Transfer Zone. Our improved geochronology shows that volcanic activity in the region occurred between 11.66 and 12.85 Ma. Middle to late Miocene palaeomagnetic data for the Soke Basin show a c. 23° clockwise rotation, whereas early Miocene data show a c. 28° counterclockwise rotation. The primary nature of the magnetization is indicated by a positive tilt test. The resulting c. 51° counterclockwise rotations during the middle Miocene signify a major tectonic reorganization, during a period when an interruption of exhumation of metamorphic massifs has been reported. We suggest that the Izmir–Balikesir Transfer Zone is the main driver of the reorganization in the region. The regional fingerprint of this tectonic reorganization coincides with the acceleration of trench retreat and illustrates the surface impact of tearing of the Hellenic slab. Supplementary material: Details of 40 Ar/ 39 Ar analysis including heating steps and the output (.pmag) file including details of paleomagnetic analysis performed in this study are available at https://doi.org/10.6084/m9.figshare.c.3690871

In situ Terrestrial Cosmogenic Nuclides (hereafter TCNs) are increasingly important for absolutely dating terrestrial events and processes. This study aimed at improving our knowledge of the production rate of Terrestrial Cosmogenic 3 He formed in situ in rock surfaces at low latitude and sea level as well as re-evaluation of the Canary Islands as a calibration site for TCNs. For this purpose, we sampled basaltic lava flows from some of the youngest and yet undated volcanic sites and used the 40 Ar/ 39 Ar incremental heating method on groundmass samples and in situ cosmogenic 3 He on olivine and clinopyroxene phenocrysts. 40 Ar/ 39 Ar analysis was done on a Hiden HAL Series 1000 triple filter quadrupole mass spectrometer with extraction furnace. Incremental heating data shows ages in the Late Pleistocene from 52.7 ± 21.6 ka to 398.6 ± 27.6 ka. We measured cosmogenic 3 He concentrations in olivine and clinopyroxene phenocrysts from flow top samples on a MAP 215-50 sector mass spectrometer with a crushing device and a diode laser extraction system. Exposure age calculations yielded ages in the range 38.9 ± 4.0 ka to 62.3 ± 6.7 ka for the youngest lava flow and the data series is in broad agreement with the argon data up to 250 ka and reveals a more continuous time line of volcanism during the late Pleistocene on the island. However, the dataset was not sufficient for calculation of production rates for in situ Terrestrial Cosmogenic 3 He as many samples showed signs of erosion. Calculated erosion rates range from none to as high as 7.3 mm/kyr assuming a rock density of 2.9 g/cm 2 . This finding puts a constraint on the use of Fuerteventura as a calibration site for exposure histories older than 50–100 ka. A comparison with cosmogenic 36 Cl data supports these findings and indicates substantial weathering.

Impact Dating The large mass extinction of terrestrial and marine life—most notably, non-avian dinosaurs—occurred around 66 million years ago, at the boundary between the Cretaceous and Paleogene periods. But attributing the cause to a large asteroid impact depends on precisely dating material from the impact with indicators of ecological stress and environmental change in the rock record. Renne et al. (p. 684 ; see the Perspective by Pälike ) acquired high-precision radiometric dates of stratigraphic layers surrounding the boundary, demonstrating that the impact occurred within 33,000 years of the mass extinction. The data also constrain the length of time in which the atmospheric carbon cycle was severely disrupted to less than 5000 years. Because the climate in the late Cretaceous was becoming unstable, the large-impact event appears to have triggered a state-shift in an already stressed global ecosystem.

Intercalibration between the astronomical and radio-isotopic dating methods provides a means to improving accuracy and reducing uncertainty of an integrated, multi-chronometer geologic timescale. Here we report a high-precision 40 Ar/ 39 Ar age for the Fish Canyon sanidine (FCs) neutron fluence monitor, by multi-collector noble gas mass spectrometry, through cross-calibration with A1 tephra sanidines (A1Ts) of the direct astronomically tuned Faneromeni section (Crete). The astronomically intercalibrated 40 Ar/ 39 Ar age of FCs of 28.172 ± 0.028 Ma (2σ, external errors) is within the uncertainty of, but more precise (± 0.10%) than, the previous 40 Ar/ 39 Ar age determined by intercalibration with astronomically tuned tephras from the Melilla Basin (Morocco). Using this proposed age for FCs, combined with measurements using the A1Ts as the neutron fluence monitor, a weighted mean Bishop Tuff 40 Ar/ 39 Ar sanidine age of 0.7674 ± 0.0022 Ma (2σ, external errors) is indistinguishable from the ID-TIMS U/Pb zircon age (0.7671 ± 0.0019 Ma). The consistency between the astronomically calibrated 40 Ar/ 39 Ar sanidine age and U/Pb zircon age for this Quaternary unit suggests that agreement between these two radio-isotopic dating techniques is now achievable at better than ± 0.3% (2σ) in the youngest part of geologic time (

Massive evaporites were deposited in the Central European Paratethys Sea during the Badenian salinity crisis (BSC). The scarcity of absolute age data has hampered a thorough understanding of these salt deposits. Here we present a robust chronology for this catastrophic event by 40Ar/39Ar dating of volcanic tuffs below and within the Badenian salts in southern Poland. The onset of BSC evaporite deposition is dated at 13.81 ± 0.08 Ma and the entire event is estimated to have lasted 200-600 k.y. Correlation to oxygen isotope records shows that the BSC evaporites were just preceded by glacial event Mi-3b, suggesting a causal relationship. The corresponding sea-level fall most likely restricted the open marine connection to the Mediterranean, thereby trapping the salt in the deep Paratethys basins.

The Melilla Basin (NE Morocco) formed the easternmost part of the Rifian Corridor, which was an important Mediterranean– Atlantic gateway during the Late Miocene. The sedimentary infill of the basin consists of a shallow marine, precession-related cyclic marl–diatomite succession, laterally grading into a marginal carbonate complex. Three bio-sedimentary events have been recorded within the marl succession: 1) onset of diatomite deposition, 2) major change in foraminiferal assemblages, and 3) transition to Halimeda-rich carbonates and Porites coral reef build-ups. Recent 40 Ar/ 39 Ar dating has provided a good age control for the Melilla carbonate sequences, but a high-resolution astronomical time frame is necessary to solve the climatic signature of the basin sediments. This study focuses on the shallow marine marl succession of the Melilla Basin. Integrated magneto-, cyclo- and biostratigraphy allowed a detailed correlation to the astronomical target curve, resulting in a high-resolution time frame for the Late Miocene evolution of the basin. Comparison of the Melilla data with previous results from other Moroccan and Mediterranean basins indicates that the input of Atlantic waters through the Rifian Corridor became restricted after 6.84 Ma, and was minimized by 6.58 Ma. In the final period (6.58–5.96 Ma) towards the Messinian Salinity Crisis, the Melilla Basin can be considered as a marginal basin of the Mediterranean. The astronomical time frame for the marl sequences of the Melilla Basin moreover enables a direct comparison between the independent isotopic and astrochronological dating techniques, as astronomical ages have also been assigned to intercalated volcanic tuffs for which 40 Ar/ 39 Ar ages were previously determined. We conclude that the isotopic ages are systematically younger

Tectonic uplift and sea level lowering are two proposed mechanisms to explain the development of thresholds in front of the widespread evaporite basins of the circum-Mediterrranean region during the Miocene. Here we apply a multi-disciplinary approach to the continuously marine sequences of the Murcia–Cartagena basin to investigate which mechanism is responsible for the Tortonian evaporites of the Eastern Betics. First we develop a high-resolution chronology for the Venta de la Virgen section by integration of biostratigraphic, magnetostratigraphic and isotopic dating results. Next we construct palaeobathymetry and geohistory curves for this section and the Abad composite of the Sorbas basin. We show that the apparent differential vertical motions between the two sections cannot be explained by sea-level change but only by local tectonics. The Murcia–Cartagena basin shows significant tectonic uplift during the late Tortonian and early Messinian, while the neighboring Fortuna basin was rapidly subsiding. We conclude that tectonic activity on the Alhama de Murcia Fault was responsible for the emergence of a threshold that finally led to evaporite formation in the Fortuna basin.

A new isotopic age of 7.71 ± 0.11 Ma (1σ) has been obtained with the 40Ar/39Ar incremental heating technique on phlogopites from the Miocene volcanic rocks (lamproites) of the Fortuna Basin in southeast Spain. This age is significantly older than earlier reported K/Ar ages, but confirms recent magnetostratigraphic ages on the sedimentary sequences of the eastern Betics. Because the volcanic rocks are intercalated in the stratigraphic sequence of the Fortuna Basin directly above the transition from evaporitic to continental sediments, it implies that the Fortuna evaporites are older than 7.71 Ma, and thus of Tortonian age. In addition, it shows that the volcanism in the Fortuna Basin must be attributed to a late Tortonian deformation phase and not to Messinian tectonics. Consequently, these results form an important step towards a consistent chronological framework for the sedimentary, tectonic and paleogeographic evolution of the Fortuna Basin during the late Miocene.

In this paper we present new 40 Ar/ 39 Ar data of volcanic ash layers intercalated in the astronomically dated sections of Monte dei Corvi and Monte Gibliscemi (Italy) to obtain better radioisotopic time constraints on the Serravallian/Tortonian boundary and to confirm the intercalibration of radioisotopic and astronomical time proposed by Kuiper et al. [2004; Fish Canyon Tuff (FCT)-sanidine at 28.21 ± 0.03 Ma]. The latter intercalibration is supported by astronomically calibrated FCT sanidine ages for two ash layers at Monte Gibliscemi (GiF-1: 28.28 ± 0.04; GiD-3: 28.16 ± 0.04 Ma; ±1 SE). As a consequence, our results support the astronomically calibrated age of 11.608 Ma for the Tortonian Global Stratotype Section and Point and, hence, the tuning of the Serravallian/ Tortonian boundary interval. The Ancona and Respighi levels at Monte dei Corvi give a more diffuse picture, possibly because of contamination with detrital or xenocrystic material and the inferior quality of biotite for intercalibration

Seamount chains in the southeast Atlantic Ocean are thought to have formed above plumes sourced from the deep mantle. Dating of lavas erupted along the trails show that the formation and distribution of the seamount chains is also controlled by the motion and structure of the African Plate. The origin of hotspot trails is controversial1. Explanations range from deep mantle plumes rising from the core–mantle boundary2 (CMB) to shallow plate cracking. However, these mechanisms cannot explain uniquely the scattered hotspot trails distributed across a 2,000-km-wide swell in the sea floor of the southeast Atlantic Ocean3. This swell projects down to one of the two largest and deepest distinct regions at the CMB, the Africa Low Shear Wave Velocity Province4,5,6. Here we use 40Ar/39Ar isotopic analyses to date lava samples erupted at several hotspot trails across the Atlantic swell. We combine the eruption ages with an analysis of the structure and age of the sea floor, and find that the trails formed synchronously, in a pattern consistent with movement of the African Plate over plumes rising from the edge of the Africa Low Shear Wave Velocity Province. However, we also find that the seamounts initially formed only at the edge of the swell, where the oceanic crust was spreading apart. Later, about 44 million years ago, the hotspot trails began to cross the swell, but only in locations where the lithosphere was sufficiently young and thin that magma could reach the surface. We conclude that the distribution of hotspot trails in the southeast Atlantic Ocean is controlled by the interplay between deep-sourced mantle plumes and the motion and structure of the African Plate.

The Tauride range in southern Turkey is flanked and overlain by Neogene sedimentary basins. To the south and on top of the high range, these basins are mainly marine, whereas poorly studied intramontane basins dominated by continental deposits are exposed to the north. In this paper, we study the stratigraphy and structure of the continental Altinapa Basin, and provide Ar-40/Ar-39 geochronology for volcanic deposits in the stratigraphy. The stratigraphy can be subdivided into a Lower Group, displaying similar to 400 m of fining upward fluvio-lacustrine sediments, unconformably overlain by an Upper Group with similar to 500 m of lacustrine deposits, andesitic lavas and volcaniclastic sediments. Ar-40/Ar-39 dating of three volcaniclastic samples across the Upper Group provide 11.8-11.6 Ma ages. The Altinapa Basin is an extensional basin, which formed predominantly due to N-S to NE-SW directed stretching. The main basin forming phase occurred during deposition of the Lower Group, prior to 11.8 Ma. Paleostress inversion analyses demonstrate uniaxial stress, with highly variable extension directions that are consistent with currently observed seismicity patterns. The Middle Miocene extension history of the Altinapa Basin is consistent with a regional pattern of Middle Miocene NE-SW to NW-SE extension north of the Cyprus subduction zone. This suggests that the Cyprus subduction zone has been in retreat relative to central Anatolia since at least Middle Miocene time. The continental Altinapa Basin is currently at an elevation of similar to 1 km, whereas partly contemporaneous marine sediments in the Mut Basin that lies on top of the Tauride range are elevated to 2 km. This shows strong late Cenozoic differential uplift in southern Turkey, with at least 1 km more uplift of the Tauride range than of the intramontane basins to the north. We conclude that the current high elevation of the Taurides is related to late Neogene extension and does not result from the late Cretaceous to perhaps Oligocene folding and thrusting that deformed the rocks in the range. (C) 2012 Elsevier B.V. All rights reserved.

We present a new chronology for the upper Miocene to Pliocene deposits of the Black Sea basin based on high-resolution magnetostratigraphic data coupled with 40 Ar/ 39 Ar dating from the 475 m long Zheleznyi Rog section on the Taman Peninsula (Russia). This section comprises the stratigraphic interval of the Khersonian to Kimmerian regional stages of the Eastern Paratethys. Our magnetostratigraphic record is based on biogenic and early-diagenetic greigite components and yields a magnetostratigraphic sequence of 8 polarity zones. A volcaniclastic ash layer at the upper part of the Khersonian is radio-isotopically dated at 8.69 ± 0.18 Ma. The age of the Khersonian–Meotian transition arrives at 8.6 or 8.2 Ma, which is significantly younger than earlier estimates. The new age has important consequences for the Hipparion -datum in the Eastern Paratethys, and implies that all Vallesian fossil sites are younger than 11.2 Ma. The Meotian stage has a total duration of 2.2 to maximum 2.6 Myr, and is marked by multiple erosional events. The end of the Paratethys Sea is dated at 5.5 Ma, when the Black Sea becomes isolated from the Caspian Sea, the Dacian basin and the Mediterranean.

article i nfo The early Cretaceous and younger opening of the Black Sea has obliterated much of the older record of Tethyan subduction below southeastern Europe. The earlier Mesozoic evolution was dominated by opening and closure of Tethyan oceans between Gondwana and Laurasia with their consumption, at least in part, accommodated along the southern Eurasian margin. Crimea (Ukraine), a peninsula in the northern Black Sea, represents the northernmost region of southeastern Europe that exposes a record of a pre-Cretaceous Tethyan active margin. To shed new light on the paleosubduction zone configuration of the southeastern European margin in the Jurassic, we report 40

Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of ∼1.0% or more, limiting our ability to reconstruct Earth history. To overcome this fundamental setback, we compared astronomical and 40 Ar/ 39 Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40 Ar/ 39 Ar geochronology. This calibration results in a more precise older age of 28.201 ± 0.046 million years ago (Ma) and reduces the 40 Ar/ 39 Ar method's absolute uncertainty from ∼2.5 to 0.25%. In addition, this calibration provides tight constraints for the astronomical tuning of pre-Neogene successions, resulting in a mutually consistent age of ∼65.95 Ma for the Cretaceous/Tertiary boundary.