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The Miocene Climatic Optimum (MCO, ~17-15 Ma) was a relatively warm interval that interrupted the Cenozoic cooling trend and bears analogies with projected end-of-the-century climate. Proxy data and model simulations indicate temperatures were on average ~7 – 8°C higher than present day and atmospheric pCO2 values were 500-600 ppmV. At high latitudes, upper ocean temperatures were ~10 – 15°C warmer than present day, but available tropical temperature records are limited. Importantly, to be able to use Miocene paleoclimate records to quantify key climate parameters like the polar amplification of climate change, accurate reconstructions of tropical surface oceans are required.We present high resolution Early to Middle Miocene (~15 – 18 Ma) records of tropical sea surface temperature (SST) variability based on the lipid biomarker paleothermometer TEX86 at Ocean Drilling Program (ODP) Site 959 in the eastern equatorial Atlantic Ocean and at ODP Site 1007 at Bahama Bank in the western tropical Atlantic Ocean. The age model for both sites is based on chemo- and biostratigraphy. Moreover, analyses of bulk carbonate oxygen- (δ18O) and stable carbon (δ13C) isotope ratios at ~2 – 4 kyr resolution at Site 959 facilitated orbital tuning to eccentricity, obliquity and precession. Bulk elemental composition records, total organic carbon concentrations and dinoflagellate cyst assemblages were also generated to assess paleoenvironmental change.At both sites, warming associated with the onset of the MCO (~17 Ma) was identified as an average SST increase of ~2°C (using the TEX86-H calibration). At ~16.8 Ma, bulk carbonate δ13C gradually increased by ~1‰ at both sites, indicating the onset of the Monterey carbon isotope excursion. Combined with available temperature information from the high latitudes and deep ocean, we assess meridional temperature gradients across the MCO.At ODP Site 959, sediments are characterized by alternations of biogenic silica, carbonates, and terrigenous material (i.e., clays). Following the onset of the MCO (~17 – 16.5 Ma), high variability in the oceanographical setting is reflected in striking Babio peaks, indicating productivity changes. These peaks coincide with lowest SSTs (~28°C) and increased dust supply (increased Fe and Ti) on precession and obliquity timescales. In the same interval, (inner-) neritic dinoflagellate species indicate increased water column stratification. Heterotrophic dinocyst groups vary on timescales coherent with the other geochemical records, relative to comparably stable background abundances of oceanic genera throughout the MCO. Combined, this suggests that a highly dynamic monsoon-driven upwelling regime was present at Site 959 during the MCO. Combined, these patterns imply a highly dynamic African monsoon-driven upwelling regime that intensified at the onset of the MCO.

The International Union of Geological Sciences Executive Committee (IUGS EC) voted on 13 October 2021 to ratify a proposal for the Neogene subseries/subepochs to have formal status. They are now incorporated into a six-tiered chronostratigraphic hierarchy within the International Chronostratigraphic Chart (ICC). The Lower/Early Miocene Subseries/Subepoch comprises the Aquitanian and Burdigalian stages/ages, the Middle Miocene Subseries/Subepoch comprises the Langhian and Serravallian stages/ages, the Upper/Late Miocene Subseries/Subepoch comprises the Tortonian and Messinian stages/ages, the Lower/Early Pliocene Subseries/Subepoch comprises the Zanclean Stage/Age and the Upper/Late Pliocene Subseries/Subepoch comprises the Piacenzian Stage/Age. This ratification is an important move towards both a common language in the wider Earth Sciences community and a step forward in the unification of Cenozoic chronostratigraphy, with Neogene and Quaternary subseries/subepochs now formalized.

The Messinian salinity crisis (MSC) is perceived as an environmental crisis governed by climatic and tectonic controls, affecting global oceans' salinity and shaping the Mediterranean Sea's biochemical composition. Recently drilled offshore wells in the Levant Basin retrieved a sedimentary record of the deep-basin Mediterranean MSC salt deposits and the underlying pre-evaporite unit. In this study, we have concentrated on the pre-evaporite interval and its transition into the overlying evaporites. Analysis of this data set changes the way these deposits have been perceived since the 1970s, when they were first penetrated in their uppermost part during Deep Sea Drilling Project expeditions. Using sedimentology, seismic interpretation, biostratigraphy, and astronomical tuning, we show that Messinian salt deposition in the Eastern Mediterranean began during stage 1 of the MSC. In contrast to the present paradigm, salt was deposited synchronously with gypsum in the marginal and intermediate-depth basins significantly before the 50 k.y. interval coined as the "MSC acme event", ~400 k.y. after the crisis began. Thus salt precipitation took place in a non-desiccated deep basin, having a restricted but often open connection with the Atlantic Ocean, substantially altering our understanding of the mechanisms governing the deposition of salt giants. A coeval onset of basinal halite and marginal gypsum precipitation calls for a revaluation of global-scale climatic and oceanographic models of the MSC, taking into account a much older age for the beginning of halite deposition.

Enhanced winter precipitation over the Mediterranean Sea at times of minimum precession and maximum obliquity could provide freshwater required to form orbitally-paced sedimentary cycles across the Mediterranean Sea floor, offering an alternative to monsoonal runoff. We investigate the sources of the enhanced winter precipitation by applying a moisture tracking model (WAM-2layers) on the results of idealized orbital extreme experiments with a state-of-the-art climate model (EC-Earth).Tracking the moisture sources of the enhanced winter precipitation over the Mediterranean Sea shows that the source differs during the winter half year. In fall, the majority of the precession-induced precipitation increase originates from the Mediterranean itself. However, in late winter, the increase can be attributed to enhanced moisture advection from the Atlantic. This agrees with changes in evaporation and air-sea temperature differences over the Mediterranean. The obliquity-induced precipitation increase shows much less differences, with an equal contribution of local and Atlantic sources.The mechanism behind the Atlantic source of moisture is not related to storm track activity, but to a weakened Azores High and slightly higher surface pressure over North Africa. The resulting anomalous circulation patterns generate enhanced Atlantic moisture transport towards the Mediterranean. Our combined climate and moisture tracking modelling approach thus provides an alternative mechanism for Atlantic sources of orbitally-paced Mediterranean precipitation changes.The results of this study have been published in:Bosmans, J. H. C., van der Ent, R. J., Haarsma, R. J., Drijfhout, S. S. and Hilgen, F. J.: Identifying sources of changed precipitation in paleoclimate studies through moisture tracking: A case study for orbital extremes over the Mediterranean Sea, Paleoceanogr. Paleoclimatology, accepted, doi:10.1029/2019PA003655, 2020.The atmospheric moisture tracking through WAM-2layers revealed concrete information about the evaporative sources of enhanced/reduced precipitation. This method has not been previously applied in paleoclimate studies, but thus proved to be a powerful tool in attributing reasons for precipitation changes in addition to climate model experiments and classical meteorological analyses. New ideas for collaborations to apply this method in other (paleo)climate studies are welcome.

Uncertainties on the radiometric ages of Devonian stage boundaries are currently on the order of several millions of years. A cyclostratigraphic approach is the foremost way forward to improve the Devonian geological time scale. To do so requires well-preserved continuous records, as well as reliable paleoclimatic proxies. The NY Route 199 section, from Kingston, in the Hudson Valley of eastern New York, is a road cut outcrop, which exposes most of the Schoharie Formation. It corresponds to the upper portion of the Emsian Stage (upper Lower Devonian, ~400 to ~394 Ma), with essentially continuous deposition. The lithology consists of a mixed siliciclastic-carbonate succession with overall increasing carbonate upsection, showing various degrees of bioturbation (traces includes primarily Zoophycos, Planolites and Chondrites); colors range from white to beige, brown or dark grey. The quality of most of the outcrop is so remarkable that the color variations by themselves permit recognition of Milankovitch cycles, with prominent bundles of light and dark beds. One type of cycle expression is represented by a succession of about six darker beds nested between lighter beds, which is interpreted as six precession cycles within a short eccentricity cycle (precession in the Devonian was ~17 kyr).Samples were collected every 2 cm through 38 m of the section for magnetic susceptibility measurements. On top of these measurements, we provide elemental geochemistry, carbon isotopes and hysteresis measurements (every 50 cm) to constrain the depositional setting and the diagenesis. Hysteresis measurements show that despite being remagnetized (throughout the Appalachians, these Paleozoic rock sequences are all remagnetized during the Variscan-Alleghenian Orogeny), the magnetic susceptibility reflects depositional information. The geochemistry and carbon isotopes give insight into the occurrence of oxic/reducing conditions and detrital inputs. Milankovitch cycles are visible on the outcrop and in the magnetic susceptibility record, allowing a precise floating timescale framework to be constructed for this interval.

The Global Stratotype Section and Point (GSSP) approach to define stage boundaries leaves the unit or body of the stage undefined. At the same time, previous arguments against the use of unit-stratotypes have been invalidated for the younger Cenozoic part of the geological record through the revolutionary advance in integrated high-resolution stratigraphy and astronomical dating. Combined, these provide unprecedented age control and ensure continuity of sedimentary successions, at least within the time scales of the calibrated astronomical-forced climate oscillations, and offer the possibility to introduce amended unit-stratotypes for global stages. Here we propose that such unit-stratotypes should comprise the entire stage in an astronomically age calibrated deep-marine succession, preferably but not necessarily containing the GSSP. Furthermore, cycles used for the tuning can be formally defined as chronozones, i. e. chronostratigraphic units of either unspecified rank or of a smaller scale than the stage, and independent of the standard hierarchy in global chronostratigraphy. In this way, the standard Geological Time Scale and Global Chronostratigraphic Scale can be brought in line with the progress in integrated high-resolution stratigraphy and astronomical dating. However, the more fundamental formal definition of unit-stratotypes does not depend on the formalization of astrochonozones, and both issues should be separately considered and voted upon.

Astronomical tuning of sediment sequences requires both unambiguous cycle-pattern recognition in climate proxy records and astronomical solutions, and independent information about the phase relationship between these two. Here we present two astronomically tuned age models for the Oligocene-Miocene Transition (OMT) from Integrated Ocean Drilling Program Site U1334 (equatorial Pacific Ocean) to assess the effect tuning approaches have on astronomically calibrated ages and the geologic time scale. These age models are based on different phase-assumptions between climate proxy records and eccentricity: the first age model is based on an inverse and in-phase assumption of CaCO3 weight (wt %) to Earth's orbital eccentricity, the second age model is based on an inverse and in-phase assumption of benthic foraminifer stable carbon isotope ratios (δ13C) to eccentricity. The phase-assumptions that underpin these age models represent two end-members on the range of possible tuning options. To independently test which tuned age model and tuning assumptions are correct, we assign their ages to magnetostratigraphic reversals identified in anomaly profiles. Subsequently we compute tectonic plate-pair spreading rates based on the tuned ages. These alternative spreading rate histories indicate that the CaCO3 tuned age model is most consistent with a conservative assumption of constant spreading rates. The CaCO3 tuned age model thus provides robust ages and durations for polarity chrons C6Bn.1n–C6Cn.1r, which are not based on astronomical tuning in the latest iteration of the Geologic Time Scale. Furthermore, it provides independent evidence that the relatively large (several 10,000 years) time lags documented in the benthic foraminiferal isotope records relative to orbital eccentricity, constitute a real feature of the Oligocene-Miocene climate system and carbon cycle. The age constraints from Site U1334 thus provide independent evidence that the delayed responses of the Oligocene-Miocene climate-cryosphere system and carbon cycle resulted from increased nonlinear feedbacks to astronomical forcing.

We propose a realignment of the terms geochronology and chronostratigraphy that brings them broadly into line with current use, while simultaneously resolving the debate over whether the Geological Time Scale should have a “single” or “dual” hierarchy of units: Both parallel sets of units are retained, although there remains the option to adopt either a single (i.e., geochronological) or a dual hierarchy in particular studies, as considered appropriate. Thus, geochronology expresses the timing or age of events (depositional, diagenetic, biotic, climatic, tectonic, magmatic) in Earth’s history (e.g., Hirnantian glaciation, Famennian-Frasnian mass extinction). Geochronology can also qualify rock bodies, stratified or unstratified, with respect to the time interval(s) in which they formed (e.g., Early Ordovician Ibex Group). In addition, geochronology refers to all methods of numerical dating. Chronostratigraphy would include all methods (e.g., biostratigraphy, magnetostratigraphy, chemostratigraphy, cyclostratigraphy, sequence stratigraphy) for (1) establishing the relative time relationships of stratigraphic successions regionally and worldwide; and (2) formally naming bodies of stratified rock that were deposited contemporaneously with units formally defined at their base, ideally by a GSSP (Global Boundary Stratotype Section and Point = “golden spike”) that represents a specific point in time. Geochronologic units may be defined and applied generally by either GSSPs or—as currently in most of the Precambrian—by Global Standard Stratigraphic Ages (GSSAs). Geochronologic units would continue as the time units eons/eras/ periods/epochs/ages, and chronostratigraphic units as the timerock units eonothems/erathems/systems/series/stages. Both hierarchies would remain available for use, as recommended by a formal vote of the International Commission on Stratigraphy in 2010. Geological context helps determine the appropriate usage of the component units.

Integrated data of calcareous plankton and benthic foraminifers from the pre-evaporitic interval of Trave section (Central Italy) allowed the reconstruction of surface and bottom-water conditions in the Central Mediterranean during the interval from 7.61 to 6.33 Ma, preceding the Messinian Salinity Crisis. Our data point out a three-step paleoenvironmental evolution. During the first stage (7.61–7.02 Ma) benthic foraminiferal assemblages depict stable, well-oxygenated and ventilated bottom-water conditions, while the surface water records variable temperature and high nutrient conditions, probably associated with strong seasonality. The second stage (7.02–6.70 Ma) points to unfavourable bottom-water condition, triggered by deep-sea stagnation. This is witnessed by a significant decrease in oxygen concentration and biotic diversity, and by the presence of stress-tolerant taxa. A general warming of the surface water and a strongly stratified water column, characterized by an expanded mixed layer, are also recorded. From 6.70 Ma onwards (third stage), a prominent change to more restricted, low-oxygenated, hypersaline conditions at the sea floor is testified by the total disappearance of deep-dwelling planktonic foraminifers and the increasing abundance of stress-tolerant species. Calcareous plankton reflects high instability of the surface water in terms of nutrients, temperature and salinity. During this stage the environmental deterioration reaches intermediate depths in the water column. The initial change toward a step-wise isolation of the Central Mediterranean bottom-waters is probably related to a general warming, responsible for a first slowing-down of the vertical circulation, favouring stratification of surface and intermediate waters and stagnation of bottom-waters. This warming is related to the restricted connection between the Mediterranean Sea and the Atlantic Ocean, which occurred since 7.146 Ma. In the Trave section, the isolation of bottom-waters most likely occurred at the same time as in other Mediterranean sections. However, due to the presence of a hiatus it cannot be excluded that it occurred with a delay of ~ 100 kyr, probably related to the shallower paleodepth of the basin.

Removing the Tertiary and Quaternary Periods whilst conserving the Paleogene and Neogene Periods in The Geological Timescale 2004 caused a storm of protest. One response was to advocate restoring an enlarged Quaternary and consigning the Neogene to a minor role within the Tertiary. Amongst an array of practical, traditional, sentimental and anthropocentric reasons for this response, the one hard-core justification was that the rigidly nested hierarchy of the geological timescale must be preserved. The central objective of this paper is conserving the historically legitimate, Miocene-present, Neogene Period and System. There are two options for conserving the Quaternary concurrently with the Neogene: (i) an inclusive compromise in a flexible hierarchy, and (ii) an upgrading of Pliocene and Pleistocene divisions to the level of epoch. In the inclusive compromise there coexist alternative pathways through the hierarchical ranks. Thus geohistorians and biohistorians have two options for traversing the hierarchy from era to age, as in this example using the hierarchical positioning of the Calabrian Age and Stage: either Cenozoic [era]↔Neogene [period]↔Pleistocene [epoch]↔Calabrian [age], or Cenozoic [era]↔Quaternary [subera]↔Pleistocene [epoch]↔Calabrian [age]. We reaffirm that the inclusive compromise is entirely viable. In so doing we (i) challenge the necessity of the rigidly nested hierarchy, which should be capable of a little flexibility; (ii) reject all analogies of the arbitrary and conventional chronostratigraphic hierarchy with three natural biological hierarchies; (iii) reaffirm the integrity of the Neogene extending to the present; and (iv) see no reason to doubt the harmonious coexistence of the two options preserving the Quaternary and Neogene traditions in an orderly working and stable time scale. In the alternative schema conserving the Neogene, divisions of the Pliocene and Pleistocene are upgraded, so that the Late Pleistocene, Early Pleistocene and Late Pliocene Epochs comprise the Quaternary Subperiod, itself equivalent to Late Neogene. The inflexibly nested hierarchy is preserved but the Tertiary is lost.

Our results prove that glacio-eustatic sea level oscillations in the early Oligocene were dominantly obliquity controlled with additional influence of the ∼100- and 405-kyr eccentricity cycles. This was derived from spectral analysis of resistivity records from an extended downhole section of the Boom Clay succession in Belgium, that reveals a prevailing obliquity control on the laterally persistent metre-scale alternations of shallow marine silt- and claystones in the Rupelian historical stratotype succession. These direct measurements of sea level variations in a shallow marine setting corroborate that variations with similar frequencies in benthonic oxygen isotope records from the open ocean indeed reflect, at least partly, ice volume change. A very tentative astronomical tuning has been established for the Boom Clay succession which awaits future confirmation with the addition of more accurate age calibration points.

This paper presents a review of (astrobiochronological) calibration of Recent to late Oligocene calcareous nannofossil datum events. Biohorizons included in the paper are those of the widely used “standard” nannofossil zonations of Martini, E. [1971. Standard Tertiary and Quaternary calcareous nannoplankton zonation. In: Farinacci, A. (Ed.), Proceedings of the Second International Conference on Planktonic Microfossils Roma. Rome, Ed. Tecnosci. vol. 2, pp. 739–785], and Okada, H., and Bukry, D. [1980. Supplementary Modification and Introduction of Code Numbers to the Low-Latitude Coccolith Biostratigraphy Zonation (Bukry, 1973, 1975). Marine Micropaleontology 51, 321–325], as well as supplementary biohorizons proposed in the literature. The biohorizons have been selected on the basis of the unambiguous taxonomy of the index taxa and their biostratigraphic usefulness. We emphasise the application of rigorous methodology in nannofossil studies which permits an evaluation of biohorizons in terms of reliability, and calibrates their potential correlatability. Astrochronological age estimates rely on the Geologic timescale developed by the ICS in 2004, with some new calibrations included. We provide an overview of the relative position of biohorizons versus the astronomically calibrated ages of magnetic reversals and reference isotope stratigraphies. Surprisingly, there are still few high-resolution quantitative biostratigraphic studies of astrochronologically tuned sections in spite of the central role of such studies in addressing fundamental problems such as the tempo and mode of plankton evolution.

Long (130,000 years) transient simulations with a coupled model of intermediate complexity (CLIMBER-2) have been performed. The main objective of this study is to examine leads and lags in the response to the climate system to separate obliquity and precession-induced insolation changes. Focus is on the role of internal feedbacks in the coupled atmosphere/ocean/sea-ice/vegetation system. No interactive ice sheets were used. The results show that leads and lags occur in response to the African/Asian monsoon, temperatures at high latitudes and the Atlantic thermohaline circulation. For the monsoon, leads and lags of the monthly precipitation with respect to the precession parameter were found, which are strongly modified by vegetation. In contrast, no lag was observed for the annual precipitation. At high latitudes during late winter/early spring a vegetation-induced lag with respect to the precession parameter was found in surface air temperatures. Again, no annual lag was detected. The lag in the monthly surface air temperatures induces a lag in the annual overturning in the Atlantic Ocean by changing the strength of the deep convection. The lag is several thousand years. The obliquity-related forcing does not give rise to lags in the climate system. We conclude that lags in monthly climatic variables, which are due to vegetation feedbacks, can result in an annual lag when a climatic process (like deep water formation) acts as a filter for certain months.

High-resolution planktonic foraminiferal and oxygen isotope records are presented from a Mediterranean deep marine succession, dated astronomically between 12.12 and 9.78 Ma. Planktonic and benthic oxygen isotope records are punctuated by two episodes of δ18O increase, which have astronomical ages of 11.4 and 10.4 Ma and correspond to the Mi5 and Mi6 events of Miller et al. [1991a]. These ice growth events coincide with low-amplitude variations in the 1.2 Myr obliquity cycle and are accompanied by significant faunal changes in the Mediterranean, such as the arrival of neogloboquadrinids, the increase in abundance of the G. apertura-G. obliquus group, and the areal differentiation between N. atlantica and N. acostaensis. Short-term variations in the planktonic foraminiferal and oxygen isotope records correspond to dominantly precession-controlled sedimentary cycles. Features of the sapropel/grey marl layers indicate that the short-term astronomically controlled circum-Mediterranean climate changes remained basically the same over the last 12 Myr.

A high-resolution integrated stratigraphy is presented for the Abad marls of the Sorbas and Nijar basins in SE Spain (preevaporitic Messinian of the Western Mediterranean). Detailed cyclostratigraphic and biostratigraphic analyses of partially overlapping subsections were needed to overcome stratigraphic problems in particular encountered at the complex transition from the Lower to the Upper Abad. The resulting Abad composite section contains a continuous stratigraphic record from the Tortonian/Messinian boundary up to the transition to the Messinian evaporites of the Yesares Member. All together, 18 calcareous plankton events were recognized which were shown to be synchronous throughout the Mediterranean by means of detailed (bed-to-bed) cyclostratigraphic correlations. The magnetostratigraphy allowed the identification of the four magnetic reversals of chron C3An in the Upper Abad. Details in the sedimentary cycle patterns allowed the Abad composite to be astronomically calibrated. This calibration to the 658N summer insolation curve of solution La90(1,1) yielded astronomical ages for all sedimentary cycles, calcareous plankton bioevents, ash layers and paleomagnetic reversals. Up to now, the Abad composite is the only astronomically well-calibrated section that provided a reliable cyclostratigraphy, magnetostratigraphy and calcareous plankton biostratigraphy. As such it will serve as a reference section both for the pre-evaporite Messinian in the Mediterranean as well as for the Messinian interval in the Astronomical Polarity Time Scale. q 2001 Elsevier Science B.V. All rights reserved.

One of the most striking aspects of the Mediterranean "Messinian Salinity Crisis" as observed in landbased sections, is the basin-wide synchronicity in facies change (Krijgsman et al., 1999a). The Messinian succession of the Caltanisetta Basin on Sicily serves as the classical standard for these facies changes, which can also be recognised elsewhere in the Mediterranean, i.e. on Cyprus, Crete, northern Italy and southern Spain. It starts with an alternation of open marine marls and sapropels, passes via diatomites into evaporitic limestones, gypsum and halite of the "Lower Evaporites" (of marine origin) and, following an erosional unconformity, ends with the "Upper Evaporites" and associated fresh to brackish water deposits of the Lago Mare that are essentially of non-marine origin and contain a caspi-brackish ostracode fauna. The erosional unconformity between the "Lower and Upper Evaporites" is assumed to reflect the phase of most extreme sea level drawdown in the Mediterranean that caused significant erosion and localised channel entrenchment on the continental shelves and slopes.

Three well-developed 10 Ma old sapropels from the island of Gavdos (Greece) were selected for a detailed geochemical, micropaleontological and sedimentological study. The sapropels are characterized by a high organic carbon and a low carbonate content. Productivity was higher during sapropel formation, as indicated by increased Ba contents and higher percentages of the planktonic foraminiferal species Neogloboquadrina acostaensis . Enrichment of Mo and V in the sapropels indicates less oxygenated bottom water conditions, which is supported by the flourishing of low oxygen tolerant benthic foraminifera. Variation in grainsize and the Ti/Al ratio point to an alternating dominance of fluvial (sapropels) and eolian-derived (homogeneous intervals) terrigenous clastics. Evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed-load type rivers. The increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion. The results obtained for the Gavdos sapropels are consistent with those of previous studies of younger sapropels and related CaCO 3 cycles in the Mediterranean. The consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 My, namely precession induced dry–wet oscillations in the Mediterranean climate. Still, the effect of this mechanism on the intensity of surface water productivity, dilution and diagenetic signals may differ from site to site, depending on location, depositional environment and intensity of the astronomical forcing.

A high-resolution cyclostratigraphy for the rhythmically bedded lignite‐marl sequences of the Lower Pliocene Ptolemais Formation is combined with 40 Ar= 39 Ar dating results of intercalated volcanic ash beds. Detailed field reconnaissance in three open-pit lignite mines reveals three end-member sediment types: lignites, composed primarily of organic material; grey marls, a mixture of carbonate and organic material; and beige marls, almost exclusively composed of carbonate. These lithologies are arranged in two basic types of sedimentary cycles: lignite‐grey marl and lignite‐beige marl cycles. A cyclostratigraphic composite section comprising 56 lignite‐marl cycles is constructed which combines the consistent cycle patterns from three parallel sections. The concordant positions of 20 volcanic ash beds in these sections confirm the cyclostratigraphic correlations and indicate that the lignite‐marl cycles result from regional, basin-wide forcing rather than lateral facies migrations. 40 Ar= 39 Ar ages on sanidine and biotite separates from nine volcanic ash beds were obtained by multiple total fusion and incremental-heating experiments. The 40 Ar= 39 Ar ages range between 5:00 0:05 and 4:04 0:04 Ma and are, in general, consistent with the stratigraphic order. A least-square linear regression using the measured 40 Ar= 39 Ar ages gives an average duration of 21:8 0:8 kyr per lignite‐marl cycle. Evidently, the lignite‐marl cycles in the Ptolemais Formation are linked to the precessional variation in the Earth’s orbit through its influence on Mediterranean climate. For the first time, 40 Ar= 39 Ar dating results, totally independent from any other dating and or tuning technique, confirm the astronomical theory of climate change. The 40 Ar= 39 Ar ages of the volcanic ash beds show a constant200 kyr (4.5%) age discrepancy with the astronomical ages of the same ash beds. This inconsistency remains difficult to explain. The discrepancy is unlikely to have resulted from erroneous astronomical ages, through incorrectness in the astronomical tuning, inaccuracies of the magnetostratigraphic data or the orbital time-series used, and=or errors in the APTS. The 40 Ar= 39 Ar dating results neither give clear indications for a possible source of error. From the excellent data set it is evident that neither loss of radiogenic 40 Ar, nor an underestimation of the contribution of Ca- and K-derived Ar isotopes could have caused the discrepancy. Moreover, the discrepancy is also beyond the errors in the systematic variables, like the decay constants of 40 K or the ages for the neutron-fluence monitors. © 1999 Elsevier Science B.V. All rights reserved.

The base of the Piacenzian Stage, representing the Lower Pliocene-Middle Pliocene boundary, has been recently defined and ratified by IUGS. The boundarystratotype is located in the Punta Piccola section (Sicily, Italy).

A high-resolution palynological study of the cyclically bedded Faneromeni section (upper Tortonian-lower Messinian) on Crete (Greece) is presented. This study aims to recognize orbitally-driven variations in the palynological record and to validate the age model based on the astronomical calibration of the sedimentary cycles. Four palynology-based environmental proxies were utilised using interpretations of fossil dinoflagellate associations based on modern ecological characteristics. Cross-spectral analysis between the proxy records and astronomical target curve, the 65°N summer insolation, yielded in most cases significant spectral power and coherence in the precession and/or obliquity frequency bands. Precession-controlled variations in the proxy records are related to lithology and indicate that maxima in continental input and minima in sea surface salinity coincide with sapropel formation. The influence of obliquity is most clearly reflected in the index of continental versus marine palynomorphs (S-D). The absence of a distinct time lag relative to obliquity indicates that the 41-kyr component in continental input is controlled by oscillations in regional Mediterranean climate rather than by glacial cyclicity. Phase relations in the different astronomical frequency bands of the spectrum, as compared with the Mediterranean Pliocene, essentially confirm the validity of the Miocene astronomical time scale. Finally, a major non-cyclic change in the palynological assemblage at 6.68 Ma indicates enhanced salinity and decreased river discharge. This shift coincides with a significant drop in sedimentation rate informally termed the “Early Messinian Sediment starvation Event”.

Uncertainties in the ages of the K–Pg boundary and the Fish Canyon sanidine (FCs) Ar–Ar sanidine dating standard, and in the number and tuning of 405-kyr eccentricity-related cycles, hamper the construction of a reliable tuned time scale for the Palaeogene, a critical time period marked by the occurrence of hyperthermals and the onset of ice-house conditions. Here, we present new results from integrated stratigraphic studies, including U–Pb, Ar–Ar, and astronomical intercalibration. These studies were conducted largely within the framework of the Marie Curie ITN GTSnext in an attempt to solve the discrepancies. Our results are overall consistent with an age of ~28.20 Ma for the FCs, the presence of 25 \(\times\) 405-kyr cycles in the Palaeocene, and an age of ~65.95 Ma for the K–Pg boundary.

For the first time, results of an integrated geochemical and micropalaeontological study of upper Miocene sapropelites in a land-based section in the Mediterranean are presented. Three sapropelites and adjacent homogeneous intervals in the Cretan Faneromeni section have been investigated in detail. The chemical and foraminiferal characteristics were found to be markedly similar to those of Plio-Pleistocene sapropelites. As the physiography and climate of the late Miocene Mediterranean were not fundamentally different from those of today, our preferred model for late Miocene sapropelite formation is similar to the one recently developed for Plio-Pleistocene sapropelites. Increased seasonality and freshwater input during northern hemisphere summer insolation maxima triggered high export production and oxygen consumption rates, which, in combination with a concomitant decrease in deep water formation rate, resulted in the observed high organic matter content of the sapropelites.

An astronomically calibrated timescale has recently been established (Hilgen, 1991 a, b) for the Pliocene and earliest Pleistocene based on the correlation of dominantly pre- cession controlled sedimentary cycles (sapropels and carbonate cycles) in Mediterranean ma- rine sequences to the precession time series of the astronomical solution of Berger and Loutre ( 1991 ) (hereinafter referred to as Ber90). Here we evaluate the accuracy of this timescale by (1) comparing the sedimentary cycle patterns with 65 oN summer insolation time series of dif- ferent astronomical solutions and (2) a cross-spectral comparison between the obliquity-related components in the 65 oN summer insolation curves and high-resolution paleoclimatic records derived from the same sections used to construct the timescale. Our results show that the car- bonate cycles older than 3.5 m.y. should be calibrated to one precession cycle older than previ- ously proposed. Application of the astronomical solution of Laskar ( 1990) (hereinafter refer- red to as La90) with present-day values for the dynamical ellipticity of the Earth and tidal dis- sipation by the Sun and Moon results in the best fit with the geological record, indicating that this solution is the most accurate from a geological point of view. Application of Ber90, or La90 solutions with dynamical ellipticity values smaller or larger than the present-day value, results in a less obvious fit with the geological record. This implies that the change in the plane- tary shape of the Earth associated with ice loadine$ and unloading near the poles during the last 5.3 million years was too small to drive the precession into resonance with the perturbation term, s-gt+g 5, of Jupiter and Saturn. Our new timescale results in a slight but significant modi- fication of all ages of the sedimentary cycles, bioevents, reversal boundaries, chronostrati- graphic boundaries, and glacial cycles. Moreover, a comparison of this timescale with the as- tronomical timescales of ODP site 846 (Shackleton et al., 1995a, b) and ODP site 659 (Tiede- mann et al., 1994) indicates that all obliquity-related

We propose a revised age calibration of the Messinian salinity crisis onset in the Mediterranean at 5.971 Ma based on the recognition of an extra gypsum cycle in the transitional interval of the Perales section (Sorbas basin, Spain) and the revision of the magnetostratigraphy of the Monticino section (Vena del Gesso basin, Italy). This age re-calibration allows to state more accurately that: (i) the interval encompassing the MSC-onset is continuous, thus ruling out any erosional feature or stratigraphic hiatus related to a major sea-level fall affecting the Mediterranean; (ii) the first gypsum was deposited during the summer insolation peak at 5.969 Ma associated with an eccentricity minimum and roughly coincident with glacial stage TG32; (iii) the MSC-onset was preconditioned by the tectonically-driven reduction of the hydrological exchanges with the Atlantic Ocean and finally triggered by glacial conditions in the northern hemisphere and by arid conditions in northern Africa.

An astronomical time scale is presented for the late Miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the Mediterranean to the 65”N summer insolation curve of La90 [ 1,2] with present-day values for the dynamical ellipticity of the Earth and tidd dissipation by the moon. This correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals, and planktonic foraminiferal and dinoflagellate events. The Tortonian/Messinian (T/M) boundary placed at the first regular occurrence of the Globorofuliu conomiozea group in the Mediterranean is dated at 7.24 Ma. The duration of the Messinian is estimated at 1.91 Myr because the Miocene/Pliocene boundary has been dated previously at 5.33 Ma [3]. The new time scale is confirmed by “OAr/ 3gAr ages of volcanic beds and by the number of sedimentary cycles in the younger part of the Mediterranean Messinian.

This report summarizes the international divisions and ages in the Geologic Time Scale, published in 2012 (GTS2012). Since 2004, when GTS2004 was detailed, major developments have taken place that directly bear and have considerable impact on the intricate science of geologic time scaling. Precam brian now has a detailed proposal for chronostratigraphic subdivision instead of an outdated and abstract chronometric one. Of 100 chronostratigraphic units in the Phanerozoic 63 now have formal definitions, but stable chronostratigraphy in part of upper Paleozoic, Triassic and Middle Jurassic/Lower Cretaceous is still wanting. Detailed age calibration now exist between radiometric methods and orbital tuning, making 40Ar-39Ar dates 0.64% older and more accurate. In general, numeric uncertainty in the time scale, although complex and not entirely amenable to objective analysis, is improved and reduced. Bases of Paleozoic, Mesozoic and Cenozoic are bracketed by analytically precise ages, respectively 541 0.63, 252.16 0.5, and 65.95 0.05 Ma. High-resolution, direct age-dates now exist for base-Carboniferous, base-Permian, base-Jurassic, base-Cenomanian and base-Eocene. Relative to GTS2004, 26 of 100 time scale boundaries have changed age, of which 14 have changed more than 4 Ma, and 4 (in Middle to Late Triassic) between 6 and 12 Ma. There is much higher stratigraphic resolution in Late Carboniferous, Jurassic, Cretaceous and Paleogene, and improved integration with stable isotopes stratigraphy. Cenozoic and Cretaceous have a refined magneto-biochronology. The spectacular outcrop sections for the Rosello Composite in Sicily, Italy and at Zumaia, Basque Province, Spain encompass the Global Boundary Stratotype Sections and Points for two Pliocene and two Paleocene stages. Since the cycle record indicates, to the best of our knowledge that the stages sediment fill is stratigraphically complete, these sections also may fulfill the important role of stage unit stratotypes for three of these stages, Piacenzian, Zanclean and Danian

High-resolution micropaleontological (planktonic foraminifera and calcareous nannofossils) and geochemical (stable isotopes, organic carbon, Fe, P, S, Ca, Ba, Mn, and Al) records are presented for the first sapropel-containing carbonate cycle in the Pliocene of Sicily. The carbonate cycle is characterized by a gray to white to beige to white color layering typical of the marls of the Trubi formation. A faintly laminated sapropel is intercalated in the gray-colored bed of the carbonate cycle. CaCO3 content varies from 40% in the beige to 45-50% in the white layers. Lowest CaCO3 content of 25–30% is found in the gray layer and sapropel. Variations in carbonate and organic matter percentages can best be explained by changes in paleoproductivity rather than by variations in dilution and dissolution. Total productivity was highest during deposition of the gray layer and sapropel, as indicated by high organic carbon and Ba contents and high abundance of Globorotalia puncticulata. Carbonate production reached its highest values, however, during deposition of the white layers, as evidenced by enhanced abundances of planktonic foraminifera and nannofossils. The low carbonate content in the gray layer and sapropel is explained in terms of a collapse in carbonate production caused by extreme changes in the physical and biochemical properties of the water column, which in turn resulted in siliceous plankton and opportunistic foraminifers such as Globorotalia puncticulata outcompeting most calcareous organisms. The beige layer represents a low-productivity environment similar to the present-day eastern Mediterranean basin. Several mechanisms have previously been proposed to explain variations in productivity in the eastern Mediterranean. Both sapropels and gray layers were deposited at times when perihelion occurred in northern hemisphere summer. We envisage that the increase in seasonal contrast resulting from this orbital configuration enhanced winter mixing and stabilization of the water column during summer, both leading to favorable conditions for intensification of the spring bloom. In addition, a decrease in excess evaporation, as can be deduced from the δ18O record, led to shoaling of the pycnocline and reduced circulation, thus enhancing the availability of nutrients in the photic zone. Finally, enhanced precipitation and associated runoff should have caused an increase in river-borne nutrients.

Sedimentary cycles in an upper Miocene succession of hemipelagic sediments (marls) and laminites (sapropels) were deposited in an outerarc basin and are related to the astronomical cycles of precession and eccentricity. Individual marl-laminite couplets correspond with the cycle of precession which has a periodicity of about 22 kyr. The lower part of the succession contains a turbidite interval comprising a number of distinct turbidite sequences. The turbidite sequences occur within or substitute entirely the laminite beds, so that turbidite deposition is similarly precession punctuated. The turbidite facies is characteristic for small, prograding fan lobes fed by small-volume turbidites. The abundant plant remains, the local palaeogeographic setting and the association with laminites (related to wet climate) suggest a river-fed submarine fan-lobe, where the timing of sediment transport is largely controlled by river floods during periods of high precipitation and continental run-off. The onset and ending of the turbidite interval is most likely linked with either autocyclic processes or by tectonic steepening of the hinterland relief. Sea-level changes seem least important for the triggering of turbidites, which is in contrast with current beliefs.

Jorissen, F.J., Asioli, A., Borsetti, A.M., Capotondi, L., De Visser, J.P., Hilgen, F.J., Rohling, E.J., Van der Borg, K., Vergnaud Grazzini, C. and Zachariasse, W.J., 1993. Late Quaternary central Mediterranean biochronology. Mar. MicropaleontoL, 21: 169-189. A high-resolution biochronology is presented for the Late Quaternary of the central Mediterranean. In the Late Pleistocene-Holocene successions three assemblage zones are distinguished on the basis of frequency patterns of planktic foraminifera. The age of these zones is determined by Accelerator Mass Spectrometry (AMS) t4C dating. The zonal boundaries are dated at 12,700 yr B.P. (the end of Termination la) and 9600 yr B.P. (the start of Termination Ib), respectively. The AMS dates show that major changes in the planktic and benthic realms occurred synchronously over wide areas, although records of individual species may show important regional differences. In the studied areas, resedimentation processes revealed by anomalous successions of 14C dates, play a far more important role than indicated by the sedimentological and micropaleontological data. Possibly these processes contribute to the very high accumulation rates in the glacial Zone IlL Although the AMS technique has increased the accuracy of laC-measurements, of older carbonate may still lead to substantial age differences between areas with different sedimentary regimes.

Results from transient climate modeling experiments indicate an in-phase relationship between insolation forcing and Indian summer monsoonal precipitation. This is in contrast to high-resolution radioisotopically dated speleothem oxygen isotope (δ18O) records of China, which showed that East Asian Monsoon maxima lag Northern Hemisphere peak summer insolation by ∼2,700 years, while an approximately 8,000-year time lag was derived from late Pleistocene records of Arabian Sea sediments. Here, we evaluate the precession phase of the Arabian Sea signal by comparing a new high-resolution productivity and oxygen minimum zone (OMZ) intensity record from the Arabian Sea over the past 450,000 years with the results of a transient climate modeling experiment that includes glacial-bound ice volume variations. The well established tuning technique between radioisotopically dated North Atlantic cold events and the occurrence of deep-dwelling planktonic foraminifera in the Arabian Sea for the last glacial cycle was used to extend the Arabian Sea chronology, independent of orbital tuning. Cross-spectral analysis over the last 224,000 years reveals that Arabian Sea productivity maxima lag precession minima by ∼6,900 ± 200 years, i.e., in close agreement with previous reconstructions. Also our climate modeling simulations are in accord with previous studies indicating an in-phase relationship between precession minima and maximum summer monsoon intensity. We argue that the summer monsoon is most likely not the main driver of changes in Arabian Sea biological productivity and OMZ intensity at the precession frequency band, but that changes in the intensity of the Atlantic meridional overturning circulation (AMOC) have played the prominent role in controlling the nutrient delivery into the euphotic layer of the northern Indian Ocean, and hence the amount of primary productivity and intensity of the oxygen minimum zone in the Arabian Sea. Such a mechanism explains the large precession-related time lag between minimum precession and maximum productivity and OMZ conditions in the Arabian Sea, since intensified AMOC occurred during precession maxima.

Principal Component Analysis of late Pliocene to early Pleistocene planktonic foraminiferal abundances from the Mediterranean yielded two significant components which represent first order approximations for sea surface productivity and temperature. This interpretation is confirmed by the good fit between the score plots and sea surface productivity and sea surface temperature proxy records based on selected eutrophic and temperature-sensitive species using present-day habitat characteristics. Spectral analysis revealed significant peaks in the orbital frequency bands of the spectrum suggesting that variations in sea surface productivity and temperature are controlled by the quasi-periodic variations in the Earth's orbit. Precession-forced variations are reflected primarily in sea surface productivity and to a lesser degree in sea surface temperature. Maxima in sea surface productivity and temperature in this frequency band occurred at times of sapropel formation. The sea surface productivity maxima can be explained by an increased input of river-borne nutrients and by the shoaling of the pycnocline and the associated intensification of the Deep Chlorophyll Maximum (DCM) layer. Precession-forced variations in sea surface temperature are not related to glacial cycles since this frequency component is almost completely absent in ice volume proxy records for this time interval. Sapropel-bound sea surface temperature maxima presumably reflect periods of maximum insolation during the Northern Hemisphere summer. The contrasting winter signal corresponds to minimum insolation values which may be reflected by peak abundances ofGloborotalia inflata. Obliquity-forced variations are reflected primarily in sea surface temperature and not in sea surface productivity. These temperature fluctuations correspond with ice volume changes registered in the oxygen isotope record at the North Atlantic DSDP Site 607. This shows that obliquity-forced sea surface temperature variations in the Mediterranean are primarily driven by glacial cycles.

[1] An integrated high-resolution stratigraphy and orbital tuning is presented for the Loulja sections located in the Bou Regreg area on the Atlantic side of Morocco. The sections constitute the upward continuation of the upper Messinian Ain el Beida section and contain a well-exposed, continuous record of the interval straddling the Miocene-Pliocene (M-P) boundary. The older Loulja-A section, which covers the interval from ~5.59 to 5.12 Ma, reveals a dominantly precession-controlled color cyclicity that allows for a straightforward orbital tuning of the boundary interval and for detailed cyclostratigraphic correlations to the Mediterranean; the high-resolution and high-quality benthic isotope record allows us to trace the dominantly obliquity-controlled glacial history. Our results reveal that the M-P boundary coincides with a minor, partly precession-related shift to lighter “interglacial” values in d18O. This shift and hence the M-P boundary may not correlate with isotope stage TG5, as previously thought, but with an extra (weak) obliquity-controlled cycle between TG7 and TG5. Consequently, the M-P boundary and basal Pliocene flooding of the Mediterranean following the Messinian salinity crisis are not associated with a major deglaciation and glacio-eustatic sea level rise, indicating that other factors, such as tectonics, must have played a fundamental role. On the other hand, the onset of the Upper Evaporites in the Mediterranean marked by hyposaline conditions coincides with the major deglaciation step between marine isotope stage TG12 and TG11, suggesting that the associated sea level rise is at least partly responsible for the apparent onset of intermittently restricted marine conditions following the main desiccation phase. Finally, the Loulja-A section would represent an excellent auxiliary boundary stratotype for the M-P boundary as formally defined at the base of the Trubi marls in the Eraclea Minoa section on Sicily.

International audience; The Late Pliocene to Middle Pleistocene coastal sediments of northeastern Rhodes (Greece) were deposited in an active tectonic setting. They provide an excellent opportunity to investigate the relative roles played by climate and tectonics in sedimentary processes. The tectono-sedimentary organization of these deposits is revised in the light of an integrated study combining data from field investigations, sedimentology, bio- and magnetostratigraphy, radiometric dating, palaeoecology, and palynology. Three lithostratigraphic units are recognised: the Rhodes Formation, the newly defined Ladiko–Tsampika Formation, and the Lindos Acropolis Formation. A major erosional surface separates the Rhodes Formation from the Ladiko–Tsampika Formation, which was deposited in deep and narrow palaeovalleys. The Rhodes Formation (Late Pliocene to 1.4–1.3 Ma) comprises three Members: the Kritika, the Lindos Bay clay and the Cape Arkhangelos calcarenite. The shallow-water clastic sediments of the Ladiko–Tsampika Formation (1.3 to 0.3 Ma) are subdivided into two Members: the Ladiko (mostly sandy) and the Tsampika (predominantly clayey). The Lindos Acropolis Formation is Late Pleistocene in age. Two major transgression–regression cycles occurred prior to the Lindos Acropolis cycle. The deposition of the first cycle (Rhodes Formation) is tectonically controlled, with very high rates of vertical movements (2.6–5.2 mm/year). The second cycle (Ladiko–Tsampika Formation) records sea-level changes controlled by slow vertical motions (around 0.16 mm/year) and glacioeustatic events with 40-kyr and 100-kyr periods. Finally, the tectonic and sedimentary evolution of Rhodes is integrated into the geodynamic context of the eastern Aegean fore-arc.

Recent developments in integrated high-resolution stratigraphy and astronomical tuning of continuous deep marine successions invalidate arguments against the designation of unit stratotypes for global stages, the basic building blocks of the standard Global Chronostratigraphic Scale (GCS). For the late Neogene, Global Stratotype Section and Point (GSSP) sections may also serve as unit stratotypes, covering the interval from the base of a stage up to the level that–time-stratigraphically–correlates with the base of the next younger stage in a continuous and well-tuned deep marine succession. The added value of such sections as unit stratotype lies in the integrated high-resolution stratigraphy and astronomical tuning, which combined, provides an excellent age control with an unprecedented resolution, precision and accuracy within the entire stage. As such they form the backbone of the new integrated late Neogene time scale and provide the basis for reconstructing Earth's history. In this way a stage is also defined by its content and not only by its boundaries. Our unit stratotype concept strengthens the importance of time-rock units by allowing the introduction of astronomically defined chronozones as formal chronostratigraphic units, thereby arguing against the elimination of the dual classification of chronostratigraphy and geochronology. Extending this concept to older time intervals requires that well-tuned, continuous deep marine sections are employed, thus necessitating the employment of multiple hole (I)ODP sites for defining (remaining) stages and stage boundaries in at least the Cenozoic and Cretaceous and possibly the entire Mesozoic. Evidently the construction of the Geological Time Scale (including the GCS) should be based on the most appropriate sections available while, where possible, taking the historical concept of global stages into account.

[1] High-resolution benthic and planktonic stable oxygen isotope records are presented for the upper Miocene Ain el Beida (AEB) section in northwestern Morocco and reveal the clear imprint of the (climatic) precession, obliquity, and eccentricity cycles in the interval between 6.5 and 5.5 Ma. The δ18O depth series were transformed into time series using astronomical tuning of the sedimentary color cycles to the 65°N summer insolation curve of the La93 solution with present-day values for tidal dissipation and dynamical ellipticity. Spectral analysis and band-pass filtering show that the ratios of the astronomically related spectral peaks are not consistent in the depth and time domain. The inconsistencies are mainly due to variations in sedimentation rate that are positively correlated with precession amplitude (i.e., modulated by eccentricity). In addition, they result from a long-term trend in sedimentation rate. A simple model of nonlinear response of the sedimentation rate to the eccentricity modulation of precession was used to simulate the observed shifts in the relative position of the spectral peaks in the depth domain. Cross-spectral analysis was carried out on the δ18O time series and a combined eccentricity, tilt (obliquity), and precession (ETP) curve. The precession-controlled δ18O signal varies in-phase with ETP partly as a result of the tuning procedure, while the obliquity related signal reveals a small lag of 2–3 kyr relative to obliquity. This lag is slightly reduced at the time of the Messinian Salinity Crisis (MSC) and increases to 5–6 kyr if the tidal dissipation term in the astronomical solution is reduced to half its present-day value. The obliquity-related lag is most likely associated with the slow buildup of ice caps, whereas the precession signal is interpreted as to dominantly reflect regional climate changes comparable to those associated with Mediterranean sapropels. Finally, the benthic δ18O record is compared with open ocean records and discussed in terms of an astronomically tuned oxygen isotope stratigraphic framework.

We present new 40 Ar/ 39 Ar data for sanidine and biotite derived from volcanic ash layers that are intercalated in Pliocene and late Miocene astronomically dated sequences in the Mediterranean with the aim to solve existing inconsistencies in the intercalibration between the two independent absolute dating methods. 40 Ar/ 39 Ar sanidine ages are systematically younger by 0.7-2.3% than the astronomical ages for the same ash layers. The significance of the discrepancy disappears except for the upper Ptolemais ashes, which reveal the largest difference, if an improved full error propagation method is applied to calculate the absolute error in the 40 Ar/ 39 Ar ages. The total variance is dominated by that of the activity of the decay of 40 Kt o 40 Ar (f70%) and that the amount of radiogenic 40 Arp in the primary standard GA1550 biotite (f15%). If the 40 Ar/ 39 Ar ages are calculated relative to an astronomically dated standard, the influence of these parameters is greatly reduced, resulting in a more reliable age and in a significant reduction of the error in 40 Ar/ 39 Ar dating. Astronomically calibrated ages for Taylor Creek Rhyolite (TCR) and Fish Canyon Tuff (FCT) sanidine are 28.53F0.02 and 28.21F0.04 Ma (F1 S.E.), respectively, if we start from the more reliable results of the Cretan A1 ash layer. The most likely explanation for the large discrepancy found for the younger Ptolemais ash layers (equivalent to FCT of 28.61 Ma) is an error in the tuning of this part of the sequence. D 2004 Elsevier B.V. All rights reserved.

A much improved high-resolution integrated stratigraphy (calcareous plankton biostratigraphy, magnetostratigraphy, cyclostratigraphy) is presented for the classic section of Oued Akrech (Atlantic Morocco) straddling the Tortonian^Messinian boundary. Magnetobiostratigraphic correlations with time-equivalent and astronomically dated sections in the Mediterranean indicate that cyclic alternations of indurated light beige coloured marls and softer, more clayey and reddish coloured marls are dominantly precession-controlled. Characteristic sedimentary cycle patterns, in particular those reflecting precession^obliquity interference, allow for one possible tuning, thus providing accurate astronomical ages for cycles, calcareous plankton events and magnetic reversals. The tuning further indicates that the reddish layers are the equivalent of sapropels in the Mediterranean. The Messinian Global boundary Stratotype Section and Point (GSSP) has recently been formally defined at the base of the reddish layer of cycle No. 15 in section Oued Akrech. This level coincides closely with the first regular occurrence of the Globorotalia miotumida group and is astronomically dated at 7.251 Ma. The global correlation potential is guaranteed by the straightforward calibration of the Oued Akrech magnetostratigraphy to the geomagnetic polarity time scale, locating the GSSP within C3Br.1r. In the marine realm the calcareous nannofossil genus Amaurolithus provides a series of extremely useful events to delimit the boundary on a global scale. The astronomical tuning guarantees a direct first-order calibration of the Messinian GSSP to the standard geological time scale once, as anticipated, the late Miocene part of the astronomical time scale has been incorporated. fl 2000 Elsevier Science B.V. All rights reserved.