Klaudia F. Kuiper

Synchronizing rock clocks of Earth history.

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 40Ar/39Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40Ar/39Ar geochronology. This calibration results in a more precise older age of 28.201 ± 0.046 million years ago (Ma) and reduces the 40Ar/39Ar methods 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.

Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary

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. Radiometric dating establishes the mass extinction that killed the dinosaurs as synchronous with a large asteroid impact. [Also see Perspective by Pälike] Mass extinctions manifest in Earths geologic record were turning points in biotic evolution. We present 40Ar/39Ar data that establish synchrony between the Cretaceous-Paleogene boundary and associated mass extinctions with the Chicxulub bolide impact to within 32,000 years. Perturbation of the atmospheric carbon cycle at the boundary likely lasted less than 5000 years, exhibiting a recovery time scale two to three orders of magnitude shorter than that of the major ocean basins. Low-diversity mammalian fauna in the western Williston Basin persisted for as little as 20,000 years after the impact. The Chicxulub impact likely triggered a state shift of ecosystems already under near-critical stress.

Age of the Badenian salinity crisis; impact of Miocene climate variability on the circum-Mediterranean region

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 40 Ar/ 39 Ar 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.

Stratigraphic continuity and fragmentary sedimentation: the success of cyclostratigraphy as part of integrated stratigraphy

Abstract The Milankovitch theory of climate change is widely accepted, but the registration of the climate changes in the stratigraphic record and their use in building high-resolution astronomically tuned timescales has been disputed due to the complex and fragmentary nature of the stratigraphic record. However, results of time series analysis and consistency with independent magnetobiostratigraphic and/or radio-isotopic age models show that Milankovitch cycles are recorded not only in deep marine and lacustrine successions, but also in ice cores and speleothems, and in eolian and fluvial successions. Integrated stratigraphic studies further provide evidence for continuous sedimentation at Milankovitch time scales (104 years up to 106 years). This combined approach also shows that strict application of statistical confidence limits in spectral analysis to verify astronomical forcing in climate proxy records is not fully justified and may lead to false negatives. This is in contrast to recent claims that failure to apply strict statistical standards can lead to false positives in the search for periodic signals. Finally, and contrary to the argument that changes in insolation are too small to effect significant climate change, seasonal insolation variations resulting from orbital extremes can be significant (20% and more) and, as shown by climate modelling, generate large climate changes that can be expected to leave a marked imprint in the stratigraphic record. The tuning of long and continuous cyclic successions now underlies the standard geological time scale for much of the Cenozoic and also for extended intervals of the Mesozoic. Such successions have to be taken into account to fully comprehend the (cyclic) nature of the stratigraphic record.

A metrological approach to measuring 40Ar* concentrations in K-Ar and 40Ar/39Ar mineral standards

In geochronology, isotopic ages are determined from the ratio of parent and daughter nuclide concentrations in minerals. For dating of geological material using the K-Ar system, the simultaneous determination of 40Ar and 40K concentrations on the same aliquot is not possible. Therefore, a widely used variant, the 40Ar/39Ar technique, involves the production of 39Ar from 39K by neutron bombardment and the reliance on indirect natural calibrators of the neutron flux, referred to as “mineral standards.” Many mineral standards still in use rely on decades-old determinations of 40Ar concentrations; resulting uncertainties, both systematic and analytical, impede the determination of higher accuracy ages using the K-Ar decay system. We discuss the theoretical approach and technical design of a gas delivery system which emits metrologically traceable amounts of 40Ar and will allow for the sensitivity calibration of noble gas mass spectrometers. The design of this system is based on a rigorous assessment of the uncertainty budget and detailed tests of a prototype system. A number of obstacles and proposed resolutions are discussed along with the selection of components and their integration into a pipette system.

Onset of Maikop sedimentation and cessation of Eocene arc volcanism in the Talysh Mountains, Azerbaijan

Abstract 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. Supplementary material: The full analytical data of the Ar–Ar dating are available at http://www.geolsoc.org.uk/SUP18851

Palaeomagnetic and geochronological evidence for a major middle Miocene unconformity in Söke Basin (western Anatolia) and its tectonic implications for the Aegean region

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 Söke Basin located at the southeastern rim of the İzmir–Balıkesir 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 Söke 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 İzmir–Balıkesir 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 40Ar/39Ar 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

The provenance of the Devonian Old Red Sandstone of the Dingle Peninsula, SW Ireland; the earliest record of Laurentian and peri-Gondwanan sediment mixing in Ireland

The Lower Old Red Sandstone in southern Ireland is hosted in the Early Devonian Dingle Basin, which lies immediately south of the Iapetus Suture on the Dingle Peninsula, County Kerry. The basin developed as a post-Caledonian pull-apart structure prior to Acadian deformation, which in turn was followed by end-Carboniferous Variscan deformation. Detrital zircon U–Th–Pb geochronology is complemented by mica Ar–Ar and apatite U–Pb geochronology to gain a comprehensive understanding of the provenance of the Lower Devonian Lower Old Red Sandstone of the Dingle Basin and assess contributions of major tectonic components (e.g. Laurentia, Ganderia). Sedimentary rocks in the Lower Old Red Sandstone have similar detrital zircon age distributions, which are dominated by c. 1.2 Ga zircons as well as late Neoproterozoic grains. This indicates a dominant contribution of detritus of Laurentian affinity as well as contributions from westerly and southerly derived Ganderian detritus. Caledonian uplift of the area north of the Iapetus Suture would have facilitated a large contribution of (peri-)Laurentian material. The Upper Old Red Sandstone on the Dingle Peninsula has a distinctly different detrital zircon character including few late Neoproterozoic zircons and abundant zircons of c. 1.05 Ga age, indicating sediment derivation only from Laurentia and no recycling from the Lower Old Red Sandstone. Supplementary material: The full detrital U–Pb zircon and apatite analytical dataset and the revised detrital mica age dataset are available at https://doi.org/10.6084/m9.figshare.c.3971862