The recommendation that the Anthropocene be denoted as a geological epoch was recently rejected by the International Union of Geological Sciences. Here, we compare the scientific rationales presented for the Anthropocene, the Holocene and the six other epochs in the Cenozoic Era: the Pleistocene, the Pliocene, the Miocene, the Oligocene, the Eocene and the Paleocene. We also present a historical perspective on the process through which the Holocene was accepted as a formal geological epoch. We conclude that, from a purely geological perspective, the scientific case for the Anthropocene as a geological epoch is stronger than the case for the Holocene and as good as or better than the cases for several other epochs in the Cenozoic Era.

Understanding temporal shifts of thrust transport direction and the interplay between thrusting and normal faulting during mountain building is important for better understanding orogeny. Current tectonic models of the Alps envisage Cretaceous E–W directed thrusting and subsequent extension in the same direction, mainly preserved in the upper plate (Austroalpine unit), followed by Paleogene N–S shortening. The Austroalpine-Pennine boundary region is at the transition between dominantly E–W and N–S directed orogenic movements. This study focuses on metabasite rocks of the Pennine Avers nappe, which retain evidence for early E–W directed shortening extending into the Eocene, thus conflicting with the standard orogenic models. Our new kinematic and geochronological constraints from the Avers nappe demonstrate that top-to-the-W nappe imbrication progressed into the South Pennine realm under blueschist facies conditions. Rb–Sr multimineral isochron ages constrain the waning stages of top-to-the-W shear between 47.26 ± 0.26 and ≥ 43.5 ± 0.6 Ma (2σ uncertainties). Subsequent deformation during incipient decompression from blueschist-facies metamorphism associated with N–S shearing occurred between 41.1 ± 1.7 and 40.7 ± 1.6 Ma. A summary of previously published geochronological and kinematic data shows that Cretaceous to Eocene (until ≥ 43.5 ± 0.6 Ma) deformation is best described by an overcritically tapered orogenic wedge model. The subsequent deep underthrusting and underplating of the distal European margin is considered to have caused a change in orogenic wedge dynamics, leading to extruding wedge tectonics associated with N–S shortening.

The aim of this study is to investigate the utility of speculative, fictional utopian narratives to be used as a comparative and critical tool to expose taken for granted ideas, discourses and norms in the five shared socioeconomic pathways (SSP1–5) that are used by the IPCC to build future scenarios. To achieve this goal, we first invited citizens to write stories about fictional utopian futures, which they perceived as good for “both people and the planet”. We then compared these utopian stories with the SSPs by (1) a semi-quantitative thematic analysis, and (2) a critical literary analysis. Based on the thematic analysis, we found strong similarities between the utopian futures and SSP1 (“Taking the Green Road”) at a superficial level. Based on the literary analysis, we found that this apparent similarity obscured fundamental differences between the implicit mindsets that was found in SSP1 and the utopian futures; with the former underpinned by collective anthropocentrism and the latter by collective ecocentrism. We conclude that speculative utopias, that are not bound by the requirement of perceived plausibility, can provide a powerful tool to scrutinize and extend science-based future scenarios, such as the SSPs, to consider other aspects, such as different mindsets and norm-breaking solutions.

Faults within layered basaltic sequences significantly influence hydrothermal fluid flow in shallow geothermal reservoirs and potentially during CO2 sequestration and storage. Nevertheless, their characterization regarding fault zone architecture, fluid flow, deformation mechanisms, and seismic potential remains underdeveloped. This study addresses this gap by integrating structural and microstructural observations with X-ray diffraction analyses of exposed normal-transtensional faults associated with the seismically active Húsavík-Flatey Fault in the Tjörnes Fracture Zone, Northern Iceland. Our findings demonstrate that the evolution of basalt-hosted normal-transtensional faults progresses through distinct stages: (1) low-displacement fault propagation from pre-existing cooling joints; (2) fault linkage via dilational jogs; (3) damage zone/fault core growth through brecciation and cataclastic processes; (4) shear localization along sharp slip surfaces; and (5) smearing of volcaniclastic interbeds along the principal fault plane. Evidence of shear localization, truncated clasts, and hydrothermal breccias/veins suggests repeated seismic slip events facilitated by overpressured fluids. Conversely, the presence of clay-rich foliated cataclasite indicates aseismic slips during interseismic periods. Slip along fault jogs, bends, geometric irregularities, and orientation changes causes the dilatant opening of the fault planes and extensional horsetail fractures at fault tips. These structures create main tabular zones for lateral movement of hydrothermal fluids parallel to the fault strike in shallow geothermal reservoirs situated in active extensional-transtensional tectonic settings. In addition, the dilational jogs and the intersection of horsetail veins with the hosting faults may define linear zones of high structural permeability and intense localized fluid flow parallel to the σ2 paleostress orientation and finally mineral precipitation. The results of this study can be utilized to improve models of geothermal fluid flow for enhanced recovery in basaltic reservoirs and assess seismic risk in basaltic faults.

Reconstructions of palaeoseismicity are useful for understanding and mitigating seismic hazard risks. We apply cosmogenic ³⁶Cl exposure-age dating and measurements of rare-earth elements and yttrium (REE-Y) concentrations to the palaeoseismic history of the Sparta Fault, Greece. Bayesian-inference Markov chain Monte Carlo (MCMC) modelling of ³⁶Cl concentrations along a 7.2 m long vertical profile on the Sparta Fault scarp at Anogia indicate an increase in the average slip rate of the scarp from 0.8–0.9 mm yr⁻¹ 6.5–7.7 kyr ago to 1.1–1.2 mm yr⁻¹ up to the devastating 464 BCE earthquake. The average exhumation of the entire scarp up to the present day is 0.7–0.8 mm yr⁻¹. Modelling does not indicate additional exhumation of the Sparta Fault after 464 BCE. The Sparta Fault scarp is composed of fault breccia, containing quartz and clay-lined pores, in addition to host-rock-derived clasts of calcite and microcrystalline calcite cement. The impurities control the distribution of REE-Y in the fault scarp surface and contribute spatial variation to ³⁶Cl concentrations, which precludes the identification of individual earthquakes that have exhumed the Sparta Fault scarp from either of these data sets. REE-Y may illustrate processes that localize slip to a discrete fault plane in the Earth's near-surface, but their potential use in palaeoseismicity would benefit from further evaluation.

An advance has been made towards a method for forecasting earthquakes several months before they occur. The method relies on changes of groundwater chemistry as earthquake precursors. In a study published in 2014, we showed that changes of groundwater chemistry occurred prior to and were associated with two earthquakes of magnitude 5 and higher, which affected northern Iceland in 2012 and 2013. Here we test the hypothesis that similar or larger earthquakes could have been forecast in the following decade (i.e. 2014–2023) based on our published findings. We found that we could have forecast one of the three greater than magnitude 5 earthquakes that occurred. Noting that changes of groundwater chemistry were oscillatory, we infer expansion and contraction of the groundwater source region caused by coupled crustal dilation and fracture mineralisation associated with the stress build-up before earthquakes. We conclude by proposing how our approach could be implemented elsewhere.

Naxos in the Greek Cyclades preserves a type example of polymetamorphism. The southern and northern parts of the island record different Tertiary P–T histories between Eocene and Miocene times, including a blueschist facies event, one or more amphibolite/greenschist facies overprint(s) and contact metamorphism. Age attributions for these events are inconsistent in the literature. Here, we propose a new approach that combines electron probe microanalyzer (EPMA) characterization of the white mica (WM) with ³⁹Ar-⁴⁰Ar–Rb-Sr multichronometry. Textural–petrographic–compositional observations reveal that the polygenetic WM consists of five different generations: pre-Eocene relicts, paragonite, high-Si phengite, low-Si phengite and muscovite. EPMA mapping of four WM samples, previously analysed by Rb-Sr, reveals major element compositions heterogeneous down to the μm scale. Each WM consists of chemically distinct generations, documenting submicron-scale retrogression of high-pressure (HP) phengite grains to muscovite. Four WM samples from a N-S traverse across the island were analysed by ³⁹Ar-⁴⁰Ar stepheating, comparing coarse and fine sieve size fractions to obtain overdetermined K-Ar systematics. Fine sieve fractions are richer in Cl than coarse ones. Linear arrays in Cl/K-age isotope correlation diagrams show two predominant WM generations (one Cl-poor at ca. 38 Ma and one Cl-rich at <20 Ma). A lower-grade sample from southern Naxos was less pervasively recrystallized, provides older ages and preserves at least three WM generations, including a relict WM with a pre-Palaeocene K-Ar age, consistent with the high Ar retentivity of WM in the absence of complete recrystallization. The age of the Cl-poor end-member WM approximates the age of the HP event, 38 Ma. Ar inheritance in Cretaceous mica relicts is heterogeneous at the single-grain scale. Comparing the degassing rates of the WM fractions rules out ‘multidomain’ diffusion. As no sample is monomineralic, the degassing rate of each polygenetic mica is instead controlled by the mass balanced sum of the unrelated rate constants of its constituent minerals. Given the commonness of zoned and composite micas, the approach detailed here is potentially useful for reconstructing polyphase metamorphic histories worldwide. 

Marine sedimentary rocks deposited across the Neoproterozoic Cryogenian Snowball interval, similar to 720-635 million years ago, suggest that post-Snowball fertilization of shallow continental margin seawater with phosphorus accelerated marine primary productivity, ocean-atmosphere oxygenation, and ultimately the rise of animals. However, the mechanisms that sourced and delivered bioavailable phosphate from land to the ocean are not fully understood. Here we demonstrate a causal relationship between clay mineral production by the melting Sturtian Snowball ice sheets and a short-lived increase in seawater phosphate bioavailability by at least 20-fold and oxygenation of an immediate post-Sturtian Snowball ocean margin. Bulk primary sediment inputs and inferred dissolved seawater phosphate dynamics point to a relatively low marine phosphate inventory that limited marine primary productivity and seawater oxygenation before the Sturtian glaciation, and again in the later stages of the succeeding interglacial greenhouse interval.

The low enthalpy (T < 150 °C) groundwater in the HA01 borehole at Hafralækur has a long time series (2008–2018) of chemical and isotopic data. In the previous studies, the variations in chemical and isotope parameters were statistically related to seismic activity. However, the possible effect of temperature has not yet been evaluated. To fill this gap, the results obtained from the classical geothermometric equations (silica solid phases, Na/K, Na-K-Ca) were compared. However, considering that the use of classical geothermometry using the Na/K ratio or silica solid phases solubility is limited by the presence of clay minerals and alkaline conditions (i.e., the presence of pH-dependant silicate anions), new equilibria reactions between labradorite, zeolites (analcime, stilbite) and the activity of the dissolved species in the fluid are presented to overcome this problem. In addition, kinetic reaction path models are presented to trace the possible role of both temperature and CO₂ during the most evident chemical variations during earthquakes.

We analysed temporal variations of trace element concentrations in groundwater from a 101 m-deep borehole (HA01) in northern Iceland during 2010–2018 and compared them with seismic and volcanic events that occurred in the same period to identify potential hydrogeochemical precursors. An increase of B, Al, V, Li and Mo concentrations started from eight months to one month before the 2014 Bárðarbunga eruption (~115 km from HA01), a major rifting event in central Iceland, while Ga and V concentrations began to increase one day and one month after the onset of the event, respectively. We also found that concentrations of some trace elements (Li, B, Ga, Mo, Sr, Rb and Fe) significantly increased before an M_w 5.0 earthquake that occurred ~80 km from the borehole in 2018. However, other notable hydrogeochemical changes were detected during the monitoring period without apparent correlation with the seismic and volcanic events in the region. This study shows that the systematic long-term hydrogeochemical monitoring in seismic and volcanic areas is critical to advance the science of seismic and eruptive precursors. Furthermore, the use of statistical tools, such as Principal Component Analysis (PCA) and Change Point (CP) detection can help identify the most useful chemical elements and validate the trend variability of those elements in the time series, reducing arbitrary choices of pre-seismic and pre-volcanic hydrogeochemical anomalies as potential precursors.