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Sand spikes, pin-shaped, carbonate-cemented sandstone bodies of variable size widely interpreted as sedimentary concretions, have been enigmatic for nearly two centuries. We here present a high-energy mechanism for their formation. Two classic sand spike occurrences are found in the North Alpine Foreland Basin of Central Europe and at Mount Signal in southern California, USA. A distinct seismite horizon in Mid-Miocene Molasse sediments of southern Germany, genetically linked with the Ries impact event, exhibits dewatering structures and contains numerous sand spikes with tails systematically orientated away from the Ries crater. Sand spikes at Mount Signal, strikingly similar in shape to those found in Germany, have tails that point away from the nearby San Andreas Fault. Based on their structural and stratigraphic context, we interpret sand spikes as a new type of seismite and a promising tool to identify strong impact-induced or tectonic palaeo-earthquakes and their source regions in the geologic record. Sand spikes, sandstone bodies that have been enigmatic for nearly two centuries, represent a new type of seismite and a promising tool to identify strong impact-induced or tectonic paleo-earthquakes and their source regions in the geologic record.

The Nördlinger Ries and the Steinheim Basin are widely perceived as a Middle Miocene impact crater doublet. We discovered two independent earthquake-produced seismite horizons in North Alpine Foreland Basin deposits potentially related to both impacts. The older seismite horizon, demonstrated to be associated with the Ries impact, is overlain by distal impact ejecta in situ, forming a unique continental seismite-ejecta couplet within a distance of up to 180 km from the crater. The younger seismite unit, also produced by a major palaeo-earthquake, comprises clastic dikes that cut through the Ries seismite-ejecta couplet. The clastic dikes may have formed in response to the Steinheim impact, some kyr after the Ries impact, in line with paleontologic results that indicate a time gap of about 0.5 Myr between the Ries and Steinheim events. This interpretation suggests the Ries and Steinheim impacts represent two temporally separate events in Southern Germany that, thus, witnessed a double disaster in the Middle Miocene. The magnitude–distance relationship of seismite formation during large earthquakes suggests the seismic and destructive potential of impact-induced earthquakes may be underestimated.

For decades, the Nördlinger Ries and Steinheim Basin in southern Germany have been regarded as a textbook example of a terrestrial impact crater doublet, although the oldest crater lake deposits in both craters suggest a biostratigraphic age difference of ~ 0.5 to 1 Myr. We previously presented stratigraphic arguments that challenged the double impact scenario and favoured a model of two temporally independent impact events in the Mid-Miocene. We here present, for the first time, four localities within a distance of ~ 50–100 km from the Ries and ~ 50–70 km from the Steinheim crater that expose two independent seismite horizons, together unique within the Upper Freshwater Molasse of the North Alpine Foreland Basin, each one featuring impressive water escape structures. The seismite horizons are separated by ~ 10 to 15 m of undisturbed Molasse deposits and, biostratigraphically, by an entire European Land Mammal Zone, thus providing evidence for two independent major seismic events within a time span of ~ 0.5–1 Myr. Both the lower and the upper seismite horizons can be correlated litho- and biostratigraphically with the basal crater lake sediments at the Ries and Steinheim craters, respectively, deposited immediately after the impacts. From a biostratigraphic point of view, the impact event that formed the Steinheim Basin probably occured around 14 Ma, some 0.8 Myr after the ~ 14.81 Ma Ries impact event.

Background The role of geothermal technology in the context of global efforts toward carbon-free and clean energy production is becoming increasingly important. Social acceptance is a decisive factor in the successful implementation of geothermal projects. Main text This systematic review summarizes the major aspects and evaluates the crucial outcomes of recent research on community acceptance as a dimension of social acceptance of geothermal technology since 2011, on a global scale. From the literature, we identified and grouped researched acceptance factors into five main acceptance categories, namely ‘project organization and process’, ‘environment’, ‘municipality’, ‘technology’, and ‘governance’. Each category comprises a number of specific acceptance factors addressed by different survey methods (e.g., interviews, questionnaires, content analyses) in the relevant publications. The acceptance factor categories ‘technology’ and ‘governance’ are remarkably underrepresented, whereas the acceptance factors combined in the categories ‘project organization’ and ‘municipality’ are frequently mentioned in the literature. Acceptance factors combined within the category ‘environment’, ‘trust in key actors’, and ‘information about the project’ are expectedly the most dominant ones in the papers studied. Interestingly, acceptance categories and number of mentions of acceptance factors are comparable in all survey methods applied in the various studies. Besides the acceptance factors combined in the categories ‘environment’ and ‘project organization and process’, ‘knowledge about geothermal technology’ (an acceptance factor from the category ‘municipality’) represents the predominant acceptance factor of geothermal technology. Conclusions Deeper knowledge, in particular about the technical aspects of geothermal energy generation, might enable a more comprehensive and holistic view on geothermal technology. Furthermore, the integration of all relevant groups of stakeholders in the process of implementation of geothermal projects strongly influences their social acceptance. Following the results of our systematic literature review, we propose these aspects should be addressed in more detail in future research on the community acceptance of geothermal technology and energy production.

Since the 1970s, it has been widely accepted that the Nördlinger Ries and the Steinheim impact structures represent a crater doublet formed by the simultaneous impact of a binary asteroid in the Middle Miocene. From a biostratigraphic point of view, however, the lowermost crater-lake sediments deposited in the drainless morphological depressions differ in age by ~ 0.5 to 1 Myr. Recent work additionally questioned the double-impact theory due to the occurrence of two vertically separated seismite horizons in North Alpine Foreland Basin deposits, interpreted to result from two different impact-induced seismic events. A continuous double-layer ejecta blanket originally surrounded the Ries crater within a minimum distance of 45 km from its center. Distal Ries ejecta consist of sedimentary and shocked basement rock fragments of the Ries area. The Steinheim crater is located 41 km WSW of the Ries crater and filled by a ‘basin breccia’ that consist of Middle and Upper Jurassic rock fragments. Most parts of the breccia and overlying crater-lake deposits are preserved. If both craters formed simultaneously, Ries ejecta would have reached the Steinheim area and should be incorporated in the Steinheim breccia or intercalated between the basin breccia and crater-lake deposits. However, no sedimentary or basement rock fragments derived from the Ries crater have ever been found in outcrops or drillings into the Steinheim crater. We conclude the Steinheim impact crater did not exist at the time of the Ries impact and the Steinheim asteroid rather impacted into the outer continuous distal Ries ejecta blanket some 0.5 to 1 Myr after the Ries impact. Graphical abstract Geological map of the Ries crater with the present distribution of its ejecta blanket and the geographical position of the Steinheim crater ~41 km WSW of the Ries crater. The Ries ejecta blanket consists of the more proximal type of impact breccia (Bunte Breccia) and the more distal type of impact breccia (Bunte Trümmermassen)

The ~3.8 km Steinheim Basin in SW Germany is a well-preserved complex impact structure characterized by a prominent central uplift and well-developed shatter cones that occur in different shocked target lithologies. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and electron probe microanalysis have revealed, for the first time, the occurrence of rare metals on the Steinheim shatter cone surfaces. Shatter cones produced from the Middle Jurassic (Aalenian) Opalinus Claystone (‘Opalinuston’), temporarily exposed in the central uplift in spring 2010, and shatter cones in Upper Jurassic (Oxfordian) limestones from the southeastern crater rim domain are commonly covered by faint coatings. The Opalinus Claystone shatter cone surfaces carry coatings dominated by Fe, Ca, P, S and Al, and are covered by abundant small, finely dispersed microparticles and aggregates of native gold, as well as locally elevated concentrations of Pt. On several surfaces of the claystone shatter cones, additional Fe, Ni and Co was detected. The Ca–Mn-rich coatings on the limestone shatter cone surfaces locally include patches of Fe, Ni, Co, Cu and Au in variable amounts and proportions. The intriguing coatings on the Steinheim shatter cones could either stem from the impacted Lower Jurassic to Palaeogene sedimentary target rocks; from the crystalline-metamorphic Variscan crater basement; or, alternatively, these coatings might represent altered meteoritic matter from the Steinheim impactor, possibly an iron meteorite, which may have been remobilized during post-impact hydrothermal activity. We here discuss the most plausible source for the rare metals found adherent to the shatter cone surfaces.

Isotopic and stratigraphic ages of the ~ 80 km diameter Puchezh-Katunki (Russia; 220 ± 10 to 167 ± 3 Ma) and the ~ 20 km diameter Obolon (Ukraine; 215 ± 25 to 169 ± 7 Ma) impact structures are associated with significant age uncertainties. As a case study, reconstructions of the palaeogeography at the time of crater formation (Late Triassic to Middle Jurassic) based on recent palaeogeographic maps help further to constrain impact ages. Palaeogeographic studies suggest that Puchezh-Katunki is older than 170 Ma and that Obolon is younger than 185 Ma. This also rules out that Obolon formed during a ~ 214 Ma Late Triassic multiple impact event as recently discussed.

Various uplift markers suggest asymmetrical uplift of Tenerife Island, with stable conditions in the north but significant uplift of up to 45 m in the south over the past ∼42 ka. Fossil shells in beach deposits uplifted by 7.5-9 m were 14C-dated at a Holocene age of 2460±35 bp (1σ). This confirms earlier results and documents very young, and probably still ongoing, uplift of southern Tenerife potentially caused by ascending magma. This underlines that southern Tenerife is probably undergoing a further cycle of volcanic activity that started ∼95 ka ago.

The Quaternary Bandas del Sur Formation in the south of Tenerife comprises a complex sequence of pyroclastic rocks and lavas. In contrast to the NW- and NE-Rift zone on Tenerife, the S-Rift zone comprises a number of characteristics with respect to the morphological features, eruption cyclicity and the geochemistry of the volcanic deposits. Various flank eruptions of the Las Cañadas volcano associated with basaltic lavas and the formation of cinder cones within the Bandas del Sur are important volcanic units for understanding the explosive volcanic cycles during the Pleistocene on Tenerife. A number of palaeomagnetic studies, as well as major and trace element geochemistry and two radio-isotope dates (K–Ar), have been carried out on prominent cinder cones, in order to discover their stratigraphic position. Combining our results with previous K–Ar data, the cones and lavas can be subdivided into three stratigraphic units. The first unit contains cinder cones with reverse magnetization and Y/Nb ratios between 0.37 and 0.41. Cinder cones which belong to the second unit show normal magnetization and Y/Nb ratios of < 0.35. The third unit comprises cinder cones with normal magnetization and Y/Nb ratios of about 0.47. The first two units were constructed between c. 0.948–0.779 Ma and 0.323–0.300 Ma. These units define volcanic cycles ending in violent Plinian eruptions. The third and youngest unit possibly marks the beginning of a further volcanic cycle that started c. 0.095 Ma ago.