Long-term erosion rates as a function of climate derived from the impact crater inventory

Worldwide erosion rates seem to have increased strongly since the beginning of the Quaternary, but there is still discussion about the role of glaciation as a potential driver and even whether the increase is real at all or an artifact due to losses in the long-term sedimentary record. In this study we derive estimates of average erosion rates on the timescale of some tens of millions of years from the terrestrial impact crater inventory. This approach is completely independent from all other methods to infer erosion rates such as river loads, preserved sediments, cosmogenic nuclides, and thermochronometry. Our approach yields average erosion rates as a function of present-day topography and climate. The results confirm that topography accounts for the main part of the huge variation in erosion on Earth, but also identifies a significant systematic dependence on climate in contrast to several previous studies. We found a 5-fold increase in erosional efficacy from the cold regimes to the tropical zone and that temperate and arid climates are very similar in this context. Combining our results into a worldwide mean erosion rate, we found that erosion rates on the timescale of some tens of millions of years are at least as high as present-day rates and suggest that glaciation has a rather regional effect with a limited impact at the continental scale.</p

The complex impact structure Serra da Cangalha, Tocantins State, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Serra da Cangalha is a complex impact structure with a crater diameter of 13,700 m and a central uplift diameter of 5800 m. New findings of shatter cones, planar fractures, feather features, and possible planar deformation features are presented. Several ring-like features that are visible on remote sensing imagery are caused by selective erosion of tilted strata. The target at Serra da Cangalha is composed of Devonian to Permian sedimentary rocks, mainly sandstones that are interlayered with siltstone and claystones. NNE-SSW and WNW-ESE-striking joint sets were present prior to the impact and also overprinted the structure after its formation. As preferred zones of weakness, these joint sets partly controlled the shape of the outer perimeter of the structure and, in particular, affected the deformation within the central uplift. Joints in radial orientation to the impact center did not undergo a change in orientation during tilting of strata when the central uplift was formed. These planes were used as major displacement zones. The asymmetry of the central uplift, with preferred overturning of strata in the northern to western sector, may suggest a moderately oblique impact from a southerly direction. Buckle folding of tilted strata, as well as strata overturning, indicates that the central uplift became gravitationally unstable at the end of crater formation.466875889German Research Foundation (DFG) [Re 528/9-1, Re 528/11-1]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Ph.D. grantGerman Academic Exchange Service (DAAD)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)German Research Foundation (DFG) [Re 528/9-1, Re 528/11-1]FAPESP [2008/53588-7]CNPq [30334/2009-0

Rochechouart 2017-Drilling Campaign: First Results

No abstract available

The 'lost child' as figure of trauma and recovery in early post-war cinema: Fred Zinnemann's The Search (1948) and Natan Gross's Unzere Kinder (1948)

The article examines the figure of the ‘lost child’ in feature films of the immediate post-war period. The figure’s enormous symbolic value as innocent victim and future generation, granted the ‘lost child’ a key position in post-war discourse, including films which tried to grapple with the moral and physical destruction of the continent after 1945. National film industries, particularly of the perpetrator nation, employed the ‘lost child’ for genre stories in which the post-war chaos is being mastered and a new, masculine national self is re-built. However, films made by victim groups outside a national context rely on the ‘lost child’ to broach the destruction of their identity by war and persecution. Analysing two films, Fred Zinnemann’s The Search (1948) and Nata Gross’s Unzere Kinder (1948), I argue that they use the child figure to deal with traumatization and make it part of the reconstruction of communal intergenerational relations. This does not result in stories of masculine mastery but in narratives that incorporate moments of trauma process emerging around destroyed mother-child relations. The films, encoding traumatization in film language, develop a rich cinematic language along questions of identity and form a first instance of posttraumatic cinema

The impact pseudotachylitic breccia controversy:Insights from first isotope analysis of Vredefort impact-generated melt rocks

Besides impact melt rock, several large terrestrial impact structures, notably the Sudbury (Canada) and Vredefort (South Africa) structures, exhibit considerable occurrences of a second type of impact-generated melt rock, so-called pseudotachylitic breccia (previously often termed “pseudotachylite” – the term today reserved in structural geology for friction melt in shear or fault zones). At the Vredefort Dome, the eroded central uplift of the largest and oldest known terrestrial impact structure, pseudotachylitic breccia is well-exposed, with many massive occurrences of tens of meters width and many hundreds of meters extent. Genesis of these breccias has been discussed variably in terms of melt formation due to friction melting, melting due to decompression after initial shock compression, decompression melting upon formation/collapse of a central uplift, or a combination of these processes. In addition, it was recently suggested that they could have formed by the infiltration of impact melt into the crater floor, coming off a coherent melt sheet and under assimilation of wall rock; even seismic shaking has been invoked. Field evidence for generation of such massive melt bodies by friction on large shear / fault zones is missing. Also, no evidence for the generation of massive pseudotachylitic breccias in rocks of low to moderate shock degree by melting upon pressure release after shock compression has been demonstrated. The efficacy of seismic shaking to achieve sufficient melting as a foundation for massive pseudotachylitic melt generation as typified by the breccias of the Sudbury and Vredefort structures has so far remained entirely speculative. The available petrographic and chemical evidence has, thus, been interpreted to favor either decompression melting (i.e., in situ generation of melt) upon central uplift collapse, or the impact melt infiltration hypothesis. Importantly, all the past clast population and chemical analyses have invariably supported an origin of these breccias from local lithologies only

CIRIR programs: drilling and research opportunities at the Rochechouart Impact Structure

International audienc

Effective health care for older people living and dying in care homes: A realist review

Background: Care home residents in England have variable access to health care services. There is currently no coherent policy or consensus about the best arrangements to meet these needs. The purpose of this review was to explore the evidence for how different service delivery models for care home residents support and/or improve wellbeing and health-related outcomes in older people living and dying in care homes. Methods: We conceptualised models of health care provision to care homes as complex interventions. We used a realist review approach to develop a preliminary understanding of what supported good health care provision to care homes. We completed a scoping of the literature and interviewed National Health Service and Local Authority commissioners, providers of services to care homes, representatives from the Regulator, care home managers, residents and their families. We used these data to develop theoretical propositions to be tested in the literature to explain why an intervention may be effective in some situations and not others. We searched electronic databases and related grey literature. Finally the findings were reviewed with an external advisory group. Results: Strategies that support and sustain relational working between care home staff and visiting health care professionals explained the observed differences in how health care interventions were accepted and embedded into care home practice. Actions that encouraged visiting health care professionals and care home staff jointly to identify, plan and implement care home appropriate protocols for care, when supported by ongoing facilitation from visiting clinicians, were important. Contextual factors such as financial incentives or sanctions, agreed protocols, clinical expertise and structured approaches to assessment and care planning could support relational working to occur, but of themselves appeared insufficient to achieve change. Conclusion: How relational working is structured between health and care home staff is key to whether health service interventions achieve health related outcomes for residents and their respective organisations. The belief that either paying clinicians to do more in care homes and/or investing in training of care home staff is sufficient for better outcomes was not supported.This research was funded by National Institute of Health Research Health Service Delivery and Research programme (HSDR 11/021/02)

Dike Formation, Cataclastic Flow, and Rock Fluidization During Impact Cratering: an Example from the Upheaval Dome Structure, Utah

Patterns of deformation within the Upheaval Dome structure, Utah, provide important clues for assessing its possible impact origin. The complex structure of the innermost part of the dome, in particular of the White Rim Sandstone (WRS), indicated almost complete loss of internal coherence during deformation. The WRS displays extreme thickness variations, blind terminations and frequent embranchments at nodular-like points. This, together with discordant contacts to the country rock, shows that WRS builds up a dike network that was emplaced and injected during formation of the central dome. Microstructural analysis reveals that the macroscopically ductile appearance is achieved by distributed cataclastic flow. Beside intergranular fracturing, dislocation pile-ups, dislocation arrays and tangles indicate additional dislocation glide activity in quartz of WRS during deformation. Disseminated brittle fault zone networks postdate the cataclastic flow and represent the final deformation increments during formation of the central uplift. The distributed cataclastic flow in the sandstones was initiated by grain crushing, collapse of pore space, and subsequent intergranular shear. In accordance with experimental data for a similar sandstone (Berea sandstone), it is suggested that a high effective confining pressure, most likely in excess of 250 MPa, was necessary to cause this flow. At shallow crustal levels (maximum possible depth of burial of WRS is 3 km) such a high confining pressure can only be build up dynamically by impact processes. From deformation mechanisms, a shock wave attenuation to magnitudes below the Hugoniot elastic limit of quartz can be deduced and correlates with a burial of the studied sediments of 2-3 km at the time of the impact

Numerical simulation of temperature effects at fissures due to shock loading

The localized appearance of specific shock features in target rocks and meteorites such as melt veins and high pressure polymorphs suggests that regions with a local increase in pressure and temperature exist as a shock wave propagates through an inhomogeneous rock. In this paper, we investigate the effect of planar fissures on the local temperature distribution using numerical simulations. Time-dependent parameters such as temperature, pressure, and displacement are evaluated. The simulation model is based on a shock equation of state for the involved materials, dunite and quartzite, and simulates geometries that were also used in shock-loading experiments. An artificial gap between the materials simulates an open fissure at the interface. A strong temperature increase occurs at a gap size of 0.1 mm, which potentially can cause melting in a thin layer at the interfaces. The temperature decreases with decreasing gap size. Temperature and pressure excursions at the interface are induced by the closure of the gap, which causes a second shock wave to superpose the primary wave. Open fissures and fractures, which occur ubiquitously in shallow-buried target rocks and projectiles, thus, act as local pressure and temperature amplyfiers and may be responsible for thin melt vein formation in shocked rocks.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202