Christian Koeberl’s research while affiliated with University of Vienna and other places
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Banded iron formations (BIFs) are marine chemical sedimentary rocks that serve as prime archives for Pre-cambrian paleo-environmental reconstructions. However, due to the scarcity of well-preserved Archean rocks, the aquatic environments of early Earth remain poorly constrained. In particular, fluxes derived from continents and submarine hydrothermal systems that affected Archean seawater chemistry are crucial for the understanding of the evolution of marine environments. To fill this gap, we present major-and trace element data in combination with Sm-Nd isotopes of individual BIF layers from the ca. 3.0 Ga old Murchison Greenstone Belt (MGB) of South Africa. BIF layers with low immobile element concentrations show seawater-like shale-normalized (subscript SN) rare earth and yttrium (REY SN) patterns with heavy over light REY SN enrichment and positive La SN , Eu SN , Gd SN , and Y SN anomalies, implying an anoxic marine depositional setting with contributions from high-temperature, hydrothermal systems. These BIF samples yield a Sm-Nd age of 2993 ± 97 Ma that overlaps with the proposed depositional age suggesting negligible post-depositional alteration. In contrast, BIF layers with non-seawater-like REY SN patterns yield a Sm-Nd age of 2504 ± 161 Ma, which can be linked to post-depositional alteration during the ca. 2.7 Ga Limpopo orogeny. The range of initial εNd values from − 1.74 to + 0.15 in pristine BIF samples suggests that elements of mixed juvenile and evolved material from emerged continents and/or hydrothermal systems affected Murchison seawater and indicates potential oceanic water mixing in the Murchison region with water masses derived from the northern Pietersburg and the southern Kaapvaal regions.
An experimental study at one atmospheric pressure was carried out with basalts of the Deccan Traps and black shale as a contaminant to assess the potentiality of the platinum group elements (PGEs) in the contaminated magma. The experiments involved 10%, 15% and 20% black shale as contaminants to understand the incremental concentration in the PGEs. The results show that Pd, Pt, Ru, Rh, Ir and Os substantially rise in the contaminated melt. Though the quantitative increase in the PGE content owing to contamination is evident, the increase is case-specific and related to the degree of black shale contamination, e.g. for Pt, Ru and Pd, 20% contamination yields maximum enrichment, whereas, for Rh and Ir, the maximum increment is obtained for 10% contamination; Os gives most significant increase for 15% contamination. Black shale contaminationleads to the sulfide supersaturation of the basaltic magma and the formation of the PGE-rich sulfide liquid due to immiscibility. The present experimental study revealed a significant role of black shale as a crustal contaminant for the flood basalt and consequent PGE enrichment in the contaminated magma. The findings of this study are important for the other Large Igneous Provinces of the world as well.
Mineral chemistry data of constituent silicate and oxide phases are often regarded as a useful tool for assessing the petrogenesis of mafic rocks. In view of this, the chemistry of minerals from the Kadavur gabbro-anorthosite Complex (10°35´N: 78°11´E), a magmatic intrusioninthe Southern Granulite Terrane of the Indian shield, has been evaluated using several thermo-barometric methods and tectonic discrimination diagrams. The complex represents a magmatic intrusion that consists of a highly deformed schistose gabbro-anorthosite type and an undeformed layered gabbro-anorthosite type, with local patches of pegmatoidal gabbro-anorthosite bodies. The constituent minerals in the complex include clinopyroxene,orthopyroxene, plagioclase, amphibole, and subordinate amounts of ilmenite and magnetite. Pyroxene thermometry (clinopyroxene thermometry, orthopyroxene thermometry and two pyroxene thermometry) gives mean temperatures of~1060°C for the layered gabbro- anorthosite; bodies, and~1124°Cfor the pegmatoidal bodies; and ~1130 °C for the schistose gabbro-anorthosite. Hornblende-plagioclase and amphibole thermometry give temperatures of ~1000-1190°C. The co-existing oxide (magnetite-ilmenite) thermometry gives a lowertemperature of~420°C. The mean clinopyroxene pressure value is 17kbarfor the schistose gabbro-anorthosite, 9 kbar for the layered gabbro-anorthosite, and 11 kbar for the pegmatoid bodies. During the earlier phase of deformation associated withmagmatic crystallization (responsible for schistose type), the ambient temperature and pressure of crystallization of the complex were 955 to 1285°C at ~17 kbar. The magma equilibrated at shallow to intermediate levels allowing for localized input of H2O. Consideration of whole-rock geochemical data (especially immobile trace elements) indicates thatparent magma wasof tholeiitic and alkaline composition and later underwent fractionation. The rare earth element (REE) distribution in the schistose gabbro-anorthositeis broadly similar to that of N-MORB,while the geochemical characteristics of the layered gabbro-anorthosite resemble island arc basalt (IAB). The pegmatoidal gabbro-anorthosite bodies have a transitional affinity between both the N-MORB and IAB. The mineral chemistry and whole-rock geochemistry data suggest that the schistose gabbro-anorthosite mostly corresponds to “non orogenic” and “MORB-type” while layered gabbro-anorthosite and pegmatoid bodies correspond to an ‘orogenic’ and ‘island-arc’ setting, suggesting a clear shift from a MORB setting to an arc-setting suggesting a ridge-subductionevent.The Kadavur gabbro-anorthosite Complex is analogous to other well-known Archaean gabbro-anorthosite complexes around the world.
Despite several, sometimes prominent propagators, meteorite impact research had a long period of peripheral status until the 1980s. Since then, there has been an intense search for impact-extinction pairs, driven by the rapid acceptance of Alvarez’s hypothesis of a catastrophic Chicxulub impact at the end of the Mesozoic era.
However, substantial errors have occurred for incompletely identified and/or indirectly dated impact craters in the context of purportedly coeval mass extinctions. For example, supposed giant craters based only on geophysical studies, such as those alleged as evidence of impact-driven end-Permian and Late Ordovician extinctions, are not supported by any real impact evidence (e.g., catastrophic sedimentation) in adjacent areas.
The updated three-step methodology presents an accurate approach to cause-effect inference in impact catastrophism. It begins with (1) conclusive recognition of impact craters and ejecta, followed by (2) their precise radiometric or biostratigraphic dating, and concludes with (3) assessing the impact’s “kill” potential. The impact contribution to widely defined mass extinctions has been falsified based on the latest crater information from the global database and the updated ages of stratigraphic boundaries. In the Phanerozoic, two contrasting collision phenomena occurred: the Chicxulub asteroid mega-impact and a prolonged asteroid shower from a shattered
chondritic body in the Middle to Late Ordovician. Accordingly, a distinction has been proposed between steady background conditions (impacts occurring singly and rarely in clusters) and perturbation (bombardment) intervals. Current evidence for an impact trigger has been reviewed in detail for the other four Big Five mass extinctions, but no confirmation has been found. The probability of a prolonged impact-enhanced Late Eocene to
Early Oligocene crisis, caused by an asteroid shower, is considered, as well as biotic changes accompanying other
major cratering events: the mid-Norian Manicouagan and the end-Jurassic Morokweng structures. In particular, for the Popigai asteroid swarm, implied from paired 100-km-sized craters, and the possible Morokweng-Mjølnir coincidence, the relationships between impact signatures and likely stepwise biotic events are far from conclusive. Even if medium-sized bolide impacts, recorded in ~40-km-diameter craters, may have initiated near-global climatic hazards, the killing effect is unpredictable due to the diversity of cataclysm severity controls. Also the Ordovician cosmic bombardment did not have any negative influence on the great biodiversification. However, the asteroid swarms may have (by unusual dustiness of the inner Solar System) ultimately triggered or accelerated ice ages in the Late Ordovician and Oligocene, respectively. Overall, this implies a continuum in the
biosphere’s response to extraterrestrial stimuli.
Furthermore, a first attempt was made to explain the hidden record of predicted additional Chicxulub-type mega-events. ‘Lost’ oceanic impacts in the Middle Ordovician, Late Devonian, and Late Triassic were traced in the context of previously suggested records of mega-tsunamis and seismicity. The Frasnian-Famennian transition seems to be the most likely case of such a cryptic cataclysm, manifested in the worldwide “top-Frasnian
reworking event.” In summary, of the 18 extinctions, one confirmed impact-induced mass extinction and 3–4 possible impact-enhanced biotic crises can now be considered in terms of extraterrestrial forcing. This tentative conclusion is only superficially consistent with the simplistic assertion in recent literature of four ‘mass extinctions’ associated with the four largest impacts, as much substantial evidence is still needed. In fact, well-documented volcanic cataclysms currently shape the mainstream neocatastrophic geology.
Many proposals, mostly by non-geologists, of periodic causal connections between extraterrestrial factors and biosphere turnovers are shown once more to be totally inconclusive. In this context, the future of actualistic impact catastrophism and Alvarez’s ‘bolide theory’ remains open to many fascinating topics. In contrast, ‘nonbolide’ catastrophic concepts, such as the triggering role of intergalactic dark matter, are too questionable to
provide real evidence in the fossil record for these ‘invisible’ phenomena.
The Kadavur anorthosite-gabbro complex (10°35′N: 78°11″E), Tamil Nadu, consists of the three distinct rock units which are layered anorthosite-gabbro, schistose anorthosite-gabbro, and sporadic pegmatoidal variant. Based on texture, the layered-type can again be divided into a mesocumulate unit (MCU) and a noncumulate unit (NCU). Several major oxides and oxide ratios indicate, from Harker variation diagrams that the mesocumulate unit (MCU) and schistose unit (SU) are geochemically similar. The plots for non-cumulate unit (NCU) show a compositional spread in those variation diagrams, suggesting fractionation (involving clinopyroxene and plagioclase) from the supernatant magma on separation of the MCU. Variations in the compositions of TiO2 vs P2O5, Ba vs SiO2, La vs Zr, and Yb vs Zr also indicate that NCU has a compositional spectrum, whereas plots for MCU and SU are distinctly different. The geochemical behaviour of the pegmatoidal unit (PU) shows affinity for both the NCU and MCU. The normalized rare earth element (REE) ratios as well as the Zr and Ni concentrations, strongly favour an “Archean basalt” parent magma having tholeiitic or calc-alkaline/ (or transitional) affinity. The present study strongly indicates that the Kadavur anorthosite-gabbro complex was influenced by deformation during intrusion.
The Cretaceous−Paleogene boundary is marked by a large impact and coeval mass extinction event that occurred 66 m.y. ago. Contemporaneous emplacement of the volcanic Deccan Traps also affected global climate before, during, and after the mass extinction. Many questions remain about the timing and eruption rates of Deccan volcanism, its precise forcing of climatic changes, and its signature in the marine geochemical sedimentary proxy record. Here, we compile new and existing mercury (Hg) concentration and osmium isotope (187Os/188Os) records for various stratigraphic sections worldwide. Both geochemical proxies have been suggested to reflect past variations in Deccan volcanic activity. New data from deep marine pelagic carbonate records are compared to contemporaneous records from shallower marine sites correlated through high-resolution cyclostratigraphic age models. The robustness of the proxy records is evaluated on a common timeline and compared to two different Deccan eruption history scenarios. Results show that the global 187Os/188Os signal is clearly reproducible, while the global Hg record does not form a consistent pattern. Moreover, the deep marine sections investigated do not record clear variations in the Hg cycle, particularly in the latest Cretaceous, prior to the extinction event. A detailed reevaluation of the precise depth of the redistribution of impactor-sourced platinum group elements does not exclude the possibility of a minor drop in 187Os/188Os corresponding with a pulse of Deccan volcanism ∼50,000 years before the Cretaceous−Paleogene boundary. Simple Os isotope mass balance modeling indicates that the latest Cretaceous was marked by significant levels of basalt weathering. CO2 sequestration during this weathering likely overwhelmed the emission of Deccan volatiles, thereby contributing to the end of the late Maastrichtian warming.
Evaporation can fractionate elements and their isotopes between the condensed and gas phases. The fractionation of zinc isotopes during impact-induced evaporation can be used to effectively determine the extent of volatile loss. A robust understanding of the Zn isotope system in assessing the volatile loss, however, relies on well-constrained empirical isotopic fractionation factors (α) during evaporation under a range of pressure and temperature conditions. In this study, Zn isotopic data for well-documented impact glasses from six sites (Darwin, Australia; Zhamanshin, Kazakhstan; El'gygytgyn, Russia; Boltysh, Ukraine; Lonar, India; and Ries, Germany) are reported to investigate the extent of Zn isotopic fractionation under conditions of impact-induced evaporation on Earth. Our findings suggest that the initial Zn isotopic composition in terrestrial impact glasses is comparable to that of continental crustal rocks, but this composition becomes progressively heavier as more isotopically light Zn is lost from the impact melt, reaching a maximum δ66Zn value of +1.1 ‰. The investigated samples show a statistically significant negative correlation between δ66Zn values and Zn contents, especially those from the Darwin crater (R2 = 0.90). These samples define an α value of 0.99971 ± 0.00005 (1SE). This α value is consistent with those previously estimated for melt glasses and fused sands (α = 0.9997 to 0.9998) from the Trinity nuclear detonation site, slightly higher than the value estimated from tektites (α = ∼0.998), and notably higher than that theoretically expected for evaporation into a vacuum (α = 0.985 to 0.993). This result highlights the limited fractionation of Zn isotopes during terrestrial impact processes. Moreover, the modelling suggests that the range of α values from 0.9997 to 0.9998 aligns with the observed compositions in lunar mare basalts and products from nuclear detonation, supporting α values close to but not exactly unity for Zn isotopic fractionation during various high-energy impact events. Utilizing the modelled fractionation factor (α = 0.9997), it is possible to reproduce the Zn concentration and isotopic composition of the lunar mare basalts, indicating a loss of about 98 % of the Moon's initial Zn inventory. Terrestrial impact glasses demonstrate that, under natural impact conditions, stable Zn isotopes can undergo evaporative fractionation to a degree comparable to lunar mare basalts and melted fallout glass and fused sands from nuclear detonation, suggesting an important contribution from impact to the volatile depletion of terrestrial planets.
U-Pb age data from the leuco-syenite from the Sholayar Alkaline Syenite Complex (SASC) (10°17′59.9″N: 076°47′26.3″E) is presented in this study. The present sample contains alkali feldspar (orthoclase), oligoclasic plagioclase, diopsidic pyroxene, biotite and opaque minerals (magnetite and ilmenite). The modal data of constituent minerals is plotted over the IUGS classification diagram and the data plots fall within the syenite field. Obtained age (mean age 706.7 ± 8.4 Ma) largely corresponds to the Cryogenian period. In chondrite-normalized diagrams, the syenite shows some affinity towards well-studied silica over-saturated syenites of the Southern Granulite Terrane (SGT). The Ti-in zircon thermometry indicates the crystallization temperature in the range of 613° to 755°C. The reported zircon U-Pb age suggests evidence for Cryogenian alkaline magmatism in the SGT associated either with asthenospheric upwelling in an extensional setting or subduction related continental rifting.
... Most recently, Freitas et al. (2021) presented arguments for the record of both Neoproterozoic glaciations within the Jacadigo Group, the Sturtian in the Urucum Formation, and the Marinoan in the Banda Alta Formation. Further debate on this contentious issue was recently provided by Prost et al. (2024), who presented Re Os isotope dating results of 577 ± 38 Ma for this unit, suggesting a link to the Gaskiers glaciation. However, it is noteworthy that this date overlaps with the age reported by Piacentini et al. (2013) for diagenetic imprints in manganese layers. ...
... This result is fully consistent with previous data obtained using PGE elemental ratio's (Goderis et al., 2013(Goderis et al., , 2021 or with chromium isotopes measurements (Shukolyukov and Lugmair, 1998;Trinquier et al., 2006) as well as the finding of a 2 cm-sized meteorite fragment within the K-Pg boundary in a Pacific Ocean core (Kyte, 1998). Therefore, the Chicxulub projectile most likely originated from a region far beyond the orbit of Jupiter (Fischer-Gödde et al., 2024). The key advantage of the Ru isotope fingerprinting method is that it cannot, like Cr, be diluted or modified by a terrestrial component because of the scarcity of PGE in the crust. ...
... Drivers of the Snowball Earth glaciations remain debated. Proposed causal mechanisms span the gamut from a weathering imbalance, massive aerosol injection caused by the eruption of the Franklin Large Igneous Province 166 , biological drivers 167 and even a major bolide impact 168 . No matter what the specific driver or combination of drivers, these extreme climate shifts would have imposed large changes on the sulfur cycle. ...
... 10.1029/2023JE008267 2019, 2022) as the version of iSALE containing it is not currently publically available. Therefore, we ignore the effect of large-scale fragmentation on permeability (see Alexander et al. (2024) and Marchi et al. (2024) for an indepth description about these effects). Exploring these effects is outside the scope of this contribution. ...
... The mineral assemblages in the underlying basalts indicate prehnite-pumpellyite to greenschist facies metamorphism (25). Ar-Ar radiometric dating of illite around chert veins in the underlying basalt has been interpreted to indicate hydrothermal fluid flow at ~3.25 Ga, ~3.06 Ga, and ~2.29 Ga (26), whereas Sm-Nd isochrons from jaspilites in the chert-barite unit suggest postdepositional modifications at ~2.26 Ga (27). ...
... Newsom et al. (2015) reported "possible poorly developed" shatter cones at Gale Crater, Mars; however, their interpretations remain tentative due to limited image resolution and the likelihood that the observed surfaces might be ventifacts rather than impact-generated structures. A recent study has attempted the automatic detection of shatter cones in Mars rover images using machine-learning techniques (e.g., Bechtold et al., 2023). The occurrence of shatter cones in meteorites (e.g., McHone et al., 2012;Ferrière et al., 2013) further suggests that more meteorite samples may reveal similar shock-induced features linked to impact events on their parent bodies, including planets, asteroids, moons, etc. ...
... Opponents would do that in the next article we review. Holliday et al. (2023) announced in an article of nearly 100,000 words their "comprehensive refutation" of the YDIH. The abstract concluded: "Evidence and arguments purported to support the YDIH involve flawed methodologies, inappropriate assumptions, questionable conclusions, misstatements of fact, misleading information, unsupported claims, irreproducible observations, logical fallacies, and selected omission of contrary information" (Italics added). ...
... Amongst the key areas that Bezuidenhout identified was the Vredefort Crater, the largest and oldest verified impact crater on the planet, which is located around 120 km southwest of Johannesburg, South Africa. Due to the meteoric impact, this area is rich in unique geological formations [9] and various studies have been performed in this area [10][11][12]. ...
... Furthermore, product O 2 is easily purified from the reagents and product HF. Molecular oxygen produced in the fluorination procedure is collected and its oxygen isotopic composition (δ 17 O and δ 18 O) is measured on a Thermo Finnigan MAT 253 dual inlet isotope ratio mass spectrometer (IRMS) as per the procedures in (53). Blank experiments were performed before each heating step to ensure the experimental procedure (i.e., water in the BrF 5 source, water from small leaks and that introduced with a new sample, etc.) contributed < 10% of minimum expected water yield, i.e., < 0.1μmole of water. ...
... set of possible histories [5,6], provide ground truth for estimated spatial parameters from remote sensing [7,8] and is combined with information from other sources into multiscale datasets [9]. As input for the science of regolith mechanics, they could support rover or lander operations as well as planning for in situ resource utilization. ...