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Abstract: We have studied a small, very unusual stone, here named “Hypatia”, found in the area of southwest Egypt where an extreme surface heating event produced the Libyan Desert Glass 28.5 million years ago. It is angular, black, shiny, extremely hard and intensely fractured. We report on exploratory work including X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy with EDS analysis, deuteron nuclear reaction analysis, C-isotope and noble gas analyses. Carbon is the dominant element in Hypatia, with heterogeneous O/C and N/C ratios ranging from 0.3 to 0.5 and from 0.007 to 0.02, respectively. The major cations of silicates add up to less than 5%. The stone consists chiefly of apparently amorphous, but very hard carbonaceous matter, in which patches of sub- diamonds occur. values (ca. 0‰) exclude an origin from shocked terrestrial coal or any variety of terrestrial diamond. They are also higher than the values for carbonaceous chondrites but fall within the wide range for interplanetary dust particles and comet 81P/Wild2 dust. In step heating, 40Ar/36Ar ratios vary from 40 to the air value (298), interpreted as a variable mixture of extraterrestrial and atmospheric Ar. Isotope data of Ne, Kr and Xe reveal the exotic noble gas components G and P3 that are normally hosted in presolar SiC and nanodiamonds, while the most common trapped noble gas component of chondritic meteorites, Q, appears to be absent. An origin remote from the asteroid belt can account for these features. We propose that the Hypatia stone is a remnant of a cometary nucleus fragment that impacted after incorporating gases from the atmosphere. Its co-occurrence with Libyan Desert Glass suggests that this fragment could have been part of a bolide that broke up and exploded in the airburst that formed the Glass. Its extraordinary preservation would be due to its shock-transformation into a weathering-resistant assemblage. [Copyright &y& Elsevier]

Abstract: The Cradle of Humankind cave sites in South Africa preserve fossil evidence of four early hominin taxa: Australopithecus africanus, Australopithecus sediba, Paranthropus robustus and early Homo. In order to integrate this record into a pan-African scenario of human evolutionary history it is critical to have reliable dates and temporal ranges for the southern African hominins. In the past a lack of precise and accurate chronological data has prevented the evaluation of the temporal relationships between the various sites. Here we report new uranium–lead (U–Pb) radiometric ages obtained from sheets of calcium carbonate flowstone inter-bedded between clastic cave sediments at the site of Swartkrans, providing bracketing ages for the fossiliferous deposits. The fossil bearing units of Swartkrans, specifically the Hanging Remnant and Lower Bank of Member 1, are underlain by flowstone layers dated to 2.25±0.05Ma and 2.25±0.08Ma and capped by layers of 1.8±0.01Ma and 1.7±0.07Ma. The age bracket of the Member 1 deposits is therefore between 2.31 and 1.64Ma. However, by combining the U–Pb with biostratigraphic data we suggest that this can be narrowed down to between 1.9 and 1.8Ma. These data can be compared with other recently dated sites and a radiometrically dated U–Pb age sequence formed: Sterkfontein Member 4, Swartkrans Member 1, Malapa, and Cooper''s D. From this new U–Pb dataset, a pattern of contemporary flowstone development emerges, with different caves recording the same flowstone-forming event. Specifically overlapping flowstone formation takes place at Swartkrans and Sterkfontein at ~2.29Ma and ~1.77Ma, and at Sterkfontein and Malapa at ∼2.02Ma. This suggests a regional control over the nature and timing of speleothem development in cave deposits and these flowstone layers could assist in future correlation, both internal to specific deposits and regionally between sites. [Copyright &y& Elsevier]

This is a follow-up study of a work by Kramers et al. (2013) on a very unusual diamond-rich rock fragment found in the area of south west Egypt in the south-western side of the Libyan Desert Glass strewn field. This pebble, called Hypatia, is composed of almost pure carbon. Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) results reveal that Hypatia is mainly made of defect-rich diamond containing lonsdaleite and multiple deformation bands. These characteristics are compatible with an impact origin on Earth and/or in space. We also analyzed concentrations and isotopic compositions of all five noble gases and nitrogen in several ∼mg sized Hypatia samples. These data confirm the conclusion by Kramers et al. (2013) that Hypatia is extra-terrestrial. The sample is relatively rich in trapped noble gases with an isotopic composition being close to the Q component found in many types of meteorites. 40 Ar/ 36 Ar ratios in individual steps are as low as 0.4 ± 0.3 . Cosmic-ray produced “cosmogenic” 21 Ne is present in concentrations corresponding to a nominal cosmic-ray exposure (CRE) age of roughly 0.1 Myr if produced in a typical meter-sized meteoroid. Such an atypically low nominal CRE age suggests high shielding in a considerably larger body. In addition to the Xe–Q composition, an excess of radiogenic 129 Xe (from the decay of short-lived radioactive 129 I) is observed ( Xe 129 / Xe 132 = 1.18 + / − 0.03 ). Two isotopically distinct N components are present, an isotopically heavy component ( δ N 15 ∼ + 20 ‰ ) released at low temperatures and a major isotopically light component ( δ N 15 ∼ − 110 ‰ ) at higher temperatures. This disequilibrium in N suggests that the diamonds in Hypatia were formed in space rather than upon impact on Earth ( δ N atm 15 = 0 ‰ ). All our data are broadly consistent with concentrations and isotopic compositions of noble gases in at least three different types of carbon-rich meteoritic materials: carbon-rich veins in ureilites, graphite in acapulcoites/lodranites and graphite nodules in iron meteorites. However, Hypatia does not seem to be directly related to any of these materials, but may have sampled a similar cosmochemical reservoir. Our study does not confirm the presence of exotic noble gases (e.g. G component) that led Kramers et al. (2013) to propose that Hypatia is a remnant of a comet nucleus that impacted the Earth. [ABSTRACT FROM AUTHOR]

Abstract: New evidence from uplifted marine isotope stage (MIS) 5e carbonate deposits in the Gulf of Corinth demonstrate two rapid, sub-orbitally forced, sea-level oscillations in the early part of MIS 5e. Microbial bioherms with inter-grown marine coralline algae are interpreted as early highstand deposits. Presence of thin vadose flowstone (speleothem) coating inter-bioherm surfaces mark a short-lived regression of >10 m, followed by sea-level recovery and re-establishment of the highstand, marked by coralline algae coating inter-bioherm cavity surfaces. These marine algae are then coated by a younger vadose flowstone, thick enough to provide an uncontaminated U/Th date of 134.8±2.0 ka. The dated flowstone is itself encrusted by marine fauna and the entire sequence overlain by highstand marine sediments and marine aragonite cements dated to 114–118 ka, part of the sustained MIS 5e highstand. The age of the younger flowstone demonstrates that the early highstand occurred before 134.8±2.0 ka, and uplift arguments suggest that the bioherms are unlikely to be older than ∼136 ka. These data are consistent with the notion that most of termination II (TII) sea-level rise had occurred before 135 ka; indeed they suggest sea-level at this time reached about 2–4 (±4) m below present sea-level, 6–18 (±4) m higher than previous estimates. This early highstand was itself punctuated by a rapid sea-level oscillation of >10 m (as yet undated), and this oscillation, supported by new TII sea-level data from the Red Sea [Siddall, M., Bard, E., Rohling, E.J., Hemleben, C., 2006, Sea-level reversal during termination II, Geology, 34, 817–820.], probably occurred in about 1000 yr. The flowstone dated at 134.8±2.0 ka is interpreted to record the early part of the ‘Aladdin''s Cave'' regressive event from Papua New Guinea, although in Greece only the first 16 m of the event is recorded. The new data presented here support a recently published Red Sea TII sea-level curve: they also highlight minor discrepancies in the absolute dating of these early MIS 5e sea-level events worldwide. [Copyright &y& Elsevier]

New high-precision isotope ratios of dissolved Mo in seawater from different ocean basins and depths show a homogeneous isotope composition (‘mean ocean water 98Mo/95Mo’ (MOMO)), as expected from its long ocean residence time (800 kyr). This composition appears to have been constant for the past 60 Myr at a 1–3 Myr time resolution as indicated from thick sections of Fe–Mn crusts from the Atlantic and Pacific. These records yield a constant offset from MOMO (average of −3.1 and −2.9‰). They are similar to our new data on recent oxic Mo sinks: pelagic sediments and six Fe–Mn crust surface layers range from −2.7 to −2.9‰ and −2.7 to −3.1‰, respectively. Recent suboxic Mo sinks from open ocean basins display heavier and more variable isotope ratios (−0.7 to −1.6‰ relative to MOMO). Crustal Mo sources were characterized by measuring two granites (and a mild acid leach of one granite), seven volcanic rocks and two clastic sediments. All show a narrow range of compositions (−2.0 to −2.3‰). These data indicate that isotope fractionation by chemical weathering and magmatic processes is insignificant on a global scale. They therefore represent good estimates of the composition of dissolved Mo input to the oceans and that of the average continental crust. Thus, the Mo input into the oceans appears to be distributed into lighter oxic sinks and heavier reducing sinks. This is consistent with steady-state conditions in the modern ocean. The constant isotope offset between oxic sediments and seawater suggests that the relative amounts of oxic and reducing Mo removal fluxes have not varied by more than 10% over the last 60 Myr. An equilibrium fractionation process is proposed assuming that Mo isotope fractionation occurs between (dominant) MoO42− and (minor) Mo(OH)6 species in solution, of which the latter is preferentially scavenged. [Copyright &y& Elsevier]