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Cave carbonate mineral deposits (speleothems) contain trace elements that are intensively investigated for their significance as palaeoclimate and environmental proxies. However, chlorine, which is abundant in marine and meteoric waters, has been overlooked as a potential palaeo-proxy, while cosmogenic 36Cl could, in principle, provide a solar irradiance proxy. Here, total Cl concentrations analysed from various speleothems were low (3–14 mg/kg), with variations linked to crystal fabrics. High-resolution synchrotron radiation micro X-ray fluorescence (μ-XRF) trace element mapping showed Cl often associated with Na, Si, and Al. We propose that speleothems incorporate Cl in two fractions: (1) water soluble (e.g., fluid inclusions) and (2) water insoluble and strongly bound (e.g., associated with detrital particulates). However, disparities indicated that alternate unidentified mechanisms for Cl incorporation were present, raising important questions regarding incorporation of many trace elements into speleothems. Our first measurements of 36Cl/Cl ratios in speleothems required large samples due to low Cl concentrations, limiting the potential of 36Cl as a solar irradiance proxy. Critically, our findings highlight a knowledge gap into how Cl and other trace elements are incorporated into speleothems, how the incorporation mechanisms and final elemental concentrations are related to speleothem fabrics, and the significance this may have for how trace elements in speleothems are interpreted as palaeoclimate proxies. [ABSTRACT FROM AUTHOR]

Our understanding of climatic conditions, and therefore forcing factors, in North America during the past two glacial cycles is limited in part by the scarcity of long, well-dated, continuous paleoclimate records. Here, we present the first, to our knowledge, continuous, millennial-resolution paleoclimate proxy record derived from millimeter-thick pedogenic carbonate clast coatings (pedothems), which are widely distributed in semiarid to arid regions worldwide. Our new multiisotope pedothem record from the Wind River Basin in Wyoming confirms a previously hypothesized period of increased transport of Gulf of Mexico moisture northward into the continental interior from 70,000 to 55,000 years ago based on oxygen and carbon isotopes determined by ion microprobe and uranium isotopes and U-Th dating by laser ablation inductively coupled plasma mass spectrometry. This pronounced meridional moisture transport, which contrasts with the dominant zonal transport of Pacific moisture into the North American interior by westerly winds before and after 70,000-55,000 years ago, may have resulted from a persistent anticyclone developed above the North American ice sheet during Marine Isotope Stage 4. We conclude that pedothems, when analyzed using microanalytical techniques, can provide high-resolution paleoclimate records that may open new avenues into understanding past terrestrial climates in regions where paleoclimate records are not otherwise available. When pedothem paleoclimate records are combined with existing records they will add complimentary soil-based perspectives on paleoclimate conditions.

The Cradle of Humankind (Cradle) in South Africa preserves a rich collection of fossil hominins representing Australopithecus, Paranthropus and Homo.sup.1. The ages of these fossils are contentious.sup.2-4 and have compromised the degree to which the South African hominin record can be used to test hypotheses of human evolution. However, uranium-lead (U-Pb) analyses of horizontally bedded layers of calcium carbonate (flowstone) provide a potential opportunity to obtain a robust chronology.sup.5. Flowstones are ubiquitous cave features and provide a palaeoclimatic context, because they grow only during phases of increased effective precipitation.sup.6,7, ideally in closed caves. Here we show that flowstones from eight Cradle caves date to six narrow time intervals between 3.2 and 1.3 million years ago. We use a kernel density estimate to combine 29 U-Pb ages into a single record of flowstone growth intervals. We interpret these as major wet phases, when an increased water supply, more extensive vegetation cover and at least partially closed caves allowed for undisturbed, semi-continuous growth of the flowstones. The intervening times represent substantially drier phases, during which fossils of hominins and other fossils accumulated in open caves. Fossil preservation, restricted to drier intervals, thus biases the view of hominin evolutionary history and behaviour, and places the hominins in a community of comparatively dry-adapted fauna. Although the periods of cave closure leave temporal gaps in the South African fossil record, the flowstones themselves provide valuable insights into both local and pan-African climate variability. Climate-driven periodicity of flowstone accretion between 3.2 and 1.3 million years ago in Cradle of Humankind caves reveals that the presence of hominin fossils reflects accumulation in open caves during intermittent, substantially drier phases., Author(s): Robyn Pickering [sup.1] [sup.2] , Andy I. R. Herries [sup.3] [sup.4] , Jon D. Woodhead [sup.5] , John C. Hellstrom [sup.5] , Helen E. Green [sup.5] , Bence Paul [...]

Otolith chemistry in freshwater has considerable potential to reveal patterns of origin and movement, which would benefit traditional fisheries management and provide a valuable tool to curb the spread of invasive and illicitly stocked species. We evaluated the relationship between otolith and water chemistry for five markers (Ba/Ca, Mn/Ca, Sr/ Ca, Zn/Ca, and [sup.87]Sr/[sup.86]Sr) in rainbow trout (Oncorhynchus mykiss) using the existing hatchery system in Colorado and Wyoming, USA, to provide controlled, seminatural conditions. Otolith Ba/Ca, Sr/Ca, and [sup.87]Sr/[sup.86]Sr reflected ambient levels, whereas Mn/Ca and Zn/Ca did not. Using only the markers correlated with water chemistry, we classified fish to their hatchery of origin with up to 96% accuracy when element and isotope data were used together. Large changes in [sup.87]Sr/[sup.86]Sr were evident in otolith transects, although subtler changes in Sr/Ca were also detectable. Our results suggest the relatively few otolith markers that reflect ambient chemistry can discriminate among locations and track movements well enough to provide valuable insight in a variety of applied contexts. La chimie des otolithes en eau douce presente un potentiel considerable pour reveler les patrons d'origine et de deplacement, ce qui pourrait etre benefique pour la gestion traditionnelle des peches et fournir un outil pour reduire la dispersion des especes envahissantes ou introduites de fargon illicite. Nous evaluons les relations entre la chimie des otolithes et celle de feau pour cinq marqueurs (Ba/Ca, Mn/Ca, Sr/Ca, Zn/Ca et [sup.87]Sr/[sup.86]Sr) chez la truite arc-en-ciel (Oncorhynchus mykiss) dans le reseau actuel de piscicultures du Colorado et du Wyoming, E.-U., afin d'obtenir des conditions semi-naturelles controlees. Les rapports Ba/Ca, Sr/Ca et [sup.87]Sr/[sup.86]Sr, mais non Mn/Ca et Zn/Ca, correspondent aux valeurs du milieu ambiant. En n'utilisant que les marqueurs qui sont correles avec la chimie de l'eau, nous avons reparti les poissons en fonction de leur pisciculture d'origine avec une exactitude pouvant atteindre 96 % lorsque les donnees elementaires et isotopiques sont utilisees conjointement. D'importants changements de [sup.87]Sr/[sup.86]Sr sont evidents dans les transects d'otolithes, bien que des changements plus subtils de Sr/Ca soient aussi decelables. Nos resultats indiquent que le nombre relativement restreint de marqueurs des otolithes qui representent la chimie du milieu ambiant permet de separer les sites et de suivre les deplacements assez bien pour fournir des perspectives interessantes dans une variete de contextes d'application. [Traduit par la Redaction], Introduction Otolith chemistry is emerging as a powerful method to track the origins and movement, or provenance, of fish in a variety of taxa and ecosystems. Otoliths are uniquely suited [...]

In situ Sr isotopic analyses of kimberlitic perovskite are more representative of primary magmatic compositions than conventional bulk-rock analyses of the same samples, because the latter are variably compromised by contamination and alteration processes. Bulk-rock Sr isotopic data obtained for 18 intrusions from the adjacent Narayanpet and Wajrakarur kimberlite fields of the Dharwar Craton, India, exhibit a high degree of scatter (~0.701-0.709) and have indistinguishable initial isotope ratios. In contrast, laser ablation perovskite results display strikingly uniform and distinct initial [sup.87]Sr/[sup.86]Sr compositions for each field of 0.70312-0.70333 and 0.70234-0.70251, respectively. The increased resolution provided by these new data permits the evaluation of key aspects of kimberlite genesis. It is argued that lithospheric and crustal contamination had a negligible impact on the perovskite Sr isotope compositions, and that these values are representative of the primary melt component in each field. The results cast doubt on models of kimberlite formation that invoke either the small degree melting of metasomatized subcontinental lithospheric mantle, or derivation from unusually enriched asthenospheric mantle. The data are more compatible with a source region for the Dharwar kimberlites that was similar to a common mantle component such as prevalent mantle (PREMA) or focal zone (FOZO). Keywords: Dharwar Craton, kimberlite, perovskite, strontium, isotope, India, in situ Sr analysis. doi: 10.1130/G24040A1.3

The unique low-temperature sensitivity of the apatite (U-Th)/He (AHe) technique provides valuable new information relating to the late-stage thermal evolution of metamorphic core complexes in the southern Basin and Range Province. In all the ranges studied, the data show greater complexity than previously seen from other thermochronometers. In the Chemehuevi and northern Sacramento Mountains, a trend of decreasing ages toward the northeast applies only for the structurally shallowest parts of the footwall. This is followed by essentially age-invariant segments of 15 [+ or -] 1 Ma, reflecting an increase in the rate of detachment fault movement. The timing of the change suggested by the data agrees with recently published AHe results from the nearby Harcuvar Mountains, located ~125 km to the southeast, suggesting that an underlying regional mechanism triggered this change. Plate reconstructions indicate that the Pioneer-Mendocino fracture zone migrated northward through the area at this time, leaving a slab window in its wake. We suggest that the additional heat applied to the base of the lithosphere from the slab window resulted in mechanical weakening of the area and that this, combined with the extensional strain regime present, resulted in an increased rate of slip within the actively extending metamorphic core complexes. This agrees well with timing constraints for extension onset in the central Basin and Range Province of southern Nevada, and suggests that weakening of the southern Basin and Range Province at 15 [+ or -] 1 Ma was partially responsible for the onset of extension in the central Basin and Range. These findings demonstrate that improved constraints on changes in extension rate within the Basin and Range Province should be possible through the application of the AHe technique to other metamorphic core complex footwalls. Keywords: metamorphic core complexes, Basin and Range Province, low-angle normal faults, (U-Th)/He, low-temperature thermochronology.

New major element, trace element, and Nd isotope data are reported for volcanic rocks from the 2.9 Ga Lower Greenstone and 2.7 Ga Upper Greenstone assemblages of the Belingwe Greenstone Belt. The majority of samples from five distinct stratigraphic units have generally unfractionated to slightly depleted trace element patterns similar to those observed, in the small number of previous studies. However, previously unrecognized incompatible element-enriched samples with distinct high field strength anomalies invariably also occur in close association. These are reminiscent of crustally contaminated rocks from other well-documented greenstone settings. Numerical modeling of combined assimilation-fractionation processes using both trace and major elements suggests 10%-30% incorporation of model Archean continental crust in their genesis, in accord with Nd isotope compositions. These new observations are not consistent with a mid-ocean-ridge or oceanic plateau-type setting for Belingwe Greenstone Belt volcanism, but instead favor a model in which melts interacted with preexisting continental crust. Keywords: Archean, Belingwe Greenstone Belt, crustal contamination, komatiite, Zimbabwe craton.

Detailed geologic field work in the Hamersley basin of Western Australia has identified a single horizon that contains predominantly sand-sized spherules similar to those found in impact ejecta such as at the Cretaceous-Tertiary boundary. Evidence suggests that these spherules represent a reworked distal strewn field formed by a large bolide impact in late Archean time. This so-called 'spherule marker bed' occurs throughout the main body of the Hamersley basin and in stratigraphically equivalent, but shallower-water lithologies in the northeastern corner. Carbonate constitutes both a matrix component of the spherule marker bed and minor interbeds in the local stratigraphic section. We have utilized carbonate Pb-Pb dating methods to provide, for the first time, an age estimate (2541 +18/-15 Ma) for this important marker bed and therefore of the bolide impact event. Samples from both facies define, within error, an identical isochron age that is also consistent with the few zircon-based age estimates for the Hamersley succession. These findings highlight the great potential of carbonate Pb-Pb geochronology in the dating of Archean and Proterozoic sedimentary rocks.