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Speleothems are well-proven archives of terrestrial climate variation, recording mean temperature, rainfall, and surface vegetation data at subannual to millennial resolution. They also form within the generally stable environment of caves, and thus may remain remarkably well preserved for many millions of years and, most important, can be dated radiometrically to provide robust chronologies that do not rely on orbital tuning, ice-flow modeling, or estimates of sediment deposition rates. The recent adaptation of the U-Pb dating technique to speleothems has greatly extended their potential as paleoclimate recorders back into the more distant geological past, well beyond the ~500 k.y. limit previously imposed by U-series techniques, but the opportunities presented by these new methods have yet to be fully explored. As an extreme example, here we report on samples recovered from Permian cave fills, the oldest radiometricaily dated speleothems SO far documented. Using state of the art analytical techniques it is possible to determine not only their age and state of preservation, but also to extract apparently nearly pristine climate proxy data. Armed with these methods, it now seems reasonable to apply the lessons learned from more recent speleothems to ancient materials, wherever they can be found, and of whatever age, to generate snapshots of paleoclimate that can be used to greatly refine the records preserved within the sediments and fossils of the time. doi: 10.1130/G30354.1

A severe drought in parts of low-latitude northeastern Africa and southwestern Asia ~4200 yr ago caused major disruption to ancient civilizations. Stable isotope, trace element, and organic fluorescence data from a calcite flowstone collected from the well-watered Alpi Apuane karst of central-western Italy indicate that the climatic event responsible for this drought was also recorded in mid-latitude Europe. Although the timing of this event coincides with an episode of increased ice-rafted debris to the subpolar North Atlantic, the regional ocean-atmosphere response seems atypical of similar Holocene icerafting events. Furthermore, comparison of the flowstone data with other regional proxies suggests that the most extreme part of the dry spell occurred toward the end of a longer-term climate anomaly. Keywords: speleothems, Holocene, drought, geochemistry, Italy.

The kimberlite rocks of the Udachnaya-East pipe (Siberia) are uniquely fresh and contain very high abundances of primary volatiles (Cl, C[O.sub.2], S). Alkali elements and chlorine are extremely abundant in the reconstructed kimberlite melt compositions, and this enrichment is very important for our understanding of deep-mantle melting and melt transport. Here we present new isotopic data that confirm a mantle origin for these kimberlitic chlorides and carbonates, and constrain the kimberlite emplacement age as ca. 347 Ma. The initial Nd and Pb isotope ratios in a large salt aggregate, in a CI-S-enriched water leachate of the groundmass, and in the silicate fraction of the groundmass are very similar ([[epsilon].sub.Nd] = +3 to +4, [sup.206]Pb/[sup.204]Pb = 18.6, [sup.207]Pb/[sup.204]Pb = 15.53), implying a comagmatic origin of the chlorides and carbonates and the silicates. Combined Sr, Nd, and Pb isotope data are used to rule out any significant contributions to the kimberlite chlorine budget from crustal sources, such as the Cambrian evaporite sequences of the Siberian platform. Our data support the interpretation that exsolved Na-K chloride and Na-K-Ca carbonate formed directly from original uncontaminated kimberlite magma. High Cl abundances in kimberlites suggest the presence of a Cl-rich reservoir in the deep sublithospheric mantle. Keywords: kimberlite, radiogenic isotopes, volatiles, chlorine, carbonate, mantle.

Kimberlite magmas, as the deepest probe into Earth's mantle (>150 km), can supply unique information about volatile components (hydrogen, carbon, chlorine, sulfur) in mantle-derived melts and fluids. All known kimberlite rocks are not suitable for studies of mantle volatiles because of their pervasive postmagmatic alteration; however, this study discusses an exceptionally fresh group I kimberiites ( Keywords: kimberlite, mantle volatiles, chlorine, carbonate, metasomatism, melt inclusions, immiscibility.

Formation of sedimentary opal-AG in opal fields of eastern Australia has been linked to intensive weathering of their Cretaceous host rocks—the "deep weathering" model. Here we examine possible links between weathering history as recorded in mining exposures and textural observations in thousands of opal nodules from Lightning Ridge (New South Wales, Australia) to further constrain the timing and depositional environment of opal-AG. Satellite imaging identifies river channels—now marked by pedogenic silcrete—associated with an inland river delta as the intermittent source of water that drove localized deep weathering and silicification in reactive volcanogenic sediments. Variably mineralized weathering profiles show evidence for wet/dry cycling that controlled redox and pH fluctuations critical in the conversion of detrital feldspar to kaolinite, release of silica, formation of opaline silica spheres, and opal mineralization during the initial intense phase of weathering. Subsequent less intense weathering under consistently oxidizing conditions modified the weathering profiles but produced little further opal. Textures in oriented opal nodules indicate that cavities filled rapidly under changing Eh-pH. Opal nodules formed when opaline silica spheres, nucleated and grown in perched groundwater bodies, accumulated and drained into cracks and dissolution cavities in underlying claystone. Drier conditions promoted sol-gel ripening processes that produced the solid opal. Patches and bars of precious opal-AG within common opal nodules suggest that it formed through oxidation, diffusion, and leaching in common opaline Si gel during periods of low water flux and was rate limited by the solidification of the Si gel. Ostwald ripening increased silica sphere size to produce the characteristic "play of color." Opal formation largely ceased once acidification potential was lost or all feldspar had been converted to kaolinite. [ABSTRACT FROM AUTHOR]

Dredged glass from the southern Mid-Atlantic Ridge near the Bouvet Triple Junction has unique major element, trace element, and isotopic composition, distinct from typical mid-ocean ridge basalts. It is a high-Mg (Mg# 67.8), high-Ni (NiO 290 ppm) andesite depleted in highly incompatible and heavy rare-earth elements with an isotopic signature of ancient continental lithosphere (i.e., low [sup.206]PB/[sup.204]PB and [sup.143]Nd/[sup.144]Nd and high [sup.87]Sr/[sup.86]Sr and [delta][sup.18]O). The origin of this glass is attributed to melting of a Precambrian garnet-bearing, mafic lithology, possibly related to lower crustal blocks stranded in the upper mantle during breakup of Gondwana and opening of the Atlantic. This composition can be used to explain anomalous geochemical features of oceanic rocks in the Southern Hemisphere Keywords: mid-ocean ridge basalts, isotopes, mantle heterogeneities, subcontinental lithosphere, South Atlantic, Gondwana.

Re-Os isotope data show that the ore-forming komatiites occurring in the upper mantle of the late Archaean greenstone terrains of Western Australia have been uncontaminated by radiogenic crust before and during turbulent surface flow. The Os isotopic concentrations of sulphide ores and the komatiite failed to reach radiogenic levels, the Re/Os ratio was low. The concentration of both Re and Os was also low. The results of the study indicate that ground melting and assimilation of sulphidic sediments is unimportant for ore formation.