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Carbonatites host some of the largest and highest grade rare earth element (REE) deposits but the composition and source of their REE-mineralising fluids remains enigmatic. Using C, O and .sup.87Sr/.sup.86Sr isotope data together with major and trace element compositions for the REE-rich Kangankunde carbonatite (Malawi), we show that the commonly observed, dark brown, Fe-rich carbonatite that hosts REE minerals in many carbonatites is decoupled from the REE mineral assemblage. REE-rich ferroan dolomite carbonatites, containing 8-15 wt% REE.sub.2O.sub.3, comprise assemblages of monazite-(Ce), strontianite and baryte forming hexagonal pseudomorphs after probable burbankite. The .sup.87Sr/.sup.86Sr values (0.70302-0.70307) affirm a carbonatitic origin for these pseudomorph-forming fluids. Carbon and oxygen isotope ratios of strontianite, representing the REE mineral assemblage, indicate equilibrium between these assemblages and a carbonatite-derived, deuteric fluid between 250 and 400 °C ([delta].sup.18O + 3 to + 5â°.sub.VSMOW and [delta].sup.13C - 3.5 to - 3.2â°.sub.VPDB). In contrast, dolomite in the same samples has similar [delta].sup.13C values but much higher [delta].sup.18O, corresponding to increasing degrees of exchange with low-temperature fluids (< 125 °C), causing exsolution of Fe oxides resulting in the dark colour of these rocks. REE-rich quartz rocks, which occur outside of the intrusion, have similar [delta].sup.18O and .sup.87Sr/.sup.86Sr to those of the main complex, indicating both are carbonatite-derived and, locally, REE mineralisation can extend up to 1.5 km away from the intrusion. Early, REE-poor apatite-bearing dolomite carbonatite (beforsite: [delta].sup.18O + 7.7 to + 10.3â° and [delta].sup.13C -5.2 to -6.0â°; .sup.87Sr/.sup.86Sr 0.70296-0.70298) is not directly linked with the REE mineralisation., Author(s): Sam Broom-Fendley [sup.1] , Frances Wall [sup.1] [sup.2] [sup.3] , Baruch Spiro [sup.2] , Clemens V. Ullmann [sup.1] [sup.3] Author Affiliations: (1) Camborne School of Mines, University of Exeter, [...]

Peatland is an important terrestrial carbon reservoir that contains >25% of soil carbon and accounts for 25%-38% of natural methane emissions. Most of this carbon is contained in postglacial boreal peat. Our understanding of the carbon cycle within this reservoir and its links to the atmosphere is therefore restricted to periods of < 10 k.y. A record of the longer-term behavior of the peatland carbon reservoir under nonglacial conditions does, however, exist in thick lignite deposits formed over periods of > 1 m.y. Spectral analysis of varying lignite color reveals that 120 m of early Miocene lignite from the Gippsland Basin, Australia contains a 1.7 m.y. record of orbitally paced climate oscillations dominated by the response to obliquity. Use of the regular orbital signal indicates that the average long-term rate of peatland carbon accumulation recorded in the lignite is 27.5 [g.m.sup.-2].[yr.sup.-1]. This rate is constant over periods of >100 k.y. and is independent of shorter-term, Keywords: Miocene, lignite, carbon cycle, methane, astronomical calibration.

Assessing effects of diagenesis on oxygen isotope composition of bone is essential to its use in reconstructing habitats and lifestyles of ancient vertebrates. These effects are a matter of controversy, particularly in the case of extinct animals such as dinosaurs. To investigate the effects of diagenesis on isotopic composition of fossil bone, bone samples from both marine and terrestrial Campanian sediments from Alberta, Canada, have been analysed. The isotopic compositions of oxygen ([[delta].sup.18][O.sub.SMOW]) were determined in bones sampled from articulated skeletons of exclusively terrestrial animals recovered from the terrestrial Dinosaur Park Formation, and compared with bones from the marine Bearpaw Formation. The articulated skeleton of an exclusively terrestrial dinosaur (hadrosaur) found in marine sediments yielded similar ([[delta].sup.18]O values for both structural carbonate and phosphate fractions (mean ([[delta].sup.18][O.sub.SMOW]) values 22.6 [per thousand] and 16.9 [per thousand], respectively) in bone to marine reptiles (mosasaurs) recovered from the same locality (mean ([[delta].sup.18][O.sub.SMOW]) values 24.2 [per thousand] and 17.3 [per thousand], respectively). The isotopic composition of both skeletons recovered from marine sediments was significantly more positive than that of articulated hadrosaur skeletons recovered from contemporaneous terrestrial sediments (mean phosphate ([[delta].sup.18][O.sub.SMOW]) value 12.9 [per thousand]), and outside the range of phosphate ([[delta].sup.18][O.sub.SMOW]) values previously reported for terrestrial dinosaur skeletons (c. 9-14 [per thousand]). These data suggest that the isotopic composition of oxygen in the phosphate and structural carbonate ions in the bone apatite was altered during diagenesis and can be used for neither palaeoclimate nor physiological reconstruction. Keywords: bones, isotope, oxygen, dinosaurs, diagenesis.

Researchers from Nottingham, UK collected stream water samples to test the presence of organic and sulfuric acid as a result of acid leaching from farmlands in midwestern Finland.

Epithermal veins in early Triassic turbidites on Hurd Peninsula are isotopically homogeneous over an area of 13 km x 2 km (mean [[Delta].sup.34]S = +2.2[per thousand], 1[Sigma] = 1.7, n =65) suggesting derivation from a deep circulating, neutral-chloride hydrothermal plume containing magmatic sulphur. The sense of fractionation (pyrite = +3.5, arsenopyrite = +3.2, sphalerite = +2.9, chalcopyrite = +2.5, galena = +0.9%o) and isotopic temperatures between 250 and 345 [degrees] C suggest partial isotopic equilibration. Sulphides in massive dark carbonate/peperitic dyke breccias, with abundant magnetite, hematite and titanite and traces of barite, garnet, zircon and monazite are isotopically heavy (+7 to +14.9[per thousand], n = 12) due either to dyke intrusion into the hydrothermal system resulting in degassing of [H.sub.2]S, or to a second. isotopically heavy and sulphate-bearing solution in fault zones along which dykes were subsequently intruded. Vein sulphides in nearby Cretaceous volcanic rocks are similar to the epithermal system (mean = + 1.8%o, 1[Sigma] = 0.9, n = 6, pyrite = +2.0, chalcopyrite = +1.5), suggesting sulphur-derivation by degassing of sub-volcanic magma, or remobilization of disseminated sulphides during plutonism. Sulphide in an Eocene tonalire pluton is slightly 32S-enriched (mean = 0[per thousand], 1[Sigma] = 1.9, n = 7, molybdenite = +0.7, pyrite = + 1.5, chalcopyrite = -2.6) and was exsolved directly from the cooling tonalitic magma. Keywords: Andean Orogeny, South Shetland Islands, veins, sulphur, isotopes.

The fine particles created by glacial comminution of carbonate minerals are susceptible to interaction with meltwater, and the isotopic composition of fine carbonate in glacial deposits has the potential of recording this interaction. Here, we focus on the carbonate fraction of glacial sediment and debris within basal ice at the Tsanfleuron Glacier, Switzerland. Size separates of basal ice debris and melt-out tills show a collinear isotopic trend interpreted as a mixing line between detritus (Delta18O(sub PDB) = -5 per thousand and Delta13C(sub PDB) = 0.6 per thousand) and authigenic calcite, which in one case had Delta18O values as light as -18.7 per thousand and Delta13C values as light as -5.7 per thousand. In most cases, the finer fractions (with calcite crystals as small as 0.1 micrometer) are enriched in the isotopically light component, which is interpreted to form largely by freezing in basal ice. The isotopic compositions of ice and included gases could be influenced by this process. Melt-out tills inherit the authigenic calcite; thus, carbonate-bearing till should no longer be regarded simply as clastic sediment.