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Synchrotron high‐resolution and micro‐X‐ray fluorescence elemental mapping of two coeval coralloid speleothems from Lamalunga Cave (Italy) are complemented with petrographic, morphological and microstratigraphic studies. The importance of these speleothems relies on their direct and indirect association with a complete Neanderthal skeleton ('Altamura Man') found inside the cave. The coralloids grew discontinuously between 64·6 ka and the Holocene and reveal exceptionally high concentrations of Mg, Sr and Si, particularly on convex surfaces, where evaporation is more intense. The incorporation of trace elements depends on several factors including location, shape and geometrical evolution during their growth, as well as climate and environmental parameters. This resulted in calcite precipitation with Sr compositions from 100 to 1200 ppm and an average concentration of 7000 ppm Mg. An unusually high Si content (up to 16%) is possibly derived from volcanic ash transported as particulate and in solution inside the cave. The most common fabrics observed consist of non‐fluorescent elongated columnar calcite forming clean isopachous bands and fluorescent fibre‐like crystals associated with laminated, lenticular bands high in Sr, Mg and Si. Variability in Sr, Mg and Si concentrations appears to induce fabric changes in the coralloids. Elongation and lattice distortion of the crystals was found to coincide with high Mg concentrations. The transition from compact elongated to open to fibre‐like, is here interpreted as due to high concentrations of Si and Sr, which are preferentially incorporated in the speleothem at crystal boundaries and intra‐laminae. It is here inferred that coralloid fabric changes and their elemental content potentially record local rainfall variations through time, with the clean compact calcite marking high infiltration and open fibre‐like and micrite fabrics recording dry periods. [ABSTRACT FROM AUTHOR]

Investigation by high resolution Transmission Electron Microscopy (HR-TEM) and Synchrotron-Radiation based micro X-ray fluorescence (SR-μXRF) of diagenesis in carbonates imposes uncertainties on the boundary between stages of crystal growth and post-depositional processes. Speleothems and dolomite are exemplars of the entire range of processes that result in solid materials consisting of crystals. HR-TEM investigation of speleothems suggests that there are many possible pathways of crystallization comprising classical ion-mediated, particle-mediated and formation of metastable phases. Diverse pathways influence the potential of a primary carbonate to undergo post-depositional transformation, with consequences on the accuracy of the preservation of original chemical and physical properties. The capability to date speleothems with U-series techniques is unique amongst other archives of Earth's history. It has been observed that U mobilization, which results in age inversions and uncertainties, is dependent on both crystallization and diagenetic pathways. Here, it is also proposed that the presence of organic colloids, mostly consisting of humic substances (HS), influences the extent to which U may be mobilized, as well as the capacity of original speleothem fabric to undergo dissolution and re-precipitation. Our hypothesis that colloidal HS protect the initial products of crystallization from subsequent diagenesis could explain the existence of primary dolomite preserved in Triassic sabkha facies influenced by fluvial input of siliciclastics. Primary dolomite nanocrystal aggregates coexist with single crystals, highlighting that multiple formation mechanisms were possible, which explains the variety of micro and nanostructures observed by conventional TEM investigations in dolomites. Similarly, we observed calcite nanocrystal aggregates and single crystals preserved in Triassic shallow marine facies, which are famous for their preservation of original aragonite, influenced by continental siliciclastic input. Our new data on the Triassic carbonates suggest that when HS colloids are abundant, nanocrystal aggregates are commonly preserved, possibly because of a protective coating by organic substances. These hinder both the transformation of the aggregates into larger crystals and multiple-steps diagenetic transformation that obliterate primary environmental signals. As opposed to textbook assumptions, it is here proposed that the existence of multiple crystallization pathways for carbonates within the same depositional environment, such as a cave setting or a sabkha, have repercussion on the early diagenetic processes and the extent to which diagenesis significantly resets the original chemical and physical signals. By using speleothems as paradigm for carbonates formed in natural environments where organic compounds are ubiquitous, the present review corroborates the notion that most mechanisms of carbonate crystallization, when the carbonate is not a biomineral, follow inorganic pathways. However, the role of organic substances, as inhibitors of growth and diagenesis, has profound influences on preservation of initial states of crystal formation. [ABSTRACT FROM AUTHOR]

Stalagmite SV1 from Grotta Savi, located at the SE margin of the European Alps (Italy), is the first Alpine speleothem that continuously spans the past c . 17 kyr. Extension rate and δ 18 O c record for the Lateglacial probably reflect a combination of temperature and rainfall, with rainfall exerting the dominant effect. Low speleothem calcite δ 18 O c values were recorded from c . 14.5 and 12.35 kyr, during GI-1 (Bølling–Allerød) interstadial, which, in our interpretation, was warm and wet. The GS-1 (Younger Dryas) was characterized by a shift to heavier δ 18 O c , coinciding with δ 13 C c enrichment and extremely low extension rate ( [ABSTRACT FROM AUTHOR]

Annual growth rates and the ratio of dark to light-colored calcite within single annual laminae in three contemporaneously deposited Holocene speleothems from Grotta di Ernesto, an Alpine cave in northern Italy, respond to changes in surface temperature rather than precipitation. Based on monitoring of present-day calcite growth, and correlation with instrumental data for surface climatic conditions, we interpret a higher ratio of dark to light-colored calcite and the simultaneous thinning of annual laminae as indicative of colder-than-present winters. Such dark and thin laminae occur in those parts of the three stalagmites deposited from AD 1650 to 1713 and from AD 1798 to 1840, as reconstructed through lamina counting. These periods correspond to the well-known Maunder and Dalton Minima of solar activity. An 11-yr cyclicity in growth rate, coupled with reduced calcite deposition during the historic minima of solar activity, is indicative of a solar influence on lamina thickness. Spectral analysis of the lamina thickness data also suggests that the North Atlantic Oscillation variability influenced winter temperatures. Based on the present-day controls on cave calcite formation, we infer that high-frequency changes in solar activity modulated the seasonal duration of soil CO2 production. [Copyright &y& Elsevier]

Carbonate-associated sulphate (CAS) is a useful carrier of palaeoenvironmental information throughout the geologic record, particularly through its stable isotope composition. However, a paucity of experimental data restricts quantitative understanding of sulphate incorporation into carbonates, and consequently CAS concentrations and their diagenetic modifications are rarely interpreted. However, in the case of calcite speleothems, the remarkably high-resolution CAS records which are obtainable via modern microanalytical techniques represent a potentially invaluable source of palaeoenvironmental information. Here, we describe the results of controlled experiments of sulphate co-precipitation with calcite in freshwater solutions where pH, saturation state, and sulphate concentration were varied independently of each other. Solution pH is confirmed as the principal control on sulphate incorporation into calcite. The relative efficiency of incorporation was calculated as a partition coefficient D SO 4  = (mSO 4 /mCO 3 ) solid /(mSO 4 /mCO 3 ) solution . High crystal growth rates (driven by either pH or saturation state) encouraged higher values of D SO 4 because of an increasing concentration of defect sites on crystal surfaces. At low growth rates, D SO 4 was reduced due to an inferred competition between sulphate and bicarbonate at the calcite surface. These experimental results are applied to understand the incorporation of sulphate into speleothem calcite. The experimentally determined pH-dependence suggests that strong seasonal variations in cave air PCO 2 could account for annual cycles in sulphate concentration observed in stalagmites. Our new experimentally determined values of D SO 4 were compared with D SO 4 values calculated from speleothem-drip water monitoring from two caves within the Austrian and Italian Alps. At Obir cave, Austria, D SO 4 (×10 5 ) varies between 11.1 (winter) and 9.0 (summer) and the corresponding figures for Ernesto cave, Italy, are 15.4 (winter) and 14.9 (summer). These values approximate predicted D SO 4 values based on our chamber experiments containing both low (2 ppm) and high (20 ppm) sulphate concentrations. Our experimental values of D SO 4 obtained at crystal growth rates typical of stalagmites, closely match those observed in other cave sites from around the world. This validates the universality of the controls behind D SO 4 and will enhance the use of speleothem CAS as a palaeoenvironmental proxy. [ABSTRACT FROM AUTHOR]

Organic phosphorus incorporated in calcite during laboratory precipitation experiments and in natural cave deposits was investigated by solid-state NMR spectroscopy. For calcite precipitated in the presence of organic phosphoesters of varying size and functionality, solid-state 31 P{ 1 H} CP/MAS NMR shows that the phosphoesters were incorporated intact into the solid. Systematic changes in the 31 P NMR chemical shift of the phosphate group were observed between the solid phosphoester and that incorporated in the solid precipitate, yielding 31 P NMR chemical shifts of the coprecipitates in the range of +1.8 to −2.2 ppm. These chemical shifts are distinct from that of similarly prepared calcite coprecipitated with inorganic phosphate, 3.5 ppm. Only minor changes were noted in the phosphoester 31 P chemical shift anisotropy (CSA) which suggests no significant change in the local structure of the phosphate group, which is dominated by C–O–P bonding. Close spatial proximity of the organic phosphate group to calcite structural components was revealed by 31 P/ 13 C rotational echo double resonance (REDOR) experiments for coprecipitates prepared with 13 C-labeled carbonate. All coprecipitates showed significant 31 P dephasing effects upon 13 C-irradiation, signaling atomic-scale proximity to carbonate carbon. The dephasing rate for smaller organophosphate molecules is similar to that observed for inorganic phosphate, whereas much slower dephasing was observed for larger molecules having long and/or bulky side-chains. This result suggests that small organic molecules can be tightly enclosed within the calcite structure, whereas significant structural disruption required to accommodate the larger organic molecules leads to longer phosphate–carbonate distances. Comparison of 31 P NMR spectroscopic data from the synthetic coprecipitates with those from calcite moonmilk speleothems indicates that phosphorus occurs mainly as inorganic orthophosphate in the natural deposits, although small signals occur with characteristics consistent with phosphate monoesters. The results of this study indicate that trace- to minor concentrations of dissolved organic molecules can be effectively taken up during calcite precipitation and incorporated in the structure, leaving a resilient record of materials present during crystallization. [ABSTRACT FROM AUTHOR]