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  • 1
    Publication Date: 2021-06-16
    Description: One of the principal reasons why speleothems are recognised as important palaeoclimate archives is their suitability for accurate and precise uranium-series (U-series) age determination. Sampling speleothem sections for U-series dating is straightforward in most cases because visible growth layers are preserved. However, this is not always the case, and here we describe a sampling strategy whereby growth layers are resolved from trace-element images produced by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We apply this method to a section of an Italian subaqueous speleothem (CD3) that lacks persistent visible growth layering. Trace-element imaging revealed growth layers that are strongly non-planar in their geometry owing to the speleothem's pronounced euhedral crystal terminations. The most prominent trace-element layers were first digitized as x, y vector contours. We then interpolated these in the growth-axis direction to generate a series of contour lines at ∼250-μm increments. The coordinates of these contours were used to guide the sampling via a computerised micromilling lathe. This produced a total of 22 samples for U-series dating by multi-collector ICP-MS. The dating results returned ages in correct stratigraphic order within error. Close inspection of the U-series data and the derived depth–age model suggests that the main source of model-age uncertainty is unrelated to the contour sampling but instead more associated with how closely spaced the model ages are in time, i.e. the model age density. Comparisons between stable oxygen and carbon isotope profiles derived from aliquots of the dating samples and two other stable isotope profiles from CD3 spanning the same time period compare very favourably. Taken together, this suggests that our trace-element contouring method provides a reliable means for extracting samples for dating (and other geochemical analyses), and can be applied to similar speleothems lacking visible growth layering.
    Description: Published
    Description: 38-47
    Description: 3.7. Dinamica del clima e dell'oceano
    Description: JCR Journal
    Description: reserved
    Keywords: Speleothems ; U–Th dating ; Growth layers ; LA-ICP-MS ; Trace elements ; Microsampling ; 03. Hydrosphere::03.01. General::03.01.06. Paleoceanography and paleoclimatology ; 04. Solid Earth::04.04. Geology::04.04.02. Geochronology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
    Publication Date: 2021-06-16
    Description: In this work we present the results of a stratigraphic and lithologic study of a flowstone from Tana che Urla Cave, Apuan Alps (central Italy) which grew intermittently between ca. 160 and 8 ka. The studied succession consists of an alternation of two different lithofacies (Lf-A, Lf-B): a brown, detrital-rich (Lf-A) and a white, inclusion-poor calcite (Lf-B). Using available growth rate data, the difference between the two lithofacies is thought to be the result of different amounts of meteoric precipitation, with Lf-A related to low growth rates at times of low precipitation during phases of climatic deterioration (stadial or glacial) and a higher flux of clastic material, and Lf-B related to high growth rates due to high infiltration under conditions of higher precipitation during wetter (interstadial/interglacial) periods, with lower clastic flux. Following this interpretation and the available chronology, the flowstone investigated shows a basal portion of Lf- A that was deposited during MIS6. The flowstone then passed from Lf-A to Lf B at the MIS6-5 transition, with Lf-B lasting for the full interglacial of MIS5e. A long growth interruption (hiatus H1) can be correlated with the MIS5d stadial, with resumption of lithofacies Lf-B occurring during the climatic amelioration of interstadial MIS5c. The age profile of the upper part of the flowstone is poorly constrained, and is characterised by several growth interruptions, suggesting that the last glacial was more severe compared to MIS6.
    Description: Published
    Description: 141-152
    Description: 3.7. Dinamica del clima e dell'oceano
    Description: JCR Journal
    Description: restricted
    Keywords: speleothem ; paleoclimate ; stratigraphy ; petrography ; 03. Hydrosphere::03.01. General::03.01.06. Paleoceanography and paleoclimatology ; 04. Solid Earth::04.04. Geology::04.04.02. Geochronology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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