Effect of aragonite to calcite transformation on the geochemistry and dating accuracy of speleothems. An example from Castañar Cave, Spain

Martín‐García, Rebeca; Alonso-Zarza, Ana María; Frisia, Silvia; Rodríguez‐Berriguete, Álvaro; Drysdale, Russell N.; Hellström, John

doi:10.1016/j.sedgeo.2019.01.014

Cited by 24 publications

(13 citation statements)

References 61 publications

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“…In addition, carbonate surfaces in periglacial areas are exposed not only to chemical weathering but also to intensive frost weathering, promoting the physical disintegration of minerals (Matsuoka and Murton, 2008). Therefore, had the subglacial carbonate been exposed in the past, it would be expected that it would have been eroded by dissolution or frost weathering.…”

Section: Implications For a Continuously Existing Glacier During The mentioning

confidence: 99%

Subglacial carbonate deposits as a potential proxy for a glacier's former presence

et al. 2021

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Abstract. The retreat of ice shelves and glaciers over the last century provides unequivocal evidence of recent global warming. Glacierets (miniature glaciers) and ice patches are important components of the cryosphere that highlight the global retreat of glaciers, but knowledge of their behaviour prior to the Little Ice Age is lacking. Here, we report the uranium–thorium age of subglacial carbonate deposits from a recently exposed surface previously occupied by the disappearing Triglav Glacier (southeastern European Alps) that may elucidate the glacier's presence throughout the entire Holocene. The ages suggest the deposits' possible preservation since the Last Glacial Maximum and Younger Dryas. These thin deposits, formed by regelation, are easily eroded if exposed during previous Holocene climatic optima. The age data indicate the glacier's present unprecedented level of retreat since the Last Glacial Maximum and the potential of subglacial carbonates as additional proxies to highlight the extraordinary nature of the current global climatic changes.

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Section: Implications For a Continuously Existing Glacier During The mentioning

confidence: 99%

Subglacial carbonate deposits as a potential proxy for a glacier's former presence

et al. 2021

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“…Aragonitic speleothems are affected by changes in the pH of cave water and by undersaturation with respect to aragonite, which determine its complete dissolution or its recrystallization into calcite with loss of elemental and isotopic composition (e.g., Hopley, Marshall, & Latham, 2009; Railsback, Dabous, Osmond, & Fleisher, 2002). Martín‐García, Alonso‐Zarza, and Martín‐Pérez, (2009) and Martín‐García et al (2019) showed using XRD, thin‐section petrography, SEM and electron microprobe analysis that primary aragonite in speleothems from Castañar Cave (Spain) exhibits dissolution features, secondary calcite growths on aragonite needles, and aragonite relics embedded in secondary calcite. These structural and mineralogical changes have been linked to discrepancies observed in δ 18 O and δ 13 C values.…”

Section: Archaeological Significancementioning

confidence: 99%

“…This is a consequence of the limited diffusion capability of large chemical species containing uranyl within thin films of water, and the affinity of some calcite surfaces for the incorporation of U chemical species (Reeder et al, 2001). In addition, it should be kept in mind that aragonite exposed to dripping water, for example, at the tip of stalagmites, may be affected by U leaching due to partial dissolution (Martín‐García et al, 2019). Cross‐checking of nearby speleothems can help identify anomalies in the chronological sequence.…”

Section: Archaeological Significancementioning

confidence: 99%

The significance of aragonite in the interpretation of the microscopic archaeological record

Toffolo

2020

Geoarchaeology

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Aragonite is one of the metastable polymorphs of calcium carbonate and is commonly found at archaeological sites in the form of mollusk shells and speleothems. Other occurrences include corals, fish otoliths, seed endocarps, wood ash, and lime plaster. These materials contain microscopic embedded information of fundamental importance for the assessment of the state of preservation of the archaeological record, the reconstruction of paleoenvironments, the identification of pyrotechnological processes, and the establishment of absolute chronologies. However, this information can be used only if the aragonite found at archaeological sites preserves its pristine structure and chemistry. Aragonite is metastable at ambient conditions and tends to dissolve and recrystallize into secondary aragonite or calcite, a process that entails the loss of its original elemental and isotopic signature. Therefore, well‐grounded archaeological interpretations depend on the correct identification of aragonite and the careful characterization of its basic properties. This article reviews the dissolution processes of different types of aragonite, the methods used for their identification, and the archaeological information that can be extracted. Particular emphasis is given to the discussion of key issues regarding absolute dating and postdepositional processes of archaeological sediments, and to a detailed overview of the recently observed pyrogenic aragonite.

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“…Aragonite in the mixed-mineral axial zone shows little evidence of preserved dissolutionreprecipitation fabrics indicative of neomorphic alteration (Frisia, 2015;Frisia and Borsato, 2010;Martín-García et al, 2019). Rather, aragonite growth directly off the underlying C crystals and abundant evidence of both lateral and vertical transitions from C calcite into acicular aragonite (Fig.…”

Section: Petrographymentioning

confidence: 99%

“…Speleothem surfaces could suffer leaching by aggressive drip waters following either torrential autumn-winter rains, or substantial lowering of groundwater storage levels in the epikarst. Some recent studies have examined the effects of later diagenetic replacement of aragonite by calcite on U distribution(Domínguez-Villar et al, 2017;Martín-García et al, 2019), and the likely role of micro-voids as pathways for U migration during aragonite to calcite conversion was identified in a…”

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confidence: 99%

Multi-proxy speleothem record of climate instability during the early last interglacial in southern Turkey

Rowe

Wickens

Sahy

et al. 2020

Palaeogeography, Palaeoclimatology, Palaeoecology

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A stalagmite from Dim Cave in southern Turkey contains a climate record documenting rapid and significant changes in amounts of precipitation between ~132 ka and 17~128 ka, during the penultimate glacial -interglacial transition. Some U-Th dates have been compromised by carbonate dissolution but rigorous selection and tuning to δ 18 O records from other speleothems has generated a robust age model. Growth rate was initially very slow but a rapid increase at ~129 ka was accompanied by strong negative trends in δ 18 O and δ 13 C, a combination implying the onset of much wetter conditions. Isotopic values at ~129 ka suggest that groundwater recharge rates and biogenic activity in the soil zone exceeded those of the early Holocene. A significant isotopic enrichment event at ~128 ka, during which there was alternating aragonite and calcite deposition, documents a strong drying event with a duration that lasted ~200 years. A concurrent decrease in 87 Sr/ 86 Sr ratios indicates increased groundwater residence times and the cumulative evidence suggests amounts of rainfall fell from well above to slightly below present-day levels. Similar δ 18 O enrichment events are present in coeval speleothem records from southwest France and the Northern Alps, and these, together with pollen evidence from Italy, Greece and the Iberian margin of drier conditions at this time, imply that a climate anomaly extended across the northern Mediterranean borderlands. The timing, duration and structure of this episode are consistent with marine evidence of strong North Atlantic cooling early in the last interglacial and there is a resemblance to the Holocene 8.2 ka event recorded globally in many proxy-climate archives.

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Effect of aragonite to calcite transformation on the geochemistry and dating accuracy of speleothems. An example from Castañar Cave, Spain

Cited by 24 publications

References 61 publications

Subglacial carbonate deposits as a potential proxy for a glacier's former presence

Subglacial carbonate deposits as a potential proxy for a glacier's former presence

The significance of aragonite in the interpretation of the microscopic archaeological record

Multi-proxy speleothem record of climate instability during the early last interglacial in southern Turkey

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