Abstract
Changes in the morphology and mineralogy of speleothems (flowstones) clearly respond to climate-related phenomena, such as drip rate variability and temperature-modulated cave ventilation. Detailed petrographic observations have been coupled with δ18O and δ13C values. Fabrics may show changes related to variations in supersaturation, drip rate or input of detrital particles or organic compounds. Fabrics formed under relatively constant and regular drips (columnar compact, open and elongated) show similar δ18O and δ13C values, which are more negative than those of micrite and microsparite. The combination of internal microstratigraphy studies and isotopic data (δ18O and δ13C) from two flowstones collected from two caves in the north of Almeria province (SE Spain), suggest a spectrum of environmental conditions ranging from wetter to drier periods. Both records constitute a very useful tool for screening and interpreting high-resolution paleoclimate reconstructions.
Highlights
The analysis and characterization of the growth layer sets is constructed by assignation of a code (CC columnar, CCo columnar open, calcite elongated fabric (CCe) columnar elongated, M micrite and D dentritic) to each portion of the flowstone
Optical microscopy revealed the presence of primary growth fabrics such as 1) compact columnar calcite in which the crystals present a compact aggregate, formed under relatively stable dripping conditions and lower drip rates (CC, Figure 3(a) and Figure 3(d)), 2) elongated columnar calcite resulted from the preferential growth of the acute rhombohedron and formed in very stable conditions (CCe, Figure 3(b)), 3) dendritic calcite characterized by milky, opaque appearance due to high intercrystalline porosity (D, Figure 3(e)), 4) open columnar calcite where the intercrystalline boundaries are marked by the presence of linear inclusions (CCo, Figure 3(c)), and 5) micrite fabric consisting of carbonate mud with crystals less than 2 - 4 μm (M, Figure 3(d))
Speleothems are good proxy to understand the environmental condition above the cave where they form
Summary
Speleothem δ18O values have been used to track the response of global, regional and local hydroclimate to climate change events, including variation in precipitation amount, changes in the seasonality of precipitation, and shifts in moisture sources and trajectories As δ18O and δ13C values reveal changes in temperature, seasonality, and carbonate source, the alternation of fabrics in speleothems reflects climate-related parameters, such as changes in drip rate and degassing [6] [7] [8]
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