Pleistocene speleothems of Mallorca: implications for palaeoclimate and carbonate diagenesis in mixing zones

Abstract

The Pleistocene speleothems of Sa Bassa Blanca cave, Mallorca, are excellent indicators of palaeoclimate variations, and are samples that allow evaluation of the products and processes of mixing-zone diagenesis in an open-water cave system. Integrated stratigraphic, petrographic and geochemical data from a horizontal core of speleothem identified two main origins for speleothem precipitates: meteoric-marine mixing zone and meteoric-vadose zone. Mixing-zone precipitates formed at and just below the water-air interface of cave pools during interglacial times, when the cave was flooded as a result of highstand sea-level. Mixing-zone precipitates include bladed and dendritic high-Mg calcite, microporous-bladed calcite with variable Mg content, and acicular aragonite; their presence suggests that calcium-carbonate cementation is significant in the studied mixing-zone system. Fluid inclusion salinities, d 13 C and d 18 O compositions of the mixing-zone precipitates suggest that mixing ratio was not the primary control on whether precipitation or dissolution occurred, rather, the proximity to the water table and degassing of CO 2 at the interface, were the major controls on precipitation. Thus, simple two-end-member mixing models may apply only in mixing zones well below the water table. Meteoric-vadose speleothems include calcite and high-Mg calcite with columnar and bladed morphologies. Vadose speleothems precipitated during glacial stages when sea level was lower than present. Progressive increase in d 13 C and d 18 O of the vadose speleothems resulted from cooling temperatures and more positive seawater d 18 O associated with glacial buildup. Such covariation could be considered as a valid alternative to models predicting invariant d 18 O and highly variable d 13 C in meteoric calcite. Glacio-eustatic oscillations of sea-level are recorded as alternating vadose and mixing-zone speleothems. Short-term climatic variations are recorded as alternating aragonite and calcite speleothems precipitated in the mixing zone. Fluidinclusion and stable-isotope data suggest that aragonite, as opposed to calcite, precipitated during times of reduced meteoric recharge.

Eogenetic karst, glacioeustatic cave pools and anchialine environments on Mallorca Island: a discussion of coastal speleogenesis

“…The geochemistry of coastal-karst aquifers and of diagenetic processes from the water table to the halocline -and farther down-is far from well studied (Aquilina et al, 2005;Csoma et al, 2006). But, at the same time, there is general agreement that karstic voids can be generated in the freshwater-seawater mixing zone.…”

“…Depending on the location of the cave and the depth of the cave pools it is possible to sample the water column from the oscillating surface to well below the halocline. Some authors have indicated that these kinds of freshwater-seawater mixing zones are among the most enigmatic diagenetic environments of coastal carbonates (e.g., Csoma et al, 2006). In this respect, an interesting phenomenon related to glacioeustatic cave pools is the presence of phreatic carbonate coatings on pool walls, which indicate the precise, both past and present, elevations of the water table (Ginés et al, 1981b;Vesica et al, 2000;Ginés 2000b;Fornós et al, 2002b& Tuccimei et al, 2006.…”

Process‐based Modelling of Syn‐depositional Diagenesis

“…Re--oxidation of sulfide in the overlying oxygenated waters will also drive dissolution by formation of sulfuric acid. Alternately, if the fraction of seawater in the mix is high, other dissolved ions are present and critically if the PCO 2 is close to atmospheric, mixing with fresh groundwaters can cause precipitation of carbonate cements (Frank and Lohmann, 1995;Csoma et al, 2006). Laboratory experiments to determine controls of calcite dissolution and precipitation in fresh--salt water mixing zones by Singurindy et al (2004) confirm these controls and generate a simple scale--independent transport theory that agrees well with observations from field studies at a number of sites.…”

Peculiar calcite speleothems filling fissures in calcareous sandstones and their palaeohydrological and palaeoclimatic significance: an example from the Polish Carpathians

“…They most prob a bly orig i nated as debris from dis in te grated sunken thin rafts. Raft de bris has been rec og nized in travertines (Guo and Ridinig, 1998) as well as in caves, in clud ing lit to ral ones (Hill and Forti, 1997;Csoma et al, 2006;Fornós et al, 2009;van Hengstum et al, 2011). The de bris is prob a bly an an a logue to vadose silt de scribed by Dun ham (1969) as an in di ca tor of emersion of shal low ma rine de pos its.…”