Version 1
: Received: 31 July 2024 / Approved: 1 August 2024 / Online: 2 August 2024 (08:36:41 CEST)
How to cite:
Aharon, P.; Whitehead, N. Abiotic and Biotic Processes Controlling Deposition of Calcite and Hydrotalcite Calcretes on Niue Island, Southwest Pacific. Preprints2024, 2024080104. https://doi.org/10.20944/preprints202408.0104.v1
Aharon, P.; Whitehead, N. Abiotic and Biotic Processes Controlling Deposition of Calcite and Hydrotalcite Calcretes on Niue Island, Southwest Pacific. Preprints 2024, 2024080104. https://doi.org/10.20944/preprints202408.0104.v1
Aharon, P.; Whitehead, N. Abiotic and Biotic Processes Controlling Deposition of Calcite and Hydrotalcite Calcretes on Niue Island, Southwest Pacific. Preprints2024, 2024080104. https://doi.org/10.20944/preprints202408.0104.v1
APA Style
Aharon, P., & Whitehead, N. (2024). Abiotic and Biotic Processes Controlling Deposition of Calcite and Hydrotalcite Calcretes on Niue Island, Southwest Pacific. Preprints. https://doi.org/10.20944/preprints202408.0104.v1
Chicago/Turabian Style
Aharon, P. and Neil Whitehead. 2024 "Abiotic and Biotic Processes Controlling Deposition of Calcite and Hydrotalcite Calcretes on Niue Island, Southwest Pacific" Preprints. https://doi.org/10.20944/preprints202408.0104.v1
Abstract
Calcretes are indurated terrestrial carbonates that are widespread in arid and semi-arid settings and serve as important archives of present and past environments. Here we use geochemical tools to explore the nature and origin of calcretes documented from tropical Niue Island in the Southwest Pacific. The study recognizes two types of calcretes that differ in their mineral assemblage, microfabrics, elemental chemistry and carbon and oxygen isotopes. The calcretes common in the paleo-lagoon soils consist of 90% low-Mg calcite and ~10% highly weathered Mg-Al silicates. These pedogenic calcretes formed in the soil profiles within the vadose zone and bear the following distinctions: (i) Fe/Al ratio of 0.75, identical to the ratio in soils (Fe/Al=0.76 ±0.5), substantiates the link between the calcretes and soils; (ii) presence of rhizoliths, root voids, micritic nodules and clasts are consistent with a pedogenic calcrete fabric, and (iii) 13C and 18O depletions of -10.6‰ and -5.3‰, respectively, are compatible with carbon sources from microbial and roots respiration, and formation in oxygen isotope equilibrium with vadose waters. Unlike the pedogenic calcrete, a rare calcrete from the coastal terrace contains an exceptionally rare hydrotalcite mineral (65%) coated by microbial films. We contend that the hydrotalcite-rich calcrete was deposited through interaction of dolomite with seawater, similar to the method of producing hydrotalcite in the laboratory. 13C and 18O enrichments of 0.8 to 1.7‰ and -1.0 to -1.6‰, respectively, are in agreement with (i) mixed carbon sources consisting of microbial CO2 degassing, seawater HCO3 and dolomite dissolution, and (ii) oxygen isotope equilibration with a seawater-derived fluid.
Keywords
calcrete; biotic and abiotic processes; geochemical assays; origin; provenance; archives of environment and ecology
Subject
Environmental and Earth Sciences, Environmental Science
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
