Calcite deposition

The most susceptible material for post-depositional loss or addition of radionuclides is the outer layer of samples that have been exposed to moisture for a long duration. Stratigraphic consistency between ages of the outermost material and that deposited prior to this provides valuable constraints on the technique. Four ages were derived for a band of clear, white calcite deposited on a stalactite from 53.6 m below sea level in a blue hole of Andros, Bahamas (Richards et al. 1994). Isotopic data for the outermost surface, which had been exposed to sea water for at least 8 ka was indistinguishable from the internal material (Fig. 8). 

Baker A, Smart PL and Ford DC (1993a) Northwest European palaeoclimate as indicated by growth frequency variations of secondary calcite deposits. Palaeogeog Palaeoclim Palaeoecol 100 291-301 Baker A, Smart PL Edwards RL (1995) Paleoclimate implications of mass spectrometric dating of a British flowstone. Geology 23 309-312... 

In the book edited by Ivanovich and Harmon (1992), Schwarcz and Blackwell (1992) provided an extensive review of U-series dating in archaeology, which at that time focused on the dating of calcite deposits using and Thr U disequilibria. U-... 

While U-series dating of calcite deposits undoubtedly gives the most reliable dates (see Richards and Dorole 2003) with which to construct archaeological chronologies beyond the c. 50 ky limit of radiocarbon, such deposits are by no means ubiquitous on... 

The initial methodology used assumed that all excess calcite from the solution would be deposited in a predetermined volume of the geothermal pipe. This approach is conservative considering that calcite deposition is an instantaneous process. However, the literature frequently states that calcite deposition is kinetically-controlled where the process of deposition could either be slower or faster (Sjoberg ... 

This paper evaluates the applicability of the modified precipitation rate equation in predicting the discharge duration of a calciting well compared to the observed utilization history and the results of the conservative method from direct deposition of excess calcite. Three wells in Mindanao Geothermal Production Field (MGPF) with documented output decline due to calcite deposition were studied, namely APOID, SP4D, and MD1D. 

The utilization periods for AP01D given by the direct deposition of the excess calcite method has a minimum of 1 month and maximum of 6 months as shown in Fig. 2. It should be noted that the calcite precipitation rate equation at a saturation ratio above 1.72 provided shorter utilization time than the direct deposition method, indicating that the rate law overestimated the amount of calcite deposited. At a saturation ratio below 1.72, however, the rate law indicated a longer utilization period, which was expected since the calcite deposition is kinetically controlled rather than instantaneous deposition of the excess calcite. 

The calcite saturation ratio is more responsive with regards to detecting the onset of calcite deposition through the sudden shift of the saturation ratio from consistently > 1 to < 1. 

Coccolithophorids generate a lot of calcite because they create POC and PIC in a 1-to-l ratio. The overall stoichiometry for these concurrent processes is shown next, illustrating that calcite deposition generates CO2, which is then used to create organic matter. ... 

The observed formation of calcite scales in geothermal wells is consistent with calcite saturation calculations (see Fig. 14). The intensity of calcite deposition is largely determined by two factors, the temperature of the water and its salt content (Arnorsson 1978a). In relation to temperature, calcite scale formation is most troublesome around 200 C and it decreases at both higher and lower T. The cause is the temperature variation in the solubility of C02. It is at a... 

Marian G. M., Schlesinger W. H., and Fonteyn P. J. (1985) Caldep a regional model for soil CaCOa (calcite) deposition in southwestern deserts. Soil Sci. 139, 468-481. 

Several studies have used radiogenic isotopes to study groundwater questions on relatively short (or local) length scales (<2 km). Stuckless et al. (1991) combined the use of strontium and uranium isotope measurements, in studies of groundwaters and secondary calcite deposits in fault zones at Yucca Mountain, Nevada. They tested whether veins formed by upwelling of deep-seated waters... 

As water stopped flowing into Ice Palace and Bonnies Hall, Lime Creek Cave and the similar springs around it stopped flowing and began to fill with breakdown and secondary calcite deposits. Whether the water stopped flowing because all of the ice had melted, or because flow was pirated elsewhere is unknown. 

Calcite deposition Calcite Breakdown Fault enlargement... 

White, W.B., 1986, Luminescence in cave calcite deposits A current appraisal, Natl. Speleol. Soc. Bull. 48 40... 

Gascoyne, M., 1992a, Palaeoclimate determination from cave calcite deposits, Quat. Sci. Rev. 11 609. 

Calcite speleothems are deposited in a cave when downward-percolating, carbonate-saturated grormdwaters, with a partial pressure of CO2 exceeding that of the cave atmosphere, enter a cave and become supersaturated with respect to calcium carbonate. If the degassing of CO2 from solution is slow and isotopic equilibrium is maintained between aqueous carbon phases and deposited carbonate, then two climatically-dependent variables (a fractionation effect and a water effect) will determine the O-isotopic composition of the speleothem calcite deposited in a cave. 

Figure 2. Co-variations of 6 Cct and 8 Oc, (given relative to the PDB standard) for some fossil speleothems (73951 - Igloo Cave, Nahanni Region, NWT, Canada 72040 - El Sotano de Soyate, SLP, Mexico 71003 — El Sotano de la Tinaja, SLP, Mexico 73039 — Crystal Cave, Bermuda 71042 - El Sotano del Arroyo, SLP, Mexico 74019 - Coldwater Cave, lA, USA) illustrating isotopic relationships that characterize deposition under equilibrium and non-equilibrium situations (from Harmon, 1975). Meaningful paleoclimate information can only be retrieved from speleothem calcite deposited under conditions of isotopic equilibrium.

An expression for the effect of long-term change in climate on the oxygen isotopic composition of speleothem calcite deposited at a cave site in response to climate change can be formulated as follows ... 

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