Radiocarbon ages of pedogenic carbonate nodules from Coimbatore region, Tamil Nadu

Abstract

In this paper we discuss the limitation of radiocarbon dates on the pedogenic calcic nodules formed in situ within the vertisols in the upland region of Coimbatore, Tamil Nadu. The radiocarbon ages were obtained using lowlevel scintillation counters and the dates range from ~24 to 31 14 C kyrs BP. The ages correlate with the marine isotope stage of Late MIS3. However, since the calcic nodules are pedogenised and formed in an open system, the 14 C ages should only be considered as estimates and not absolute ages because of the possibility of open-system behaviour with respect to carbon. Thus, we express caution in the interpretation of these and other radiocarbon ages obtained on pedogenic carbonate nodules. Multiple sub-mm size subsamples could provide more reliable age estimates.

Calcrete profiles in Puthukulam quarry section, Sathankulam region, Southern Tamilnadu, India: implications on palaeoclimate significance

“…The calcium carbonate content varies from pure carbonate composition of calcite to low magnesium carbonate content or low dolo-calcite mineral. Such published reports have coincided with similar reports of calcrete of Australia and India (McQueen, 2006;Hema et al, 2010;Udayanapillai and Thirugnanasambandam, 2012) The abundance of Mg content may be due to the change in pH, pCO 2 and landscape setting (Hill et al, 1999). The increases in Mg content are observed from top to bottom profiles.…”

“…Veining, lensoidal, meshwork precipitation and dendritic impregnation of dark brown sesquioxide preservation are also observed in the thin section. Such sesquioxide preservation indicates arid and semi-arid climate, which have already been reported from the calcrete of Coimbatore (Hema et al, 2010) and in the Pandalgudi region (Udayanapillai et al, 2015), respectively. Alkaline-rich groundwater fluctuation and paedogenic leaching of surface water cause for calcrete formation within the regolith part.…”

“…Regolith deposit is composed of soil, weathered rock fragments and calcrete. The formation of calcrete within the regolith represents a semi-arid and arid climate (Hema et al, 2010;Udayanapillai et al, 2014). Calcrete is formed either by evapotranspiration of groundwater or by paedogenic leaching of meteoric or surface water under arid and semi-arid climate conditions (Hill et al, 1999).…”

Pedogenic carbonate nodules as soil time archives: Challenges and investigations related to OSL dating

“…Durand et al, 2007;Violette et al, 2010) and radiocarbon dating (e.g. Williams and Polach, 1971;Achyuthan et al, 2010). Furthermore, pedogenic carbonates may also contain a substantial non-carbonate fraction and we show here that this fraction can give important temporal constraints for sedimentary processes and soil formation.…”