Comparison of stable isotope values of Quaternary calcretes from Adana and Mersin provinces: implications on controlling factors

Authors: MUHSİN EREN, MERYEM YEŞİLOT KAPLAN, SELAHATTİN KADİR, SELİM KAPUR

Abstract: Calcretes are widespread in Adana and Mersin provinces and form under different morphologies. Most calcrete profiles comprise a hard laminated crust/hardpan at the top, gradually intergrading into the nodular and/or tubular/columnar horizon with depth. This study compares the δ¹⁸O and δ¹³C values of calcretes from both provinces and discusses the controlling factors and environmental conditions. The δ¹⁸O and δ¹³C values are characteristic for the pedogenic calcretes. The Adana calcrete mean δ¹⁸O values of the hardpan, nodules and tubes, and fractures-infills are 0.69‰, 0.77‰, and 1.04‰ PDB heavier than those of the Mersin calcretes,respectively. The overall difference between the two groups is 0.78‰ PDB. The differences are related to the high evaporation rate in Adana province in respect to Mersin province under similar climatic conditions, except for the evaporation rate. The high evaporation rate in Adana province is due to higher ventilation. The δ¹³C values of both provinces are almost the same, reflecting calcrete formation in soil with abundant C₃ vegetation similar to contemporary vegetation. In addition, the mean δ¹⁸O and δ¹³C values of the hardpan calcretes slightly differ from those of the columnar horizon, showing a depletion in heavy isotopes. The depletion in the mean δ¹⁸O values of hard laminated crust in respect to the columnar horizon is 0.09‰ PDB for Adana calcretes and 0.12‰ PDB for Mersin calcretes. This is related to the relatively thick water film from which the calcretes formed by precipitation and displacive replacement processes. The difference in the mean δ¹³C values is 0.32‰ PDB for the Adana calcretes and 0.11‰ PDB for the Mersin calcretes, and the depletion in δ13C values of the hard laminated crust reflects proximity of the bioactive horizon in the soil.

Keywords: Calcrete, stable isotope, hard laminated crust, columnar horizon, southern Turkey

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