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

Muhsin Eren,Meryem Yeşi̇lot Kaplan,Selim Kapur,Selahattin Kadi̇r

doi:10.3906/yer-1902-29

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.

Highlights

The calcretes are terrestrial carbonates that accumulate and/or replace the host materials in near-surface settings and occur in a variety of morphologies (Wright and Tucker, 1991; Kelly et al, 2000; Alonso-Zarza and Wright, 2010)
This study aims to compare isotopic compositions of calcretes in these provinces and attempts to discuss the climatic controlling factors and environmental conditions affecting the formation of “calcrete profiles” (term first used by Meléndez et al (2011) for the Ebro Basin calcretes and Eren et al (2018) for the Adana and Mersin calcretes), which has not been undertaken to date
The δ18O values of calcretes vary in a wide range in respect to the δ13C values in the Mersin area, whereas the Adana calcretes have δ18O and δ13C values varying almost in the same range (Figure 5)

Summary

Introduction

The calcretes are terrestrial carbonates (predominantly CaCO3) that accumulate and/or replace the host materials in near-surface settings and occur in a variety of morphologies (Wright and Tucker, 1991; Kelly et al, 2000; Alonso-Zarza and Wright, 2010). They are often associated with authigenic clays as a minor constituent, generally including palygorskite and sepiolite (Wang et al, 1994; Verrecchia and Le Coustumer, 1996; Garcia-Romero et al, 2004; Silva et al, 2018; Elidrissi et al, 2018). A great number of studies exist on the different aspects of calcretes in the world and in Turkey, including isotopic studies

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