Isotopic composition of calcrete deposits from Europe, Africa and India

Abstract

The four models postulated for the formation of calcrete layers all involve the three-stage process: provision of a carbonate-rich solution, the movement of that solution and the precipitation of solid carbonate. The last step originates from either or both of two main alternatives: loss of CO2 out of the solution increasing the pH and consequently the CO concentration, or evaporation of the water effecting an increase in the ionic concentration. This paper presents theoretical calculations for the isotopic composition of the carbonate resulting from these two alternative processes. The isotopic composition of calcrete deposits from France, Spain, Italy, Libya, Cyprus, Kenya, Morocco, South Africa and India are compared with the theoretical models. The calcrete samples from Spain, Cyprus and India are probably the result of evaporation processes.