Study of a modern calcrete forming in Guadalajara, Central Spain: An analogue for ancient root calcretes

Abstract

The Pajares calcrete in Central Spain, a modern calcrete, consists of an accumulation of powder carbonate around the roots of living trees and bushes which penetrates Miocene deposits by more than 3 m. Calcrete development is mostly vertical and oblique, but thinner horizontal calcified root mats also occur. Carbonate accumulation, up to 15 cm thick, is made up of micrite with some etched clasts, alveolar septal structures, calcified rootlets, coated grains and micrite grains. In detail many of these features are composed of needle fibre calcite and micro-rods. Accumulation of carbonate was produced both by roots through direct calcification of their cells and also by microbial activity within the rhizosphere. This case study provides a good example of how carbonate is accumulating around roots at present and may allow better understanding of ancient calcretes, especially those which formed directly around roots in direct contact with the host rock. In addition the calcrete's setting, and its occurrence around roots belonging to various types of plants, suggest that carbonate accumulation in modern landscapes may be a relatively rapid, common process even in erosive regimes, and unrelated to specific vegetation types.