Marine Sr (Ca) input in Quaternary volcanic rock weathering profiles from the Mediterranean coast of Morocco: Sr isotopic approach

Carbonate commonly accumulates in weathering profiles developed on noncalca reous parent material under arid and semiarid climatic conditions. Such wea thering profile types are widespread in Morocco, making it critical to know the sources of the calcium in order to understand the genesis of carbonate -rich soils. In this study, we use Sr-87/Sr-86 as a geochemical tracer of t he Ca sources in weathering profiles developed on volcanic rocks (basalt, t uff, andesite and latite) in the Mediterranean coast of Morocco. The result s show that the most of the Sr, and hence Ca, is of an external origin, der ived from (i) sea-water for the profiles located near to the coast or (ii) sea-water plus Liassic carbonate outcropping in the catchment for the profi les more distant from the coastline. The contribution of the host rock is s mall, being less than 25%. The ratio of the Sr (Ca) from the parent materia l to that from the external sources is controlled by the degree of porosity developed in the profile.