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

Abstract

Carbonate commonly accumulates in weathering profiles developed on noncalcareous parent material under arid and semiarid climatic conditions. Such weathering 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 87Sr/86Sr as a geochemical tracer of the Ca sources in weathering profiles developed on volcanic rocks (basalt, tuff, andesite and latite) in the Mediterranean coast of Morocco. The results show that the most of the Sr, and hence Ca, is of an external origin, derived 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 profiles more distant from the coastline. The contribution of the host rock is small, being less than 25%. The ratio of the Sr (Ca) from the parent material to that from the external sources is controlled by the degree of porosity developed in the profile.

The role of climate and aeolian dust input in calcrete formation in volcanic islands (Lanzarote and Fuerteventura, Spain)

“…The 87 Sr/ 86 Sr ratios of calcretes developed on basalts differs notably from those of basalt samples analyzed, suggesting that basaltic host rock did not supply much Sr (Ca) to the calcretes, as observed in other studies in which calcretes developed on volcanic or plutonic host rocks (Chiquet et al, 1999;Hamidi et al, 1999;Hamidi et al, 2001). On the contrary, the 87 Sr/ 86 Sr ratio is indicative of an important external source of Sr within the soluble fraction of aeolian dust.…”

“…Ca can derive from sea spray, from an aeolian source of marine calcite (Herut et al, 1993;Rognon and Coudé-Gaussen, 1996;Hamidi et al, 1999), or from internal aeolian sand deposits such El Jable sands. These sands contain marine carbonate bioclasts sourced from the nearby beach.…”

“…As a result of island proximity to the Sahara desert, they are regularly affected by dust (Menéndez et al, 2007) sourced from northern Africa, the largest source area on earth for mineral dust (Goudie and Middleton, 2001;Laurent et al, 2008;Scheuvens et al, 2013). Several Ca sources can be considered in these islands, 1) the basalt plagioclases, 2) the Sahara and Sahel wind-blown dust (Coudé-Gaussen and Rognon, 1988;Mizota and Matsuhisa, 1995;Muhs et al, 2010), 3) marine sands during the last glacial (Coudé-Gaussen and Rognon, 1988), and 4) marine spray (Hamidi et al, 1999;Whipkey et al, 2000).…”

Sr isotopic tracing in a lagoonal system : example of surficial carbonate sediments in the Nador lagoon (northeastern Morocco)

“…La composition isotopique des andésites fraîches est de 0,708188, celle des latites de Beni Bou Ifrour est de 0,709279, et celle des tufs et des basaltes est respectivement de 0,703815 et de 0,703929. Notons cependant que dans les niveaux supérieurs des profils, ces signaux isotopiques se rapprochent de celui de l'eau de mer actuelle [Hamidi et al, 1999], ce qui montre que la contribution des carbonates marins est significative dans la formation des carbonates pédologiques. Notons cependant que dans les niveaux supérieurs des profils, ces signaux isotopiques se rapprochent de celui de l'eau de mer actuelle [Hamidi et al, 1999], ce qui montre que la contribution des carbonates marins est significative dans la formation des carbonates pédologiques.…”

Sr-isotopes as a tracer of Ca sources and mobility in profiles hosting regolith carbonates from southern Australia

“…Previous studies have investigated the source of Sr in profiles that have developed over/within basalts (Hamidi et al 1999(Hamidi et al , 2001, tephra (Whipkey et al 2000), limestone (Wood & Macpherson 2005), marl (Elbersen et al 1999), loess (Yang et al 2000), fluvial sediments (Capo & Chadwick 1999), and granite (Chiquet et al 1999). The Sr isotope ratios reported from the majority of these studies support a predominant atmospheric (extrinsic) source of Sr (and through association Ca) throughout most of the profile with a tendency to approach the Sr isotope value of the parent material with depth.…”