Conjugated enrichments in arsenic and antimony in marine deposits used as paleoenvironmental proxies: preliminary results

Abstract

Two redox-sensitive metalloids, arsenic (As) and antimony (Sb), are examined here to determine what can be their help in the deciphering of past depositional conditions. The enrichment factors of the two elements are compared for a set of geological formations and marine deposits covering a relatively wide range of paleoenvironmental settings, from oxic to euxinic conditions. This work confirms that As and Sb are not robust paleoredox proxies but examining their relative enrichment may be useful. These preliminary results indicate that a co-enrichment of both elements with Sb being more enriched than As could be the mark of the so-called particulate shuttle effect. Notably, Sb would be more sensitive to Mn-shuttling than As. If confirmed, this trend could be used to further identify the cause of As-enrichment in marine sediments impacted by cold seepage fluids.

Groundwater red beds in Holocene fluvial sediments as a product of iron and manganese redox cycling; Morava River, Czechia

“…This may indicate a different response of both elements to different palaeoenvironmental/redox conditions (cf. Tribovillard, 2021).…”

“…Redox reactions in redox sequence (redox ladder) are catalysed by bacteria (Stumm & Morgan, 1996). At the study site, the shrubby and botryoidal morphology of the black Mn-rich, and partly the Fe-rich cements suggests their bacterial origin.…”

“…In oxidized environments, Fe and Mn oxyhydroxide minerals adsorb and/or co-precipitate trace elements (Appelo & Postma, 2005). Adsorption behaviour is different for elements forming cations such as Cu, Zn and Pb which are adsorbed in alkaline environments, and elements forming oxyanions such as As, Mo and Sb which are adsorbed in moderately acidic and neutral environments (Stumm & Morgan, 1996;Appelo & Postma, 2005). In moderately reducing environments, Fe(III)-oxyhydroxides are dissolved releasing adsorbed or co-precipitated trace elements, but dissolved Fe(II) concentration can be controlled by precipitation of siderite and vivianite (Heinrich et al, 2021).…”