Source and mobility of Rare Earth Elements in a sedimentary aquifer system: Aquitaine basin (Southern France)

Philippe Négrel (1) , Emmanuelle Petelet-Giraud (1) , Romain Millot (1) , Eline Malcuit (1)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

The large Eocene Sand aquifer system of the Aquitaine sedimentary basin was studied through various hydrological, chemical and isotopic tools. This system extends over 116,000 km² in the South west part of the French territory. The aquifer being artesian in the west of the district and confined with piezometric levels around 250-m depth in the east. The 'Eocene Sands', composed of sandy Tertiary sediments alternating with carbonate deposits, is a multi-layer system with high permeability and a thickness of several tens of metres to a hundred metres. The Eocene Sand aquifer system comprises at least five aquifers: Paleocene, Eocene infra-molassic sands (IMS), early Eocene, middle Eocene, and late Eocene. One important feature, in these confined systems isolated from anthropogenic influence, is the range in salinities by a factor of 10, from 250 mg/L up to 2.5 g/L. The ΣREE, in the range 2-54 ng/L, with a dependence on salinity when expressed in % HCO3 or SO4, reflect the carbonate or evaporite source of REEs. The UCC normalized-REE patterns show a large variability as exemplified by the REE flat patterns-low SREE associated with salinity controlled by HCO3.

Domains: Geochemistry; Global Changes

Philippe Négrel, Emmanuelle Petelet-Giraud, Romain Millot, Eline Malcuit. Source and mobility of Rare Earth Elements in a sedimentary aquifer system: Aquitaine basin (Southern France). AGU Fall meeting 2011, Dec 2011, San Francisco, United States. pp.H34C-02. ⟨hal-00630766⟩