Quaternary tufas of the Inglares River valley: An example of changing slope stepped fluvial system, Álava, N Spain

Larena, Zuriñe ; Arenas, Concha (Universidad de Zaragoza) ; Ortiz, José Eugenio ; Sanjuan, Josep ; Pascual, Ana ; Larraz, Mariano ; Murelaga, Xabier ; Baceta, Juan Ignacio

Resumen: This study examines the factors that controlled the formation of Quaternary calcareous tufa deposits along the valley of the Inglares River (Álava, north Spain), currently fed by a karst-carbonate aquifer. It is based on stratigraphic, chronological (Amino Acid Racemisation, AAR), sedimentological, and δ13C and δ18O analyses, complemented by palaeontology (molluscs, ostracods and charophytes). The examined deposits occur as isolated bodies in the uppermost and downmost stretches of the valley, reaching 45 and 25m in thickness, respectively. AAR dating classified them into two groups: Middle Late Pleistocene (MIS 5e) and Middle and Late Holocene (MIS 1). The former only occurred in the downstream stretch. Up to eleven carbonate facies and minor allochthonous coarse detrital facies have been characterised and arranged into four distinct facies associations. Their features and bedding geometries suggested two main depositional settings: a low- to moderate-slope stepped stretch with small barrage cascades, dammed areas, and abundant palustrine zones (downstream system) and a high-slope stretch with steep stepped cascades and pools (upstream system). These settings respond to bedrock lithology and structural changes throughout the valley, which appear to be the principal factors controlling the tufa depositional architecture. Based on δ13C, an increase in aridity was inferred from the Middle–Late Pleistocene to Holocene. The isotopic differences between the upstream and downstream Holocene tufa might reflect the spatial evolution of δ13C and δ18O in stream water through the approximately 8km long surveyed transect. Erosion due to sudden changes in water discharge may have caused the stratigraphic gap between the two tufa groups.

Idioma: Inglés

DOI: 10.1344/GeologicaActa2025.23.10

Año: 2025

Publicado en: Geologica Acta 23 (2025), 1-32
ISSN: 1695-6133

Financiación: info:eu-repo/grantAgreement/ES/DGA/E32-23R

Tipo y forma: Article (Published version)

Área (Departamento): Área Estratigrafía (Dpto. Ciencias de la Tierra)