Orbital-climate control of mass-flow sedimentation in a Miocene alluvial-fan succession (Teruel Basin, Spain)

Abstract

The role of climate change in driving alluvial-fan sedimentation is hard to assess in pre-Quaternary successions, for which detailed chronologies and climate-proxy records cannot be easily established. In the Teruel Basin (Spain), high-resolution (104-105 years) chronological and palaeoclimatic information was derived by orbital tuning of Late Miocene mudflat to ephemeral- lake deposits. The semi-arid palaeoclimate made this low-gradient, basinal environment sensitive to thresholds in the local hydrological balance. Basic facies rhythms are attributed to alternating, relatively humid/arid phases controlled by the climatic precession cycle. The lower stratigraphic interval of this reference section interfingers with distal, coarse-clastic beds from a coeval alluvial fan. The consistent interdigitation of debris-flow deposits with distal strata indicative of arid-to-humid climate transitions shows that fan sedimentation was regulated by climate cyclicity. In particular, the largest volumes of terrigenous debris were shed from the fan onto adjacent mudflats during transitions to relatively humid periods with pronounced seasonality, during precession minima. Distal to medial sections within alluvial-fan outcrops also feature prominent, laterally continuous alternations of coarse- and fine-clastic packages. This high degree of architectural organization, uncommon in fan successions, and stratigraphic relationships with the reference section suggest orbitally controlled climate change to have been the forcing mechanism.