Lithofacies, diagenetic spectra and sedimentary cycles of messinian (Late Miocene) evaporites in SE Spain

Abstract

Messinian evaporites have been deposited within a number of connected basins that formed the so-called 'Betic Strait’ in SE Spain during the Late Miocene. Pre-, syn- and postevaporitic sedimentary successions may well be compared with other strata of the same age surrounding the Mediterranean Sea. There is no evidence for a cataract-like connection of these basins with a strong unidirectional flow regime before and during the formation of Messinian evaporites as previously suggested.The most frequently occurring gypsum lithofacies presumably related to shallow-water depositional environments are crystalline selenitic gypsum (‘grass-like gypsum’), laminated gypsum and cross-bedded gypsarenite. Only few real sabkha type chicken wire alabastrine gypsum have been identified. Evenly laminated gypsum together with graded gypsarenites (turbidites), gypsrudites (debrites) and slumps is restricted to basins or parts of basins with considerable paleoslopes. Evidence for diagenetic overprinting is abundant in all outcrop areas studied. This includes the formation of giant gypsum twin crystals, ‘super cones’ and alabastrine nodular gypsum.The formation of Messinian evaporites in SE Spain is thought to be controlled by a superimposed third-order sea-level lowstand. Smaller sedimentary units fall well into the range of fourth- to sixth-order cyclic and rhythmic successions. They are clearly related to basin dynamics or to autogenetic processes of the local facies zone (facies dynamics). None of the smaller-scale cycles (fourth and higher order), as observed in outcrops, are related to high-frequency eustasy.