Early Ordovician volcanism in the Iberian Chains (NE Spain) and its influence on the preservation of shell concentrations

Research is described to evaluate the influence of volcanic activity Oil studies of shell-concentration taphonomy and biodiversity Patterns in strata that commonly display poor densities of skeletal debris. Two volcanic episodes are re corded in the Lower Ordovician of the Iberian Chains: (i) a succession of Tremadocian-earliest "Arenig". eruptive felsic products. expelled explosively and characterized by the onset of rhyolitic and dacitic tuffs embedded in the Borachon and Santed formations: and (ii) in "Arenig", effusive basaltic volcanic episode, represented by a single lava flow embedded in the Armorican Quartzite. The volcanic activity reflects a change from sub-alkaline to alkaline geochemical affinities. related to the Early Ordovician magmatism recorded in southwestern Europe that is commonly attributed to the opening of the Rheic Ocean. The felsic explosive tuffs are associated with two ecosystem disturbance events: (i) a short-term colonization event of opportunistic linguliformean brachiopods that proliferated ill the aftermath of a multi-event rhyolitic pyroclastic surge deposit: and (ii) several single-event mass-mortality horizons associated with dacitic pyroclastic flows responsible for the preservation of high-diverse allochtonous coquinas. Our knowledge of the biodiversity patterns achieved by the benthic communities preserved in the poorly fossiliferous, siliciclastic strata of the Iberian Chains is, as a result, strongly biased by the presence Of Skeletal WITS, directly Controlled by the onset of neighbouring eruptive explosions