Geometria del margen S.E. de la Cuenca del Ebro: discordancias progresivas en el Grupo Scala Dei. Serra de La Llena. (Tarragona)

Abstract

The Scala Dei Group, located at the southern margin of the Ebro foreland basin, represented the sedimentary response to the Catalan Coastal Ranges thrusting. At la Serra de la Llena the 1600 m of continental deposits can be divided in 4 main megasequences (M,- M,) separated by angular unconformities. New time-control data based on micromammal fauna indicates an influx of coarse material from Upper Lutetian-Bartonian to Middle-Upper Chattian (although the conglomeratic sedimentation related with la Serra del Montsant continued ti11 the Uppermost Chattian). Sedimentation rates at the la Serra de la Llena were 13 cm/Ky during the first megasequence (M,), 7,s cm/Ky during M,-M, and 6 cm/Ky during the last and finer grained M,. The general configuration of the syntectonic Scala Dei deposits with a double monoclinal flexure dipping to the northwest indicates tectonic control by two different structures at depth, interpreted as a fault-propagation folds. Theprogressiveunconformities developed in both forelimbs of these folds show continuous motion and a general steady state between rates of uplift and rates of sediment accumulation. The progressive unconformities are developed mainly by the vertical component of the tectonic motion and by a continuous rotation of the forelimb of the anticlines.