Estratigrafía secuencial de sistemas deltaicos en cuencas de antepais: ejemplos de Sant Llorenç de Munt, Montserrat y Roda (paleógeno, cuenca de antepaís surpirenaica)

Abstract

After the sedimentological study of the Sant Llorenc del Munt, Montserrat and Roda deltaic systems, a stratigraphic subdivision based on three different scale transgressiveregressive sequences has been developed. This subdivision has been established on the coastal facies belts from the deduced shoreline (and associated facies belts) migration.
These transgressive-regressive sequences are formed by a lower transgressive part with a deepening-upwards trend and a retrogradational staclung pattern and an upper regressive part, with shallowing-upwards trend and a progradational stacking pattern. The lowest scale sequences (metrical) have been named "fundamental sequences". A series of "composite sequences", intermediate scale (decametric to hectometric), have been defined afier the study of the staclung pattem of the fundamental sequences. After the study of the stacking pattem of composite sequences there have been defined a series of large-scale (decametric to kilometric) "composite megasequences".

A sequential subdivision based on non interpretative models (which does not imply the recognition of a controlling factor or set of factors) can be effective. However, to reach some predictive results is necessary to estimate (qualitative and quantitatively) the greater nurnber of controlling pararneters on the cyclicityAfter the analysis of the field examples, there hasbeen demonstrated that there are three main controlling factors of the cyclicity (eustacy, subsidence and sediment supply) worlung in a combined way. In foreland basins the rates of action of the non-global controlling factors (subsidence and sediment supply) are variable in time and space. That variability makes sequences local for correlation purposes. Sequences will only be correlatable for those areas where the controlling-parameters have operated with a similar magnitude and a similar periodicity. Most of the changes on controlling parameters have not a determined periodicity, so, the resulting sequences will not either have a determined periodicity (or duration).