Tectonic Versus Climatic Controls on Basin- margin Alluvialfan/fan Delta Complex Development, Montserrat, NE Spain

摘要

New Magnetostratigraphic data from the Montserrat alluvial fan and fan-delta system led to an unambiguous correlation to the GPTS and provided the basis for a quantitative estimate of its tectonosedimentary evolution. Local isostatic backstripping analysis has been performed. Tectonic pulses in the basin margin during the initial synsedimentary folding episode, expressed by unconformities and forelimb rotation rates, correlate to tectonic subsidence which shows a trend similar to the forelimb rotation rates. Three different frequency scales of sequential arrangement have been analysed on the fan-delta. The lowest frequency megasequence (3.2My) resulted from a combination of different factors (local subsidence-related architecture, long-term eustacy and regional basin configuration). The intermediate frequency Composite sequences (457±70ky) can be tied to astronomical cyclicity that controlled accommodation. Lack of periodicity (15 to 125ky) at higher-order sequential arrangement indicates that autocyclic processes were the main control. In tectonically active basin margins, sediment supply and subsidence are usually considered as major controls on sedimentary arrangement. In our study this assumption has been confirmed only for large-scale sequences. However, at intermediate scale sequences tectonics results in high accumulation rates favouring the development and preservation of astronomical- related cycles.