The Cretaceous post-rift series from the Portuguese onshore ranges of the West Iberian Margin and their history of research

Abstract

The thick post-rift series that covers the Triassic to Lower Cretaceous sedimentary succession of the Lusitanian Basin, in west central Portugal, is crucial to understanding the Mesozoic evolution of the West Iberian Margin, motivating a long history of studies, including those by Daniel Sharpe (1806–56). They record platform carbonates interbedded with marginal marine and alluvial facies. The post-rift infill was deposited above a late Aptian breakup unconformity and is organized into three unconformity bounded sequences: ‘UBS-4A’ (upper Aptian–upper Cenomanian), ‘UBS-4B’ (lower Turonian–lower Campanian) and ‘UBS-5B’ (lower Campanian–Maastrichtian). The first comprises alluvial siliciclastics and shallow-marine, carbonate sequences rich in Tethyan faunas with ammonites and rudists. During the late Cenomanian, the carbonate platform entirely covered the onshore sectors of the Lusitanian Basin. Several diapiric axes controlled the differentiation of inner platform areas with corals and rudists. The infill of ‘UBS-4B’ occurred after the tectonic uplift and emersion of the sectors located to the south of first-order Nazaré Fault Zone. The platform carbonate facies were overlain by regressive micaceous and alluvial coarse siliciclastics. The sequence ‘UBS-5’ overlies a lower Campanian unconformity and has a Campanian–Maastrichtian thick record of alluvial to lagoonal, reddish pelites, rich in vertebrate assemblages.