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A clear relationship exists between eustatic sea-level rises and falls recorded as cyclical depositional sequences and ammonite faunas during the Cenomanian-Santonian in the Iberian and West Portuguese basins. Most of the faunal turnovers correlate with stratigraphic intervals related to marine transgressions, maximum flooding of the shelf (locally associated to anoxic events), and the marine regressions. Specifically, within each depositional sequence, three distinct and identical events of morphological change occur, involving ammonoids belonging to different groups. Transgressive sediments are characterized by moderately ornamented, inflated and evolute shells, which are replaced by smooth, involute and compressed oxycones (the most hydrodynamic shells) during maximum flooding (and to a lesser extent at the early highstand) of the sequences, which in turn are replaced by coarsely ornamented and evolute shells during late highstands. We conclude that ammonoid faunal analysis can be used to trace sea-level changes and provide an additional tool for sequence stratigraphy.

The Utrillas Formation represents clastic wedges that accumulated in relation to continental-coastal areas of Iberian Basin during the worldwide Late Cretaceous sea-level rise. At the Tamajón outcrop the Late Cenomanian Utrillas wedges are composed of four facies associations (FA1 to FA4), which unconformably overlay Triassic deposits. Basal sediments (FA1) are interpreted as high energy, braided fluvial deposits, characterized by coarse-grained (conglomerate-sandstone) facies; which grade upwards to tide-influenced, estuarine sedimentation (sandstones and mudstones with inclined heterolithic stratification, FA2), and then to high-energy, coastal sheet and channelled sandstones with different tidal features (FA3); and finally, to fine-grained (mudstones and minor burrowed sandstones) of an offshore marine associations (FA4). The depositional architecture based in the presence and hierarchy of several ranks of bounding surfaces and the overall upward-fining succession show the long term retrogradational trend of these facies associations. Peculiar sedimentary features of these sediments are 1) the presence of large-scale, single sets of cross beds infilling large erosive channels, which are tidal in origin. 2) The size and length of the cross-bedding defined by couplets of different grain size; here interpreted as originated by flow unsteadiness in relation to changing tides. And 3) an unusual association of ironstones, wrinkle structures and vertebrate tracks with microbial mats and penecontemporaneous iron encrusting allowing track preservation in the sedimentary record.Keywords: continental-coastal facies, large-scale channels, ferruginous crusts, wrinkle marks, vertebrate tracks, Cenomanian. ResumenLa Formación Utrillas está compuesta por una serie de cuñas clásticas que se depositaron en las áreas continentales y costeras de la Cuenca Ibérica durante el ascenso eustático global del Cretácico Superior. En el afloramiento de Tamajón las cuñas del Cenomaniense Superior de la Formación Utrillas están compuestas por 4 asociaciones de facies (FA1 a FA4), que se disponen discordantes sobre materiales triásicos. Los sedimentos basales (FA1) se interpretan como depósitos de sistemas fluviales de tipo braided, de alta energía, caracterizados por facies de grano grueso (conglomerados y areniscas); que pasan hacia techo a facies estuarinas con influencia mareal (areniscas y lutitas con estratificación heterolítica inclinada, FA2), y estas a areniscas tabulares y canalizadas costeras de alta energía que presentan diferentes características mareales (FA3); y, finalmente la sucesión da paso a una asociación marina somera (FA4), de grano fino y baja energía (lutitas con areniscas bioturbadas subordinadas). La arquitectura deposicional se basa en la presencia y jerarquía de varios rangos de superficies erosivas y la tendencia granodecreciente general de la sucesión, que caracteriza la tendencia retrogradacional general de esas asociaciones de facies. Los materiales estudiados presentan una serie de características se...