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Abstract

The investigation of the Late Cretaceous sedimentary series in the Basco-Cantabrian Basin (BCB) using sequence stratigraphic methods allows the establishment of a regional chart of relative sea-level changes. Twenty Late Cretaceous sequence boundaries with 19 depositional sequences can be followed through the whole basin. The sequence stratigraphic model explains lateral sediment thickness and facies variations. High-resolution biostratigraphy was successfully applied to correlate sections and to compare the BCB with other basins. The regional cycle chart of the BCB correlates with some sequence boundaries on published global cycle charts, but there are also important misties. The correlation with more recent regional sequence stratigraphic results from Tunisia and northwestern Europe is much better.

The analysis of sedimentary cycles in the Late Cretaceous carbonate ramp system of the BCB is based on detailed study of outcrops, boreholes, and 2-D reflection seismic profiles. The interpretation of outcrop sections and boreholes in terms of sequence stratigraphy included the evaluation of deepening events, facies stacking patterns and depositional geometries. The analysis of seismic profiles allowed no further refinement of the regional cycle chart; however, it contributed with additional information about halokinesis, tectonic setting and large-scale depositional geometries.

In sedimentary settings dominated by a strong 2nd-order transgressive trend, lowstand systems tracts (LST) in the BCB are thin and composed of calciturbidites or absent. In distal sedimentary environments, the transgressive systems tracts (TST) are composed of bemipelagic marl-limestone alternations and the highstand systems tracts (HST) mainly of marlstones. In contrast, depositional sequences dominated by a regressive trend have a thick LST, and this systems tract is mainly composed of autochthonous, shallow-marine carbonates (basinward shift of the carbonate factory). The basinward part of a TST in such a sequence is formed of hemipelagic marl-limestones alternations and marlstones. and the HST is composed of neritic marls and marly limestones with detrital carbonate and has a strong progradational pattern.

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