Through only moderate structural deformation, the Upper Cretaceous carbonates of the Tremp, region in the Spanish Pyrenees can be studied in the form of a platform to basin cross-section, comparable in scale to that of a seismic section. This study examines the Upper Turonian to mid-Coniacian Congost platform and its associated basinal succession. The sedimentology, facies geometries and cycle stacking patterns, along with evidence of exposure of the platform, are interpreted in terms of fluctuations in relative sea-level and variations in accommodation space. Differences in the facies and early diagenesis of carbonates from different parts of the Congost platform suggest two separate phases of platform development. An earlier, more land-ward platform was dominated by clinoforms prograding on to a sloping basin-floor, with a thin lagoonal-sand bank facies upon the platform itself, supplying abundant excess sediment to the clinoforms. A later, more basin-ward platform has a more complex internal geometry of depositional units and marginal rudist-coral buildups. The interpretations are used to propose a new sequence stratigraphic architecture for the Congost platform involving two sequences, the second produced through dynamic 'forced regression'. Sequence boundaries are characterised by subaerial exposure on the platform top that can be correlated with hardgrounds and/or glauconitic horizons within the more basinal locations, overlain by deeper-water facies. The presence of a submarine onlap surface and down-slope slide deposits immediately above the sequence boundary suggests that the major transgressive event that followed sequence boundary development was brought about by local extensional tectonic activity. The small-scale cyclicity within the sequences and the major falls in sea-level that produced the sequence boundaries are interpreted to have resulted largely from eustatic processes, probably with tectonic enhancement. (C) 2002 Elsevier Science B.V. All rights reserved.
