Unusual features of sediment supply-dominated, transgressive-regressive sequences: Paleogene elastic wedges, SE Pyrenean foreland basin, Spain

The Paleogene marine to nonmarine succession in the southeastern Pyrenean f oreland basin consists of a series of 3rd-order (3-5 m.y.) transgressive-to -regressive sequences that can be related directly to the stacking and sout hward displacement of successive basement-cover thrust sheets. The regressi ve limbs of the 3rd-order elastic wedges are coeval with thrust movement, w ith maximum subsidence developing towards peak regression. This relationshi p between sedimentation and tectonics is sediment supply-driven. One of these 3rd-order wedges, which was produced by the Montserrat and San t Llorenc del Munt fan-delta systems, demonstrates how such steep-sloped, c oarse-grained, high sediment supply systems generate a hierarchy of transgr essive-regressive architectures. Striking features of this rapidly subsidin g, supply-dominated basin margin, in addition to the tectonics/wedge archit ecture relationship, include: the nonperiodic character of the contained high-frequency sequences; the unusual thickness and landward-thickening geometry of transgressive sys tems tracts; a tendency for "misfit" between alluvial fan and shorezone sectors of seque nces; a lack of marked incision associated with the tops of coarse-grained, regre ssive phases of sequences. Most of the features are symptomatic of high subsidence rates and very high sediment-supply. The last feature, suggestive of few major relative falls of sea level, is also consistent with continuous rapid subsidence. However, it should be remembered that lack of incision may be a poor indicator for lack of base-level fall in a setting where the steepness of alluvial slopes exceeds the slope of the coeval shelf. (C) 2000 Elsevier Science B.V. All rights reserved.