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

• Published in: Sedimentary geology 2000-12, Vol.138 (1), p.3-15
• Main Authors: Marzo, M., Steel, R.J.
• Format: Article
• Language: English
• Subjects: Brackish; Fan-delta; Freshwater; Marine; Pyrenean foreland basin; Supply-dominated sequence; Syntectonic clastic wedge; Trangressive–regressive sequence
• ISSN: 0037-0738; 1879-0968
• DOI: 10.1016/S0037-0738(00)00141-X

The Paleogene marine to nonmarine succession in the southeastern Pyrenean foreland 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 southward displacement of successive basement-cover thrust sheets. The regressive limbs of the 3rd-order clastic wedges are coeval with thrust movement, with maximum subsidence developing towards peak regression. This relationship between sedimentation and tectonics is sediment supply-driven. One of these 3rd-order wedges, which was produced by the Montserrat and Sant Llorenç del Munt fan-delta systems, demonstrates how such steep-sloped, coarse-grained, high sediment supply systems generate a hierarchy of transgressive–regressive architectures. Striking features of this rapidly subsiding, supply-dominated basin margin, in addition to the tectonics/wedge architecture relationship, include: • the nonperiodic character of the contained high-frequency sequences; • the unusual thickness and landward-thickening geometry of transgressive systems tracts; • a tendency for “misfit” between alluvial fan and shorezone sectors of sequences; • a lack of marked incision associated with the tops of coarse-grained, regressive 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.