An ebb-tide delta depositional model—a comparison between the modern Eastern Scheldt tidal basin (southwest Netherlands) and the Lower Eocene Roda Sandstone in the southern Pyrenees (Spain)

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This paper documents the succession, internal structural organization and sequential accretion of an ebb-tide delta in the Lower Eocene Roda Sandstone in southern Pyrenees, Spain. Special attention is given to the relationship between preserved sequences of this fossil ebb-tide delta and sedimentary processes in the present-day estuary and ebb-delta environment of the Eastern Scheldt mesotidal basin, southwest Netherlands. Based on the similarities and the differences between these two ebb deltas, a depositional model has been constructed for the ebb delta and its associated estuary channel system. This consists mainly of: prograding terminal lobes at the delta front, extensive ebb-dominated subtidal depo-lobes and wide shallow ebb channels on the delta platform, as well as extensive intertidal shoals and relatively deep, actively migrating tidal channels in the estuary basin. Distinctive geometry and internal structures of both ebb-delta and estuary channel sand bodies clearly reflect the characteristic hydrodynamic and morphological conditions in the estuaries. The common occurrence of submarine abandonment surfaces and erosional surfaces is an important feature of ebb deltas and estuary channel sequences. Their sequential build-up is critically dependent upon the influences of marine transgressions and the tectonic movements of the tidal basin.