Morphostratigraphy of an ebb-tidal delta system associated with a large spit in the Piedras Estuary mouth (Huelva Coast, Southwestern Spain)

The Piedras Estuary is one of the most significative estuarine systems on t he mesotidal Huelva Coast, in the Northwestern portion of the Cadix Gulf. T he river mouth is presently an estuarine lagoon partially closed by a large spit constructed from an old barrier island system. This estuary is in an advanced state of infilling and its tidal prism has decreased during the Ho locene causing instability and clogging of old inlets and transforming the barrier island chain into a spit. Sedimentation is controlled by the intera ction of ebb tide currents and the prevailing SW waves. The main sediment s upply is provided by an intensive West-to-East longshore current, transport ing sand material from Portuguese cliffs and the Guadiana River. Tidal rang e is mesotidal (2.0 m) and the mean significant wave height is 0.6 m with a n average period of 3.6 s. A boxcore study allowed five depositional facies to be distinguished in the Piedras Estuary mouth: (1) main ebb channels; (2) marginal flood channels; (3) ebb-tidal delta lobes; (4) marginal levees; and(5) curved spits. The r ecent evolution studied in this area suggests a cyclic evolutionary model f or the ebb-tidal delta system. The architectural facies relations shown by the vibracore/boxcore study confirm that the apical growth of the spit occu rred over the innermost of these ebb-tidal deltas. Consequently the preserv ed sequence shows the ebb-tidal delta facies under the spit facies. (C) 200 1 Elsevier Science B.V. All rights reserved.