The Holocene transgression into the estuarine central basin of the Odiel River mouth (Cadiz gulf, SW, Spain):: lithology and faunal assemblages

Six estuarine facies were distinguished recording the Holocene history of sea level rise relating according to the start and development of the Holocene transgression which flooded the coast of Huelva: Facies 2 (gravels), Facies 3 (grey clayey silts), Facies 5 (well sorted sands), Facies 4 (silty sands), Facies 5 (black clayey silts), and Facies 6 (red muds). This group overlies Neogene sediments(Facies 1). Three faunal assemblages (Open bay (OB), Central estuary (CE), and Wave domination (WD)) including remains of macrofauna, foraminifers and ostracods plus depositional features, are identified in a sedimentological log constructed from a borehole with a continuous core, sunk in the central basin of the Odiel River estuary, Huela coast, SW. Spain. The OB assemblage requires shallow and protected zones controlled by low energy tidal currents; the CE assemblage is located within an intertidal zone, where reworked marine forms of foraminifers, ostracods and scattered macrofauna co-exist with small estuarine foraminifers and ostracods; the WD assemblage comprises tests of marine macrofauna with fractured shells plus large marine foraminifers and estuarine ostracods. During the first stage of continuous sea, level rise (8720 +/- 260 BP to 5390 +/- 155 BP), estuarine accretion, high energy tidal currents and wave action took place successively, allowing the development of the OB, CE and WD assemblages. The second stage (5390 +/- 155 BP to Present), with a stabilized sea level, comprised a vertical decrease of energy, with tidal currents favouring deposition in shallow tidal channels and marsh zones, leading to less energetic CE assemblages within the estuarine central basin. High sediment supply resulted in deposition during this stage, which shows a regressive nature. (C) 1999 Elsevier Science Ltd. All rights reserved.