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 s ea level rise relating according to the start and development of the Holoce ne transgression which flooded the coast of Huelva: Facies 2 (gravels), Fac ies 3 (grey clayey silts), Facies 5 (well sorted sands), Facies 4 (silty sa nds), Facies 5 (black clayey silts), and Facies 6 (red muds). This group ov erlies Neogene sediments(Facies 1). Three faunal assemblages (Open bay (OB) , Central estuary (CE), and Wave domination (WD)) including remains of macr ofauna, foraminifers and ostracods plus depositional features, are identifi ed 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 intert idal zone, where reworked marine forms of foraminifers, ostracods and scatt ered macrofauna co-exist with small estuarine foraminifers and ostracods; t he WD assemblage comprises tests of marine macrofauna with fractured shells plus large marine foraminifers and estuarine ostracods. During the first s tage of continuous sea, level rise (8720 +/- 260 BP to 5390 +/- 155 BP), es tuarine accretion, high energy tidal currents and wave action took place su ccessively, allowing the development of the OB, CE and WD assemblages. The second stage (5390 +/- 155 BP to Present), with a stabilized sea level, com prised a vertical decrease of energy, with tidal currents favouring deposit ion in shallow tidal channels and marsh zones, leading to less energetic CE assemblages within the estuarine central basin. High sediment supply resul ted in deposition during this stage, which shows a regressive nature. (C) 1 999 Elsevier Science Ltd. All rights reserved.