Recent marine lithofacies in Cadiz Bay (SW Spain) Sequences, processes and control factors

The analysis of the lithofacies preserved in recent marine sediments in Cadiz Bay, shows major fluctuations in the depositional regime, which are characterized by significant energy variations. Drilling and geophysical data indicate the presence of coarse materials such as gravel, imbricated shells and plant remains, and frequent flow structures which have been interpreted as a result of the action of high energy events, while the finest sediments present in the cores are interpreted as a consequence of the ordinary depositional regime, fundamentally controlled by normal storm surge and tidal currents. Three types of sequence are differentiated: Very High Energy (VHE) sequences, High Energy (HE) sequences and Low Energy (LE) sequences. The VHE and HE sequences were caused by highly energetic oceanic agents such as great waves generated by major storms or tsunamis. There is no historical evidence of the action of sufficiently energetic storms, while the geological setting of Cadiz Bay is located near the Azores-Gibraltar fault, the limit between the African and European plates, points to tsunami action as being the most plausible option to explain the origin of these deposits. The radiocarbon age indicates that these high energy events happened between 898 +/- 120 BC and 849 +/- 121 AD, some of which coincide with several historically documented tsunamis affecting the Cadiz coast. This data indicates that the period from 849 AD to 1200 AD was a time of intense seismic and tsunamigenic activity. (C) 2009 Elsevier B.V. All rights reserved.