THE LAST INTERGLACIAL IN THE MEDITERRANEAN AS A MODEL FOR THE PRESENTINTERGLACIAL

Deposits of the Last Interglacial on the south and southeastern coasts of Spain are shallow marine and coastal sediments, with a warm fauna of Strombus bubonius. These units exhibit a diversity of morpho-sedime ntary models controlled by the tectonic activity of the Mediterranean area, which is closely related to the approximation of Africa and Iber ia during the Quaternary. There are three well-dated peaks of maximum sea level (T-I: isotopic substage 7a, T-II: isotopic substage 5e, T-II I: isotopic substage 5c). A younger episode, T-IV, probably correspond s to the isotopic substage 5a. Episodes T-II, T-III and T-IV were laid down during Last Interglacial age. In addition, three Holocene peaks of maximum sea level: H-1 ca. 5100 yr B.P., H-2 ca. 3500 yr B.P. and H -3 ca. 2400 yr B.P. were found. The three main peaks of the Last Inter glacial correspond to the morpho-sedimentary Tyrrhenian units T-II, T- III and T-IV, deposited during a time span of some 45,000 years. Sever al smaller oscillations can be distinguished within each of these unit s as subunits separated by erosional surfaces. At least three of such mapable subunits were distinguished within the peak T-II (5e); each la sted ca. 10,500 yr. As the positive oscillations of sea level (H-1, H- 2, and H-3) recorded during the present Interglacial (Holocene) are mu ch shorter, we infer that they are smaller-scale fluctuations (2500-11 00 yr cycles) within the first oscillation (duration: ca. 10,500 yr) o f the first Holocene peak of sea level which has not yet been complete d. In addition to changes of sea level, the vertical and lateral arran gement of morpho-sedimentary units, which can be designated as the str atigraphic architecture, depends on tectonics and oceanography, includ ing geoidal and steric changes and coastal dynamics. The coastal dynam ics factor largely depends on the exchange of waters between the Atlan tic and the Mediterranean. Maximum incursions of water coincides with warm periods (highstands) when the coastal accretion increases. The te ctonic factor greatly influences and modifies the effects of sea-level changes in the coastal areas of tectonically-active regions such as t he Mediterranean. Areas with tectonic uplift will be characterized by a staircase of prograding gravelly beaches, whereas sinking areas will favour the deposition of vertically stacked sequences with coastal on lap of barrier island and lagoon deposits. Rates of sea-level rise for the coming years of 1 cm/yr, have been suggested by some authors. The se gradients greatly exceed those produced by any tectonic factor in t he Spanish coast during the last 100 kyr. Shoreface erosion and transg ression with landward migration of barrier islands and lagoons will oc cur in subsiding areas (Murcia-Alicante and Valencia), even with relat ively low rates of sea-level rise (less than 0.5 cm/yr). Higher rates of sea-level rise (0.5-1 cm/yr) will increase the transgressive trend. Areas with subsidence rates higher than 7.5 cm/kyr (Mar Menor and Ova l of Valencia) are prone to transgression and erosion of barrier islan ds and lagoons both in the cases of stable and rising sea levels. Risk s are smaller in areas with lower rates of subsidence (La Mata, Santa Pola and Torrevieja lagoons) when a stable sea level is considered; ho wever, any rise of sea level will trigger coastal erosion.