The Late Pleistocene ami Holocene evolution of the estuaries in !he Gulf of Cadiz is interpreted for the first time using drill cores, logs, trenches, and 38 new radiocarbon data, and the results compared with lhe she!f The Odie!, Tinto and Guadalete Rivers deposited conglomerales during a highstand lhat did not reach the present sea level dated al ca. 25-30 ka (Isotopic Stage (IS) 3), corresponding lo a relatively humid period in the area. Rivers incised these coarse-grained deposits during the last main lowsland at ca. 18 ka, when sea level dropped to -120 m and the coastline lay 14 km seawards from !he presenL The erosional surface is a sequence boundary and the f100ding slIrface of tl1e postglacial eustatic rise, overlain by !he valley fill deposits of the transgressive and highstand phases of the last fourth-and fif!h-order depositional sequences recognised in !he shelf The first marine int1uence in the estuaries during the transgression occurs at -25/ -30 m at ca. 10,000 years BP. According to tossil assemblages, the transgressed basins changed fmm brackish to more open marine as !he sea rose lIntil ca. 6500 years BP, when it reached !he maximum f100ding ami the sandy estuarine barriers ceased to retrograde toward the muddy central basins. Then, the rate of eustatic rise decreased drastically, and !he estuarine filling followed a two-fold pattem govemed by the progressive change from vertical accretion to lateral (centripelal) progradation. At ca. 4000 years BP the t1uvial input surpassed !he already negligible rate of rise, causing partial emergence of tidal f1ats and spit barriers in the largely filled estuarine basins. Prevalence of coastal progradation upon vertical accretion al ca. 2400 years BP caused accelerated expansion of tidal t1ats and rapid growth of the sandy barriers. Further changes since the 16th century ref1ect widespread anthropic impacts.
The coastal evolution of the El Abalario area (Huelva, southern Spain) during the Late Pleistocene and Holocene is reinterpreted after a refinement of the available geochronology by means of optically stimulated luminescence (OSL) dating. New data come from the analysis of soft sediment deformation, palaeosols, geomorphological mapping, and published seismic surveys on the onshore and offshore Gulf of Cadiz.The present structure of El Abalario dome resulted from the complex interaction of littoral-catchment processes and sealevel changes upon an emergent coastal plain, conditioned by the upwarping of the underlying Pliocene-Pleistocene prograding deltaic sequence. Upwarping is probably related to escape of over-pressurized fluids, accompanied by dewatering, prior to (?) and during OIS (Oxygen Isotopic Stage) 5. Continued upwarping produced the large NW-SE gravitational fault of Torre del Loro (TLF) in the southwestern flank of the dome, roughly parallel to the present coastline during OIS 5-OIS 4. The resulting escarpment favoured the accumulation of aeolian sand dunes (units U1, U2, and U3) from OIS 5 to early OIS 1. Unit U1 (OIS 5) ends upwards in a supersurface with a thick weathering profile that suggests moist and temperate climatic conditions. Unit U2 accumulated mainly during OIS 4 and OIS 3 with prevailing W/E winds. The supersurface between U2 and U3 records a part of OIS 2, with relative low sea level. Sedimentation of unit U3 took place during the Last Deglaciation (radiocarbon and OSL ages) with prevailing W/SW winds, under a temperate moist climate, that became more arid towards the top (Holocene). A major supersurface with an iron crust-like layer (SsFe) developed during the Holocene Climatic Optimum (OIS 1) under wetter and more temperate conditions than before, fossilizing the TLF. The supersurface is covered by younger aeolian dunes (U4, U5, U6, and U7) transported by W-SW winds since the Late Neolithic-Chalcolithic cultural period (~5.0 ky cal BP).
Sea level and clima te changes archived in various coastal environments during the last part of the last glacial and present interglacial periods are investigated by interpolating available geomorphology, sedimentology, palaeontology and geochronology data. The coastal response to these changes depended on the environment and geographic location. Changes of sea level during the rising, transgressive phase are well recorded in the sedimentary filling of the estuaries, whereas during the phase of highstand they are best recorded in beach-barrier environments. The postglacial rise of sea level took place in two phases: a rapid rise until 6500 cal BP, and a second phase of near stability with minor oscillations of metric magnitude. Regarding climate changes, there is no record of changing temperatures in the coastal zones of southern Spain, although there is in precipitation and wind intensityjvelocity. After 7-5 cal ka BP, the general climatic trend towards aridity was punctuated by several short-lived (centennial) episodes of increased aridity that occurred with a millennial cycle, often coincident with Bond cool events and, in sorne cases, with decreases of sea surface temperatures. The absence of human in ter ventio n in vegetation composition until 2000 BP suggests that most environmental coastal shifts were climatically driven,
-The interaction between global (glacio-eustatic sea-level rise) and regional factors (oceanographic and tectonic) has controlled the evolution of coastline during the Holocene in Southem Iberia.At ca. 10,000 14C years BP a deceleration of relative sea-level rise took place both in the Atlantic and Mediterranean littorals, with a maximum transgression at 6450 14C years BP. In subsiding areas (present tidal flats) estuaries illustrate a clear marine influence recorded both in sediments and the fauna while in uplifting areas prograding spit-bar systems developed. Two phases of major progradation are distinguished in these systems: the first one between 6450 and 3000 14C years BP, with a sedimentary gap at ca. 4000 14C years BP; and the second one from 2750 14C years BP up to present, with an intervening gap between 1200 and 1050 14C years BP. These progradation phases develop during stillstands followed by relative sea-level fall, while the sedimentary gaps represent relative high sea level. In the Mediterranean areas, with a higher uplift rate, marine terraces almost coeval to those gaps occur.The most pronounced modifications in littoral dynamics occurred at between 3000 and 2750 14C years BP represented by changes in the direction of longshore drift and prevailing winds and in the predominance of progradation over aggradation processes.At ca. 1000 14C years BP the estuaries record a greater fluvial than marine influence, and at 500 years ago an extraordinary increase in coastal progradation took place in all littoral zones. The European Medieval Warm period is characterized, at least during its initial phase, by low pressure climate conditions, while during the Little Ice Age anticyclonic conditions gave rise to a strong coastal progradation.
This study represents the first paleoseismic approach in Spain in which archaeological remains are considered. The ancient Roman city of Baelo Claudia (1st-4th centuries AD), located at the axial zone of the Gibraltar Strait (Cadiz, south Spain), contains abundant disrupted architectural relics and ground collapses (i.e. landsliding, liquefacion) probably related to historic earthquake damage of intensity IX-X MSK. The archaeological stratigraphy of the city evidence two major episodes of abrupt city destruction bracketed in AD 40-60 and AD 350-395 separated by an intervening horizon of demolition for city rebuilding, otherwise characteristic for many earthquake-damaged archaeological sites in the Mediterranean. The second episode led the eventual city abandonment, and it is evidenced by good examples of column collapse, distortion, failure and breakdown of house and city walls, and pavement warping and disruptions documented during different archaeological excavations, which can be catalogued as secondary coseismic effects. Main damaged relicts observable today are the set of pop-up like arrays and warping developed in the ancient Roman pavement. Their analysis indicate an anomalous westwards ground displacement oblique to the main gentle southward slope of the topography, as also evidence failures, collapses and breakdown of walls and columns, suggesting that stress acted in a broad SW-NE/WSW-ENE orientation consistent whit the expectable motion along the largest NE-SW strike-slip faults of the zone, which in turn can be catalogued as seismic sources of moderate events (ca. 5 mb). Major disruptions and city abandonment were hesitantly related to relatively far strong earthquakes occurred during the late 4th century AD in the Mediterranean or western coast of Iberia by Menanteau et al. [Menanteau, L., Vanney, J.R., Zazo, C., 1983. Belo II : Belo et son environment (Detroit de Gibraltar), Etude physique d'un site antique. Pub. Casa de Velazquez, Serie Archeologie 4., Ed. Broccard, París.]. However, this study indicates that the occurrence of close moderate earthquakes jointly with the unstable character of the ground at the zone (site effect) is a more reliable hypothesis to explain the observed deformations. D
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