Depositional history of estuarine infill during the last postglacial transgression (Gulf of Cadiz, Southern Spain)

Abstract

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 archives of the last 15ka in the Atlantic–Mediterranean Spanish linkage area: Sea level and climate changes

“…1). The best, more continuous results were obtained in Guadalete (Goy et al , 1996;Dabrio et al, 1999Dabrio et al, , 2000 and OdielTinto estuaries. In the Guadalquivir estuary, the biggest of all, results are still fragmentary (Zazo et al, 1999c), and reconstructions of the fossil infill of the paleo-valley are most difficult at present owing to the lack of dated cores and complex tectonic activity.…”

“…Radiocarbon data available from previous authors are used (Rodriguez-Ramirez et al, 1996;Zazo et al, 1999bZazo et al, , 2005Dabrio et al, 2000;Lario et al, 2002;Goy et al, 2003). Usually, sediments were dated by accelerator mass spectrometry (AMS) and conventional radiocarbon techniques applied on mollusc shells: Glycymeris glycymeris in beach and barrier systems, the available molluscs and wood fragments in estuaries, and charco al in aeolian dunes.…”

“…1). Much information comes from coastal sectors studied in previous papers (e.g., Zazo et al, 1994Zazo et al, , 1999aZazo et al, c, 2005Borja et al, 1999;Dabrio et al, 1999Dabrio et al, , 2000Goy et al, 1996Goy et al, , 2003Lario et al , 2000Lario et al , , 2002Luque, 2002;YIl et al, 2003), and from Doñana-Huelva (Rodrí-guez-Ramírez et al, 1996Ruiz et al, 2005;Cáceres et al, 2006). The paper also ineludes data from Portuguese (Bard et al, 2000); M39-008 (Cacho et al, 2001; MD95-2043 (Cacho et al, 1999(Cacho et al, , 2001Sánchez-Goñi et al, 2002);H-658 C (de Menocal et al, 2000).…”

Late Holocene evolution of the southwestern Doñana National Park (Guadalquivir Estuary, SW Spain): a multivariate approach

“…The ¢nal results correspond to calibrated ages (cal.) using 2c intervals, with a reservoir correction (3440 Q 85 yr) as suggested in Lario (1996) and Dabrio et al (1999Dabrio et al ( , 2000 for this area. Ages discussed below will be expressed as the highest probable age of the 2c calibrated range (e.g., Van der Kaars et al, 2001) 4.…”

Natural to anthropogenic forcing in the Holocene evolution of three coastal lagoons (Caldas da Rainha valley, western Portugal)

“…In what relates the latter, periods of population growth reflect in development of agriculture, deforestation and consequently more sediment availability to the coastal areas, particularly obvious in sheltered locations as estuaries and lagoons (e.g. Dabrio et al, 2000;Komar et al, 2004). In contrast, periods of demographic recession relate with forest expansion and regain of natural vegetation.…”