Sequence stratigraphy of Holocene incised-valley fills and coastaludevolution in the Gulf of Cádiz (southern Spain)

摘要

This first sedimentary interpretation of two incised-valley fills in the Gulf of Cádiz (southern Spain), whichudaccumulated during the last fourth-order eustatic cycle in response to fluvial incision, changes of sea level, andudcorrelative deposition, relates the filling of the estuarine basins and their barriers with four regional progradationudphases, H1 to H4. The cases studied are the wave-dominated Guadalete, and the mixed, tide and wave-dominatedudOdiel-Tinto estuaries. The sequence boundary is a type-1 surface produced during the lowstand of the Last Glacialudperiod ca. 18 000 14C yr BP. No fluvial lowstand deposits were found in the area. Due to rapid transgression theudvalley fills consist of transgressive and highstand sediments. The maximum landward advance of the estuarineudbarriers occurred ca. 6500–6000 14C yr BP during the maximum of the Flandrian transgression, but there is noudevidence of sea level rising appreciably above the present. A large part of the estuaries was filled during H1 (ca.ud6500–4400 14C yr BP) but ravinement by shifting tidal inlets destroyed most of the coeval barriers. During theudH2 phase (ca. 4200–2550 14C yr BP) sedimentation was favoured by arid conditions and concentrated in the axialudestuarine zones and the barriers. Between H2 and H3 prevailing winds changed from W to WSW, increasing spitudgrowth to the east and south-east. Progradation of bay-head deltas and flood-plains during H3 (ca. 2300–800 14C yrudBP) and H4 (500 yr ago to the present) further reduced the accommodation space in the largely-filled valleys, andudsediment by-passed the estuaries and accumulated in the estuarine barriers as fast-growing spits. Arid conditionsudand increasing human activity have caused rapid coastal modifications.