ELSEVIER Sedimentary Geology 117 (1998) 11-32 Sed~menta~ Geology Architectural stacking patterns of the Ebro delta controlled by Holocene high-frequency eustatic fluctuations, delta-lobe switching and subsidence processes a* L. Somoza ' , A. Barnolas a, A. Arasa h, A. Maestro a, J.G. Rees c, F.J. Hernandez-Molina d a Marine Geology Division, ITGE, Geological Survey of Spain, R[os Rosas 23, 28003 Madrid, Spain b Departament Geologia Din~mica, Geofisica i P. Universitat de Barcelona, Campus de Pedralbes, 08071 Barcelona, Spain c Coastal and Engineering Geology Group, British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK d Facultad Ciencias del Mat', Universidad de Cddiz, Rio San Pedro s/n. 11510 Puerto Real, Cadiz, Spain Received 15 January 1997; accepted 10 November 1997 Abstract During the Late Pleistocene and Holocene (125 ka B.P. to present) a Type l, 4th-order, depositional sequence, comprising regressive, lowstand, transgressive and highstand system tracts, formed worldwide. The Holocene (10 ka B.E to present) part of this contains the latest and present highstand systems tract (HST). Within this and the underlying transgressive systems tract (TST) of the Ebro delta, in northeastern Spain, higher-frequency, 5th- to 6th-order, sea-level fluctuations are recognised. These form retrogradational and progradational high-frequency depositional sequence sets within the TST and HST, respectively. Each high-frequency sequence comprises: (1) a basal, highly reflective, shell lag, associated with an erosional (transgressive) surface; (2) aggradational deposits which seawards consist of a wedge of marine clays with transparent seismic facies, but inland are represented by thick peats; (3) progradational deposits, composed of sandy delta-front facies, displaying slope clinoforms; these pass seawards into prodeltaic grey silts, and landwards, into red silts and pebbly sands of delta-plain facies. The progradational deposits downlap towards their bases. The aggradational deposits formed in response to a period of rising sea-level and a rapid increase in accommodation space. Progradation began when sediment supply to the delta exceeded accommodation space as a result of relative sea-level fall. The relative sea-level curve for the delta has a stepped character, caused by the punctuation of the 4th-order sea-level trend by higher-frequency eustatic fluctuations as well as by high subsidence rates, of about 1.75 mm per year. The TST comprises retrogradational parasequences that onlap the underlying Pleistocene gravels. The maximum flooding surface separating the TST from the HST, was formed about 6900 yrs B.E on the basis of ~4C dating of peats. The HST comprises progradational deltaic and aggradational units, stacked as progradational high-frequency parasequence sets. The HST of the Ebro delta is compared with other deltaic sequences around the world, in particular with that of the Mississippi delta. A tentative chronology of the high-frequency climatic and eustatic oscillations influencing deltaic sedimentation globally over the last 7000 years is presented. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Holocene; delta; sea-level changes; high-resolution seismic; sequence stratigraphy; radiocarbon dating; high- frequency cycles; subsidence rates; Mediterranean; Spain * Corresponding author. 0037-0738/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PH S0037-0738(97)00121-8