Surface facies and sediment dispersal patterns: southeastern Gulf of Cadiz, Spanish continental margin

Grain size of 294 samples and mineralogical analysis of 364 surface samples from the Spanish continental shelf and upper slope of the Gulf of Cadiz de lineate four sediment facies that derive mainly from siliciclastic sources. The northern area is formed by the mud-rich prodelta of the Guadalquivir R iver, parallel to the coast and progradational towards the southeast. It ex hibits a typical bulk mineral association of illite >> smectite > kaolinite + chlorite. In the north-central area, there is a smaller, coarser-grained prodelta in the Bay of Cadiz, linked to the Guadalete River, which offshor e becomes connected to the Guadalquivir prodelta. Its mineral association i s quartz >> illite > kaolinite + chlorite. In the southern area, where fluv ial input is negligible, the characteristic coarse-grained facies generally corresponds to relict, Late Pleistocene reworked deposits. The typical min eral association is quartz > calcite > aragonite >> smectite-mixed layer cl ay minerals. The fourth area corresponds to the shelf break and upper slope offshore Cadiz Bay, where a westward grain-size coarsening differentiates the deposits of the last low sea-level stand and no typical mineral associa tion exists. The mineralogy of the terrigenous deposits indicates a source area from Paleozoic sequences of the Sierra Morena to the north and the Sub betic Units and Gibraltar flysch to the east. The Neogene deposits of the G uadalquivir depression are an additional source of shelf sediments. The sur face sediment distribution on the inner continental shelf is largely determ ined by the southeastern Atlantic water flow, the terrigenous input from ri vers, and the shelf physiography. Sediment dispersal on the outer continent al shelf and upper slope, in contrast, largely reflects the location of low sea-level stand, the development of palimpset deposits, and the location o f the Mediterranean undercurrent over the margin. (C) 1999 Elsevier Science B.V. All rights reserved.