Utility of clay Minerals in the Determination of Sedimentary Transport Patterns in the Bay of Cadiz and the Adjoining Continental Shelf (SW-Spain)

Abstract

The contents and the distribution of clay minerals in modern sediments of the Cadiz bay and the continental shelf have been studied aiming to establish the sedimentary exchange model and the pathways followed by the clay fraction between the bay and the adjoining continental shelf. The most abundant clay minerals in the muddy sediments consist mainly of illite, smectite, interstratified illite-smectite, kaolinite and chlorite. The application of factor analysis method (PCA) to clay minerals data are considered to be useful in the determination of sedimentary transport patterns. The data from clay mineral assemblages, and their distribution map, make possible to establish the fine sediments transport paths in the study area using clay mineral as natural tracers. This model of transport takes in consideration the facies distribution, the supplies sources and the way of fine sediments are incorporated to the marine environment Two flows paths have been established: the outflows coming from Cadiz bay and the littoral zones; and the inflows coming from external marine zones of the bay. These flows are controlled by tidal currents and the morphology of the coast. The action of surge and the marine currents, specially the Atlantic Surface Water flow, are also important in the transport of fine sediments coming from sources located to the north of the study zone.

Dynamics of Sediments Exchange and Transport in the Bay of Cadiz and the Adjacent Continental Shelf (SW - Spain)

“…Their origin is clearly detrital or inherited, and may reflect the combined effects of the influence of the source areas, the type of weathering on the adjacent continents, and the process of transport and sedimentation (Millot, 1970;Sawheney & Frink, 1978;Stanley & Liyanage, 1986;Weaver,1989;Chamley, 1989;Naidu et al, 1995). In the present www.intechopen.com Dynamics of Sediments Exchange and Transport in the Bay of Cadiz and the Adjacent Continental Shelf (SW -Spain) 31 study, clay minerals have been used as tracers, since their small size makes them the only particles susceptible of being transported away from the bay, out towards the continental shelf (Gutierrez-Mas et al, 2006;Achab et al, 2008). Other studies indicate that the clay mineral assemblages deposited in front of the rivers mouth and toward deep marine areas can be used as dynamic tracers to deduce transport path and the sources areas of clay minerals (Neiheisel & Weaver, 1967;Bhukhari & Nayak, 1996;Parhan, 1996).…”

“…The most important being North Atlantic Surface Water (NASW) and littoral currents moving towards the southeast, and are responsible for the dispersal of fine sediments from the Guadalquivir and Guadiana Rivers (Gutierrez-Mas et al, 2006;Achab et al, 2008); and the Mediterranean Outflow Water (MOW) moving west to deeper water (Maldonado & Stanley, 1981;Baringer & Price, 1999). The tidal regimes in the Bay of Cadiz is mesotidal and of a semidiurnal character, with a mean tidal range of 2.39 m, mean spring tidal range of 3.71 m and neep tide of 0.65m (Benavente et al, 2000).…”

“…The tidal regimes in the Bay of Cadiz is mesotidal and of a semidiurnal character, with a mean tidal range of 2.39 m, mean spring tidal range of 3.71 m and neep tide of 0.65m (Benavente et al, 2000). The tidal currents are considered to be responsible of fine sediment transport (Achab et al, , 2008. Wind and wave action are also essential factor in the sedimentary dynamics.…”

“…Its development is a consequence of the sedimentary infilling when the sea level was a few meters above the present, and also by growth of inside tidal deltas. After of the last eustatic fall (5.000-6.000 years B.P), the partial emerging of the bottoms has given cause for a wide marshes zone, occupied by halophyte vegetation and drained by a complex system of tidal creeks and channels; that constituted the hydrodynamics and sedimentological transmission from the inner bay zones and the marine environments Dabrio et al, 2000;Achab et al, 2008). The continental shelf has a gentle slope and a slight inclination toward the west, with an average width of 40 km, although there are important variations in the area close to the Straits of Gibraltar, where it narrows to 20-30km.…”

“…Several studies focused on sedimentary dynamics associated with water mass movements have been realized by several authors (Madelian, 1970;Kenyon and Belderson, 1973;Melières, 1974;Palanques et al, 1987;Grousset et al, 1988;Maldonado & Nelson, 1999a;Nelson et al, 1999;LopezGalindo et al, 1999;Lobo et al, 2000). Others studies have been focused on the dynamics of fine sediments and clay minerals in the Cadiz bay and the adjacent marine deeper zones (Gutierrez Mas et 1996b, 1997Achab et al, 1998Achab et al, , 2000bAchab et al, 2008). Also, they have been approached studies about the dispersal of the suspended matter in the bay of Cadiz and its effects on the inner continental shelf as well as their influence on the recent marine www.intechopen.com Sediment Transport in Aquatic Environments 20 sedimentation en general (Palanques et al, 1987, Gutierrez Mas et al, 1999Achab et al, 2000a;Gutierrez Mas et al, 2006).…”