José M. Gutiérrez-Mas

Cost of beach maintenance in the Gulf of Cadiz (SW Spain)

Beach erosion problems have been solved by adding sand to the beaches along the Gulf of Cadiz. The Gulf is located in SW Spain between the Portuguese border and the Strait of Gibraltar. During the last decade, more than 12×106 m3 of sand have been nourished in 38 restoration operations carried out on 28 beaches. The main characteristics of the nourishment campaigns (year, volume, budget, transport method, sand data, etc.) are presented. Location of sand borrow sites and distance to the beaches are also shown. Monitoring programs have been performed in order to calculate sediment loss rates. These results have been related to the beach length, the berm width and the budget in order to obtain a variety of relationships for maintenance cost as, for example, the total annual cost for each beach. This information is very useful when developing a strategy in coastal zone management. Furthermore, at least in reef-protected beaches, small yearly renourishments similar to the yearly losses, instead of greater nourishments performed with a periodicity of many years, lead to an economical saving, as well as to a better use of the natural resources.

Holocene sedimentary dynamics on the Iberian continental shelf of the Gulf of Cádiz (SW Spain)

Abstract The Holocene evolution of the Iberian continental shelf of the Gulf of Cadiz (SW Spain) has been elucidated from a study of the granulometric facies of surficial sediments and high-resolution seismic profiles. The relationship between different facies depends on eustatic events and oceanographic conditions associated with the North Atlantic Surficial Water (NASW) on the shelf. A Transgressive Systems Tract (TST) developed as a response to a transgression (14,000–6500 yr) and deposited a transgressive sand bed on the transgressive (or ravinement) surface. A backstepping para-sequence related to a brief stillstand period has produced an onlapping shelf-transgressive erosion surface. The change in eustatic regime from transgressive to highstand in the last 6500 years has resulted in the formation of a sedimentary wedge of a Highstand Systems Tract (HST), extending from the mouth of the Guadalquivir river towards the southeast because of NASW circulation. These prodeltaic mud deposits are prograding over the older transgressive sand. The present surficial sediment distribution has been influenced greatly, therefore, by the last eustatic rise of sea level and has been divided into three main areas: (a) the littoral area; (b) northern prodeltaic mud; and (c) a southern area of relict and palimpsest sand and muddy sand, generated in a high-energy littoral environment of the Late Pleistocene-Holocene shoreline transgression.

Multicycle sediments on the continental shelf of Cadiz (SW Spain)

Abstract The study of recent sedimentation in the Gulf of Cadiz continental shelf (SW Europe) is of interest due to its proximity to the Strait of Gibraltar, where the Atlantic and Mediterranean waters are interchanged and the Western Mediterranean Alpidic Orogen closes through the Gibraltar Arch. The existence of relict materials hinders the distinction of the past and present hydrodynamic regimes in present day sediments. An adequate combination of techniques has allowed the establishment of the multicyclic character of the sediments, as well as the stages undergone by the terrigenous grains. Different stages were identified: eolian and energetic fluvial provenance, chemical alterations acquired in a pedological environment, and a marine coastal origin. To verify the source areas, textural and mineralogical features of marine sediments were compared with those found in geological units from fluvial basins. Three zones were differentiated: (a) a sandy littoral, which receives local sediment supplies; (b) a clayey zone between the Guadalquivir River and Cadiz, controlled by contributions from this river provenant of the Iberian Massif and Betic Mountain range; and (c) a sandy continental shelf, between Cadiz and the Cape of Trafalgar, with a low rate of supplies coming from the Guadalete and Barbate rivers, which include materials from the Occidental Betic Mountain range and Neogene units.

Present-day sedimentation patterns of the Gulf of Cadiz northern shelf from heavy mineral analysis

The sedimentary processes on the northern shelf of the Gulf of Cadiz (SW Spain) are basically controlled by two factors: the different rates of fluvial supply between the northern and southern sectors and the dominant water flows toward the SE. The distribution of heavy minerals shows differences between the two sectors with predominance of ultrastable minerals in the southern sector, in relation to the different supply rates. This distribution is related to the sea-level change during the Holocene, fluvial supplies, and oceanographic factors. The application of statistical multivariate methods to heavy mineral data shows the principal heavy mineral association (epidote—garnet—rutile), which is very similar to that in neighboring terrestrial areas and offers the possibility of referring factors to source areas.

Clay minerals as dynamic tracers of suspended matter dispersal in the Gulf of Cadiz (SW Spain)

Abstract The dispersal of suspended matter in the Gulf of Cadiz (SW Spain) is related to its geographical position near the Strait of Gibraltar, and the continental margin, and to Atlantic and Mediterranean water flows and their interaction with the littoral tidal processes. The main direction for transport of suspended matter is towards the southeast, along the continental margin, from the mouths of the rivers Guadiana and Guadalquivir to the Mediterranean. This general transport pattern is perturbed by littoral processes such as those occurring in Cadiz Bay, where a portion of Atlantic suspended matter, driven by flood tide, comes into the inner bay and is deposited in the shallow waters of lagoons and salt marshes. Subsequently, because of the southeast wind and waves, these sediments are remobilized and transported to the west by the ebb tide, to deeper Atlantic waters. This dynamic interaction between Atlantic and littoral waters generates a different type of sediment layout, the origin of which is difficult to establish. In order to understand the dispersal of the suspended matter and its effects on the inner continental shelf, the distribution of the main clay minerals has been determined by means of X-ray and Q-mode and R-mode factor analysis. The suspended matter dispersal paths were established through the distribution of main clay mineral associations and from the ratios amongst these minerals. The results allow us to determine the importance of the tidal flows in the suspended matter transport system of the Gulf of Cadiz. Therefore, a record was kept of which of the outgoing tidal flows from the inner parts of Cadiz Bay reached the continental shelf. The flows intercept the clear Atlantic waters giving rise to a complex sediment distribution and to the mix of clay minerals. The study has also allowed us to establish the sediment source areas and the extent of sediment transport and the paths they follow.

Structural and physiographic control on the Holocene marine sedimentation in the bay of Cadiz (SW Spain)

The Quaternary tectonic activity in the Gulf of Cadiz has considerably influenced the depositional regime and distribution of Holocene marine deposits. The aim of this work is to determine the nature of the recent sedimentary filling in the Bay of Cadiz sea bottom and adjacent continental shelf and to establish the main controlling factors on the Holocene marine sedimentation. The sedimentary record indicates siliciclastic sedimentation supplied from the continent, with alternating episodes of high and low sedimentation rates. The recent sedimentary evolution of this marine area was controlled by the Late Quaternary eustatic fluctuations. Bathymetric, geophysical and drilling data have been employed to prepare a detailed isopach map of the non-consolidated recent sedimentary cover. Thickness distribution shows significant variations related to the infilling of former fluvial palaeochannels incised during the Late Pleistocene lowstand, and highly controlled by the structural neotectonic trends of faults and joints: NNW-SSE, NNE-SSW and ENE-WSW. The general distribution of isopachs in this area is clearly influenced by these morphostructural lines, which controlled the sedimentary processes during the Holocene. These results are coherent with the main regional neotectonic structures previously described in the nearby continental area, and confirm their prolongation towards the marine domain.

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

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.

Record of very high energy events in Plio-Pleistocene marine deposits of the Gulf of Cadiz (SW Spain): facies and processes

The depositional conditions that characterized the sedimentary filling in the southern sector of the Guadalquivir Basin during the late post-orogenic Neogene have been established through the sedimentological study of the Plio-Pleistocene outcrops along the Cadiz coast (SW Spain). The study has contributed to a better interpretation of the regional stratigraphy and helped to establish both depositional mechanisms and processes. Deposits show different lithofacies according to the dominant climatic and prevailing environmental conditions. Pliocene deposits show bioclastic lithofacies with abundant warm-water fossils, whereas Pleistocene sediments have a low fossil content. Stratigraphic sections indicate important depositional changes: sandstone and grainstone were deposited under a seasonal regime, whereas accumulations of large boulders and bioclasts are interpreted as event deposits, the product of episodic oceanographic processes, such as huge storms or tsunamis. These deposits do not have a seasonal character; however, given their relative frequency in the stratigraphic sections, they were probably associated with neo-tectonic activity in the Guadalquivir Foreland Basin, which was an important controlling factor in this basin. The proximity to the Africa-Eurasia plate boundary together with several historically documented earthquakes and tsunamis in the study area, suggest that these processes could explain the origin of these deposits. The seismic-tectonic activity was more intense between the late Pliocene and early Pleistocene, as shown by the presence of a well-marked angular unconformity, as well as by a higher frequency of the very high energy clastic and bioclastic accumulations.

Sedimentary Provenance and Depositional History of Cadiz Bay (SW Spain) Based on the Study of Heavy Minerals Surface Textures

Mineralogical and Scanning Electron Microscope (SEM) analysis was used to study heavy mineral grains present in recent marine sediments from Cadiz Bay (SW Spain) and the adjacent continental shelf, in order to establish the provenance of sediments and to determine physical and chemical processes which took place during their depositional history. Surface features analysis has been used to detect mechanical and chemical textures; euhedral, sub-euhedral and anhedral grain morphologies have been observed. Different phases or stages in the sedimentary evolution of these heavy mineral grains can be differentiated. The oldest one corresponds to eolian environments, followed by fluvial and coastal environments. The third phase is represented by chemical alterations acquired in shallow marine environments. The recent phase is characterized by presence of textures generated in pedogenic environments. Heavy mineral assemblages established in this work were compared with those found in the nearby continental areas; they are used to identify likely sediment sources. The most important source is the Iberian Massif, which provided euhedral and sub-euhedral metamorphic minerals, while the secondary sediment sources correspond to pre-orogenic formations of the Betic Cordilleras with predominance of anhedral grains of high degree of maturity. Other sediment sources are the post-orogenic Tertiary deposits present in the Guadalquivir basin and the plio-quaternary and fluvial deposits outcropping along coastal and continental areas near the bay of Cadiz.