Sedimentary Provenance and Depositional History of

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Thalassas DOI 10.1007/s41208-016-0018-6

Sedimentary Provenance and Depositional History of Cadiz Bay (SW Spain) Based on the Study of Heavy Minerals Surface Textures M. Achab 1 & J. P. Moral Cardona 2 & J. M. Gutiérrez-Mas 2 & A. Sánchez Bellón 2 & J. L. González-Caballero 3

# Springer International Publishing Switzerland 2016

Abstract 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

* M. Achab [email protected]; [email protected]

1

Département des Sciences de la Terre, Institut Scientifique, Université Mohamed-V, BP 703, Rabat, Morocco

2

Departamento de Ciencias de la Tierra. Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz, Apto. 40, 11510, Puerto Real, Cádiz, Spain

3

Departamento de Estadística e Investigación Operativa. Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz, Apto. 40, 11510, Puerto Real, Cádiz, Spain

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. Keywords SEM analysis . Heavy minerals . Surface features . Provenance . Cadiz Bay

Introduction and Objectives Studies of provenance and transport of sediments have been traditionally based on the use of accessory minerals, particularly heavy minerals. These minerals appear in small quantities in most sediment, usually less than 5 %. They have been considered to be a significant tool to interpret provenance and depositional history and maturity of the sediments (Pettijohn 1975; Morton 1985; Schäfer and Dörr 1997; Moral Cardona et al. 1997b; Dill 1998; Hegde et al. 2006; Popp et al. 2007; Haredy 2008). Moreover, heavy mineral assemblages have been often used to establish sediment sources and the depositional conditions in sedimentary environments (Hubert 1962; Komar et al. 1989; Morton and Hallsworth 1999; Ergin et al. 2007). Other techniques such as surface texture analysis with Scanning Electron Microscopy (SEM), have provided useful information on the superficial micromorphological features of detrital grains and on the processes that they have undergone during their depositional history (Krinsley and Donahue 1968; Stiglitz 1969; Brown 1973; Le Ribault 1975; Moral Cardona et al. 1996a; Mahaney 2002; Madhavaraju et al. 2004; Kasper and Faustinos Morales 2007). The study of surface textures of heavy mineral grains can also be applied in provenance studies because; first it helps in the better identification and differentiation of source area, and second, it can provide a deeper

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knowledge of the provenance history (Moral Cardona et al. 2005 among others). In the Gulf of Cadiz, several studies have already been done on heavy minerals distribution in recent marine sediments such as those realized by Meliéres (1974), Gutierrez-Mas et al. (1993, 2003), Achab (2000), and Achab and Gutierrez-Mas (2009). In the nearby continental areas, previous heavy mineral studies have been carried out by Mabesoone (1966), Viguier (1974), Zazo (1980), Perez-Mateos et al. (1982) and Moral Cardona et al. (1996b, 1997a, 2005). In this work, textural, mineralogical and micromorphological analysis has been applied to establish the provenance and the depositional history of recent marine sediments from Cadiz Bay (SW Spain). The objective of this study was also to distinguish possible stages undergone by different heavy mineral grains in their sedimentary evolution and to establish the relationships of these minerals with the possible sediments source supplies and source areas.

Regional Setting The study zone is located in the Gulf of Cadiz (SW Spain), between the Guadalquivir river mouth and Trafalgar Cape (Figs. 1 and 3b). The Bay of Cadiz is about 28.5 km long and 13.5 km wide, two specific sectors can be distinguished: the outer bay to the north which is well connected to the continental shelf, this last has an average width of 40 km, with shelf break at 150–200 m deep and the inner bay or lagoon system located to the south which is protected from waves and storms of the west and southwest. The coast is orientated from NNW to SSE with east–west sections, which gives a stepped morphology, as a consequence of recent faults (Sanz de Galdeano and López Garrido 1991). The current regime is controlled by littoral currents and the North Atlantic Surface Water Flow (NASW), which sweep the continental shelf towards the south-east (Fig. 2a). These current transport fine sediments from the Guadiana and Guadalquivir river mouths towards the Gibraltar Strait (Gutierrez-Mas et al. 2004; Achab et al. 2008), while Mediterranean Outflow Water (MOW) is confined to deeper water (Baringer and Price 1999) and does not influence the present day sediments in the study zone (Gutiérrez-Más et al. 2006; Achab 2000). The wave regime is seasonal, with the strongest storms in the November-March period (MOPT 1992). Waves from the northwest to southwest are dominant offshore zone with a significant wave height (Hs) of 2.2 m; although the highest waves exceed 4 m during autumn and winter storms. Tidal regime is semidiurnal and mesotidal, with average tidal range of 2.39 m, and spring tidal range of 3.6 m.

Sedimentation Conditions The distribution of present-day marine sediments in Cadiz bay and the adjacent continental shelf show the prevalence of terrigenous sediments (Achab et al. 1999; Gutierrez-Mas et al. 2003). Considering the relationships between grain size of sediments and hydrodynamic regime, the study area can be divided into several specific sectors (Fig. 2b). In the inner bay mud are the dominant facies with up of 75 %, the clay and silt fractions are present with 55 and 20 % respectively, reflecting low-energy characterizing the sheltered zone. Their hydrodynamic regime is almost exclusively dominated by tidal currents and wind-wave action especially in the East. In the outer Cadiz bay, the sandy facies predominate, especially in the littoral zone. The sand fraction consists of 75 %, fundamentally of fine (22 %) and very fine (40 %) nature. This facies was found to be associated to energetic environments (Achab et al. 2005). The presence of muddy sand and sandy mud facies covering sandy bottoms indicates deposition and transport of fine sediments from the inner bay towards the inner continental shelf. These sediment facies derive from resuspension of fine-grained materials in the inner bay and from fine materials supplied by the Guadalete River and the Guadalquivir prodelta. Muddy facies are also present in the inner continental shelf as a prodeltaic muddy zone situated to the north (Fig. 2a). These fine grained sediments are related to supplies coming from the Guadalquivir River (Gutiérrez-Más et al. 2006; Achab et al. 2008). Geological Setting Geologically, the study area comprises the western part of the Betic Cordilleras and the Guadalquivir Depression (Sanz de Galdeano and López Garrido 1991; GonzálezDelgado et al. 2004; Martínez del Olmo W et al. 2005) (Fig. 3a). Different geological units and formations constitute the sedimentary strata outcropping in the surrounding continental areas of Cadiz bay (Fig. 3b). The preorogenic allochthonous materials correspond to different units of the Betic Cordilleras, which shows a chaotic tectonic structure. These materials are constituted by marls and gypsum of Trias, limestone and marls of Tertiary and Aljibe sandstones of Oligocene and diatomaceous marls of lower Miocene. Over the previous are deposited post-orogenic materials (autochtonous units), mainly from the Neogene Guadalquivir depression such as marls and calcarenites of upper Miocene, and Pliocene sand and calcarenites (Fig. 3b). Upon all those materials Pleistocene marine conglomerates, sands and sandstones are deposited, over which red sands with quartzite pebbles lie. The coexistence of pre-orogenic

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Fig. 1 Map of geographic setting and samples location of surface sediment. Bathymetry in meters

sedimentary materials with post-orogenic sedimentary terrains provides suitable conditions for a study of provenance and depositional history of marine sediments in the area.

Materials and Methods Sediment Sampling and Textural Analysis A total of 140 sediments samples were extracted and collected from different sectors of the Cadiz bay and adjacent continental shelf by means of piston core and Van-Veen dredge (Fig. 1). Geographical position was carried out by mean of the Differential Global Position System (D-GPS). Grain size analysis has been made in several phases: i) wet separation of coarse and fine fractions using a sieve of 4 Phi, ii) The coarser material (from −1 Phi to 4 Phi) was dry-sieved at phi intervals for 15 min, iii) The fine fraction size ( H > Goe > A > R). The second assemblage obtained by factor 2 (19.76) is represented by Tourmaline-Topaz-Zircon-Ilmenite (T > Top > Z > Ilm). The mineralogical assemblage defined by Factor 3 (16.05 %) is Andalusite-Chloritoide-Epidote (A> > Chl > E). The factor 4 (10.46 %) presents minor significance in the study area and associates the Zircon and Garnet (Z > G).

1

2,532054

28,13393

28,1339

2

1,778691

19,76324

47,8972

3 4

1,444972 0,941805

16,05525 10,4645

63,9524 74,4169

Morphologies and Microtextures (SEM) Main morphologies observed in heavy mineral grains are: a) euhedral (idiomorphic), b) sub-euhedral (subidiomorphic) and c) anhedral (xenomorphic). Regarding the superficial microtextures, different marks affecting all or part of the surface of mineral grains are identified,: Conchoidal fractures, Arcuate steps, Grooves, Bulbous edges, Upturned plates, Chemical etch pits, Solution pits, Irregular surface solution, Surface polishing. Table 2 describes surface textures and morphologies of different mineral grains.

a) Euhedral grains (Fig. 6c) showing surface mechanical features, such as conchoidal fractures and grooves. b) Sub-euhedral grains (Fig. 6b and d) with polished conchoidal fractures and solution pits c) Rounded anhedral grains (Fig. 6a) showing eolic-origin features, such as upturned plates, arcuate steps and curved grooves.

Tourmaline - Grains show mechanical textures, such as conchoidal fractures, grooves, arcuate steps and upturned plates. Furthermore, grains are affected by solution processes, which show textures such as oriented etch pits and solution pits. Two types of morphologies are observed: a) Euhedral-sub-euhedral grains (Fig. 7a and b, d) with small polished conchoidal fractures and grooves. b) Angular anhedral grains (Fig. 7c) with a predominance of conchoidal fractures. Other textures are arcuate steps, grooves

Zircon - grains show mechanical marks such as, grooves, arcuate steps, and polished conchoidal fractures. They were later modified by chemical processes, resulting in oriented etch and solution pits. In addition, some grains show a superficial fine crust and surface polishing (Fig. 6). Mineral grains show three morphology types, which are associated with different surface textures: %

Goethite

Hematite

Topaz

Chloritoid

Epidote

Anatase

Pyrite

Enstatite

Ilmenite

Magnetite

Andalusite

Tourmaline

Rutile

Garnet

Zircon

Hornblende

14 12 10 8 6 4 2 0

Fig. 4 Mineralogical composition of the heavy fraction in the study area

Fig. 5 Projection of the variables on the factor-plane (1x2), from Principal Components Analysis (PCA)

Thalassas Table 2 self

Morphology, surface textures and provenance of different studied heavy-minerals grains from Cadiz Bay sediments and adjacent continental

Mineral

Morphology Surface textures

Possible source areas

Zircon

Euhedral

Igneus rocks (Iberian Massif), Pliocene sands (Jerez)

Conchoidal fractures and grooves

Sub-euhedral Polished conchoidal fractures and solution pits Rounded Tourmaline Euhedral

Surface polishing, upturned plates and solution pits Conchoidal fractures, grooves and chemical textures

Aljibe sandstones (Betic Cordilleras), Guadalete terraces Igneus rocks (Iberian Massif)

Sub-euhedral Polished conchoidal fractures and chemical solution processes Pliocene sands (Jerez) Garnet

Angular Euhedral

Conchoidal fractures, grooves and arcuate steps Grooves widned by solution pits

Miocene calcarenites (Guadalquivir basin) Metamorphic rocks (Iberian Massif) Pliocene sands (Jerez), Aljibe sandstones (Betic Cordilleras)

Sub-euhedral Chemical solution processes Sub-rounded Large polished conchoidal fractures widened by solution pits Aljibe sandstones (Betic Cordilleras) Epidote

Angular Euhedral

Conchoidal fractures, grooves and arcuate steps Conchoidal fractures and grooves

Miocene calcarenites (Guadalquivir basin), coastal cliffs Triassic ofites (Betic Cordilleras)

Sub-euhedral Polished conchoidal fractures, grooves and solution pits

Pliocene sands (Jerez), Guadalete terraces

Sub-rounded Mechanical marks and chemical solutions pits Angular Polished conchoidal fractures and grooves

Metamorphic rocks (Iberian Massif) Miocene Calcarenites (Guadalquivir basin)

Andalusite Sub-euhedral Polished conchoidal fractures and chemical solution processes Pliocene sands (Jerez), Guadalete terraces Sub-angular Conchoidal fractures, grooves and arcuate steps Miocene Calcarenites (Guadalquivir basin)

Garnet - Grains show different morphologies: a) Euhedral and sub-euhedral grains (Fig. 8c and d). These present small conchoidal fractures and grooves with old mechanical and chemical marks. b) Anhedral grains. Angular grains with surface mechanical textures. Two sub-types are distinguished: Angular grains (Fig. 8a) with mechanical textures and conchoidal fractures (angular or polished). Other textures are arcuate steps, Fig. 6 Morphology and surface features of zircon grains from SEM images (a) Rounded grain with old mechanical marks (arcuate steps and upturned plates) affected by chemical solution processes. b and d Subeuhedral grain showing polished conchoidal fractures and solution pits. c Euhedral grains with conchoidal fractures and grooves

grooves and upturned plates. Sub-rounded grains (Fig. 8b) showing oriented etch and solution pits affecting previous textures. In some grains a generalized surface polishing is observed.

Epidote - Grains display chemical surface textures, but mechanical marks are also observed (Fig. 9). Chemical textures are manifested by the presence of oriented etch pits and

Thalassas Fig. 7 Morphology and surface features of tourmaline grains from SEM images. a Sub-euhedral grain with polished conchoidal fractures. b Magnification of grain 8A showing solution processes. c Grain with large angular conchoidal fracture. Note the primitive surface with old mechanical marks (arcuate steps and upturned plates) affected by solution processes. (d) Euhedral grain with mechanical (conchoidal fractures and grooves) and chemical textures (oriented etch pits)

solution pits, which seem to overprint older mechanical marks (arcuate steps, grooves and polished conchoidal fractures). Different morphologic types are observed: a) Euhedral grains: these show angles and edges, and present very few mechanical marks on their surfaces, such as conchoidal fractures (Fig. 9d). b) Sub-euhedral grains (Fig. 9a): these show abundant chemical textures, but mechanical marks can also be observed. Chemical textures are manifested by presence of oriented etch pits and solution pits, which overprint older mechanical marks (grooves and polished conchoidal fractures). Fig. 8 Morphology and surface features of garnet grains from SEM images. a Grain with angular conchoidal fractures and arcuate steps. Chemical marks appear as oriented etch pits and oriented Vs affecting to previous mechanical textures. b Grain with large polished conchoidal fracture. Note old mechanical marks widened by dissolution. c Euhedral grain showing grooves widened by solution. d Subeuhedral grain affected by chemical solution processes

c) Anhedral grains: Two subtypes are differentiated: Subangular anhedral grains, characterized by presence of significant mechanical marks (Fig. 9c), and Subrounded anhedral grains, with bulbous edges and solutions pits (Fig. 9b).

Andalusite - Grains show surface textures that indicate predominance of solution processes, such as oriented etch pits and solution pits, which re-worked older mechanical marks (polished conchoidal fractures and arcuate steps). Mineral grains show two morphology types (Fig. 10):

Thalassas Fig. 9 Morphology and surface features of epidote grains from SEM images. a Sub-euhedral grain with mechanical marks (polished conchoidal fractures and grooves) widened by solution. b Sub-rounded grain showing mechanical marks and chemical solution pits. c Angular grain with chemical textures (oriented etch and solution pits), which seem to overprint older mechanical marks (conchoidal fractures and grooves). d Euhedral grain showing conchoidal fractures and grooves

a) Sub-euhedral grains. This is the most frequently observed morphology. Surface textures are similar to the subeuhedral epidote grains, with predominance of chemical features, such as irregular surface solution, oriented etch pits and solution pits. These textures usually have reworked old mechanical marks, such as polished conchoidal fractures (Fig. 10c and d). b) Sub-angular anhedral grains with surface mechanical features, essentially grooves, arcuate steps and conchoidal fractures (Fig. 10a). Chemical textures are manifested by presence of chemical etch pits, which overprint older mechanical marks (Fig. 10b). Fig. 10 Morphology and surface features of andalusite grains from SEM images. a Sub-angular grain with conchoidal fractures, arcuate steps and grooves. b Detail of a grain showing a chemical solution stage. c and d Sub-euhedral grains with polished conchoidal fractures, affected by chemical marks (oriented etch pits, solution pits and hollows)

Discussion Processes, Depositional Environments and Stages The surface features analysis of siliciclastic grains with SEM techniques can provide useful information on different sedimentary stages suffered by mineral grains, as well as on the characterization of depositional environments (Krinsley and McCoy 1977; Bull 1981; Moral Cardona et al. 1997b; Madhavaraju et al. 2009). In this work, surface textures observed on euhedral-subeuhedral grains of different heavy minerals (Table 2)

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helped identify several depositional processes and environments: a) Oldest processes are characterized by conchoidal fractures and grooves, attributed to very energetic aqueous flows occurring in coastal and fluvial environments (Krinsley and Donahue 1968; Margolis and Krinsley 1971; Brown 1973; Torcal and Tello 1992). b) Others processes are characterized by chemical dissolution, which affected old mechanical marks, such as arcuate steps, upturned plates and conchoidal fractures. These processes could be caused by prolonged presence of detrital grains in marine environments (Le Ribault 1975; Legigan and Le Ribault 1976; Legigan 2002; Moral Cardona et al. 2005). c) Chemical textures on surface of epidote, andalusite and garnet grains, indicate pedogenetic processes (chemical weathering). On the other hand, microtextures observed on anhedral (rounded, sub-rounded and angular) grains of unstable and ultraestable heavy minerals (Table 2), could be indicators of the action of dynamic agents and depositional processes, such as: a) Arcuate steps and upturned plates, which are cited as indicative of eolian environments (Margolis and Krinsley 1974; Krinsley et al. 1976). b) Intensive re-working processes, occurring in high-energy coastal environments, causing angular conchoidal fractures widely developed on grain surfaces. c) A more recent depositional process provoking chemical features such as oriented etch pits and solution pits, which indicate that grains were present in marine environments for a long time, and which affect older mechanical marks. From different morphologic types and surface textures previously analyzed (Table 2), several sedimentary stages and depositional environments can be distinguished (Table 3): 1) Oldest stage corresponds to an eolian phase characterized by upturned plates and arcuate steps

Table 3

4

Sediment Provenance Heavy mineral assemblages present in marine sediments are highly affected by fluvial sediments coming from adjacent continental areas (Mezzadri and Saccani 1988; Frihy and Dewidar 2003). The heavy mineral assemblages established in this work reminiscent those obtained in oldest sedimentary formations, present in the nearby continental areas (Table 4), with some differences in the secondary minerals. The zircon is the predominant mineral in the first association; is also appears as the first mineral in the association defined by Viguier (1974) in the Neogene materials of the Guadalquivir depression, and is present in the association defined by Mabesoone (1966), Zazo (1980) and Moral Cardona et al. (2005) in the terraces of the Guadalete basin. Tourmaline and Andalusite, which are the dominant minerals in the second and third associations respectively, are also present in the majority of mineralogical assemblages established by other authors (Viguier 1974; Zazo 1980; Perez-Mateos et al. 1982; Moral Cardona et al. 2005). The coexistence in the study area of different mineralogical assemblages could mean the existence of more than one sediment sources. Fluvial sources could be deduced as one of the origins, in particular, the sediment supplies coming from areas located to the north of Cadiz bay, such as the Guadalquivir River, whose contributions reach the Bay through littoral currents (Fig. 2a). Viguier (1974), Zazo (1980), Perez-Mateos et al. (1982) and Gutierrez-Mas et al. 2003 consider that main source of sediments in the Guadalquivir basin came from the Iberian Massif, which provides metamorphic minerals (Fig. 11). Other sediment sources seem to be representative

Textural features and stages differentiated in heavy minerals grains on sediments of the Cadiz bay and the adjacent continental shelf

Stage Surface features 1 2 3

2) Conchoidal fractures and grooves indicate high-energy action in fluvial and coastal environments. 3) A more recent stage shows chemical features caused by dissolution processes that affect old mechanical marks, and which indicate they have been present in marine environments for a long time. 4) Several stages can be deduced from presence of textures generated in pedogenetic environments in continental areas.

Depositional environment

Lithology (Age)

Upturned plates, Grooves Eolian Aljibe sandstones (Early Miocene) Conchoidal fractures, Grooves, Arcuate steps Coastal and Fluvial Calcarenite (Late Miocene) Oriented etch pits, Solution pits Fluvial, Pedologic and Intertidal Fluvial terraces (Plio-Quaternary) Alluvial fans Surface polishing Infratidal Sand, Mud (Holocene)

Sediment source areas Betic Cordilleras Guadalquivir basin Guadalete basin Recent marine sediments

Thalassas Table 4 Zircon)

Mineralogical assemblages defined in continental areas close to the study zone (A: Andalusite; E: Epidote; G: Garnet; T: Tourmaline; Z:

Continental areas

Mineralogical assemblages

Authors

Neogene material of the Guadalquivir Depression

Z>T>G

Viguier (1974)

Alluvial deposits of Guadalete river

E>Z>G

Mabesoone (1966)

Guadalete bassin Terraces of Guadalete river

A>E>T+G+Z T>G>E>A>Z

Zazo (1980) Moral Cardona et al. (2005)

Beaches between Trafalgar and Guadalquivir river mouth

A>G>E

Perez-Mateos et al. (1982)

of rivers that pour directly into the Bay of Cadiz, especially the Guadalete River. This last, injects sediments coming from areas located to the South and East of the bay especially the preorogenic outcrops of the Betic cordilleras like the Aljibe sandstone (Fig. 3b) that contain very well rounded grains of high degree of maturity whose origin attributed to intense reworking processes (Moral Cardona et al. 1997b, 2005) (Fig. 11). The surface texture analysis of heavy-mineral grains can also be applied to sediment provenance and contributes to improve knowledge regarding the sedimentary stages that detrital grains go through, and the depositional environments (Schäfer and Dörr 1997; Gutierrez-Mas et al. 2003; Moral Cardona et al. 2005). In our case (the bay of Cadiz), heavyminerals have suffered several sedimentary cycles and stages and they show similar features to those present in some detritic out crops from continental area close to the study area. The SEM study of these mineral grains reveals that some morphologies are, in part associated with particular textures presented by these grains (Table 2 & Figs. 6, 7, 8, 9 and 10). Comparing surface textures and morphologies of heavy mineral grains obtained in this work with those of outcropping rocks in the Fig. 11 Provenance diagram of different morphologic types of heavy minerals from marine sediments of Cadiz Bay and adjacent continental shelf

nearby continental areas, the following facts can be established: The chemical textures, such as oriented etch pits and solution pits exhibited by sub-euhedral epidote, andalusite and garnet grains and the mechanical marks (conchoidal fractures and grooves) in euhedral/sub-euhedral tourmaline and zircon grains present in recent marine sediments from Cadiz Bay, are also recognizable in the Pliocene sands outcropping in nearby continental areas (Moral Cardona et al. 2005). These morphological types of heavy minerals was found to be related with igneous (ultrastable grains) and metamorphic (unstable grains) rocks present in the Iberian Massif (Fig. 11) reaching Cadiz Gulf through the Guadiana and Guadalquivir rivers, although they can, indirectly, come from the Pliocene outcrops close by. They may have reached the marine environments through the Guadalete River and other smaller fluvial courses or directly from the erosion of the coastal cliffs (Mabesoone 1966; Meliéres 1974; Viguier 1974; Achab 2000; Gutierrez-Mas et al. 2003; Moral Cardona et al. 2005; Achab and Gutierrez-Mas 2009). With respect to euhedral epidote grains (Fig. 9d), this could come from the Triassic Subbetic ophites that outcrop in the upper area of the Guadalete River Basin. Nevertheless, this morphological form of epidote,

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could also come from the metamorphic rocks (the Iberian massif), reaching the Cadiz Gulf through the Guadiana and Guadalquivir rivers. The predominance of conchoidal fracture in anhedral angular grains (garnet, tourmaline, andalusite and epidote) suggest that these minerals should come from the Miocene calcarenites whose mineral grains are characterized by similar mechanical marks and present in the current Guadalquivir basins (Fig. 11). The angular grains of Garnet can also be established in the Upper Miocene calcarenites present in the coastal cliffs between Trafalgar Cape and Barbate (PerezMateos et al. 1982; Torcal 1989; Moral Cardona et al. 1996b). The exoscopic analysis of the anhedral rounded-subrounded grains show old mechanical marks affected by chemical solution. These surface textures were derived from multicycle sediments present in nearby continental areas, such as the Aljibe sandstones (Betic cordilleras) and fluvial terraces (Guadalete basin), which provide detritic grains with polycyclic morphologies, reaching Cadiz Bay through the Guadalete River (Fig. 11). These types of morphologies can also come from coastal areas such as modern dunes and beaches (Moral Cardona et al. 2005). From previous data, it can be deduced that the current sediment sources in Cadiz Bay and the adjacent continental shelf are varied, with up to five identified sources (Fig. 11). A major source is established in the Iberian Massif, which provided metamorphic minerals and the pre-orogenic units from external zones of the Betic Cordilleras whose mineral grains present a high degree of maturity. Other sources are post-orogenic deposits from the Guadalquivir and Guadalete Basin, such as the upper Miocene calcarenites and Pliocene sands, which previously received material from the Iberian Massif and Western Betic Cordilleras. The Quaternary deposits outcropping along coastal and continental areas (marine and fluvial terraces) can also be one of sediment sources to the study area.

Conclusions The combination of mineralogical and surface texture analysis (SEM) of heavy mineral grains in recent shallow marine sediments from Cadiz Bay and the adjacent continental shelf has permitted the detection of a long history of mechanical and chemical processes, generated during several stages and at different depositional environments. These surface textures have allowed the establishment of the multicyclic character and a high textural and mineralogical maturity of the sediments. Several depositional stages were identified: the oldest corresponds to eolian environments, followed by energetic fluvial and coastal processes. Another younger stage is shown by chemical alterations acquired in marine environments, and is

characterized by dissolution processes that affected old mechanical marks. Provenance of sediment has been deduced from mineral assemblages and surface textural features. The main supplies sources of sediment to the study area come mainly from the Guadalquivir and Guadalete rivers. These rivers cross different geological formations, of metamorphic (Iberian massif) and sedimentary (Betic Cordilleras) rocks. Acknowledgments This paper was produced under Project GL201016878 of the Ministerio de Economía y Competitividad (Spain)/FEDER.

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