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Sediment supply from the BeticRif orogen to basins through Neogene L. Iribarren a,b , J. Vergés a, , M. Fernàndez a a Group of Dynamics of the Lithosphere (GDL), Institute of Earth Sciences Jaume Almera, CSIC, Lluís Solé i Sabarís s/n, 08028 Barcelona, Spain b Department of Marine Geology, INETI-National Institute for Engineering, Technology and Innovation, Estrada da Portela, Zambujal, 2721-866 Amadora, Portugal abstract article info Article history: Received 12 March 2008 Received in revised form 22 October 2008 Accepted 25 November 2008 Available online 6 December 2008 Keywords: Sedimentary volumes Sedimentation rates Sedimentary contributions IberiaAfrica plate boundary Erosion and vertical movements We present a quantication of total and partial (divided by time slices) sedimentary volumes in the Neogene basins of the BeticRif orogen. These basins include the Alboran Sea, the intramontane basins, the Guadalquivir and Rharb foreland basins and the Atlantic Margin of the Gibraltar Arc. The total volume of Neogene sediments deposited in these basins is ~209,000 km 3 and is equally distributed between the internal (Alboran Basin and intramontane basins) and the external basins (foreland basins and Atlantic Margin). The largest volumes are recorded by the Alboran Basin (89,600 km 3 ) and the Atlantic Margin (81,600 km 3 ). The Guadalquivir and Rharb basins amount 14,000 km 3 and 14,550 km 3 , respectively whereas the intramontane basins record 9235 km 3 . Calculated mean sediment accumulation rates for the earlymiddle Miocene show an outstanding asymmetry between the Alboran basin (0.24 mm/yr) and the foreland basins (0.060.07 mm/yr) and the Atlantic Margin (0.03 mm/yr). During the late Miocene, sedimentation rates rangebetween 0.17 and 0.18 mm/yr recorded in the Alboran Basin and 0.04 mm/yr in the intramontane basins. In the PlioceneQuaternary, the highest sedimentation rates are recorded in the Atlantic Margin reaching 0.22 mm/yr. Sedimentary contribution shows similar values for the inner and outer basins with a generalized increase from late Miocene to present (from 3500 to 6500 km 3 /My). Interestingly, the Alboran Basin records the maximum sedimentary contribution during the late Miocene (5500 km 3 /My), whereas the Atlantic Margin does during the PlioceneQuaternary (6600 km 3 /My). The spatial and time variability of the sediment supply from the BeticRif orogen to basins is closely related to the morphotectonic evolution of the region. The high sedimentation rates obtained in the Alboran Basin during the earlymiddle Miocene are related to active extensional tectonics, which produced narrow and deep basins in its western domain. The highest sedimentary contribution in this basin, as well as in the foreland and intramontane basins, is recorded during the late Miocene due to the uplift of wide areas of the Betics and Rif chains. The analysis of the sedimentary supply also evidences strong relationships with the post-Tortonian crustal thickening and coeval topographic amplication that occurred in the central Betics and Rif with the concomitant evolution of the drainage network showing the uvial capture of some internal basins by rivers draining to the Atlantic Ocean (the ancestral Guadalquivir). © 2008 Elsevier B.V. All rights reserved. 1. Introduction Quantifying tectonic and sedimentary processes is a signicant challenge in contemporary geology and sometimes the only way to constrain the evolution of regions with complex geodynamic evolu- tions. For long periods of time, the volumes of sedimentary uxes from growing mountains to basins and their rates are closely related to the intensity and duration of tectonic events rather than to climate. Therefore, accurate quantication of sediment transfer within tec- tonically active areas is essential for understanding and modelling the tectonic evolution of orogenic systems. The development of the BeticRif orogen on top of the AfricaIberia plate boundary across the transition zone between the Atlantic Ocean and the Mediterranean Sea resulted in a complex scenario mostly developed during the Alpine orogeny. The orogenic system encompasses the BeticRif chain, the inner extensional Alboran Basin, the outer Guadalquivir and Rharb foreland basins, the Gulf of Cadiz region, and various small intramontane basins (Fig. 1). So far, there is no general consensus on the Neogene evolution of the BeticRif orogen and different and competing models have been proposed. These models include convective mantle removal and orogenic collapse (e.g., Dewey, 1988; Platt and Vissers, 1989; Vissers et al., 1995; Platt et al., 2003a,b); mantle delamination (e.g., García-Dueñas et al., 1992; Docherty and Banda, 1995; Seber et al., 1996; Mezcua and Rueda, 1997; Calvert et al., 2000); slab roll-back (e.g., Frizon de Lamotte et al., 1991; Lonergan and White, 1997); active subduction (Gutscher et al., 2002; Duggen et al., 2004; Faccenna et al., 2004); slab break-off (Zeck, 1996; Wortel and Spakman, 2000); and slab roll-back combined with lithosphere tearing (Spakman and Wortel, 2004; Faccenna et al., 2004; Govers and Wortel, 2005). Most of these models, Tectonophysics 475 (2009) 6884 Corresponding author. Fax: +34 934110012. E-mail addresses: [email protected] (L. Iribarren), [email protected] (J. Vergés), [email protected] (M. Fernàndez). 0040-1951/$ see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2008.11.029 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto

Sediment supply from the Betic–Rif orogen to basins through Neogene

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Page 1: Sediment supply from the Betic–Rif orogen to basins through Neogene

Tectonophysics 475 (2009) 68–84

Contents lists available at ScienceDirect

Tectonophysics

j ourna l homepage: www.e lsev ie r.com/ locate / tecto

Sediment supply from the Betic–Rif orogen to basins through Neogene

L. Iribarren a,b, J. Vergés a,⁎, M. Fernàndez a

a Group of Dynamics of the Lithosphere (GDL), Institute of Earth Sciences “Jaume Almera”, CSIC, Lluís Solé i Sabarís s/n, 08028 Barcelona, Spainb Department of Marine Geology, INETI-National Institute for Engineering, Technology and Innovation, Estrada da Portela, Zambujal, 2721-866 Amadora, Portugal

⁎ Corresponding author. Fax: +34 934110012.E-mail addresses: [email protected] (L. Iribarre

(J. Vergés), [email protected] (M. Fernàndez).

0040-1951/$ – see front matter © 2008 Elsevier B.V. Aldoi:10.1016/j.tecto.2008.11.029

a b s t r a c t

a r t i c l e i n f o

Article history:

We present a quantification Received 12 March 2008Received in revised form 22 October 2008Accepted 25 November 2008Available online 6 December 2008

Keywords:Sedimentary volumesSedimentation ratesSedimentary contributionsIberia–Africa plate boundaryErosion and vertical movements

of total and partial (divided by time slices) sedimentary volumes in the Neogenebasins of the Betic–Rif orogen. These basins include the Alboran Sea, the intramontane basins, theGuadalquivir and Rharb foreland basins and the Atlantic Margin of the Gibraltar Arc. The total volume ofNeogene sediments deposited in these basins is ~209,000 km3 and is equally distributed between theinternal (Alboran Basin and intramontane basins) and the external basins (foreland basins and AtlanticMargin). The largest volumes are recorded by the Alboran Basin (89,600 km3) and the Atlantic Margin(81,600 km3). The Guadalquivir and Rharb basins amount 14,000 km3 and 14,550 km3, respectively whereasthe intramontane basins record 9235 km3. Calculated mean sediment accumulation rates for the early–middle Miocene show an outstanding asymmetry between the Alboran basin (0.24 mm/yr) and the forelandbasins (0.06–0.07 mm/yr) and the Atlantic Margin (0.03 mm/yr). During the late Miocene, sedimentationrates range between 0.17 and 0.18 mm/yr recorded in the Alboran Basin and 0.04 mm/yr in the intramontanebasins. In the Pliocene–Quaternary, the highest sedimentation rates are recorded in the Atlantic Marginreaching 0.22 mm/yr. Sedimentary contribution shows similar values for the inner and outer basins with ageneralized increase from late Miocene to present (from 3500 to 6500 km3/My). Interestingly, the AlboranBasin records the maximum sedimentary contribution during the late Miocene (5500 km3/My), whereas theAtlantic Margin does during the Pliocene–Quaternary (6600 km3/My). The spatial and time variability of thesediment supply from the Betic–Rif orogen to basins is closely related to the morphotectonic evolution of theregion. The high sedimentation rates obtained in the Alboran Basin during the early–middle Miocene arerelated to active extensional tectonics, which produced narrow and deep basins in its western domain. Thehighest sedimentary contribution in this basin, as well as in the foreland and intramontane basins, isrecorded during the late Miocene due to the uplift of wide areas of the Betics and Rif chains. The analysis ofthe sedimentary supply also evidences strong relationships with the post-Tortonian crustal thickening andcoeval topographic amplification that occurred in the central Betics and Rif with the concomitant evolution ofthe drainage network showing the fluvial capture of some internal basins by rivers draining to the AtlanticOcean (the ancestral Guadalquivir).

© 2008 Elsevier B.V. All rights reserved.

1. Introduction

Quantifying tectonic and sedimentary processes is a significantchallenge in contemporary geology and sometimes the only way toconstrain the evolution of regions with complex geodynamic evolu-tions. For long periods of time, the volumes of sedimentary fluxesfrom growing mountains to basins and their rates are closely relatedto the intensity and duration of tectonic events rather than to climate.Therefore, accurate quantification of sediment transfer within tec-tonically active areas is essential for understanding and modelling thetectonic evolution of orogenic systems.

The development of the Betic–Rif orogen on top of the Africa–Iberia plate boundary across the transition zone between the Atlantic

n), [email protected]

l rights reserved.

Ocean and the Mediterranean Sea resulted in a complex scenariomostly developed during the Alpine orogeny. The orogenic systemencompasses the Betic–Rif chain, the inner extensional Alboran Basin,the outer Guadalquivir and Rharb foreland basins, the Gulf of Cadizregion, and various small intramontane basins (Fig. 1). So far, there isno general consensus on the Neogene evolution of the Betic–Riforogen and different and competing models have been proposed.These models include convective mantle removal and orogeniccollapse (e.g., Dewey, 1988; Platt and Vissers, 1989; Vissers et al.,1995; Platt et al., 2003a,b); mantle delamination (e.g., García-Dueñaset al., 1992; Docherty and Banda, 1995; Seber et al., 1996; Mezcua andRueda, 1997; Calvert et al., 2000); slab roll-back (e.g., Frizon deLamotte et al., 1991; Lonergan and White, 1997); active subduction(Gutscher et al., 2002; Duggen et al., 2004; Faccenna et al., 2004); slabbreak-off (Zeck, 1996; Wortel and Spakman, 2000); and slab roll-backcombined with lithosphere tearing (Spakman and Wortel, 2004;Faccenna et al., 2004; Govers andWortel, 2005). Most of thesemodels,

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Fig. 1. Tectonic map showing principal structural units of the Betic–Rif Orogen and the associated Neogene basins.

69L. Iribarren et al. / Tectonophysics 475 (2009) 68–84

however, are based on the tectonic style of the orogenic system, and/or on deeper signatures such as hypocenter location and regional orglobal tomography, but they lack incorporating surfacemass transportstudies.

Studies related to the Neogene sedimentary infilling and itstectonic significance are restricted to few basins within the Betic–Riforogen. Various works used the stratigraphic record at a regional scalein order to attain the paleogeographic and the tectonic evolution ofthe Betic Chain (Sanz de Galdeano, 1990; Sanz de Galdeano and Vera,1992; Sanz de Galdeano et al., 1993; Sanz de Galdeano and Rodríguez-Fernández,1996; Vera, 2000; Andeweg, 2002; Hanne et al., 2003). TheNeogene sedimentary record of the Alboran Basin has been widelyanalysed by the integration of well data and multichannel seismicprofiles. Studies based on the age of the sedimentary sequences, theirstratigraphic relations, the basin architecture and the relationshipwith onshore sediments, have permitted to establish the timing andtectonic regime of different events controlling the evolution of thebasin (Comas et al., 1992; Soto et al., 1996; Comas et al., 1999;Rodríguez-Fernández et al., 1999). In the Gulf of Cadiz the interactionof sedimentation and the successive deformation phases has been alsostudied (Maldonado and Nelson, 1999; Maldonado et al., 1999; Gràciaet al., 2003a; Medialdea et al., 2004). Other recent works deal with theregional distribution of sedimentary markers such as coastal andmarine shallow deposits in order to obtain the late orogenic uplifthistory (Weijermars et al., 1985; Sanz de Galdeano and Alfaro, 2004;Braga et al., 2003). Recently, Iribarren et al. (2007) presented thestructure of the Gulf of Cadiz with especial emphasis on the geometryof the Miocene chaotic units with the Gulf of Cadiz Imbricate Wedgeand the Horseshoe Gravitational Unit. One limitation with previousstudies is that they focussed on the mountain chains or the inner/outer basins lacking of regional sedimentary studies that integrate theentire Betic–Rif orogenic system. In this context, the main objective of

this work is to provide a quantitative analysis of sedimentary volumesfor all the sedimentary basins that developed during the Betic–Riforogenic evolution since early–middle Miocene to Present. Thisquantification involves volumes of sediment (km3), rates of sedimentaccumulation (mm/yr) and sedimentary contribution (km3/My).

To this end, we have integrated available geological and geophy-sical data including well data, stratigraphic columns, cross-sections,seismic profiles, geologic maps and isopach maps. The time intervalsto calculate the sedimentary contribution and the sedimentation ratesthrough time have been chosen according to their widespreadrecognition in the study region. The distribution, volume quantifica-tion and rates of sedimentation of the Betic–Rif Neogene sedimentaryproducts and their time evolution add new quantitative constraints tothe tectonic evolution models and contribute to better understand themorphotectonic evolution of this region. We finally discuss the im-plications of these results during the Betic–Rif orogenic buildingthrough middle–late Miocene, Pliocene and Quaternary periods.

2. Geological setting

The Betic–Rif orogen occupies the Southern IberianMargin and theNorthern Moroccan Margin and is classically divided in the InternalZones, the External Zones, the Flysch Units, and the Neogene basins(Fig. 1). The Internal Zones, which constitute the so-called AlboranCrustal Domain, include Late Paleozoic to Triassic different grademetamorphic complexes. These units were affected by a Tertiarycompression, followed by a pervasive extensional event that started inthe early Miocene (e.g., García-Dueñas et al., 1992; Crespo-Blanc et al.,1994). The External zones correspond to an imbricate system thatdeforms the cover sequences of the south-west Iberian and north-westMaghrebian paleomargins (e.g., Crespo-Blanc and Campos, 2001;Platt et al., 2003a,b). The compression in the External Zones was

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70 L. Iribarren et al. / Tectonophysics 475 (2009) 68–84

contemporary to the extension in the Internal Zones. The Flysch Unitscomprise deep marine turbidites that were transported westwards inan imbricate system of thrusts that crop out mainly in the western-most part of the orogen (e.g., Crespo-Blanc and Campos, 2001;Michard et al., 2002) (Fig. 1). The Internal and External zones, as wellas the Flysch Units, are roughly continuous from the Betics to the Rifchains. In the Atlantic margin, the direction of the structure swingsfrom the Betics Cordillera to the Rif, west of the Gibraltar Strait(Iribarren et al., 2007). This swing in the structure produces an arcuateshape that has led different authors to refer this orogenic system asthe Gibraltar Arc System.

According to their position in the orogen and their genetic origin,the Neogene basins are here divided in some internal basins thatinclude the Alboran Basin and the intramontane basins, and theexternal basins that correspond to the Guadalquivir and Rharbforeland basins, related to the Betics and Rif chains, respectively,and the Gulf of Cadiz basin including the South Iberian and NorthwestMoroccan Atlantic Margins.

The Alboran Basin is situated in the westernmost Mediterraneanbetween Iberia and Africa and represents the innermarine basin of theBetic–Rif orogen. Its basement ismade ofmetamorphic complexes thatform the Internal Zones of the Betics and the Rif, and by Neogenevolcanic rocks. This basin evolved in an ENE–WSWextensional regimefrom the late Oligocene or early Miocene to the Tortonian (at approx-imately 9 Ma) (Comas et al., 1992; Rodríguez-Fernández et al., 1999).FromTortonian to Present theAlboran Basin records folding and strike-slip faulting associated to a roughly NNW–SSE compressive tectonicregime (Comas et al., 1999).

Other sedimentary basins that formed and evolved during theNeogene in the Betic–Rif orogen are represented by the intramontanebasins. These basins were under sea level during Tortonian times,when they were individualized, and uplifted above the sea level indifferent ages from late Tortonian onwards (Sanz de Galdeano and

Fig. 2. Isopach map of Neogene sediments in the Alboran Basin from Torne et al. (2000). Thvolume derived from the Betics and the Rif. To the East of this line, sediments likely come fAlboran Basin, SAB: South Alboran Basin, YB: Yusuf Basin.

Vera,1992). Currently they constitute small nonmarine basins most ofthem situated over the contact between the Internal and the Externalzones (Fig. 1).

The external basins were already marine sedimentary basins whencompression started to affect these areas. The Guadalquivir and Rharbbasins evolved from foredeep to foreland basins during theMiocene bydownward flexure of the basement in response to the loading of thethrusted and imbricated External Units (Sanz de Galdeano and Vera,1992; Berástegui et al., 1998; García-Castellanos et al., 2002). To thewest, the successive imbricate units of the Betic–Rif orogen emplacedwestwards from early to late Miocene invading the Atlantic Marginregion that includes the Gulf of Cadiz and the NW Moroccan marginforming the so-called Gulf of Cadiz ImbricateWedge (Maldonado et al.,1999; Gràcia et al., 2003a; Gutscher et al., 2002; Iribarren et al., 2007).

3. Sedimentary volumes

A first objective of this work is to quantify the total sedimentaryvolume that is related to the building-up of the Betic–Rif orogenthrough the Neogene. To this end we have used different methodol-ogies according to the available data for each analyzed tectonicdomain. Depending on the basin these data have consisted of isopachmaps in which case the volume can be directly calculated, deep wellsreaching the basement, seismic profiles and geological cross-sections.

In addition to the total volume, we calculated the partial sedimentarysupplycorresponding to several predefined time intervals. These intervalshave been chosen according to theirwide-spread recognition in the studyarea corresponding to: i) early to middle Miocene (c.a. 24 to 11.6 Ma);ii) late Miocene (c.a. 11.6 to 5.3 Ma), and iii) Pliocene–Quaternary (5.3 to0 Ma). In the Alboran Basin, however, the first time period spans from20.4 to 9Ma. Similarly, in other basins the time spanmay vary slightly. Inthis section we present the data and the different methods used in eachbasin, together with the results derived from the calculations.

e dashed line indicates the limit established in this study to calculate the sedimentaryrom the Atlas Mountains or are mainly pelagic. WAB: West Alboran Basin, NAB: North

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3.1. The Alboran Basin

The data used to calculate the Neogene sedimentary volume in theAlboran Basin come from the gridded maps elaborated by Soto et al.(1996) and Torne et al. (2000), who constructed a sediment isopachmap based on the interpolation of 9000 km of multichannel seismicprofiles (Fig. 2). The isopach map shows an irregular infill, with aprominent depocentre in the West Alboran Basin where sedimentsreach a thickness of more than 8 km. The depocentre is elongated andarcuated matching the shape of the Betic–Gibraltar–Rif. The northernbranch of the basin continues into the North Alboran Basin (NAB in Fig.2). The sedimentary thickness is reduced in the centre of the basinwhere it has a mean value of about 500 m.

The Alboran Basin acts as a semi-confined basin and receivesmainly detritic sediments from the Betic and the Rif mountains.However, the Taza-Guercif Basin situated between the Rif and Atlasmountains (see Fig. 2 for location), is mainly filled by detritic depositsderived from the Atlas Mountains (Krijgsman et al., 1999). Thestructural high that bounds the Yusuf and the South Alboran basins tothe S (Fig. 2), likely separates sediments coming from the Taza-GuercifBasin from those coming from the Rif since the upper Miocene. Inconsequence, the quantification presented in this study does notinclude the sediments deposited to the E of this structural high sincewe consider that they have an Atlas provenance.

The sedimentary sequence of the Alboran Basin was divided intothree time intervals bounded by the well-known regional unconfor-

Fig. 3. (A) Data used to construct isopach maps for the Pliocene–Quaternary and the late MMiocene (5.3 to 9 Ma) sediments. (D) Early to early late Miocene (9 to 20.4 Ma) sediments

mities: Tortonian reflector R-3 and top of the Messinian reflector M(Comas et al., 1999). Fig. 3 shows the data used to construct the depth tobasement maps of both reflectors and the isopach maps for each timeinterval. The data include previous partial depth-to-basementmaps andinterpreted seismic profiles. The reflectors were depth converted bypublished P-wave seismic velocities from well-log data in the AlboranBasin (Soto et al., 1996). According to these authors we assigned Vpvelocities of 1.8 km s−1 for the Pliocene–Quaternary, 2.5 km s−1 for thelate Miocene, and 4.0 km s−1 for the early–middle Miocene.

The isopach maps in Fig. 3 represent, respectively, the thicknessand distribution of the Pliocene–Quaternary sequence (5.3 Ma toPresent) (Fig. 3B), the late Miocene sequence (from 9 Ma to 5.3 Ma)(Fig. 3C), and the early to early late Miocene sediments (from 20.4 Mato 9Ma) (Fig. 3D). Thesemaps show an irregular infill of the Pliocene–Quaternary and late Miocene sediments. In these time intervals, themaximum thicknesses are similar and range between 1600 and1800 m (Fig. 3B and C). Pliocene–Quaternary sediments aredistributed across the entire sedimentary basin (Fig. 3B), whereaslate Miocene sediments accumulate mainly in theWest Alboran basin,although they also extend to the whole current basin (Fig. 3C). Theearly to early late Miocene (from 20.4 Ma to 9 Ma) sediments arerestricted to the depocentres of the West Alboran Basin, where thesesediments exceed 6000 m of thickness and to a lesser extend to theNorth Alboran Basin (Fig. 3D). To the E and central parts of the AlboranBasin, these older sediments are absent or do not constitute significantaccumulations.

iocene time intervals. (B) Isopach map of the Pliocene–Quaternary sediments. (C) Late.

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72 L. Iribarren et al. / Tectonophysics 475 (2009) 68–84

Well data descriptions indicate that Pliocene–Quaternary sedi-ments are constituted by detritic deposits in the near-shore areas anddepocentres, and by hemipelagic sediments in the central parts of thebasin where only a fraction less than 10% may correspond to detriticsediments (Skilbeck and Tribble, 1999). Consequently, we eliminated90% of the sedimentary volume of the central parts of the AlboranBasin, corresponding to the hemipelagic deposition, since its sourcearea is not related to the Betic–Rif orogen.

The total amount of clastic sedimentary volume accumulated inthe Alboran Basin is of about 89,600 km3. Their distribution throughtime corresponds to 44,600 km3 during early to early late Miocene(20.4 Ma to 9 Ma), 24,400 km3 during late Miocene (9 Ma to 5.3 Ma),and 20,600 km3 during the Pliocene–Quaternary (5.3 Ma to Present).

3.2. The AtlanticMargin (Gulf of Cadiz and NW-MoroccanAtlanticMargin)

The Atlantic Margin of the Betic–Rif orogen includes the shelvesand slopes of SW Iberia (Gulf of Cadiz region) and NW Morocco. Theproximal parts of the margin received a detritic supply from the Beticsand the Rif during Miocene and Pliocene–Quaternary, whereas thedeep and distal parts are dominated by ocean-type sedimentation.The limit of the continental contribution, as well as the total andpartial sedimentary volumes with a Betic–Rif provenance, have beendetermined from a dataset that consists of scientific and oil ex-ploration wells together with seismic reflection profiles (Fig. 4).

A total of 25 oil exploration wells from the SW Iberian shelf in theGulf of Cadiz (Lanaja et al., 1987) and two scientific wells from theDeep Sea Drilling Project (Hayes et al., 1972; Ryan et al., 1973), allowedthe determination of the continental or oceanic nature of the sedi-

Fig. 4. Bathymetric map of the studied area and available seismic reflection profiles and wCPR: Coral Patch Ridge, GoB: Gorringe Bank, GB: Guadalquivir Bank, PB: Portimao Bank; GCIWseismically chaotic unit.

ments and to extrapolate well-recognized reflectors towards the distalparts of the Gulf of Cadiz (Fig. 4).

Seismic interpretation has been performed on a total of 28multichannel seismic profiles, and has been correlated with the welldata and previous interpretations (Tortella et al., 1997; Gràcia et al.,2003a; Medialdea et al., 2004). The seismic profiles were acquired indifferent scientific cruises from 1992 to 2002 and include the Arrifanolines, acquired in 1992 (Sartori et al., 1994); the IAM lines in 1993(Banda et al., 1995; Tortella et al., 1997); the BIGSET lines in 1998(Gràcia et al., 2003b; Zitellini et al., 2002); the SISMAR lines in 2001(Gutscher et al., 2002); and the Voltaire lines in 2002 (Zitellini et al.,2002). The African shelf was analyzed using multiple seismic linesdocumented in Flinch et al. (1996).

All these dataset have been integrated and depth converted tocalculate the Neogene sedimentary volume. We assigned an averageP-wave velocity of 2 km/s to these sediments according to refractionseismic experiments developed within this area (Purdy, 1975;González-Fernández et al., 2001; Gutscher et al., 2002).

The Miocene tectonic activity produced the emplacement of aseismically chaotic unit occupying most of the Gulf of Cadiz and NorthMoroccan Atlantic Margin (e.g., Flinch et al., 1996; Tortella et al., 1997;Gràcia et al., 2003a). This unit is referred as the Gulf of Cadiz ImbricateWedge and represents the most external unit of the Betic–Rif thrustbelt whose emplacement finished in the late Miocene (Iribarren et al.,2007). Since early and middle Miocene sediments are deformed bytectonic imbrications, the resultant isopach maps correspond to thelate Miocene and Pliocene–Quaternary sediments, which lie above theGulf of Cadiz Imbricate Wedge, while the early and Middle Miocenesediments cannot be properly calculated with the available data.

ells used for this study are depicted. GS: Gibraltar Strait, CPS: Coral Patch Seamount,: Gulf of Cadiz ImbricateWedge and HGU: Horseshoe Gravitational Unit of the Miocene

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73L. Iribarren et al. / Tectonophysics 475 (2009) 68–84

The resultant isopach maps and the limit between detritic andocean-type sediments are depicted in Fig. 5. Results show that thesedimentary thicknesses are lower and more homogeneous in theoceanic domain, whereas in the continental influence area, sedimentsshow higher thicknesses and accumulate in depocentres. The extendof the continental influence areas varies from late Miocene toPliocene–Quaternary as a consequence of changes in eustatic sealevel and tectonics, which resulted in variations of the coastline andposition of the emerged areas, and in changes in the oceaniccirculation regimes. Nevertheless, both maps share some similaritiesin the sedimentary distribution, showing an arcuate-shape depocen-tre from the Iberian margin to the African margin, and small sub-rounded basins on top of the Gulf of Cadiz ImbricateWedge, which arecontrolled by the convex structure of the top of this tectonic unit(Iribarren et al., 2007).

To constrain the volume of the early and middle Miocene sedi-ments we have considered the thickness of these sequences far away

Fig. 5. Isopach maps in the Atlantic Margin for Pliocene–Quaternary sediments (A) and late MThick dashed lines represent the westwards extent of the siliciclastic analyzed deposits.

from the influence of the Gulf of Cadiz ImbricateWedge. In these areasthe thickness of early and middle Miocene sediments ranges between0 and 700 m with common values between 300 and 500 m.

An estimation of the total volume accumulated in the AtlanticMargin of the Betic–Rif orogen amounts 81,600 km3 corresponding to24,000 km3 deposited during the early–middle Miocene (23 to11.6 Ma), 22,600 km3 during the late Miocene (11.6 to 5.3 Ma), and35,000 km3 during the Pliocene–Quaternary (5.3 to 0 Ma).

3.3. The Guadalquivir and Rharb foreland basins

The Guadalquivir basin is a narrow ENE–WSW elongated forelandbasin associated with the Western and Central Betics and limited tothe east by the Pre-Betic Units of the Sierra de Cazorla (Figs. 1 and 6).The basin is floored by a basement dipping 2–4° towards the Beticsand constituted by Paleozoic rocks of the Hercynian Iberian Massifand, occasionally, by Mesozoic rocks (Fernàndez et al., 1998). The

iocene sediments (B). Seismic database is also depicted in both maps as thin grey lines.

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Fig. 6. (A) Geologic map of the Guadalquivir Basin and data used to construct the isopach map. (B) Isopach map of Neogene sediments infilling the Guadalquivir Basin.

74 L. Iribarren et al. / Tectonophysics 475 (2009) 68–84

downward bending of the basement is a consequence of the thrustingand loading of the External Betic Units and the action of an extra loadof subcrustal origin (García-Castellanos et al., 2002). Berástegui et al.(1998) divided the sedimentary infill of the Guadalquivir Basin in 6sedimentary sequences, bounded by unconformities, from the lateLanghian to the Messinian. The first sequence (late Langhian–earlySerravallian) consists of a thin coastal calcarenitic sedimentary unit(20–40 m) formed of conglomerates and sandstones followed bydeeper water turbidites. Pliocene sediments unconformably lie on topof these sequences and consist of shallow marine deposits as well aslacustrine sediments in the central part of the basin.

The Rharb Basin is the foreland basin of the Central and WesternRif and shares similar characteristics with the Guadalquivir Basin. Thebasement consists of the Hercynian and Mesozoic rocks of theMoroccan Messeta, which dips towards the External Rif fronts as aconsequence of the bending of the lithosphere (Zouhri et al., 2001)(Figs. 1 and 8). The sedimentary infill in the Rharb Basin includesisolated patches of Aquitanian sediments and middle Miocene toQuaternary sediments. TheMiddleMiocene (Langhian to Serravallian)

is composed by marine turbiditic deposits (Esteban et al., 1996). Themain sedimentary infill of the basin corresponds to the period fromlate Miocene to Pleistocene and consists of blue marine marls, whichin the western part are more argillaceous.

The total and partial volumes in these two basins were constrainedby datasets that include seismic profiles, geological sections, oilexploration wells and local isopach maps (Figs. 6A, 7A). The reflectorsof the seismic profiles were depth converted by considering anaverage p-wave velocity of 2 km/s for Miocene–Pliocene sediments,according to values proposed by Berástegui et al. (1998) for theGuadalquivir Basin. Isopach maps were obtained by the interpolationof these reflectors together with sedimentary thickness fromwell dataand geological sections.

The total isopach map of the Guadalquivir shows an ENE–WSWelongated depocentre in front of the External Units with the thicknessgently decreasing toward the northern passive margin of the basin(Fig. 6B). The maximum thickness is reached in the western regionwith values exceeding 2600 m. The total isopach map of the RharbBasin displays very similar features than that obtained in the

Page 8: Sediment supply from the Betic–Rif orogen to basins through Neogene

Fig. 7. (A) Map of the Rharb Basin showing the data used to construct the isopach map (B) Isopach map of Neogene sediments infilling the Rharb Basin.

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Guadalquivir Basin. The depocentre is aligned with the front of theExternal Rif Units with maximum thickness values located near theshore and locally exceeding 2200 m (Fig. 7B).

The sedimentary infill of both the Guadalquivir and the Rharbbasins was divided into three time intervals: middle Miocene (from 14to 11.6 Ma in the Guadalquivir Basin and from 16 to 13Ma in the RharbBasin), late Miocene (from 11.6 to 5.3 Ma) and Pliocene–Quaternary(from 5.3 to 0 Ma).

In the Guadalquivir Basin, the Pliocene–Quaternary (2810 km3) isdistributed in two depocentres: central and western depocentres(Fig. 8A). The central depocentre, with maximum thicknesses ex-ceeding 600 m, is filled up by non marine sediments, while marinesediments accumulate in the western depocentre reaching 1800 m ofmaximum thickness. The late Miocene (8400 km3) constitutes themain infill of the basin. These sediments are distributed along thewhole basin and accumulate mainly in an elongated depocentre(Fig. 8B). The middle Miocene sediments (2790 km3) also occupy thewhole basin, but with a considerably lower thickness (100–600 m)and with a more homogeneous distribution (Fig. 8C). The total sedi-mentary volume for the Guadalquivir Basin is of about 14,000 km3.

In the Rharb Basin, the marine Pliocene and Quaternary sedimentsaccumulated preferentially in the Atlantic side of the basinwhere theylocally reach 1100 m of thickness and a volume of 2200 km3 (Fig. 9A).Like in the Guadalquivir Basin, the late Miocene deposits (9900 km3)constitute the main infill and form a sedimentary wedge with max-imum thickness values in the depocentres ranging from 800 to morethan 2000 m (Fig. 9B). The middle Miocene deposits (2450 km3) areconcentrated in the western part of the basin with lesser thicknessvalues (100–400 m) (Fig. 9C). The total sedimentary volume for theRharb Basin is of about 14,550 km3, which is strikingly similar to thetotal volume calculated for the Guadalquivir Basin.

3.4. The intramontane basins

The intramontane basins are situated in the currently emergedland of the Betics and the Rif (Fig. 1). In the Betics these sedimentarybasins are very common and constitute the low areas between ranges.

Most of these basins show an early phase of open marine conditionswhen no major uplifts existed and the study area was the connectionbetween the Atlantic and the Mediterranean domains through theBetic corridor (e.g. Sanz de Galdeano and Vera, 1992; Braga et al.,2003). In the Rif, the intramontane basins are less frequent and arelimited to the Ouerrah Basin, Taza-Guercif and Melilla basins thatinitially formed part of the Riffean Corridor (e.g., Krijgsman et al.,1999; Gelati et al., 2000), and small basins in the Mediterranean coastthat have a negligible volume for the purpose of this study (Fig. 1). Thesedimentary record in the major basins includes late Serravallian/early Tortonian to Quaternary sediments with several hiatuses. Theypresent awide variety of facies but all of themwere essentially marineduring early stages emerging at different ages depending on theirposition, from the late Tortonian on.

To determine the sedimentary volumes in the intramontanebasins, we first compiled different type of data from the literature.In some basins (e.g., Granada and Malaga basins) the volumes weredirectly deduced from already existing isopach maps (Rodríguez-Fernández and Sanz de Galdeano, 2006, and López-Garrido and Sanzde Galdeano,1999, respectively). In the other basins, the data coverageand accuracy was very irregular and volumes were calculated bymeans of seriated cross-sections (Fig. 10). This method consists ofthe following steps: i) dividing the basin in sectors or polygons,ii) constructing a depth to basement section in the middle of eachsector, and iii) calculating the partial volumes of each sector and thenthe total volume. The uncertainties related to this method werecalculated from the maximum and minimum depth to basementestimates in each section, such that the maximum uncertaintiescorrespond to regions where data are scarcer. This method was alsoused to obtain the partial sedimentary volumes for the different timeintervals. In this case, however, the selected intervals were Pliocene–Quaternary and late Miocene. In those basins where available dataallowed more detail, we differentiated the Messinian and Tortonianintervals. The potential errors of these calculations are included in theplot of Fig. 11A that are less than 10% in most of the basins. Only 3basins with small total sedimentary volumes can reach 18–25% oferror.

Page 9: Sediment supply from the Betic–Rif orogen to basins through Neogene

Fig. 8. Isopach maps of the Guadalquivir basin for Pliocene–Quaternary sediments (A), late Miocene sediments (B) and middle Miocene sediments (C).

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The intramontane basins of the Betic Cordillera have been sepa-rated in three different domains according to their position withrespect to the present-day coastline (Fig.11): the distal domain, whichencompasses those basins located on the Internal–External boundary(Pre-Betic basins, Guadix-Baza, Granada, Fortuna, Lorca, Almanzora,and Ronda basins); the intermediate domain, including those basinslocated in the Internal units (Huercal-Overa, Pulpi-Hinojar, andSorbas-Tabernas basins); and the near-shore domain, which includesthose basins located along the coastline (Alicante-Cartagena, Malaga,Vera, and Nijar-Carboneras basins). Fig. 11A summarizes the totalsedimentary volumes for each intramontane basin, as well as the timeat which the marine to non-marine transition occurred. Partial vol-umes for the Pliocene–Quaternary and late Miocene are summarizedin Fig. 11B.

Although the individual contributions of these basins are smalltheir exposure onshore and their variability are extremely useful toconstrain the evolution of the area. Globally the distal basins, locatedalong the boundary between the Internal and the External units, showthe larger volumes of sediments. In addition, most of them show theolder marine to non-marine transition age around the late Tortonian.The largest basin is the Guadix-Baza basinwith a sedimentary volume

of 2380 km3, whereas the rest of the basins show volumes less than1000km3 (Fig.11). The intermediate basins, locatedwithin the InternalUnits, are relatively small with maximum volumetric contributions of500 km3. However, their marine to non-marine transition is youngerranging from late Messinian for the Sorbas-Tabernas basin to earlyPliocene for both Huercal-Overa and Pulpi-Hinojar basins (Fig. 11).Intramontane basins located in the near-shore domain show contrast-ing results. The Alicante-Cartagena basin shows a sedimentarycontribution of 2500 km3, which is equivalent or slightly larger thanthat of the Guadix-Baza basin in the distal domain, whereas the rest ofthe basins are very small. Their marine to non-marine transition ismore variable ranging from latest Messinian for certain areas of theAlicante-Cartagena basin to Quaternary for the rest of the basins.

Interestingly, most of the intramontane basins of the Betics showthat marine to non-marine transition occurred several million yearsago (as much as 7–8 Ma) but they continued to infill because theirintramontane condition surrounded by high ranges. These closedbasins only opened and eroded after river capture, as we will brieflycomment later.

The intramontane basins in the Rif Mountains are smaller and lessdeveloped than in the Betic Cordillera. They constitute a remnant of a

Page 10: Sediment supply from the Betic–Rif orogen to basins through Neogene

Fig. 9. Isopach maps of the Rharb Basin for Pliocene–Quaternary sediments (A), late Miocene sediments (B) and middle Miocene sediments (C).

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foredeep basin that connected the Atlantic and the Mediterraneanuntil the Tortonian/Messinian boundary, the so-called RiffeanCorridor (Cirac, 1987). Tectonic activity uplifted this corridor after7.2 Ma, producing the isolation of the Rharb foreland basin and somesmall intramontane basins (Krijgsman et al., 1999). The intramontanebasins from W to E are the Ouerrah basins, the Melilla basin and theTaza-Guercif basin. Moreover, some small fault-limited basins devel-

oped in the Mediterranean coast from the late Miocene onwards. As inthe Betic Cordillera, all Rif intramontane basins have recorded achange from marine to non-marine conditions, which seems to haveoccurred slightly later than in the Betics. The first continental depositsin the Taza-Guercif basin are dated at 6 Ma (Krijgsman et al., 1999).However, sediment provenance analysis has shown that the Taza-Guercif infill is supplied mainly from the Atlas Mountains (Krijgsman

Page 11: Sediment supply from the Betic–Rif orogen to basins through Neogene

Fig. 10. Sketch showing the application of seriated cross-sections to calculate volumes in some intramontane basins.

Fig. 11. Results of the volume calculations in the intramontane basins (see Fig. 1 for location). (A) Volumes are shown in the horizontal panel and in the vertical panel the age ofsedimentation and facies in each basin. Pr: Prebetic basins, G-B: Guadix Basin, Gr: Granada Basin, F: Fortuna, L: Lorca, Al: Almanzora Corridor, R: Ronda Basin, H-O: Huercal-OveraBasin, P-H: Pulpi-Hinojar Corridor, S-T: Sorbas-Tabernas, A-C: Alicante-Cartagena Basin, M: Malaga Basin, V: Vera Basin (Situation in Fig. 1). (B) Partial sedimentary volumes for thePliocene–Quaternary and late Miocene time intervals.

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Page 12: Sediment supply from the Betic–Rif orogen to basins through Neogene

Fig. 12. Sedimentary contributions to basins in km3/My. The total amount for external and internal basins shows a very similar evolution only diverging during the Pliocene andQuaternary interval.

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et al., 1999) and therefore its contribution has not been considered inthis study. The Ouerrah basins, situated in a central positionwithin theRif Mountains, have a total sedimentary volume of 90 km3, which is avery low value compared to the Betic central intramontane basins(Granada or Guadix-Baza). Ages of the sedimentary infill in thesebasins are not well constrained and the transition frommarine to non-marine conditions is considered to be somewhere in the Messinian.The Melilla basin contribution was calculated together with theAlboran basin and the small coastal basins have a negligiblecontribution. These coastal basins record an emersion around5.7 Ma, a marine transition in the early Pliocene and a definitiveemersion around 3.6 Ma (Rouchy et al., 2003).

4. Sedimentation rates and sedimentary contribution

The calculated sedimentary volumes have been used to quantify thesedimentary supply in each basin. This quantification is expressed assedimentation rates and sedimentary contribution. The sedimentationrate indicates thevelocityatwhich sediments accumulate and is obtainedby dividing the sedimentary volumes (km3) by the basin surface (km2)and the time interval (My), expressed in mm/yr or km/My. The sedi-mentary contribution is defined as the sedimentary volume per timeinterval and is expressed in km3/My.

Sedimentation rates average both the sediment supply to the basinand the basin geometry (surface) through time and therefore, denotethe growth of the sedimentary layer thickness in each basin. Sedi-mentation rates are useful to describe the evolution of a single basinbut are not a good indicator to be compared among several basinsbecause their different size. In contrast, the sedimentary contributiondenotes the total volume of sediments supplied to the basin per unit oftime and is irrelevant of the changes in the geometry of the basin andthe variations of the sedimentary thickness. Hence, the sedimentarycontribution can be compared among basins and is somehow relatedto the topographic and fluvial evolution (Figs. 12 and 13).

The most outstanding result for the early to middle Miocene timeinterval is the great asymmetry in sedimentation rates between theAlboran Basin (so-called internal basin) and the Gulf of Cadiz andforeland basins (so-called external basins). While in the Alboran Basinthe sedimentation rate is of 0.24 mm/yr, the external basins recordrates between 0.01 and 0.03 mm/yr in the early Miocene increasingto 0.06 and 0.07 mm/yr in the foreland basins during the MiddleMiocene (Fig. 13). The higher sedimentary contribution is alsorecorded in the Alboran Basin (3900 km3/My). Although muchlower sedimentary rates for the external basins, their total sedimen-tary contribution of 3980 km3/My is very similar to the calculated onefor the Alboran Basin.

The sedimentary contribution increased by a factor of 1.4–1.8 in allbasins during the late Miocene (Fig. 13). Only the Guadalquivir Basinshows similar values relative to the previous time interval. Sedimenta-tion rates also experienced a conspicuous increase in the Rharb Basin(0.1 mm/yr) and a decrease in the Alboran Basin (0.17–0.18 mm/yr),remaining almost constant in the rest of the basins. These variations inthe sedimentary contribution and sedimentation rates are likely relatedto: i) the increase of the relief and the total surface of emerged lands fromthe late Tortonian on (Krijgsman et al., 1999; Braga et al., 2003; Sanz deGaldeano and Alfaro, 2004), and ii) the increase of the accommodationspace in somebasins and the generation of newbasins. TheAlboranBasinrecords a regional subsidence that extended the basin area from theWestAlboran basin to thewhole current basin and adjacent areas (Rodríguez-Fernández et al., 1999). Subsidence studies indicate that the basementflexure in the Guadalquivir and Rharb basins was maximum during thelate Miocene (Barbieri and Gabriele Ori, 2000; Hanne et al., 2003). Theisopach maps presented in our study also support this observation.The sediment distribution in late Miocene maps (Figs. 8 and 9) clearlyshow the sedimentary wedge structure, while during previous and latertime intervals, sedimentation is more homogeneously distributed. Theintramontane basins record an average sedimentation rate of 0.4 mm/yrand a sedimentary contribution of about 950 km3/My.

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Fig. 13. (A) Total sedimentary volumes calculated in the Neogene basins of the Betic–Rif orogen. (B) Rates of sediment accumulation for the internal domain (Alboran Basin) andexternal domain (Atlantic Margin, Guadalquivir and Rharb foreland basins, and intramontane basins).

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During the Pliocene–Quaternary interval, sedimentation concen-trated in the Atlantic Margin (Gulf of Cadiz and NW Morocco) as it isevidenced by the huge increase in the sedimentary contribution andthe sedimentation rate (Fig. 13). In all the other basins thesedimentary contribution decreased notably, whereas the sedimenta-tion rates kept almost constant. The decrease in the sedimentarycontribution observed in the currently emerged basins (Guadalquivirand Rharb foreland basins and intramontane basins) can be explainedby the partial infilling of these basins due to the reduction ofsedimentation areas and loss of endorreism. Changes in the drainagenetwork also contributed to increase the sedimentary supply of theAtlantic Margin at expenses of the internal basins and particularly theAlboran Basin, as it is evidenced by the capture of the Guadix-BazaBasin and the Granada Basin by the Guadalquivir River during thePleistocene (Martín-Penela, 1987; Ruíz-Bustos et al., 1990).

5. Discussion

The total and partial sedimentary volumes as well as the sedi-mentary contribution and sedimentation rates obtained in thedifferent basins are closely related to the tectonic evolution of theBetic–Rif orogen. The evolution of this arcuate orogenic systemresulted in the formation of internal and external basins that roughlymimics the shape of the orogen. The internal basins are represented bythe Alboran basin, occupying the present-day westernmost Mediter-ranean region, and the intramontane basins located in the contactbetween the Internal and the External units of the Betic and Rif chains.The external basins are represented by the Guadalquivir and Rharbforeland basins and their prolongation to the Atlantic Margin (the Gulfof Cadiz region and the NW Moroccan margin).

To analyze the sedimentary supply of the Betic–Rif orogen to basinsthrough the Neogene, we have summarized the total sedimentaryvolumes, sedimentary contribution and sedimentation rates in eachbasin for different time intervals (Table 1). The time period consideredin these intervals varies slightly from one basin to another due to thedifferent nature and quality of the data used and hence, we havecalculated the total volume and the sedimentary contribution to makethe results comparable. In this calculation we have assumed that thesedimentation rate kept constant along the considered time interval.Another caution refers to the calculated total volume (29,240 km3) forthe external basins along the early to middle Miocene period, which

must be considered as a minimumvalue due to the large uncertaintiesin defining the bottom of the basins in the Atlantic Margin.

From early to middle Miocene, the sedimentary flux preferentiallydirected towards the West Alboran Basin, where the largest depocen-tres are found, as evidenced by the very high sedimentation ratecalculated in the Alboran Basin (0.24 mm/yr) relative to all the otherbasins (~0.04 mm/yr). During this period, theWest Alboran Basinwasdominated by extensional tectonics and large subsidence, whereas theAtlanticMargin and the foreland basins evolved in a compressive regime.This tectonic scenario produced very deep basins in the back-arc regionthat trapped the sedimentary supply and resulted in very highsedimentation rates. Interestingly, the total sedimentary volume accu-mulated in the external and the internal basins, for this period of time,differs only by 10–12% and could eventually be similar if we consider thatthe total calculated volume for the Atlantic Margin in Table 1 is a mini-mum value. During this period of time the internal basins occupied amuch smaller area than external basins (early forelands andGuf of Cadiz)and thus giving a much smaller rate of sediment accumulation.

During the late Miocene, the balance of the sedimentary supplyremained similar as for the early–middle Miocene. The totalsedimentary volume (~40,700 km3) and the sedimentary contribu-tion (~6450 km3/My) are virtually the same for the internal andexternal basins and increased almost twice with respect to the early–Middle Miocene. The progressive infilling of the Alboran Basin and theconsequent enlargement of its surface, resulted in a decrease of thesedimentation rate from 0.24 to 0.18 mm/yr. Coeval to extensionaltectonics in the back-arc basin of the Betic–Rif orogen, the AtlanticMargin and the foreland basins were submitted to compression untillate Miocene. The emplacement during this period of the Gulf of CadizImbricate Wedge produced the disruption of previous deposits andconditioned the structure of the overlying basins in the AtlanticMargin. According to the documented distribution of sediments in theisopach maps, the foreland basins recorded their maximum flexureduring the late Miocene (Barbieri and Gabriele Ori, 2000; García-Castellanos et al., 2002; Hanne et al., 2003).

Along the Pliocene–Quaternary, the symmetry of the sedimentarysupply between the internal and external basins breaks and the externalbasins record a total sedimentary volume around 25% larger than theinternal basins. The sedimentary contribution and sedimentation ratesfor the internal basins are very similar to the values registeredduring thelateMiocene. However, the external basins showa clear increase in both

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Table 1Sedimentary budget for the Neogene basins infilled by rocks belonging to the Betic–Rif orogen.

Basin Time period(Ma)

Time interval(My)

Sediment contribution(km3/My)

Sediment rate(mm/a)

Total volume(km3)

Early–Middle Miocene Alboran B. 20.4–9 11.4 3912 0.24 4460034425⁎

Intramontane b. 20.4–11.6 8.8 42 b0.01 370Internal basins 3954⁎ ~0.24 34795⁎Guadalquivir B. 14–11.6 2.4 1162 0.07 2790Atlantic Margin 23.7–11.6 12.1 1983 0.03 24000Rharb B. 16–13 3 817 0.06 2450External basins 3323 ~0.04 29240

Late Miocene Alboran B. 9–5.3 3.7 6600 0.18 244005490⁎ 34575⁎

Intramontane b. 11.6–5.3 6.3 945 0.04 5953Internal basins 6433 ~0.18 40588Guadalquivir B. 11.6–5.3 6.3 1333 0.06 8400Atlantic Margin 11.6–5.3 6.3 3587 0.06 22600Rharb B. 13–5.3 7.7 1286 0.1 9900External basins 6492 ~0.07 40900

Pliocene–Quaternary Alboran B. 5.3–0 5.3 3890 0.19 20600Intramontane b. 5.3–0 5.3 549 0.05 2912Internal basins 6021 ~0.19 31912Guadalquivir B. 5.3–0 5.3 530 0.04 2810Atlantic Margin 5.3–0 5.3 6604 0.22 35000Rharb B. 5.3–0 5.3 415 0.06 2200External basins 7550 ~0.20 40010

Total Neogene Alboran B. 20.4–0 20.4 4363 0.2 89600Intramontane b. 20.4–0 20.4 452 0.08 9235Internal basins 4815 ~0.18 98835Guadalquivir B. 14–0 14 1000 0.06 14000Atlantic Margin 23.7–0 23.7 3443 0.06 81600Rharb B. 16–0 16 909 0.08 14550External basins 5147 ~0.06 110150

Numbers with asterisk in the Alboran Basin indicate values averaged over time spans from 20.4 to 11.6 Ma and from 11.6 to 5.3 Ma.

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sedimentary contribution (from 6490 to 7550 km3/My) and sedimen-tation rate (from 0.07 to 0.20 mm/yr). This increase is entirelyimputable to the Atlantic Margin basins which receive the largestsedimentary input among all the other basins, either internal orexternal. It is worth noting from Table 1 that, with the exception ofthe AtlanticMargin, in all the other basins the sedimentary contributiondecreases notably from the late Miocene to the Pliocene–Quaternary,whereas the sedimentation rate does in less extend or even increases(internal basins). These changes in the sediment supply pattern are aconsequence of a more active development of the drainage network ofthe rivers draining to the Atlantic at expenses of those draining to theMediterranean. This development is related to the regional convergencebetween Iberia and Africa, which lead to folding and uplift and theconsequent increase of the emerged areas, and includes the capture ofsome internal drainage basins, such as the Granada and Guadix basins(Martín-Penela, 1987; Ruíz-Bustos et al., 1990).

The total sedimentary volume supplied by the Betic–Rif orogen(209,000 km3) is distributed almost half and half between the internaland external basins. The largest sedimentary volumes are recorded bythe Alboran Basin (89,600 km3) and the Atlantic Margin basins(81,600 km3), which represent about 43% and 39% of the total volume,respectively. The Guadalquivir and Rharb foreland basins amount14,000 km3 and 14,550 km3 respectively, representing about 6.8% eachone from the total volume. Finally, the intramontane basins summarize9235 km3 and 4.4% of the total volume. Interestingly, the Alboran Basinrecords the maximum sedimentary contribution during the Miocene,whereas theAtlanticMargindoes during the Pliocene–Quaternary. Thesedimentary volumeswere also converted to equivalent rock volumes,changing sedimentary densities into densities of the source rocks. Rockdensities of the source areas in both, the Internal and External zones,have a mean value of 2700 kg m−3 according to experimental labo-ratory measurements (Zappone et al., 2000). Densities for Neogenedeposits inferred from seismic experiments (Berástegui et al., 1998;González-Fernández et al., 2001; Gutscher et al., 2002) or used in

gravity modeling (Torne et al., 2000) fluctuate between 2000 and2400 kgm−3. We assigned an average ratio between eroded rocks andsediments of 1.2 which results in a total eroded volume of about173,600 km3. This represents an important constraint to the proposedpaleogeographic reconstructions, which must provide a sufficientemerged surface to account for both the total and the time-to-timeerosion volumes.

In addition to the sediment supply balance, we have analyzed thetime at which the marine to non-marine transition occurs in thedifferent basins of the Betic–Rif orogen (Fig. 14). The first basinsemerging from a marine environment were the so-called Pre-Beticbasins located in the north-easternmost part of the Betic chain andoccurred at late Serravallian–early Tortonian times (starting at about11 Ma). From this time on, the emersion of the sedimentary basins inthe Betics followed a concentric pattern regardless of the nature of thebasin. The core of this concentric emersion is middle Tortonian in ageand located around the Sierra Nevada in the Internal Betics. Theyounger basins emersion took place in the coastal Mediterraneanbasins (e.g., Alicante-Cartagena, Níjar, Campo de Dalias) and thewesternmost Guadalquivir basin, spanning from Tortonian to Plio-cene. In the Rif, the basin emersion followed a radial pattern directedfrom Ouerrah and Taza-Guercif basins to the Rharb and Melilla basins,spanning from Messinian to Pliocene times.

Interestingly, most of this marine to non marine transitionoccurred after the cessation of both major thrust tectonics in theouter domain of the Betic–Gibraltar–Rif System (Berástegui et al.,1998; Maldonado et al., 1999; Gràcia et al., 2003a; Frizon de Lamotteet al., 2004; Iribarren et al., 2007) and extensional tectonics in its innerdomain (Comas et al., 1999). Starting in late Tortonian times, the studyregion was characterized by the uplift of large regions as determinedfrom the present position of shallow marine late Tortonian deposits,which can reach altitudes above 1000 m (Braga et al., 2003; Sanz deGaldeano and Alfaro, 2004). This uplift was produced by the large-scale folding that affected the Internal Units forming domes (e.g.,

Page 15: Sediment supply from the Betic–Rif orogen to basins through Neogene

Fig. 14. Map of the Betic–Gibraltar–Rig orogenic system to show the age of the marine to non marine transition for the different sedimentary basins onshore.

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Weijermars et al., 1985; Crespo-Blanc et al., 1994; Martínez-Martínezet al., 2002; Platt et al., 2003a,b).

Concentric uplifted zones in the Betic–Gibralter–Rif System show aclearmatchwith the crustal thickness distributionbelow these regions(Fullea et al., 2007). The close correspondence between elevated lateTortonian shallowmarine deposits and thick crustal thickness indicatetheir genetic link and the time atwhich the crust started its thickening.The concentric emersion of sedimentary basins was thus a conse-quence of the crust thickeningdue to theNNWconvergence of Africa. Ifthis correlation is correct, then the emergence of the basins of the Rif,which showyounger ages, would indicate that the crustal thickening isyounger in the Rif than along the central Betics domain.

Assuming that most of the present crustal thickening is post-lateTortonian and that before this period most of the Betic–Gibraltar–RifSystemwas below sea levelwith a constant crustal thickness averaging27.5 kmwe determine the amount of shortening produced during thelast 8 My. The total shortening across the central part of the SierraNevada (where the crust is thicker) is of 39 km that rapidly decreasestowards the west across the Serranía de Ronda where it only accountsfor 15.5 km where the emersion time is Messinian (5.3 Ma). Theseamounts give rates shortening of about 4.8mm/yr in the Sierra Nevadatransect (from 8 Ma) and about 2.9 mm/yr in the Serranía de Rondatransect (from 5.3 Ma), which match with maximum reconstructedmagnitudes of Africa–Iberia convergence determined by Argus et al.(1989) along this segment of the plates boundary. These relatively highrates of tectonic shortening calculated from crustal thickness recon-structionsmay correspond tomaximumvalues sincewe used constantinitial thickness through the profile whereas paleogeographic maps of

the Betic–Gibraltar–Rif System show a large area around the presentSierra Nevada that was emerged above sea level before late Tortonian(e.g., Sanz de Galdeano and Rodríguez-Fernández, 1996; Geel andRoep, 1998; Andeweg, 2002; Braga et al., 2003). This region probablyhad a thicker pre-late Tortonian crust than assumed in our calculation.

6. Conclusions

The presented work allows us to draw the following conclusions:

i) The total sedimentary volume of the Neogene infilling thesedimentary basins of the Betic–Rif orogen is of approximately209,000 km3. Around 50% of this volume is accumulated in theinternal basins (Alboran Basin and intramontane basins) and theother 50% is distributed among both the Guadalquivir and Rharbforeland basins and the Atlantic Margin. This similar amount ofsediment flux to internal and external basins suggests a long-term symmetric development of the orogenic topography.

ii) The volumetric contribution of the intramontane basins onlyrepresents the 4.6% of the total sedimentary budget. However,these basins record the full geological history of sedimentation,uplift and erosion and are thus very important to decipher thecoupled sedimentary-tectonic history.

iii) Mean sedimentation rates during early and middle Mioceneshow an outstanding difference between the basins in theinternal and external domains. The Alboran Basin, morerestricted shows a sediment accumulation rate of 0.24 mm/yrwhereas the foreland basins and the Atlantic Margin, forming

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the external domain, account for only 0.06–0.07 mm/yr and0.03 mm/yr, respectively.

iv) During the late Miocene, sedimentation rates average 0.17–0.18 mm/yr recorded in the Alboran Basin and 0.04 mm/yr inthe intramontane basins. The total sedimentary input duringlate Miocene is maximum for all the basins in the Betic–Gibraltar–Rif System except for the Atlantic Margin.

v) During the Pliocene and Quaternary the maximum meansedimentation rates shifted to the Atlantic Margin reachingvalues as high as 0.22 mm/yr. The increase in the sedimenta-tion rate in this basin is a consequence of the progressive upliftof the Betic–Gibraltar–Rif System together with the develop-ment of the present fluvial drainage network characterized bythe capture of some of the intramontane basins by the riversthat drain to the Atlantic side (paleo Guadalquivir River).

vi) Neogene mean sedimentation rates show a general patterncharacterized by low values (b0.1 mm/yr) for all basins with theexception of the Alboran Basin, which results in ~0.20 mm/yr. Allthe basins showa slight increase in sedimentation rates during thelate Miocene reflecting the onset of present-day topography. TheAtlanticMargin shows a rapid increase of the sediment accumula-tion rate at the Miocene–Pliocene boundary. Only the AlboranBasin shows a slight decrease in sedimentation rates during lateMiocene probably partly related to its surface widening.

vii) The sedimentary contribution (km3/My) is a good indicator tocompare the amount of sediment supply to basins per unit oftime. There is a generalized increase of the sedimentarycontribution during the late Miocene and Pliocene–Quaternaryfits with the independent results that proves the initiation oftopographic growth in the Betic–Gibraltar–Rif orogen. Thisincrease, however, took place close to the cessation of boththrust tectonics along the outer domain and extensional tec-tonics in the inner domain and is therefore related to theprotracted N–NW convergence of Africa and to the initiation ofconcomitant crustal thickening.

viii) LateMiocene–Pliocene crustal thickening appears to be roughlyconcentric and nucleated around the Sierra Nevada range asindicated by the age distribution of the marine to non-marinetransitions in the Betics and Rif. According to these ages, thecrustal thickening in the Rif could be younger than in the Betics.Using present day crustal thickness we calculate post-lateTortonian shortening of 4.8 mm/yr across the Sierra Nevadatransect that fits with Neogene calculated motions of Africa.

ix) The results from this study must help to constrain tectonicmodels applied to the Betic–Rif orogen providing volumes,sedimentation rates and sediment contribution for differenttime slices since the early–middle Miocene to Present.

Acknowledgements

This is a contribution of the Team Consolider-Ingenio 2010 nr.CSD2006-00041. This research was partly funded by projects MARSI-BAL (REN 2001-3868-CO3-MAR), WESTMED (REN 2002-11230-E-MAR), SAGAS (CTM2005-08071-C03-03/MAR), IMPULS (REN 2003-05996/MAR) and ESF Eurocores-EUROMARGINS (01-LEC-EMA22F).L Iribarren benefited from a PhD Grant from the Spanish Ministerio deEducación y Ciencia. J. Fàbrega helped with the figures. D. Frizon deLamotte, an anonymous reviewer and G. Bertotti improved the manu-script with their comments.

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