Sediment supply from the BeticRif orogen to basins through Neogene

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

    Keywords:Sedimentary volumesSedimentation ratesSedimentary contributionsIberiaAfrica plate boundaryErosion and vertical movements

    Tectonophysics 475 (2009) 6884

    Contents lists available at ScienceDirect


    .e lQuantifying tectonic and sedimentary processes is a signicantchallenge 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 uxesfrom growing mountains to basins and their rates are closely relatedto the intensity and duration of tectonic events rather than to climate.Therefore, accurate quantication of sediment transfer within tec-

    mostly developed during the Alpine orogeny. The orogenic systemencompasses the BeticRif 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 BeticRiforogen 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.,tonically active areas is essential for understatectonic evolution of orogenic systems.

    The development of the BeticRif orogeIberia plate boundary across the transition zo

    Corresponding author. Fax: +34 934110012.E-mail addresses: (L. Iribarre

    (J. Vergs), (M. Fernndez).

    0040-1951/$ see front matter 2008 Elsevier B.V. Aldoi:10.1016/j.tecto.2008.11.029Ocean and the Mediterranean Sea resulted in a complex scenario1. IntroductionWe present a quantication of total and partial (divided by time slices) sedimentary volumes in the Neogenebasins of the BeticRif 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 earlymiddle Miocene show an outstanding asymmetry between the Alboran basin (0.24 mm/yr) and the forelandbasins (0.060.07 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 PlioceneQuaternary, 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 PlioceneQuaternary (6600 km3/My). The spatial and time variability of thesediment supply from the BeticRif orogen to basins is closely related to the morphotectonic evolution of theregion. The high sedimentation rates obtained in the Alboran Basin during the earlymiddle 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 amplication that occurred in the central Betics and Rif with the concomitant evolution ofthe drainage network showing the uvial capture of some internal basins by rivers draining to the AtlanticOcean (the ancestral Guadalquivir).

    2008 Elsevier B.V. All rights reserved.Article history:a b s t r a c ta r t i c l e i n f oSediment supply from the BeticRif oroge

    L. Iribarren a,b, J. Vergs a,, M. Fernndez a

    a Group of Dynamics of the Lithosphere (GDL), Institute of Earth Sciences Jaume Almerab Department of Marine Geology, INETI-National Institute for Engineering, Technology and

    j ourna l homepage: wwwnding and modelling the

    n on top of the Africane between the Atlantic


    l rights basins through Neogene

    C, Llus Sol i Sabars s/n, 08028 Barcelona, Spainovation, Estrada da Portela, Zambujal, 2721-866 Amadora, Portugal


    sev ie locate / tecto1995; Platt et al., 2003a,b); mantle delamination (e.g., Garca-Dueaset 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,

  • 69L. Iribarren et al. / Tectonophysics 475 (2009) 6884however, 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 inlling and itstectonic signicance are restricted to few basins within the BeticRiforogen. 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 Rodrguez-Fernndez,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 seismicproles. 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;Rodrguez-Fernndez 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; Grciaet 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 BeticRif orogenic system. In this context, the main objective of

    Fig. 1. Tectonic map showing principal structural units of ththis work is to provide a quantitative analysis of sedimentary volumesfor all the sedimentary basins that developed during the BeticRiforogenic evolution since earlymiddle Miocene to Present. Thisquantication 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 proles, 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 quantica-tion and rates of sedimentation of the BeticRif 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 nally discuss the im-plications of these results during the BeticRif orogenic buildingthrough middlelate Miocene, Pliocene and Quaternary periods.

    2. Geological setting

    The BeticRif 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., Garca-Dueas 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

    e BeticRif Orogen and the associated Neogene basins.

  • 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 theBeticRif 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 ENEWSWextensional regimefrom the late Oligocene or early Miocene to the Tortonian (at approx-imately 9 Ma) (Comas et al., 1992; Rodrguez-Fernndez et al., 1999).FromTortonian to Present theAlboran Basin records folding and strike-slip faulting associated to a roughly NNWSSE compressive tectonicregime (Comas et al., 1999).

    Other sedimentary basins that formed and evolved during theNeogene in the BeticRif 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 in

    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 exure of the basement in response to the loading of thethrusted and imbricated External Units (Sanz de Galdeano and Vera,1992; Berstegui et al., 1998; Garca-Castellanos et al., 2002). To thewest, the successive imbricate units of the BeticRif 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; Grcia et al., 2003a; Gutscher et al., 2002; Iribarren et al., 2007).

    3. Sedimentary volumes

    A rst objective of this work is to quantify the total sedimentaryvolume that is related to the building-up of the BeticRif 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 proles and geological cross-sections.

    In addition to the total volume, we calculated the partial sedimentarysupplycorresponding to several predened 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) PlioceneQuaternary (5.3 to0 Ma). In the Alboran Basin, however, the rst 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 each

    ). The f

    70 L. Iribarren et al. / Tectonophysics 475 (2009) 6884different ages from late Tortonian onwards (Sanz de Galdeano and

    Fig. 2. Isopach map of Neogene sediments in the Alboran Basin from Torne et al. (2000volume derived from the Betics and the Rif. To the East of this line, sediments likely com

    Alboran Basin, SAB: South Alboran Basin, YB: Yusuf Basin.basin, 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

  • 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 seismicproles (Fig. 2). The isopach map shows an irregular inll, 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 BeticGibraltarRif. 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-conned 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 lled 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 quantication 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-

    mities: Tortonian reector R-3 and top of the Messinian reector M(Comas et al., 1999). Fig. 3 shows the data used to construct the depth tobasement maps of both reectors and the isopach maps for each timeinterval. The data include previous partial depth-to-basementmaps andinterpreted seismic proles. The reectors 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 s1 for the PlioceneQuaternary, 2.5 km s1 for thelate Miocene, and 4.0 km s1 for the earlymiddle Miocene.

    The isopach maps in Fig. 3 represent, respectively, the thicknessand distribution of the PlioceneQuaternary 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 inll of the PlioceneQuaternary and late Miocene sediments. In these time intervals, themaximum thicknesses are similar and range between 1600 and1800 m (Fig. 3B and C). PlioceneQuaternary 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 signicantaccumulations.

    e M

    71L. Iribarren et al. / Tectonophysics 475 (2009) 6884Fig. 3. (A) Data used to construct isopach maps for the PlioceneQuaternary and the lat

    Miocene (5.3 to 9 Ma) sediments. (D) Early to early late Miocene (9 to 20.4 Ma) sedimentsiocene time intervals. (B) Isopach map of the PlioceneQuaternary sediments. (C) Late


  • Well data descriptions indicate that PlioceneQuaternary 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 BeticRif 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 PlioceneQuaternary (5.3 Ma to Present).

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

    The Atlantic Margin of the BeticRif 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 PlioceneQuaternary, 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 BeticRif provenance, have beendetermined from a dataset that consists of scientic and oil ex-ploration wells together with seismic reection proles (Fig. 4).

    A total of 25 oil exploration wells from the SW Iberian shelf in theGulf of Cadiz (Lanaja et al., 1987) and two scientic 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-

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

    Seismic interpretation has been performed on a total of 28multichannel seismic proles, and has been correlated with the welldata and previous interpretations (Tortella et al., 1997; Grcia et al.,2003a; Medialdea et al., 2004). The seismic proles were acquired indifferent scientic 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(Grcia 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;Gonzlez-Fernndez 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;Grcia et al., 2003a). This unit is referred as the Gulf of Cadiz ImbricateWedge and represents the most external unit of the BeticRif thrustbelt whose emplacement nished 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 PlioceneQuaternary sediments, which lie above theGulf of Cadiz Imbricate Wedge, while the early and Middle Miocenesediments cannot be properly calculated with the available data.

    d wCIW

    72 L. Iribarren et al. / Tectonophysics 475 (2009) 6884Fig. 4. Bathymetric map of the studied area and available seismic reection proles anCPR: Coral Patch Ridge, GoB: Gorringe Bank, GB: Guadalquivir Bank, PB: Portimao Bank; G

    seismically chaotic unit.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

  • 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 inuence area, sedimentsshow higher thicknesses and accumulate in depocentres. The extendof the continental inuence areas varies from late Miocene toPlioceneQuaternary 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

    from the inuence 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 BeticRif orogen amounts 81,600 km3 corresponding to24,000 km3 deposited during the earlymiddle Miocene (23 to11.6 Ma), 22,600 km3 during the late Miocene (11.6 to 5.3 Ma), and35,000 km3 during the PlioceneQuaternary (5.3 to 0 Ma).

    3.3. The Guadalquivir and Rharb foreland basins

    The Guadalquivir basin is a narrow ENEWSW 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 oored by a basement dipping 24 towards the Beticsand constituted by Paleozoic rocks of the Hercynian Iberian Massifand, occasionally, by Mesozoic rocks (Fernndez et al., 1998). The

    te M

    73L. Iribarren et al. / Tectonophysics 475 (2009) 6884Fig. 5. Isopach maps in the Atlantic Margin for PlioceneQuaternary sediments (A) and la

    Thick dashed lines represent the westwards extent of the siliciclastic analyzed deposits.iocene sediments (B). Seismic database is also depicted in both maps as thin grey lines.

  • 74 L. Iribarren et al. / Tectonophysics 475 (2009) 6884downward 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 (Garca-Castellanos et al., 2002). Berstegui et al.(1998) divided the sedimentary inll of the Guadalquivir Basin in 6sedimentary sequences, bounded by unconformities, from the lateLanghian to the Messinian. The rst sequence (late LanghianearlySerravallian) consists of a thin coastal calcarenitic sedimentary unit(2040 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 inll in the Rharb Basin includesisolated patches of Aquitanian sediments and middle Miocene toQuaternary sediments. TheMiddleMiocene (Langhian to Serravallian)

    Fig. 6. (A) Geologic map of the Guadalquivir Basin and data used to construct the isopis composed by marine turbiditic deposits (Esteban et al., 1996). Themain sedimentary inll 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 proles, geological sections, oilexploration wells and local isopach maps (Figs. 6A, 7A). The reectorsof the seismic proles were depth converted by considering anaverage p-wave velocity of 2 km/s for MiocenePliocene sediments,according to values proposed by Berstegui et al. (1998) for theGuadalquivir Basin. Isopach maps were obtained by the interpolationof these reectors together with sedimentary thickness fromwell dataand geological sections.

    The total isopach map of the Guadalquivir shows an ENEWSWelongated 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

    ach map. (B) Isopach map of Neogene sediments inlling the Guadalquivir Basin.

  • isop

    75L. Iribarren et al. / Tectonophysics 475 (2009) 6884Guadalquivir 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 inll 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 PlioceneQuaternary

    Fig. 7. (A) Map of the Rharb Basin showing the data used to construct the(from 5.3 to 0 Ma).In the Guadalquivir Basin, the PlioceneQuaternary (2810 km3) is

    distributed in two depocentres: central and western depocentres(Fig. 8A). The central depocentre, with maximum thicknesses ex-ceeding 600 m, is lled up by non marine sediments, while marinesediments accumulate in the western depocentre reaching 1800 m ofmaximum thickness. The late Miocene (8400 km3) constitutes themain inll 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 (100600 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 inll 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 (100400 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.,

    ach map (B) Isopach map of Neogene sediments inlling the Rharb Basin.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 rst 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 (Rodrguez-Fernndez and Sanz de Galdeano, 2006, and Lpez-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 PlioceneQuaternary 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 1825% oferror.

  • 76 L. Iribarren et al. / Tectonophysics 475 (2009) 6884The 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 InternalExternal 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 PlioceneQuaternary 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

    Fig. 8. Isopach maps of the Guadalquivir basin for PlioceneQuaternary sedimof 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 78 Ma) but they continued to inll because theirintramontane condition surrounded by high ranges. These closedbasins only opened and eroded after river capture, as we will brieycomment later.

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

    ents (A), late Miocene sediments (B) and middle Miocene sediments (C).

  • 77L. Iribarren et al. / Tectonophysics 475 (2009) 6884foredeep 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-

    Fig. 9. Isopach maps of the Rharb Basin for PlioceneQuaternary sedimentoped 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 rst 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 inll is supplied mainly from the Atlas Mountains (Krijgsman

    s (A), late Miocene sediments (B) and middle Miocene sediments (C).

  • 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 thePlioceneQuaternary and late Miocene time intervals.

    78 L. Iribarren et al. / Tectonophysics 475 (2009) 6884

  • and

    79L. Iribarren et al. / Tectonophysics 475 (2009) 6884et al., 1999) and therefore its contribution has not been considered inthis study. The Ouerrah basins, situated in a central positionwithin the

    Fig. 12. Sedimentary contributions to basins in km3/My. The total amount for externalQuaternary interval.Rif 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 inll 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 denitiveemersion 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 quantication 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 dened 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 uvial evolution (Figs. 12 and 13).The most outstanding result for the early to middle Miocene timeinterval is the great asymmetry in sedimentation rates between the

    internal basins shows a very similar evolution only diverging during the Pliocene andAlboran 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 1.41.8 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 (0.170.18 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 (Rodrguez-Fernndez et al., 1999). Subsidence studies indicate that the basementexure 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.

  • f ornta

    80 L. Iribarren et al. / Tectonophysics 475 (2009) 6884During the PlioceneQuaternary 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 inlling 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 (Martn-Penela, 1987; Ruz-Bustos et al., 1990).

    Fig. 13. (A) Total sedimentary volumes calculated in the Neogene basins of the BeticRiexternal domain (Atlantic Margin, Guadalquivir and Rharb foreland basins, and intramo5. 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 theBeticRif 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 BeticRif 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, whichmust be considered as a minimumvalue due to the large uncertaintiesin dening the bottom of the basins in the Atlantic Margin.

    From early to middle Miocene, the sedimentary ux 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 1012% and could eventually be similar if we consider thatthe total calculated volume for the Atlantic Margin in Table 1 is a mini-

    ogen. (B) Rates of sediment accumulation for the internal domain (Alboran Basin) andne basins).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 earlymiddle 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 earlyMiddle Miocene. The progressive inlling 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 BeticRif 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 exureduring the late Miocene (Barbieri and Gabriele Ori, 2000; Garca-Castellanos et al., 2002; Hanne et al., 2003).

    Along the PlioceneQuaternary, 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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    81L. Iribarren et al. / Tectonophysics 475 (2009) 6884sedimentary contribution (from 6490 to 7550 km3/My) and sedimen-tation rate (from 0.07 to 0.20 mm/yr). This increase is entirely

    Table 1Sedimentary budget for the Neogene basins inlled by rocks belonging to the BeticRif

    Basin Time period(Ma)


    EarlyMiddle Miocene Alboran B. 20.49

    Intramontane b. 20.411.6Internal basinsGuadalquivir B. 1411.6Atlantic Margin 23.711.6Rharb B. 1613External basins

    Late Miocene Alboran B. 95.3

    Intramontane b. 11.65.3Internal basinsGuadalquivir B. 11.65.3Atlantic Margin 11.65.3Rharb B. 135.3External basins

    PlioceneQuaternary Alboran B. 5.30Intramontane b. 5.30Internal basinsGuadalquivir B. 5.30Atlantic Margin 5.30Rharb B. 5.30External basins

    Total Neogene Alboran B. 20.40Intramontane b. 20.40Internal basinsGuadalquivir B. 140Atlantic Margin 23.70Rharb B. 160External basins

    Numbers with asterisk in the Alboran Basin indicate values averaged over time spans frimputable 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 PlioceneQuaternary,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(Martn-Penela, 1987; Ruz-Bustos et al., 1990).

    The total sedimentary volume supplied by the BeticRif 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 PlioceneQuaternary. 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 m3 according to experimental labo-ratory measurements (Zappone et al., 2000). Densities for Neogenedeposits inferred from seismic experiments (Berstegui et al., 1998;Gonzlez-Fernndez et al., 2001; Gutscher et al., 2002) or used ingravity modeling (Torne et al., 2000) uctuate between 2000 and2400 kgm3. We assigned an average ratio between eroded rocks and


    erval Sediment contribution(km3/My)

    Sediment rate(mm/a)

    Total volume(km3)

    3912 0.24 4460034425

    42 b0.01 3703954 ~0.24 347951162 0.07 27901983 0.03 24000817 0.06 2450

    3323 ~0.04 292406600 0.18 244005490 34575945 0.04 5953

    6433 ~0.18 405881333 0.06 84003587 0.06 226001286 0.1 99006492 ~0.07 409003890 0.19 20600549 0.05 2912

    6021 ~0.19 31912530 0.04 2810

    6604 0.22 35000415 0.06 2200

    7550 ~0.20 400104363 0.2 89600452 0.08 9235

    4815 ~0.18 988351000 0.06 140003443 0.06 81600909 0.08 145505147 ~0.06 110150

    20.4 to 11.6 Ma and from 11.6 to 5.3 Ma.sediments 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 sufcientemerged 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 BeticRif orogen (Fig. 14). The rst basinsemerging from a marine environment were the so-called Pre-Beticbasins located in the north-easternmost part of the Betic chain andoccurred at late Serravallianearly 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, Njar, 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 BeticGibraltarRif System (Berstegui et al.,1998; Maldonado et al., 1999; Grcia 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.,

  • 82 L. Iribarren et al. / Tectonophysics 475 (2009) 6884Weijermars et al., 1985; Crespo-Blanc et al., 1994; Martnez-Martnezet al., 2002; Platt et al., 2003a,b).

    Concentric uplifted zones in the BeticGibralterRif 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 BeticGibraltarRifSystemwas 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 Serrana 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 Serrana de Rondatransect (from 5.3 Ma), which match with maximum reconstructedmagnitudes of AfricaIberia 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 prole whereas paleogeographic maps of

    Fig. 14. Map of the BeticGibraltarRig orogenic system to show the age of the mthe BeticGibraltarRif System show a large area around the presentSierra Nevada that was emerged above sea level before late Tortonian(e.g., Sanz de Galdeano and Rodrguez-Fernndez, 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 inlling thesedimentary basins of the BeticRif 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 ux 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

    arine to non marine transition for the different sedimentary basins onshore.

  • 83L. Iribarren et al. / Tectonophysics 475 (2009) 6884the external domain, account for only 0.060.07 mm/yr and0.03 mm/yr, respectively.

    iv) During the late Miocene, sedimentation rates average 0.170.18 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 BeticGibraltarRif 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 BeticGibraltarRif System together with the develop-ment of the present uvial 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 reecting the onset of present-day topography. TheAtlanticMargin shows a rapid increase of the sediment accumula-tion rate at the MiocenePliocene 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 PlioceneQuaternaryts with the independent results that proves the initiation oftopographic growth in the BeticGibraltarRif 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 NNW convergence of Africa and to the initiation ofconcomitant crustal thickening.

    viii) LateMiocenePliocene 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 ts with Neogene calculated motions of Africa.

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


    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 beneted from a PhD Grant from the Spanish Ministerio deEducacin y Ciencia. J. Fbrega helped with the gures. D. Frizon deLamotte, an anonymous reviewer and G. Bertotti improved the manu-script with their comments.


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    Sediment supply from the BeticRif orogen to basins through NeogeneIntroductionGeological settingSedimentary volumesThe Alboran BasinThe Atlantic Margin (Gulf of Cadiz and NW-Moroccan Atlantic Margin)The Guadalquivir and Rharb foreland basinsThe intramontane basins

    Sedimentation rates and sedimentary contributionDiscussionConclusionsAcknowledgementsReferences


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