Transcript
See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/229631723 Structure and evolution of a Messinian mixedcarbonate-siliciclastic platform: The role of evaporites (Sorbas Basin... Article in Sedimentology · September 2009 DOI: 10.1111/j.1365-3091.2009.01092.x CITATIONS 20 READS 176 7 authors , including: Some of the authors of this publication are also working on these related projects: CLAYCOAT: CLAY COATings in shallow marine deposits to improve reservoir quality prediction ViewprojectDiagenesis of the Mid-Jurassic dolomite bodies from the Beaune/Santenay area (France) View projectRaphaël BourillotInstitut Polytechnique de Bordeaux 23 PUBLICATIONS 105 CITATIONS SEE PROFILE Emmanuelle VenninUniversity of Burgundy 111 PUBLICATIONS 1,086 CITATIONS SEE PROFILE Vincent RommevauxNational Council for Scientific Research, Leb… 5 PUBLICATIONS 28 CITATIONS SEE PROFILE Christophe KolodkaCentre Européen de Recherche et d’Enseigne… 8 PUBLICATIONS 52 CITATIONS SEE PROFILE All content following this page was uploaded by Raphaël Bourillot on 25 December 2016. The user has requested enhancement of the downloaded file. Structure and evolution of a Messinian mixed carbonate-siliciclastic platform: the role of evaporites (Sorbas Basin,South-east Spain) RAPHAE¨ L BOURILLOT*, , EMMANUELLE VENNIN*, , JEAN-MARIE ROUCHY ,§,CHRISTOPHE DURLET*, , VINCENT ROMMEVAUX ,§, CHRISTOPHE KOLODKA*, and FREDERIC KNAP*, * Laboratoire Bioge´ osciences, Universite´ de Bourgogne, 6 Bd Gabriel, F-21000 Dijon, France(E-mail:
[email protected]) CNRS, UMR 5561 DepartmentofEarthHistory,MuseumNationald’HistoireNaturelle,43rueBuffon,F-75005Paris,France § CNRS, UMR 5143 Associate Editor – Stephen Lokier ABSTRACT TheSorbasMemberisalateMessiniancomplexsedimentarysystemthatformedimmediately following deposition of the Messinian evaporites in the SorbasBasin (South-east Spain). This work describes the sequence architecture andfaciesorganization ofacontinuouskilometrelong,alluvialfantoopenplatformtransect near the village of Cariatiz in the north-east of the basin. The post-evaporitic Cariatiz platform was a mixed carbonate-siliciclastic systemcomposed of four intermediate-frequency, fifth-order depositional sequences(Depositional Sequences 1 to 4) arranged in an overall prograding trend. Theintense fracturing and brecciation of these deposits is attributed to thedeformation and dissolution of an evaporite body measuring several tens of metres in thickness. The four sequences display significant spatial–temporalvariabilityinbotharchitectureandfaciesdistribution,withtwomainphases:(i)Depositional Sequences1and2areooidandoobioclasticdominated,andshownormal marine faunas; and (ii) Depositional Sequences 3 and 4 show a highersiliciclastic contribution and are microbialite dominated. These importantchanges are interpreted as modifications of the primary controlling factors.Followinganinitial70 mdrowning,possiblylinkedtoincreasedoceanicinput,DepositionalSequences1to3werecontrolledmainlybyeustaticvariationsandinherited topography; their progradation destabilized the evaporite body nearthe end of the Depositional Sequence 2 period. During the second phase,Depositional Sequences 3 and 4 recorded a progressive restriction of the SorbasBasinrelatedtoa30to40 mfallinwaterlevelthatwasdrivenmainlybyregionalfactors.Theseregionalfactorsweredissolutionandgravity-induceddeformationoftheevaporitesandcorrelativeevaporativefluidcirculationassociatedwiththecontrasted arid/humid regional climate that, respectively, controlled sequencegeometryandfluctuatingwatersalinitywhichcausedamicrobialitebloom. Keywords Evaporite collapse and deformation, late Messinian, microbialites,mixed carbonate/siliciclastic platform, ooids. INTRODUCTION Eustatic changes, climatic variations, tectonicsubsidence and palaeoceanographic circulationpatterns on both global and regional scales areoften regarded as major controls on lithofacies,architecture and floral–faunal associations of carbonate, siliciclastic or mixed platforms. The Sedimentology (2010) 57, 477–512 doi: 10.1111/j.1365-3091.2009.01092.x 2009 The Authors. Journal compilation 2009 International Association of Sedimentologists 477 slope, topography and rheology of platform sub-strata affect palaeocirculation patterns and coastaldynamics thereby influencing the type, locationand intensity of carbonate production and thepotential for sediment accumulation, i.e. theaccommodation space (Tucker & Wright, 1990;Franseen et al. , 1998; Johnson et al. , 2005).Evaporitic substrata are a potential source of: (i)variations in accommodation space, because theyare both ductile and easily deformable under theaction of gravity and are highly soluble; and (ii)fluctuations in water chemistry, as they formevaporative brines when dissolved in undersa-turated solutions (Warren, 1999; Rouchy & Blanc-Valleron, 2007).Giant evaporite bodies, composed mostly of gypsum and halite, formed in the deep Mediter-ranean Basin and on its margins as a result of theconjugated tectonic and eustatic isolation of theMediterranean during the Messinian SalinityCrisis (MSC) between 5 Æ 96 and 5 Æ 33 Ma (Rouchy& Caruso, 2006; CIESM, 2008). Offshore seismicreflection profiles across the deep Mediterraneanclearly show the influence of Messinian evaporitedeformation structures (listric faults, domes,diapirs, etc.) on the geometry of post-evaporiticdeposits (Rouchy, 1982; Letouzey et al. , 1995;Lofi et al. , 2005). In several Western Mediterra-nean marginal basins, Messinian evaporite depo-sition was superseded by the emplacement of ooid and microbialite-rich carbonate platforms of the Terminal Carbonate Complex (TCC). In allthese areas, post-MSC waters returned to near-pre-MSC levels, leading some workers to suggestthat Atlantic to Western Mediterranean seawaysreopened before the Pliocene (Rouchy & SaintMartin, 1992; Franseen et al. , 1998). Although theTCC is commonly believed to have been depos-ited in a marine environment (Riding et al. ,1998), it appears that its palaeoenvironments areinsufficiently constrained to rule out a continen-tal srcin for contemporaneous waters (Esteban et al. , 1996).In the Sorbas Basin, TCC deposits (i.e. theSorbas Member) consist of mixed siliciclastics,regularly supplied by deltaic inputs from theBetics, and ooid and microbialite carbonates(Roep et al. , 1979; Ott d’Estevou, 1980; Dabrio &Polo, 1995). The Cariatiz outcrops, situated on thenorth-eastern margin of the basin, are the focus of the present study and provide continuous expo-sures of the TCC from the landmass in the north-west to the outer platform in the south-east. Inthis area, the post-evaporitic platform formed thetop of a complex substratum: the northern part of the platform overlies highly variable topographycreated by erosion of pre-evaporitic fringing reefs,the Top Reef Unconformity (TRU); the south-eastern part exhibits deformation and solution-collapse brecciation which strongly suggest that itwas once underlain by evaporites.Using mapping and stratigraphic sections to-gether with facies and microfacies analysis alongthe 1 km long Cariatiz transect, this study pro-poses to: (i) identify the TCC palaeoenvironments;(ii) define the lateral and vertical facies distri- bution associated with stratal patterns so as toreconstruct the platform architecture; (iii) discussthe evidence for, and the timing and causes of,evaporitedissolutionanddeformationunderneaththe platform; and (iv) identify the relative role of water-level variations, topography, the evaporiticsubstratum, salinity and clastic supply within acomprehensivescenarioofplatformdevelopment.During the MSC, Mediterranean water masses,including the Sorbas Basin, were disconnectedfrom the global ocean most of the time, so thattheir respective water levels (regional versusglobal) were independent. In order to simplifythe discussion, the term ‘water level’ will be usedwhen describing the Sorbas Basin for all periods,including those when the Mediterranean waseither connected to or disconnected from theglobal eustatic sea-level. GEOLOGICAL SETTING The Sorbas Basin forms an intramontane east–west trending basin some 25 km long and 15 kmwide. It is bounded to the north by the Sierra deLos Filabres and to the south by the SierraAlhamilla and Sierra Cabrera. The sierras arecomposed of metamorphic and metasedimentaryseries of the Late Palaeozoic, Mesozoic andCenozoic Betic substratum (Fig. 1A and B). TheSorbas Basin is one of the Late Neogene peri-Betic basins, structured by Serravalian to late Tortonian Fig. 1. (A) Geological map of South-east Spain (modified after Cuevas Castell et al. , 2007). (B) Detailed geologicalmap of the Sorbas Basin (modified after Ott d’Estevou & Montenat, 1990). (C) North–south cross-section illustratingthe Messinian stratigraphy of the Sorbas Basin (modified after Martı´ n & Braga, 1994) and corresponding ages.Astronomical and magnetostratigraphic calibrations are after Krijgsman et al. (2001). Italicized ages are uncertain. 478 R. Bourillot et al. 2009 The Authors. Journal compilation 2009 International Association of Sedimentologists, Sedimentology , 57 , 477–512 ABC Messinian platform: the role of evaporites 479 2009 The Authors. Journal compilation 2009 International Association of Sedimentologists, Sedimentology , 57 , 477–512 north–south extensional movements caused bythe exhumation of the metamorphic complexes of the Sierra de los Filabres (Augier et al. , 2005; Jolivet et al. , 2006). The overall early Messinianseries (Figs 1C and 2) records the progressive pre-evaporitic restriction of the basin (7 Æ 24 to 5 Æ 96 Ma,Krijgsman et al. , 2001). Like all the peri-Mediter-ranean basins, the Sorbas Basin became isolatedfrom the Atlantic during the MSC by the tectonicclosure oftheBetic and Rif Straits, an event whichmay have been compounded by a global fall insea-level. Messinian Salinity Crisis related depos-its of the Yesares Member, astrochronologicallydated between 5 Æ 96 and 5 Æ 67 Ma (Krijgsman et al. ,2001), are composed mostly of selenite gypsumlayers of predominantly marine srcin (Rouchy,1982; Lu & Meyers, 2003). These deposits reachthicknessesof120 m.Duringevaporitedeposition,the subaerially exposed margins underwentintenseerosionresultingintheTRU(Riding et al. ,1998). This major, intra-Messinian erosional sur-face extends laterally for several kilometres andcan be correlated throughout most of the peri-Mediterranean basins (Esteban, 1979; Rouchy,1982; Rouchy & Saint Martin, 1992). The firstpost-evaporitic deposits, i.e. the Sorbas Member,mark a significant resumption of carbonate pro-duction. These deposits are locally up to 80 mthick and form a mixed siliciclastic/carbonateplatform system rich in ooids and microbialitesthat were deposited as a result of reflooding of theSorbas Basin margins (Figs 1C and 2; Roep et al. ,1979; Ott d’Estevou, 1980; Dabrio & Polo, 1995;Roep et al. ,1998).TheSorbasMemberoverlapstheTRU near the basin margins and the Yesaresgypsum basinward. These platforms record a sig-nificant source of siliciclastic deposits and freshwater corresponding to an alluvial fan located onthe northern margin of the basin, in the Sierra deLos Filabres (Ott d’Estevou, 1980; Ott d’Estevou &Montenat, 1990). Roep et al. (1998) dividedthe Sorbas Member into three sequences at theSorbas locality (Fig. 1B). Considering these threesequences, Krijgsman et al. (2001) estimated anagebetween5 Æ 67and5 Æ 60to5 Æ 54 MafortheSorbasMember,withadurationofbetween60and120 ka,depending on precession or obliquity control. Thelatest Messinian to early Pliocene ZorrerasMember marks the progradation of continentaldeposits of ‘Lago-Mare’ affinities (Fig. 2) thatcorrespond to the final episode of Mediterraneanrestriction during a more humid climatic phase(Martı´ n-Sua´ rez et al. ,2000;Krijgsman et al. ,2001;Rouchy & Caruso, 2006). Two white lacustrinecarbonate levels intercalated in these deposits(WL1 and WL2) are marker beds correlatable fromthe basin centre to its northern margin (Ottd’Estevou & Montenat, 1990; Roep et al. , 1998). THE CARIATIZ OUTCROPS The Cariatiz outcrops are situated in the north-east of the Sorbas Basin (Fig. 1B), in the Rambla` Fig. 2. Description of the Messinian series of the Sorbas Basin, compared with regional and Mediterranean events(based on Montenat, 1990; Martı´ n & Braga, 1994; Rouchy & Caruso, 2006). 480 R. Bourillot et al. 2009 The Authors. Journal compilation 2009 International Association of Sedimentologists, Sedimentology , 57 , 477–512
