The Messinian of the Nijar Basin (SE Spain): sedimentation, depositional environments and paleogeographic evolution

Sedimentary Geology 160 (2003) 213 – 242 www.elsevier.com/locate/sedgeo

The Messinian of the Nijar Basin (SE Spain): sedimentation, depositional environments and paleogeographic evolution A.R. Fortuin a,*, W. Krijgsman b b

a Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081HV Amsterdam, The Netherlands Paleomagnetic Laboratory ‘‘Fort Hoofddijk’’, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands

Received 29 May 2002; accepted 1 November 2002

Abstract The reconstruction of the depositional events related to the Messinian Salinity Crisis (MSC) of the Mediterranean is generally hampered by an incomplete stratal record in the circum-Mediterranean basins. The sediments of the northern part of the Nijar Basin, however, provide an excellent and continuous record of Late Messinian sediments because features of severe erosion are lacking. Especially, the successions of the deeper part of the basin had sufficient accommodation space to warrant ongoing deposition and may thus serve as a testing ground for existing hypotheses regarding the MSC. Conformable contacts with the overlying Pliocene and good correlation possibilities with the adjacent, astronomically dated, Messinian of the Sorbas Basin provide the necessary age constraints. The main body of evaporites in the Nijar Basin (Yesares Formation) has been affected by local dissolution and erosion prior to deposition of the latest Messinian (Lago – Mare) facies. Pelitic float breccias show textures indicating flowage and/or mass transport and include slumped and slided stratal packets due to foundering of the mixed evaporitic – clastic margin. Increased runoff of meteoric waters probably played an important role as these packet slides are perfectly sealed by the hyposaline Lago – Mare strata. Field observations show that marginal sediments, commonly classified as the Terminal Carbonate Complex (TCC), are a lateral equivalent of the basinal Yesares evaporites. The latest Messinian deposits (Feos Formation) are characterized by a sedimentary cyclicity, related to fluctuating base levels, consisting of chalky – marly laminitic strata alternating with continental coarser clastic intervals. Despite considerable W – E facies changes and indications for discrete tectonic events, a persistent sequential pattern of eight Lago – Mare cycles is present, which are interpreted as precession-controlled variations in regional climate. Instead of one major desiccation event in the latest Messinian, the repeatedly fluctuating water levels of the Lago – Mare episode may have been the cause of the widespread vigorous erosion and canyon cutting in the ‘‘Lower Evaporites’’. Abrupt, non-erosional contacts with the normal marine Pliocene take place above the continental interval of the last Lago – Mare cycle, indicating that flooding took place during a period of lowered water levels. The paleogeographic configuration of the Nijar, Sorbas and Vera basins has changed considerably during the Messinian. Separation of the formerly interconnected basins is thought to have started in the late Yesares times by tectonic uplift of the basement complexes. In the latest Messinian of the Nijar Basin, two different coarse clastic supply areas can be distinguished which point to the partial emergence of the Sierra Cabrera and the Cabo de Gata block and activity of the Sierra Alhamilla and

* Corresponding author. Tel.: +31-20-444-7351; fax: +31-20-444-9941. E-mail address: [email protected] (A.R. Fortuin). 0037-0738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0037-0738(02)00377-9

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Carboneras faults. Concerning the overall regional tectonic activity, tectonics were probably also instrumental for the restoration of the Atlantic gateway in the basal Pliocene. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Messinian; Mediterranean; Spain; Sedimentation; Paleogeography; Lago – Mare

1. Introduction Since the discovery of the pan-Mediterranean extension of Messinian evaporites and associated facies types (Hsu¨ et al., 1973; Ryan et al., 1973), numerous papers and working hypotheses have contributed to a better understanding of the complex and enigmatic scenario of rapidly changing biotic and depositional environments that governed this Messinian salinity crisis (MSC being the period of evaporite deposition and subsequent Lago – Mare facies, Hsu¨ et al., 1977; Cita, 1982; Cita and McKenzie, 1986; Rouchy and Saint Martin, 1992; Krijgsman et al., 1999). Sedimentation in the increasingly restricted Mediterranean basins was controlled by a combination of tectonic, eustatic and climatic factors (Weijermars, 1988; Clauzon et al., 1996; Krijgsman et al., 1999). Astronomical dating of the post-evaporitic Pliocene and the pre-evaporitic Messinian sediments now provides an accurate time frame for the MSC, which occurred between 5.96 and 5.33 Ma (Lourens et al., 1996; Krijgsman et al., 1999; Krijgsman et al., 2002). Although most MSC interpretations converge to a scenario of progressive isolation of the Mediterranean basins in a two-step model, the precise course of events is still a matter of debate (Clauzon et al., 1996; Krijgsman et al., 1999). Certain is that constriction of the Mediterranean – Atlantic gateways under relatively dry and warm climates (Suc and Bessais, 1990) ultimately led to deposition of marine evaporites all over the Mediterranean area. The ‘Lower Evaporites’ of Sicily, the Gessoso –Solfifera Formation of the Northern Apennines and the Yesares Formation of SE Spain are attributed to this first phase. The presence of such evaporites in the deep Mediterranean basins, however, has not been proven because they have never been drilled to their base. During the second phase, the Mediterranean seems to have been almost completely isolated from the Atlan-

tic, then at least periodically forming predominantly oligohaline water masses providing characteristic biofacies, the Lago – Mare (Hsu¨ et al., 1977; Cita et al., 1978). The ‘‘Upper Evaporites’’ of Sicily, the Colombacci Formation of the Northern Apennines and the Zorreras and Feos formations of SE Spain are but a few examples of this Mediterranean-wide occurring terminal Messinian environment in both onand offshore basins. The restriction of the Mediterranean – Atlantic gateway was suggested to have initially caused a major draw-down of sea-level up to at least 2 km (Clauzon, 1973; Stampfli and Ho¨cker, 1989). In many marginal basins, a network of subaerial drainage channels and canyons formed, as has been concluded from numerous indications for local scouring of valley incisions, or formation of ravinement surfaces above the marine evaporites (Cita and Ryan, 1978; Cita, 1982; Rouchy, 1982; Stampfli and Ho¨cker, 1989; Savoye and Piper, 1991; Alonso et al., 1991; Delrieu et al., 1993; Druckman et al., 1995). Periodically, waters may have risen again to approximately pre-existing levels as indicated by strontium isotope ratios of euryhaline ostracods (DeDeckker et al., 1988; McCulloch and DeDeckker, 1989). In many of the classic Messinian basins, such as Sicily and the Northern Apennines, the second phase sediments overly the first phase evaporites with an erosional and often angular unconformity. The Sorbas and Nijar basins of SE Spain, however, have been protected from vigorous erosion—as will be discussed here—because tectonic uplift of basement complexes during the MSC created isolated to semi-enclosed basins that remained favourable for sediment accumulation despite changing water levels. Therefore, these basins contain one of the most complete landbased Messinian successions including a substantial body of evaporites in the basin centres and reefal carbonates along part of their margins (Dronkert, 1976, 1985; Ott d’Estevou, 1980; Rouchy, 1982). In

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contrast to the intensively studied sediments of the Sorbas Basin, surprisingly little attention has been paid to the Upper Messinian of the Nijar Basin apart from detailed studies of the evaporite record (Rouchy, 1982; Dronkert, 1985; De la Chapelle, 1988; Van de Poel, 1991, 1994; Lu et al., 2001). Therefore, the main objective of this paper is to further elucidate the physical stratigraphy of the Nijar deposits, their lateral and vertical changes and their potential for increased understanding of the late Messinian events. In addition, the diverging upper Messinian stratigraphy with regard to the Sorbas Basin plus paleogeographic aspects will be discussed.

2. Geological setting The Neogene intramontane basins of SE Spain are situated in the internal part of the Betic Cordilleras

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(Fig. 1) and formed by motion along the NE – SW Trans-Alboran shear zone due to continental collision between the African and European plates (de Larouzie`re et al., 1988). The resulting transpressional to transtensional basins tend to be oriented parallel to the main direction of master strike-slip faults and originated in the Late Miocene when convergent motions in the Alboran domain became oblique. Fault kinematic studies indicate that the basin dynamics was fundamentally influenced by rotation of the major compressional axis during the Neogene (Montenat et al., 1987a,b; De la Chapelle, 1988; Coppier et al., 1990; Biermann, 1995; Stapel et al., 1996; Huibregtse et al., 1998; Montenat and Ott d’Estevou, 1999; Jonk and Biermann, 2002). These stress variations resulted in the alternation of free-sliding and locking regimes in relation to movements on master faults. In Tortonian times, a NW –SE orientation resulted especially in dextral displacements along the W – E-oriented

Fig. 1. Map showing the outline of the SE Betic Neogene basins plus the distribution of the Messinian reef tract and the sinistral Palomares and Carboneras strike-slip faults. The line through the Sorbas – Nijar basins indicates the position of the cross-section shown in Fig. 3.

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Fig. 2. Geological map of the study area in the northern Nijar Basin (modified after Van de Poel, 1991) giving the locations of the stratigraphic columns shown in Fig. 9.

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Fig. 3. N – S – SE cross-section through the Sorbas and Nijar basins. N.B. Vertical scale 9  exaggerated with regard to the horizontal scale. Note the overall higher elevation of the Sorbas Basin. The Cerro Cantona high, which is the corridor connecting Sierra Cabrera with Sierra Alhamilla, is bordered along its southern margin by a fault zone delimiting the northern Nijar Basin (modified after Van de Poel, 1994).

boundary faults such as the faultzone bordering the northern parts of Sierra Alhamilla—and continuing into Sierra Cabrera towards the coastal area (Gafarillos fault). During the Early Messinian, an abrupt clockwise rotation to N –S compression ended this activity and activated the NNE – SSW to NE – SW trending sinistral faults (e.g. Palomares and Carboneras faults, Fig. 1). The Nijar Basin is the southeasternmost basin bordering the Albora´n Sea (Fig. 1). The still active, NE – SW oriented, sinistral Carboneras (or Serrata) strikeslip zone separates the basin from the Sierra de Gata volcanic high (De la Chapelle, 1988; Montenat and Ott d’Estevou, 1999a,b). This high forms part of the Albora´n volcanic province and various volcanic suites such as Serravallian –calcalkaline volcanic complexes (Zeck, 2000) and Early Messinian ultrapotassic rocks and alkali– basalts (Serrano, 1992) attest to a complex history. The Messinian sediments that overlie this up to 1500 m thick volcanic sequence are, unfortunately, strongly reduced in thickness (De la Chapelle, 1988). The most extensive successions here are located between Carboneras and Agua Amarga (Van de Poel

et al., 1984; Brachert et al., 1996) and connect the northern part of the Nijar Basin with the Mediterranean. Our study focuses especially on the northern part of the Nijar Basin because much of the low-lying central parts (Campo de Nijar) are covered by Quaternary deposits. The study area (Figs. 1 and 2) is at present separated from the adjacent Sorbas Basin by the W –E oriented Sierra Cabrera (Fig. 3). The two basins were, however, still connected during most of the Messinian as the marginal Messinian reef tracts fringing the Sierra Alhamilla continue uninterruptedly from the southern margin of the Sorbas Basin to the western margin of the Nijar Basin (Fig. 2).

3. Stratigraphic background Late Miocene sedimentation in the Nijar Basin started, like in the adjoining Sorbas and Vera basins, with a latest Tortonian –Early Messinian transgressive unit (Fig. 4). This mixed bio- and lithoclastic unit (Azagador Member of Turre Formation, Vo¨lk and Rondeel, 1964) onlaps over either the metamorphic

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Fig. 4. Lithostratigraphic overview of the Messinian – Pliocene successions in the northern Nijar Basin (Gafares area) and correlation with the (partly equivalent) units in the Sorbas Basin.

basement or the folded and eroded Early Tortonian turbiditic basin fill (Chozas Formation). The Azagador unit passes upward, and laterally towards the basin center, into an over 100 m thick marly unit (Abad Member of Turre Formation). These marls are characterized by a cyclic pattern of alternating whitish marly chalks and beige marls in the lower part which display a sudden change towards sapropelitic laminites, marls and chalks in the upper part. The ‘‘Lower Abad’’ marls comprise well-preserved open marine, upper bathyal– lower epibathyal foraminiferal assemblages (Baggley, 2000) while the ‘‘Upper Abad’’ marls show an upward shoaling, plus change towards increased restriction of marine conditions (Van de Poel, 1992; Baggley, 2000). Various studies have shown that the sedimentary cyclicity in the Abad marls is related to orbital forcing with dominance of precession cycles (Sierro et al., 1997, 1999, 2001; Krijgsman et al., 1999, 2001; Va´zquez et al., 2000). The marls become less thick and sandier toward the western basin margin where they interfinger with reefal debris forming the distal parts of the clinoforms of the well-developed marginal reefal complex (Cantera Member of Turre Formation).

The upward change of laminitic Abad marls into dominantly gypsiferous strata (Yesares Member, modified into Yesares Formation by Van de Poel, 1991) is rapid, but conformable. Van de Poel (1991) distinguishes three members in his Yesares Formation: Oolite Member, Gypsum Member and Manco Member. The Oolite Member comprises the mixed clastic – evaporitic strata, rich in oolites, which onlap eroded Cantera clinoforms along the western basin margin. The member as such is a local equivalent of the well known Late Messinian Terminal Carbonate Complex (TCC; Esteban, 1979; Esteban and Giner, 1980; Dabrio et al., 1981; Riding et al., 1991a; Rouchy and Saint Martin, 1992). The Gypsum Member is characterized by massive gypsum beds alternating with pelitic (laminitic) and/or sandier interbeds. Both gypsum deposited from brines and reworked gypsum occurs, showing an upward trend towards dominantly detrital gypsum. Geochemical and sedimentary investigations suggest that the Yesares selenites were formed in ‘deep’ marine brines (Rosell et al., 1998; Lu et al., 2001; Corne´e et al., 2002), although fossil assemblages from muds intercalated in the gypsum of

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the western part of the Sorbas Basin reflect deposition around the transition from inner to outer shelf depth (Saint Martin et al., 2000). The Manco Member comprises the diagenetically affected levels that consist of vuggy limestone and/or dolomite and associated marly and sandy strata. Van de Poel (1991) considers fresh water alteration of gypsum to be the essential mechanism for their genesis. The uppermost Messinian is a relatively poorly studied unit named Feos Formation (Van de Poel, 1991; modified after Feos Member, Van de Poel et al., 1984). It more or less covers the ‘‘complexe postevaporitique’’ of French authors and corresponds to the ‘‘Lago – Mare episode’’ in the Mediterranean following current usage of Late Messinian facies types (Hsu¨ et al., 1977; Cipollari et al., 1999; OrszagSperber et al., 2000; Rouchy et al., 2001). This up to 100 m thick unit comprises a rich variety of lithologies witnessing strongly fluctuating environmental conditions. Pliocene sediments (Cuevas Formation, Vo¨lk and Rondeel, 1964) overlie the Messinian strata and consist of poorly stratified fossiliferous calcisiltites and calcarenites. They contain the earliest Pliocene Sphaeroidinellopsis– Globorotalia margaritae association in their basal part, while the benthic foraminiferal association indicates deposition in an outer shelf environment (Van de Poel, 1991 and own observations).

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4. Sedimentation of the Late Messinian evaporites (Yesares Formation) Before discussing the facies distribution and paleogeographical evolution of the Nijar Basin during the evaporitic phase of the MSC (Section 6), additional lithological data will be provided concerning the rapid lateral syn- and post depositional changes already indicated by Van de Poel (1991). Extensive outcrop studies permit some deviating interpretations concerning lateral changes, local importance of slumping and sliding associated with evaporite dissolution and collapse phenomena and the prominent role of detrital gypsum towards the top of the unit. The diagenetically affected Yesares sediments were divided by Van de Poel (1991) in the Lower and Upper Manco Limestone unit (LML and UML). The LML, developed as several metres of thick vuggy, dolomitic limestone breccia, is found at the very base of the formation especially in the neighbourhood of river Gafares and in the Collado del Manco (Fig. 2). The UML comprises the dissolved gypsum fragments of often graded, calcareous gypsarenites (Figs. 5 and 6d) of the upper half of the formation. In contrast to the chaotic, totally altered dissolution facies of the LML, the UML strata kept their bedding characteristics.

Fig. 5. Lithostratigraphic overview of the Yesares Formation in the Gafares area plus the transition to the overlying Feos Formation indicated by the presence of a black manganese level. The chaotic strata, exposed along Arroyo Gafares, are interpreted as a result of local evaporite dissolution and collapse plus associated sliding, mainly consisting of packets of broken strata derived from the Upper Manco Member. The chaotic mass is sealed by proximal sandy turbidites forming part of the uppermost UMM cycle, the top of which includes the first hyposaline marly beds. For legend, see Fig. 4.

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4.1. The regular basinal successions The Yesares Formation (Fig. 6a,b) starts with massive primary evaporites, but gradually, the depo-

sitional gypsum becomes replaced by detrital elements such as terrigenous clastics, oolitic grains and reworked gypsum. Evaporitic, clastic and calcareous pelitic interbeds regularly alternate which results in a

Fig. 6. Photographs of the Yesares Formation. (a) View on Gafares with the Loma de los Yesares ridge seen from the western valley margin of Arroyo Gafares. The arrow in the middle part of the photo indicates the base of the Yesares Formation, whereas the arrow at right in the foreground indicates the exposures of slided UML strata in Arroyo Gafares. An interrupted line indicates the contact between regular and slided strata. (b) View on the Yesares-type succession exposed in Loma de los Yesares. The left part exposes the Yesares evaporites and interbedded fines. The arrows 1 – 4 indicate the 4 coarsening-up cycles forming the UML unit. (c) Erosional contact between massive Yesares gypsum (lower right) and conglomerates rich in reworked gypsum. Contact indicated with an interrupted line. Hammer for scale. (d) Example of a vuggy sandy limestone of the UML unit. The vugs are the voids of dissolved gypsum clearly showing upward grading. Such beds pass laterally in non-dissolved turbiditic gypsarenites.

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distinct cyclic pattern (Rouchy, 1982). The type section of the Yesares Formation in the Nijar Basin located just E of Gafares (Fig. 5) includes approximately nine gypsum –pelite cycles followed by four calciclastic – gypsarenitic sequences (Fig. 6b). The top of the formation is formed by a gypsarenitic brown– black Mn-hydroxide-enriched level that forms the top of the 4th clastic sequence. This ‘‘Mn bed’’ is a useful markerbed as it can be traced laterally over several kilometres. The basal Yesares Member is widely exposed in the area NE of Los Feos (Fig. 2). Here, around 50 m is exploited. The gypsum is developed as metres thick beds alternating with only decimeters thick clayey to sandy interbeds (seven cycles exposed). This massivelooking succession is comparable to the Yesares cycles such as quarried 5 km to the north in the Sorbas Basin, although individual gypsum beds may be thicker there. A pronounced erosional unconformity (Barranco Gordo, Fig. 6c) separates the upper gypsum beds, here developed as very thick beds (2– 4-m range) alternating with 1 – 5 dm thick calcarenitic interbeds from four crudely stratified conglomerate sheets. These sheets consist of abundant reworked gypsum (clast size up to 30 cm) and poorly rounded lithoclasts (basement dolomites and quartzites, Porites blocks and Manco limestones) and form the local transition to the overlying Feos Formation. Eastward, this erosional unconformity decreases in significance. The gypsum conglomerates pass into mixed sandy to conglomeratic and gypsiferous strata forming the four sandy –calcarenitic sequences of the upper part of the type section. The UML calciclastics of the type area tend to be graded and laminated ranging in composition from a very high content of detrital gypsum to extremely sandy varieties. Some beds clearly show Bouma Ta– c turbidite sequences (paleocurrent directions to SSE). Selenitic gypsum interbeds are uncommon. The proportion of fine-grained and laminated detrital gypsum beds increases upward and eastward versus a decreasing amount of lithoclastic input and overall thinning. West of Gafares, the four UML sequences attain their sandiest aspect in the northernmost part of Section D (Fig. 5). Crudely graded and amalgamated sandstones suggest transport to SE directions. Selenitic gypsum interbeds are more common here. The lateral changes and cyclic aspect suggest that the

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UML clastics were deposited in small (proximal) submarine fan lobes. The dark Mn-enrichment layer at the top of the Yesares Formation has strongly affected 2 m of graded, amalgamated and slumped gypsarenites near the village of Gafares. Just below this level, sapropelitic marls occur which contain the remains of a monospecific fish fauna characterized by Aphanius crassicaudus (De la Chapelle and Gaudant, 1987). Samples from the top of this bed yielded, besides numerous fish remains, also some Chara oogonia. Further east, in the Collado del Manco area, turbidite a – c intervals from this level indicate transport to N200jS, while slumpfold orientations also indicate a SSW downslope movement. 4.2. Dissolution-affected successions Chaotically arranged stratal packets are exposed along Arroyo Gafares and in the Collado del Manco where they are sandwiched between the roughly 10 m thick top part of the formation and the basal LML (Fig. 5). These chaotic intervals are characterized by the combination of dissolution phenomena, affecting the intercalated evaporites, plus features indicating slumping and sliding of packets of strata. At Gafares, these deposits pass eastward rapidly into undisturbed and undissolved Yesares sediments via a partially exposed slide scar (oriented N110jE; Figs. 5 and 6a). The stratigraphic thickness of the chaotic mass exposed along the riverbed equals that of the undeformed Yesares – Upper Manco successions laterally. The slide mass is hardly exposed W of the riverbed where it has a maximum lateral extent of 400 m judging from the reappearing evaporites. The Gafares slide mass starts closely above a thin veneer of sheared marls forming contact with Uppper Abad sediments and limestone-pack breccia (1.5 m; Fig. 7a). Then, the lithology changes abruptly into an upward fining, blocky float breccia (7 m thick; Fig. 7a) with rounded fragments of metamorphic basement rocks and Cantera reefal debris. The pack breccias are representative for dissolution and collapse of evaporites, as exemplified by Van de Poel (1991), but the mud-rich floatstone with extralithoclasts clearly reflects mass transport. Higher up, interrupted by non-exposed intervals, follow packets of partially broken and crumpled sandy limestones of the UML

222 A.R. Fortuin, W. Krijgsman / Sedimentary Geology 160 (2003) 213–242 Fig. 7. The Gafares slide mass as exposed in Arroyo Gafares. (a) Sketch of the basal contact as exposed in the valley wall below the house standing in the foreground of Fig. 6a (N.B. this part of the succession is presently poorly exposed). (b and c) Examples of local brittle deformation within stratal packets of UML lithology suggesting some degree of (early) diagenesis before deformation. Hammer for scale. (d) Slide sealing erosional contact between dominantly deformed pelitic strata of the slided UML unit and graded thick-bedded gypsiferous sandstones belonging to the 4th UML cycle. Hammer at contact.

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unit (Fig. 7b,c), suggesting that some degree of lithification had already taken place before the entire mass was erosively covered by the coarse sandy turbidites of the uppermost detrital UML cycle (Fig. 7d). Eastward, in the Collado del Manco (Fig. 2), collapse pack float breccias also replace Yesares evaporites. The highly chaotic association is followed by up to 50 m of slumped and slided UML strata consisting of deformed packets of brownish clays, grey marls and calcisiltites. The top is again formed by highly crumpled pelites and is sealed by 10 m of sandy, laminated calcisiltitic and calcarenitic turbidites and associated fines. The rapid lateral transition from chaotic, dissolution related, stratal packets to undisturbed and unaltered Yesares successions is interpreted as slumping and sliding of an already semi-indurated overburden towards newly created space after local dissolution of Lower Yesares evaporites. This process must have taken place before the topmost UML sequence was deposited, as indicated by the sharp sealing contact of the chaotic strata by gravelly and sandy gypsum turbidites forming the base of the highest UML fan lobe (Fig. 7d). Dissolution-related massflow deposits, carrying basement metamorphics and Cantera limestone, are common along the NW basin margin. Their basinward occurrence suggests that tongues of mass transported debris from the basin margin could reach the dissolution-bound depressions. The dolomitic limestone breccias are suggested to be the product of freshwater alteration (Van de Poel, 1991). Although we do not have direct geochemical evidence for freshwater influences, indirect evidence comes from finding Chara in marls just above the slumped and slided strata. Moreover, vuggy limestones investigated from the top of the formation suggest karst and vadose diagenesis (C. Taberner, 2001; personal communication). Consequently, we conclude that the Nijar Basin must have been temporarily flushed with brackish to fresh waters after deposition of the main body of evaporites. 4.3. The NW basin margin deposits The evaporitic succession of the Yesares Formation progressively wedges out towards the basin margin where it also becomes increasingly chaotic. Between

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motorway A 340 and Polopos (Fig. 2), the combination of post-depositional evaporite dissolution, plus collapse and sliding of Upper Yesares sediments, gives this unit a chaotic, olistostrome-like aspect. Gypsum still occurs as broken, decameter sized, rafts embedded in pelitic float breccias. These gypsum rafts tend to be arranged in an imbricated, SE dipping position with regard to the overall stratal dip suggesting basinward (SE) displacement. The associated, highly inhomogeneous float breccia consists of many irregular tails of muddy intervals indicating viscous flowage. Rounded blocks of Porites limestones, derived from the Cantera Member, become a dominant element in the marly float breccias towards the reefal tract where primary gypsum is entirely absent. Dissolution and collapse did locally continue after the Messinian because the Pliocene cover has in some places been incorporated in the chaos. The general pattern, however, is that this chaotic mass is covered by the Oolite Member towards the reefal flanks (which is also partly incorporated in it) or the Feos Formation more distally. The stratigraphic relation between evaporites and reefal facies is not exposed in the Nijar Basin because unaltered evaporites do not occur in the marginal areas. Nevertheless, the replacing dissolution facies can be traced laterally until the reefal flanks of the Cantera Member (Cerro de la Lancha– Barranco del Pino area, Fig. 2) where approximately 15 m of chaotic float breccia overlies the Abad marls. This float breccia also overlaps the distal parts of the Cantera clinoforms and is topped by sandy oolites and associated skeletal and lithoclastic packstones of the Oolite Member. Clinoform upward, the float breccia rapidly pinches out, making place for oolithic deposits. This situation shows much affinity with the stratigraphic position of collapse breccias in the Algerian Murdjadjo reef near Oran (Saint Martin, 1990) and indicates that evaporitic strata were deposited on the distal flanks of the clinoforms. The facies architecture of the Oolite Member occurring along the NW basin margin is complex due to rapid lateral changes with the local intercalation of a prograding, coarse clastic fan-shaped unit. Where oolithic strata onlap over the youngest Halimeda-rich clinoform bed of the Cantera Member, the contact is erosional because various cliff-like paleoescarpments of several metres height have been cut

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into Cantera carbonates. In front of these, and also more distally, up to 30 m3 large blocks of displaced Porites is often found associated with coarse clastics and overgrown by stromatolite beds, suggesting that

they formed mini reliefs in a quiet coastal area and situated in front of a partially emerged reefal front (Fig. 8a). The associated clastics (blocks up to 50 cm in diameter) mainly consist of angular dark schists and

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white quartz embedded in a sandy matrix, although flat pebble beds (suggesting a beach environment), thrombolites and gypsum pseudomorphs in oolithic grainstones can also be observed. Distally from the youngest Halimeda bed, the basal oolites have been incorporated in float breccias (Fig. 8b). Just distal from the reef front near Barranco del Pino (Fig. 2), marly float breccias on top of sandy Abad strata are followed by up to some 15 m of whitish coated to entirely oolithic sandstones, strongly reminiscent of the Sorbas Member in the Sorbas Basin. Near the basal contact with the marly float breccia, the sandy strata are still deformed and include thin pelitic interbeds with gypsum ghosts (Fig. 8c,e). Thrombolites occurring at the top point to similarity with TCC successions in the Nijar area (Riding et al., 1991a). To the N of Barranco del Pino up to 25 m thick and SE prograding, coarse clastics overly both the youngest reefal Halimeda bed and laterally also marly float breccias. These clastic deposits consist of low angle ( f 15j) SE prograding alternations of very coarse and angular basement debris embedded in a sandy matrix and sandier intervals. Stromatolites and occasionally fossiliferous flat pebble beds occur at the base. The composition of the clastics reflects the lithology of the nearby Sierra Alhamilla and its reefal fringe. Large Porites blocks occur at various levels. Evidently, it concerns a small prograding clastic wedge, which partly filled-up an erosional depression in between the reefs and flowed out in front of the reefs in a coastal area. Summarizing and concluding, it appears that evaporites were deposited on the deepest parts of the reefal clinoforms and distally above sandy Abad marls. Simultaneously, oolithic grainstones were deposited in a somewhat shallower position. These grainstones were partly reworked and can now be retrieved more to the basin centre in the younger part of the formation. The preserved beds of the Oolite Member have been deposited in a topographic position still under the highest parts of the Cantera reef. Above the

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gypsum, sandstones have been deposited which show a high similarity with the Sorbas Member. The approximately coeval coarse clastic prograding fan points to a relatively short-lived, regressive event capable to scour a valley in between the reefal tract, filling it up with clastics. We correlate this event with the erosional event affecting the Upper Yesares further eastward which is also related to dissolution, collapse plus basinward sliding.

5. Sedimentation of the latest Messinian Lago –Mare facies (Feos Formation) The latest episode of the MSC is very well represented in the Nijar Basin and provides one of the most complete onshore records of the western Mediterranean. The corresponding sediments belong to the Feos Formation that comprises the strata deposited above the Mn-enrichment level and below the Pliocene (Van de Poel, 1991). The most complete stratigraphic record of the Feos Formation is present in sections near Gafares (Sections E and D; Figs. 2, 9 and 10f), where the formation is conformably overlain by fossiliferous Pliocene sandy marls (Cuevas Formation, Fig. 10a). Towards the basin margin in the west and the Carboneras fault zone in the east, the Feos Formation becomes incomplete due to onlapping and thinning or erosion prior to deposition of the overlying Pliocene (Fig. 11). 5.1. The regular basinal successions In the central parts of the Nijar Basin, the Feos Formation shows a distinct cyclic alternation of varicoloured (reddish to greyish) continental clastics and whitish Lago– Mare deposits (Fig. 10f,j). The latter intervals are characterized by an oligohaline microfauna occurring in marly to chalky sediment but including varying amounts of usually thin bedded and well-sorted sands and silts (laminites). A total

Fig. 8. Photographs illustrating the Oolite Member (TCC equivalent) at the NW basin margin. (a) Displaced Porites blocks overgrown by stromatolites (hammer for scale). (b) Barranco del Pino, eastern part (hammer for scale). Oolitic grainstone block with gypsum pseudomorphs reworked into a mass flow deposit forming the local transition between chaotic dissolution and collapse float breccia to sandstones shown in (d) forming the base of the Feos Formation (hammer for scale). (c and e) Barranco del Pino, western outcrops (pen for scale). Close-ups of deformed sandy strata, here forming the transition between chaotic dissolution and collapse float breccia to oolithic sandstones of the Oolite Member (coin of 1.5 cm diameter for scale). The basal mudstone bed includes gypsum pseudomorphs.

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number of eight Lago – Mare intervals have been distinguished (Fig. 9). These intervals alternate in the lower part of the formation with intervals dominated by graded and laminated gypsum-rich sandstones and/ or balatino gypsum and higher up with continental clastics (varying from clays to conglomerates). Terrestrial environments can be concluded from the common presence of red and grey calcrete-rich paleosols and/or root burrowing. Coarse clastic intervals are common (Fig. 10c). The formation shows an upward change to decreasing influence of saline waters within the overall cyclic pattern caused by wet Lago – Mare and dry evaporitic to continental intervals. The cyclic arrangement of continental clastics and Lago – Mare laminites indicates that the basin underwent alternating periods of drying-up and reflooding. The lowermost cycles, however, only give evidence for drying up in the marginal areas where erosion of Messinian and older strata has been significant. The continental episodes lasted long enough to enable the development of calcretic soils that were often interrupted by episodic supply of coarse-grained debris flows. The conformable transition to the Pliocene is characterized (Sections D and G, Figs. 9 and 10a) by an abrupt change in lithology, from non-fossiliferous, greyish, silty sands showing mottling by plant roots to strongly burrowed bioclastic sandy marls containing an open marine microfauna (Van de Poel, 1992). Burrows penetrated up to 50 cm deep into the underlying Feos Formation. Since these marine Pliocene strata overlie the relatively thin continental interval (of cycle 8), it is concluded that the Pliocene flooding followed abruptly after a period of lowered water levels. The vertical transition from Lago – Mare facies to continental clastics is generally rather abrupt (Fig. 10j) and can even be erosional in case the overlying clastic unit consists of conglomerates displaying scour-andfill structures. When the transition is gradational, the amount of sand increases rapidly upward resulting in both thickening and coarsening-up patterns, indicating shoaling (hummocky cross-bedding may be devel-

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oped) and rapid transition to terrestrial conditions with all the features of deposition on braid plains, development of soils (calcretic) and episodic overwash. The transitions from continental intervals to Lago – Mare beds are abrupt as well, but generally not erosional. The Lago– Mare intervals of the upper cycles start with a conspicuous 1– 2 cm grey, clayey drape, extremely rich in the ostracod Cyprideis agrigentina. This sudden ‘transgression’ points to relatively rapid and quiet flooding without (or with only very poorly developed) ravinement surfaces and shoreface deposits. Micropaleontological investigations of the various Lago –Mare intervals reveal that the ostracod assemblages are dominated by Cyprideis pannonica, although Loxoconcha and Tyrrhenocythere (Roep and Van Harten, 1979; Van de Poel, 1991, 1992) are also present. Some Cyprideis-rich samples also contain a dwarfed planktonic foraminiferal association with or without an oligotypic small-sized association of Ammonia spp. and Bolivina spp., which is similar to the Lago – Mare associations from elsewhere in Mediterranean basins (cf. Iaccarino et al., 1999). SEM investigations of these samples show that micrite from disintegrated and probably reworked calcareous nannofossils forms a relevant part of the sediment (Fig. 10h). In addition, washed residues from Lago –Mare fines include frequently celestite crystals (Fig. 10g), of which the corroded nature also suggests reworking. A few samples from the uppermost part of the formation yield a more marine, plankton-rich association, but also in these cases, faunal reworking cannot be ruled out (W.J. Zachariasse, personal communication). A gradual change in both the composition of the lithoclasts and paleocurrent orientation can be noted from west to east. In the western outcrops, the overall paleocurrent trend is to SE; southern transport directions prevail in the intermediate sections, whereas SSW to W-directed transport is indicated in the Collado del Manco area close to the Carboneras fault zone. The most common lithoclasts consist of reworked gypsum, oolites, Cantera limestones, other types of Messinian limestones and metamorphics

Fig. 9. Simplified and correlated lithological logs of the cyclic facies association in the Feos Formation expressed by repetitions of coarser and finer, often laminitic, intervals. The sections (A – F) are located between the ruined houses of Los Feos and the Collado del Manco (see Fig. 2 for location). The base of the Pliocene has been used as a datum surface for correlation. The formation attained its largest thickness in Section G (Cerro de los Ranchos; 110 m, upper part shown in Fig. 10f). Further eastward from there, the Pliocene starts to overly the formation with an (low angle) erosional unconformity related to activity of the Carboneras fault zone.

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Fig. 11. Interpreted W – E stratigraphic cross-section through the northern Nijar Basin with the base of the Pliocene as datum level. Lithological symbols as used in Fig. 9.

(dark phyllites and dolomites, angular white quartsites). In the Collado del Manco area, however, fragments derived from red sandstones belonging to the Malaga – Betic nappe and volcanites appear in the lower part of the formation, indicating supply from a different sediment source probably located east of the Carboneras fault zone. 5.2. Basal gypsum-bearing successions The three lower cycles of the Feos Formation are still characterized by the abundance of (often reworked) gypsum (Fig. 10e). NE of Los Feos (Sections B and C, Fig. 9), the relationship between the Yesares and Feos gypsum is complicated by the presence of an erosional unconformity (Fig. 6c). The

overlying gypsum conglomerates are correlated with the uppermost gypsarenites of the Yesares UML further east. The Mn-enrichment level marking the Yesares –Feos boundary is positioned just southward from these strata. Towards the basin margin, contacts with collapsed and olistostrome-like Yesares point to a gradual transition from highly chaotic Yesares float breccias via crudely stratified massflow deposits to whitish Feos sandstone and conglomerates. Here, the Lago – Mare intervals include a higher amount of interbedded graded sandstones than further east (Sections G and H, Fig. 9), where laminated gyparenites and balatino gypsum form the lateral equivalents of westward coarsening units also rich in detrital gypsum. Selenitic gypsum is locally developed as circular, up to 1 m elevated, mounds (‘teepees’) measuring up

Fig. 10. Photographs illustrating the Feos Formation. (a) Details of contact with the Pliocene, Section D. The contact (arrow) is marked by the sudden transition from greyish, root mottled and vaguely bedded continental strata to yellowish, strongly burrowed bioclastic calcarenites. Pocket knife for scale. (b) Proximity of Section C: gypsum mound (‘teepee’) developed on top of a graded gypsrudite forming the transition to laminitic Lago – Mare deposits of cycle 4 (Fig. 9) that can be seen to onlap over this mini relief. Hammer for scale. (c) Section B, southeastward slumped sandstones intercalated in laminitic strata of cycle 4 (Fig. 9). The outcrop clearly shows that laminites onlapped over the slumped sands and were subsequently erosively overlain by conglomeratic mass-flow deposits forming the transition to the next continental interval. (d and j) Proximity of Section C: Lago – Mare interval 4 (7.5 m thick) developed on top of an undulating gypsrudite (bottom photo, j) and showing a gradual upward increase of laminitic sandy interbeds. At the top where the number of graded sands increases rapidly, over 1 m long subvertical fissures are present that appear to be filled-in from above from places where sand became fluidized (photo d, upper right) and interpreted as giving evidence for a seismic origin. (e) Section B, interval above the basal gypsum conglomerates showing laminated and contorted finegrained gypsarenites. (f) Section C, as seen from the east, showing the alternation of Lago – Mare cycles with coarser grained, mostly continental, sandy – conglomeratic intervals. The picture starts, at right, at the level of the manganese-enriched boundary bed where it is followed by fine-grained and laminated ‘balatino’ gypsum. (g) SEM backscatter image of a celestite crystal (  250) common in Lago – Mare fines. The corroded surface suggests reworking. (h) SEM micrograph of Lago – Mare mud (  8000) showing the relative importance of reworked and fragmented nannofossils. (k) Proximity of Section C, thinly bedded and laminated grey to pink pelitic to sandy strata including irregular gypsiferous beds showing small teepee-like structures and interpreted as deposited in a sabkha-like environment.

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to 3 m in diameter (Fig. 10b). They are common in the western barranco’s (top of cycle 3, Sections B, C and D, Fig. 9), following above up to 50 cm thick, laminated gypsarenite, including outsize clasts of reworked gypsum or Cantera coral boundstone. In the neighbourhood of Section D just below the top of cycle 3, a sabkha-like gypsum variety is developed, overlying muds and sands with large root burrows. The gypsum is banded, forming irregular, small teepee-like elevations (Fig. 10k). Intercalated clastic beds vary laterally in texture and structure and include wave-ripple cross-lamination. The selenitic gypsum mounds at the top are directly followed by the first Lago –Mare laminites of cycle 4. This facies pinches out eastwards and graded gypsarenites or balatino gypsum is found east of Gafares. Concluding, an upward change is evident from partly evaporitic cycles to partly continental cycles. Because the Lago –Mare intervals do not show marked upward changes, this vertical trend suggests increased evaporative drawdown during the younger cycles, when continental environments prevailed during relatively dry intervals. Geochemical investigations (Lu et al., 2001) confirm the more continental character of the Feos evaporites compared to Yesares evaporites, in which more isolated environments provided more concentrated brines. The environments in the Feos area were on average shallower than E of Gafares, where the relative amount of coarse clastics is lower versus increased amounts of balatino gypsum and gypsarenites. Features such as observed in the mixed clastic – evaporitic facies near Section D, cycle 3 suggest that sabkha-like environments associated with salty mudflats and mangrove vegetation existed locally, indicating rapidly vertically and horizontally changing facies patterns. Abundance of outsize clasts in the mass transported sandy evaporites points to considerable erosion of marginal gypsum. In view of the evidence for periodic drawdown of the water level leading to accumulation of continental deposits above otherwise offshore facies, fluctuations of Lago – Mare water levels were considerable. 5.3. Fissure fillings Coarse sand-filled fissures, pointing downward towards the top of the laminites, are a remarkable feature of the upward coarsening – shallowing se-

quence of cycle 4. The fissures are up to 50 cm in length in Section A, but can be up to 1 m in Section C. In the latter locality (Fig. 10j), cracks can be seen to pass at their top into the first graded sands, which were locally subjected to liquefaction (Fig. 10d). This indicates that the fissures were filled from above by fluidized sand. The fissures, on average f 1 cm wide, vary in shape from a slightly jagged to almost straight course, and both vertical and oblique orientations are common. The sand, filling the fissures at Los Feos, however, is hardly present anymore as it was scoured by an overlying graded bed. Here groove and flute casts indicate transport to 170jS (13 measurements), while Tc intervals of very thin distal turbidites indicate S to SSE transport directions. In other outcrops of the same cycle 4, slumping and small-scale syndepositional faulting is common (Figs. 9 and 10c). The fissures are not interpreted as large shrinkage cracks due to the drying up of a Lago– Mare succession, but as seismites, because fluidization of sand with associated ‘draw-in’ infilling of fissures in unconsolidated sediment indicates sediment stretching by seismic shocks. Their association with slumps and small-scale syndepositional faults also indicates tectonic instability.

6. Paleogeographic evolution 6.1. Paleogeography during pre-evaporitic sedimentation The Late Tortonian was a period of intense basin structuration during which the basin fill was folded and faulted (Fig. 3). Along the southern margin of the Sorbas Basin, dextral slip along the Gafarillos fault came to an end and the Messinian depot centre shifted northwards (Ott d’Estevou, 1980). The contours of the Nijar Basin must have been influenced considerably by the gradual NE movement of the Sierra de Gata massif. Approximately 30 km of horizontal slip is inferred to have taken place along the Carboneras fault since the Tortonian, with an estimated 7.5 km of Pliocene – Quaternary displacement (Coppier et al., 1990; Boorsma, 1993). The more southern position of the Cabo de Gata volcanics probably enabled a joint eastward outlet to the offshore for the combined Nijar, Sorbas and Vera basins (Fig. 12.1). In Early

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Messinian times, at least the Nijar and the Sorbas basins were still connected to the deep Mediterranean, as proven by fossil fish fauna’s (Gaudant, 1989). Even the younger diatom assemblages from ‘‘Upper Abad’’ marls in the Sorbas Basin indicate a marine connection (Saint Martin et al., 2001). The northern shoreline of the Nijar Basin probably coincided with the northern margin of the Sorbas Basin. This is evidenced by local accumulations of swash rounded megaboulders (up to 1 m in diameter) at the base of the Azagador transgression in various places along the northern margin of the Sorbas Basin. Such boulders indicate a high-energy swash, tormenting a rocky coast, which is unlikely to have existed in a narrow basin that was protected from the open sea to the south by the Sierra Cabrera. Moreover, the stratigraphic trend of the Azagador Member as exposed along the southeastern margin of the Sorbas Basin is one of eastward thickening and fining, suggesting also an open connection to the present Vera Basin. Intercalated lithoclasts in these sections reflect a northern, Sierra de los Filabres origin, which also indicates that Sierra Cabrera was not yet emergent (Braga et al., 2001). The western margin of the Nijar Basin was formed by the Sierra Alhamilla topographic high which shed a mixture of coarse clastics and bioclastics into the basin well before it became covered by the Cantera reef trend (Ott d’Estevou, 1980). The position of the northwestern basin margin during deposition of the Early –Middle Messinian Abad marls is clearly indicated by the reefal tract of Cantera carbonates fringing Sierra Alhamilla (Figs. 1 and 2). The almost uninterrupted reef trend from Sierra Alhamilla, via Sierra de los Filabres to Sierra Bedar (Fig. 12.1), implies that the Nijar, Sorbas and Vera basins were still interconnected. Moreover, the absence of Cantera reefs along Sierra Cabrera strongly suggests that massif was still submerged, an interpretation which deviates from earlier paleogeographic and fault kinematic maps (De la Chapelle, 1988; Coppier et al., 1990). In addition, the open marine Abad successions N and S of the present Cabrera massif are strikingly similar in microfaunal and lithological aspect. This indicates similar upper bathyal environments (Troelstra et al., 1980; Van de Poel, 1992), suggesting as well that much of the present Sierra Cabrera was still a basinal part of the interconnected Vera, Sorbas and Nijar basins. Recent paleobathymetric estimates based on extensive study of the

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benthic foraminifera (Baggley, 2000) indicate that the deepest parts of the Sorbas Basin may have attained f 1000 m after the initial phase of rapid subsidence. The regular, and laterally persistent, depositional pattern of the ‘‘Lower Abad’’ marls points to an episode of tectonic quiescence. This suggests that during the Azagador –‘‘Lower Abad’’ episode, transpressional stresses were strongly reduced, thus inducing subsidence in zones of former compression. During deposition of the ‘‘Upper Abad’’, turbidites and slumps in the Nijar, Sorbas and Vera basins periodically disturbed the regular depositional pattern pointing to increased tectonic instability. This could well be related with the initiation of the new N – S oriented principal stress regime that first affected the Palomares fault. Activity along this fault is indicated by the occurrence of small volcanic eruption centres in the Vera Basin, intercalated in the so-called Santiago turbidites of the ‘‘Upper Abad’’ (Vo¨lk, 1967; Fortuin et al., 1995). These Santiago turbidites accumulated in bathyal parts of the basin, as proved by abundant Palaeodictyon tracks being derived from northeastern sources (Vo¨lk, 1967), suggesting that the south(west)ern parts of the Vera Basin were the deepest. This is another indication that there was not yet a trace of an extensive Cabrera landmass such as present nowadays. Paleocurrent directions are rather scarce in the ‘‘Upper Abad’’ of the study area. Nevertheless, various slumpfolds and a cross-bedded turbidite (Tc) interval indicate eastward sediment dispersal, suggesting transport towards the eastern offshore. 6.2. Paleogeography during evaporite deposition The basal Yesares evaporites of the Nijar and Sorbas basins probably still formed an integral basinal succession like before in mid-Messinian times (Fig. 12.2). Initially, the connection to the Vera Basin was probably still open. In that basin, evaporites probably were deposited as well, but little has remained because of post-depositional erosion (Fortuin et al., 1995). Separation of the Sorbas and Vera basins was probably caused by a NE – SW trending, fault bounded uplift zone. This is the area presently exposing the older Neogene successions along the NW Cabrera margin. The thickest ( f 75 m) and most massive appearance of Yesares evaporites in the Sorbas Basin is located in the eastern segment of the basin, border-

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ing the western spurs of Sierra Cabrera. The thickest gypsum deposits in the Nijar Basin are observed in the quarry directly to the south of this present structural high. Splitting up of the formerly united Sorbas – Nijar – Vera basins is thought to have started in Late Yesares times, when the stratigraphies of the basins started to diverge. Overall Yesares shoaling, inferred from geochemical studies (Rosell et al., 1998), is witnessed by the overlying coastal sequences around Sorbas and southeastward proliferation of UML gypsarenites in the study area. Consequently, this uplift also started to constrict the Sorbas – Nijar connections. In the study area, shoaling is proved by local erosion of the main gypsum body in the Los Feos area and the eastward transition to mixed calciclastic – gypsarenitic turbidite lobes. In addition, coarse clastics could also enter the basin from the western Alhamilla margin. The most logical explanation for the supply of reworked gypsum into the study area is uplift with southward tilting along the northern boundary of the Cabrera –Alhamilla sierras. In other words, reactivation of the Gafarillos fault zone now under N – S compression seems likely. In the study area, the overall upward increase of detrital gypsum, plus local erosion towards the top of the Yesares Fm, is undoubtedly related to the same overall shallowing tendency recognized in the Sorbas Basin. Whereas the basal Yesares gypsum formed in deep marine brines (Rosell et al., 1998; Lu et al., 2001), upward shallowing in the Sorbas Basin with strong salinity fluctuations resulted in deposition of the coastal sequences of the Sorbas Member on top of the evaporites (Roep et al., 1998). This member shows a prograding sandy coastal succession consisting of 3 –4 upward shoaling sequences around the village of Sorbas (Roep et al., 1998; Krijgsman et al., 2001). Further east and south, these coastal sands pass

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rapidly into laminitic offshore muds and sands in which shoaling ultimately also led to the formation of wave-rippled near-coastal strata. In the generally deeper Nijar Basin, an overall regressive trend is also reflected by the Upper Yesares beds with the appearance of calciclastic strata and gypsarenites, here developed as prograding fan lobes in four UML sequences. The fact that both the UML and the Sorbas members are the first sand-rich intervals suggests a lateral relationship. Moreover, calcite coated sandstones are a common lithology in the Sorbas Member, and they also occur in the UML sequences and in the marginal sandstones directly overlying the marginal dissolution facies. We thus conclude a lateral equivalence of the Sorbas and UML members (Fig. 4), which implies that episodes of increasing salinity had more impact in the somewhat deeper Nijar Basin than in Sorbas. The dominantly marly, laminitic intervals at the top of the UML reflect brackish conditions as unambiguously proven by microfauna (Van de Poel, 1994) and presence of Chara spp. plus A. crassicaudus (De la Chapelle and Gaudant, 1987). The latter fish is also reported from the basinal Sorbas laminites (Gaudant and Ott d’Estevou, 1985) and typically thrives in euryhaline, near coastal waters. The lack of other marine fish species, however, indicates that the basins were separated from open marine environments (Gaudant, 1989). This exemplifies the increased restriction of the Nijar and Sorbas basins from the Mediterranean, which ultimately resulted in the first hypohaline Lago –Mare conditions. 6.3. Paleogeography during Lago –Mare deposition Paleogeographic reconstructions based on the study of continental facies in the Sorbas Basin and

Fig. 12. Paleogeographic cartoons depicting the rapid overall changing configuration of the Neogene basins in SE Spain between 6.4 and 5.2 Ma. Fault patterns and fault kinematically restored position of fault blocks after Coppier et al. (1990). Map 1 shows the approximate basin contours at the onset of late Abad time when the Cantera reefs started to fringe the basin margin. In Yesares time (map 2), evaporites accumulated in the deeper parts and in the course of this episode faulting along the northern margin of Sierra Alhamilla and continuing eastward caused initial uplift in the present Sierra Cabrera area. As a result, erosion and reworking of evaporites into the now separately evolving Nijar Basin took place. Map 3 shows the maximum distribution of hyposaline Lago – Mare distribution for the Sorbas Basin based on Mather (2001). Indicated are transport directions and areas where evaporite dissolution, collapse and subsequent lateral transport took place. Map 4 depicts the basin configuration shortly after the early Pliocene flooding. Open marine strata were deposited in the central parts of the Nijar, Vera and Agua Amarga basins. Increased activity took place along the Carbonera fault zone together with regional uplift responsible for considerable shoaling in the course of the Pliocene. Sierra Cabrera only then gradually obtained its modern topography and the seaway between the Agua Amarga and Nijar basins was closed.

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the Sorbas –Nijar corridor in the Polopos area (Mather, 1993a,b, 2001) indicate that the NW Nijar Basin was still connected to the Sorbas Basin during the latest Messinian – Early Pliocene, despite tectonic activity occurring along the Sierra Alhamilla– Sierra Cabrera faults (Fig. 3). The post-evaporitic continental unit of the Sorbas Basin (Zorreras Member) contains only two brackish Lago– Mare incursions (Ott d’Estevou, 1980) on a total of eight sedimentary cycles of alternating reddish silts and yellowish sands (Krijgsman et al., 2001). This suggests that only the highest Lago –Mare water levels were able to penetrate into the Sorbas Basin, leaving the latter basin dominantly continental. Such a scenario also fits well with the decreasing significance of the Lago – Mare facies to the northwestern margin of the Nijar Basin. Hence, the number of cycles in the Zorreras Member correlates very well with the eight sedimentary cycles of the Feos Formation. This strongly suggests that the Zorreas Member (excluded its Pliocene top bed) and the Feos Formation are lateral equivalents. Details of syn-Zorreras facies distribution are given by Mather (2001), who explains the Zorreras lacustrine incursions in the Sorbas Basin as a result of variations in the overall vertical uplift. Climatologically constrained shifts in the position of the coastline, however, seem more likely, especially regarding the Lago – Mare lake-level fluctuations. The large amounts of reworked Alpujarrid basement schists, quartsites and older basinal deposits can be explained as a result of periodically falling base level. The indications for seismic shocks or the changes in the overall direction of sediment transport from SE to S – SSW orientations suggest that next to periodic evaporative drawdown also tectonic uplift of Sierra Cabrera must have played a role. In general, differential uplift of the two basins is the most logical explanation for the more continental character of the Zorreras deposits of the Sorbas Basin. At the onset of the Early Pliocene transgression, the Nijar Basin became again an open marine basin in which thick marine successions were widely deposited (Fig. 12.4). The marine Pliocene in the Sorbas Basin, however, is restricted to a 1 m thin veneer of shallow marine sands (Ott d’Estevou, 1980) followed by exclusively fluvial strata. Comparison of the topographic position of the basal Pliocene in both basins N and S of Sierra Cabrera also suggests ongoing differ-

ential uplift. The oldest shallow marine Pliocene of the Sorbas Basin (as observed at Cortijo El Cerro Colorado) is presently elevated 450 m and with a paleobathymetry not exceeding 20 m, this indicates a minimum average rate of Plio –Quaternary uplift of f 90 mm/ka. In contrast, the basal Pliocene of the Nijar Basin (around Gafares) was deposited at 100– 150-m depth (outer shelf depths, Van de Poel, 1992) and with a present elevation of f 250 m, the average rate of Plio – Quaternary uplift has been in the order of 70 mm/ka. The gradual emergence of both Nijar and Sorbas basins was caused by regional uplift, which probably also controlled the lateral variations in depositional environment of the latest Messinian. An important W –E change can be noted in the composition of the lithoclasts of the Feos Formation, which indicates supply from different sediment sources. This is furthermore supported by paleocurrent measurements indicating SE transport directions near the western basin margin, S directions in the intermediate sections and W to SW directed transport in the east. The Feos Formation is not (or only poorly) developed east of the Carboneras Fault. There, the basal Pliocene directly overlies float breccias of collapsed and transported evaporitic Yesares strata. The entry of volcaniclastics in the Feos Formation at the easternmost part of the study area strongly suggests supply from the ‘incoming’ and uprising Cabo de Gata block, thus for the first time demonstrating uplift along the Carboneras fault. Faulting and anticlinal warping in the Sierra Cabrera area had gradually cutoff the mutual passages between the Nijar and Sorbas basins during the Pliocene – Quaternary. Nowadays, the Rambla de Lucainena, Rio Alias and Arroyo Gafares drainage systems are transverse systems crossing this topographic high, initiated in Early Pliocene time after definitive withdrawal of the sea from the Sorbas Basin (Mather, 1993b). With regard to the Late Messinan episodes of considerably shifting coastlines, however, we suggest that the initial drainage pattern already developed in Late Messinian time prior to the main uplift of Sierra Cabrera. Tectonic uplift of Sierra Cabrera is interpreted to have also played a role in the formation of the angular unconformity separating the Yesares and Feos Formations in the western part of the study area. Ongoing tectonic activity is fur-

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thermore required to explain the position of the Early Pliocene deposits which not only overlie the Feos formation unconformably towards the western basin margin but also towards the Serrata strike-slip fault zone. The study area therefore can be reconstructed using the base of the Pliocene as a datum level (Fig. 11). Compared to the WSW and ENE margins, the central parts underwent net subsidence which resulted in ongoing sedimentation and deposition of a fairly, if not most complete, record of Late Messinian depositional environments with a high potential for comparison with other Late Messinian successions.

7. Discussion The Nijar Basin contains one of the most complete land-based Messinian successions of the Mediterranean mainly because tectonic uplift of the surrounding basement complexes during the MSC has protected its sediments from vigorous erosion. Consequently, the Nijar Basin became a semi-enclosed basin during the latest Messinian in which a substantial body of evaporites and post-evaporitic deposits has accumulated despite drastic changes in environment and water level. The Nijar Basin has occupied a less restricted position than the neighbouring and wellstudied Sorbas Basin, and as such, these sediments are very suitable to increase our understanding of Late Messinian paleoceanographic changes. 7.1. Chronology Late Miocene sedimentation in the Nijar Basin started with deposition of the Azagador Member, a transgressive unit of mixed bio-siliciclastics. Biostratigraphic data indicate that the Azagador Member is entirely of Late Tortonian age, but more accurate age constraints are not available. The Azagador/Abad transition straddles the Tortonian/Messinian boundary as the first regular occurrence of the G. miotumida group is observed in the basal part of the Abad marls (Sierro et al., 2001). Time control for the Abad Member has recently been considerably improved by magnetostratigraphic, biostratigraphic and especially cyclostratigraphic dating (Gautier et al., 1994; Krijgsman et al., 1999; Sierro et al., 2001). A highresolution integrated stratigraphy has been developed

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for the Abad marls, based on numerous sections in both the Nijar and Sorbas basins (Sierro et al., 2001). Astronomical tuning of the sedimentary cyclicity of the Abad marls to the insulation curve has provided very accurate and reliable ages for all sedimentary cycles and allows an unambiguous bed-to-bed correlation to other astronomically dated sections in the Mediterranean. The resulting astrochronological age for the base of the Abad Member is 7.24 Ma, while the transition from ‘‘Lower Abad’’ to ‘‘Upper Abad’’ arrived at 6.70 Ma (Krijgsman et al., 1999; Sierro et al., 2001). Astrochronology furthermore revealed that the onset of evaporite precipitation in the Nijar Basin took place at an age of 5.96 Ma, approximately four cycles above paleomagnetic reversal C3An.1n, synchronous with the Sorbas Basin and other astronomically dated sections of both west and east Mediterranean basins (Krijgsman et al., 1999, 2001, 2002). Biostratigraphic and magnetostratigraphic techniques are, however, not very useful for dating the latest Messinian sequences of the Messinian Salinity Crisis because these are confined to a single magnetic chron and lack age diagnostic planktonic foraminifera. As a consequence, we will have to rely on cyclostratigraphic (and radiometric) data to derive age constraints for the top of the Yesares and the end of marine sedimentation in the Nijar Basin. Cyclostratigraphic studies of the Yesares Formation in the Nijar Basin are, however, complicated by the considerable lateral changes, the erosional unconformities, the common dissolution and collapse phenomena and the various diagenetic alterations. Sections W and E of Gafares are probably the best candidates to establish a complete cyclostratigraphic framework for the Yesares Formation in the future, but they will require an additional very detailed geochemical or sediment petrological study. Field evidence from both the Sorbas and Nijar basins indicates that the marl – sapropel cycles of the ‘‘Upper Abad’’ are at their top replaced by gypsum – sapropel cycles of the Yesares, indicating that the evaporite cyclicity is related to astronomical (precession) controlled oscillations in (circum) Mediterranean climate as well. Unfortunately, the tuning of the Yesares cycles to the astronomical curves was less straightforward because characteristic cycle patterns could not be resolved. Upward calibration of the gypsum cycles resulted in

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an age of 5.67 Ma for the top of the Yesares (Krijgsman et al., 2001). The recognition of sedimentary cycles in the Sorbas Member is even more complicated as deposition took place in a highly dynamic near-coastal environment, although 3 – 4 distinct shoaling-up sequences are present (Roep et al., 1998). Nevertheless, a best estimate for the end of marine sedimentation in the Sorbas Basin was derived at an age between 5.60 and 5.54 Ma (Krijgsman et al., 2001). Based on our paleogeographic reconstructions, which show a similar evolution of the Sorbas and Nijar basins during the latest Messinian, we can confidently assume that these age constraints are also valid for the Nijar Basin. The latest Messinian Feos Member includes eight sedimentary cycles (including the first LM interval just below this unit) which are interpreted as ‘‘wet– dry’’ alternations. This number agrees well with the eight sedimentary cycles that are present in the Zorreras Formation of the Sorbas Basin, in the ‘‘Upper Evaporites’’ of the Caltanissetta Basin in Sicily and in the Colombacci Formation of the Northern Apennines (Decima and Wezel, 1973; Colalongo et al., 1976; Rouchy, 1976; Krijgsman et al., 2001). It suggests that these units, which all contain the characteristic Lago – Mare facies, are deposited in the same time interval bounded by Mediterranean-wide events. The upper boundary is clearly related to the reestablishment of marine conditions in the Mediterranean during the Pliocene flooding, which is astronomically dated to have occurred at an age of 5.33 Ma (Lourens et al., 1996). The age estimate of 5.60– 5.54 Ma for the base of the Feos is in good agreement with Ar/Ar ages of 5.40 F 0.06 and 5.51 F 0.05 Ma for the volcanic ash layer at the base of post-evaporitic unit in the Northern Apennines (Odin et al., 1997). Hence, it can be concluded that the sedimentary cyclicity in the Feos Member is dominantly related to circum-Mediterranean climate changes driven by changes in the Earth’s precession. This results in a total duration of approximately 175 ky for the post-evaporitic unit in the Nijar Basin. 7.2. Yesares formation in a Mediterranean context Messinian astrochronology suggests that the onset of evaporite precipitation during the MSC was perfectly synchronous over the entire Mediterranean

basin and therefore independent of the paleogeographic and geodynamic setting of the individual basins (Krijgsman et al., 1999). During Late Messinian times, the Nijar Basin was still connected to the Mediterranean in the east and to the Sorbas Basin through on open marine gateway over the present Sierra Cabrera Massif. Consequently, the onset of the massive primary evaporites of the basal Yesares Formation in Nijar is synchronous with the Mediterranean-wide onset of the MSC as also shown by astronomical tuning of the underlying Abad marls (Sierro et al., 2001). The evaporitic succession of the Yesares Formation progressively wedges out towards the basin margin where it merges into a chaotic mass where collapse and sliding took place, including deposits of the Oolite Member. The presence of stromatolites, thrombolites and Porites blocks points to similarity of TCC successions in the Nijar area and Sorbas Basin (Riding et al., 1991b). In the Sorbas Basin, not only a lateral relationship has been shown to exist between oolites and part of the gypsum (Conesa et al., 1999) but also with the Sorbas Member (Dabrio and Polo, 1995; Roep et al., 1998). This suggests that the TCC unit is indeed the lateral, marginal, equivalent of the Yesares evaporites and the Mediterranean ‘‘Lower Evaporites’’ and not as originally defined on Mallorca as the lateral equivalent of the ‘‘Upper Evaporites’’ (Esteban et al., 1977; Esteban, 1979; Dronkert, 1985). Magnetostratigraphic and radiometric dating of other TCC units in the Albora´n domain also agree with this older age. In the Cabo de Gata region of southeast Spain (Franseen et al., 1998; Montgomery et al., 2001) and in the Melilla Basin of northeast Morocco (Cunningham et al., 1994), the base of the TCC was magnetostratigraphically determined to occur slightly above the top of the normal chron C3An.1n which corresponds to an age slightly younger than 6 Ma (recalibrated to the latest time scale). In addition, radiometric datings on a volcanic ash layer slightly below the base of the TCC in Melilla give Ar/Ar ages of 5.95 F 0.10 Ma (Cunningham et al., 1996) and recalculated as 6.01 F 0.10 Ma by Mu¨nch et al. (2001). Dissolution-affected successions are a very characteristic feature of the Yesares Formation of the Nijar Basin. Dissolution is mainly restricted to the basin margin and to some local occurrences in the basin centre; an archetype of these is the exposure along

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Arroyo Gafares (Fig. 6). Because the latter occurrences are directly overlain by intervals with first evidence for at least temporary presence of brackish water mass in the basin, this dissolution event can be linked to fundamental changes in the hydrologic budget. Such changes are in agreement with dolomitization studies in the Nijar marginal reef deposits showing that most dolomitization occurred during and possibly after TCC deposition but before the Pliocene during multiple sealevel changes (Meyers et al., 1997; Lu and Meyers, 1998). Circulation of Mg through the platform rocks was primarily driven by buoyant circulation of the mixing zone beneath freshwater lenses. Field observations show that evaporite dissolution is a less common feature in the Sorbas Basin, where it is only locally concentrated at the southern margin. A solution for this striking difference could be the more restricted Late Messinian character of this basin, with only partial flooding by hypohaline Lago– Mare waters. In general, the MSC shows an overall effect of increasing isolation of the Mediterranean culminating with deposition of the Lago –Mare facies. Therefore, it is most logical to expect maximum draw down during intervals of total isolation, which is during Lago – Mare time. The exact age for the end of open marine sedimentation in the Nijar Basin and hence in the Mediterranean is, however, still uncertain. Astronomical tuning of the upper part of the marine sequences is hampered both in the Nijar and Sorbas basins by the presence of less suitable sediments. Moreover, we cannot neglect the influence of obliquity forcing for this specific time interval, which corresponds to a minimum in the f 400 ky eccentricity cycle (Krijgsman et al., 2001). Nevertheless, our best estimates for the end of marine sedimentation arrive between 5.60 and 5.54 Ma. This is in agreement with recent Ar/Ar ages from the Melilla Basin which indicate that no major sea-level fall took place before 5.77 Ma (Corne´e et al., 2002). 7.3. Feos regressive – transgressive cyclicity In earlier studies, Mediterranean-wide evidence has been gathered indicating a Late Messinian episode with strongly lowered base-level and associated scouring of deep channels and other erosion phenomena, causing a prolonged disturbance of the natural equi-

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librium between erosion and deposition (Delrieu et al., 1993; Clauzon et al., 1996; Cita et al., 1999). Our sedimentary observations on the Feos record, however, suggest that the overwhelming erosional effects in places of much sediment bypass must have been caused by repetitions of large, but relatively short, base level fluctuations. Together with strongly restricted oceanic connections, precession-controlled periods of alternating relatively dry (negative waterbalance) and relatively wet (positive water balance) conditions dominantly determine the Upper Messinian sedimentary patterns. Due to differential uplift from the end of the Yesares evaporitic episode onwards, the Nijar Basin became in a less restricted position with regard to open connections to the Mediterranean than the neighbouring Sorbas Basin. Consequently, the Nijar successions have a more pronounced Lago – Mare facies and therefore provide an even better Upper Messinian record. One of the most interesting aspects of the Feos Formation is the cyclic arrangement of offshore Lago – Mare laminites and continental strata. This pattern is similar to some lacustrine series in which fluctuating lake levels are controlled by climatic oscillations causing rapid transgressive – regressive sequences. The lack of coastal barrier development and the evidence for sudden drowning of the continental environment also fits in this analogy. Initially, brackish waters and hypersaline intervals alternated, whereas the basin floor fell dry later. These changes suggest an increase in the fluctuation of water level draw down. This is also indicated by reconstructed relative sea level fluctuations just before the onset of the Lago – Mare episode. During deposition of the Sorbas Member (Roep et al., 1998), respectively the TCC of the Cabo de Gata massif (Franseen et al., 1998), sea level fluctuations were estimated to have been in the order of up to 30 m. In the Nijar Basin, the Lago –Mare water levels must have fluctuated over at least 100 m/cycle when compared to the conformably overlying Early Pliocene strata, which reflect deposition in open marine waters of at least 100-m depth. The Feos water level fluctuations may have been much smaller in case the average Lago – Mare water levels were far under normal sealevel. Field data, however, suggest that this was not necessarily true. The presence of Lago– Mare facies along the NW basin margin (at equal altitude and on top of TCC

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oolites) indicates that Lago – Mare water levels at least temporarily could equal previous sea levels. This is especially interesting because data from the eastern Mediterranean suggest the presence of lakes below the world sea level (Orszag-Sperber et al., 2000). If true, the Lago –Mare time might have been an episode of enormously shifting coastlines caused by the waxing and waning water supply. In addition, the strontium isotope composition of Upper Messinian sequences in central Sicily (Keogh and Butler, 1999) and west Mediterranean basins (Tyrrenian Sea, Mu¨ller et al., 1990; Vera Basin, Fortuin et al., 1995) is indistinguishable regardless of salinity, but different from coeval oceanic water masses. This implies that the local basins must have been linked to a main Mediterranean water mass that was isolated from the outside world. In theory, the oceanic gateways could be temporarily flooded during periods of maximum sea level and maximum continental runoff, automatically reestablishing short-living connections. Such connections might also explain the sparse indications for open marine microfaunas at the top of the Feos unit in the Nijar Basin and elsewhere in the Mediterranean (Spezzaferri, 1998; Iaccarino and Bossio, 1999). However, reworking of the unstable Upper Messinan sediments remains a factor not to be neglected. 7.4. Comparison with east Mediterranean basins With more and more evidence indicating that not only the beginning but also the end of the MSC were pan-Mediterranean synchronous events (Di Stefano et al., 1999; Iaccarino et al., 1999; Krijgsman et al., 1999; Sierro et al., 2001; Krijgsman et al., 2002), it is interesting to note that indeed striking similarities exist between comparable east and west Mediterranean successions. Especially, the Pissouri Basin of Cyprus (Rouchy et al., 2001) is well comparable as it too was moderately deep due to its position close to a gradually rising hinterland and at the same time connected to the offshore Mediterranean. Both the Nijar and Pissouri successions show (1) an upward transition from precipitated evaporites to reworked evaporites. (2) Erosion and dissolution (including the local formation of olistostrome like megabreccias) affected the evaporites, which in both basins can be attributed to the transition to oligohaline intervals. (3) The basal Lago –Mare intervals still alternate with

hypersaline periods before these were replaced by continental intervals. (4) Where conformable Messinan – Pliocene transitions can be found, it appears that the Pliocene flooding occurred above a continental episode. 7.5. Pliocene transgression Many new and unambiguous data indicate that the flooding plus re-colonisation of the Mediterranean basin floors by normal marine benthic organisms at the base of the Pliocene was an abrupt and synchronous pan-Mediterranean event (Di Stefano et al., 1999; Iaccarino et al., 1999). Because the conformable Messinian – Pliocene transitions in the study area are razor sharp, following above a continental interval, we conclude that (a) flooding occurred almost instantaneously, as also concluded by Pierre et al. (1998) and Iaccarino et al. (1999) for other basins and (b) that flooding terminated a relatively thin continental interval, which means that it concluded a relatively dry period with lowered water levels.

8. Conclusions During the Messinian, the existing open marine connections between the Sorbas, Vera and Nijar basins became progressively blocked (Fig. 12). All three basins provide a gradually deviating, but wellknown record of the Messinian Salinity Crisis. The Yesares and especially the Feos Formation of the Nijar Basin provides important information concerning significant, precession-controlled, base-level fluctuations. The first oligohaline conditions, characteristic of the Lago– Mare facies, occurred prior to the last occurrence of evaporitic strata. Reworking of evaporites in these intervals points both to strongly fluctuating base level and tectonic changes, related to uplift of Sierra Cabrera, a massif nowadays separating the Sorbas, Vera and Nijar basins. The Yesares successions of the Nijar Basin indicate that the turnover to brackish environments initiated in various places, especially near the basin margin, evaporite dissolution. Dissolution and collapse were able to trigger localized sliding and slumping of stratal packets and created olistostrome-like mass movement along tectonically active faultzones in the NW of the basin.

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Sedimentological and cyclostratigraphical studies on the Feos Formation indicate the presence of eight precession cycles including hypohaline Lago– Mare deposits, while the uppermost four include continental deposits. These cycles can directly be correlated with the Zorreras Member in the adjoining Sorbas Basin and have been dated astrochronologically as deposited between 5.52 and 5.33 Ma. During episodes of strongly positive water budget, the Lago – Mare level could reach the same position as the Yesares sea level before, but water levels may have been considerably lower during the continental phases. Correlation with coeval strata in the Sorbas Basin, at that time, a more elevated basin where only two Lago –Mare intervals are developed, indicates that only the highest water levels could still invade this basin. The sudden return to open marine conditions at the onset of the Pliocene closed such a continental episode of lowered water level. Concerning the overall regional tectonic activity, tectonics were probably instrumental in the restoration of an Atlantic gateway. Strong similarities with other circum-Mediterranean onshore basins substantiate the indications that the transition to the Lago – Mare facies marks a panMediterranean event governed by precession-induced changes in the subtle balance between dominantly precipitation or evaporation in a largely isolated Mediterranean. Finally, we conclude that instead of one major downdrop event, it might have been the repeatedly fluctuating water level during this latest Messinian period which caused the widely reported effects of locally vigorous erosion above the ‘‘Lower Evaporites’’.

Acknowledgements This paper is dedicated to the late Th. B. Roep, with whom the senior author started the field investigations. Especially former MSc. students Frans-Bart Cornelisse, Arjan van Doorn, Eelco Felser and Karin van der Zel are thanked for their contribution to unravel parts of local Messinian mysteries. Discussions in the field with colleagues T. Geel, C. Dabrio, C. Taberner and W.J. Zachariasse and constructive remarks by the reviewers J.M. Rouchy and J.P. Saint Martin were greatly appreciated. Technical and artistic assistance was provided by

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S. Kars (SEM), M. Konert (sediment lab), H.A. Sion and N. Schaefers (drafting). This work was conducted under the programme of the Netherlands School of Geosciences (NSG; paper nr 20021001) and the Vening Meinesz Research School of Geodynamics (VMSG). WK acknowledges financial support from the Dutch research center for Integrated Solid Earth Sciences (ISES).

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