5.a. Palaeoenvironmental setting

The palaeoenvironmental setting of the Abad Member can be examined from two perspectives: (1) the sediments, and (2) the ichnoassemblages. Both provide important and useful information for the characterization of the depositional setting. As noted above, the sandstone beds of the Abad Member can be uniformly described according to the Bouma (Reference Bouma1962) scheme, and can thus be termed classical turbidites (albeit thinner Ta-c, Tbc turbidites, i.e. Facies C2.2, 2.3 of Pickering et al. Reference Pickering, Stow, Watson and Hiscott1986). The presence of sandstone turbidites records the depositional passage of turbidity currents, which can be found in a variety of areas, including deep-marine settings, ramps or slope aprons but also in lacustrine settings (e.g. Stelting, Bouma & Stone, Reference Stelting, Bouma, Stone, Bouma and Stone2000; Mulder & Alexander, Reference Mulder and Alexander2001; Talling et al. Reference Talling, Masson, Sumner and Malgesini2012; Moernaut et al. Reference Moernaut, van Daele, Heirman, Fontijn, Strasser, Pino, Urrutia and Batist2014; Pickering & Hiscott, Reference Pickering and Hiscott2015). Thus, while the presence of turbidites does not automatically imply a deep-marine setting, the presence of interdigitated muddy to silty structureless marls and associated marine fossils (e.g. microfauna, macrofauna, ichnofauna) would suggest a marine setting for the sediments of the Abad Member. Indeed, the relative thicknesses of the turbiditic sandstone beds would imply a broadly distal setting, although whether this can be classified and integrated into an existing submarine fan model (e.g. Pickering et al. Reference Pickering, Stow, Watson and Hiscott1986; Mulder & Alexander, Reference Mulder and Alexander2001; Talling et al. Reference Talling, Masson, Sumner and Malgesini2012; Pickering & Hiscott, Reference Pickering and Hiscott2015) is questionable.

Based on the ichnofossils present, the sediments of the Abad Member are considered to have been deposited in a setting represented by the classical Nereites ichnofacies (cf. Seilacher, Reference Seilacher1964), with a mixture of facies-crossing and facies-controlled ichnogenera present. Seilacher (Reference Seilacher1964) introduced the concept of ichnofacies, using them to reconstruct specific palaeoenvironmental conditions, with the Nereites ichnofacies representing a deep-marine depositional environment. In detail, this ichnofacies is characterized by the ethologies of the trace-producing organisms and their related trophic styles. These styles are described as complex grazing and patterned feeding or dwelling structures. They occur below the sediment/water interface, and form as a result of organized and efficient feeding strategies (c.f. table 1 of MacEachern et al. Reference MacEachern, Bann, Gingras, Zonneveld, Dashtgard, Pemberton, Knaust and Bromley2012). These features result in the formation of a suite of characteristic traces that represent the ichnofacies (i.e. graphoglyptids: meanders and networks). The majority of the ichnogenera present within the Abad Member (e.g. Desmograpton, Glockerichnus, Helminthoida, Helminthopsis, Paleodictyon, Scolicia and Urohelminthoida) are considered to be characteristic for the Nereites ichnofacies (Seilacher, Reference Seilacher1964, Reference Seilacher2007; Leszczyński & Seilacher, Reference Leszczyński and Seilacher1991; Uchman, Reference Uchman and Miller III2007; MacEachern et al. Reference MacEachern, Bann, Gingras, Zonneveld, Dashtgard, Pemberton, Knaust and Bromley2012; Uchman & Wetzel, Reference Uchman, Wetzel, Knaust and Bromley2012). Additionally, the interpreted palaeoenvironmental conditions as determined by the detailed analysis of the sedimentary facies and facies associations within the Abad Member (i.e. muddy to silty marls with interstratified sandy turbidites) would support, the typical conditions of such environments (i.e. muddy sediments as a result of very slow sedimentation with intercalated sandy turbidites; MacEachern et al. Reference MacEachern, Bann, Gingras, Zonneveld, Dashtgard, Pemberton, Knaust and Bromley2012). Thus, a possible depositional setting within a lower slope or basin floor environment (and related fan/lobe system) would successfully integrate both the sedimentary and ichnological observations (cf. MacEachern et al. Reference MacEachern, Bann, Gingras, Zonneveld, Dashtgard, Pemberton, Knaust and Bromley2012).

The Nereites ichnofacies has been revised by a number of workers (e.g. Seilacher, Reference Seilacher, Crimes and Harper1977; Uchman, Reference Uchman2001, Reference Uchman and Miller III2007; Heard & Pickering, Reference Heard and Pickering2008; Knaust, Reference Knaust2009; Uchman & Wetzel, Reference Uchman, Wetzel, Knaust and Bromley2012) who subdivided it into three sub-ichnofacies (Nereites, Paleodictyon and Ophiomorpha rudis) based primarily on the lithological characteristics within the individual environmental settings. This subdivision allows more subtle ichnoassemblages to be recognized and classified, and in particular it better reflects the bathymetric differentiation of a typical deep-sea fan system (i.e. inner to outer fan) as well as lateral changes within such a system (i.e. interchannel areas, channel axis, levee and overbank deposits; cf. Seilacher, Reference Seilacher, Crimes and Harper1977; Uchman, Reference Uchman2001, Reference Uchman and Miller III2007; Heard & Pickering, Reference Heard and Pickering2008; Knaust, Reference Knaust2009; Uchman & Wetzel, Reference Uchman, Wetzel, Knaust and Bromley2012).

The ichnoassemblages present within the Abad Member, together with the sedimentary successions, suggest a depositional setting corresponding to the Paleodictyon sub-ichnofacies (i.e. medium- to thin-bedded sandstone turbidites in a mud-rich succession; cf. Uchman & Wetzel, Reference Uchman, Wetzel, Knaust and Bromley2012), and suggest an intermediate setting in terms of both bathymetric and lateral differentiation of the Nereites ichnofacies. Such a setting could include overbank, interchannel, interlobe or distal depositional-lobe environments (Wetzel & Uchman, Reference Wetzel and Uchman1997; Uchman, Reference Uchman and Miller III2007; MacEachern et al. Reference MacEachern, Bann, Gingras, Zonneveld, Dashtgard, Pemberton, Knaust and Bromley2012; Uchman & Wetzel, Reference Uchman, Wetzel, Knaust and Bromley2012).

However, the absence of obvious channel sediments (both, main or distributary channel) in the outcrop area, suggests a possible depositional-lobe-type setting. The palaeogeographic setting of the Almocáizar Corridor, and its extension into the Vera Basin, is that of a mixed siliciclastic–carbonate shelf extending into a deeper-marine environment (Fig. 11). The shelf is oriented E–W and has been classified as relatively narrow, with the shelf-slope break located close to the shoreline (cf. Braga, Martín & Wood, Reference Braga, Martín and Wood2001; Martín et al. Reference Martín, Braga, Sánchez-Almazo, Aguirre, Mutti, Piller and Betzler2012). In this respect, it was probably similar to other published examples of narrow shelf areas (e.g. the Oligocene of New Zealand, Carter & Lindqvist, Reference Carter and Lindqvist1975; present-day Albany Shelf, Australia, James & Bone, Reference James and Bone2010). Along the northern margin of the shelf (i.e. Sierra de los Filabres) coastal (including beach systems) and inner-platform sediments were deposited, while small deltas also formed along the coast (e.g. in the area of Almocáizar; Braga, Martín & Wood, Reference Braga, Martín and Wood2001; Martín et al. Reference Martín, Braga, Sánchez-Almazo, Aguirre, Mutti, Piller and Betzler2012). In areas where delta development is marked, the shelf is more clastic (with sediment also being transported parallel to the shoreline by ENE-directed longshore currents), whereas away from the areas of delta formation, the shelf sediments are mixed (i.e. carbonate/siliciclastic).

Figure 11. Block diagram reconstructing the depositional setting of the Almocáizar Corridor, Vera Basin (SE Spain) in early Messinian times. This schematic model illustrates the palaeogeography at this time, with the Sierra de los Filabres located in the north, and the shelf/slope/deep-marine areas located further south. Two possible scenarios are envisaged: (a) where a channel-fan system developed downcurrent of a shelf/slope channel system, and (b) a detached lobe system developed basinwards of the narrow shelf with sediment supplied from turbidity currents generated by storms on the shelf. Additionally, a third model would combine aspects of these two scenarios (see text for details). (Shelf morphology and facies modified after Martín et al. Reference Martín, Braga, Sánchez-Almazo, Aguirre, Mutti, Piller and Betzler2012).

The coastal systems prograded southwards into shallow shelf deposits, comprising a mixed siliciclastic–carbonate succession, which has been interpreted in terms of a ramp (with distal steepening; Martín et al. Reference Martín, Braga, Sánchez-Almazo, Aguirre, Mutti, Piller and Betzler2012) or platform (Braga, Martín & Wood, Reference Braga, Martín and Wood2001) system. Subaqueous sand-filled channels (Fig. 11) cross-cutting the inner-platform sediments, and located at the mouths of fluvial systems, have also been noted (Braga, Martín & Wood, Reference Braga, Martín and Wood2001; Martín et al. Reference Martín, Braga, Sánchez-Almazo, Aguirre, Mutti, Piller and Betzler2012). Areas adjacent to these channels were presumably subjected to bypass, with sediment being transported across the narrow shelf and deposited along the shelf-slope break, or indeed, being directly transported into deeper-marine areas (i.e. the area forming the subject of this study). Braga, Martín & Wood (Reference Braga, Martín and Wood2001) suggested that lobe deposits in the deeper-marine area are fed by sediment originating in the Sierra de los Filabres (based on clast analysis) and transported across the shelf.

However, the preserved submarine channel/lobe systems described above (i.e. from Braga, Martín & Wood, Reference Braga, Martín and Wood2001) do not appear to be correlatable with the turbidites described as part of this study. Certainly, there are problems both with regard to (a) the precise location (i.e. Braga, Martín & Wood, Reference Braga, Martín and Wood2001 describe lobes from the area to the south of Turre, see Fig. 3 for location, whereas the present lobes occur in the area of the Almocáizar Corridor), and (b) the stratigraphic position (i.e. the lobes described by Braga, Martín & Wood, Reference Braga, Martín and Wood2001 would appear to be younger in age and to have been deposited in a shallower marine setting). In addition, these lobes appear to be smaller in scale and they comprise mainly coarse-grained sediments (sandstones, conglomerates). The lobes in the present study are composed of finer-grained sediments (sandstones). Additionally, there would appear to be a clear correlation between the channels, extending from the fluvial systems north of the Almocáizar Corridor and crossing the narrow shelf, and the deep-marine lobes to the south. This would suggest that the lobes of the Almocáizar Corridor region were directly fed from erosion of the Sierra de los Filabres, with sediment being transported across the shelf and deposited seawards of the shelf-slope break (Fig. 11).

Two hypotheses are proposed for the precise depositional setting of the Almocáizar lobes. In the first situation (Fig. 11a), sediments were transported down the slope via a submarine channel leading to the establishment of a small mud-rich channel-fan system (cf. Richards, Bowman & Reading, Reference Richards, Bowman and Reading1998). In such a system, a number of features would be anticipated including, for example, clear proximal–distal changes, the presence of a range of turbiditic facies, as well as clear evidence of channelization within the channel-fan system. However, as noted above, the sediments in the Almocáizar Corridor area do not contain evidence of any of these features. The fact that a pronounced channel system was developed on the shelf would certainly suggest that at the shelf-slope break the system would extend basinwards into the deep-marine area. The absence of any evidence of a channel-fan system in the deep-marine parts of the basin does not imply that it never existed, but rather that it was, not preserved or that the current outcrop situation is not extensive enough to allow full recognition of the entire system.

A second option (Fig. 11b) is that the shelf channel system played a minor role, in that the sediments were transported from the coastal areas and deposited in the outer shelf area. In such a scenario, storms on the narrow shelf would have resulted in the generation of slope aprons, and associated turbidity flows, transporting the sediment into the deep-marine area and resulting in the formation of lobe deposits. These lobes, detached from a direct source, would have been formed from individual turbidity currents generated in the shelf/slope region. The fact that the lobes in the present study are generally of similar grain size would suggest pre-sorting in the source area of the transported sediment, an aspect which might correlate with outer shelf deposition. Indeed, the presence of tempestites in the shelf area would support the idea of storm-generated sediment bodies on the shelf.

An alternative option (in addition to the two described above) is that the lobes were produced by a combination of both models, i.e. possible channelization on the slope but with the development of detached lobes, rather than a channel-fan system (i.e. Fig. 11a), coupled with detached lobes developing from slope aprons generated by storm deposits on the shelf (i.e. Fig. 11b). In such a system, the emphasis would be on the lobe morphology and composition (i.e. lobate forms extending basinwards of the slope; finer-grained sediments) rather than the direct presence of feeder systems. The current outcrop situation, however, does not allow any one model to be favoured.

5.b. Bathymetry of the Abad Member

As noted above, the succession is dominated by turbiditic sandstones and marls, although the presence of the former says nothing definitively per se about absolute depths in the depositional area. Seilacher's (Reference Seilacher1964) ichnofacies, while useful for generalized water depth determinations in the fossil record, are, however, not always directly applicable and, indeed, may lead to a false interpretation (e.g. Fürsich, Taheri & Wilmsen, Reference Fürsich, Taheri and Wilmsen2007). MacEachern et al. (Reference MacEachern, Bann, Gingras, Zonneveld, Dashtgard, Pemberton, Knaust and Bromley2012) have suggested that neo-ichnology plays an important role in determining precise depth ranges (or maxima) for organisms in particular settings. For example, Helminthoida-like traces have been recorded at depths of 5248 m from the Japan Trench (Fujioka et al. Reference Fujioka, Taira, Kobayashi, Nakamura, Ilyama, Cadet, Lallemand and Girard1987), while Scolicia-like trails have been noted from 3830 m from the Taira deep-sea fan and from 3835 m from the Tenryu deep-sea fan (Fujioka et al. Reference Fujioka, Taira, Kobayashi, Nakamura, Ilyama, Cadet, Lallemand and Girard1987). The possible water depths at which these organisms can exist, therefore, are deep. While similar water depths for the Abad Member are not probable (based on palaeogeographical evidence, see below), it does suggest that similar conditions (e.g. very low energy and related slow rates of deposition) can be presumed. When extrapolating to the fossil record, however, the problematics of depth determination become more obvious. While estimated bathymetries are, at best, imprecise, some ichnofossils (particularly those considered to be facies-controlled, e.g. Desmograpton) can be used to provide rough depth estimates of the depositional setting.

As noted above, ichnofacies models have been determined on the basis of trace-fossil morphology, and this is controlled by the feeding behaviour of the trace-producing organisms (Książkiewicz, Reference Książkiewicz1977). Thus, the pattern of the traces and their complexity is dependent on the amount of food available within the sediment. Consequently, with increasing depth a decrease in nutrient availability can be generally assumed (e.g. Thibodeau et al. Reference Thibodeau, Lehmann, Kowarzyk, Mucci, Gélinas, Gilbert, Maranger and Alkhatib2010; Moore et al. Reference Moore, Mills, Arrigo, Berman-Frank, Bopp, Boyd, Galbraith, Geider, Guieu, Jaccard, Jickells, La Roche, Lenton, Mahowald, Maranon, Marinov, Moore, Nakatsuka, Oschlies, Saito, Thingstad, Tsuda and Ulloa2013), resulting in the development of more complex trace patterns (e.g. graphoglyptids or networks; Książkiewicz, Reference Książkiewicz1977; Seilacher, Reference Seilacher, Crimes and Harper1977, Reference Seilacher2007; Uchman & Wetzel, Reference Uchman, Wetzel, Knaust and Bromley2012). Furthermore, the type of sediment (e.g. turbidites or deep-sea muds) and the composition of the water (e.g. oxygenation levels) may influence both the form and amount of nutrients present within the sediments of the deep sea. These variations may be independent of depth, thus suggesting that palaeobathymetric reconstructions need to take a number of factors into account and not just the morphology of the particular ichnofossils. Additionally, with the Nereites ichnofacies broadly considered to represent ‘deep-marine’ settings, there is an increasing body of work which suggests otherwise (e.g. Häntzschel, Reference Häntzschel and Teichert1975; Ernst & Zander, Reference Ernst, Zander, Abbate, Sagri and Sassi1993; Fürsich, Taheri & Wilmsen, Reference Fürsich, Taheri and Wilmsen2007). Paleodictyon, for example, has been reported from shallow-marine locations in the Lower Palaeozoic (Stanley & Pickerill, Reference Stanley and Pickerill1993), while Gierlowski-Kordesch & Ernst (Reference Gierlowski-Kordesch, Ernst, Matheis and Schandelmeier1987) and Ernst & Zander (Reference Ernst, Zander, Abbate, Sagri and Sassi1993) have reported it in Upper Cretaceous-age midshelf deposits where it was associated with other ichnofossils considered typical of the Nereites ichnofacies (e.g. Cosmorhaphe, Spirorhaphe, Urohelminthoida). Other evidence for comparatively shallow-marine Paleodictyon has been provided by Hantzpergue & Branger (Reference Hantzpergue and Branger1992), who reported the ichnofossil from an upper Oxfordian limestone unit which they suggested was deposited at a depth of not > 100 m. Depths of 200–300 m have been suggested by Uchman, Janbu & Nemec (Reference Uchman, Janbu and Nemec2004) from the Cretaceous–Eocene-age central Pontides of Turkey. Considered together, these data question the assumption that the Nereites ichnofacies can always be considered as ‘deep marine’. Indeed Fürsich, Taheri & Wilmsen (Reference Fürsich, Taheri and Wilmsen2007) have gone further, suggesting that the bathymetric range of Paleodictyon was wider than generally assumed, and that its dominance in deep-marine turbiditic successions is at least partly a preservational effect. Furthermore, Fürsich, Taheri & Wilmsen (Reference Fürsich, Taheri and Wilmsen2007) suggested that bathymetric interpretations are best made on the basis of complete ichnoassemblages rather than single ichnogenera/ichnospecies.

This approach, i.e. using complete ichnoassemblages, but also combining them with other factors, was used by Książkiewicz (Reference Książkiewicz1977) in order to provide a broad bathymetric range for a series of particular ichnospecies found within Cenozoic-age sediments (and which are comparable with the samples from this study). According to these results, the palaeobathymetry of the Abad Member would fall within the epibathyal zone (200–600 m of Książkiewicz, Reference Książkiewicz1977; cf. his table 11) and extending down to the onset of the mesobathyal zone (600–1000 m of Książkiewicz, Reference Książkiewicz1977; cf. his table 11; p. 40). Interestingly, the water depth estimates suggested by the foraminiferal assemblage present within the Abad Member correlate well with those of the ichnofossils. Baggley (Reference Baggley2000) analysed foraminiferal assemblages (predominantly benthic) from several sections within the Sorbas Basin and the Almocáizar Corridor (connecting the Sorbas and Vera basins, and overlapping with the sampling location (I) of this study, Fig. 3a). Nine samples were collected from an 84.5 m thick section (i.e. the ‘Barranco de Los Giles (BG)’ section, which is located within the older sediments of this study (i.e. within the Almocáizar Corridor) and c. 500–600 m to the south of our sampling area; Baggley, Reference Baggley2000). The foraminiferal assemblage includes Eponides pusillus, Pullenia bulloides and Quinqueloculina venusta suggesting a lower epibathyal to upper mesobathyal depth (500–1300 m; Baggley, Reference Baggley2000), and thus broadly encompassing the 200–1000 m as suggested by the ichnoassemblage.

5.c. Variations between the Vera Basin and the Sorbas/Nijar basins

The Turre Formation (i.e. Azagador and Abad members, Figs 3, 4) crops out in the Vera Basin, as well as in the adjacent Sorbas and Nijar basins (Fig. 4). In all three basins, the Azagador Member is similar in terms of its lithological composition and appearance. However, the overlying Abad Member differs markedly between the Vera Basin, where it contains turbiditic sandstones, and the Sorbas and Nijar basins where it does not. Additionally, foraminiferal studies reflect a clear lateral deepening of the Abad Member towards the Vera Basin (Baggley, Reference Baggley2000). Thus, the depositional history of the Abad Member in the Vera Basin marks a caesura in terms of the regional sedimentary evolution. The question, as to why deepening occurred within the Vera Basin, is problematic. In contrast, the deposits of the basins to the south represent a clear shallowing trend.

The tectonic evolution of the area in Messinian times resulted in basin separation during the period of the deposition of the upper Abad Member leading to the tectonic restriction and isolation of the Sorbas and Nijar basins (Fig. 2; Braga et al. Reference Braga, Martín, Riding, Aguirre, Sánchez-Almazo and Dinarès-Turell2006). Coevally, extensive carbonate platforms and reefs (e.g. Cantera Member) along the basin margin topographic highs in the Sorbas and Nijar basins developed (Fig. 2b). However, this development did not occur in the Vera Basin, except for some rare and minor occurrences along the central-western margin of the basin (Fig. 3, cropping out to the west of Antas). The reefal growth, especially in the Sorbas Basin (Fig. 2b), would also have resulted in the formation of a topographic barrier to the free movement of water bodies between the Vera Basin to the north (with open contact to the Mediterranean Sea) and the Sorbas and Nijar basins to the south-west (Fortuin & Krijgsman, Reference Fortuin and Krijgsman2003; Krijgsman et al. Reference Krijgsman, Leewis, Garcés, Kouwenhoven, Kuiper and Sierro2006). These barriers would thus have reinforced the basin separation between the two regions, which from this point in time underwent differing depositional evolutions (cf. see above/regional geology; Fig. 2).

5.d. The lower Abad Member (rapid rise in sea level)

As noted above, there are clear changes in terms of the ichnoassemblage between the older part of the Abad Member (i.e. Almocáizar Corridor) and the younger sediments in the central part of the Vera Basin. This change is characterized by a marked decrease in the amount of recognizable ichnospecies and ichnogenera (Tables 1, 2). In addition, typical ichnofossils of the mesobathyal zone (i.e. Desmograpton ichthyforme; Helminthoida labyrintica) are no longer present. The changes in terms of ichnoassemblage between the two locations can be interpreted in terms of a temporal change in bathymetry from a deeper (upper meso- to lower epibathyal: i.e. older deposits) setting in the basin margin/older deposits through to a shallower setting (mainly epibathyal; i.e. younger deposits) in the basin centre. Such a shallowing trend was also noted by Baggley (Reference Baggley2000) in his study of the benthic foraminifera, where a deep-to-shallow trend could also be seen in both the Sorbas and Vera basins. In addition, sequence-stratigraphic models for the Vera Basin (Braga, Martin & Wood Reference Braga, Martín and Wood2001), as well as for the Sorbas Basin (Martin et al. Reference Martín, Braga, Betzler and Brachert1996), support the recognized deep-shallow trend obviously. These models were established on the basis of the Azagador Member deposits immediately underlying (and sometimes interdigitating with) the Abad Member, which comprise shallow-marine sandstones and temperate carbonates. Such sediments are generally deposited in shelf regions at depths of < 200 m (e.g. James & Bone, Reference James and Bone2010). The presumed depth of the upper part of the Abad Member, therefore, would involve a sudden and geologically rapid increase in water depth to a maximum depth of c. 1100 m. The question is how such a rapid increase in water depth could be explained.

The Azagador Member was deposited along the basin margin, while the Abad Member extended towards the basin centre (Figs 3, 4). However, it cannot be stated with any certainty that a specific stratigraphic level within either member corresponds to a specific stratigraphic time since it is entirely probable that the finer-grained sediments in the basin centre were deposited relatively slowly, in comparison with the coarser basin margin units. Thus, while the stratigraphic interval represented by the joint succession (i.e. basin margin and basin centre) ranges in age from upper Tortonian to uppermost Messinian, the precise ages of the respective successions (i.e. Azagador Member, Abad Member; Fig. 4) and their relationship to one another is unclear.

The rapid change in sea level (i.e. water depth reconstructions between the Azagador and the Abad members) may have been related to tectonic activity in the region. An increase in subsidence of the Vera Basin during the time of deposition of the Abad Member would have coincided with the onset of uplift in the eastern most part of the Sierra de Filabres, which began in late Tortonian times (Fig. 2; Braga, Martín & Quesada, Reference Braga, Martín and Quesada2003). This would have been coeval with the initial phase of deposition of the Azagador Member in the southwest. By mid-Messinian times, uplift of the crystalline massifs surrounding the basin had progressed to the point that the Sierra Cabrera was uplifting (Braga, Martín & Quesada, Reference Braga, Martín and Quesada2003; Booth-Rea et al. Reference Booth-Rea, Azañón, Azor and Garcı́a-Dueñas2004). Additionally, there is a clear correlation between the initial activity of the Palomares Fault Zone (in late Tortonian times) and uplift activity of the Sierra Cabrera in the Vera Basin (c.f. Booth-Rea et al. Reference Booth-Rea, Azañón, Azor and Garcı́a-Dueñas2004).

5.e. The uppermost Abad Member (end of full marine conditions)

As noted above, there is an obvious change in terms of the ichnofossil assemblages present within the succession between two of the measured profiles (i.e. sections 2.1 and 2.2; Fig. 6) in the central part of the basin. The former area contains an assemblage corresponding to the Nereites ichnofacies, while the latter is characterized by the complete absence of ichnofossils. The latter section (i.e. 2.2) is stratigraphically younger, and comprises finer-grained sediments, including both marls and turbiditic sandstones. A possible explanation for these observed changes may be owing to variations in the palaeoenvironmental conditions, related to temperature, nutrient availability, oxygen level and/or salinity (cf. Wetzel & Uchman, Reference Wetzel and Uchman1998). All of these changes would suggest a transition in terms of the environmental conditions from one favouring the presence of trace-producing organisms to one that could be considered a non-viable zone. In the case of the Vera Basin, which was affected by the Messinian Salinity Crises in latest Messinian times (i.e. uppermost Abad Member), a change in the degree of salinity is the most probable cause. A number of authors have recorded similar facies (i.e. marls and turbidites including Paleodictyon and marls with interbedded very thin turbidites) in the eastern Vera Basin (e.g. Cuevas de Almanzora Section; Montenat et al. Reference Montenat, Bizon, Bizon, Carbonnel, Muller and Reneville1976; Gonzalez Donoso & Serrano, Reference Gonzalez Donoso and Serrano1978; Cita, Schilling & Bossio, Reference Cita, Schilling and Bossio1980; Benson & Bied, Reference Benson and Bied1991; Fortuin, Kelling & Roep, Reference Fortuin, Kelling and Roep1995). Within the Cuevas del Almanzora profile, for example, Fortuin, Kelling & Roep (Reference Fortuin, Kelling and Roep1995) recognized the occurrence of ostracods (e.g. Cyprideis sp.) and the algae Chara, both indicative of brackish conditions. These fossils are found close to the boundary between the Messinian and the Pliocene, and would appear to correlate with the change in facies as noted in the southern part of the Vera Basin (i.e. from sediments containing a Nereites ichnofacies assemblage to sediments which are barren in terms of ichnofossils). Thus, the observed radical change in the ichnofossil assemblages may be related to a shift from full marine to brackish conditions, and thus reflect the changes wrought on the basin by the onset of the Messinian event.

A variety of foraminiferal studies have been carried out for stratigraphical purposes in the area (e.g. Montenat et al. Reference Montenat, Bizon, Bizon, Carbonnel, Muller and Reneville1976; Gonzalez Donoso & Serrano, Reference Gonzalez Donoso and Serrano1978; Cita, Schilling & Bossio, Reference Cita, Schilling and Bossio1980; Benson & Bied, Reference Benson and Bied1991; Fortuin, Kelling & Roep, Reference Fortuin, Kelling and Roep1995; Sierro et al. Reference Sierro, Hilgen, Krijgsman and Flores2001). These biostratigraphic analyses were mainly based on changes (quantitative and qualitative) in planktonic foraminifera. The aim of these studies was to provide a detailed stratigraphic subdivision of the Tortonian- to Pliocene-aged deposits within the Vera Basin (and the adjacent Sorbas Basin, e.g. Sierro et al. Reference Sierro, Hilgen, Krijgsman and Flores2001), which are dominated by similar, and almost indistinguishable, marl deposits (cf. in the Vera Basin the marls of the Tortonian-aged Chozas Formation, Tortonian- to Messinian-aged Abad Member and the Pliocene-aged Cuevas Formation). Based on these studies, the Tortonian was subdivided into two biostratigraphic units: Tortonian I (of Montenat et al. Reference Montenat, Bizon, Bizon, Carbonnel, Muller and Reneville1976) characterized by Neogloboquadrina acostaensis and the stratigraphically younger Tortonian II characterized by Globorotalia (G.) miocenica. The onset of the Messinian was defined by the occurrence of G. mediterranea and G. conomiozea. The onset of the youngest marine period in the regional basins (i.e. Pliocene) is characterized by the presence of G. margaritae and G. puncticulata (c.f. Montenat et al. Reference Montenat, Bizon, Bizon, Carbonnel, Muller and Reneville1976; Benson & Bied, Reference Benson and Bied1991; Fortuin, Kelling & Roep, Reference Fortuin, Kelling and Roep1995).

The biostratigraphic subdivisions were supplemented and supported by studies on magnetostratigraphy and geochemistry (e.g. Montenat et al. Reference Montenat, Bizon, Bizon, Carbonnel, Muller and Reneville1976; Benson & Bied, Reference Benson and Bied1991; Fortuin, Kelling & Roep, Reference Fortuin, Kelling and Roep1995; Sierro et al. Reference Sierro, Hilgen, Krijgsman and Flores2001). The extensive analyses carried out at the Cuevas de Almanzora Section (located in the northeastern part of the Vera Basin), which is a representative section for the Messinian to Pliocene transition, were integrated into high-resolution stratigraphical studies of the region. The description of Montenat et al. (Reference Montenat, Bizon, Bizon, Carbonnel, Muller and Reneville1976), Benson & Bied (Reference Benson and Bied1991) and Fortuin, Kelling & Roep (Reference Fortuin, Kelling and Roep1995) of the Cuevas de Almanzora Section sediments (grain size, internal structures and bed thickness) as well as their general descriptions of ichnofaunal observations (e.g. presence of Paleodictyon isp. compared to absence of ichnofossils) matches the observations within the deposits of the younger sediments of this study (e.g. sections 2.1 and 2.2; Fig. 6).

In addition to the stratigraphical work, a number of studies focused on palaeoenvironmental reconstructions. Examination of the foraminiferal and ostracod assemblages showed clear evidence of changes in salinity (e.g. Montenat et al. Reference Montenat, Bizon, Bizon, Carbonnel, Muller and Reneville1976; Benson & Bied, Reference Benson and Bied1991; Fortuin, Kelling & Roep, Reference Fortuin, Kelling and Roep1995; Sierro et al. Reference Sierro, Hilgen, Krijgsman and Flores2001; Rouchy & Caruso, Reference Rouchy and Caruso2006; Bourillot et al. Reference Bourillot, Vennin, Rouchy, Blanc-Valleron, Caruso and Durlet2010). Indeed, three different phases of the MSC (5.971–5.33 Ma, cf. Roveri et al. Reference Roveri, Lugli, Manzi, Gennari and Schreiber2014) could be identified across the entire Mediterranean area. These three phases were interpreted as representing: (1) the onset of the MSC, (2) the isolation of the Mediterranean area from the Atlantic Ocean, and (3) the reflooding of the Mediterranean Sea (Rouchy & Martin, Reference Rouchy and Martin1992; Krijgsman et al. Reference Krijgsman, Hilgen, Raffi, Sierro and Wilson1999; Bourillot et al. Reference Bourillot, Vennin, Rouchy, Blanc-Valleron, Caruso and Durlet2010; Manzi et al. Reference Manzi, Gennari, Hilgen, Krijgsman, Lugli, Roveri and Sierro2013; Do Couto et al. Reference Do Couto, Popescu, Suc, Melinte-Dobrinescu, Barhoun, Gorini, Jolivet, Poort, Jouannic and Auxietre2014; Roveri et al. Reference Roveri, Lugli, Manzi, Gennari and Schreiber2014; Flecker et al. Reference Flecker, Krijgsman, Capella, Castro Martíns, de, Dmitrieva, Mayser, Marzocchi, Modestou, Ochoa, Simon, Tulbure, van den Berg, van der Schee, Lange, de, Ellam, Govers, Gutjahr, Hilgen, Kouwenhoven, Lofi, Meijer, Sierro, Bachiri, Barhoun, Alami, Chacon, Flores, Gregory, Howard, Lunt, Ochoa, Pancost, Vincent and Yousfi2015). The second of these phases encompasses the Lago Mare Facies (5.55–5.32 Ma, Stoica et al. Reference Stoica, Krijgsman, Fortuin and Gliozzi2016), interpreted as representing predominantly brackish conditions, and which is widely observed in the Mediterranean region (e.g. Deckker, Chivas & Shelley, Reference Deckker, Chivas and Shelley1988; Rouchy et al. Reference Rouchy, Orszag-Sperber, Blanc-Valleron, Pierre, Rivière, Combourieu-Nebout and Panayides2001; Warny, Bart & Suc, Reference Warny, Bart and Suc2003; Clauzon et al. Reference Clauzon, Suc, Popescu, Marunteanu, Rubino, Marinescu and Melinte2005; Orszag-Sperber, Reference Orszag-Sperber2006; Do Couto et al. Reference Do Couto, Popescu, Suc, Melinte-Dobrinescu, Barhoun, Gorini, Jolivet, Poort, Jouannic and Auxietre2014; Roveri et al. Reference Roveri, Lugli, Manzi, Gennari and Schreiber2014; Marzocchi et al. Reference Marzocchi, Flecker, van Baak, Lunt and Krijgsman2016; Stoica et al. Reference Stoica, Krijgsman, Fortuin and Gliozzi2016). This particular phase occurred during the time of the continued separation of the Mediterranean Sea from the Atlantic. Thus, waters entering the Vera Basin (and related basins) were derived from freshwater influx from the surrounding region. The marine influence at this time was confined to occasional influxes from the Paratethys, as evidenced from a diverse assemblage of Paratethyan ostracod species (e.g. Cyprideis and Loxoconcha; Benson & Bied, Reference Benson and Bied1991; Fortuin, Kelling & Roep, Reference Fortuin, Kelling and Roep1995; Do Couto et al. Reference Do Couto, Popescu, Suc, Melinte-Dobrinescu, Barhoun, Gorini, Jolivet, Poort, Jouannic and Auxietre2014; Stoica et al. Reference Stoica, Krijgsman, Fortuin and Gliozzi2016). The combination of the ichnofossil (i.e. absence of bioturbation) and microfossil (ostracods and foraminifera) records from the Abad Member sediments of the central part of the Vera Basin thus suggest that brackish conditions were active at this particular time. This would suggest a possible correlation with the extant Lago Mare Facies elsewhere in the Mediterranean region (e.g. Benson & Bied, Reference Benson and Bied1991; Fortuin, Kelling & Roep, Reference Fortuin, Kelling and Roep1995; Do Couto et al. Reference Do Couto, Popescu, Suc, Melinte-Dobrinescu, Barhoun, Gorini, Jolivet, Poort, Jouannic and Auxietre2014; Stoica et al. Reference Stoica, Krijgsman, Fortuin and Gliozzi2016), and that the Abad Member succession in the Vera Basin represents a shift from full marine through to early post-MSC deposition. Thus, the correlation of the sediments of section 2.2 with the Lago Mare Facies would imply that these particular deposits should not be assigned to the Abad Member. A clear stratigraphical assignment to the period of the Messinian Salinity Crises and the corresponding Lago Mare Facies (Fortuin, Kelling & Roep, Reference Fortuin, Kelling and Roep1995; Do Couto et al. Reference Do Couto, Popescu, Suc, Melinte-Dobrinescu, Barhoun, Gorini, Jolivet, Poort, Jouannic and Auxietre2014; Stoica et al. Reference Stoica, Krijgsman, Fortuin and Gliozzi2016) is necessary.