Miocene tectono-sedimentary evolution of the eastern external Betic Cordillera (Spain)

ABSTRACT An interdisciplinary study of Miocene successions in the eastern External Betic Zone (South Iberian Margin) was carried out. Evidences of syn-sedimentary tectonic activity were recognized. The results enabled a better reconstruction of the stratigraphic architecture (with an improved chronostratigraphic resolution) in the framework of the Miocene foredeep evolution of the eastern EBZ. Two main depositional sequences were dated as uppermost Burdigalian-upper Serravallian p.p. and middle-upper Tortonian. p.p., respectively. The vertical and lateral diversification of lithofacies associations and thicknesses resulted from the syn-depositional tectonic complexity of the area. A great variety of sedimentary depositional realms is due to different subsidence rates, and the growing of anticlines and synclines during the Langhian p.p.-Serravallian. After a regression with an early Tortonian erosional gap, platform to hemipelagic realms developed during the middle Tortonian. The end of the sedimentation coincided with the emplacement of an important olisthostrome-like mass consisting of Triassic material related to either the development of thrust systems or diapirs emerged in the middle-late Tortonian, during the nappe emplacement. Correlations with other external sectors of the Betic Chain, and the external domains of the Rif, Tell, and northern Apennine Chains highlighted a similar Miocene foredeep evolution during the building of these orogens.


Introduction
The study area belongs to the eastern External Zone of the Betic Cordillera (Spain, Figure 1(A)). This cordillera and the Rif Chain (Morocco) constitute the Betic-Rifian Arc that represents the westernmost Mediterranean Alpine orogenic belt originated by a Miocene tectonics.
The External Betic Zone (EBZ) consists of the Mesozoic to Tertiary sedimentary cover of the South Iberian Margin (Figure 1(B)). This passive Alpine margin started to develop during the Mesozoic rifting of the western Tethys that caused the formation of deep and shallow marine pelagic successions separated by normal faults. In the region a Cretaceous tectonic inversion from extension to compression occurred, similarly to what was observed in the western Mediterranean Alpine chains (Guerrera et al., 2014;Guerrera & Martín-Martín, 2014a; and references therein). In the EBZ the Mesozoic normal faults evolved during the Tertiary under compressive deformation as strike-slip faults, and later as thrusts (Sanz de Galdeano & Buforn, 2005;Martín-Martín et al., 2018a;Martín-Martín, Guerrera, Alcalá, Serrano, & Tramontana, 2018b;Sissingh, 2008). In the Miocene many intramontane basins developed whose geometry and stratigraphic architecture were controlled by re-arrangements of blocks and faults. These intramontane basins were related to the evolution of the North Betic Strait (or Proto-Guadalquivir Foreland Basin) that represented a foredeep area connecting the Atlantic Ocean and the Mediterranean Sea during a part of the Miocene (Sanz De Galdeano & Vera, 1992).
Most of knowledges about the Tertiary sediments of these intramontane basins in the eastern EBZ appear in old papers. Recent studies are mainly focused on Paleogene evolution (e.g. Guerrera et al., 2006Guerrera et al., , 2014Guerrera & Martín-Martín, 2014a) and late Miocene bio-chronostratigraphy (e.g. Garcés, Krijgsman, & Agustí, 2001;Lancis et al., 2010). This paper tries to fill the current gap concerning the Miocene stratigraphic evolution of the eastern EBZ through an interdisciplinary study taking advantage both from the good quality of outcrops and the continuity of the stratigraphic record in the Sierra del Carche-Pinoso Corridor-Sierra de la Pila sector. The results were compared and completed with the previous studies concerning the EBZ (Sanz De Galdeano & Buforn, 2005;Guerrera et al., 2014;Martín-Martín et al., 2018a, 2018b; and references therein).
Data were used to reconstruct the Miocene stratigraphic evolution of the eastern EBZ based on methodological criteria established in the previous interdisciplinary studies both in the Betic Chain (e.g. Guerrera et al., 2014;Guerrera & Martín-Martín, 2014a) and otherchains (e.g. Belayouni et al., 2009Belayouni et al., , 2006Belayouni, Guerrera, Martín-Martín, & Serrano, 2013). The logic was to make comparison between the External Betic sector and other external domains of the northern Africa (Rif and Tunisian Tell) and Apennine Chain in order to highlight common regional tectonic events for a better comprehension of the Miocene evolution of the central-western Mediterranean region.
The Tertiary Africa-Iberia convergence (and related subduction) and the opening of the Alboran area as a back-arc basin caused folding, thrusting, and strikeslip faulting that controlled the paleogeography and the evolution of the basin-margin systems. During the Cretaceous-Paleogene a gentle basement flexure also affected the overlying successive sedimentation, resulting in some lateral lithofacies changes and unconformities (e.g. Guerrera et al., 2006Guerrera et al., , 2014Guerrera & Martín-Martín, 2014b). During the early Miocene the region underwent to an E-W compression that rotated at about N-S from the middle Miocene (De Ruig, 1992;Sanz De Galdeano & Buforn, 2005). The Miocene nappe stacking started in the innermost EBZ while a major strike-slip faulting occurred in a large portion of the outermost EBZ (Sanz De Galdeano & Vera, 1992). Because of this deformation the main faults acted as strike-slip faults during most of the Miocene, bringing about corridorshaped intramontane basins and mountain alignments bounded by N70°E, N155°E, and N120°E trending fault systems as in the study area.
The EBZ consist of SW-NE aligned ridges related to similarly trending folds and thrusts separating narrow depressions (corridors) filled with Miocene-Quaternary sediments (Figure 1(C)). The EBZ is usually subdivided into two main sub-domains: (1) the Prebetic which represents a platform realm stratigraphically continuous with the foreland (Iberian Meseta); and (2) the unrooted Subbetic (located south of the previous  Vera, 2000Vera, , 2004 with the location of the study area. (C) Geographical sketch showing localities and geological features mentioned in the text. one) which represents a deeper area corresponding to the Internal, Median, and External Subbetic sub-zones. Both sub-domains are characterized by Triassic to Tertiary sedimentary successions progressively deformed from south to north during the middle-late Miocene to generate a pile of nappes (Vera, 2000;Arias et al., 2004;and references therein). The presence of major unconformities led Vera (2004) to define VIII Main Sedimentary Cycles for the EBZ (Figure 2).
The study area corresponds to the Sierra de El Carche (SC), Pinoso Corridor (PC), and Sierra de La Pila (SP) sectors (Figure 2(A)), where several structural sub-zones can be distinguished as a result of different fault systems ( Figure 2): E-W, NW-SE, and N-S dextral strike-slip faults; SW-NE sinistral strike-slip faults; and W-E to SW-NE, N-S, and NW-SE normal faults.

Methods
The Miocene stratigraphic record of the Sierra de El Carche (SC) (Logs 5 and 6 p.p.), Pinoso Corridor (PC) (Log 6 p.p.), and Sierra de La Pila (SP) (Logs 1 to 4) sectors ( Figure 2) was reconstructed by means of six representative stratigraphic sections. In Logs 1 to 6, 95 samples ( Figure 3) were collected for different analyses (biostratigraphy, mineralogy, and petrography). Based on the main Sedimentary Cycles of Vera (2000Vera ( , 2004 a specific geological map ( Figure 2) including a tectonic sketch of the main structures and location of stratigraphic sections was realized.
For the chronologic control of deposition, biostratigraphic studies on planktonic foraminifera of 80 samples (Figures 3) were performed. The bio-chronostratigraphic scheme was based on the standard zonal scale by Blow (1969), the Global Standard Chronostratigraphic Scale (Lourens, Hilgen, Laskar, Shackleton, & Wilson, 2004;Hilgen et al., 2005Hilgen et al., , 2009; and references therein), and the most significant foraminiferal bio-events in the Mediterranean during the Miocene.
A Nikon TK-1270E ® polarized-light optical microscope equipped with a digital camera for image acquisition was used to study the arenite petrography of 15 samples (11 from SC and 4 from SP).

Lithostratigraphy
Three main formations were recognized in all studied sectors: the Congost, Lower Tap, and Upper Tap Formations. The Congost Formation was previously defined by Tent-Manclús (2003), meanwhile a Tap Formation was defined by Vera (2000). The Congost Formation (Figure 3) unconformably overlies the Miñano and Murtas Formations (Guerrera & Martín-Martín, 2014a) consisting of Eocene Nummulite limestones, and Oligocene-Aquitanian lacustrine limestones and fluvial conglomerates, respectively. The Congost Formation was subdivided into four lithofacies (C to F) and progressively passes laterally and upwards to the Lower Tap Formation. In this paper, the previously defined Tap Formation has been divided into the Lower and Upper Tap Formations separated by a recognized unconformity with a related gap of about 3 Ma. The Lower Tap Formation was subdivided into 5 lithofacies (G to N) and shows more lateral and upward lithofacies variations compared to the Congost Formation. The Upper Tap Formation was subdivided into four lithofacies (O to R). In the study area, the Upper Tap Fm is unconformably covered by Pliocene to Quaternary deposits (Lithofacies S). Stratigraphic data, tectonic contacts, unconformities, samples, thicknesses, and lithofacies defined in the studied successions are listed in Table 1 and represented in Figure 3.

Sedimentology
Sedimentological features of the above mentioned formations have been studied with the aim to define the sedimentary realm of different recognized lithofacies and in particular taking into account lithotypes, sedimentary structures, carbonate and arenite microfacies and fossil content. Special attention has been addressed to relationships between planktonic and benthonic foraminifera assemblages. The main sedimentological results are shown in Table 2 and some pictures of field details are exposed in Figure 4.
Congost Formation. This unit displays a great variety of shallow marine realms: (i) lagoon and shore marked by calcarenites with a foreshore parallel and wavy lamination (Figure 4(A)), bioturbation, and mollusk fragments (Lithofacies C), ostracods and echinoderm clasts with dominance of very significant benthic foraminifera (Ammonia); (ii) internal and external platform to biostrome front, characterized by biocalcarenites (Lithofacies D) containing preserved bivalves (frequent ostreids) ( Figure. 4(B)) and predominance of planktonic foraminifera; (iii) internal to external platform with massive algal biocalcarenites and marls (Lithofacies E) with red algae ( Figure. 4(C)); (iv) external platform to upper slope (Lithofacies F) with marls and stratified biocalcarenites ( Figure. 4(D)), nodular and reefal structures, biostromes and preserved bivalves, dominance of planktonic foraminifera, and presence of sponge spicules and echinoderms.
Lower Tap Formation. This formation displays several marine realms that are deeper than those of the Congost Formation: (i) external platform to upper slope (Lithofacies G) with sandy marls and biocalcarenite intercalations showing marked prevalence of planktonic foraminifera and presence of sponge spicules and echinoderms; (ii) slope (Lithofaies H)  Vera (2000Vera ( , 2004 showing the three study sectors: Sierra de El Carche, Pinoso Corridor, and Sierra de La Pila; location of the measured logs as in Figure 3 is also indicated. (B) Structural sketch map showing the different structural zones and sub-zones described in the text. characterized by marls and turbiditic sublitharenites with Bouma intervals ( Figure. 4(F,G)) and a marked prevalence of planktonic foraminifera, with also sponge spicules and echinoderms; (iii) deep basin with silexitic marls (Lithofacies I) containing radiolarians (Figure 4(H)); (iv) slope (Lithofacies J and L) with lenticular quartzarenite turbidites with Bouma intervals and diatomaceous marls, and with predominance of planktonic foraminifera; (v) internal platform with algal biocalcarenites and marly intercalations (Lithofacies K); (vi) slope with diatomaceous silty sands (Litofacies M) and deformed (slump) turbiditic arenites (Figure 4(I)); (vii) external platform to upper slope with diatomaceous silty sands (Litofacies N) and deformed (slump) turbiditic quartzarenites, and dominance of benthic foraminifera, and with sponge spicules and echinoderms.

Biostratigraphy and chronostratigraphy
Congost Formation. It could begin towards the Burdigalian-Langhian passage ( Figure 5) by considering that the G. trilobus group including G. bisphaericus (see Table 3 for formal names) appears from the lowest levels of the formation, and the presence of P. sicanus is uncertain due to poor preservation. The upper part (lithofacies D) provides assemblages made up predominantly by Globoquadrina and the plexus Globigerinoides gr. trilobus-Praeorbulina with P. sicanus and P. glomerosa, which are characteristic of the upper N8 zone of the lower Langhian. The top of the formation (lithofacies F; Log 2, P53-P55) contains O. suturalis, marking the N9 Zone and thus belonging to the upper Langhian.
Lower Tap Formation. Based on the presence of Praeorbulina, the lithofacies (G) of this formation is lower Langhian in the SP sector (Log 1, P39; Log 4, Pila6). The occurrence of Orbulina in successive levels (P44 and Pila7) already denotes deposition of the upper Langhian. Lithofacies I (Log 2) can be attributed  Figure 2); details about lithofacies and boundaries in Table 1. Correlation of the local relative sea-level curve deduced from the dimensionless (S + K):I ratio in the studied Sierra de El Carche (left), Pinoso Corridor (center), and Sierra de La Pila (right) successions is also reported; see the original values in Table 4. to the uppermost Langhian, since the basal level (P63) of the overlying Lithofacies H contains G. peripheroacuta (base of the N10 Zone). The couple G. praemenardii-G. peripheroacuta, which is considered as a reference of the lowermost Serravallian, appears near the top of the Lithofacies H (Log 2, P64). The uppermost Lithofacies K would belong to the lower Serravallian. In the SC sector, this formation begins in the lower Langhian with Praeorbulina in Log 6. The successive biostratigraphic references (continuation of Log 6 in the PC): Acme intervals of P. siakensis (Di Stefano et al., 2008) between the samples C31 and A6, the Orbulina datum (A7), and the first observance (FO) of O. universa allow the tracking of the Langhian sedimentation. Deposits close to the Langhian-Serravallian passage occur between the samples A9 and A11, as deduced from transitional morphologies between G. peripheroronda and G. peripheroacuta, and typical G. praemenardii. Components of the Foshella group (e.g. G. peripheroronda and G. peripheroacuta) persist until the level A15, thus indicating lowest Serravallian. The most noticeable in the top of the formation (Lithofacies N; A17-A18 and C43) is the appearance of G. menardii and the absence of components more recent than the upper Serravallian. Upper Tap Formation. In the PC sector, above the unconformity the Lithofacies R yielded Tortonian assemblages. The lowest level (C48) contains N. acostaensis (with right-and left-coiled specimens), G. menardii, and G. obliquus, an assemblage characterizing the N16 Zone (middle part of the Tortonian). Upper levels (C49) show G. plesiotumida, G. extremus, and N. acostaensis-humerosa plexus predominantly rightcoiled. Thus, considering that the FO of G. plesiotumida marks the beginning of the N17 Zone and using the dex/sin coiling shift of the Neogloboquadrina populations as a reference for the middle/upper Tortonian boundary (Serrano, Palmqvist, Guerra-Merchán, & Romero, 1995), these beds must have been deposited close to the end of the middle Tortonian. In fact, in the following level (C50) Neogloboquadrina shows a predominant left coiling, suggesting deposition already of the upper Tortonian. In the SP sector, a marked cartographic unconformity is well recognized in Logs 2 and 4 separating the Lower and Upper Taps Formations. Nevertheless, Lithofacies O (Log 2) and Lithofacies P (Log 4) from the Upper Tap Formation have not yielded fossils of biostratigraphic relevance.

Mineralogy and petrography
The whole-rock mineralogy in the SC (Logs 5, 6 p.p.), PC (Log 6 p.p.), and SP (Logs 1, 2) successions includes, respectively quartz (< 5-9% and < 5-20%), calcite (20-58% and 33-84%), phyllosilicates (18-32% and < 5-31%), dolomite (5-30% and 6-35%), and minor amounts of K-feldspar, plagioclase, and gypsum  (Table 4). In the SC and PC successions, quartz is quite homogeneous, and the carbonate fraction (calcite and dolomite) and phyllosilicates vary somewhat more ( Figure 6(A)), thus indicating relatively stable supplies of these minerals. K-feldspar, plagioclase, and gypsum are systematically found in all samples, except gypsum in some samples of Lithofacies C and D (Log 5) in the Congost Formation in the SC sector, thus suggesting a continuous minor supply of reworked Triassic materials (Martín-Martín et al., 2018b) rich in these minerals (Dorronsoro, 1978). Regarding the SC and PC successions, the SP successions show (Figure 6(C)): (1) more heterogeneous amounts of quartz, carbonate fraction, and phyllosilicates, thus suggesting a more proximal and fluctuating carbonate-vs. terrigenous-rich mineral supply with predominance of the carbonate one; (2) increasing abundance of quartz from the Congost Formation to the Lower Tap Formation, thus indicating a more terrigenous influence in the second one; (3) higher; (4) occurrence of K-feldspar and plagioclase only in the Lithofacies G and H (Log 1), and I (Log 2); and (5) absence of gypsum both in the Congost and Lower Tap Formations.
The different hydrodynamic behaviour of detrital clay minerals in the marine depositional environment allows assessment of supplies distality induced by relative sea-level variations (Daoudi, Deconinck, Witan, & Rey, 1995;Alcalá et al., 2013a; and references therein). In smectite-rich environments (as the SP, PC, and SC successions), the comparison of smectite and kaolinite vs. illite ((S + K):I) changes with the global sea-level curves and enables to identify the influence of the global eustasy (Clark et al., 2009;Daoudi et al., 1995), and local tectonics (Jamoussi et al., 2003;Martín-Martín et al., 2001). A low diagenetic overprint is needed for using the temporal distribution of claymineral assemblages (Alcalá et al., 2013b(Alcalá et al., , 2013aRuffell et al., 2002). The presence of smectite (and mixed layer I-S) in all SP, PC, and SC successions indicates weak burial diagenesis because this mineral phase is quite sensitive to temperature rise with burial depth, and tends to disappear above 200°C after an exponential rate of illitisation between 120°C and 150°C (Lanson, Sakharov, Claret, & Drits, 2009;Nadeau & Bain, 1986). The dimensionless (S + K):I ratio varies in the 1.21-2.17 range in the SC, in the 0.75-2.76 range in the PC, and in the 0.40-1.39 range in the SP successions (Figure 3), thus suggesting a more proximal sediment supply in SP (both in the Congost, Lower Tap, and Upper Tap Formations) than in the corresponding SC and PC successions.
Information deduced from reworked clasts identifies whitish marls and turbiditic arenites of probable Cretaceous-Paleogene origin in most of the studied samples. Both in the SC, PC, and SP successions, inherited calcite and dolomite grains combines with neo-formed dolomite-and calcite-rich cement rims (Table 5). As described by Alcalá et al. (2013b) and Martín-Martín et al. (2018b) in comparable Miocene Subbetic successions, calcite and dolomite come from a combination of neo-formation processes in lacustrine and internal platform realms and detrital supplies from source areas. These realms are marked by warm and shallow water under certain thermodynamics conditions and abundance of base cations, and detrital supplies from a given source area in variable (usually unknown) proportions. Reworked (and probably weathered) Triassic reddish clays and gypsum appear systematically in Lithofacies P (Log 4) and O (Log 2, P65) in the SP successions. The whole-rock mineralogy has identified this inherited Triassic influence in studied Lithofacies in the PC and CS successions. See Tables 1 and 5 for further details on Lithofacies and petrography.

Depositional sequences and sedimentary realms
The stratigraphic record is characterized by a Miocene p. p sedimentary cycle that: (1) encompasses the Congost Formation (upper Burdigalian-upper Langhian p.p.) and the Lower and Upper Tap Formations (upper Langhian   Table 4. Average whole-rock and clay-fraction mineralogy (in wt. %) of samples from Sierra del Carche (SC), Pinoso Corridor (PC), and Sierra de la Pila (SP) sectors (Qtz, quartz; Cal, calcite; Dol, dolomite; Phy, phyllosilicates; Kfs, K-feldspar; Pl, plagioclase; Gp, gypsum; Sme, smectite; Ill, illite; I-S, mixed layer illite-smectite; and Kln, kaolinite), and the dimensionless (smectite+ kaolinite): illite ((S + K):I) ratio.  (4) is covered by the Plio-Quaternary p.p. depositional one. The analyzed succession ( Figure 8) fits with the Main Cycle VII proposed by Vera (2000Vera ( , 2004). An erosive boundary divides the sedimentary cycle into the upper Burdigalian-upper Serravallian and middle Tortonian depositional sequences: (1) the oldest shows a transgressive-regressive trend with a maximum flooding surface dated upper Langhian; and (2) the upper sequence shows a regressive trend only. The whole cycle shows a transgressive to regressive depositional trend with several secondary fluctuations reflected by parasequences. Lithofacies, mineralogy (including (S + K):I ratios), and petrography evidence shallower environments in SP than in SC and PC sectors.
(1) The upper Burdigalian-upper Serravallian Depositional Sequence displays a transgressive-regressive trend (Guerrera & Martín-Martín, 2014a). The transgression begins in the upper Burdigalian (Lithofacies C), reaches the late Langhian (Lithofacies L, G, H, and I), and seems younger in Log 6 (early Langhian, Lithofacies D) than in Log 5 although the different age might be related to an onlap arrangement of transgressive deposits on the previous deformed substratum (Figure 8). The occurrence of an internal platform environment marked by warm and shallow water during the early Langhian in both the SC and SP sectors is suggested by lithofacies association, lower (S + K):I ratios, calcite and dolomite neo-formation, and fossil assemblages. The transition to arenites in the upper part of the early Langhian (Table 5) marks the occurrence of a mixed carbonate and terrigenous input that is consistent with the evolution to an external platform to upper slope. Data allowed proposing for the Congost Formation a deposition occurring in lagoon to upper slope environments.   The Congost Formation passes laterally and upward into the Lower Tap Formation. The presence of clastic rocks suggests a transition from a platform to a basinal environment marked by a terrigenous supply. So, according to the sedimentological data above exposed, the Lower Tap Formation represents the sedimentation on an external carbonate platform to upper slope realms (Lithofacies G, J, and H) changing upward to deeper basinal conditions (Lithofacies I, L, and N). Lateral variations of these two formations are probably related to a different age of the Congost Formation top, that is lower Langhian p.p (lower part) in SC (Logs 5, 6) and lower Langhian p.p. (upper part)upper Langhian p.p. in SP (Logs 1, 2, 4). This lateral diachronism may be caused by variations in the local paleogeography. The Lower Tap Formation shows deeper marine lithofacies in SC than in SP with a quartzarenitic supply (Lithofacies J) in SC that is missing in the SP sector. The deepest environment is marked by the upper Langhian p.p. Lithofacies I (silexites; Log 2) (Bally & Snelson, 1980). In turn, the presence of slumps in the SC (Lithofacies M) implies a slope environment (Bosellini, Mutti, & Ricci-Lucchi, 1989). Both silexites and slumps are considered to indicate a maximum flooding surface. The presence of fine-grained deposits in the SC during the upper Serravallian may indicate a more open pelagic and distal environment (Figure 3). Bio-calcarenite Prevalent carbonatic rock fragments (mainly mudstones, rarely wackestones), and bioclasts of planktonic foraminifera, Bryozoa, and coralline red algae. Low amount of mono-and poly-crystalline quartz. Cement supported. Two types of calcite cement: very fine-grained bounding the clasts and druzy mosaic filling pores. 6 (SC)

C36
J Lower Tap Formation (lower Langhian) Litharenite Angular monocrystalline quartz, abundant rock fragments (mudstones and wackestones) and skeletal clasts, rare polycrystalline quartz, K-feldspar, and glauconia. Bioclasts are mainly foraminifera both benthic (Miliolids) and lesser of planktonic. Poorly sorted with a medium-grained class of about 300 µm: a finegrained fraction of about 100 µm and coarser bioclasts reaching about 700 µm. Intergranular spaces are filled by sparry cement, while no matrix was found. Syntaxial overgrowth of calcite cement on rock fragments (in optical continuity). C34 Quartz-arenite (Q 96 F 2.5 L + C 1.5 ) Angular crystals of mono-and poly-crystalline quartz, carbonatic rock fragments (mudstones/wackestones, and sparites), bioclastic fragments (e.g. benthic larger and planktonic foraminifera, coralline red algae, and individual component of echinoderm stalks and spines), chert, mica flakes (mainly muscovite), K-feldspars, plagioclase, and glauconite. Bad-sorted. The average clast size is about 250 μm, with exception of skeletal fragments that reach almost 1 mm. Grains are cemented by sparite. Symmetrical cement rims (isopachous) around grains consisting of microcrystalline crystals; micrite as a matrix is found; siliceous cement (chalcedony) is also within bioclasts. C33 H Bio-calcarenite Several bio-skeletal fragments, unbroken fossils of benthic foraminifera (Miliolids), and minor amount of planktonic foraminifera and echinoids. Crystals of quartz and plagioclase in very low quantities. All clasts are cemented by sparite-microsparite.
At the end of this depositional sequence, the main latest Serravallian p.p.-Tortonian p.p. 3 Ma gap recorded in the study area was probably related to a local/regional regression that leads to an emersion at the beginning of the compressional thin-skinned tectonics. A similar situation has been recently mentioned for the eastern External Betic Zone in the Alicante area (Martín-Martín et al., 2018a, 2018b where a gap related to compressional tectonics has been proposed affecting the Langhian-Serravallian p.p. In the study area, this tectonics was pre-dated both by compression and folding and by lithostatic load of the Sierra de La Pila Nappe. So that, subsiding areas developed in the PC sector while uplifting areas took place in the SP and SC sectors. This assertion is corroborated by the thicknesses of the Langhian-Serravallian successions in these sectors (higher in the PC, and lower in the SP and SC sectors, respectively).
(2) The Middle Tortonian Depositional Sequence is a new transgressive-regressive depositional sequence deposited above the former unconformity, and represented by the Upper Tap Formation well exposed in the SC and PC (Log 6). According to the sedimentological data above exposed, in these sectors this sequence deposited on internal mixed (carbonate and siliciclastic) platform (Lithofacies Q and S) to external platform (Lithofacies R) environments. In the middle Tortonian after the initial transgression, calcite and smectite decrease, and detrital minerals such as quartz, K-feldspar, plagioclase, illite, and kaolinite increase (Table 4; Figure 6(A,B)), thus indicating a new relative sea-level fall and sediment reworking (Figure 3).
In the SP sector an equivalent unconformity has been recognized above the Lower Tap Formation. Above this unconformity, the Lithofacies O and P belonging to the Upper Tap Formation have been found. In spite of that, no biostratigraphically significant fauna has been found and so the age attribution Figure 8. Depositional sequences, and vertical and lateral lithofacies variations resulting from the stratigraphic architecture reconstructed through interdisciplinary analyses of the studied successions. Stratigraphic gaps and associated unconformities are interpreted as non-depositional and/or erosive phases. Depositional trends recognized from the facies evolution and their comparison with the synthetic local relative sea-level curve deduced from the dimensionless (S + K):I ratio and the global sealevel curve from Haq et al. (1987) are reported. The main and secondary transgressive and regressive trends are also indicated.
for these levels was inferred. This sequence shows the supply of reworked clays and gypsum from the erosion of Triassic terrains and is thought to be deposited on a slope realm (Lithofacies O and P) by the presence of olisthostromes. Equivalent deposits have been described recently in the eastern External Betic Zone from the Alicante area and assigned to the late Miocene (Martín-Martín et al., 2018a, 2018b. In this sector this sequence is unconformably followed by the Pliocene-Quaternary succession (Lithofacies T).

Tectonic control on sedimentation
The Miocene syn-sedimentary tectonic activity is evidenced by: (1) Lithofacies record a variable terrigenous supply, indicating the uplift of source areas, a shallower platform sedimentation, and the decrease of distality (lower (S + K):I values) evidencing a short transport (appearance of angular quartz grains). The Congost Formation is composed mainly of carbonate rocks while arenites predominates regarding carbonates in the Lower and Upper Tap Formations. The terrigenous component of both formations is made up mainly of angular quartz grains, bioclasts and/or carbonate fragments, and minor amounts of K-feldspar, plagioclase, micas (biotite and muscovite), glauconia, dolomite, and chert. Reworked (and probably weathered) Triassic reddish clays and gypsum grains appear systematically in the SC, PC, and SP sectors. Arenites of the Lower Tap Formation in the SC sector are quartzricher. Rock fragments (mostly carbonatic) are more abundant in the SP sector. A minor amount of carbonate fragments could be attributed to a longer transport for the SC with respect to the SP. Relationships between source/basin areas are also thought to be controlled by tectonics. Taking the former tectonic alignments and the south-to-north migrating deformation into account, a southern main rising source area including mainly Cretaceous and Paleogene terrains, and Triassic materials to a lesser extent is proposed, as deduced from the clay-mineral association, presence of detrital gypsum, K-feldspar, and plagioclase, and the planktonic foraminifera reworking.
(2) Frequent syn-sedimentary upper Langhian slumps in the Lower Tap Formation in the SC (Log 6) indicate a pronounced tectonic activity characterized by sliding of unconsolidated materials in a slope environment. These 'tectofacies' predate a local regression that leads to an emersion occurring during the latest Serravallian and probably related to the beginning of the thin-skinned tectonics. A second 'tectofacies' from the Upper Tap Formation consisting of middle Tortonian olistostromes of reworked Triassic material was observed in the SP sector. Tent-Manclús, Estévez, and Martín-Martín (2000; and references therein) interpreted these deposits as olithostrome-like or 'salt glacier' deposits. In the eastern External Betics the salt glaciers are related to overflow of Triassic clays and gypsum from the basal level of stacked superficial nappes or from diapirs (Martín-Martín et al., 2018a, 2018b. In the SP sector, this event appears to be contemporaneous with the emplacement of the Subbetic Nappe, despite a continuous minor supply of reworked (and probably weathered) Triassic terrains and seems to extend over the whole Miocene record, as deduced from mineralogical and petrographic data.
(3) Lithofacies thicknesses and lateral changes ( Figure 8) are also thought to be related to paleogeographic changes due to tectonics. In particular, the SC sector shows greater sedimentary thicknesses, indicating a greater subsidence. Conversely the studied SP successions are thinner. Also the Congost Formation (internal platform) is thicker in the SC indicating a low subsiding area. A similar sedimentary evolution characterizes the deeper Lower and Upper Tap Formations, which show the thickest and deepest deposition in the SC and the thinnest and shallowest deposition in the SP sector. Nevertheless, during the late Langhian this trend is inverted and deeper silexitic facies in the SP indicate a deepening regarding the SC.
(4) The comparison of the (S + K):I ratio changes (synthetic local sea-level curve) with the global sea-level curve of Haq, Hardenbol, and Vail (1987) enabled to deduce the influence of global eustasy (Daoudi et al., 1995;Clark et al., 2009;Alcalá et al., 2013a) and local tectonics Jamoussi et al., 2003;Alcalá et al., 2013a) on the SC, PC, and SP successions (Figure 8). For a common sampling density, such as in this study, the (S + K):I ratio allowed drawing the global sea-level cycles defined by Haq et al. (1987) and to propose local tectonics as the cause of divergences defining low-order cycles during the Langhian and especially during the Serravallian.

Tectono-sedimentary evolutionary model
An evolutionary Miocene paleotectonic framework is presented in four steps and discussed below (Figure 9). In the early Miocene the area was affected by a blind thrusting and related gentle folds (Figure 9(A)).
(1) Burdigalian p.p.-Langhian p.p. (Figure 9(B)). An internal platform (Congost Formation) transitionally develops upwards to an external platform realm (Lower and Upper Tap Formations). The progressive deformation could produce vertical and lateral lithofacies variations and environmental changes from the Congost Formation to the Lower Tap Formation. Main thrusts are thought to display a transpressive dextral strike-slip displacement related to the SW-NE orientation of these faults regarding the W-E to NW-SE maximum compressive stress axis. This evolution could cause the development of gentle synclines and anticlines in areas between strike-slip faults (cf. Figure 2).
(2) Langhian p.p.-Serravallian (Figure 9(C)). A great variety of hemipelagic, platform, and slope deposits developed in the Lower Tap Formation. Marked differences in the subsidence rate are interpreted as due to the reactivation of faults and progressive syn-sedimentary folding. During this time span main thrusts are characterized by a transpressive dextral strike-slip displacement related to a NW-SE oriented maximum compressive stress. The occurrence of the deepest environment (slope) in the synclines of the PC and SP is indicated by siliceous deposits and a large terrigenous supply with a slump interval developed in the uppermost Langhian, probably due to uplifting of source areas.
(3) Middle Tortonian (Figure 9(D)). The platform sedimentation settled (Upper Tap Formation) and a subsidence inversion occurred since the SC sector is transformed into a rising area with the development of an internal platform zone. On the other hand, in the SP sector olisthostrome-like and/or 'salt glacier' deposits fed by Triassic terrains developed. The main faults are now thought to display only a reverse movement according to a N-S oriented maximum compressive stress. The beginning of the Subbetic Nappe emplacement above the SP should occur in this period generating a tectonic load in the SP that caused a deepening of this area, the rising of the SC, and the extensive supply of Triassic material into the basin.
(4) Late Tortonian (Figure 9(E)). No sedimentation was verified, and in the SC-PC boundary the emergence of thrusts affecting the upper deposits (Log 6) occurred. These factors caused the complete emplacement of the Subbetic Nappe to override the upper sediments of the SP sector due to N-S compression (De Ruig, 1992;Sanz De Galdeano & Buforn, 2005).

Lateral correlations and geodynamic implications
In this section we present: (1) a central-western Mediterranean paleogeographic-geodynamic interpretative framework (Figure 10(A)), as developed and discussed by Guerrera and Martín-Martín (2014b; and references therein); and (2) a regional comparison/correlation of the tectono-sedimentary Miocene evolution across the central-western Mediterranean area by means of synthetic and representative external successions reconstructed along the Betic, Maghrebian, and northern Apennine Chains (Figure 10(B)).
The comparison between the study area and other External Betic Zone sectors (Guerrera et al., 2014;Guerrera & Martín-Martín, 2014b;Sissingh, 2008;Vera, 2000) highlights a similar tectono-sedimentary evolution (Figure 10(B1)). Calcareous and marly formations representing the transition from an internalexternal platform realm to a basinal environment are widespread. In deep realms, deposits characterized by olistostromes (Vera, 2000) occur. Several major unconformities linked to the tectonic deformation characterize the middle Burdigalian, Serravallian-Tortonian boundary, and late Tortonian, and related depositional sequences were recognized as pointed out by previous authors (i.e. De Ruig, 1992; Montenat, Ott D 'Estevou, & D'autrey, 1996). The progressive EBZ deformation is presumably related to the NW migration of the Alboran Block (Sanz De Galdeano & Vera, 1992), which is responsible also for the formation of a foredeep depression (proto-Guadalquivir Basin) located between the EBZ and the Iberian Meseta ( Figure 10(A)). As shown in Figure 10(B1) the sedimentation in the study area seems to be less continuous regarding that proposed by Vera (2000).
Another common feature in the compared margins is the occurrence of olithostrome-like or 'salt glacier' deposits related to the overflow of Triassic terrains at different stratigraphic levels coming from the basal level of the stacked superficial nappes or from diapirs, being the latter the most common features placed in the late Miocene (Martín-Martín et al., 2018a, 2018bSissingh, 2008;Tent-Manclús et al., 2000).

Conclusions
The studied Miocene successions have been better defined with greater resolution.
(1) The Congost Formation (upper Burdigalian p.p.upper Langhian p.p.) deposited in a marine platform to upper bathyal slope realm while the Lower and Upper Tap Formations (upper Langhian p.p.-middle Tortonian p. p.) was in a deep (basin, and slope) to shallow marine (internal and external platform) realms. Sedimentary and mineralogical data indicate during the early Langhian a marine-vadose environment evolving to an external platform realm. In late Langhian a transition from platform to basin environment occurred. During the Serravallian a sea-level rise generated pelagic environments (SC sector) and in the middle Tortonian a new sea-level fall took place. The comparison of the (S + K):I ratio (synthetic local sea-level curve) with the global sea-level curve reveals minor dissimilarities during the Langhian and a great divergence during the Serravallian, probably induced by the local tectonic activity and predating the Tortonian nappe emplacement.
(2) Two depositional transgressive-regressive sequences (upper Burdigalian p.p.-upper Serravallian p.p. and middle Tortonian p.p. respectively) have been recognized, the lower indicating the transgressive transition from platform to slope realms and the upper showing a regressive trend with development of different platform realms.
(3) The terrigenous supply of the Congost, Lower Tap, and Upper Tap Formations points out a short transport of detrital components from the erosion of uplifting southern internal areas located near the basin. The same clay-mineral association S + I±(I-S) + K found in all the studied SC, PC, and SP successions identifies a same and main source area from the Subbetic Cretaceous-Paleogene terrains, and a continuous minor supply of reworked Triassic materials.
(4) A paleotectonic model and an early Miocene paleogeographic sketch have been proposed (Figure 9). A folding related to a blind thrusting developing during the Burdigalian p.p.-Langhian p.p. is considered contemporaneous to the sedimentation transition from internal to external platform realm. A great variety of platform and slope realms induced by different subsidence rates of the basin together with the growing of anticlines and synclines occurred during the Langhian p.p.-Serravallian. After the early Tortonian regression, platform realms developed in the middle Tortonian. In the same time the emplacement in the southern basinal area of olisthostrome-like deposits is related to emerging thrust systems or rising of diapirs before the complete emplacement of the Subbetic Pila-Nappe.
(5) The Miocene tectono-sedimentary evolution of the External Betic Zone is similar to that recognized in the external sectors of other central-western Mediterranean Chains (Rif, Tell, and northern Apennines). The similarities probably derived from the comparable evolution of different migrating minor blocks (e.g. Alboran, Kabilides, Peloritani and Calabria) originated from the fragmentation of a single microplate (the 'Mesomediterranean Microplate' sensu Guerrera & Martín-Martín, 2014a; and references therein) originally located since the late Jurassic between Europe and Africa Plates (Figure 10(A)). The southern margins of this microplate and the northern ones of the African Plate constituted their external domains. In this evolutionary framework a progressive Miocene deformation migrating toward the External Zones of each single system is well recognizable, even if the age of the deformation turns out to be older in the Betic Cordillera and North Africa compared to the Apennines.
(6) The comparison of these evolutionary margins reflects their tectonic complexity which controlled each depositional history together with the relative sea-level changes causing numerous unconformities and gaps.
(7) The tectono-sedimentary evolution of four representative external zones along the Betic, Maghrebian, and Apennine Chains has been included to compare the sedimentary evolutive records and the progressive deformation ( Figure 10(B)).