Tectono-Sedimentary Evolution of the Cenozoic Basins in the Eastern External Betic Zone (SE Spain)

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Review Tectono-Sedimentary Evolution of the Cenozoic Basins in the Eastern External Betic Zone (SE Spain)

Manuel Martín-Martín 1,* , Francesco Guerrera 2 and Mario Tramontana 3

1 Departamento de Ciencias de la Tierra y Medio Ambiente, University of Alicante, 03080 Alicante, Spain 2 Formerly belonged to the Dipartimento di Scienze della Terra, della Vita e dell’Ambiente (DiSTeVA), Università degli Studi di Urbino Carlo Bo, 61029 Urbino, Italy; [email protected] 3 Dipartimento di Scienze Pure e Applicate (DiSPeA), Università degli Studi di Urbino Carlo Bo, 61029 Urbino, Italy; [email protected] * Correspondence: [email protected]

Received: 14 September 2020; Accepted: 28 September 2020; Published: 3 October 2020

Abstract: Four main unconformities (1–4) were recognized in the sedimentary record of the Cenozoic basins of the eastern External Betic Zone (SE, Spain). They are located at different stratigraphic levels, as follows: (1) Cretaceous-Paleogene boundary, even if this unconformity was also recorded at the early Paleocene (Murcia sector) and early Eocene (Alicante sector), (2) Eocene-Oligocene boundary, quite synchronous, in the whole considered area, (3) early Burdigalian, quite synchronous (recognized in the Murcia sector) and (4) Middle Tortonian (recognized in Murcia and Alicante sectors). These unconformities correspond to stratigraphic gaps of different temporal extensions and with different controls (tectonic or eustatic), which allowed recognizing minor sedimentary cycles in the Paleocene–Miocene time span. The Cenozoic marine sedimentation started over the oldest unconformity (i.e., the principal one), above the Mesozoic marine deposits. Paleocene-Eocene sedimentation shows numerous tectofacies (such as: turbidites, slumps, olistostromes, mega-olistostromes and pillow-beds) interpreted as related to an early, blind and deep-seated tectonic activity, acting in the more internal subdomains of the External Betic Zone as a result of the geodynamic processes related to the evolution of the westernmost branch of the Tethys. The second unconformity resulted from an Oligocene to Aquitanian sedimentary evolution in the Murcia Sector from marine realms to continental environments. This last time interval is characterized as the previous one by a gentle tectonic activity. On the other hand, the Miocene sedimentation was totally controlled by the development of superficial thrusts and/or strike-slip faults zones, both related to the regional geodynamic evolutionary framework linked to the Mediterranean opening. These strike-slip faults zones created subsidence areas (pull-apart basin-type) and affected the sedimentation lying above the third unconformity. By contrast, the subsidence areas were bounded by structural highs affected by thrusts and folds. After the third unconformity, the Burdigalian-Serravallian sedimentation occurred mainly in shallow- to deep-water marine environments (Tap Fm). During the Late Miocene, after the fourth unconformity, the activation of the strike-slip faults zones caused a shallow marine environment sedimentation in the Murcia sector and a continental (lacustrine and fluvial) deposition in the Alicante sector represented the latter, resulting in alluvial fan deposits. Furthermore, the location of these fans changed over time according to the activation of faults responsible for the tectonic rising of Triassic salt deposits, which fed the fan themselves.

Keywords: eastern External Betic Zone; Cenozoic basins; strike-slip tectonics; tectono-sedimentary evolution

Geosciences 2020, 10, 394; doi:10.3390/geosciences10100394 www.mdpi.com/journal/geosciences Geosciences 2020, 10, 394 2 of 20

1. Introduction The study area is located in the Murcia and Alicante provinces of the SE Spain (Figure1A), whichGeosciences belong 2020 to the, 10, 394 eastern External Betic Zone (EBZ). This cordillera is included in the2 of 20 Alpine chains of the western Mediterranean (Figure1B), resulting from the continental collision of 1. Introduction the Mesomediterranean Microplate (MM) (Guerrera et al. [1]) at first with the Iberia-Europe Plate (Cretaceous-Paleogene:The study area is located Eo-Alpinein the Murcia phase),and Alicante and provinces subsequently, of the SE Spain (Miocene: (Figure 1A), Neo-Alpine which or Maghrebianbelong phase)to the eastern with theExternal Africa Betic Plate Zone and (EBZ). due This to thecordillera ocean is closures included drivenin the Alpine by oppositely chains of the oriented western Mediterranean (Figure 1B), resulting from the continental collision of the subductions [1–6]. These processes affected the western branches of the Tethys (Figure1C), generating Mesomediterranean Microplate (MM) (Guerrera et al. [1]) at first with the Iberia-Europe Plate Mesozoic(Cretaceous-Paleogene: to Tertiary successions Eo-Alpine related phase), to several and subs tectono-sedimentaryequently, (Miocene: Neo-Alpine domains [7 or]. TheMaghrebian development of a riftingphase) aff withecting the theAfrica South Plate Iberianand due Marginto the ocean generated closures basinsdriven by with oppositely alpine-like oriented platforms subductions (extended and wide,[1–6]. and These structured processes inaffected horsts the and western grabens), branches characterized of the Tethys by (Figure marine 1C), domains generating which Mesozoic are deeper from northto Tertiary to south, successions forming related the Prebetic to several (to tectono-sedimentary the north) and the Subbeticdomains [7]. (to theThe south)development of the of EBZ a [7–9]. Therifting deposition affecting the in South the Iberian Cenozoic Margin basins generate followedd basins with the alpine-like tectonic platforms inversion (extended (from extensionand to compression)wide, and structured occurring in horsts at theand grabens), latest Cretaceous, characterized beingby marine usually domains marked which are by deeper a generalized from north to south, forming the Prebetic (to the north) and the Subbetic (to the south) of the EBZ [7–9]. unconformity [10]. Sometimes, Paleogenic deposits show paleoenvironmental conditions similar to The deposition in the Cenozoic basins followed the tectonic inversion (from extension to those ofcompression) the Mesozoic occurring successions, at the latest and Cretaceous, sedimentation being usually is a continuation marked by a generalized of the former. unconformity In these cases, shallow[10]. water Sometimes, sediments Paleogenic deposited deposits above show the paleoenvironmental inherited structural conditions highs (horsts), similar to passing those of laterally the to deep realmsMesozoic (grabens). successions, In particular,and sedimentation the deep is a deposits continuation are characterizedof the former. In by these turbidite cases, depositsshallow with olisthostromewater sediments and slumps deposited on the above slope the and inherited more deepstructural areas highs [11 –(horsts),15]. passing laterally to deep Verarealms [16 ,(grabens).17] provided In particular, a general the frameworkdeep deposits of are the characterized Mesozoic toby Cenozoicturbidite deposits sedimentation with of the EBZ,olisthostrome dividing theand slumps stratigraphic on the sl recordope and intomore eight deep areas main [11–15]. sedimentary cycles. Recently, detailed Vera [16,17] provided a general framework of the Mesozoic to Cenozoic sedimentation of the multidisciplinary studies carried out in the eastern EBZ suggested the following remarks about EBZ, dividing the stratigraphic record into eight main sedimentary cycles. Recently, detailed the tectono-sedimentarymultidisciplinary studies evolution carried out of thein the area: eastern (1) EBZ the suggested definition the of following a new andremarks earlier about Paleogene the deformationtectono-sedimentary stage [15,18 ,19evolution], (2) the of Paleogenethe area: (1) deformation the definition was of relateda new and to the earlier Internal Paleogene Betic Zone (IBZ) tectonicsdeformation paleo-geographically stage [15,18,19], (2) the close Paleogene to the deformation IBZ, as proposed was related by Guerrerato the Internal et al. Betic [15 ],Zone Guerrera and Mart(IBZ)ín-Mart tectonicsín paleo-geographically [18] and Guerrera close et al. to [the19 ],IBZ, (3) as the proposed importance by Guerrera of strike-slip et al. [15], MioceneGuerrera fault systemsand [20 Martín-Martín,21] and (4) [18] the and influence Guerrera of et salt al. tectonics[19], (3) the also importance during theof strike-slip Miocene Miocene evolution fault [22 –24]. systems [20,21] and (4) the influence of salt tectonics also during the Miocene evolution [22–24]. Therefore, the knowledge of these Cenozoic basins has been considerably improved because these Therefore, the knowledge of these Cenozoic basins has been considerably improved because these paperspapers show show their their tectono-sedimentary tectono-sedimentary evolution. evolution.

FigureFigure 1. The 1. BeticThe Betic Cordillera Cordillera (after (after Reference Reference [[19];19]; modified). modiﬁed). (A) ( AGeological) Geological map mapof the of Betic the Betic CordilleraCordillera with thewith location the location of Cenozoicof Cenozoic Basins Basins of the the eastern eastern External External Betic Betic Zone Zone (EBZ) (EBZ) (study (study area), area), the Murcia (Figure 2) and Alicante (Figure 3) sectors. (B) Geographic location of the Betic Cordillera the Murcia (Figure2) and Alicante (Figure3) sectors. ( B) Geographic location of the Betic Cordillera in in the context of the western Mediterranean alpine chains. (C) Paleogeographic sketch of the western C the contextMediterranean of the western area during Mediterranean the Cretaceous. alpine chains. ( ) Paleogeographic sketch of the western Mediterranean area during the Cretaceous. Geosciences 2020, 10, 394 3 of 20

In short, the main aim of this paper is to present a review of the evolution of the Cenozoic basins in the eastern EBZ, considering previous reconstructions and the broad recent literature. In concrete, the considered area corresponds to the Pila-Carche sector (Figure 2) and the Alicante sector (Figure 3) in the Murcia and Alicante provinces, respectively. The review also aims to propose the considered Geosciencesstudied2020 sector, 10, 394as a key area for studies addressed to the tectono-sedimentary evolution of Cenozoic3 of 20 basins in the western Mediterranean chains

FigureFigure 2. 2.Geological Geological maps maps of of the the eastern eastern EBZ EBZ in in the the Murcia Murcia sector sector (after (after Reference Reference [20 [20];]; modiﬁed). modified). ( A) Detailed(A) Detailed geological geological map map of the of Pila-Carche the Pila-Carche area. area. (B) ( StructuralB) Structural sketch sketch map map of of the the Pila-Carche Pila-Carche area.area. Geosciences 2020, 10, 394 4 of 20 Geosciences 2020, 10, 394 4 of 20

Figure 3. Geological mapsmaps ofof thethe eastern eastern EBZ EBZ in in the the Alicante Alicante sector sector (after (after Reference Reference [21 ];[21]; modiﬁed). modified). (A) Detailed(A) Detailed geological geological map map of the of Alicantethe Alicante sector. sector. (B) Structural(B) Structural sketch sketch map map of the of Alicantethe Alicante sector. sector.

2. BackgroundIn short, the History main aim of this paper is to present a review of the evolution of the Cenozoic basins in the eastern EBZ, considering previous reconstructions and the broad recent literature. In concrete, The regional geological studies in the eastern Betics started at the end of the XIX century (e.g., the considered area corresponds to the Pila-Carche sector (Figure2) and the Alicante sector (Figure3) the authors of References [25–29] pointed out that this area belonged to the Prebetic-Subbetic in the Murcia and Alicante provinces, respectively. The review also aims to propose the considered transition of the eastern EBZ). Several geomorphological alignments (mountains), bounded by studied sector as a key area for studies addressed to the tectono-sedimentary evolution of Cenozoic Cenozoic basins, were signaled. These reliefs correspond with tectonic elements related to north- basins in the western Mediterranean chains vergent fold-thrust nappes, as indicated by Rodríguez-Estrella [30,31]. Other authors [32–39] have 2.also Background indicated that History the area was affected by several Miocene-Quaternary strike-slip fault systems. The previous authors have also pointed the occurrence of salt tectonics processes associated to the strike- The regional geological studies in the eastern Betics started at the end of the XIX century (e.g., slip faulting. the authors of References [25–29] pointed out that this area belonged to the Prebetic-Subbetic transition According to previous works [29–31], during the Jurassic, the Prebetic (external-most domain) of the eastern EBZ). Several geomorphological alignments (mountains), bounded by Cenozoic basins, constituted a distal shallow carbonate platform, while the Subbetic (internal-most domain) was were signaled. These reliefs correspond with tectonic elements related to north-vergent fold-thrust represented by a subsiding area, with deposition of deep-water pelagic marls. Later, during the nappes, as indicated by Rodríguez-Estrella [30,31]. Other authors [32–39] have also indicated that Cretaceous, deep realms were widespread both in Prebetic and Subbetic domains. The Cenozoic the area was aﬀected by several Miocene-Quaternary strike-slip fault systems. The previous authors shows a greater variety of sediments, which are marked by detritic supplies alternating with deep- have also pointed the occurrence of salt tectonics processes associated to the strike-slip faulting. or shallow-water deposits [16,29,40]. Many Neogene deformation phases were proposed [33]: According to previous works [29–31], during the Jurassic, the Prebetic (external-most domain) thrusting (Early Miocene), normal faulting (Middle Miocene) and development of strike-slip faulting constituted a distal shallow carbonate platform, while the Subbetic (internal-most domain) was (Late Miocene). Furthermore, studies concerning the Eocene platform areas were carried out by Geel represented by a subsiding area, with deposition of deep-water pelagic marls. Later, during [12,13] and Geel et al. [14]. Also, analyses on deeper marine sediments were developed by Roep and the Cretaceous, deep realms were widespread both in Prebetic and Subbetic domains. The Cenozoic Everts [11]. shows a greater variety of sediments, which are marked by detritic supplies alternating with deep- or More recently, specific papers concerning the tectono-sedimentary evolution of Cenozoic basins shallow-water deposits [16,29,40]. Many Neogene deformation phases were proposed [33]: thrusting in the eastern EBZ have been published. Guerrera et al. [15] and Guerrera and Martín-Martín [18] (Early Miocene), normal faulting (Middle Miocene) and development of strike-slip faulting (Late propose the Paleogene evolution of the Cenozoic Alicante Trough Basin characterized by a narrow Miocene). Furthermore, studies concerning the Eocene platform areas were carried out by Geel [12,13] shaped sedimentary basin with tectonically active margins located to the NNW in the Jijona-Elda and Geel et al. [14]. Also, analyses on deeper marine sediments were developed by Roep and Everts [11]. area (mainly functioning during the Eocene) and to the SSE in a position now under the More recently, speciﬁc papers concerning the tectono-sedimentary evolution of Cenozoic basins Mediterranean sea (during the Oligocene), respectively. The infilling of the Alicante Trough, which in the eastern EBZ have been published. Guerrera et al. [15] and Guerrera and Martín-Martín [18] is subdivided by two unconformities into two depositional sequences (Eocene p.p. and Oligocene p.p. propose the Paleogene evolution of the Cenozoic Alicante Trough Basin characterized by a narrow in age, respectively), pointed out “catastrophic” syn-sedimentary tectonic processes including shaped sedimentary basin with tectonically active margins located to the NNW in the Jijona-Elda area slumps, mega-olisthostromes, “pillow-beds” and turbidite deposits. Analyzing the Paleogene evolution of the Pila and Carche basins (EBZ, north of the Murcia province), Guerrera et al. [19] recognized several depositional sequences (defined Middle–Upper Geosciences 2020, 10, 394 5 of 20

(mainly functioning during the Eocene) and to the SSE in a position now under the Mediterranean sea (during the Oligocene), respectively. The infilling of the Alicante Trough, which is subdivided by two unconformities into two depositional sequences (Eocene p.p. and Oligocene p.p. in age, respectively), pointed out “catastrophic” syn-sedimentary tectonic processes including slumps, mega-olisthostromes, “pillow-beds” and turbidite deposits. Analyzing the Paleogene evolution of the Pila and Carche basins (EBZ, north of the Murcia province), Guerrera et al. [19] recognized several depositional sequences (defined Middle–Upper Maastrichtian, Upper Paleocene–Middle Eocene, and Oligocene–Lower Aquitanian in age) with associated slumps and olisthostromes that can justify a syn-sedimentary tectonic activity. Martín-Martín et al. [20] studied the Miocene evolution of the same area, and by means of a better chronostratigraphic resolution, proposed a more advanced reconstruction of the stratigraphic architecture. These studies detected the presence of two main depositional sequences (Upper Burdigalian–Upper Serravallian and Upper–Middle Tortonian in age) in the Pila and Carche Cenozoic basins. According to the lateral-vertical distribution of the lithofacies and the thicknesses of the stratigraphic formations, the migration of the foredeep has been better specified, highlighting a complex tectono-sedimentary evolution. The same authors (Martín-Martín et al. [21,22]) studying the Cenozoic basins in the Alicante province recognized that the Miocene-Quaternary shallow marine and continental infilling has been controlled by the evolution of several curvilinear faults involving salt tectonics. These authors also specified that the occurrence of Triassic shales and evaporites played a fundamental role in the tectonic evolution of the study area since the salt material flowed along faults, generating salt walls in root zones and salt push-up structures at the surface. In conclusion, the extensive information from the numerous previous studies, if taken as a whole, and analyzed and correlated, allow for synthesizing the tectono-sedimentary evolution of the Cenozoic basins of the eastern EBZ, evidencing its character of a key area.

3. Geological Setting The Mesozoic of the EBZ is classically subdivided into the following domains: (1) the Prebetic Domain, which represents the Jurassic platform realm, having stratigraphic continuity with the foreland (Iberian Massif), and (2) the southern and southeastern Subbetic Domain, representing a Jurassic deeper-water area subdivided into several sub-Domains (i.e., Internal, Median and External sub-Domains). Both domains are characterized by Triassic to Cenozoic deposits, progressively deformed from south to north with development of fold and nappes during the Middle–Late Miocene [16]. The presence of major unconformities led Vera [17] to deﬁne the occurrence of VIII Main Sedimentary Cycles in the EBZ (Figure2). The EBZ in the Murcia sector consists of SW–NE aligned structural highs (folds and thrusts), that separate irregular depressions, usually narrow strips (corridors), which during the Cenozoic, represented basinal areas (Figure2). Diﬀerently, the EBZ of the Alicante sector is characterized by a net of strike-slip fault systems (Figure3) roughly oriented as follows: N70E (Cadiz-Alicante Accident system), N155E and N120E. These faults, which were active from the Early–Middle Miocene onwards [21,22], are recognizable nowadays through the presence of outcrops of Triassic clays with gypsum. Neogene deposits also appear associated to subsiding areas linked to the strike-slip faulting [23,24]. Moreover, blocks with folded Mesozoic rocks are present. This structural system is related to a transpressive tectonic regime in the context of a compressive tectonics regional framework, established from the Middle Miocene onwards [21,22]. Nevertheless, the Cenozoic basins are now fragmented again into several blocks limited by main dextral faults (Figure3).

4. Stratigraphic Framework Previous studies on Cenozoic basins of the eastern EBZ [15,18–22] reconstructed a detailed stratigraphic framework of the Pila-Carche, Campello and Agost Cenozoic basins in the Murcia Geosciences 2020, 10, 394 6 of 20

(Figure2) and Alicante (Figure3) provinces. On the basis of these previous works, the reconstructed geological history allows for considering these basins as key areas, well representative of the Cenozoic evolutionary stratigraphic framework. The resulting data and the recognized main tectonic events can be extended to other areas of the eastern EBZ. The stratigraphy is shown in Figures4–7 and

Geosciencesthe description 2020, 10, is 394 synthesized in the following lines. 6 of 20

Figure 4. StratigraphicStratigraphic framework framework and and regional regional correlati correlationon of of the the Paleogene-Aquitanian Paleogene-Aquitanian sedimentary sedimentary suite in the the Pila-Carche Pila-Carche Basin Basin (Murcia (Murcia sector) sector) of of the the eastern eastern EBZ EBZ (after Reference [19]; [19]; modified). modiﬁed). Two Two sections are presentedpresented inin thethe SierraSierra de de El El Carche Carche (La (La Replana Replana and and Barranco Barranco Pardinas) Pardinas) and and six six sections sections in inthe the Sierra Sierra de de la Pilala Pila (Estaci (Estaciónón de de Blanca, Blanca, Barranco Barranco de de El Tollo,El Tollo, El Portillo,El Portillo, La GarrapachaLa Garrapacha and and Pista Pista del delMulo). Mulo). In the In correlation,the correlation, the main the main and secondaryand secondary sequence sequence boundaries boundaries (SB, Sb, (SB, respectively) Sb, respectively) are shown. are shown.Also, the Also, erosive the and erosive depositional and depositional gaps are mentioned. gaps are mentioned. In the right In part the of right the ﬁgure, part of the the transgressive figure, the transgressive(TR) or regressive (TR) (RE)or regressive trending are(RE) marked, trending and are also, marked, the correlation and also, the with correlation the standard with eustatic the standard curve. eustatic curve. Geosciences 2020, 10, 394 7 of 20 Geosciences 2020, 10, 394 7 of 20

Figure 5. StratigraphyStratigraphy and and lateral correla correlationtion of the Neogene successi successionon of the Pila-Carche Basin (Murcia sector)sector) in in the the eastern eastern EBZ EBZ (after (after Reference Reference [20 ];[20]; modified). modified). Two Two stratigraphic stratigraphic sections sections have have been reconstructedbeen reconstructed in the Sierrain the deSierra El Carche de El (BarrancoCarche (Barranco Pardinas Pardinas and Alberquilla) and Alberquilla) and four in and the Sierrafour in de the la PilaSierra (El de Buitre, la Pila Estaci (El Buitre,ón de Estación Blanca, Umbr de Blanca,ía de Moreno Umbría andde Moreno Pista del and Mulo). Pista The del correlationMulo). The highlightedcorrelation mainhighlighted and secondary main and sequence secondary boundaries sequence (SB, Sb,boundaries respectively). (SB, TheSb, erosiverespectively). and depositional The erosive gaps and are alsodepositional detected gaps together are withalso thedetected transgressive together (TR) with and the regressive transgressive (RE) trend(TR) and (separated regressive by a (RE) maximum trend flooding(separated surface). by a maximum A correlation flooding with surface). the standard A correlation eustatic with curve the is alsostandard shown eustatic in the curve right sideis also of theshown figure. in the right side of the figure. Geosciences 2020, 10, 394 8 of 20 Geosciences 2020, 10, 394 8 of 20

Figure 6. Stratigraphic columns and correlation of Paleogene-Aquitanian sediments of the Cenozoic Alicante Trough (Alicante(Alicante sector)sector) inin thethe easterneastern EBZEBZ (after(after ReferencesReferences [15[15,18];,18]; modiﬁed).modified). Three stratigraphic sections are representative for the We Westernstern Depositional Area of the Alicante Trough (Peñas Montesas,Montesas, Agost Agost and and Villafranqueza) Villafranqueza) and six an stratigraphicd six stratigraphic sections forsections the Eastern for Depositionalthe Eastern AreaDepositional of the same Area trough of the (Amadorio,same trough Busot, (Amadorio, Pantanet, Busot, Torre Pantanet, del Charco, Torre Playa del NudistaCharco, andPlaya Relleu). Nudista and Relleu). Geosciences 2020, 10, 394 9 of 20

Geosciences 2020, 10, 394 9 of 20

FigureFigure 7. Stratigraphic 7. Stratigraphic columns columns ofof thethe NeogeneNeogene stratigraphic stratigraphic units units of ofthe the Agost Agost Basin Basin (Alicante (Alicante province)province) of the of easternthe eastern EBZ EBZ (after (after Reference Reference [[22];22]; mo modified).dified). Four Four stratigraphic stratigraphic sections sections are presented are presented to characterize the succession of the Agost Basin. Two stratigraphic units (Serravallian p.p. and Upper to characterize the succession of the Agost Basin. Two stratigraphic units (Serravallian p.p. and Upper Miocene p.p. in age, respectively) were identified. Five isochronous lines are used for correlation Miocene p.p. in age, respectively) were identified. Five isochronous lines are used for correlation deduced from the geological map. The direction of the sediment supply is indicated by the blue deducedarrows, from while the geologicala synthetic column map. The is presented direction in of the the upper sediment left corner. supply is indicated by the blue arrows, while a synthetic column is presented in the upper left corner. 4.1. Murcia Sector (Cenozoic Pila-Carche Basin) 4.1. Murcia Sector (Cenozoic Pila-Carche Basin) The Upper Cretaceous stratigraphic succession (Figure 4) is represented by the following Theformations Upper (Fm): Cretaceous El Charche stratigraphic Fm and Quípar-Jorquera succession (Figure Fm 4(Lithofacies) is represented A: Figure by the 4), following which are formations made (Fm):of El limestones, Charche Fm marly and limestones Quípar-Jorquera and thin Fmbeds (Lithofacies of sandy marls A: Figure (neritic4 ),to which pelagic are environment), made of limestones, and marlyRaspay limestones Fm (Lithofacies and thin B: beds Figure of sandy4), which marls is made (neritic up toof pelagicsandy marls environment), and thin beds and of Raspay marly Fm (Lithofacieslimestones B: of Figure hemipelagic4), which environm is madeent. upA minor of sandy paraconformity marls and between thin beds this last of marlyformation limestones and the of hemipelagicunderlying environment. succession Awas minor detected paraconformity by means of between biostratigraphic this last formationanalysis with and theplanktonic underlying successionforaminifera. was detected by means of biostratigraphic analysis with planktonic foraminifera. Lithofacies C, D, K, N and M (Figure 4), corresponding to the Alberquilla and Garapacha fms Lithofacies C, D, K, N and M (Figure4), corresponding to the Alberquilla and Garapacha fms (Paleocene to Lower Ypresian), deposited above a main angular unconformity well controlled in the (Paleocene to Lower Ypresian), deposited above a main angular unconformity well controlled in field and with a gap affecting the Lower–Middle Paleocene, and checked in most of the examined the fieldsections. and withThese a units gap aareffecting characterized the Lower–Middle by limestone Paleocene,s, microcodites and and checked marls inwith most the ofpresence the examined of sections.slumps These and olistostromes units are characterized coming from by a carb limestones,onate platform microcodites and deposited and marlson the slope. with the presence of slumps andThe olistostromes Pinoso-Rasa Fm coming (Lower from Ypresian–Upper a carbonate Luteti platforman, defined and deposited as Lithofacies on the E, slope.Figure 4) has Thebeen Pinoso-Rasarecognized subdivided Fm (Lower into Ypresian–Upper two stratigraphic Lutetian, members defined(E1 and asE2), Lithofacies and deposited E, Figure above 4a) has been recognized subdivided into two stratigraphic members (E1 and E2), and deposited above a minor unconformity. This formation consists mainly of pelites, and channelized turbidite arenites, indicating a probable slope environment. Geosciences 2020, 10, 394 10 of 20

The Miñano Limestones Fm (Lithofacies F and J: Figure4), which is represented by nummulite-alveoline limestones (Middle–Upper Eocene), appears after a gradual transition. This unit indicates an internal carbonate platform sometimes affected by tectonic instability, resulting in the presence of syn-sedimentary folds. The top of the Paleogene sedimentation corresponds with the Murtas Fm (Lithofacies G: Figure4), which deposited above a main angular unconformity. This unit probably represents a transition from a marshy/beach/lagoon environment (yellowish marls and sands) to fluvial (continental red beds with conglomerates, sands, silts and clays) and lacustrine (whitish gastropod limestones) continental environments (Oligocene to Early Aquitanian). This formation clearly lies unconformably above the underlying formations, which are topped by an unconformity with a paleokarst surface well-recognized in several outcrops. The Miocene succession of the Pila-Carche Basin is represented by the Upper Burdigalian to Lower Langhian Congost Fm, and the Lower and Upper members of Tap Fm (Figure5). The Congost Fm unconformably (angular unconformity) overlies the Miñano and Murtas Fms and is subdivided into four lithofacies (C to F: Figure5), which are made up of a great variety of shallow-water marine deposits: calcarenites with thick beach laminations, marine platform biocalcarenites and marls and marls with biocalcarenites and recifal biostromes of external platform-upper slope. The formation gradually passes to the Lower member of the Tap Fm (Upper Langhian–Upper Serravallian), which is characterized by eight lithofacies ((G to K) Figure5). In fact, the unit displays these lithofacies: external platform algal biocalcarenites with marly intercalations, external platform to upper slope sandy marls and biocalcarenites, probably slope-related marls with intercalations of turbidite arenites, slumps and olisthostromes, and deep basin siliceous and diatomaceous marls. The Upper member of the Tap Fm (Middle Tortonian) lies above another paraconformity corresponding to a time gap of 3 Ma. This member is characterized by four lithofacies (O to R: Figure5) formed by deposits belonging to di fferent realms, from deep- to shallow-water marine environments: reworked Triassic included in olisthostromic deposits (slope), calcarenites (internal platform), diatomaceous silty sands and mudstones with diatomites (external platform). This unit is unconformably (angular unconformity) covered by the Pliocene-Quaternary succession (Lithofacies S, Figure5).

4.2. Alicante Sector (Cenozoic Alicante Trough and Agost Basin) Also, in this sector, the main unconformities observed in the previous sectors were recognized, but with some important differences. The Paleogene-Aquitanian succession (Figure6) studied in the Alicante Trough [15,18] allowed to define only informal stratigraphic units referable to the Eocene p.p. and Oligo-Aquitanian p.p. The first difference with respect to the Murcia sector consists in the absence of the Paleocene deposits (Alberquilla and Garapacha fms) and in the fact that the lower main unconformity is present at the base of the Eocene. The Eocene deposits are referable to an external platform environment located in the western part of the trough, and to a slope to deep basin in the eastern one. Furthermore, they can be correlated with the lithofacies of the Pila-Rasa Fm of the Murcia sector. Turbiditic arenites, slumps and olisthostromes are also well exposed in the eastern portion of the Alicante Trough. Another difference with respect to the Murcia sector is that the Upper Eocene deposits developed on the slope of a deep basin and are not related to a platform, as in the case of the Miñano Fm. The platforms are located northward, in continuity with the Iberian Massif [12–14] and since the turbidite deposits contain clasts of nummulites, these platforms constitute the most probable source areas for the Alicante Trough. After the second main unconformity, the Oligocene-Aquitanian succession is well represented, but in this sector, it indicates an external platform to slope marine environment; this is in contrast to the Murcia sector, where the corresponding deposits (Murtas Fm) are of continental environment. The main lithofacies are represented by turbidite arenites, olisthostromes, slumps and pillow-beds, Geosciences 2020, 10, 394 11 of 20 which are indicative of syn-sedimentary tectonic activity in the southern and south-eastern source areas [18]. The Burdigalian-Langhian Congost Fm and the Lower member (Upper Langhian–Upper Serravallian) and Upper member (Middle Tortonian) of the Tap Fm have not been recognized in the Alicante Trough. Instead, the two members of the Tap Fm are represented in the Agost Basin, where they correspond to four representative stratigraphic successions (Figure7)[ 21,22]. In this case, the whole succession was subdivided into two main stratigraphic units separated by an angular unconformity (corresponding to the previously mentioned fourth main unconformity recognized in the area), correlated with the Lower member and Upper member of the Tap Fm. The Lower Stratigraphic Unit (Serravallian p.p.) consists of marine deposits (Figure7), while the Upper Stratigraphic Unit (upper Miocene p.p.) is characterized by continental deposits (Figure7). Both the units are contemporary to a strike-slip tectonics involving salt deposits. The overlying sub-horizontal Pliocene deposits seal the previous deposits and all tectonic structures by a major angular unconformity (Figure7). The Lower Stratigraphic Unit of the Agost Basin (Figure7) is made up of three shallow marine lithofacies: (i) whitish marls and marly limestones (Lithofacies A, Figure7), (ii) calcarenitic beds with conglomerate intercalations (Lithofacies B, Figure7) and (iii) calcarenitic beds (Lithofacies C, Figure7). This succession indicates a relative sea-level fall (from open- to shallow-water, with restricted marine conditions) and shows a typical regressive evolution. This local reconstruction corresponds to the evolutionary trend recognized at the regional scale [22], which is related to a progressive shallowing of the environment towards the northern Prebetic sub-Domain and a consequent deepening to the W–SW, where several structural highs and deep areas occur. The Upper Stratigraphic Unit is more widespread and better preserved and is represented by five lithofacies (Figure7). In more detail, in the lower part: (i) blocks, conglomerates, arenites and whitish clays and silts (Lithofacies D, Figure7), which are referable to a continental foot-cli ff depositional environment, (ii) whitish clays and silts with local black layers (lignite), arenites and channelized conglomerate intercalations (Lithofacies E, Figure7), related to a fluvial and lacustrine realms, (iii) reddish conglomerates with blocks of Triassic gypsum (Lithofacies F, Figure7), arranged in a fan shape depositional geometry and interpreted as a progradational deposition of alluvial fan in a fluvial to lacustrine environment, (iv) pinkish clays and silts with occasional arenites and conglomerate intercalations (Lithofacies G, Figure7) arranged in a fan shape deposition of an alluvial realm and (v) progradational conglomerates with Cretaceous-Paleogene calcareous clasts and Triassic reddish clays (Lithofacies H, Figure7), arranged in a fan structure sealing some faults. In summary, this unit is related to a fluvial and lacustrine depositional system in the central area of the basin, and to alluvial fans and cliff deposits in the basinal margins. Alluvial fan and cliff sediments were deposited in different margins of the basin according to the order of succession of faults’ activation and development.

5. Tectono-Sedimentary Evolution of the Cenozoic Basins of the Eastern External Betic Zone

5.1. The Murcia Sector (Cenozoic Pila-Carche Basin) In the Cenozoic successions of these basins, the recognition of unconformity boundaries allows for subdividing the sedimentary record into four tectono-stratigraphic successions characterized by a diﬀerent temporal extension: (i) Upper Paleocene–Upper Eocene, (ii) Oligocene–Lower Aquitanian, (iii) Upper Burdigalian–Upper Serravallian and (iv) Upper Miocene p.p. (Figures8 and9). The whole stratigraphic record represents a geological cycle indicative of a regressive general trend and starting with a regressive phase (from hemipelagic to continental environments), then continuing with a second transgressive-regressive phase during the Middle to Late Miocene (Figures8 and9).

(i) The Upper Paleocene–Upper Eocene tectono-stratigraphic unit (Figure8) shows, after an initial transgression, a progressive shallowing upward marine trend. During the Paleocene to Early Eocene, the sedimentation (Alberquilla, Garapacha, Pinoso-Rasa fms) reﬂects a slope environment Geosciences 2020, 10, 394 12 of 20

(Miñano Fm). A main unconformity boundary in the Early Oligocene marks a stratigraphic gap also evidenced by a widespread paleokarst, pointing out an emersion of the basin. (ii) During the Oligocene (Murtas Fm), a transgression occurred with the development of marshy Geosciencesand2020 ,beach10, 394 lithofacies (Figure 8), followed by a new regressive depositional trend indicated by12 of 20 continental lacustrine and fluvial deposits during most of the Oligocene up to the Aquitanian. Thickness and areal distribution of lithofacies of this tectono-stratigraphic unit indicate a that evolved during the Middle–Late Eocene to a carbonate platform environment (Miñano Fm). subsidence area located between other uplifting ones (Figure 8). During the Paleogene-Aquitanian, A main unconformity boundary in the Early Oligocene marks a stratigraphic gap also evidenced the tectonic framework was characterized by a blind tectonics for the reactivation of old faults and theby presence a widespread of Jurassic-Cretaceous paleokarst, pointing blocks outaffected an emersion by folding of in the deep basin. levels. These tectonics caused (ii) differentialDuring the vertical Oligocene movements (Murtas generating Fm), a transgression areas affected occurredby subsid withence and the developmentother uplifting ofareas. marshy Theand thick beach marine lithofacies and transitional (Figure8), environment followed by sedimentation a new regressive is usually depositional followed trend by continental indicated by depositscontinental formed lacustrine in a condition and ﬂuvial of relative deposits subsidence. during Instead, most of the the uplifted Oligocene areas up are to highlighted the Aquitanian. by paleokarst surfaces and a thin continental cover.

FigureFigure 8. 8.Paleogene Paleogene tectono-sedimentary tectono-sedimentary evolution evolution of the of Pila-Carche the Pila-Carche Cenozoic Cenozoic Basin (Murcia Basin sector) (Murcia sector)of the of eastern the eastern EBZ EBZ(after (afterReference Reference [19]; modified). [19]; modified). (A) Paleogeographic (A) Paleogeographic sketch showing sketch a cross- showing a cross-sectionsection referable referable to the toLate the Ypressian-Early Late Ypressian-Early Lutetian interval, Lutetian (B interval,) paleogeographic (B) paleogeographic sketch showing sketch a cross-section referable to the Oligocene-Early Aquitanian interval, (C) paleogeographic sketch showing a cross-section referable to the Oligocene-Early Aquitanian interval, (C) paleogeographic showing a cross-section referable to the Triassic-Senonian interval, (D) paleogeographic sketch sketch showing a cross-section referable to the Triassic-Senonian interval, (D) paleogeographic sketch showing a cross-section referable to the Late Paleocene-Earliest Ypressian interval, (E) showing a cross-section referable to the Late Paleocene-Earliest Ypressian interval, (E) paleogeographic paleogeographic sketch showing a cross-section referable to the Early Miocene. sketch showing a cross-section referable to the Early Miocene. (iii) The Upper Burdigalian–Upper Serravallian tectono-stratigraphic unit (Pila-Carche Basin, Figure Thickness and areal distribution of lithofacies of this tectono-stratigraphic unit indicate 9) shows a transgressive-regressive trend. The transgression, which began in the Late a subsidenceBurdigalian, area located reaching between the Late other Langhian uplifting (Congost ones (FigureFm), results8). During younger the in Paleogene-Aquitanian, some sectors of the the tectonic framework was characterized by a blind tectonics for the reactivation of old faults and the presence of Jurassic-Cretaceous blocks affected by folding in deep levels. These tectonics caused differential vertical movements generating areas affected by subsidence and other uplifting areas. The thick marine and transitional environment sedimentation is usually followed by continental deposits formed in a condition of relative subsidence. Instead, the uplifted areas are highlighted by paleokarst surfaces and a thin continental cover.

(iii) The Upper Burdigalian–Upper Serravallian tectono-stratigraphic unit (Pila-Carche Basin, Figure9) shows a transgressive-regressive trend. The transgression, which began in the Late Burdigalian, Geosciences 2020, 10, 394 13 of 20

basins because of the onlap arrangement of transgressive deposits on the previous deformed succession. The evolution begins with an internal platform environment sedimentation, while during the Early Langhian, a mixed carbonate and terrigenous supply indicates an external platform to upper slope environment. Later, the Burdigalian upper Langhian Congost Fm passes laterally and upwards to the Lower member of the Tap Fm (Figure 9), and the presence of clastic deposits suggests a transition platform, slope and basinal environments, with an increase of terrigenous inputs. The Lower member of the Tap Fm is characterized by deeper marine lithofacies, showing a quartzarenitic supply. The deepest environment is also marked by Upper Langhian p.p. silexites. In turn, the presence of slumps implies the presence of a slope. Both silexites and slumps are considered to indicate a deepening phase occurring during Miocene. Compression, folding and lithostatic load related to the overlapping nappes resulted in the development of subsidence or uplifting areas, as shown by the increasing thicknesses of the Langhian-Serravallian successions. The fourth main unconformity is probably related to a new emersion at the beginning of the Geosciencescompressional2020, 10 thin-skinned, 394 tectonics and recorded by a marked stratigraphic gap (early Tortonian).13 of 20 (iv) The Middle Tortonian tectono-stratigraphic unit (Pila-Carche Basin) shows a new transgressive- regressivereaching the cycle Late (Upper Langhian member (Congost of the Fm), Tap results Fm). youngerAccording in someto the sectors sedimentological of the basins data, because the depositionalof the onlap environment arrangement of ofthis transgressive unit ranges be depositstween internal on the mixed previous (carbonate deformed and siliciclastic) succession. platformThe evolution to external begins platform. with an Reworked internal platformTriassic cl environmentays and gypsum sedimentation, (olisthostromes) while indicate during a depositionthe Early Langhian, on a slope a mixedrealm. carbonateIn this phase, and the terrigenous faulting supplyreached indicates the surface, an external generating platform thrusts to andupper strike-slip slope environment. faults and related features. The blocks between the faults were also folded and sometimes developed to form nappes.

Figure 9. Neogene tectono-sedimentary evolutionevolution of of the the Cenozoic Cenozoic Pila-Carche Pila-Carche Basin Basin (Murcia (Murcia sector) sector) in inthe the eastern eastern EBZ EBZ (after (after Reference Reference [20]; [20]; modiﬁed). modified). (A) Paleogeographic (A) Paleogeographic sketch sketch showing showing a cross-section a cross- sectionreferable referable to the Burdigalian-Langhian to the Burdigalian-Langhianp.p. interval, p.p. (B interval,) paleogeographic (B) paleogeographic sketch showing sketch a cross-section showing a cross-sectionreferable to the referable Langhian to thep.p. -SerravallianLanghian p.p. interval,-Serravallian (C) paleogeographic interval, (C) paleogeographic sketch showing sketch a cross-section showing areferable cross-section to the referable Middle Tortonian,to the Middle (D )Tortonian, paleogeographic (D) paleogeographic sketch showing sketch a cross-section showing a cross-section referable to referablethe Late Tortonian. to the Late Tortonian.

Later, the Burdigalian upper Langhian Congost Fm passes laterally and upwards to the Lower member of the Tap Fm (Figure9), and the presence of clastic deposits suggests a transition platform, slope and basinal environments, with an increase of terrigenous inputs. The Lower member of the Tap Fm is characterized by deeper marine lithofacies, showing a quartzarenitic supply. The deepest environment is also marked by Upper Langhian p.p. silexites. In turn, the presence of slumps implies the presence of a slope. Both silexites and slumps are considered to indicate a deepening phase occurring during Miocene. Compression, folding and lithostatic load related to the overlapping nappes resulted in the development of subsidence or uplifting areas, as shown by the increasing thicknesses of the Langhian-Serravallian successions. The fourth main unconformity is probably related to a new emersion at the beginning of the compressional thin-skinned tectonics and recorded by a marked stratigraphic gap (early Tortonian).

(iv) The Middle Tortonian tectono-stratigraphic unit (Pila-Carche Basin) shows a new transgressive-regressive cycle (Upper member of the Tap Fm). According to the sedimentological data, the depositional environment of this unit ranges between internal mixed (carbonate and siliciclastic) platform to external platform. Reworked Triassic clays and gypsum (olisthostromes) indicate a deposition on a slope realm. In this phase, the faulting reached the surface, generating thrusts and strike-slip faults and related features. The blocks between the faults were also folded and sometimes developed to form nappes. Geosciences 2020, 10, 394 14 of 20

5.2. Alicante Sector (Cenozoic Alicante Trough and Agost Basin) The Paleogene deposition of the Alicante Trough shows a clear regressive trend from a slope environment (Eocene) to a shelf environment (Oligocene-Aquitanian), accompanied by an increase of tectofacies upwards. During the Eocene, turbidite arenites and slumps coming from the western– northwestern area and showing a transgressive trend, deposited. Oligocene–Lower Aquitanian slumps, olisthostromes, mega-olisthostromes and pillow-beds (coming from the eastern– southeastern area) are instead arranged to show a regressive-transgressive-regressive trend. During the Paleogene, the Alicante Trough (Figure 10) is a subsidence area bounded by two northwestern and southeastern margins related to the Prebetic Zone and External Subbetic Geosciencessubdomain,2020 respectively, 10, 394 [15]. 14 of 20 During the Eocene (Figure 10), the sedimentation of this trough was mainly influenced by the western5.2. Alicante or northwestern Sector (Cenozoic Prebetic Alicante margin, Trough and by Agost an in Basin)cipient tectonic instability that gave rise to turbidites associated with hemipelagic deposits, arranged in triplet para-sequences. This Eocene sedimentationThe Paleogene is correlated deposition with the of Pila-Rasa the Alicante Fm (M Troughurcia sector). shows In a contrast, clear regressive during the trend Oligocene from anda slope up to environment Early Aquitanian (Eocene) (Figure to a 10), shelf the environment basin was mainly (Oligocene-Aquitanian), influenced by the opposite accompanied margin, by locatedan increase southeastwards of tectofacies (Subbetic upwards. substratum). During the Eocene,In this case, turbidite the sedimentation arenites and slumps is related coming to marine from realms,the western–northwestern differently with respect area to and the showing continental a transgressive environments trend, of the deposited. Murtas Fm Oligocene–Lower (Murcia sector). AquitanianThe lithofacies slumps, association olisthostromes, (marls with slumps, mega-olisthostromes olistostromes, mega-olistostromes and pillow-beds and (coming pillow-beds) from indicatesthe eastern–southeastern the dismantling area) of are a insteadplatform, arranged also by to showmeans a regressive-transgressive-regressive of paleocurrents, and the west- trend. or northwestwards-facingDuring the Paleogene, of slumps, the Alicante from which Trough a tectonic (Figure 10activity) is a subsidenceof the margin area is deduced. bounded Pillow- by two beds,northwestern which are and structures southeastern interpre marginsted as related seismites to the as Prebetic a result Zone of high-magnitude and External Subbetic earthquakes subdomain, [11], favoredrespectively the construction [15]. of submarine fan systems.

Figure 10. Eocene and Oligo-Aquitanian tectono-sedime tectono-sedimentaryntary evolution evolution of th thee Cenozoic Alicante Trough and neighbor areas (Alicante province) of the eastern EBZ (after Reference [18]; [18]; modified). modiﬁed). Paleogeographic sketchsketch showing showing a cross-sectiona cross-section referable referable tothe to Oligo-Aquitanianthe Oligo-Aquitanian interval, interval, in the inlower the partlower, and part to, and the Eocene,to the Eocene, in the upperin the upper part. part.

During the the Miocene, Eocene (Figure the Congost 10), the Fm sedimentation is not represented of this but trough the Tap was Fm mainlyis recognizable influenced in the by Alicantethe western sector. or northwesternIn any case, the Prebetic Cenozoic margin, basins by evolved an incipient in a different tectonic way instability in the Alicante that gave region rise to turbidites associated with hemipelagic deposits, arranged in triplet para-sequences. This Eocene sedimentation is correlated with the Pila-Rasa Fm (Murcia sector). In contrast, during the Oligocene and up to Early Aquitanian (Figure 10), the basin was mainly influenced by the opposite margin, located southeastwards (Subbetic substratum). In this case, the sedimentation is related to marine realms, differently with respect to the continental environments of the Murtas Fm (Murcia sector). The lithofacies association (marls with slumps, olistostromes, mega-olistostromes and pillow-beds) indicates the dismantling of a platform, also by means of paleocurrents, and the west- or northwestwards-facing of slumps, from which a tectonic activity of the margin is deduced. Pillow-beds, which are structures interpreted as seismites as a result of high-magnitude earthquakes [11], favored the construction of submarine fan systems. Geosciences 2020, 10, 394 15 of 20

During the Miocene, the Congost Fm is not represented but the Tap Fm is recognizable in Geosciences 2020, 10, 394 15 of 20 the Alicante sector. In any case, the Cenozoic basins evolved in a diﬀerent way in the Alicante region (Agost Basin, Figure 1111).). In In this region, fault bendsbends acted as transtensive dextral strike-slip systems delimiting pull-apart-like basins with shallow marine and continental deposits. The reorientation of the main regional stress caused changes in the kine kinematicsmatics of the strike-slip faults, which evolved as reverse (compressive) (compressive) faults faults at at first, ﬁrst, and and as as sinistral sinistral (transpressive) (transpressive) faults faults later later (Figure (Figure 10). 10 During). During the transtensivethe transtensive phase, phase, the Triassic the Triassic salt saltrisen risen from from a deep a deep stratigraphic stratigraphic level level tended tended to escape to escape to the to surfacethe surface as salt as saltwalls walls to be to eroded be eroded and anddeposited deposited as alluvial as alluvial fan fanin the in thebasins. basins. The Thedeposition deposition of the of alluvialthe alluvial fans fans changed changed its itsposition position over over time, time, wi withth these these depositional depositional systems systems being being progressively progressively replaced by others according to the displacement of the active faults.faults.

Figure 11.11. NeogeneNeogene tectono-sedimentary tectono-sedimentary evolution evolution of theof th Agoste Agost Basin Basin (Alicante (Alicante province) province) of the easternof the easternEBZ (after EBZ Reference (after Reference [21]; modiﬁed). [21]; modified). The main regionalThe main stress, regional motion stress, of blocks, motion faults’ of blocks, actuation faults’ and actuationmain terrigenous and main supply terrigenous is represented. supply (Ais )represented. paleogeographic (A) paleogeographic sketch map and section sketch of map the Serravallian,and section of(B ,theC,D Serravallian,) paleogeographic (B,C,D sketch) paleogeographic maps and sections sketch ofmaps the Lateand sections Miocene. of the Late Miocene.

Geosciences 2020, 10, 394 16 of 20 Geosciences 2020, 10, 394 16 of 20

6. Discussion and Conclusions The Cenozoic basins of the eastern EBZ were located over a Mesozoic sedimentary substratum after thethe tectonictectonic inversion inversion (from (from extensional extensional to compressional) to compressional) occurring occurring at the at latest the Cretaceouslatest Cretaceous [15,18]. These[15,18]. basins These were basins subsidence were subsid areasence nourished areas nourished by located by nearby located structural nearby heights.structural Some heights. diﬀerences Some indifferences the sedimentary in the sedimentary record observed record in observed these basins in th canese bebasins summarized can be summariz as follows:ed as (1) follows: The Paleocene (1) The depositsPaleocene are deposits not present are not in thepresent Alicante in the sector Alicante where sector they arewhere replaced they byare a replaced marked unconformity,by a marked locatedunconformity, at the baselocated of the at Eocene;the base in of the the Murcia Eocene sector,; in thethe gravitationalMurcia sector, slope the environment gravitational related slope toenvironment the Paleocene related deposits to the Paleocene are well represented. deposits are we (2)ll Therepresented. deeper Eocene(2) The depositsdeeper Eocene recognized deposits in therecognized Alicante in sector the Alicante (external sector platform, (external slope plat andform, deep slope basin and environment) deep basin environment) are in contrast are with in thecontrast Middle–Upper with the Middle–Upper Eocene shallow-water Eocene shallow-wate marine onesr marine (internal ones platform) (internal of platform) the Murcia of the sector. Murcia (3) Thesector. Oligocene-Aquitanian (3) The Oligocene-Aquitanian deposits are deposits related are to arelated continental to a continental environment environment and are very and reduced are very in thereduced Murcia in sector,the Murcia while sector, they are while well representedthey are well in therepresented Alicante sectorin the where Alicante they sector indicate where an initial they marineindicate external an initial platform marine environment,external platform which environment, passes to a slopewhich environment. passes to a slope environment. In bothboth areas,areas, terrigenous terrigenous supplies supplies have have been been supplied supplied from from the activethe active basinal basinal margins, margins, in the in Early the PaleogeneEarly Paleogene from the from northwestern the northwestern area and area in the an Lated in Paleogene-Aquitanian the Late Paleogene-Aquitanian from the southeastern from the area.southeastern In these area. successions, In these turbidites,successions, olistostromes, turbidites, olistostromes, slumps and pillow-bedsslumps and pillow-beds have been interpreted have been asinterpreted indicative as of anindicative early tectonic of an activity early (Guerreratectonic activity and Mart (Guerreraín-Martín [and18]). Martín-Martín A progressive eastward[18]). A reductionprogressive of subdomaineastward reduction areas in the of EBZsubdomain has been areas interpreted in the EBZ as due has to been the action interpreted of the Cadiz-Alicante as due to the strike-slipaction of the fault Cadiz-Alicante zone [35] from strike-slip the Lower–Middle fault zone [35] Miocene from the onwards. Lower–Middle Nevertheless, Miocene according onwards. to GuerreraNevertheless, et al. according [15] and Guerrerato Guerrera and et Martal. [15]ín-Mart and Guerreraín [18], this and progressive Martín-Martín sub-domain’s [18], this progressive reduction shouldsub-domain’s be older reduction and related should to the transformbe older and fault related responsible to the for transform the Internal–External fault responsible Zone Boundary for the tectonicInternal–External contact (References Zone Boundary [1,5,6], tectonic and references contact (R therein),eferences which [1,5,6], is related and references to the collision therein), between which theis related Mesomediterranean to the collision Microplatebetween the (MM) Mesomedi and theterranean EBZ (Figure Microplate 12A). (MM) In our and opinion, the EBZ the (Figure early and12A). local In our tectonic opinion, activity the early recorded and local in tectonic the eastern activity EBZ recorded is probably in the due eastern to theEBZ paleogeographic is probably due positionto the paleogeographic of the eastern position EBZ located of the very eastern close EBZ to thelocated IBZ very during close this to period. the IBZ Thisduring activity this period. could explainThis activity the dismantling could explain of the the External dismantling Subbetics of th duringe External the Oligocene–EarlySubbetics during Aquitanian, the Oligocene–Early since this sub-DomainAquitanian, since was the this most sub-Domain internal Subbetic was the one,most located internal close Subbetic to the MMone, andloca separatedted close to with the respectMM and to theseparated latter by with the respect mentioned to the active latter transform by the mentioned fault. active transform fault.

Figure 12. GeneralGeneral geodynamic geodynamic framework framework of the of theeastern eastern EBZ EBZ in the in context the context of the of western the western peri- peri-MediterraneanMediterranean alpine alpine chains. chains. (A) geodynamic (A) geodynamic interpretation interpretation of the western of the Tethys western during Tethys the Eocene during (afterthe Eocene Reference (after [19], Reference modified), [19 ],(B modified),) geodynamic (B )framework geodynamic of frameworkthe central-western of the central-westernMediterranean areaMediterranean during the Miocene area during (modified the Miocene from Reference (modified [20]), from (C) Referencesynthetic columns [20]), (C of) the synthetic Cenozoic columns Bains inof the the Murcia Cenozoic and Bains Alicante in thesectors Murcia of the and easter Alicanten EBZ sectors(after Guerrera of the easternet al. [19], EBZ modified) (after Guerrera et al. [19], modified) The Miocene deposits (Congost and Tap fms) are absent in the Alicante Trough but the Lower and UpperThe Miocene Members deposits of the (Congost Tap Fm andare Taprecognizable fms) are absent in the inAgost the Alicante Basin [21,22]. Trough During but the the Lower Middle and UpperMiocene, Members the EBZ of was the affected Tap Fm areby recognizablea net of strike-s inlip the fault-related Agost Basin [bend21,22 zone]. Durings experiencing the Middle kinematic Miocene, thechanges EBZ wasover atimeffected from by a a transtensive net of strike-slip dextral fault-related to a transpressive bend zones sinistral experiencing one, according kinematic to the changes main overregional time stress. from aSubsidence transtensive areas dextral delimited to a transpressive by fault traces sinistral andone, folded according structural to the highs main were regional also developed and the fault traces, usually present as Triassic salty materials, were injected. During the Late Miocene, this salty material was eroded and redeposited during the construction of the alluvial Geosciences 2020, 10, 394 17 of 20 stress. Subsidence areas delimited by fault traces and folded structural highs were also developed and the fault traces, usually present as Triassic salty materials, were injected. During the Late Miocene, this salty material was eroded and redeposited during the construction of the alluvial fans, which occurs in relation to and under the control of the strike-slip fault zones movement. This tectonic activity, and related bends of strike-slip faults, should be connected with the regional framework characterized by the Mediterranean opening (Figure 12B) and the westward migration of the Internal Betic Zone (the previous MM) by means of a transform fault. In the sedimentary record of the Cenozoic basins (eastern EBZ), the following four main unconformities are recognizable (Figure 12C): (1) at the Cretaceous-Paleogene boundary (angular unconformity), recorded at the K/Paleocene boundary (with a related Danian gap) in the Murcia sector, and at the K/Eocene boundary (with a gap covering the entire Paleocene) in the Alicante sector, (2) at the Eocene-Oligocene boundary (with an angular unconformity, a paleokarst surface and a stratigraphic gap corresponding to the Bartonian-Priabonian and the Rupelian p.p.). This unconformity is quite synchronous in the whole area. (3) In the Burdigalian (with an angular unconformity and a stratigraphic gap corresponding to the Late Aquitanian–Early Burdigalian), this unconformity is also quite synchronous, and (4) in the Late Miocene (Lower/Middle Tortonian) and recorded in the whole eastern EBZ as a paraconformity with a gap affecting the Serravallian p.p. and the Early Tortonian. The detected unconformities delimitate the following depositional sequences: (1) the Paleocene p.p.–Late Eocene p.p., showing a transgressive-regressive trend with a maximum flooding surface at the Paleocene/Eocene boundary, (2) the Oligocene p.p.–Aquitanian p.p., showing a transgressive-regressive trend but with a too-reduced sedimentation to deduce anything more, (3) the Burdigalian p.p.–Serravallian p.p., showing a transgressive-regressive trend with a maximum flooding surface at the latest Langhian and (4) the Middle Tortonian p.p., showing a transgressive-regressive trend but with a too-reduced sedimentation to deduce anything more. The comparison among unconformities and trend evolution of the depositional sequences with the standard eustatic curves (Figures4 and5) allow some important constraints: (1) the Paleocene transgression corresponds with an eustatic lowering (Figure4) because the evolution should be tectonically controlled, (2) the Eocene/Oligocene boundary unconformity is well correlated with an eustatic lowering (Figure4) and the Oligocene-Aquitanian depositional sequence can be explained as caused by an eustatic phenomenon, (3) the Langhian transgressive trend corresponds with several transgressive-regressive variations in the eustatic curve (Figure5), so that it should be controlled by tectonics and (4) the transgressive-regressive trend of the Middle Tortonian p.p. depositional sequence corresponds with a stand in the eustatic curve (Figure5) that should be explained by tectonics. In short, depositional sequences and unconformities partially match with the sedimentary cycles and cycle boundaries of the EBZ proposed by Vera [16,17]. So, the K/T unconformity marks the beginning of the Cycle VI and the intra-Burdigalian boundary unconformity indicates the beginning of the Cycle VII. Nevertheless, two new unconformities have been described before dividing in turn the Cycles VI (at the Eocene/Oligocene boundary) and VII (Lower/Middle Tortonian). These two new unconformities add more detail to the reconstruction of the stratigraphic architecture of the Cenozoic basins of the EBZ. Cenozoic basins started to develop over the Mesozoic basement after the first main unconformity. The Paleocene-Eocene slope and deep basin deposition is characterized by numerous sedimentary inputs consisting of turbidites, slumps, olisthostromes, mega-olistostromes and by pillow-beds, which point out early blind (deep-seated) tectonics acting mainly in the most internal subdomains of the EBZ and related to the geodynamic evolution of the western-most Tethys. The second unconformity leads to a shallowing during the Oligocene to Aquitanian marked by a shallow-water marine sedimentation in the Alicante sector, and even a continental deposition in the Murcia sector. In this latter period, tectonic conditions were similar to those of the previous period. Differently, the Miocene sedimentation was controlled by the development of superficial thrusts and/or bends on strike-slip faults, with all these structures being related to the geodynamic evolution linked to the Mediterranean opening. Geosciences 2020, 10, 394 18 of 20

Thrusts and bends on strike-slip faults created subsidence areas (pull-apart basin-like), which created accommodation for successive sediments that deposited after the above-mentioned unconformity (3). Subsiding areas were bounded by structural highs aﬀected by thrusts and folds. So, after the third unconformity, the sedimentation of these latest basins was mainly made by marine shallow-water to deep sediments (Lower member of Tap Fm) from Burdigalian to Serravallian. After the unconformity (4), during the Late Miocene (Tortonian), the bend development along strike-slip faults caused salt tectonic processes and the presence of shallow-water marine basins characterized by the Upper member of the Tap Fm (Murcia sector), or by continental (lacustrine and ﬂuvial) deposition with alluvial fans in the Alicante sector. These alluvial fans were changing their position over time following the fault development, being mainly fed from fault-controlled rising of the Triassic material.

Author Contributions: All the authors (M.M.-M., F.G. and M.T.) contributed to the different parts of the article. All authors have read and agreed to the published version of the manuscript. Funding: Research supported by: Research Project CGL2016-75679-P, Spanish Ministry of Education and Science; Research Groups, Projects of the Generalitat Valenciana, Alicante University (CTMA-IGA); University of Urbino Carlo Bo (funds to M.T.). Acknowledgments: Authors wish to acknowledge two anonymous reviewers for useful comments and suggestions. Conflicts of Interest: The authors declare no conflict of interest.

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