ELSEVIER Sedimentary Geology 129 (1999) 71–84

A review of polyphase karstification in extensional tectonic regimes:Jurassic and Cretaceous examples, Betic Cordillera, southern Spain

J.M. Molina a,Ł, P.A. Ruiz-Ortiz a, J.A. Vera b

a Departamento de Geologıa, Facultad de Ciencias Experimentales, Universidad, 23071 Jaen, Spainb Departamento de Estratigrafıa y Paleontologıa, Facultad de Ciencias, Universidad, 18071 Granada, Spain

Received 2 December 1998; accepted 26 July 1999

Abstract

Five karstification phases are recognized and analysed in the Mesozoic carbonate sequences of the External andInternal Subbetic (Betic Cordilleras, southern Spain). These phases are related to important stratigraphic discontinuitiesin the following ages: (1) Intra-Carixian, (2) Early–Middle Jurassic boundary, (3) late Bathonian–early Callovian, (4)Intra-Kimmeridgian, and (6) late Albian. The importance of each karstification phase is variable according to the region.Moreover, not all the karstic phases occur in every area, although in some places several phases may be superimposed,appearing as discrete palaeokarst features or overprinting earlier ones. In the case of polyphase karstification eachsuccessive karstic process modified earlier features and was also conditioned by them. This interdependence complicatesany attempt to isolate the individual karst events. The interpretation of the genetic history of the palaeokarst as a whole,therefore, requires the integration of data from different outcrops, where they need to be particularly well exposed. This isthe only way to arrive at an accurate hypothesis. The five described palaeokarst phases are closely related to the riftingevolution of the Southern Iberian palaeomargin. They coincide with episodes of sudden sea-level fall in the External andInternal Subbetic caused by local tectonic events, commonly involving block-tilting related to the movement of listric faultsdiffering in magnitude in each palaeogeographic–palaeotectonic range, and eustatic sea-level changes. 1999 ElsevierScience B.V. All rights reserved.

Keywords: palaeokarst; listric faults; tilted blocks; Mesozoic; Subbetic

1. Introduction

The term karst has been used to designate specificlandforms (including subterranean, coastal, and sub-marine landforms) that result mainly from the disso-lution of certain types of rocks, and any geographicregion characterized by such landforms. Karst alsoconstitutes a distinctive ‘diagenetic facies’ (Esteban

Ł Corresponding author. Fax: C34 953 212141;E-mail: jmmolina@ujaen.es

and Klappa, 1983). There are many definitions, termsand concepts in relation to karst, which can occurin: (1) terrestrial environments away from coastalinfluences, (2) coastal-subaerial environments (seaor lake), (3) beneath the sea, in some cases manymetres below the coastal-exposure zone (submarinekarst), and (4) hydrothermal environments (Esteban,1991).

Palaeokarst refers to karstic (dissolution-related)features formed in the past, related to an earlier hy-drological system or landsurface (Wright and Smart,

0037-0738/99/$ – see front matter 1999 Elsevier Science B.V. All rights reserved.PII: S 0 0 3 7 - 0 7 3 8 ( 9 9 ) 0 0 0 8 9 - 5

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1994). Broadly speaking three types of palaeokarstare recognised: relict, exhumed, and buried. Asspecial cases of buried subsurface palaeokarst, in-terstratal and subjacent types can be differentiated(Wright, 1982).

There is a vast amount of literature on karst,palaeokarst and related subjects. Most of it empha-sizes karst geomorphology, hydrology or speleology.Some of the most noteworthy studies on karst andpalaeokarst over the last 20 years include the booksand papers of Bogli (1980), Esteban and Klappa(1983), James and Choquette (1984), Paterson andSweeting (1986), Jennings (1987), James and Cho-quette (1988), White (1988), Ford and Williams(1989), Bosak et al. (1989), Wright et al. (1991) andWright and Smart (1994).

Whenever carbonate platforms are subaerially ex-posed, karst development occurs, since karst fea-tures can develop very rapidly, even as depositioncontinues. This phenomenon is called syngenetickarst (Jennings, 1987). Many carbonate sequencesrecord not just one, but multiple phases of karstifi-cation (polyphase palaeokarst), and their history cantherefore be difficult to interpret. Moreover, somepolyphase karst may result in discrete palaeokarstfeatures, whereas others overprint earlier stages.The simplest case of polyphase karst results frommultiple changes in sea-level, and produces stackedkarst systems (Wright, 1991). In some circumstancespalaeokarst develops on an unconformity that mayinfluence later subjacent karstification. The term‘legacy karstification’ refers to dissolution occur-ring in the present or past whose distribution iscontrolled by an earlier palaeokarst system (Wright,1991). Another simple case occurs when a land-scape is undergoing erosion and an earlier phreaticsubsurface karst is emplaced in the vadose zone. Itmay be more realistic to consider the reverse situ-ation for many ancient carbonate sequences, wherephreatic, subsurface karst may overprint earlier va-dose karst (Wright, 1991). The situation can be evenmore complex in carbonate sequences exposed eitherto prolonged continuous exposure, or to complexburial and erosional histories in long-term polyphasekarstification. Not all karst phases occur in all areas,and these gaps are a common feature of regionalpolyphase karstification.

Successful identification of palaeokarst in out-

crops and cores has important implications for se-quence stratigraphy, palaeoenvironmental interpre-tation and hydrocarbon reservoirs. The very highporosity and permeability of karst areas, and theimportance of palaeokarst processes in the develop-ment of porosity is therefore becoming increasinglywidely appreciated (Mylroie and Carew, 1995).

In this paper we present a synthesis of the mainpalaeokarst features, their genetic interpretation, anda palaeokarst system model for the Jurassic andCretaceous of the Subbetic Zone (Betic Cordilleras,southern Spain).

Mesozoic palaeokarsts have been analysed in nu-merous previous works dealing with various aspectsof the regional stratigraphy or sedimentology of theSubbetic Zone (including the Penibetic) (Seyfried,1978, 1979, 1981; Busnardo, 1979; Garcıa-Hernan-dez et al., 1979; Dabrio and Polo, 1985; Molina etal., 1985; Ruiz-Ortiz et al., 1985; Martın-Algarra,1987; Molina, 1987; Vera et al., 1989; Rey, 1993;Nieto, 1997), or in monographs (Vera et al., 1988;Martın-Algarra et al., 1989; Martın-Algarra andVera, 1996). Some studies have focused, however,on palaeokarst and related features such as baux-ites (Vera et al., 1986; Molina, 1991; Molina etal., 1991), calcretes and speleothems (Jimenez deCisneros et al., 1990, 1991, 1993; Molina et al.,1992), and neptunian dykes and other related aspectsof the associated discontinuities (Company et al.,1982; Gonzalez-Donoso et al., 1983; Martın-Algarraet al., 1983; Vera et al., 1984; Garcıa-Hernandez etal., 1986a,b, 1988a,b; Molina et al., 1989; Vera etal., 1989; Castro et al., 1990; Martın-Algarra andCheca, 1990; Ruiz-Ortiz et al., 1990, 1997; Cas-tro and Ruiz-Ortiz, 1991; Vera and Martın-Algarra,1994; Martın-Algarra and Vera, 1995; Molina et al.,1995).

Our methodology in this study basically coincideswith the unconformity-palaeokarst analysis proposedby Esteban (1991) and it has mainly involved thefollowing aspects of the palaeokarst unconformitiesat the regional and local scales: (a) unconformitymapping; (b) analysis of exposure profiles; (c) inter-pretation of exposure environments; and (d) analysisof underlying and overlying rocks to recognize im-mediately pre- and post-unconformity events. It isimportant to note that, mainly due to the stronglyerosional nature of the analysed unconformities, the

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exposure facies and profiles may be reworked ordestroyed, which considerably complicates the re-construction of palaeoenvironments and necessitatesthe use of indirect methods.

In the identification of exposure surfaces we havecompared the rock fabrics within their sequential andregional stratigraphic context, primarily since veryfew rock fabrics can be considered diagnostic of thedifferent subaerial exposure facies and environmentsin themselves (Esteban and Klappa, 1983; James andChoquette, 1988).

2. Geological and stratigraphic setting

The Subbetic Zone is one of the main palaeogeo-graphic realms of the External Zones of the BeticCordillera of southern Spain (Fig. 1). Jurassic sedi-mentation in the Subbetic began with shallow-marinecarbonate deposition (Gavilan Formation). Duringthe middle Liassic (Carixian), the carbonate shelfbegan to break up and founder, resulting in predom-inantly pelagic sedimentation (Garcıa-Hernandez etal., 1980) similar to that which occurred in otherareas exposed in the Alpine Mediterranean ranges(Bernoulli and Jenkyns, 1974). This Carixian eventhas been interpreted as the initiation of the ‘mainintracontinental rifting stage’ in the South Iberiancontinental palaeomargin in the westernmost end of

Fig. 1. Geological map of the Betic Cordilleras showing the main areas (External and Internal Subbetic) where Jurassic and Cretaceouskarstification phases appear.

the European margin of the Tethys (Garcıa-Hernan-dez et al., 1986a; Vera, 1999). During the rest of theJurassic and Cretaceous, the Subbetic was a pelagicbasin that underwent marked differential subsidence,resulting in troughs and swells. Three realms formedas a result of this palaeogeographic differentiation(Fig. 1). The realms to the north and south (Exter-nal and Internal Subbetic, respectively) were mainlypelagic swells during the Middle and Late Jurassicand were covered by red, nodular pelagic limestoneswith ammonites (‘Ammonitico Rosso’ facies) andcondensed sequences. The third realm (Median Sub-betic) was a trough, and received deposits of marls,radiolarian marls, and limestones intercalated withsubmarine volcanic and subvolcanic rocks (Garcıa-Hernandez et al., 1980).

The stratigraphic discontinuities in the Jurassicand Cretaceous sedimentary rocks of the Subbetichave been recognized and characterized by detailedstratigraphic analyses over the last two decades(Vera et al., 1984, 1988; Garcıa-Hernandez et al.,1989; Ruiz-Ortiz et al., 1997). The palaeokarst ex-amples presented here are associated with five im-portant stratigraphic breaks recognized in differentparts of the External and Internal Subbetic. The first(Intra-Carixian) corresponds to the breakup of theextensive Liassic carbonate shelf, accompanied bylocal episodes of emergence and karstification ofthe shallow-marine limestones (Gavilan Formation).

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The second break is a discontinuity of Early–MiddleJurassic age developed at the top of a shallowing-upward sequence on some of the sedimentary swells(Molina et al., 1985; Molina, 1987), in some placesoverprinting the features of the first karst event.The third event occurred in the late Bathonian–earlyCallovian, and likewise led to the local emergence ofthe swells (mainly the Camarena Formation), whereshallow-marine limestones were exposed to subaerialconditions. The fourth episode of emergence andkarstification of Intra-Kimmeridgian age is recog-nized only locally (Garcıa-Hernandez et al., 1988a)in ‘Ammonitico Rosso’ facies (Ammonitico RossoSuperior Formation). The last significant episode ofemergence and karstification is easier to recognize.It is marked by condensed sediments of mainly latestHauterivian–late Aptian in age in some places, withfossilization of the irregular karstic surface begin-ning in the late Albian. The burial ended completelyin the Maastrichtian (Molina, 1987). This karstifi-cation clearly affected the previous palaeokarst fea-tures, and in some places it is superimposed onthem.

Regionally, the importance of each karstificationphase varies from area to area, but in general thefirst, third and fifth are the most noticeable. In someplaces they are superimposed, clearly correspond-ing to legacy karstification. This is very noteworthyin the outcrops described in the above-cited pub-lications: such as the Sierra de Cabra with thethird, fourth and fifth karst phases locally super-imposed; Las Angosturas, Gracia, Noguerones andSierra Gorda with the first and second phases su-perimposed; and Zarzadilla de Totana with the first,second and third karst phases overprinted. For pre-cise location of these cited areas see fig. 17.2 in Veraet al. (1988).

The main criteria jointly used for recognizingin the Subbetic the subaerial exposure facies orpalaeokarst terranes are: (a) the morphology of thesurfaces (Figs. 2 and 3A,D), that is, karst land-forms such as sinkholes, closed depressions, kar-ren morphologies, kamenitzas, towers, dissolution-enlarged fractures, borings, etc. (Molina, 1987; Veraet al., 1988; Molina et al., 1995; Martın-Algarraand Vera, 1996; and other references cited above);(b) the nature of the materials filling in the cav-ities or directly covering the irregular surfaces

(Fig. 2C and Fig. 3B,C,E) (such as, bauxites, cal-cretes and other edaphic features, collapse breccias,vadose silt or fine-grained brownish-red karst sed-iments, speleothems, neomorphic microsparitic fa-cies appearing as concretions and palisades, locallywith prismatic morphologies, serpulid bioconstruc-tions on solution pans or kamenitzas) (Vera et al.,1986; Molina, 1987; Jimenez de Cisneros et al.,1990, 1991, 1993; Molina et al., 1991); (c) silcretes,dolomites and other diagenetic features of the wall-rock (Molina, 1987; Bustillo et al., 1998); (d) thevery shallow-marine character of the wallrocks withshallowing-upward sequences culminating in strati-graphic discontinuities (Molina, 1987; Vera et al.,1988; Molina et al., 1995; and papers cited above).Fig. 4 presents a simplified model with the differ-ent morphologies of the palaeokarst in the analysedareas. The numbers and capital letters in the smallsquares correspond to similar morphologies or struc-tures in Figs. 2 and 3.

The palaeokarstic surfaces appearing locally atsome stratigraphic discontinuities change laterally tosurfaces with very different morphologies and char-acteristics, such as littoral or submarine erosion sur-faces, omission surfaces and hardgrounds. In someareas farther from the contemporaneous coastlineeven pelagic sediments occur.

3. Discussion and genetic model

The stratigraphic discontinuities at which thepalaeokarst appears, are mainly related to tectonicevents during the intracontinental rifting and riftedpassive continental margin phases of the historyof the Southern Iberian continental margin, withfootwall uplift block-tilting related to listric faults(Molina et al., 1985; Vera et al., 1988).

The higher parts of these tilted blocks could havetemporarily emerged, mainly during sea-level low-stands. In marine areas, far from the continent, theemerged blocks give rise to carbonate islands wherekarstification occurred. At those times the karst cav-ities of mixed origin, fracturing and=or subaerial orsubmarine dissolution, were filled by speleothemsand=or various sediments.

Some of the analysed karstic morphologies couldcorrespond to large dissolution voids called flank

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Fig. 2. Photographs with palaeokarst examples and features used for their recognition. (A) Irregular palaeokarst surface on the top ofthe Camarena Formation (CF). The Ammonitico Rosso Superior (AR) covers this karstic surface. Third karstification phase (Camarena–Lanchares unit). (B) Palaeosinkhole (PS), approximately 180 m in diameter, with Cretaceous marl (non-vegetated area) infilling thesurrounding Middle Jurassic oolitic limestones (Camarena Formation). It is approximately 180 m in diameter. The third, fourth andfifth karstification phases are superimposed (Camarena–Lanchares unit). (C) Bauxites (Bx) in Zarzadilla de Totana (Canteras unit). Theboundary between the lower Liassic Gavilan Formation (G) and the Oxfordian–Berriasian Ammonitico Rosso Superior Formation (AR)is a palaeokarstic surface with the first, second and third karstification phases superimposed. (D) Karstified palaeofault in the ooliticlimestones of the Camarena Formation (CF) with infilling of nodular limestones (Ammonitico Rosso Superior Formation) (AR). Thirdkarstification phase in the Camarena–Lanchares unit. (E) Karstic surface on the top of the shallow-platform carbonates of the GavilanFormation (G) (lower Liassic) covered by pelagic marls and limestones of the Zegrı Formation (Z) (upper Liassic). First karstificationphase in Sierra de Algayat.

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Fig. 3. Photographs with palaeokarst examples and features used for their recognition. (A) Cross-section of a fracture enlarged bydissolution (neptunian dyke) in oolitic limestones (Camarena Formation) (CF) and infilling of Oxfordian–Callovian pelagic sediments(Ammonitico Rosso Superior Formation) (AR) (neptunian dyke). Camarena–Lanchares unit. (B) Karstic breccias on the CamarenaFormation (Camarena–Lanchares unit). (C) Calcrete (Cc) and speleothems (Sp) on the top of the Gavilan Formation (Ventisquerounit). (D) Borings on a karstified rockground surface (Bathonian, Reclot unit). (E) Serpulid bioconstruction (Se) covering a karstifieddiscontinuity surface (Ds) (Bathonian, Camarena Formation, Camarena–Lanchares unit).

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Fig. 4. Simplified model of the palaeokarstic surface morphologies. Scale is only approximate. Numbers and letters in squares correspondto photographs in Figs. 2 and 3.

margin caves (Mylroie and Carew, 1995), thatformed preferentially in the discharging margin ofthe freshwater lens due to freshwater=saltwater mix-ing, or in relation to fracture systems like in theBahamas (Smart et al., 1988). Sea-level changesoverprint the dissolutional record of many carbonateislands with multiple episodes of vadose, freshwaterphreatic, mixing zone, and marine phreatic condi-tions.

We do not discard the possibility that some ofthe karstic morphologies may be submarine featuresthat might reflect patterns of ground-water circula-tion within continental margins, such as described byLand et al. (1995) in the Florida Straits, which orig-inated by calcium-carbonate dissolution associatedwith the submarine discharge of fresh ground-waterflowing from the Florida aquifer in the nearby plat-form.

The situation is similar to the discontinuity sur-faces separating pelagic from platform sediments de-

scribed by Zempolich (1993) and Clari et al. (1995).Existing evidence indicates that platform drowning,mainly related to tectonic collapse by listric faultsand sea-level rise, was preceded by a phase of emer-sion and karstification. In some places a prolongedphase of erosion in the pelagic realm, mainly cur-rent-related, is responsible for reducing sedimenta-tion and causing erosion of the surface, like in theQuaternary Serranilla Bank on the Nicaragua Rise(Triffleman et al., 1992). Such submarine erosion,cutting more or less deeply into the underlying rock,might have wiped out all the clues of a subaerialexposure phase preceding the drowning. In bothscenarios, only submarine erosional features wouldhave been preserved. A submarine erosional surfacewas generated that is hardly distinguishable from adiscontinuity surface due to sediment bypassing inthe pelagic realm. Lateral differences in the stratig-raphy of the sediments overlying the discontinuityresult from the local balance between deposition and

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erosion. The renewal of sedimentation is mainly con-trolled by current energy; specifically, when currentactivity decreases, pelagic sediments are preservedon the discontinuity surface. The age of the firstpelagites on the discontinuity surface varies fromplace to place. On an irregular seafloor, the higherparts were most likely affected by current activitystrong enough to locally erode previous sediments,or to totally hinder sediment accumulation for longertime spans than in the lower parts. Rapid block tilt-ing of more than 2–5 degrees is envisaged as a majorcause of non-deposition in settings where sedimenta-tion is very low, such as in starved pelagic carbonateenvironments with Ammonitico Rosso facies depo-sition. In these settings loose carbonate mud cannotaccumulate on slopes steeper than 2 to 5 degrees (seediscussion in Santantonio, 1996).

During the 1970s and 1980s a number of geo-tectonic models were proposed for the origin andevolution of rift basins, and the effects of fault-block rotation on carbonate depositional sequencesat the half-graben scale have been described in manyexamples from the geological record (for instance,Bosence et al., 1998, and references here). Theseexamples have largely confirmed the tectono-sedi-mentary model of Leeder and Gawthorpe (1987) thatfootwall areas are often escarpment or accretionaryplatform margins with shelf margin buildups andfootwall-derived redeposited facies, while hanging-wall dip-slopes develop margins or ramps evolvinginto rimmed shelf margins (Bosence et al., 1998).

Analysis of the locations of areas with evidenceof emergence, their position in the palaeogeographicreconstructions, and the precise dating of relatedsedimentary rocks, have allowed us to establish agenetic model based on real cases observed in theSubbetic. Several phases of palaeokarst developmentwere superimposed in the same place. Detailed map-ping of the region has made it possible to recog-nize differences in the degree of karstification acrossthe various tilted blocks. The highest parts of theemerged blocks were preferentially karstified, withthe degree of dissolution and karstification decreas-ing downward (Vera et al., 1988). Whereas someblocks remained exposed until the Late Cretaceous,others were exposed for only short periods of timeand were relatively lightly karstified. Where pro-longed exposure took place, extensive cavern devel-

opment occurred. As a general rule, such palaeokarstsystems were relatively localized, capping individualtilted blocks, and there are thus considerable dif-ferences in karst development even in neighbouringareas.

The pelagic filling of the karstic cavities allows usto date the karstification process and to distinguishthe different phases of karstification and filling. Thesuperposition of different phases makes a complexnetwork of neptunian dykes of diverse age and typesof infill. In the Subbetic, these phenomena recurredin different sectors (External and Internal Subbeticin Fig. 1) of the basin at different times, betweenthe Pliensbachian and the Maastrichtian (about 120Ma). The present model is applied to those caseswhere at least two phases, fracturing (F1 and F2) andemergence with karstification (K1 and K2), coincidein the same place, separated by a time span withpelagic, but not necessarily deep, sedimentation. We

Fig. 5. Graphic showing the nine possibilities (a–i) in areas withtwo karst (K1, K2) and two fracturing (F1, F2) phases locallysuperimposed. a D F1; b D F1 C K1; c D F1 C K1 C F2; d D F1

C K1 C F2 C K2; e D F1 C F2; f D F1 C F2 C K2; g D F2; h DF2 C K2; i D without karstification or fracturation.

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Fig. 6. Evolution model of a polyphase karst in an extensive continental margin (mainly based on the Camarena–Lanchares unit, Sierrade Cabra); 1 D initial stage of the carbonate platform prior to the rifting; 2 D first stage of fracturing (F1) with local emergence andkarstification (K1) on the higher parts of the tilted blocks; 3 D second stage of fracturing (F2) and karstification (K2) affecting in somecases areas common to the earlier stage, and in others different areas; 4 D final burial of the tilted blocks. The degree of karstificationdecreases to the right of each block. The letters a to g in small circles correspond to the presented possibilities in Fig. 5.

recognize nine different possibilities (a–i, in Fig. 5)in these two fracturing and karstification phases, asyou can see explained in Fig. 5. Considering theinteraction of only these two fracturing (F1 and F2)and karstification (K1 and K2) phases, Fig. 6 showsthe evolution model of a polyphase palaeokarst in

an extensive continental margin, mainly based on theoutcrops in the Sierra de Cabra (External Subbetic).For simplification, in Fig. 6 we only show the possi-bilities a, b, d, h, f and g from the left to the right.The analysis and precise dating of the sediments fill-ing the cavities have allowed us to reconstruct the

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complex sedimentary history of every sector in thebasin. Only by jointly considering the conclusionsfrom the study of many different outcrops can aproper hypothesis about the genesis of the cavitiesbe arrived at. Tectonic and eustatic sea-level fluctua-tions were the two main factors causing fault-blockemersion. Relative sea-level lowstands, locally withfault-block emersion, were followed by relative sea-level highstands and the renewal of sedimentation.Detailed analysis of the palaeokarst-correlative para-conformity surfaces has provided great precision inthe dating of the events controlling the genesis of allthese phenomena.

There are certain well-described examples ofpolyphase karst that are, in some important aspects,similar to our examples. One of the most similar sit-uations lies perhaps in the Amposta Marino field offthe coast of northeastern Spain. Those rocks showfeatures that are typical of many ancient carbon-ate sequences where phreatic karst overprints earliervadose karst. In the Amposta Marino field, the kars-tified Lower Cretaceous Montsia limestone is sealedby Miocene shales at a ‘buried hill’ trap. Wigley etal. (1988) and Bouvier et al. (1990) have interpretedthis as the result of a marine mixing corrosion zoneoverprinting the original phreatic system as a resultof a net sea-level rise. Several examples illustratinglong-term polyphase karstification such as the Tur-onian limestones of Israel (Buchbinder et al., 1983)and the Carboniferous limestone of South Wales(Wright, 1986) have also been documented. Juhaszet al. (1995) have recognized seven karst phasesin the platform carbonates of the Upper TriassicDachstein limestone in Naszaaly Hill, each includingkarst events (from the Late Triassic to the Miocene)over the past 200 million years.

3.1. Palaeokarst phases and history of thesedimentary filling during the rifting of the SouthIberian continental palaeomargin

During the Jurassic and Cretaceous the South-ern Iberian continental palaeomargin was a passivecontinental margin cut by major transform faults. Asingular characteristic of this continental palaeomar-gin is the great width of its thinned continental crust(Vera, 1988). It is possible to correlate the above-described palaeokarst phases with the history of the

sedimentary filling during the rifting phases of theSouthern Iberian palaeomargin. Vera (1999) differ-entiated three phases in the extensional evolution ofthis continental margin.

(1) The intracontinental rifting phase, which be-gan with the onset of sedimentation on the Variscanbasement in the Early Triassic and ended in theCallovian, coinciding with the third karst phase.This rifting phase can be further subdivided intotwo stages. (a) The ‘initial intracontinental rift-ing stage’ (Triassic–pre-Domerian Liassic) is earlierthan the extensional faulting and platform drowningthat marked the separation into two main palaeo-geographic domains (Prebetic and Subbetic), and thebeginning of the subdivision into lesser palaeogeo-graphic domains, mainly in the Subbetic. Its upperboundary coincides with the initiation of pelagicsedimentation in this palaeogeographic domain, im-mediately after the first phase of karstification. (b)The ‘main intracontinental rifting stage’ (Domerian–Callovian), in which significant amounts of pelagicsediment were deposited in the Subbetic, contrast-ing with the deposition of shallow-water platformcarbonates that continued in the Prebetic

(2) Rifted passive continental margin phase. Thisphase began near the Callovian–Oxfordian boundaryand ended during the Albian, with a change in theevolution of the passive continental margin from aphase with prevailing tectonic subsidence to anotherphase dominated by thermal subsidence. This lastboundary or event coincides with the fifth karstifica-tion phase.

(3) Post-rifted passive continental margin phase.This phase began during the Albian, coinciding withthe event that caused the intra-Albian discontinuity,one of the most representative stratigraphic discon-tinuities in the Betic External Zones (Vera, 1988),and ended near the time of the Cretaceous–Tertiaryboundary, when the continental margin changedfrom an extensional (or passive) margin to a con-vergent margin.

In the context of this rifting evolution we can con-sider the position of the five karstic phases analysedin this paper. The first corresponds to the beginningof the boundary between the ‘initial intracontinentalrifting stage’ and the ‘main intracontinental riftingstage’, while the third and fifth karstification phasescorrespond to the boundaries of the ‘rifted passive

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continental margin phase’ (Vera, 1999). The secondkarstification phase is located in the ‘main intra-continental rifting phase’ (Domerian–Callovian) butcorresponds to a boundary between two megase-quences and an important stratigraphic discontinuityin the Subbetic Zone, mainly recognized in shallowpelagic sediments (Garcıa-Hernandez et al., 1989;Ruiz-Ortiz et al., 1997). The fourth karstificationphase (Intra-Kimmeridgian) is located during the‘rifted passive continental margin phase’ but is cor-related with the boundary between two depositionalsequences established in the Upper Jurassic of thePrebetic, the area adjacent to the continent, with alocal stratigraphic discontinuity in the AmmoniticoRosso facies of the Subbetic. An important accumu-lation of turbidite breccias in adjacent troughs is re-lated to this discontinuity (Ruiz-Ortiz, 1983; Molinaand Ruiz-Ortiz, 1990; Ruiz-Ortiz et al., 1997).

4. Conclusions

The Mesozoic carbonate sequences in the Sub-betic reveal multiple phases of karstification witha pattern which should prove useful in interpretingcomplex palaeokarst systems. Such phases can re-sult in discrete palaeokarst features, or can overprintearlier phases. The interdependence created as eachsuccessive karstic process modified earlier features,and was also conditioned by them, complicates anyattempt to isolate the individual karst events. Fivephases of palaeokarst development have been iden-tified: (1) Intra-Carixian, (2) Early–Middle Jurassicboundary, (3) late Bathonian–early Callovian, (4) In-tra-Kimmeridgian, and (5) late Albian. Not all thefive karst phases occur in every area and, in addition,the associated features are different according to thezone. The distinct significance of the stratigraphicdiscontinuities related to palaeokarst makes it nec-essary to study many outcrops in order to correctlyinterpret these complex polyphase karsts.

The five palaeokarst phases are intimately re-lated to the rifting evolution of the Southern Iberianpalaeomargin, and they coincide with episodes ofsudden sea-level fall. In our model, emergence andthe different genetic stages described were caused bylocal block-tilting related to the movement of listricfaults and by eustatic sea-level changes.

Acknowledgements

This study has been financed by the D.G.E.S.Research Projects PB-96-429 and PB-96-1430. Wethank C. Laurin for the corrections to the Englishtext and G. de Gea and Dr. L.M. Nieto for theirhelp with the figures. We also like to thank Drs. V.Paul Wright and James L. Carew for their detailedreviews and constructive comments.

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