THE ORIGIN AND DEVELOPMENT OF NEOGENE BASINS IN THE SE BETIC CORDILLERA (SE SPAIN): A CASE STUDY OF THE TABERNAS-SORBAS AND HUERCAL OVERA BASINS

Journal of Petroleum Geology, vol. 22(1), January 1999, pp. 97-114 97

THE ORIGIN AND DEVELOPMENT OF NEOGENE BASINS IN THE SE BETIC CORDILLERA

(SE SPAIN): A CASE STUDY OF THE TABERNAS-SORBAS AND HUERCAL OVERA BASINS

A. M. Poisson#*, J. L. Morel*, J. Andrieux", M. Coulon**, R. Wernli*** and C. Guernet+

Neogene- Quaternary sedimentary basins in SE Spain contain a record of the geodynamic evolution of the Internal Zone of the Betic Cordillera. The basement of the Internal Zone is composed of Palaeozoic and Mesozoic metasediments which have undergone variable degrees of metamorphism. The External Zones consist of largely unmetamorphosed sedimentary rocks which were deposited on the SE margin of the Iberian Plate during the Mesozoic and Early Cenozoic. Westward tectonic emplacement of these terranes onto the Iberian Plate took place between the end of the Palaeogene and the middle Miocene. In this paper, we investigate the late Miocene (Tortonian- Messinian) stratigraphy of two basins in the Internal Zone - the Tabernas-Sorbas and Huercal Overa Basins. We also consider some recently-acquired structural data.

The Tabernas-Sorbas and Huercal Overa Basins are east-west trending depressions bounded to north and south by sierras in which basement rocks are exposed. The basins contain very similar sedimentary successions in which planktonic foraminifera have been preserved. However, the faunal composition is very variable, and the observed sporadic and abrupt changes in foraminifera1 populations imply palaeo-ecologic and palaeo-oceanographic instabilities which may be associated with local tectonism. Stratigraphic markers were affected by these changes, making precise dating difficult near the Tortonian-Messinian boundary.

* Laboratoire de Ge'odynamique Interne et Ge'ophysique Universite'Paris-Sud, Bat. 504,

* * Laboratoire de Ge'ologie, Faculte' des Sciences, Universite'de Champagne-Ardennes,

*** De'partement de Ge'ologie et Pale'ontologie, Universite' de Gendve, 13 rue des

+ Laboratoire de Micropale'ontologie (CNRS URA No 1761) Universite' P. et M. Curie,

# corresponding author: email [email protected]>

91405 Orsay cedex, France (EP I748 CNRS).

51 Reims, France.

Maranchers, CH 121 1 Geneva 4, Switzerland.

15 place Jussieu, 75 Paris, France.

98 Tabernas - Sorbas and Huercal Overa Basins, SE Spain

Our data indicate that Messinian rocks are more widely distributed than has hitherto been suspected. A Messinian age for the prominent coral limestones in the Tabernas- Sorbas Basin has long been accepted; similar coral limestones in the Huercal Overa Basin have previously been dated as Tortonian. However, our data show that these carbonates are of Messinian age in both basins.

The origin and development of the Tabernas-Sorbas and Huercal Overa Basins have previously been interpreted in a number of ways. Many (but not all) models favour strike- slip movement on NE-SW or east-west trending basin-bounding faults. The formation and deformation of the basins occurred during the Tortonian and Messinian, at the same time as the uplift of the sierras. The sierras are here interpreted to represent structural culminations above westward-verging, deep-seated thrust faults, and the basins to be lateral folds (or lateral ramps, i.e. oriented parallel to the thrust transport direction). The east-west trending strike-slip faults at the margin of the Sorbas- Tabemas Basin may be compatible with such a model.

Major NE-SW trending, left-lateral wrench faults have been described in this area. These faults cut through late Miocene and Pliocene deposits, and are still active at the present day. Although these faults were initiated during the late Miocene, they do not appear to have influenced the development of the Tabernas-Sorbas and Huercal Overa Basins during the early Tortonian.

INTRODUCTION

The development of the Betic Cordillera has been influenced by the convergence of the African and European Plates since the Jurassic (Dewey et al., 1973). In this regional context, development of Neogene-Quaternary sedimentary basins in the Internal Betic Zone was also influenced by thinning of the continental crust in the Western Mediterranean. Basement rocks in the Internal Zones were emplaced as a series of nappes during Palaeogene-early Miocene crustal thickening. The direction of thrust movement is not clear, and has variously been interpreted as east-to-west (Frizon de Lamotte et al., 1989) or south-to-north (Weijermars, 1991). These basement nappes were thrust over the SE margin of the Iberian Plate (External Zones) in the early Miocene (in the Aquitanian, or perhaps Burdigalian in the case of the Fortuna-Murcia Basin), giving rise to a stack of west-verging nappes (Martin Algara et al., 1988). Recent interpretations (Martinez- Martinez and Azanon, 1997) suggest that following this initial emplacement, the contacts between the basement thrust sheets were subsequently reactivated as extensional detachments during the mid-Miocene.

At the present day, over half of the area of the Internal Zone is occupied by a series of Neogene and later basins (Fig. 1) (Egeler and Simon, 1969; Durand-Delga, 1980). This paper is concerned with two of these basins - the east-west trending Tabernas-Sorbas and Huercal Overa Basins. Fig. 2 illustrates the regional geology of these two basins, which are separated by the Sierra de 10s Filabres. The structural cross-sections in Fig. 3 illustrate the relationship between metamorphic basement and Neogene cover rocks in the Tabernas-Sorbas Basin.

In previous interpretations (Montenat, 1977), the post-Serravallian basins in the Internal Zone were considered to be “post-nappe” structures. However, more recent studies have shown that thrusting continued until the late Miocene (Messinian) in the northern Fortuna- Murcia Basin (Poisson and Lukowski, 1990). These thrusts are related to those accommodating the initial collision of the Internal and External zones and their emplacement onto the Iberian Plate. The most important thrusts are deep-seated and may be blind structures (Frizon de Lamotte et al., 1989; Guezou et al., 1990). These interpretations indicate that syntectonic basin development in the Internal Zone continued through the Tortonian (Montenat et al., 1987) and into the Messinian. The basins are therefore best

A. M. Poisson et al. 99

38"-

Huercal- Overa Basin

Tabernas - Sorbas Basin

KI ,c, - . - 8

Sub-betic 1 2 3 - Neogene B a s h

Iberianplate Prebetic

External Zones Internal Zones

Fig. 1. Sketch map showing the location of the Tabernas-Sorbas and Huercal Overa Basins in SE Spain. Basement complexes in the Internal Zones: 1. Malaguide; 2. Alpujarride;

3. Nevado- Filabride.

described as frontal, lateral or transported piggy-back basins, depending upon their precise structural location.

Models of basin formation Various different models for the formation of the Neogene basins in the Betic Internal

Zone have been advanced. These models have attempted to explain the basins' development in the context of the complex evolution of the arcuate Betic-Rif orogenic belt (see review in Lonergan and White, 1987). During the late Miocene, the Internal Zones of the orogen were characterised by simultaneous uplift of basement sierras and subsidence of intervening basins. (For further discussion, see Montenat et al., 1987; Montenat and Ott d'Estevou, 1990; Weijermars, 1991; Sanz de Galdeano and Vera, 1992; Frizon de Lamotte et al., 199 1, 1995; Biermann, 1995; Vissers et al., 1995; and Martinez-Martinez and Azanon, 1997). For the purposes of this paper, the following models of basin formation can be distinguished:

i. North-south extension associated with late orogenic collapse (Vissers et al., 1985). ii. Subsidence associated with activity on a major NE-SW trending, sinistral strike-slip

100 Tubemas - Sorbas and Huercal Overu Basins, SE Spain

Fig. 2. Simplified geological map of the Tabernas-Sorbas and Huercal Overa Basins. Sections A, B, C and D are illustrated in Fig. 2.


E

lo I NE sw

Turrillas

--- _ _ _ _ _ _ _ - -

Sierra Alhamilla N

SE Alfaro Sierra Alhmilla

, , <,,,,,, - - - - - I - - _

Gypsum reefal lmst upper coarse turbidtes with mega breccia dolomite graphitic conglom. marls clastics clastics slumps and olistoliths schist

Fig. 3. Cross-sections of the Tabernas Basin (see location of profile lines in Fig. 2): (a) Near Cantona, in the east of the basin. Drawing from photo showing the angular unconformity between the sub-horizontal reefal limestones and the underlying Upper Clastics. Further north, the angularity of this unconformity diminishes, and the contact becomes conformable in the centre of the basin. (b) Section across the northern margin of the Sierra Alhamilla in the Turrillas-Lucainena area. Folds and flat-lying thrusts indicate tectonic movement towards N310". (c) Interpreted section near Tabernas. The basement is uplifted along thrust faults, and small basinal depressions are infilled by Messinian marls. (d) Section across the western extremity of the Sierra Alhamilla. Frontal folds and faults emphasise the westward translation of the sierra, according to our interpretation.

fault zone (Montenat et al., 1987; Montenat and Ott d'Estevou, 1990) (see Montenat and Ott d'Estevou, this issue, pp 61 - 80). However, the fault zone appears in general to be significantly younger than most of the basins (Bousquet and Montenat, 1974), and deforms Pliocene and younger sediments. Note, however, that the Palomares-Carboneras segment of this major fault may have been initiated during the late Miocene (Weijermars, 1987).

iii. Subsidence associated with east-west trending, dextral strike-slip faults (Sanz de Galdeano, 1989; Sanz de Galdeano and Vera, 1992; Stapel et al., 1996).

iv. Subsidence associated with a mantle diapir in the Alboran region (Weijermars, 1991).

v. Basin formation associated with isostatic adjustments above a basal floor thrust (Guezouetal., 1991; Frizon deLamotteetal., 1991; 1995). In thiskinematic framework,

102 Tabemas - Sorbas and Huercal Overa Basins, SE Spain

the sierras correspond to sites where the thrust has climbed to an upper flat, while the thrust has remained at a lower position beneath the basins.

vi. Reactivation of the contacts between the basement thrust sheets as extensional detachments (Martinez-Martinez and Azanon, 1997) may also have influenced basin formation.

In order to test these models, we studied the Tabernas-Sorbas and Huercal Overa Basins.

LITHO- AND BIOSTRATIGRAPHY OF THE TABERNAS-SORBAS AND HUERCAL OVERA BASINS

The tectono-stratigraphic evolution of Neogene basins in the Betic Cordillera has been reviewed by Boccaletti et al. (1987), Montenat et al. (1987), Montenat and Ott d’Estevou (1990), Sanz de Galdeano (1990), Weijermars (1991), and more recently by Sanz de Galdeano and Vera (1992) and Vissers et al. (1995). The regional stratigraphy of the Tabemas-Sorbas and Huercal Overa basins is well illustrated on regional 1 :50,000 scale maps published by the Spanish Ministry of Mines (Voermans et al., 1978). The Tabernas- Sorbas Basin was described by Ott d’Estevou (1980), and the Huercal Overa Basin by Briend (1981) and Benson and Rakic-el-Bied (1991). These reviews are complemented by more specialised publications, including sedimentological (Weijermars et al., 1985; Kleverlaan, 1987, 1989) and tectonic (Weijermars, 1987; Sanz de Galdeano, 1989) studies.

In spite of significant lateral and vertical facies variations, the studied basins contain fairly similar sedimentary fills (Figs 4 and 5).

Stratigraphy of the Tabernas-Sorbas and Huercal Overa Basins Pre-Tortonian deposits have not been observed in the Huercal Overa Basin. They have

been reported from the east of the Sorbas Basin (Ott d’Estevou, 1980), around the Sierra Alhamilla near Nijar (Serrano 1990), and in a graben structure at Huebro which formed due to arching of the Alhamilla Anticlinorium (Weijermars, 1991; Weijermars et al., 1985). These deposits (Langhian-Serravallian) are contemporaneous with deformation of the Internal Zones and the internal part of the Sub-Betic. They were deformed during the collision between the Internal and External Zones, and were transported towards the west with the basement. Tortonian-Messinian sediments were deposited over large areas in both basins following the westward migration of the main deformation front.

In both basins, important facies variation occur from east to west and north to south (Figs 4 and 5) , in spite of which the sequences are generally similar. Three principal stratigraphic units can be recognised: Red Lower Clastics; Grey Upper Clastics; and bioclastic limestones and marls. The marls are overlain by evaporites in the Tabernas- Sorbas Basin (Dronkert, 1977), but evaporites are not present in the Huercal Overa Basin.

The Red Lower Clastics (Tortonian?) These deposits correspond to the fomuzcion de conglomerados of Voermans et al.

(1978), and of the poudingue lie de vin (Briend 1981). The Almajalejo breccias in the Huercal Overa Basin (“coarse-grained clastics”: Fig. 5) , and the conglomeruts rouges (Ott d’Estevou, 1980) or the “Tortonian I” (Ott d’Estevou and Montenat, 1990) in the Tabemas-Sorbas Basin (Fig. 4: base of the Lucainena section) can also be assigned to this unit.

Near Tabernas (in the Rio Molinos and its tributaries), and near Almajalejo and Zurgena in the Huercal Overa Basin (locations in Fig. 2), the unit crops out in a series of anticlines and its base is only exposed locally. It consists of thick beds (between 1 and


Gypsum

Mrssiiiian reefal Sandy Red algal Breccies

Mark limestones t u r b i d i t e s limestones debris flows

Conglomerates

Oriein A i r o y o

c z W

tn 4

s m

L u c a z n e n a

Origin

:Ems

Fig. 4. Schematic lithostratigraphic columns for the Tabernas-Sorbas Basin, showing vertical and lateral facies changes at four locations (locations in Fig. 2).

50-m thick) composed of ungraded breccia with clasts up to several metres in size, which were probably deposited as non-cohesive debris flows. The breccias are polymict and were derived from the Nevado-Filabride Complex which is exposed in the Sierra de 10s Filabres. There are also intervals of grey-yellow to red, clayey silt and sand, together with subordinate conglomerates.

The thickness of the unit is variable: 300 to 400m near Tabernas, and 400m in the Huercal Overa Basin. The deposits correspond to the resedimentation of a weathered crust which developed on the sierra when it became emergent prior the Tortonian. The occurrence of stratified deposits record the existence of basins around the Sierra de 10s Filabres.

Along the margins of the sierra and on basement culminations within the basins, the unit is unconformably overlain either by the Grey Upper Clastics, or by bioclastic and reefal limestones. The deposits assigned to this unit seem to be synchronous on either flank of the Sierra de Los Filabres, and record one of the last phases of its uplift. Although they have been attributed to the Tortonian, they remain poorly dated. They could be older in the Huercal Overa Basin, but are probably not in the Tabernas- Sorbas Basin where a mid-Miocene age has been assigned to them (Weijermars, 1991).

1 04 Tabernas - Sorbas and Huercal Overa Basins, SE Spain

The Grey Upper Clastics (Tortonian and earliest Messinian) This unit is also known as arenas y Zutitas grises (Voermans et al., 1978), turbidites

micace'es (Briend,l981; Briend et al., 1990) and turbidites et coulee's boueuses (Ott d'Estevou and Montenat, 1990). It surrounds the Red Lower Clastics with which it partially interfingers in the central part of the basins. Its grey colour is due to the micaschists, micaceous sands and marls which dominate the clastic components.

The Grey Upper Clastics are of variable facies and include marine turbidites, micaceous sands and marls, conglomerates and dkbris flow deposits. The succession fines upwards at a basin scale, and it fines laterally from the margins towards the centres of the basins, where it grades into micaceous yellow marls and locally into calcarenites including coral limestones. The coarse fraction includes tourmaline gneisses and garnet micaschists derived from the Nevado Filabride complex of the Sierra de 10s Filabres. Kleverlaan (1 989) interpreted the dkbris-flow deposits and coarse turbidites near Tabemas as seismites.

This fining-upward sequence may be related to the end of rapid uplift of the sierras. The turbidites represent the deepest-water deposits in the basins, and several lines of evidence (planktonic microfauna, bryozoa and ichnofacies) suggest water depths of 400- 600m (Ott d'Estevou 1980).

Weijermars et al. (1985) studied the relationship between sedimentation in the Tabernas- Sorbas Basins and uplift of the Sierra de 10s Filabres. We propose a similar interpretation for the Huercal Overa Basin to the north of the sierra. There, the clastics record the initiation of basin subsidence and a subsequent marine transgression, also resulting from tectonic subsidence. On both sides of the Sierra de 10s Filabres, the initiation and filling of the basins was closely dependent on uplift and erosion of the intervening sierra. The marine transgression seems to have occurred suddenly, with the basinal area deepening by several hundreds of metres. These events are clearly indicated by the rapid upward transition from thick, coarse-grained subaerial deposits to marine turbidites and marls. The decreasing input of detrital material (both coarse- and fine-grained) records the end of significant hinterland erosion, probably due to a cessation in the uplift of the sierras andor a sea-level rise. Shortly afterwards (during the earliest Messinian), the basins ceased to subside and water depths became shallow, probably as a consequence of a hiatus in tectonic activity. The end of erosion can be related to the cessation of uplift, which caused a change in the type of sedimentation.

Bioclastic and reefal limestones (Messinian) A dominantly carbonate depositional regime (reefal limestones) became established

following the end of significant clastic input. The limestones grade laterally into fine- grained turbidite sandstones and marls (Figs. 4 and 5). They cover large areas in the Tabemas- Sorbas Basin, and onlap the Sierra Alhamilla to the south and the Sierra de 10s Filabres to the north, indicating the maximum extent of the transgression (Weijermars et al., 1985).

Calcarenites with rhodolithic algae, interbedded with marls, were described at the base of the Messinian sequence in the Tabernas- Sorbas Basin by Ott d'Estevou (1980). The coral limestones are younger and lie directly on top of basement rocks in the Sierra Alhamilla to the south (Ott d'Estevou, 1980; Dabrio et aZ., 1981). They precede the regressive stromatolitic limestones and evaporites which are confined to the centre of the Sorbas Basin.

Calcarenites are also associated with coral limestones in the Huercal Overa Basin (Fig. 5). Briend (198 1) described isolated outcrops in which they conformably overlie the Lower Clastics (e.g. in north of the basin at La Ventica, La Parata and La Loma near Sta. Maria de Nieva: Fig. 2). In the west of the basin, they unconformably overlie the lowermost clastics (at Cantoria and LaPerulea). Further east (at Almajalejo) and south (at Albanchez), we have observed reefal limestones interfingering with the upper part of the Grey Upper Clastics.


Parta loa

Tortonian - Messinian mark, SS and conglomerates

Messinian reefal limestones

Bioclastic sands

Coarse-grained clastics

1 % 71 1 Basement

Fig. 5. The Huercal Overa Basin, showing Messinian reefal limestones and lateral changes of facies between Partaloa and La Loma (near Sta. Maria de Nieva: locations on Fig. 2) towards

the basin centre.

Thus, the carbonates appear to have developed in a number of settings, but appear most frequently to be located near the margins of the basins where they take the form of shallow-water fringing reefs. The limestones are 1- to 30-m thick and serve as a useful lithostratigraphic marker (Fig. 3) .

In the central and northern parts of the basins, limestones are apparently intercalated within the clastic sequences. They occasionally rest directly upon the basement, indicating that they are regionally transgressive. On the other hand, in the southern parts of both basins, they rest unconformably both on basement and on clastic units which were previously deformed.

In the south of the Tabemas-Sorbas Basin near Cantona (Fig. 3a) (Ott d'Estevou, 1980), the contact between the limestones and the underlying clastics is marked by an angular unconformity with angles of up to 90". Further north (for example, on the road between Lucainena and Sorbas), there is an apparently conformable relationship between these two units. In both basins, this contact may be interpreted as aprogressive unconformity recording the progressive deformation of the northern borders of the sierras as a result of asymmetric uplift during Tortonian-Messinian times.

On the margins of the Sierra de 10s Filabres (i.e in the south of the Huercal Overa Basin and in the north of the Tabernas-Sorbas Basin), the lateral facies gradations and the interstratification of reefal limestones at the top of the clastic sequence underline the persistence of erosional processes affecting the sierra. By contrast, the Sierra Alhamilla and the surrounding area appear to have been the site of shallow-water carbonate deposition without important clastic input. The two sierras did not therefore have identical tectonic

106 Tabemas - Sorbas and Huercal Overa Basins, SE Spain

histories during Messinian times. Most parts of ’the Sierra de 10s Filabres remained exposed, uplifted and subject to erosion, while the Sierra Alhamilla was submerged.

BIOSTRATIGRAPHIC DATA

The taxonomic concepts we have used were described by Wernli (1988), and are consistent with numerous papers dealing with Late Neogene planktonic foraminifera of the Mediterranean area (e.g. Bizon et al., 1972a and b; Sierro, 1985; Iaccarino, 1985).

Age of the carbonates Although the carbonate facies in the Tabernas-Sorbas Basin and nearby areas have

been described in detail (Ott d’Estevou, 1980; Dabrio et al., 198 1; Briend, 198 1; Briend et al., 1990; Ott d’ Estevou and Montenat, 1990), a re-evaluation of their age was undertaken as part of this study. In the Huercal Overa Basin, Briend (1981), Briend et al. (1990), and more recently Guerra-Merchan and Serrano (1993) assigned a late Tortonian age to these limestones; Voermans et al. (1978) placed them in the Andalusian (early Messinian), but did not provide accurate biostratigraphic data. Our own data indicate that the reefal limestones in the north of the Huercal Overa Basin (at La Loma, near Santa Maria de Nieva), together with those in the west of the basin at Partaloa (Fig. 5 ) grade laterally into marls and turbidites which have been dated as Messinian (typically containing large Globorotalia conomiozea). In Neogene basins in the northern Betics such as the Fortuna Basin near Murcia, reefal limestones which were previously assigned to the Tortonian (Montenat, 1977) are also now accepted to be Messinian (Lukowski et al., 1988).

In the Tabernas-Sorbas Basin, a Messinian age for the reefal limestones and the underlying calcarenites is well established (Ott d’Estevou, 1980) (Fig. 4). However, in this basin, we have dated the upper part of the turbidite sequence (including redeposited red-algal limestones), and the overlying coral limestones as Messinian. The section we studied is located on the road north of Lucainena. Reefal limestones near Nijar on the southern margin of the Sierra Alhamilla are of the same age (Dabrio et al., 198 1 ; Serrano, 1990).

In the Internal Betics, it therefore seems likely that most (or probably all) of the pre- evaporite reefal limestones are Messinian in age. This excludes a pre-Messinian age for the overlying evaporites.

The Tortonian-Messinian boundary This boundary is of particular interest in the basins studied, because it supposedly

corresponds to an important phase of tectonism. This tectonism is thought to have occurred during the late Tortonian but prior to the Messinian. In these basins, and also in northern basins such as Fortuna-Murcia, the lack (or extreme rarity) of good biostratigraphic markers has led to the usage of imprecise terminology such as “Tortono- Messinian” or “Tortonian 11” for the units which lie beneath the unconfonnity. We have focused our sampling on this poorly-dated interval in order to date the tectonic phase precisely.

The planktonic foraminifera1 assemblages we recovered were generally fairly diverse and well preserved. Important variations in faunal composition were found to occur throughout sections which lithologically were fairly uniform. Thus, we frequently observed both low-diversity assemblages, and others in which major groups of species (such as carinate Globorotalia, Globigerinoides and scituloides Globorotalia) were completely absent. These abrupt changes probably imply palaeo-ecological and palaeo- oceanographical instabilities which warrant further study.

This sporadic species distribution also meant that biostratigraphic markers could be absent from fauna-rich samples, occasionally making accurate dating very difficult. In the Lucainena section, for example, Globorotalia conomiozea was always scarce and


Fig. 6. Location of sites at which structural measurements were made (see Figs. 7 and 8).

individuals were small and poorly evolved. Most ostracod species ranged from the late Miocene to the Pleistocene (or later). However, Ruggieru tetrupteru andMutitus seminulutus are not known in the Mediterranean area after the Pliocene.

As a result of our sampling, we propose that the so-called “Tortonian 11” should be assigned to the Messinian. Therefore, we propose that the phase of tectonism which occurred during the Tortonian was not restricted to this stage, but extended into the Messinian.


aaf2 ' 4 arf3 ' 4

Fig. 7. Structural measurements in the Tabernas-Sorbas Basin.

LATE MIOCENE TECTONICS

Structural data In both the Tabernas-Sorbas and Huercal Overa Basins, slickensides have been measured

on fault planes which cut the Tortonian-Messinian strata (Fig. 6). (At site e41, the faults cut into basement rocks). An inversion procedure (Carey, 1979) was applied to these

A. M . Poisson et al. 109

Fig. 8. Structural measurements in the Huercal Overa Basin.

measurements in order to characterize the orientation and form of the deviatoric stress tensor in each case. However, owing to the non-coaxial nature of the deformation, particularly along the basin margins where strike- slip and reverse faults are abundant, this type of calculation proved to be of little value. Moreover, as a consequence of the uplift of the sierras, both bedding planes and early-formed faults have been tilted, so that a single fault can display extensional slickensides as well as those indicating reverse or


strike-parallel slip. The nature of the sediments did not permit a chronology for the different slickensides to be deduced. For this reason, we subdivided measurements at some sites and the inversion procedure was applied to each sub-group, generally giving more reliable results. Thus, for example, measurements at site e2 were divided into e2nl and e2dl (Fig. 7).

Being aware of the limitations of the method, we set a high value on the geological and structural setting of the sites where the measurements were taken. The Tabernas- Sorbas and Huercal Overa Basins both have fairly simple northern margins (see cross- section 1-11: Fig. 2). On these margins, synsedimentary normal faults (Fig. 3d) are related to NE-SW extension, and the Tortonian- Messinian sequences are only slightly tilted. By contrast, the basins’ southern margins are highly deformed, and the basement may be thrust over the basin fill.

For example, in the central part of the southern margin of the Tabemas-Sorbas Basin near Lucainena and Turrillas (Fig. 2), upper Tortonian strata are deformed into NE-SW oriented overturned folds associated with N33P-directed thrusts and with minor faults (Fig. 3b). The obliquity of the fold axis with respect to the basement-Miocene contact is in accordance with the transcurrent movements described by Sanz de Galdeano (1989). However, the minor faults depict a strain field characterized by a N150”-trending compressional axis, at high angle to the strike of the above contact. Therefore, the component of strike-slip was reduced when the Sierra Alhamilla basement was being thrust over the basin (from Tortonian to early Messinian time, and it is still active).

As a result of our stratigraphic data, we propose that the earliest Messinian interval is folded together with the Tortonian section in the Tabemas-Sorbas Basin (Figs. 2 and 3). We do not agree with the existence of a prominent unconformity at the base of the Messinian evaporite sequence in the central part of the basin, as proposed by Weijermars et al. (1985). Such an unconformity is only present along the margins of the Sierra Alhamilla, to the south of the Tabernas-Sorbas Basin.

In the same area, other microfaults indicate a state of strain (Fig. 7: turi2) which does not fit either that described above or the meso-scale structures. NNE-directed compression could be related to gravitational deformation resulting from the high relief of the Sierra Alhamilla. In the eastern part of the Tabemas-Sorbas Basin (around Gafarillos on the SW flank of the Sierra Cabrera), dextral wrench faults cut through the Tortonian and Middle Miocene sequences (Sanz de Galdeano, 1989). However (Fig. 7: 37, g a p ) , a number of normal faults were also recorded here, and these may be explained in terms of releasing step-overs or releasing bends on the wrench’ faults.

In the west-central part of the Tabernas Basin, microstructures associated with the El Marchante anticline suggest that the strain field could be both dextral-transcurrent and extensional in the same place (Fig. 7: e2dZ and e2nl). Pervasive NE-SW extension coeval with NW-SE compression is clearly recorded near the town of Tabernas. This area is located along strike from the dextral wrench zone (Sanz de Galdeano, 1989) which runs along the northern margin of the Sierra Cabrera. Similar NE-SW extension was also observed at the western pericline of the Sierra Alhamilla antiform (the Banos Fault of Weijermars, 1991). This transtensional to transpressional strain field is also a significant feature of the Huercal Overa Basin (Fig. 8: som, e31, aZm2, ulu), where it is also associated with east-west trending dextral wrench faults (Fig. 8: bay, par). In some places, however, the strain was transpressive, as shown along basement culminations in the basin (Fig. 8: inJ), and as indicated by folds in the Tortonian (Fig. 2). At some sites (Fig. 8: e41), purely extensional strain can be related to gravitational spreading.

During the late Tortonian-early Messinian, NE-SW extension was the principal influence on the Huercal Overa and Tabernas Basins. This extension fits well with NW-SE compression, which explains the presence of meso-scale folds, reverse faults and overall dextral wrench faults. However, it is important to note that the dextral wrench-faulting

A. M. Poisson et al. 1 1 1

and associated NW-SE compression was more intense during the middle Miocene, as noted by Biermann (1 995). Local departures from this simple strain field can be explained in term of gravitational instabilities of the uplifted southern margin of the basins.

Such a close association between the transtensional strain field and the uplift of the sierras is consistent with the three of the six tectonic models for basin formation mentioned on p. 99 et seq. (models iii, iv and v). These three models are not mutually exclusive, if one accepts that westward movement on a basal thrust zone was more rapid below the southernmost Betic Cordilleras, and that the Alboran High was located further to the east.

DISCUSSION AND CONCLUSIONS

Sedimentation in the Tabemas-Sorbas and Huercal Overa Basins is closely related to erosion of the neighbouring sierras. Weijermars et aE. (1985), Kleverlaan (1989) and Ott d’Estevou (1980) noted this relationship for the Tabernas Basin; we now propose that it also applies to the Huercal Overa Basin. These two basins developed synchronously to the north and south of the Sierra de 10s Filabres which was a high during the Tortonian (Weijermars, 1991) and into the Messinian.

During the late Tortonian, the basins deepened to a water depth of 400-600m. The Sierra de 10s Filabres acted as a source of coarse detrital material, and rapid uplift was initiated in the Sierra Alhamilla. The unstable southern margins of both basins were sites for the deposition of olistoliths and large-scale slumps (Ott d’Estevou, 1980; Briend, 198 1 ; Kleverlaan, 1989), but this did not occur on the northern margins. This suggests that the northern margins of the sierras were rapidly uplifted, became unstable, and collapsed into the basins. Bedding planes dip at progressively greater angles near the margins of the sierras, but remain quite flat-lying in the central parts of the basins. This type of progressive unconformity is well exposed at the northern margin of Sierra Alhamilla (Cantona area: Fig. 2 and 3a). The same relationship can also be observed in the Huercal Overa Basin. There, Messinian reefs unconformably overlie the margins and the culmination between Almajalejo and Albox (Fig. 2). These progressive unconformities record the progressive deformation of the basins, which cannot be assigned to a single, short-lived tectonic phase but which reflects continuous synsedimentary deformation.

Erosional processes remained locally active at the beginning of the Messinian, and a number of thick dCbris flows have been recorded (Lucainena section, Fig. 4; north and west of Tabernas). Nevertheless, pelagic marls are dominant in the central parts of the basins (‘‘rnames Zivides”: Ott d’ Estevou, 1980; Briend, 198 l), indicating a very significant decrease in the intensity of the erosional processes. Shortly afterwards, the basins became progressively emergent, and both basins and sierras were sites of reefal limestone development. This is particularly significant in the central part of the Tabernas-Sorbas Basin (Fig. 2).

During the late Tortonian and early Messinian, rapid vertical tectonic movements occurred in both basins. These movements consisted firstly of deepening by 400-600m, followed by progressive emergence; Messinian reefs are now at an elevation of 600m above sea level. A similar evolutionary history has been observed in the Fortuna Basin (Poisson and Lukowski, 1990).

The late Tortonian - early Messinian is a critical period in the Mediterranean area, as it precedes the Messinian “salinity crisis” during which thick (ca. 1 km) evaporites were deposited (Hsu et aZ., 1972). In the Sorbas type-section (Ott d’Estevou, 1980), the base of the evaporites has recently been dated as 5.7 MM yr old (Gautier et al., 1994). This section is a lateral equivalent of the Lucainena section. Using a combination of biostratigraphy and magnetostratigraphy , these authors increased the precision of the chronology between the late Tortonian and the pre-evaporitic Messinian, in agreement with the time scale of Cande and Kent (1992). Their results indicate that the entire fill of the Tabernas Basin (from the red breccias up to the base of the evaporites) corresponds

112 Tabernas - Sorbas and Huercal Overa Basins, Sf? Spain

to deposition during a time interval of less than 2 MM yrs. Subsequent inversion took place, probably in less than 0.5 MM yrs.

In the Betic Cordilleras, the Tortonian-Messinian period corresponds to the time when rapid westward translation of the Prebetic nappes occurred (Guezou et al., 1991). The allochthonous olistostromes of the Guadalquivir Basin developed at the same time.

Consequences for hydrocarbon exploration In terms of their overall setting, the Tabernas-Sorbas and Huercal Overa Basins are

not particularly favourable for oil and gas exploration as they have been inverted and most of their structures are breached. However, conditions favourable for oil generation may have existed in the nearby Vera Basin, as reported by Dupuy de Lome (1933) (cited in Weijermars, 1991). Nevertheless, the basins' developmental history may provide a useful model for the interpretation of on- and offshore basins elsewhere in the Western Mediterranean.

In summary, the following conclusions can be drawn: (i) Reefal limestones in the Tabernas-Sorbas and Huercal Overa Basins are early

Messinian; they developed before the salinity crisis whose onset has been dated as 5.7 MM yrs ago.

(ii) The fining-upward successions in both basins include continental breccias grading upward into shallow-marine debris flows. These coarse clastic deposits are succeeded by turbidites and/or bathyal planktonic marls and reefal limestones. The carbonates are widespread in the Tabernas-Sorbas Basin, but are restricted to the margins of the Huercal Overa Basin and to antiformal culminations in the central area. In many sections, the carbonates are intercalated as lenses (2- to 10-m thick) within coarse conglomerates and are capped by evaporites and Pliocene marls. Armstrong et al. (1 980) noted that the Messinian reefal limestones may represent a possible reservoir rock offshore.

(iii) Important vertical tectonic movements have taken place in both the Huerval Overa and Tabernas-Sorbas Basins. The basins have undergone rapid, high-amplitude vertical and horizontal deformation which probably precludes the preservation of hydrocarbons

ACKNOWLEDGMENTS

We are indebted to Genevieve Roche and Laurent Daumas for the drawings, and to Rachel Flecker for her revision of the English version. Comments by two anonymous reviewers, and detailed reviews by Drs P. Haughton (University College Dublin, Ireland) and R. Weijermars (KFUPM, Saudi Arabia) improved the original manuscript and are acknowledged with thanks.

REFERENCES

ARMSTRONG, A.K., SNAVELY, P.D. and ADDICOTT, W.O., 1980. Porosity of Upper Miocene reefs, Almeria Province, southern Spain. AAPG Bull., 64, 188-208.

BENSON, R.H. and RAKIC-EL-BED, K., 199 1 a. The Messinianparastratotype at Cuevas del Almanzora, Vera basin, SE Spain: refutation of the deep-basin, shallow water hypothesis? Micropaleontology,

, RAKIC-EL-BED, K. andBONADUCE, G., 1991b. An important current reversal (influx), jn the Rifian Corridor (Morocco), at the Tortonian-Messinian boundary: the end of the Tethys ocean. Palaeoceanography, 6,( I), 164- 192.

BIERMANN, C., 1995. The Betic Cordilleras (SE Spain). Anatomy of a dualistic collision type orogenic belt. Geologie en Mijnbouw, 74, 167-182.

BIZON, G., BIZON, J.J., AUBERT, J. and OERTLI, H.J., 1972a. Atlas des principaux foraminifkres planctoniques du bassin mediterranien. Oligocene - Quatemaire. Edit. Technip Paris.

37, 3, 289-302.


BIZON, G. and BIZON, J.J., 1972b. Etude de quelques coupes relevCes dans le bassin de Murcia. Foraminifbres planctoniques. In: BIZON, G., BIZON, J.J. and MONTENAT, Ch., (Eds.): Le Miocene terminal dans le Levant espagnol (provinces d’ Alicante et de Murcia). Rev. Inst. Franc. Ptftrole, 27, 6, 845-863.

BOCCALETIT, M., GELATI, R., LOPEZ GARRIDO, A.C., PAPANI, G., RODRIGUEZ-FERNANDEZ, J. and SANZ DE GALDEANO, C., 1987. Neogene- Quaternary sedimentary-tectonic evolution of the Betic Cordillera. Acta Naturalia Ateneo Parmense, 23, 4, 179-200.

BOUSQUET, J.C. and MONTENAT, C., 1974. Presence de dCcrochements NE-SW plio-quaternaires dans les Cordillbres Betiques orientales. Extension et signification generale. C. R. Ac. Sci. Paris, 278,

BRIEND, M., 198 1. Evolution morpho-tectonique du bassin de Huercal Overa (Cordill&res Betiques orientales, Espagne). Doc. et Trav. iGAL, Paris, 4, 1-208.

, MONTENAT, C. and OTT d’ESTEVOU, P., 1990. Le bassin de Huercal Overa. Doc. e f Trav. IGAL, Paris, 12-13, 239-259.

CANDE, S.C. and KENT, D., 1992. A new geomagnetic polarity time scale for the Late Cretaceous and Cenozoic. Journ. Geophys. Res., 97, B10, 13917-13951.

CAREY, E., 1979. RCcherche des directions principales de contraintes associCes au jeu d’une population de failles. Rev. Geol. Dyn. Gtfogr. Phys. Paris, 21, 1, 57-66.

DABRIO,C.J.,ESTEBAN,M., andMARTIN, J.M., 1981. ThecoralreefofNijar,Messinian(Uppermost Miocene), Almeria province SE Spain. Journ. Sed. Petrol., 51, 2, 521-539.

DEWEY, J.F., PITMAN. W.C., RYAN, W.B. andBONNIN, J., 1973. Plate tectonics and theevolution of the Alpine system. Geol. SOC. Am. Bull., 84, 3137-3180.

DRONKERT, H., 1977. The evaporites of the Sorbas Basin. Rev. del Instituto de invesigaciones Geologicas, Dip. Prov. Barcelona 32, 55-76.

DUPUY de LOME, E., 1933. Nota acera de la industria petrolifera rumana y application de sus datos geologicos a la investigacion de algunos yacimientos petroliferos espanoles. Bol. Inst. Geol. Min.

DURAND-DELGA M., 1980. La Mediterranke occidentale: Ctapes de sa genbse et problbmes structuraux lies ?i celle-ci. Livre Mem. Pr. P. Fallot. Mem. H. S. SOC. Gkol. France, 10, 203-224.

EGELER, C.G. and SIMON, O.J., 1969. Orogenic evolution of the Betic zone (Betic Cordilleras, Spain), with emphasis on the nappe structure. Geol. en Mijnb., 48, 296-305.

FRIZON DE LAMOTTE, D., GUEZOU, J.C. and ALBERTINI, M.A., 1989. Deformation related to westward translation in the core of the Betic zone. Implications on the tectonic interpretation of the Betic orogen (Spain). Geodinamica Acta, 3-4, 267-281.

FRIZONDELAMOIITE,D.,ANDRIEUX, J. andGUEZOU, J.C., 1991. Cinematiquedeschevauchements neogenes dans I’arc betico-rifain: discussion sur les modkles gkodynamiques. Bull. SOC. Gkol. France, 162,611-626.

FRIZON DE LAMOTTE, D., AVERBUCH, 0. and GUEZOU, J.C., 1995. Distinguishing lateral folds in thrust-systems. Examples from Corbibres (SW France), and Betic Cordilleras (SE Spain). Journ. Struct. Geol., 17, 2, 233-244.

GAUTIER, F., CLAUZON, G., SUC, J.P., CRAVATTE, J. and VIOLANTI, D., 1994. Age et durke de la crise de salinitC messinienne. C. R. Acad. Sci. Paris, 318, sene 11, 1103-1 109.

GUERRA-MERCHAN, A. and SERRANO, F., 1993. Tectonosedimentary setting andchronostratigraphy of the Neogene reefs in the Almanzora corridor (Betic Cordillera, Spain). Geobios, 26, 1, 57- 67.

GUEZOU, J.C., FRIZON DE LAMOTTE, D., COULON, M. and MOREL, J.L., 1991. Structure and kinematics of the Prebetic nappe complex (southern Spain): definition of a “Betic Floor Thrust” and implications in the Betic-Rif orocline. Annales Tectonicae, 5 , 1, 32-18.

HSU, K. J., CITA, N. B. and RYAN, W.B.F., 1972. The origin of the Mediterranean evaporites. initial Reports of the DSDP, XIII, pt. 2, 695-708.

IACCARINO, S., 1985. Mediterranean Miocene and Pliocene planktonic Foraminifera. In: BOLLI, H.M. et al. (Eds.): Plankton Stratigraphy. Cambrigde University Press, pp. 283-3 14.

KLEVERLAAN, K., 1987. Gorgo megabed: apossible seismite in aTortonian submarine fan, Tabernas basin, province Almeria, SE Spain. Sedimentary Geol., 51, 165-180.

, 1989. Neogene history of the Tabernas basin (SE Spain), and its Tortonian submarine fan development. Geol. en Mijnb., 68, 421-432.

, WERNLI, R. and POISSON, A., 1988. Mise en evidence de I’importance des dep8ts messiniens dans le bassin miocene de Fortuna (prov. de Murcia, Espagne). C.R.Ac.Sci. Paris, 307, 94 1 - 947.

2617-2620.

ESP., 53, 139-217.

114

LONERGAN, L. and WHITE, N., 1997. Origin of the Betic-Rif Mountain Belt. Tectonics, 16, 504- 522.

MARTIN-ALGARRA, A., SANZ DE GALDEANO, C. and ESTEVEZ, A., 1988. L’evolution sedimentaire miocene de la region au nord de la sierra Arana (CordillBres Betiques) et sa relation avec la mise en place du bloc d’Alboran. Bull. SOC. GPol. France, 8,4, 1, 119-127.

MARTINEZ-MARTINEZ, H. M. and AZANON, J. M., 1997. Mode of extensional tectonics in the SE Betics (SE Spain); implications for the tectonic evolution of the peri-Alboran orogenic system. Tectonics, 16,205-225.

MONTENAT, C., 1977. Les bassins neogBnes du Levant d’ Alicante & Murcia. Stratigraphie, paleogBographie et Bvolution dynamique. Doc. Lab. Gdol. Fac. Sci. Lyon, 69, 1-345.

, Om D’ESTEVOU, P. and MASSE, P., 1987. Tectonic sedimentary characters of the Betic Neogene basins evolving in a crustal transcurrent shear zone (SE Spain). Bull. Centres Rech. Expl. Prod. ElfAquitaine Pau, 11, 1-22.

and OTT D’ESTEVOU, P., 1990. Eastern Betic Neogene basins. A review. Doc. Trav. IGAL Paris, 12-13, 9-15.

MORA, M., 1991. Extensional tectonics in an intramontane basin in SE Spain. Terra Abstracts, 3, 1, p.244.

OTT D’ESTEVOU, P., 1980. Evolution dynamique du bassin neogene de Sorbas (Cordillc5res Betiques Orientales, Espagne). Doc. Trav. IGAL, Paris, 1, 264p.

and MONTENAT, C., 1990. Le bassin de Tabemas-Sorbas. Doc. et Trav. IGAL, Paris,

PLATT, J.P., VAN DEN EECKHOUT, B., JANZEN, E., KONERT, G., SIMON, O.J., and WEIJERMARS, R., 1983. The structure and tectonic evolution of the Aguilon fold-nappe, Sierra Alhamilla, Betic Cordillera, SE Spain. Journ. Struct. Geol., 5, 519-538.

POISSON, A. and LUKOWSKI, P., 1990. The Fortuna basin: a piggy back basin in the Eastern Betic Cordilleras (SE Spain). Annales Tectonicae, IV, 52-67.

SANZ DE GALDEANO, C., 1989. Las fallas de desgarre del borde Sur de la cuenca de Tabernas- Sorbas (norte de Sierra Alhamilla, Cordilleras Beticas). Bol. Geol. Min., 101,73-85.

, 1990. Geologic evolution of the Betic Cordilleras in the Western Mediterranean; Miocene to Present. Tectonophysics, 172, 107-1 19.

and VERA, J. A., 1992. Stratigraphic record and palaeogeographic context of the Neogene basins in the Betic Cordillera, Spain. Basin Research, 4,21-36.

SERRANO, F., 1990. Presencia de Serravalliense marino en la cuenca de Nijar (Cordillera Betica, Espana). Geogaceta, 7,95-97.

SIERRO, F. J., 1985. The replacement of the “Globorotalia menardii” group by the “Globorotalia miotumida’ group. An aid to recognizing the Tortonian-Messinian boundary in the Mediterranean and adjacent Atlantic. Mar. Micropaleontol., 9, 525-535.

STAPEL, G., MOEYS, R., and BIERMANN, C., 1996. Neogene evolution of the Sorbas Basin (SE Spain) determined by paleostress analysis. Tectonophysics, 255, 29 1-305.

VISSERS, R.L., PLATT, J.P. and VAN DER VAAL, D., 1995. Late orogenic extension of the Betic Cordilleras and the Alboran Domain: a lithospheric view. Tectonics, 14,786-803.

VOERMANS, F.M., SIMON, O.J., MARTIN GARCIA, L. and GOMEZ PRIETO, J.A., 1978. Mapa geologic0 de Espana. 1/50 OOO, Huercal Overa. Serv. Publ. Minist. Indust. y Energia, Madrid.

WEIJERMARS, R., 1987. The Palomares brittle-ductile shear zone of southern Spain. Journ. Struct. Geol., 9, 139-157.

, 1991. Geology and tectonics of the Betic Zone, SE Spain. Earth Science Reviews, 31,

, ROEP, T.B., VANDENEECKHOUT, B., POSTMA, G. and KLEVERLAAN, K., 1985. Uplift history of a Betic fold nappe inferred from Neogene Quaternary sedimentation and tectonics (in the Sierra Alhamilla and Almeria, Sorbas and Tabernas basins of the Betic Cordilleras, SE Spain). Geol. en Mijn., 64, 397-4 1 1.

WERNLI, R., 1980. Le Messinien & Globorotalia conomiozea (foraminif5re planctonique) de la c8te mkditerrankenne marocaine. Eclogue Geol. Helv., 73, 1 , 7 1-93.

WERNLI, R., 1988. MicropalBontologie du NiogBne post-nappe du Maroc septentrional et description systematique des foraminifBres planctoniques. Notes MPm. Serv. Ggol. Maroc, 331, 1-270.

Tabemas - Sorbas and Huercal Overa Basins, SE Spain

12-13, 101-128.

153-236.

Documents

THE ORIGIN AND DEVELOPMENT OF NEOGENE BASINS IN THE SE BETIC CORDILLERA (SE SPAIN): A CASE STUDY OF THE TABERNAS-SORBAS AND HUERCAL OVERA BASINS