Palaeomagnetic study of the Ronda peridotites (Betic Cordillera, southern Spain)

A palaeomagnetic study of the Ronda peridotites (southern Spain) has been carried out on 301 samples from 20 sites, spread along the three main outcrops of the ultrabasic complex: Ronda, Ojén and Carratraca massifs. Different lithologies and outcrops with different degrees of serpentinization have been sampled and analysed. Rock magnetic experiments have been carried out on a representative set of samples. These measurements include: Curie curves, hysteresis cycles, isothermal remanent magnetization (IRM) acquisition curves, thermal demagnetization of IRM imparted along three orthogonal axes and magnetic bulk susceptibility. Results indicate that magnetite is the main magnetic mineral present in the samples. Stepwise thermal and alternating field (AF) demagnetization of the natural remanent magnetization (NRM) reveals the presence of a characteristic remanent magnetization (ChRM) carried by magnetite, and in some sepentinized samples, a northward component with variable unblocking temperatures up to 250–575 °C. The appearance and the relative intensity of this northward component are strongly related to serpentinization degree. Taking into account the geological history of the peridotites, the ChRM has been considered as a thermo-chemical remanent magnetization acquired during the first serpentinization phase associated to the post-metamorphic cooling of this unit. On the basis of radiometric and fission track analysis, the ChRM is proposed to have been acquired between 20 and 17–18 Ma. The inclination of the mean direction of the ChRM statistically coincides with the expected inclination for stable Iberia during the Oligocene–Miocene. The declination of the ChRM differs from the expected declination, indicating clockwise block rotations of 41±12° about vertical axes since the cooling of the peridotites. When applying a compositional layering correction, the ChRM directions fail to pass this kind of fold test, thus, the compositional layering was not a palaeohorizontal during ChRM acquisition time. Normal and reversed polarities of the ChRM are reported, showing that at least one reversal of the Earth's magnetic field took place during ChRM acquisition process. A tentative polarity zonation within the peridotitic outcrops is also suggested. No evidence is found from these data for the previously proposed simultaneity between post-metamorphic cooling and rotation of the peridotites.     

Quantitative subsidence-uplift analysis of the Bajo Segura Basin (eastern Betic Cordillera, Spain): tectonic control on the stratigraphic architecture

The Bajo Segura Basin is located in the eastern Betic Cordillera, at present connected with the Mediterranean Sea to the east. It has a complete stratigraphic record from the Tortonian to the Quaternary, which has been separated into six units bounded by unconformities. This paper is concerned with the northern edge of the basin, controlled by a major strike–slip fault (the Crevillente Fault Zone, CFZ), where the most complete stratigraphic successions are found. The results obtained (summarised below) are based on an integrated analysis of the sedimentary evolution and the subsidence-uplift movements. Unit I (Early Tortonian) is transgressive on the basin basement and is represented by ramp-type platform facies, organised in a shallowing-upward sequence related to tectonic uplift during the first stages of movement along the CFZ. Unit II (lower Late Tortonian) consists of shallow platform facies at bottom and pelagic basin facies at top, forming a deepening-upward sequence associated with tectonic subsidence due to sinistral motion along the CFZ. Unit III (middle Late Tortonian) is made up of exotic turbiditic facies related to a stage of uplift and erosion of the southern edge of the basin. Unit IV (upper Late Tortonian) consists of pelagic basin facies at bottom and shallow platform facies at top, defining a shallowing-upward sequence related to tectonic uplift during continued sinistral movement on the basin-bounding fault. Units V (latest Tortonian–Messinian) and VI (Pliocene–Pleistocene p.p.) consist of shallowing-upward sequences deposited during folding and uplift of the northern margin of the basin. No definitive evidence of any major eustatic sea-level fall, associated with the ‘Messinian salinity crisis’, has been recorded in the stratigraphic sections studied.     

The Baza Fault: a major active extensional fault in the central Betic Cordillera (south Spain)

In the Guadix-Baza Basin (Betic Cordillera) lies the Baza Fault, a structure that will be described for the first time in this paper. Eight gravity profiles and a seismic reflection profile, coupled with surface studies, indicate the existence of a NE-dipping normal fault with a variable strike with N-S and NW-SE segments. This 37-km long fault divides the basin into two sectors: Guadix to the West and Baza to the East. Since the Late Miocene, the activity of this fault has created a half-graben in its hanging wall. The seismic reflection profile shows that the fill of this 2,000–3,000 m thick asymmetric basin is syntectonic. The fault has associated seismicity, the most important of which is the 1531 Baza earthquake. Since the Late Tortonian to the present, i.e. over approximately the last 8 million years, extension rates obtained vary between 0.12 and 0.33 mm/year for the Baza Fault, being one of the major active normal faults to accommodate the current ENE–WSW extension produced in the central Betic Cordillera. The existence of this fault and other normal faults in the central Betic Cordillera enhanced the extension in the upper crust from the Late Miocene to the present in this regional compressive setting.     

A cross section of the eastern Betic Cordillera (SE Spain) according field data and a seismic reflection profile

The BT3 multichannel seismic profile was acquired by the C.G.G. (Compagnie General de Géophysique) in 1977 for hydrocarbon exploration in the eastern Betic Cordillera. REXIMseis Ltd scanned and vectorized a paper copy and then performed post-stack processing, including coherence filtering and deconvolution. The receiver functions of a broad-band seismic station located near the village of Vélez Rubio, at the SE end of the profile, were analysed by Julia et al. [Julia, J., Mancilla, F., Morales, J., 2005. Seismic signature of intracrustal magmatic intrusions in the Eastern Betics (Internal Zone), SE Iberia, Geophysical Research Letters 32, L16304, doi:10.1029/2005GL023274.] to determine the structure of the underlying crust. We have used these Vp data to convert the profile to depth. The profile has a mean SE–NW trend, with a SE-Section 44 km in length followed by a NW-Section 20 km in length. The record includes the first 4 s (twtt), which corresponds to 11 km.Two main areas can be seen in the profile. At the SE-end, a band of high-amplitude discontinuous reflectors dips towards the north. The band is 100 to 200 ms thick, increasing even more northwards. This band reaches the surface at the top of the Maláguide Complex (the upper complex of the Internal Zones). Above these reflectors, an area with chaotic seismic facies and no reflectors corresponds to the outcrops of the olistostromes and turbidites of the Solana Formation, and it is in turn overlain by discontinuous reflectors of the Subbetic rocks.At the NW-end of the profile, a set of high-amplitude continuous reflectors with SE dips point to the location of the Prebetic. Below this section, oblique reflectors of intermediate amplitude indicate the Variscan basement. Over the Prebetic, we have marked the basal thrusts of the Intermediate Units and the Subbetic. Using this seismic data, as well as field observations, we propose a geological cross-section of the upper crust of the eastern Betic Cordillera and a model of the most recent evolution of the orogen. In this model, the Internal Zones and the Subbetic have been welded together from the Middle Burdigalian to the present day and acted as an orogenic wedge that deformed the Intermediate Units and the Prebetic.     

Partial crustal melting beneath the Betic Cordillera (SE Spain): The case study of Mar Menor volcanic suite

The Neogene Volcanic Province (NVP) within the Betic Cordillera (SE Spain) consists of three main metapelitic enclave suites (from SW to NE: El Hoyazo, Mazarrón and Mar Menor). Since the NVP represents a singular place in the world where crustal enclaves were immediately quenched after melting, their microstructures provide a “photograph” of the conditions at depth just after the moment of the melting.

The thermobarometric information provided by the different microstructural assemblages has been integrated with the geophysical and geodynamical published data into a model of the petrologic evolution of the Mar Menor enclaves. They were equilibrated at 2–3 kbar, 850–900 °C, and followed a sequence of heating melt producing reactions. A local cooling event evidenced by minor melt crystallization preceded the eruption.

The lower crustal studies presented in this work contribute to the knowledge of: (i) the partial melting event beneath the Mar Menor volcanic suite through a petrologic detailed study of the enclaves; (ii) how the microstructures of fast cooled anatectic rocks play an important role in tracing the magma evolution in a chamber up to the eruption, and how they can be used as pseudothermobarometers; (iii) the past and current evolution of the Alborán Domain (Betic Cordillera) and Mediterranean Sea, and how the base of a metapelitic crust has melted within an active geodynamic setting.     

Deformation related to Miocene westward translation in the core of the Betic zone Implications on the tectonic interpretation of the Betic orogen (Spain)

Abstract

The Cenozoic westward motion of the Betic-Rif internal zone (“Alboran block”) between Iberia and Africa is constrained by paleogeographic considerations and by wrench faulting which affects both sides of the external zones. However, in the Alboran domain itself there was so far no evidence of significant internal deformation related to this westward displacement which was consequently consider as an en bloc” motion. Our work, in Eastern Andalucia, demonstrates that the main tectonic units building up the Betic zone should be regarded as large-scale tectonic sheets with a typical duplex style. The direction of the tectonic transport is to the West. At meso-scale, the major structures exhibit a combination of hindward and foreward dipping imbricates on the respective east and west sides of antiformal stacks or “rigid cores”. On a broader scale, the same geometric framework appears on both east and west sides of the Sierra Nevada window which we interpret as a tectonic culmination on the hangingwall of a Subbetic décollement zone. The development of this tectonics, in retrogressive metamorphic conditions, postdates the ductile deformation of the internal complexes. The morpho-tectonic relationships between the culmination of the metamorphic cores and the Neogene basins give a way to date the westward motion of the “Alboran System of Nappes” of the middle and upper Miocene.     

Striated and pitted pebbles as paleostress markers: an example from the central transect of the Betic Cordillera (SE Spain)

Striated and pitted pebbles provide scarce structures that preserve information on the stresses that their host rocks have undergone. This information can be obtained by the measurement of a large number of microfaults with striae and solution marks within a small rock volume. For non-rotational deformation, the statistical procedures for microfault analysis provide a valid tool for determining the overprinting of successive stress ellipsoids, including their axial ratios and the orientations of the main axes. The trends of compressions obtained from striae can be compared with the determinations from the pole of pebble solution pits. However, in complex tectonics settings, the solution pits of several deformation phases are mixed and only striae analysis allows overprinted paleostresses to be accurately distinguished. The analysis of several pebbles from the same outcrop, including five from moderately complex settings, allows determination of the homogeneity of the paleostresses at outcrop scale, the detection of redeposited pebbles, and supports the results of microtectonic analysis for large areas. Solution mark distributions on pebbles depend on the burial and tectonic stresses. Conglomerates from shallow levels, such as those from Quaternary fluvial terraces, only record horizontal compressional solution marks because the minimum vertical stress needed to develop these structures are not reached by burial.In the central Betic Cordillera, striated and pitted pebbles are composed of carbonate surrounded by a matrix containing siliciclastic elements. The study of several outcrops located across a transect of the Cordillera shows a change in the recent stress field. While conglomerates near the Internal–External zone boundary show extensional stresses that may be related to the uplift of the Cordillera since Tortonian times, the outcrops located in the External Zone and up to the mountain front indicate the existence of horizontal NW–SE and NE–SW compressions related to prolate ellipsoids. These two compression directions, which affect conglomerates up to the Quaternary in the same outcrop, may be produced by a local permutation of stress axes, which in general indicates NW–SE compression related to the Eurasia–Africa plate boundary convergence, but which locally may switch to an orthogonal compression.     

Landslide-hazard mapping through multi-technique activity assessment: an example from the Betic Cordillera (southern Spain)

Landslide hazard in a region limited to data from a regional scale about triggering factors is assessed via cross tabulation between determining factors and landslides with recent activity. Firstly, landslide susceptibility was evaluated and validated through a bivariate statistical method between the previously identified stability conditioning factors and the mapped landslides. In this way, the most susceptible areas for assessing landslide hazards were selected. The main problem to solve in this type of research is the landslide activity. For this purpose, several techniques were applied: news reports, differential interferometric synthetic aperture radar, digital photogrammetry, light detection and ranging, photointerpretation, and dendrochronology. Both the strong and weak points of these techniques are also mentioned. The landslide return period was computed via the association between landslide activity and triggering factors, in this case annual rainfall. Finally, landslide hazard was mapped solely based on landslides with recent activity and their computed return period. The relationship between landslide occurrence and triggering factors shows that, according to both the considered assumptions and the observations made, deep-seated landslides are triggered or reactivated together with superficial landslides once every 18 years, while superficial landslides as flows or falls occur once every 5 years. The results show that there is generally a low landslide hazard in the study zone, especially when compared to landslide susceptibility. This means that landslides are mainly dormant from a natural evolution point of view, but could be reactivated as a result of geomorphological, climate, or human changes. In any case, the landslide hazard is successfully assessed, with a prediction of a 6% annual probability of a high hazard in 5% of the area, intersecting with the main infrastructures of the region; thus, control strategies are justified in order to avoid damage in extraordinary rainfall periods.     

Structural and geomorphological aspects of the Kat landslides (Tokat—Turkey) and susceptibility mapping by means of GIS

Kat County, which is located in a slope of hilly region and constructed in the side of a mountain along the North Anatolian Fault Zone, is frequently subject to landslides. The slides occur during periods of heavy rainfall, and these events cause destruction to property, roads, agricultural lands and buildings. In the last few decades, a lot of houses and buildings have been damaged and destroyed. Settlement areas have remained evacuated for a long time. The slope instabilities in the study area are a complex landslide extending from north to south containing a lot of landslides. Field investigations, interpretation of aerial photography, analyses of geological data and laboratory tests suggest that some factors have acted together on the slopes to cause the sliding. In the wet season, the slopes became saturated. As the saturation of the earth material on the slope causesa rise in water pressure, the shear strength (resisting forces) decreases and the weight (driving forces) increases; thus, the net effect was to lower the safety factor. Previous failures have affected the rock mass, leading to the presence of already sheared surfaces at residual strengths. The relation between the joint planes and the instability of the slope in the study area was discussed and it was found that the potential slope instabilities are mainly in the directions of NW–SE, NE–SW and N–S. The landslide susceptibility map obtained by using the geographical information system showed that a large area is susceptible and prone to landslides in the northern part of the study area.An erratum to this article can be found at     

Geomorphology and landslide susceptibility assessment using GIS and bivariate statistics: a case study in southern Italy

In this article, the results of a study aimed to assess the landslide susceptibility in the Calaggio Torrent basin (Campanian Apennines, southern Italy) are presented. The landslide susceptibility has been assessed using two bivariate-statistics-based methods in a GIS environment. In the first method, widely used in the existing literature, weighting values (Wi) have been calculated for each class of the selected causal factors (lithology, land-use, slope angle and aspect) taking into account the landslide density (detachment zones + landslide body) within each class. In the second method, which is a modification of the first method, only the landslide detachment zone (LDZ) density has been taken into account to calculate the weighting values. This latter method is probably characterized by a major geomorphological coherence. In fact, differently from the landslide bodies, LDZ must necessarily occur in geoenvironmental classes prone to failure. Thus, the calculated Wi seem to be more reliable in estimating the propensity of a given class to generate failure. The thematic maps have been reclassified on the basis of the calculated Wi and then overlaid, with the purpose to produce landslide susceptibility maps. The used methods converge both in indicating that most part of the study area is characterized by a high–very high landslide susceptibility and in the location and extent of the low-susceptible areas. However, an increase of both the high–very high and moderate–high susceptible areas occurs in using the second method. Both the produced susceptibility maps have been compared with the geomorphological map, highlighting an excellent coherence which is higher using method-2. In both methods, the percentage of each susceptibility class affected by landslides increases with the degree of susceptibility, as expected. However, the percentage at issue in the lowest susceptibility class obtained using method-2, even if low, is higher than that obtained using method-1. This suggests that method-2, notwithstanding its major geomorphological coherence, probably still needs further refinements.     

Joints,faults and palaeostress evolution in the Campo de Dalias (Betic Cordilleras,southeastern Spain)

The Campo de Dal??as, located between the central and eastern Betic Cordilleras, shows an evolution determined by the overprinting of two main stress fields since Pliocene times. The first of these develops hybrid and tensional joint sets up to Pleistocene (100 000 yr) and is characterized by NNW–SSE horizontal trend of compression and an ENE–WSW horizontal extension. The second stress field has prolate to triaxial extensional ellipsoids, also with ENE–WSW horizontal extension, and continues to be active today. The most recent stresses produce the reactivation of previous joints as faults whose trends are comprised mainly from N120°E to N170°E and have a normal and transtensional regime, with dextral or sinistral components. The palaeostress evolution of this region is similar to that undergone by other basins of the Eastern Betic Cordilleras, although the Pliocene–Pleistocene transcurrent deformations in the Campo de Dal??as only develop joints and not strike-slip faults.     

Chert occurrences in carbonate turbidites: examples from the Upper Jurassic of the Betic Mountains (southern Spain)

In Upper Jurassic carbonate turbidites of the Betic mountains (southern Spain), chert occurs in three morphologies: bedded chert, nodular chert and mottled chert. The last refers to a weak dispersed and selective silification which gives a speckled appearance to the rock. The three types of chert are formed by replacement of limestones and are associated with different calcareous facies. Turbidite packstones of Saccocoma and peloids, and turbidite lime mudstones of pelagic material contain bedded and nodular cherts. The silicification textures are mainly micro- and cryptocrystalline quartz, with local chalcedonic quartz (both length-fast and length-slow) which is more common in the packstones. Only mottled chert is produced where calcareous breccia beds are silicified. Mottled chert consists of micro- and cryptocrystalline quartz, length-slow chalcedonic quartz and mosaics or individual crystals of euhedral megaquartz. Beds and nodules are the result of early diagenetic silicification, with silica derived from the calcitization and dissolution of radiolarians and, subordinately, sponge spicules, whereas mottled chert is the consequence of later silicification in a probably Mg-rich environment. Early silicification is mainly confined to turbidite beds and only rarely occurs in the interbedded pelagic limestones. Turbidite sedimentation favours silicification because rapid burial of the transported siliceous tests prevents silica from the dissolution of tests passing into overlying sea water. A silica-rich interstitial fluid develops in the turbidite layer and this migrates to more permeable zones giving rise to bedded and nodular chert.     

The geodynamic evolution of the Internal Zone of the Betic Cordilleras (south-east Spain): a model based on structural analysis and geothermobarometry

ABSTRACT The Internal Zone of the Betic Cordilleras consists of several superimposed major thrust sheets with different P-T-t evolutions. On the basis of an integrated field, microscopic and laboratory study, the tectono-metamorphic history of the Mulhacen Complex and Almanzora Unit has been reconstructed in detail. The Mulhacen Complex has been affected by at least five phases of penetrative deformation, which have been labelled D_x-1, D_x, D_x+1, D_x+2 and D_x+3. D_x-1, and D_x are related to continent-continent collision, which is indicated by high pressure-low temperature (HP/LT) and subsequent intermediate P/T metamorphic conditions. D_x+1 is related to crustal thinning and heterogeneous extension. During this event the Almanzora Unit was juxtaposed against the Mulhacen Complex. This phase was succeeded by the establishment of low pressure-high temperature (LP/HT) conditions and at least two phases of folding and overthrusting. The Almanzora Unit shows a comparable tectono-metamorphic evolution post D_x+1. However, the P/T conditions prior to D_x+1 indicate a higher crustal position with respect to the Mulhacen Complex during the collisional event.     

Carbon and oxygen isotopes: a tool for Jurassic and early Cretaceous pelagic correlation (southern Spain)

The isotopic evolution of δ¹³C and δ¹⁸O is reported for the Jurassic and early Cretaceous in two pelagic sections of the External Zones in the Betic Cordilleras (SE Spain). Stable isotope curves from pelagic trough and swell sections display similar patterns. Variations in δ¹⁸O and δ¹³C values from strata at equivalent age probably reflect both early diagenetic cementation and later temperature‐related burial diagenesis. Comparison of global isotope curves with those presented in this work allows the differentiation of global from local events. Thus, the anoxic event during the early Toarcian (falciferum Zone) is characterized by elevated δ¹³C and depressed δ¹⁸O values. The isotopic record also allows the detection of the middle Oxfordian transgression. There are other peaks for the late Toarcian, early Bajocian, Callovian and early Berriasian that can also be used as tools for correlation purposes. Copyright © 2002 John Wiley & Sons, Ltd.     

Dynamics of sedimentary environments in the accelerated siltation of a reservoir: the case of Alhama de Granada,southern Spain

An analysis has been made of sedimentary systems involved in the rapid silting of a reservoir constructed in 1974 in Alhama de Granada (S. Spain); in only 30 years the storage capacity of the reservoir has shrunk by 80% and its perimeter has decreased by 64%. A study of sediment lithofacies identified in a series of shallow trenches and of georadar facies identified in a series of almost 900 m lines of ground penetrating radar (GPR) images, together with a survey of surface geology, has identified 3 alluvial systems (2 transversal systems and a longitudinal system) whose deltas have filled in the reservoir. Thus, there are three phases in the evolution of the reservoir siltation: (1) an initial stage (1974–1977) typified by northward progradation of the longitudinal river delta of about 100 m year⁻¹ and an eastward progradation of the transversal system delta of about 20 m year⁻¹; (2) an intermediate stage (1977–1984) in which the longitudinal river delta progradation slowed to 25 m year⁻¹ and the axial drainage became obstructed due to the considerable eastward progradation of the transversal delta; and (3) a final phase (1984–present) in which there have been few changes in the areal distribution of the deltas apart from a southeastward expansion of the transversal delta. Generally, aggradational growth patterns (vertical accretion) have dominated in this final phase. The lithology of the source area, the slope and precipitation distribution has a significant effect not only on the sediment supply, but also indirectly on the creation of accommodation space and on the evolution of stratal growth patterns.     

Exhumation, doming and slab retreat in the Betic Cordillera (SE Spain): in situ40Ar/39Ar ages and P–T–d–t paths for the Nevado-Filabride complex

The combination of metamorphic petrology tools and in situ laser ⁴⁰Ar/³⁹Ar dating on phengite (linking time of growth, compositions and P–T conditions) enables us to identify a detailed P–T–d–t path for the still debated tectonometamorphic evolution of the Nevado‐Filabride complex and infer new geodynamic‐scale constraints. Our data show an isothermal decompression (at 550 °C) from 20 kbar for the Bédar‐Macael unit and 14 kbar for the Calar Alto unit down to c. 3–4 kbar for both units at 2.8 mm year^?1. At 22–18 Ma, this first part of the exhumation is followed by a final exhumation at 0.6 mm year^?1 along a high‐temperature low‐pressure (HTLP) gradient of c. 60 °C km^?1. The age of the peak of pressure is not precisely known but it is shown that it is around 30 Ma and possibly older, which is at variance with recent models suggesting a younger age for high‐pressure (HP) metamorphism. Most of the exhumation is related to late‐orogenic extension from c. 30 to 22–18 Ma. Thus the formation of the main ductile extensional shear zone, the Filabres Shear Zone (FSZ), occurred at 22–18 Ma and is clearly associated with a top‐to‐the‐west shear sense once the FSZ is well localized. The transition from ductile to brittle then occurred at c. 14 Ma. The final exhumation, accommodated by brittle deformation, occurred from c. 14 to 9 Ma and was accompanied, from 12 to 8 Ma, by the formation of nearby extensional basins. The duration of the extensional process is c. 20 Myr which argues in favour of a progressive slab retreat from c. 30 to 9 Ma. The change in the shape of the P–T path at 22–18 Ma together with strain localization along the main top‐to‐the‐west shear zone suggests that this date corresponds to a change in the direction of slab retreat from southwards to westwards.     

Resedimented carbonate and volcanic rocks in the Berriasian-Hauterivian of the Subbetic (Alamedilla, Betic Cordillera, southern Spain)

Sedimentary rocks of the Lower Cretaceous in the Subbetic of the Alamedilla area (province of Granada) were studied. In this area, a significant amount of redeposited sediments within the Carretero Formation were recorded. Resedimented material is mainly composed of Jurassic oolitic limestones and volcanic rocks, as well as of Neocomian hemipelagic sedimentary rocks (marly limestones and marls). All these redeposited sediments corresponding to rock fall and debris flow originated as the result of significant slopes in a very sharp submarine topography. Volcanism and the resultant volcanic edifices created this sharp slopes making up in some cases guyots. The volcanism was mainly active in the Middle Jurassic, although it persisted locally until Late Jurassic and Early Cretaceous, and controlled the sedimentation in this area of the Subbetic basin during most of the Mesozoic. The proposed genetic model is in agreement with a base-of-slope apron model with two significant special features: (1) the provenance of the clasts mainly from Jurassic outcrops with oolites deposited in guyots and isolated marine platforms, and volcanic submarine rocks, and (2) the palaeobathymetry of the deposits, relatively shallow and sporadically affected by storm waves.     

Lower Aptian Subbetic organic-rich facies, radiolarites, and associated deposits: the local expression of Oceanic Anoxic Event 1a (Carbonero Formation, southern Spain)

The Carbonero Formation represents a scarce, well documented example of Aptian anoxic facies in the Betic Cordillera. Generally, the Aptian record in the pelagic Subbetic basin is both very discontinuous and affected by frequent hiatuses, but in some subsident areas controlled by extensional faults (as in the Carbonero trough) an interesting record is preserved. The Carbonero Formation is characterised by a thick pelagic succession composed of marls with intercalations of calcareous turbidites and a thick interval of anoxic facies. This interval, dated as early Aptian, most likely represents the local expression of Ocean Anoxic Event 1a in the Subbetic basin. A multidisciplinary study including lithostratigraphy, biostratigraphy, and sedimentology has been carried out in the Carbonero Formation, with special attention to the anoxic interval. A collection of facies and sedimentary features has been characterised and interpreted, including barite concretions, calcareous concretions, black shales, siliceous marls and radiolarites, and calcareous turbidites. All these facies seem to have been deposited under oxygen-depleted conditions on a fault-bounded depression with a high subsidence rate. The accumulation and burial of sediments and the preservation of organic matter were controlled by both local and regional factors, such as the physiography of the basin and tectonic setting, as well as by global factors, such as palaeoceanographic and climatic changes.     

Lithostratigraphical correlation of micromammal sites and biostratigraphy of the Upper Pliocene to Lower Pleistocene in the Northeast Guadix‐Baza Basin (southern Spain)

The Plio‐Pleistocene non‐marine sequence in the northeast Guadix–Baza Basin (southern Spain) comprises alluvial and lacustrine deposits (Baza Formation). The results of a revised lithostratigraphical correlation between sections from the middle and upper members of the Baza Formation in the northeast part of the basin, supported by detailed mapping, is presented. The position of micromammal sites in the lithostratigraphical scheme, together with the results of intensive palaeontological sampling for small mammal remains, has allowed us to develop a high‐resolution biostratigraphical framework for the area. This provides an opportunity to refine the biozonation for the Plio‐Pleistocene micromammal faunas, and to define faunal events from the late Villanyian (late Pliocene) to the early Pleistocene. On the basis of the lithostratigraphical and biostratigraphical approaches we obtain the following sequence of biozones for the late Pliocene to early Pleistocene: Kislangia gusii, Mimomys cf. reidi, M. oswaldoreigi, Allophaiomys pliocaenicus and A. burgondiae. Copyright © 2000 John Wiley & Sons, Ltd.     

Mesozoic thermal history of the Prebetic continental margin (southern Spain): Constraints from apatite fission-track analysis

Apatite fission-track analysis was applied to Triassic and Cretaceous sediments from the South-Iberian Continental Margin to unravel its thermal history. Apatite fission-track age populations from Triassic samples indicate partial annealing and point to a maximum temperature of around 100–110 °C during their post-depositional evolution. In certain apatites from Cretaceous samples, two different fission-track age populations of 93–99 and around 180 Ma can be distinguished. Track lengths associated with these two populations enabled thermal modelling based on experimental annealing and mathematical algorithms. These thermal models indicate that the post-depositional thermal evolution attained temperatures ≤ 70 °C, which is consistent with available vitrinite-reflectance data. Thermal modelling for the Cretaceous samples makes it possible to decipher a succession of cooling and heating periods, consisting of (a) a late Carboniferous–Permian cooling followed by (b) a progressive heating episode that ended approximately 120 Ma at a maximum T of around 110 °C. The first cooling episode resulted from a combination of factors such as: the relaxation of the thermal anomaly related to the termination of the Hercynian cycle; the progressive exhumation of the Hercynian basement and the thermal subsidence related to the rifting of the Bay of Biscay, reactivated during the Late Permian. Jurassic thermal evolution deduced from the inherited thermal signal in the Cretaceous sediments is characterized by progressive heating that ended around 120 Ma. This heating episode is related to thermal subsidence during Jurassic rifting, in agreement with the presence of abundant mantle-derived tholeiitic magmas interbedded in the Jurassic rocks. The end of the Jurassic rifting is well marked by a cooling episode apparently starting during Neocomiam times and ending at surface conditions by Albian times.