Baza Basin Research Articles

New magnetostratigraphic and numerical age of the Fuente Nueva-3 site (Guadix-Baza basin, Spain)

Sediments of the Plio-Pleistocene Guadix – Baza basin have provided a wealth of information on the first hominin populations in Western Europe. To better constrain the age of the Fuente Nueva-3 archaeological site within the basin, and to complement previous magnetostratigraphic studies, two vertical boreholes were taken that provide a continuous record of the lower part of the sequence. Results indicate that the sequence is dominated by negative inclinations, but some additional intervals with positive inclination are also identified in the lower part of the sequence. A new cosmogenic nuclide burial age of 1.50 ± 0.31 Ma helps constrain the magnetostratigraphic record. The abundance of normal polarity directions at the bottom of a borehole may indicate proximity to the Olduvai Subchron; however, further analyses are required to confirm this hypothesis.

The geochemistry of biogenic carbonates as a paleoenvironmental tool for the Lower Pleistocene Barranco León sequence (BL-5D, Baza Basin, Spain)

The Barranco (creek) León section is located in the NE marginal area of the lacustrine Plio-Pleistocene Baza Basin (Southern Spain). The Barranco León BL-5D mammal and archeological site has delivered abundant lithic tools and a hominin tooth; the age ascribed to this site is comprised between the Olduvai and Jaramillo subchrons, close to 1.4 Ma, based on magnetostratigraphy, biostratigraphy and ERS dating. The studied BL-5 section consists from base to top, of dark sandy mudstones and lutites with interbedded sandy marls. The lower part of the dark sandy mudstones contains a brackish fauna of foraminifera, ostracods, and mollusks. Sandy carbonate mudstones and sandy lutites with freshwater-oligosaline ostracods and mollusks form the upper part of the archeological excavation sequence. Stable isotope (δ13C, δ18O) and trace element analyses on ostracod and mollusk shells allow depicting the paleoenvironmental conditions recorded in the lacustrine sequence. Moreover, indications on provenance for waters have been obtained from 87Sr/86Sr ratios from shells and opercula from mollusks. The isotopic composition of the biogenic carbonates shows a strong correlation between δ13C and δ18O, which is noticeable for some gastropod shells. This correlation is a characteristic feature of closed lake settings. In our case, the more negative isotopic values reflect the input of meteoric waters and the more positive ones the skeletal carbonates formed in more isotopically concentrated waters. Some of the more negative isotopic values correspond to biogenic carbonates from the BL-5D level. They correspond to isotopically diluted waters, although the trace element data and the invertebrate fauna indicate oligosaline to mesosaline waters. Moreover, the presence in BL-5D of shells from Melanopsis tuberculata, a thermophilous gastropod, together with their isotopic signatures suggest the input of oligosaline waters with a thermal influence. The available geochemical data indicate a first stage of varying influence of several water types under changing water level in a closed lake recorded in the base of the studied sequence (brackish fauna level). The overlying beds record a through flowing open lacustrine environment mainly fed by meteoric surface and ground waters with significant inputs of stream waters.

Hydrothermal activity and its paleoecological implications in the latest Miocene to Middle Pleistocene lacustrine environments of the Baza Basin (Betic Cordillera, SE Spain)

The continental sedimentary record of the Baza Basin (Guadix–Baza Depression, Betic Cordillera, SE Spain) shows six sedimentary units of lacustrine origin deposited from the latest Miocene to the Middle Pleistocene. Depending on the interval considered, the lacustrine deposits are mainly composed of marls, carbonates or gypsiferous evaporites, showing lithological, mineralogical and geochemical features (i.e., magnesium, strontium and sulfur contents, celestine deposits and travertine growths) that are evidence of intense, tectonically-induced hydrothermal activity. According to the high concentrations of strontium and sulfur as well as the abundance of travertines and magnesium clays, the supply of hot waters was greater during the Zanclean, the Gelasian and the Calabrian, as a result of tectonic activity. Hydrothermal activity has continued until the present time and is responsible of the hot springs that are nowadays active in the Guadix–Baza Depression. The paleoenvironmental consequences of these sublacustrine hot springs were that during some intervals the lakes maintained a relatively permanent water table, not subject to periodic desiccations in the dry season, and warmer temperatures throughout the year. This resulted in a high level of organic productivity, especially for the Calabrian, which allowed the development of a rich and well diversified mammalian community, similar to those of modern African savannas with tree patches. In this mild environment, the permanent water sheet favored the presence of drought intolerant megaherbivores such as the giant extinct hippo Hippopotamus antiquus. The high standing crop biomass of ungulates resulted in the availability of abundant carcasses for scavengers such as hyenas and hominins, which explains the very high densities of skeletal remains preserved in the sediments distributed along the lake surroundings.

Isotopic evidence for dolomite formation in soils

Dolomite formation in soils constitute a particular challenge because of: 1) scant magnesium content in continental environments as opposed to the marine medium, 2) the kinetic problem related to the incorporation of magnesium into the carbonate, and 3) the unknown role of soil dolomites in the global carbon cycle.Pedogenic dolomite formed at deeper soil levels (subsoil) before the development of petrocalcic horizon barriers was investigated in a semiarid region of SE Spain (Guadix–Baza basin). Mineralogical characterization, textural relationships and isotopic data concerning soil dolomite, together with the results of a precipitation experiment, provided fuller knowledge of the processes and conditions governing neoformation of dolomite in these soils.In the study case, dolomite enrichment occurs beyond the limit of major biological activity, which coincides with the rooting depth of native perennial plants in the semiarid soils studied. Textural studies reveal the corrosion of inherited dolomite crystals in the upper soil horizons and the formation of dolomite in depth in relation to a clayey material, composed mainly of smectites. Stable isotope distribution in dolomites throughout the profiles indicates a fractionation with depth. This is explained by the formation of dolomites after the dissolution of the pedogenic calcite. The calcite detected in the subsoil is interpreted here as a precursor of the neoformed dolomites that transport the isotopic signal associated with biological activity of soils to deeper layers. Dolomite formation appears to be favoured by the presence of clay minerals in the precipitation media. Clays retain water during evapotranspiration stages, which drastically change the transport properties of the media and promote the incorporation of Mg into the structure of the neoformed Ca,Mg-carbonate. As confirmed by laboratory experiments, diffusion-controlled crystal-growth processes lead to the formation a precursory “protodolomite” with disordered Ca,Mg distribution from a fluid locally supersaturated in dolomite.

Contribution à la paléolimnologie du Plio-Pléistocène du bassin de Baza (SE Espagne) à partir de l’étude des diatomées

Several outcrops with diatoms have been identified in the Neogene-Quaternary Baza basin. The most relevant two are located in the NE margin, in different lithostratigraphic units. Their diatom flora is dominated by Epithemia adnata and Epithemia turgida, a littoral epiphytic aquatic plants. These diatom assemblages are typical of fresh to slightly brackish waters in shallow and alkaline lakes. Those two diatomitic deposits are interstratified between alluvial sediments and represent permanent shallow lakes developed during two wet periods of time. Barranco de las Lumbres is the oldest of these lake events and is dated by fauna and paleomagnetism as late Miocene (Turolian). The upper beds of the younger lake episode (Rincon de la Losa) is dated by paleomagnetism and mammals at 1.9 Ma. In addition to these marginal diatomitic deposits, other outcrops with diatoms have been identified in more central areas of the Basin in Galera village, the lower part of Barranco del Agua section is composed of gypsum, carbonates and dark-brown clays and marls. Here epiphytic shallow-water diatoms Epithemia adnata, Epithemia turgida and some planktonic littoral forms (Fragilaria sp.) suggest a shallow fresh to oligosaline water environment. Additional diatomaceous deposits were located in a more evaporitic zone of the basin near the town of Castillejar. This outcrop presents species (Navicula digitoradiata and Surirella ovalis), which indicate distinctive more saline waters and environment. The distribution of the diatom flora in the Baza basin is consistent with stratigraphic data, which indicates an increase of evaporitic facies towards the center of the basin and the occurrence of different kinds of waters within the lake system. The isotopic composition (δ34S, δ18O) of the gypsum samples of Baza basin (Gibert et al.,2007a) is consistent with a Triassic origin of the sulphate as a result of chemical recycling. These data also suggest that a similar recycling mechanism operated in the saline lake system, where the gypsum sediments from the margins were coevally recycled towards the inner part.

Comments on “Quaternary landscape evolution and erosion rates for an intramontane Neogene basin (Guadix–Baza basin, SE Spain)” by J.V. Pérez-Peña, J.M. Azañón, A. Azor, P. Tuccimei, M. Della Seta, M. Soligo, (2009) Geomorphology 106, 206–218

Pérez-Peña et al. (2009) recently estimated erosion rates for an intramontane basin based on the age of the petrocalcic horizon developed in the uppermost basin fill surface. This new interpretation contradicts well-established and reliable evidence for the origin of the travertines deposited after this surface was cut by a new exorheic drainage system. We argue that their interpretations are incorrect and that they have ignored much of the previous dating and field geomorphological evidence. Morphological, sedimentary and chronological evidence indicate that the reported incision rates are incorrect.

The challenge of dating early pleistocene fossil teeth by the combined uranium series–electron spin resonance method: the Venta Micena palaeontological site (Orce, Spain)

AbstractThe palaeontological site of Venta Micena (Orce, Andalusia, Spain) lies in the eastern sector of the Guadix–Baza basin, one of the best documented areas in Europe for Plio‐Pleistocene biostratigraphy. The combination of biochronological and palaeomagnetic results, combined with the radiometric data obtained for Atapuerca Sima del Elefante, indicated that the Venta Micena stratum was formed between the Jaramillo and Olduvai palaeomagnetic events, most likely between 1.22 and 1.77 Ma. Five fossil teeth from two outcrops (sites A and B) were selected to assess the potential of combined uranium series–electron spin resonance (US‐ESR) dating of Early Pleistocene sites. Although the US‐ESR results of the first outcrop showed a large scatter between the three teeth, the mean age of 1.37 ± 0.24 Ma can be considered a reasonable age estimate for Venta Micena. The mean ESR age of 0.62 ± 0.03 Ma obtained for site B seems to be a severe underestimation when compared with the independent age control. This underestimation is attributed to a relative recent U‐mobilization event that led to some U‐leaching. The results show that any ESR age calculations of old samples are extremely sensitive to variations in the measured 230Th/234U ratios in dental tissues. Although the results demonstrate that ESR can in principle be applied to Early Pleistocene sites, they also reveal the complexity of dating such old teeth. It is necessary to continue research in several directions, such as study of the behaviour of ESR signals in old teeth and understanding recent U‐mobilization processes, to improve the reliability of the combined US‐ESR dating method applied to Early Pleistocene times, a period for which the number of available numerical dating techniques is very limited. Copyright © 2011 John Wiley & Sons, Ltd.

Geology and chronology of the continental Pleistocene archeological and paleontological sites of the Orce area (Baza basin, Spain)

The Guadix-Baza Basin hosts a continuous continental record of paleoenvironmental, paleobiological and geological changes from around 8 Ma to 205 ka. A remarkable succession of Pleistocene mammal sites is found in the Lower and Upper members of the Baza Formation in the Orce area. The Upper Member contains the Early Pleistocene paleontological and archeological sites of Barranco León-5 and Fuente Nueva 3. Both sites belong to the early Pleistocene zone defined by Allophaiomys aff. lavocati and a small Mimomys savini. This zone can be correlated with that of central Europe containing Mimomys savini and Microtus praehintoni. These sites are located in the marginal lacustrine deposits of the Baza lake system and originated in expanded phases of the main lake when meteoric surface and shallow groundwater inputs were predominant. The Barranco León-5 site is related to a sudden event of high-energy currents entering a lacustrine - palustrine domain. These currents transported gravels, bones and lithic industries from a short distance (maximum, hundreds of meters). In contrast, the diverse levels in Fuente Nueva 3 do not show evidence of noticeable transport by traction currents. The age of the mammal succession and sites is based on magnetostratigraphy. In the Middle and Upper members of the Baza Formation, only reversed polarities are found (Matuyama epoch). The location of the Olduvai chron is still unclear and could have not been recorded due to the common hiatuses observed in the sedimentary successions. In the Lower Member, normal and reverse polarities (Gauss epoch) are found in the Galera and Vélez-Salar sections. The later contains the site of Fuente Nueva 1, which is pre-Olduvai chron in age according to paleontological data and biostratigraphic correlation.

Trophic interactions in an arid ecosystem: From decomposers to top-predators

In this review we compile results on interactions above and below ground and food web functioning in an arid environment at the Baza Basin, in the Iberian southeast. Our data reveal that herbivory is difficult to estimate in our system. Some herbivores (rabbits) and granivores ( Messor ants) create nutrient and detritus-rich patches, with important effects on the diversity and abundance of species both above and below ground. Fluctuations of prey availability, especially those caused by changes in their circadian rhythms, provoke seasonal migrations and omnivory in predators. We also present experimental evidence of the effects of interactions between aboveground and belowground macroarthropods on litter degradation; belowground detritivores are responsible for a high percentage of ground surface litter decomposition. We demonstrate that belowground herbivores and decomposers can dramatically change aboveground multitrophic interactions. Finally, we identify the biotic and abiotic factors controlling aboveground and belowground macrofaunal distribution at a broad scale. We conclude that trophic interactions in this semi-arid area are numerous and complex with many of the interactions involving more than two or three organisms. The interactions between above- and belowground organisms added complexity to this system. These habitats in which organisms deal with extreme abiotic conditions promote odd interactions resulting in an increase of biodiversity. Finally, despite the large research effort devoted to understanding food web structure and dynamics in this area recently, our state of knowledge is still far from providing a complete picture of interactions and their implications in the regulation and functioning of the system.

Glacis geometry as a geomorphic marker of recent tectonics: The Guadix–Baza basin (South Spain)

The Guadix–Baza basin occupies 4000 km 2, and constitutes the largest intramontane basin of the Betic Cordillera (Southern Spain). It has a well preserved geomorphic surface, a glacis, which started to be eroded when the basin conditions changed from endorheic to exorheic. Taking into account its large preserved surface area (more than 1200 km 2) and its pre-deformational geometry, this geomorphic surface is a useful marker of recent deformation. Combining geological and geomorphological data and high resolution DEM, topographic profiles of the glacis have been produced to estimate vertical displacements caused by active compression and extension structures. These structures have produced relative vertical displacements of up to 100 m from the late middle Pleistocene to the present. Assuming an age for the glacis of between 205 and 600 ka, it has been possible to estimate long-term minimum and maximum vertical rates of the activity of normal faults and folds using this geomorphic surface as a marker. Vertical slip rates range from 0.07 to 0.49 mm/year for the main active normal faults and vertical folding rates range from 0.05 to 0.17 mm/year for several active folds. These long-term vertical slip and folding rates are in accordance with other values previously estimated in other sectors of the Betic Cordillera. When present, detailed geomorphic study of recent glacis is an excellent tool for evaluating active tectonics over large regions.

Soil–vegetation relationships in semi-arid Mediterranean old fields (SE Spain): Implications for management

In recent decades a large proportion of agricultural lands have been abandoned in European countries, mainly in semi-arid or mountain Mediterranean areas. Environmental processes in old fields have attracted the attention of many scientists, but several issues remain unanswered. This study seeks to identify the edaphic factors determining changes in perennial-plant communities in old fields of a Mediterranean semi-arid area (Baza Basin, SE Spain) and elucidate the main relationships between these communities. For this goal, we mapped all old fields in this study area and calculated the surface area occupied by each community (single and mixed). Floristic data and soil samples were collected for all the communities, through a stratified sampling, and the data were subjected to several statistical treatments (ANOVA, DCA, CCA, Spearman correlation). The joint study of floristic and edaphic variables confirmed that the soil determines mainly the establishment of vegetation in old fields of this area. Specifically, salinity, moisture, and gravel content accounted for most of the floristic variation. The results may be useful for old-field management, for example, to identify areas that should not be cultivated due to salinity or to the high ecological value.

Active tectonics in the Sierra Nevada (Betic Cordillera, SE Spain): Insights from geomorphic indexes and drainage pattern analysis

The Sierra Nevada of the central Betic Cordillera is a 3000 m-high mountain range surrounded by Neogene–Quaternary sedimentary basins, having been uplifted since Late Miocene times. The southern and western mountain fronts of the Sierra Nevada are fault-bounded, while the northern one is an unconformity between the Neogene–Quaternary sediments of the Guadix–Baza basin and the metamorphic rocks of the Nevado–Filabride complex. We have carried out a geomorphic study by examining drainage patterns and characteristics of mountain fronts in order to reveal areal variations and styles of rock uplift. Mountain front sinuosity ( S mf), area–altitude relations (hypsometric curves), and valley floor entrenchment differ significantly between the northern, western, and southern mountain fronts. The lack of important faults along the northern Sierra Nevada mountain front, together with the elevated topographic position of the Guadix–Baza basin (average altitude is around 1100 m), points to similar uplift of both geomorphic units (sierra and basin) in a single large-scale crustal block. The asymmetry factors show systematic asymmetries at both sides of the Lanjarón River, probably due to the presence of an active NNE–SSW oriented antiform in the western Sierra Nevada. Finally, river profiles indicate maximal river entrenchment in the western part of the Sierra Nevada, probably related to the uplift of the footwall of the Padul–Nigüelas fault-system. Therefore, our geomorphic analysis suggests that the western part of the Sierra Nevada is tectonically active by means of a combination of normal faults along the mountain front and NNE–SSW oriented active folds, which, in turn, likely have a gravitational origin related to the exhumation of the footwall of the normal fault-system.

The significance of giant seismites in the Plio-Pleistocene Baza palaeo-lake (S Spain)

Terra Nova, 22, 172–179, 2010 Abstract Giant load-type seismites, uncommon in the geological record, are described in Plio-Pleistocene lacustrine deposits of the Baza Basin (Betic Cordillera, S Iberia). Deformed beds of the marginal lacustrine and distal alluvial facies of the Baza palaeo-lake can be traced continuously for several kilometres. Soft-sediment deformation is represented by load-type structures of large dimensions (pillows around 4 m in width and 2 m in height). Three-dimensional exposures show ellipsoidal pillows separated by fluidized channels without any preferred orientation. The final size of these load-type seismites is strongly influenced by sedimentary factors such as the presence of a reverse density gradient in sediments and the bed thickness. The giant seismites of the Baza basin are located in a region, which is unlikely to have been subjected to high magnitude earthquakes (maximum around 7.0). Therefore, magnitude is not the main factor that controls the size of these load-type structures.

Paleoenvironmental evolution of the Early Pleistocene lacustrine sequence at Barranco León archeological site (Orce, Baza Basin, Southern Spain) from stable isotopes and Sr and Mg chemistry of ostracod shells

Stable isotope and trace element contents of Cyprideis torosa valves from the Lower Pleistocene marginal lacustrine sequence of Barranco Leon, Baza Basin (Southern Spain), allow us to reconstruct the geochemical record of environmental change in this marginal area of the basin and to compare these data with the environmental changes inferred from the faunal associations. Hydrochemical features of the Baza Lake system have been influenced by changes in water source, solute composition, and water level during the past. Three water types may have been involved in a complex mixing in the marginal area during the studied intervals (1) waters of the Baza lacustrine system that underwent large P/E changes, (2) dilute, meteoric water inputs (surface and shallow groundwaters), (3) saline groundwater inputs of meteoric origin that acquired their salinity by halite and gypsum dissolution. Four stages in the Pleistocene paleoenvironmental evolution of the Barranco Leon area have been differentiated: stage I records a high lake level (highstand) of the saline closed-lake system. Stage II corresponds to very shallow, palustrine conditions. Stage III records the varying influence of the three water types under changing water level in a closed-lake. Stage IV corresponds to a through-flowing, open lacustrine environment mainly fed by meteoric saline groundwaters with minor inputs of stream waters. This small through-flowing lake was connected to a larger, inner saline closed-lake system. The BL 5 mammal site with lithic tools of an early human occupation phase in Western Europe corresponds to a particular episode within this stage of the environmental evolution in the marginal zone of the Baza Lake.

Quaternary landscape evolution and erosion rates for an intramontane Neogene basin (Guadix–Baza basin, SE Spain)

The landscape evolution in Neogene intramontane basins is a result of the interaction of climatic, lithologic, and tectonic factors. When sedimentation ceases and a basin enters an erosional stage, estimating erosion rates across the entire basin can offer a good view of landscape evolution. In this work, the erosion rates in the Guadix–Baza basin have been calculated based on a volumetric estimate of sediment loss by river erosion since the Late Pleistocene. To do so, the distribution of a glacis surface at ca. 43 kyr, characterised by a calcrete layer that caps the basin infilling, has been reconstructed. To support this age, new radiometric data of the glacis are presented. The volume of sediment loss by water erosion has been calculated for the entire basin by comparing the reconstructed geomorphic surface and the present-day topography. The resulting erosion rates vary between 4.28 and 6.57 m 3 ha − 1 yr − 1 , and are the consequence of the interaction of climatic, lithologic, topographic, and tectonic factors. Individual erosion rates for the Guadix and Baza sub-basins (11.80 m 3 ha − 1 yr − 1 and 1.77 m 3 ha − 1 yr − 1 respectively) suggest different stages of drainage pattern evolution in the two sub-basins. We attribute the lower values obtained in the Baza sub-basin to the down-throw of this sub-basin caused by very recent activity along the Baza fault.

Tracing the ecophysiology of ungulates and predator–prey relationships in an early Pleistocene large mammal community

Research into the reconstruction of ancient communities in terms of dietary regimes, habitat preferences and ecological interactions of species has focused predominantly on biogeochemistry or ecomorphology alone and not in combination. The Venta Micena site (Orce, Guadix–Baza basin, SE Spain) has an early Pleistocene vertebrate assemblage with exceptional biomolecular preservation. Collagen was successfully extracted from 77 bone samples of 18 species of large mammals, which allowed analyses of carbon- and nitrogen-isotopes. δ 13C, δ 15N and δ 18O ratios combined with ecomorphological indexes provide interesting clues on the autecology and palaeophysiology of extinct species, which help in deciphering aspects of community trophic structure and predator–prey interactions. Specifically, morphometric ratios (e.g., hypsodonty index and relative length of the lower premolar tooth row; [Palmqvist, P., Gröcke, D.R., Arribas, A., Fariña, R. 2003. Paleoecological reconstruction of a lower Pleistocene large mammals community using biogeochemical ( δ 13C, δ 15N, δ 18O, Sr:Zn) and ecomorphological approaches. Paleobiology 29, 204–228.]) allow classifying the ungulates among grazers ( Equus altidens, Bison sp., Praeovibos sp., Hemitragus albus, Hippopotamus antiquus, and Mammuthus meridionalis), mized-feeders ( Soergelia minor and Pseudodama sp.) and browsers ( Stephanorhinus sp. and Praemegaceros cf. verticornis). However, δ 13C values reveal that these ungulates consumed exclusively C 3 plants and significant differences in isotopic values between perissodactyls (monogastric, hindgut fermenters) and ruminants (foregut fermenters) must reflect physiological differences related to their rates of methane production and digestive efficiency. δ 18O ratios allow the interpretation of the dietary water source of these species, suggesting that fallow deer Pseudodama sp., goat H. albus and ovibovine S. minor obtained a significant fraction of their metabolic water from the vegetation consumed. Carnivore species have higher δ 15N values than herbivores, which records the isotopic enrichment expected with an increase in trophic level. However, the unexpectedly high δ 15N values of hippo H. antiquus and muskoxen Praeovibos sp. suggest that these ungulates predominantly consumed aquatic plants and lichens, respectively. Inferences on predator–prey relationships within this ancient community, derived from the dual linear mixing model, indicate resource partitioning among sympatric predators, suggesting that sabre-tooth Megantereon whitei and jaguar Panthera cf. gombaszoegensis were ambushers of forest environments while sabre-tooth Homotherium latidens and wild dog Lycaon lycaonoides were coursing predators in open habitat . The giant, short-faced hyena Pachycrocuta brevirostris scavenged the prey of these hypercarnivores.

The Early to Middle Pleistocene boundary in the Baza Basin (Spain)

The continental vertebrate fauna of Cúllar Baza-1 (Granada, Spain) occur immediately above the Matuyama/Brunhes polarity boundary, and therefore represent an initial record for the Middle Pleistocene. All polarity zones for the Late Pliocene through Middle Pleistocene are found in an 80 m section, which includes this fossil quarry. The existing collection of abundant remains of micro-mammals, macro-mammals and lithic artifacts (indicating human activity) can now be assigned an earliest Middle Pleistocene age of 0.75 Ma. Another section, 25 km across the Neogene Baza Basin, also has the Matuyama/Brunhes polarity boundary. However, in this case the Huéscar-1 fossil quarry and the Puerto Lobo sites are both below the polarity boundary, thus representing a record of the late Early Pleistocene at ∼0.9 Ma. Differences in micro-mammal species across these Matuyama/Brunhes boundaries are significant and justify an approximately coincident biostratigraphic boundary between the Biharian and Toringian stages.

Plio-Pleistocene lacustrine evaporites of the Baza Basin (Betic Chain, SE Spain)

The Baza Basin (the eastern part of the Guadix–Baza Basin, in SE Spain) underwent a significant evaporitic sedimentation in non-marine settings during the Plio-Pleistocene. The largest of these settings developed in the central part of the basin as a shallow, saline lake system, where abundant gypsum deposits occur (Benamaurel and Galera Gypsum units). This paper studies these deposits from the cartographic, stratigraphic, sedimentologic, petrographic and isotopic points of view. All the gypsum has been preserved as primary enabling a good characterization of the environmental conditions of the original precipitates. Three interconnected subenvironments or zones –inner, intermediate and marginal– are differentiated in this saline lake system. In the inner zone (shallow to relatively deeper central lake), a regular alternation of gypsum and carbonate laminae accumulated suggesting a seasonal regime. Many of the gypsum laminae display size-gradation (both reverse and symmetrical) indicating free precipitation in a stable brine body. In the intermediate zone (mosaic of shallow lakes), carbonate (dolomitic) beds formed in association with dark lutite levels, gypsum beds, and gypsum nodules and micronodules. Moreover, anoxic conditions developed in this zone, which resulted in the formation of native sulphur occurrences of economic value. In the marginal zone, the evaporitic deposits are developed only locally (the Galera Gypsum unit, in particular). The various gypsum lithofacies in these marginal deposits suggest the presence of a number of shallow to exposed settings (saline mudflat, saline marsh and gypsiferous pond). The isotopic composition ( δ 34S, δ 18O) of the gypsum samples is consistent with a Triassic origin of the sulphate as a result of chemical recycling. These data also suggest that a similar recycling mechanism operated in the saline lake system, where the gypsum sediments from the margins were coevally recycled towards the inner part. Both the evaporitic mineralogy and the gypsum and carbonate lithofacies suggest that semiarid conditions prevailed in this basin during the accumulation of the evaporite units.

Magnetostratigraphy of the Orce region (Baza Basin), SE Spain: New chronologies for Early Pleistocene faunas and hominid occupation sites

The Orce fossil quarries, in the Baza Basin of southeastern Spain, are a rich source of Early Pleistocene Palaeolithic tools and vertebrate remains. Geologic fieldwork during the last decade has placed these fossiliferous strata within the context of a thick Neogene continental sequence. Detailed lithostratigraphic and magnetostratigraphic results indicate that at least the upper 60m of this sequence are of Early Pleistocene age. The quarried strata (Venta Micena, Barranco León and Fuentenueva-3) are from a narrow time span (<100ka) starting before 1.3Ma. A new, lower excavation at ∼1.5Ma (Fuentenueva-1 quarry) has a distinctly older fauna. These Orce strata provide a high resolution, Early Pleistocene record of grassland fauna that shows the end of Mammal Neogene fauna (MN17) in the Fuentenueva-1 site (with Gazella borbonica, Equus stenonis) and the beginning of more characteristic Pleistocene fauna in the Venta Micena site (with Hippopotamus antiquus, Equus granatensis, Homo sp.). Thus far, no evidence for human occupation has been found within the earlier Fuentenueva-1 quarry, although many of the same terminal MN17 species have been found with hominids on the other side of Europe at the Dmanisi site (earliest Pleistocene) in the Republic of Georgia.

Geochronological position of badlands and geomorphological patterns in the Guadix–Baza basin (SE Spain)

The Guadix–Baza basin is one of a number of intramontane depressions located within the Betic Cordillera (SE Spain), where the geological and geomorphological evolution is controlled by tectonic activity. The basin ceased to be closed after capture by the Atlantic network, when five main land systems developed. Late Pleistocene geological evolution basically consisted of erosional modelling, when badlands were deeply incised in highly erodible materials (marls and silts). Three travertine platforms and several Palaeolithic sites were used to determine that this main incision period fell within a 115,000–48,000 yr range. There are few signs of geomorphological evolution of this basin in the last 48,000 yr. Based on these geomorphological data and soil development, tectonic uplift of the basin probably played a secondary role in its evolution, and climatic conditions in southern Iberia in the 144,000–48,000 yr period were more humid and variable than later.