Guadix-Baza Basin Research Articles

Resource Limitation of Nesting: Chance Favors the Prepared Dung Beetle

Over a period of 2 yr, physiological and morphological traits related with nesting in two dominant dung beetle species in the Guadix-Baza Basin (Onitis ion [Ol.] and Onthophagus merdarius Chevr., Coleoptera: Scarabaeidae) were analyzed. The role of physiological conditions and resource availability for nesting as factors determining reproductive output in these species is discussed. Our results show that food does not seem to constrain sexual maturation. Both species reached sexual maturation and stored large amounts of reserves after a short period of nourishment. In addition, females were inseminated shortly after emergence, so they were ready to lay eggs only a few days after emergence. Although both species reached sexual maturation quickly, the number of nests dug by the females and the number of eggs laid were low, as indicated by the very low tibial wear and the low proportion of yellow bodies found. Although the rate of dung colonization was high, the number of beetles per dung pat was generally low. Therefore, aggregation of beetles does not seem to explain the low proportion of eggs laid by females of these species. Most dung pats in the study site were small, and only a small proportion (10.4%) was large enough to be suitable for nesting. In conclusion, both species were ready to reproduce soon after emergence, allowing beetles to increase their chances of reproductive success in a harsh environment in which high dung desiccation rates cause a low availability of suitable dung for nesting.

Numerical dating algorithms of amino acid racemization ratios from continental ostracodes. Application to the Guadix-Baza Basin (southern Spain)

Age calculation algorithms for the D/L ratios of five amino acids (isoleucine, leucine, aspartic acid, phenylalanine and glutamic acid) analysed in continental ostracodes were determined for southern and central Iberian Peninsula, and allow the numerical dating of deposits in the Mediterranean area since Lower Pleistocene time to present. In order to obtain more accurate results for young samples, other algorithms were calculated for aspartic acid, phenylalanine and glutamic acid. Using these algorithms, together with paleomagnetism, the chronostratigraphy of the “composite-stratotype-section” of the east domain of the Guadix-Baza Basin that covers most of the Pleistocene (from the Plio/Pleistocene boundary to 279±77 ka) has been obtained. Ostracodes represent a formidable tool for amino acid racemization dating purposes in view of their abundance, valves mineralogy and the high degree of preservation of amino acids within their caparaces, even in old (Early Pleistocene) samples. These results suggest that the range of the amino acid racemization dating method in the Iberian Peninsula is older than 1.1 Ma.

Paleoecological reconstruction of a lower Pleistocene large mammal community using biogeochemical (δ13C, δ15N, δ18O, Sr:Zn) and ecomorphological approaches

Abstract Ecomorphological and biogeochemical (trace element, and carbon, nitrogen, and oxygen isotope ratios) analyses have been used for determining the dietary niches and habitat preferences of large mammals from lower Pleistocene deposits at Venta Micena (Guadix-Baza Basin, Spain). The combination of these two approaches takes advantage of the strengths and overcome the weakness of both approaches. The range of δ13Ccollagen values for ungulate species indicates that C3 plants were dominant in the diet of these mammals. δ13Ccollagen values vary among ungulates: perissodactyls have the lowest values and bovids the highest ones, with cervids showing intermediate values. The hypsodonty index measured in lower molar teeth and the relative length of the lower premolar tooth row indicate that the horse, Equus altidens, was a grazing species, whereas the rhino, Stephanorhinus etruscus, was a mixed feeder in open habitats. The similar δ13Ccollagen values shown in both perissodactyls does not reflect differences...

Organic and inorganic carbon in soils of semiarid regions: a case study from the Guadix–Baza basin (Southeast Spain)

Intramontane sedimentary basins are an important landscape component for the evaluation of soil carbon stored in semiarid regions with Mediterranean climate. We determined the soil organic and inorganic carbon (SOC and SIC) stored at various depths in 81 profiles sampled specifically in one such basin (3317 km 2) located in Southeast Spain. Sampling reached down to 2.0–4.0 m and the samples were analysed by conventional methods. The mean SOC content for a 2.0-m depth column was 7.8 kg m −2, and the mean SIC content (calcite plus dolomite) was 134.4 kg m −2, 23% of total SOC contents and 51% of total SIC contents in the 2.0-m column were found in the second meter. The figures for SIC are considerably higher than those reported in other evaluations for semiarid regions.

Paleoecological reconstruction of a lower Pleistocene large mammal community using biogeochemical (δ13C, δ15N, δ18O, Sr:Zn) and ecomorphological approaches

Ecomorphological and biogeochemical (trace element, and carbon, nitrogen, and oxygen isotope ratios) analyses have been used for determining the dietary niches and habitat preferences of large mammals from lower Pleistocene deposits at Venta Micena (Guadix-Baza Basin, Spain). The combination of these two approaches takes advantage of the strengths and overcome the weakness of both approaches. The range of δ13Ccollagen values for ungulate species indicates that C3 plants were dominant in the diet of these mammals. δ13Ccollagen values vary among ungulates: perissodactyls have the lowest values and bovids the highest ones, with cervids showing intermediate values. The hypsodonty index measured in lower molar teeth and the relative length of the lower premolar tooth row indicate that the horse, Equus altidens, was a grazing species, whereas the rhino, Stephanorhinus etruscus, was a mixed feeder in open habitats. The similar δ13Ccollagen values shown in both perissodactyls does not reflect differences in feeding behavior with other ungulates, but rather a lower isotope enrichment factor in these monogastric herbivores than in ruminants, owing to their lower metabolic efficiency. The cervids Eucladoceros giulii and Dama sp. show low hypsodonty values, indicating that they were mixed feeders or browsers from forested habitats, an ecomorphologically based conclusion corroborated in the former by its low δ15Ncollagen content (canopy effect). Bovid species (Bovini aff. Leptobos, Soergelia minor, and Hemitragus albus) presumably inhabited open environments, according to their comparatively high hypsodonty and δ15Ncollagen values. Carnivore species (Homotherium latidens, Megantereon whitei, Pachycrocuta brevirostris, Canis falconeri, and Canis etruscus) exhibit higher δ15Ncollagen values than ungulates. These results record the isotopic enrichment expected with an increase in trophic level and are also supported by low bone Sr.Zn ratios. The elevated δ15Ncollagen value for a sample of Mammuthus meridionalis, which came from an individual with unfused epiphyses, confirms that it was a suckling animal. The δ15Ncollagen value of the scimitar-cat H. latidens is well above that obtained for the young individual of Mammuthus, which indicates that juvenile elephants were an important part of its diet. The hippo, Hippopotamus antiquus, yielded unexpectedly high δ15Ncollagen values, which suggest feeding on aquatic, non-N2-fixing plants. The high δ18Ohydroxyl values of bovids Hemitragus and Soergelia and of cervid Dama indicate that these ungulates obtained most of their water requirements from the vegetation. The megaherbivores and Eucladoceros exhibit the lowest δ18Ohydroxyl values, which suggest increased water dependence for them. Paleosynecological analysis was based on the relative abundance of species of large mammals from different ecological categories, determined by feeding behavior and locomotion types. The comparison of the frequencies of such categories in Venta Micena with those found in modern African communities indicates that the composition of the paleocommunity closely resembles those of savannas with tall grass and shrubs. The net above-ground primary productivity estimated for the on-crop biomass of the mammalian species preserved in the fossil assemblage also yields a figure congruent with that expected for an open environment.

The first human dispersal to Europe: Remarks on the archaeological and palaeoanthropological record from Orce (Guadix-Baza basin, southeastern Spain)

The chronology of the first arrival ofHomo in Europe is a rather controversial issue, with most scholars claiming until very recently that there were no permanent human settlements before the middle Pleistocene. However, new findings at Atapuerca, Dmanisi and Orce, as well as the re-evaluation of the evidence from Java, Israel and China indicate a protracted chronology for the arrival of hominids in Eurasia, during late Pliocene/lower Pleistocene times. The systematic study of the macrovertebrate assemblages from circummediterranean sites such as Orce and Dmanisi has shown a faunal replacement at the Plio-Pleistocene boundary, marked by the arrival in Europe of African immigrants such as the hippopotamus, an equid similar to modern grevy’s zebra, a large cercopithecoid and several carnivores, including a giant hyaena, a sabre-tooth and a wild dog. An analysis of the relative frequency of bones and teeth for those species of large mammals preserved in Venta Micena indicates the improbability thatHomo sp. is represented in the fossil assemblage by several bones and no tooth remain. Finally, new data on the stratigraphy of Barranco Leon are offered, with remarks on the discovery in this locality of lithic artefacts and molar tooth fragment BL5-0.

Long Plio-Pleistocene Terrestrial Record of Climate Change and Mammal Turnover in Southern Spain

Cyclostratigraphic analysis of the Pliocene Zújar section (Guadix-Baza Basin, southeastern Spain) has enabled the recognition of a number of climatically forced cycles reflecting alternating dry and wet periods. Peaks of aridity are recorded at ca. 3.95, 3.55, 3.2, 2.8, and 1.8 myr B.P. The first dry period at about 4.0 myr B.P. corresponds to the early Ruscinian Mammal age, while the second arid interval at about 3.6 myr B.P. corresponds to the establishment of the Mediterranean double seasonality. The significant mammal turnover between the late Ruscinian and early Villanyian stages is placed between chron 2An.2n and the very base of chron 2An.1n, coincident with the dry phase recognized at about 3.2 myr B.P. The fourth aridity maximum at 2.8 myr B.P. roughly coincides with the Equus event in western Europe and is probably related to the beginning of the glacial–interglacial dynamics in the Northern Hemisphere. Finally, the last dry peak at about 1.8 myr B.P. is probably related to the set of mammalian events characterizing the transition from the late Pliocene faunas to those of the early Pleistocene.

On the age of the last hipparionine faunas in western Europe

Abstract In this paper, a survey on the dating of the hipparionine fauna in the site of Villarroya (Spain) is provided. Recently, the age of Villarroya has been the subject of controversy, and an age close to the Reunion chron has been proposed. However, a detailed analysis of Kislangia ischus from this site and its comparison with samples of this species in the magnetostratigraphically well calibrated section of Zujar (Guadix–Baza basin), enables one to propose an alternative dating for the short Vill-2 section where the fossiliferous locality occurs. Therefore, the normal event present in this section is correlated to chron 2An.1n (Upper Gauss). Thus, the last hipparionine faunas can be placed in the upper part of the Gauss chron, shortly before the first evidence of Equus in Europe.

Vertebrate taphonomy in circum-lake environments: three cases in the Guadix-Baza Basin (Granada, Spain)

This work analyses the origin and taphonomy of three Plio-Pleistocene mammal assemblages from the Guadix-Baza basin (Granada, Spain): Huélago; Huéscar-1; and Cúllar de Baza-1. Similarities and differences in the taphonomic features are evaluated with regard to marginal lacustrine sedimentary processes involved in the accumulation of these mammal assemblages. Selective preservation of skeletal-part and taxa in relation to facies have been explored to determine their suitability for palaeoecological analysis. The mortality in Cúllar de Baza-1 and Huélago-1 corresponds to a catastrophic pattern, but other taphonomic features of the bones indicate that accumulation processes were diachronic as occurred in Huéscar-1. This could be explained by selective-predation and/or seasonal accumulation of bones. Hydraulic sorting and transportation greatly controlled the size and shape of accumulated skeletal elements, and the different preservational circumstances of each environment largely constrained the taxonomic composition of the fossil bone assemblages. Autochthonous fauna only occurs in Huéscar-1 corresponding to subaquatic environments. The absence of carnivores among the identifiable remains from Huélago-1 has no plausible taphonomic or sedimentological explanation. Nevertheless, after taking into account the taphonomic factors, the differences in taxonomic composition between these three mammal assemblages reflect differences in the surrounding habitats. The great diversity of ruminant artiodactyls, in particular browsers, is indicative of wooded or bushy areas in the surroundings of Huélago-1 although not in the immediate area of the lake margin. This diversity coincides with that observed in other Villafranchian localities and represents the greatest diversity of artiodactyls known from the Neogene and Quaternary record of Western Europe. In turn, the high diversity of sub-aquatic forms and a smaller variety of artiodactyl species in Huéscar-1, reflects an open, sparsely forested environment susceptible to seasonal drought. A similar sparse forested environment has been deduced for Cúllar de Baza-1. The climate and environmental conditions in Huéscar-1 and Cúllar de Baza-1 are consistent with a climatic deterioration at the beginning of the Middle Pleistocene (‘Glacial Pleistocene’).

Africa and Iberia in the Pleistocene

The Strait of Gibraltar would logically seem to be a major point of contact between Africa and Europe. Yet, controversy about possible trans-Gibraltar human movements in the Lower, Middle and even Upper Pleistocene has reigned for over a century and continues to do so. Imbricated with biogeographical arguments about faunal transfers and the creation of hominid niches in Iberia, the problem of the relationships between Africa and Iberia is one of the knottiest in Stone Age prehistory . Did early Homo ( H. ergaster , erectus , or “ antecessor ”) cross into Iberia from the Maghreb , as has long been argued on the basis of general archeological similarities? This old hypothesis, still unproven, is made somewhat more plausible by the re-dating of the site of Ain Hanech in Algeria and, in particular, by the spectacular Lower Pleistocene fossil and artifactual discoveries at Atapuerca in north-central Spain and, less securely, in the Guadix-Baza Basin of Granada. Middle Pleistocene contacts remain problematic, with direct peopling of Iberia from northwest Africa during the mid-Upper Pleistocene seeming (ironically) to be out of the question, as southern Spain and Portugal were one of the last refugia of Neanderthals using Mousterian technology, despite proximity to the putative source of anatomical modernity and cultural superiority. Similarly, despite years of speculation on a migrationist cause for the similarity between tanged points in the Aterian of North Africa and in the Solutrean of Mediterranean Spain and Portugal, the chronological and archeological data solidly disprove this seductive hypothesis. For the Upper Pleistocene, it is only in the terminal Paleolithic that, with clear evidence of marine fishing and probable navigation, a credible case can be made for trans-Gibraltar human contacts.

Early human occupation of Western Europe: paleomagnetic dates for two paleolithic sites in Spain.

The lacustrine deposits infilling the intramontane Guadix-Baza Basin, in the Betic Range of Southern Spain, have yielded abundant well-preserved lithic artifacts. In addition, the lake beds contain a wide range of micromammals including Mimomys savini and Allophaiomys burgondiae and large mammals such as Mammuthus and Hippopotamus together with the African saber-toothed felid Megantereon. The association of the lithic artifacts along with the fossil assemblages, themselves of prime significance in the Eurasian mammal biochronology, is providing new insight into the controversy of the human settlement in Southern Europe. Despite the importance of the artifacts and fossil assemblage, estimates of the geological age of the site are still in conflict. Some attempts at dating the sediments have included biochronology, uranium series, amino acid racemization, and stratigraphic correlation with other well-dated sections in the basin, but so far have failed to yield unambiguous ages. Here we present paleomagnetic age dating at the relevant localities and thus provide useful age constraints for this critical paleoanthropological and mammal site. Our data provide firm evidence for human occupation in Southern Europe in the Lower Pleistocene, around 1 mega-annum ago. The current view of when and how hominids first dispersed into Europe needs to be reevaluated.

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.

Calibration of the Early-Middle Pleistocene transition in the continental beds of the Guadix–Baza Basin (SE Spain)

The magnetostratigraphic and palaeontologic studies carried out in two sections in the Guadix–Baza Basin (SE Spain) have enabled an accurate calibration of the Early-Middle Pleistocene boundary in the continental beds of this basin. The palaeontological record (rodents) in the Cortes de Baza section indicates an age ranging from the earliest Pleistocene (latest Villanyian or early Biharian) to the late Early Pleistocene (late Biharian). The whole Cortes de Baza Section is placed in a reversed magnetic interval identified as the upper part of the Matuyama Chron. In the Guadix–Baza Basin, the Middle Pleistocene (early Toringian) was already known at the locality of Cúllar–Baza I, but new studies in the area have resulted in the recognition of Early Pleistocene deposits in the lower part of the section. Thus, the locality of Cúllar–Baza B is placed in a reversed magnetozone correlated with the uppermost Matuyama, while the locality of Cúllar–Baza C is placed in a normal magnetozone correlated to the lower Bruhnes Epoch. Therefore, the Biharian–Toringian boundary (based on the presence of Arvicola cantiana) falls well within the Bruhnes epoch. This result is consistent with what is found in other Early–Middle Pleistocene sections of Spain (Atapuerca Gran Dolina).

Relationships between tectonic and geomorphological linear features in the Guadix-Baza basin, southern Spain

Linear elements of the landscape of the Guadix-Baza basin, southern Spain, were identified from a Landsat TM image. Three important lineament trends have been identified in the Guadix-Baza basin. The first is NE–SW, which is the dominant trend in the basin; the second is NW–SE, and the third is ENE–WSW. These three trends are correlated to the major faults of the Guadix-Baza basin. The study of linear features by the analysis of satellite data has revealed a strong link between the buried tectonic structures and the morphological features appearing at the surface. The distribution and density of lineaments explains much of the morphology of the land surface. It is possible to reconstruct elements of the tectonic and denudational history of the region and show that during Quaternary times lineaments controlled the sedimentation of the basin and the drainage pattern. Copyright © 1999 John Wiley & Sons, Ltd.

Relationships between tectonic and geomorphological linear features in the Guadix‐Baza basin, southern Spain

Linear elements of the landscape of the Guadix-Baza basin, southern Spain, were identified from a Landsat TM image. Three important lineament trends have been identified in the Guadix-Baza basin. The first is NE–SW, which is the dominant trend in the basin; the second is NW–SE, and the third is ENE–WSW. These three trends are correlated to the major faults of the Guadix-Baza basin. The study of linear features by the analysis of satellite data has revealed a strong link between the buried tectonic structures and the morphological features appearing at the surface. The distribution and density of lineaments explains much of the morphology of the land surface. It is possible to reconstruct elements of the tectonic and denudational history of the region and show that during Quaternary times lineaments controlled the sedimentation of the basin and the drainage pattern. Copyright © 1999 John Wiley & Sons, Ltd.

Ecomorphological study of large canids from the lower Pleistocene of southeastern Spain

An ecomorphological analysis of the skeletal remains of large canids, Canis (Xenocyon) falconeri and Canis etruscus (Mammalia, Carnivora, Canidae), preserved in an assemblage of large mammals from the lower Pleistocene site at Venta Micena (Guadix–Baza Basin, Orce, Granada, southeastern Spain) is reported. Mean body mass of adult individuals was estimated to be around 10 kg for C. etruscus and approximately 28 kg for C. falconeri using multiple regression. A comparative study of tooth measurements in modem canids, using principal components and discriminant function analysis, infers quite different ecomorphological adaptations and feeding behavior for both fossil species. The craniodental morphology of C. falconeri is similar to that shown by extant hypercarnivorous canids whose diet include more than 70% of vertebrate meat, whereas C. etruscus shows a cranial morphology similar to those of modem omnivorous species, thus indicating a dietary niche in which vertebrate meat represented less than 70% of its diet, with other feeding resources making up the balance. These results suggest that there was a marked ecological segregation between both sympatric species of large canids. The find of a complete skull of C. falconeri showing bilateral asymmetry and marked dental anomalies could suggest high levels of genetic homozygosis in the population which inhabited this region during early Pleistocene times, possibly as a consequence of isolation and the low number of individuals. This may have subsequently led to the extinction of C. falconeri in the Western fringe of Europe. The survival of this pathological individual to adulthood indicates that this species may have developed cooperative behavior similar to that of modem African wild dogs.

Refinements of the European Mammal Biochronology from the Magnetic Polarity Record of the Plio–Pleistocene Zújar Section, Guadix-Baza Basin, SE Spain

The magnetobiostratigraphy study of the 130-m-thick Zújar section (Negratı́n clays unit, Guadix-Baza Basin, Spain) provides a remarkable opportunity to improve the correlation of European mammal biostratigraphy to the Geomagnetic Polarity Time Scale. The occurrence of 12 well-defined magnetozones and four paleontological sites with diagnostic faunas ranging from the MN 15 biozone (Ruscinian) to the MN 17 biozone (Villanyian), leads to an unambiguous correlation to chrons spanning from the Gilbert to the Matuyama epochs. This provides two new time constraints: (1) the boundary between MN 15 (Ruscinian) and MN 16 (Villanyian) biozones is recorded between chron C2An.3n and the base of chron C2An.2n and (2) the boundary between the upper and lower MN 16 subzones (Villanyian) is located between chron C2An.2n and the base of chron C2An.1n. The correlation between the Ruscinian–Villanyian boundary and the 3.3-myr-B.P. cooling event seems to be confirmed, while the early/late Villanyian boundary could be tentatively correlated to the glacial event at 2.6 myr B.P. Furthermore, MN 15 faunas are found in the lowermost part of chron C2Ar, which is in agreement with and reinforces the emplacement of the MN 14–MN 15 Ruscinian zones boundary at the reversal from chron 3n.1n to chron C2Ar.

Taphonomy and palaeoecology of an assemblage of large mammals: Hyaenid activity in the Lower Pleistocene site at Venta Micena (Orce, Guadix-Baza Basin, Granada, Spain)

We report taphonomic and palaeoecologic data on the rich, diverse and well preserved assemblage of large mammals from lower Pleistocene deposits at Venta Micena (Orce, Granada, south-east Spain). The biostratinomic and diagenetic characteristics of the assemblage are congruous with the sedimentary context deduced from the study of the site, and both confirm that: (i) the assemblage represents an accumulated taphonomic stage, (ii) it was formed by demic, autochtonous palaeobiologic entities, which were preserved and recorded in situ, and (iii) it is the result of biological processes and agents. Interspecific analysis of size/abundance patterns in ungulates shows that the main taphonomic bias affecting the bones was produced by biological destruction before burial, and that the loss of information was greater for species of smaller body size. Factor correspondence analysis was used to compare the frequencies at which some groups of postcranial elements are represented in several recent and archaeological bone assemblages accumulated by carnivores, rodents and hominids. The results obtained strongly suggest that the bones from Venta Micena were collected mainly by hyaenids, which deposited them near shallow dens excavated around the ponds that surrounded the Pleistocene lake of Orce. An analysis of the abundance of major long bones has shown that differential fragmentation was produced by hyaenas as a function of their structural density and mean marrow content. All these data allow to formulate a descriptive-quantitative model for the characterization of bone assemblages generated from hyaenid activity, in which Venta Micena is an example of bone concentration and modification activities by Pachycrocuta brevirostris. Strong selection of prey by carnivores (which killed preferably juveniles, females and individuals with diminished locomotive capabilities among ungulate prey species of larger body size) is indicated by (i) the abundance of juvenile individuals with deciduous teeth in relation to the average weight estimated for adults in each ungulate species, by (ii) the U-shaped attritional mortality profiles deduced from crown heigth measurements, by (iii) the presence of many metapodials with different osteopathologies, and by (iv) a biased sexual ratio deduced from the metacarpals of large bovids. Comparison between the frequencies in which modern African carnivores kill and scavenge ungulates from different size classes and the abundance of these size categories in the assemblage suggests that the Venta Micena hyaena was a bone-cracking scavenger which fed largely on carcasses of ungulates preyed upon and partially consumed by flesh-eating carnivores such as saber-toothed felids and wild dogs.

Late Pliocene continental magnetochronology in the Guadix-Baza Basin (Betic Ranges, Spain)

The late Pliocene shallow lacustrine sequences in the Guadix-Baza basin (Betic Ranges, southeast Spain) are a suitable setting for mammal chronology because of the abundance of rich, mammal-bearing sites. Stratigraphic superposition of late Ruscinian and Villanyian vertebrate fossils makes the Galera Section very appropriate for magnetostratigraphic dating. Sediments are characterized by a weak but measurable magnetization predominantly carried by magnetite. Other remanence carriers, such as iron sulphides and hematite, may be significant only in some particular lithologies, such as dark palustrine organic silts and red alluvial beds, respectively. Direct correlation of the Galera Section to the geomagnetic polarity time scale provides a reliable dating of the late Ruscinian and Villanyian mammal units. The Ruscinian/Villanyian boundary (MN15/MN16) is found to occur in the lower Gauss chron, and approximately correlates to the 3.3 Ma cooling event observed in stable-isotope and planktonic foraminifera deep sea records. The earliest occurrence of late Villanyian assemblages (MN17) in the lower part of the Matuyama chron allows dating of the early/late Villanyian boundary (MN6/MN17) to approximately 2.4–2.6 Ma. Based on the presence of late Villanyian assemblages underlying the base of the Olduvai chron, a maximum age of 1.95 Ma (top of C2r) is attributed to the Villanyian/Biharian (MN17/MmQ) boundary. A 300 kyr sedimentary gap in the Galera Section is suggested to correlate with a probable early Villanyian hiatus, an hypothesis that agrees with the absence of fossils of this age elsewherein the Baza Formation.

Calibration of the late Pliocene-early Pleistocene transition in the continental beds of the Guadix-Baza basin (southeastern Spain)

In this paper a survey of the correlation between magnetic polarity and the mammalian succession in the Plio-Pleistocene sequence of the Guadix-Baza basin is presented. In this basin a complete continental sequence from the early Pliocene to the Middle Pleistocene is present, allowing the correlation of mammalian biozones with the geomagnetic polarity scale. Two sections of the Baza sector of the basin have been analyzed in order to calibrate the Pliocene-Pleistocene transition: the Galera (middle Pliocene to early Pleistocene) and the Orce (late Pliocene to early Pleistocene). It is concluded that the boundary between the MN 15 (late Ruscinian) and the MN 16 (early Villanyian) is placed between the 2An. 3n chron and the 2An. In subchron. The late Villanyian (MN 17) extends up to the upper part of chron 2r. 1r. The entry of the Pleistocene marker Allophaiomys pliocaenicus can be placed within subchron 2n (Olduvai).