Despite the paleontological relevance of the terrestrial Early Pleistocene Venta Micena bonebed (Baza Basin, Spain), it lacks a comprehensive geochemical/sedimentological study. Here, we demonstrate ...that the 1.5-m-thick Venta Micena limestone formed in a relatively small freshwater wetland/pond located at the periphery of the large saline Baza paleolake. Two microfacies are observed, with high and low contents of invertebrate fossils, and which originated in the centre and margin of the wetland, respectively. X-ray diffraction (XRD) mineralogy and paleohydrological characterization based on ostracod and bulk-rock geochemistry (δ
C and δ
O) indicate that the limestone reflects a general lowstand of the Baza lake, permitting the differentiation of freshwater wetlands that were fed by adjacent sources. Conversely, during highstands, the Baza lake flooded the Venta Micena area and the freshwater fauna was replaced by a saline one. Bulk-rock isotopic data indicate that the lower interval C1 of the limestone (bone-rich in marginal settings) displays general negative values, while the upper interval C2 (bone free) displays less negative values. The bones of predated mammals accumulated in the marginal areas, which were flooded and buried by recurring water-table fluctuations. Lake dynamics played a critical role in bone accumulation, which was previously considered as representing a hyena den.
The Orce region has one of the best late Pliocene and early Pleistocene continental paleobiological records of Europe. It is situated in the northeastern sector of the intramontane Guadix-Baza Basin ...(Granada, Andalusia, southern Spain). Here we describe a new fossil hominin tooth from the site of Barranco León, dated between 1.02 and 1.73 Ma (millions of years ago) by Electron Spin Resonance (ESR), which, in combination with paleomagnetic and biochronologic data, is estimated to be close to 1.4 Ma. While the range of dates obtained from these various methods overlaps with those published for the Sima del Elefante hominin locality (1.2 Ma), the overwhelming majority of evidence points to an older age. Thus, at the moment, the Barranco León hominin is the oldest from Western Europe.
The Libros Gypsum is the thickest evaporite unit of the Miocene infill of the Teruel Basin in NE Spain. During the deposition of this unit, intense bacterial sulfate-reducing (BSR) activity in the ...lake depocenter generated a native sulfur deposit. Diagenetic gypsum resulted from subsequent sulfur oxidation. The different processes involved in these transformations were first investigated by Anadón et al. (1992). The present paper is concerned with this diagenetic gypsum from the stratigraphic, petrographic, isotopic and genetic points of view.
Diagenetic gypsum occurs mainly as continuous or discontinuous layers, individual levels or lenses, irregular masses, nodules and micronodules, and veins. Its main textures are coarse-crystalline anhedral and fine-grained (alabastrine), both of which can replace any former lithology (carbonate, gypsum, and sulfur). The following sequence of processes and mineral/textural transformations is deduced: primary gypsum deposition — BSR and biodiagenetic carbonate/H
2S production — growth of native sulfur — growth of diagenetic gypsum — partial recrystallization of the diagenetic gypsum textures. The gypsification of the native sulfur generated two types of banded structures in the diagenetic gypsum: (1) concentric structures of centripetal growth, and (2) expansive, roughly concentric structures. In the first type, the gypsification operated from the outer boundaries towards the inner parts. In the second type, part of the carbonate hosting the sulfur was also gypsified (replaced/cemented).
In the diagenetic gypsum, the
δ
34S values are in agreement with a native sulfur and H
2S provenance. The
δ
18O
sulfate values, however, enable us to differentiate two main groups of values: one with positive values and the other with negative values. In the group of positive values, interstitial (evaporated) solutions participated in the sulfur oxidation; this process presumably occurred in a first oxidation stage during shallow-to-deeper burial of the Libros Gypsum unit. In the group of negative values, however, only meteoric waters participated in the oxidation, which presumably occurred in a second oxidation stage during the final exhumation of the unit. A third group of values is characterized by very high sulfur and oxygen values, suggesting that BSR residual solutions also participated in the oxidation processes locally. During the two oxidation stages, both the textural characteristics and the isotopic composition of the diagenetic gypsum indicate that gypsification operated as a multistadic process.
Authigenic barite and carbonates (dolomite, high-Mg calcite and aragonite) have been recovered from active gas seep sites of the pull-apart Consag and Wagner basins, the northernmost and shallowest ...(∼225 m deep) active basins in the Gulf of California. This gulf encompasses a transform–spreading ridge transitional plate boundary; while seafloor spreading is known to take place in a few basins of the central and southern gulf, in the northern basins mantle upwelling is only suspected. Despite of their tectonic framework, the studied authigenic deposits show fabrics, minerals and isotope compositions similar to those reported for common gas seeps in passive continental margins and in accretionary active margins, and suggest that methane accompanied by Ba- and Sr-rich basinal cold fluids is released to the seafloor. Authigenic carbonates occur as centimeter-sized concretions scattered within silty sands. These concretions consist of cryptocrystalline carbonate pervasive cement (high-Mg calcite to dolomite) containing bioclasts in variable amounts. Aragonite forms crack-fill fibrous cement in association to barite. In addition, well-sorted, sandy sediments largely constituted by barite spheroids with subordinate pyrite have been recovered. The δ13CPDB from carbonates (cements and skeletal grains) has an overall variation of −45.5 to +1.7‰. The δ18OPDB of carbonates varies from −3.1 to +4.0‰. The cryptocrystalline cement yielded the lowest δ13C, indicating that it formed through the anaerobic oxidation of methane. The highest δ18OPDB values (>+3.0‰) correspond to this cement. The range of δ18OSMOW calculated for water (+1.3 to +2.1‰) is compatible with pore fluid compositions of typical deep-water methane seeps. Barite yielded δ34S from +38.2 to +44.8‰, well above that of sulfate from pore- and seawater (+14.8 to +23.6‰). Barite precipitates within the sediments through mixing of (a) reducing, Ba-rich seep fluids, with (b) pore-water, containing sulfate residual from microbial reduction. The reaction of sulfate reduction is coupled to the oxidation of methane. Skeletal carbonates (coral and bivalves) yielded the lowest 87Sr/86Sr ratios (0.709133–0.709177), so they do not show further influence than that of seawater. Barite from sandy deposits yielded high 87Sr/86Sr values (0.709477–0.709698). The source of radiogenic strontium could be the clastic infill of the basins, while an oceanic crust isotopic signature is absent.
► Carbonates and barite occur around shallow gas seeps at a transform plate boundary. ► Textures, minerals and isotope ratios are similar to those of common methane seeps. ► Carbonates are 13C-depleted and form through anaerobic oxidation of methane. ► Barite forms from Ba-rich fluids plus sulfate residual after microbial reduction. ► An oceanic crust Sr isotopic signature is absent in the gas seep-related minerals.
The very labile (decay-prone), non-biomineralized, tissues of organisms are rarely fossilized. Occurrences thereof are invaluable supplements to a body fossil record dominated by biomineralized ...tissues, which alone are extremely unrepresentative of diversity in modern and ancient ecosystems. Fossil examples of extremely labile tissues (e.g. muscle) that exhibit a high degree of morphological fidelity are almost invariably replicated by inorganic compounds such as calcium phosphate. There is no consensus as to whether such tissues can be preserved with similar morphological fidelity as organic remains, except when enclosed inside amber. Here, we report fossilized musculature from an approximately 18 Myr old salamander from lacustrine sediments of Ribesalbes, Spain. The muscle is preserved organically, in three dimensions, and with the highest fidelity of morphological preservation yet documented from the fossil record. Preserved ultrastructural details include myofilaments, endomysium, layering within the sarcolemma, and endomysial circulatory vessels infilled with blood. Slight differences between the fossil tissues and their counterparts in extant amphibians reflect limited degradation during fossilization. Our results provide unequivocal evidence that high-fidelity organic preservation of extremely labile tissues is not only feasible, but likely to be common. This is supported by the discovery of similarly preserved tissues in the Eocene Grube Messel biota.
Recent finds of tetrapod ichnites in the red-bed and volcaniclastic succession of the Iberian Pyrenean Basin permits an assessment of the faunal diversity and palaeoenvironment of a late early ...Permian setting. The tetrapod ichnoassemblage is inferred with the aid of photogrammetry and constituted by Batrachichnus salamandroides, Limnopus isp., cf. Amphisauropus (these three ichnotaxa present associated swimming traces, assigned to Characichnos), cf. Ichniotherium, Dromopus isp., cf. Varanopus, Hyloidichnus isp. and Dimetropus leisnerianus. These ichnotaxa suggest the presence of temnospondyls, seymouriamorphs, diadectomorphs, araeoscelids, captorhinids and synapsid pelycosaurs as potential trackmakers. These faunas correlate to the late early Permian. Two ichnoassociations correspond to two different palaeoenvironments that were permanently or occasionally aquatic (meandering fluvial systems and unconfined runoff surfaces, respectively). Ichnotaxa in the fluvial system is more diverse and abundant than in the runoff surfaces system. The Iberian Pyrenean ichnoassemblage reveals the faunistic connection and similarities among nearing basins (Spain, southern France and Morocco) differing from the Central European basins (i.e. German Tambach Formation). Based on the palaeogeography and the climate models of the early Permian, we suggest the correlation of ichnofaunal composition with different palaeoclimate biomes. This results in a diffuse boundary of Gondwana–Laurasia land masses, indicating no geographic barriers but a possible climate control on the faunal distribution. Further studies, integrating data from distant tracksites, should refine these biome boundaries.
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.
The most severe biotic crisis on Earth history occurred during the Permian–Triassic (PT) transition around 252Ma. Whereas in the marine realm such extinction event is well-constrained, in terrestrial ...settings it is still poorly known, mainly due to the lack of suitable complete sections. This is utterly the case along the Western Tethys region, located at Pangaea's equator, where terrestrial successions are typically build-up of red beds often characterised by a significant erosive gap at the base of the Triassic strata. Henceforth, documenting potentially complete terrestrial successions along the PT transition becomes fundamental. Here, we document the exceptional Coll de Terrers area from the Catalan Pyrenees (NE Iberian Peninsula), for which a multidisciplinary research is conducted along the PT transition. The red-bed succession, located in a long E-W extended narrow rift system known as Pyrenean Basin, resulted from a continuous sedimentary deposition evolving from meandering (lower Upper Red Unit) to playa-lake/ephemeral lacustrine (upper Upper Red Unit) and again to meandering settings (Buntsandstein facies). Sedimentary continuity is suggested by preliminary cyclostratigraphic analysis that warrants further analysis. Our combined sedimentological, mineralogical and geochemical data infer a humid-semiarid-humid climatic trend across the studied succession. The uppermost Permian strata, deposited under an orbitally controlled monsoonal regime, yields a relatively diverse ichnoassemblage mainly composed of tetrapod footprints and arthropod trace fossils. Such fossils indicate appropriate life conditions and water presence in levels that also display desiccation structures. These levels alternate with barren intervals formed under dry conditions, being thus indicative of strong seasonality. All these features are correlated with those reported elsewhere in Gondwana and Laurasia, and suggest that the Permian–Triassic boundary might be recorded somewhere around the Buntsandstein base. Consequently, Coll de Terrers and the whole Catalan Pyrenees become key regions to investigate in detail the Permian extinction event and the Triassic ecosystems recovery.
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•Coll de Terrers: the continental Permian-Triassic transition in Pangaea equator.•Combined analyses constrain the Guadalupian–Middle Triassic environmental changes.•The continuous record suggests the presence of the Permian-Triassic boundary.
The sedimentary record of the maar lake succession at Camp dels Ninots (Pliocene, NE Spain) reflects mineralogical shifts that correlate with orbitally forced climate changes. X-ray powder ...diffraction was obtained from a 47 m-long core collected from a borehole drilled in the centre of the paleolake. The results show compositional variations in terms of allogenic/authigenic mineral assemblages which, in turn, correlate with climate proxies such as pollen. Intervals that are dominantly composed of allogenic minerals (quartz, feldspar, smectite) correlate with wet periods. These periods are characterised by an increase in the percentage of Abies pollen. Conversely, intervals enriched in carbonates correlate with dry periods, with decreased amounts of Abies pollen. This cyclicity is attributed to rainfall variations leading to hydrologically open lake conditions during periods of relative high precipitation (when clastic input is enhanced) and hydrologically closed lake conditions during drier periods (when precipitation of authigenic carbonates is enhanced). It is concluded that the mineralogy of maar paleolakes may be highly sensitive to record climate changes.
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