Palaeoenvironmental Inferences Research Articles

Palaeoenvironmental inferences of a Mexican Konservat-Lagerstätte (Tlayúa Quarry; Lower Cretaceous) based on the geochemistry of rare earth elements

The Tlayúa Quarry is considered one of the most important Cretaceous outcrops in Mexico. Its well-preserved palaeobiota has allowed this outcrop to be considered a Konservat-Lagerstätte. Geochemical proxies such as major, minor and trace elements were evaluated from selected Zones of the Tlayúa Quarry, in order to infer some features of the depositional environment in which Tlayúa limestones originated. Aluminum, Thorium and Zirconium concentrations in addition to a low Phosphorous content evidence little terrigenous contamination, as well as a phosphate-free environment. Additionally, proxies such as Fe vs ΣREE, Mn vs ΣREE, Al vs ΣREE, Fe vs NdSN/YbSN, Al vs NdSN/YbSN, and Ce/Ce∗ vs Eu/Eu∗ show low correlation values (r2 less than 0.25 in all cases with n = 128 and p < 0.05), thus suggesting a negligible influence of diagenetic effects or terrigenous contamination. These conditions are necessary for carrying out reliable palaeoenvironmental interpretations. Rare Earth Elements + Yttrium (REE+Y) concentrations were normalised to the Post-Archean Australian Shale standard to evaluate REE+Y patterns and anomalies. Following traits were identified: a slightly enrichment of heavy REE relative to light REE and moderate REE; positive La/LaSN, Gd/GdSN and Y/YSN anomalies; negative/positive Ce/CeSN anomalies; superchondritic and chondritic Y/Ho ratios. Here, we described that most of our limestone samples show the influence of marine waters and well oxidising conditions. However, freshwater signals that have been reported for some regions of the Tlayúa Quarry were also verified. Geochemical data are in agreement with the depositional environment evidenced by microfacies.

Comparing the impact of live-tree versus historic-timber data on palaeoenvironmental inferences in tree-ring science, eastern North America

Dendroarchaeological data from historic structures and artefacts have the potential to extend tree-ring chronologies spatially and temporally, especially where old-growth forests have been extensively modified or harvested. While these data may contribute to an improved understanding of past climate and ecology, critical differences in the properties of live-tree and historic-timber data might affect results and interpretations of large-scale studies, such as those relying on large datasets from public databases like the International Tree-Ring Data Bank (ITRDB). The objective of this work was to compare summary measures of live-tree versus historic-timber datasets likely to affect outcomes and inferences of typical paleoenvironmental applications. We used 99 live-tree (LT) and 41 historic-timber (HT) datasets collected in the Appalachian region of the eastern United States and compared common analytical measures for understanding past climate and ecology, including temporal coverage, species composition, recruitment patterns, segment length, series coherence/mean interseries correlation (as Rbar), expressed population signal (EPS), subsample signal strength (SSS) and response to drought and extreme climate events. We found that tree-ring data from historic timbers record some ecological events similarly to live trees and are sensitive to some climate conditions, with important caveats related to the influence of site and tree selection on analytical measures. In some cases, these caveats can be overcome through improved collection of metadata and additional analyses. In all cases, potential differences in LT and HT data should be considered by those who perform large-scale analyses using public tree ring databases, especially as more scientists contribute historic-timber datasets.

Solving a ‘puzzle’. The global 4.2 ka Bond Event at El Mirador cave (Sierra de Atapuerca, Burgos, Spain) and the importance of small mammal taphonomy to the interpretation of past environments and their climatic controls

The regional climatic context in which Chalcolithic (MIR5) and Bronze Age (MIR4) levels from El Mirador cave (Sierra de Atapuerca, Burgos, Spain) are framed is affected by the 4.2 ka cal. BP event, a global event defined as a cooling and aridification phase. Previous works based on palaeoenvironmental inferences indicate conflicting results regarding the possible impact of the event on vegetation and small mammals from MIR5. Pollen record illustrates a possible aridification episode that could match with the 4.2 ka cal. BP event, while the signal of this event is not clearly recorded in the small mammal assemblage, which indicates more humid environmental conditions than pollen record. Taphonomic analyses confirmed that the small mammal assemblages from MIR4 and MIR5 are the result of predation, supporting the involvement of European eagle owls ( Bubo bubo) in its formation. This avian raptor shows a marked preference for hunting animals living in the more open and wetter parts of their hunting range. Likewise, spontaneous specialisation on abundant prey species could also be observed under certain environmental conditions. This characteristic behaviour of eagle owls may have provided the contradictory results observed between the small mammal assemblage and palynological evidence. Nonetheless, taphonomic analyses also provided information about climatic conditions and fluctuations along time. The low incidence of manganese coatings and carbonate crusts deposits in small mammal bone remains from MIR5 support the presence of arid conditions during the formation of this level, which agreed with the aridification phase probably related to the 4.2 ka Bond Event inferred by palynological data from MIR5. These results provided a more robust conclusion about the paleoenvironmental contexts during the formation of Chalcolithic and Bronze Age levels at El Mirador cave.

Organic molecules based palaeoenvironmental inferences and U mineralization in Palaeoproterozoic Bijawar basins of Central India

Palaeoproterozoic, siliclastic, intracratonic rocks of the Bijawar and Sonrai basins contain anomalous U concentration and abundant Organic Matter (OM), although, earlier studies documented rare data on commonality between high U content and closely associated OM. Moreover, OM contains several biomolecules of complex carbonaceous compounds with macro-molecular structures, but insignificant information is available on the origin and associated palaeoenvironmental conditions. Thus, present study on organo-uranyl-complexes is relevant and carried out to understand palaeoenvironmental reasons accountable for U mineralization. For this purpose, OM (isolated from each bulk sample) was analyzed for Total Organic Carbon (TOC), n-alkanes, n-fatty acids and Polycyclic Aromatic Hydrocarbon compounds (PAHs). Obtained TOC values range between 0.02 and 0.23 wt%. Mostly, calculated [(C/S)/12] and [(C/N)/12] values are low; indicate algal source and anoxic depositional conditions, but, Rohini carbonate, Bandai sandstone and Chloritic shale high values signify sub-oxic conditions. Also, low (<1.25) U/Th and high authigenic U data of mineralized Chloritic shale imply anoxic conditions and post-depositional enrichment of U ions (mostly as organo-uranyl-complexes), respectively.GC-MS data show high concentration of n-alkane, fatty acid methyl ester (FAME) and PAH molecules in the OM associated with the rocks signifying high U values. The predominance of Short Chain (SC) n-alkanes together with the SC n-fatty acids revealed derivation of OM from marine algae and bacteria. The Rohini carbonate and Chloritic shale show low isoprenoids, Pristane (Pr)/Phytane (Ph), CPI, OEP, Pr/n-C-17, Ph/n-C18, but high TC-/(Pr/Ph), TC/(Pr + Ph), MP, MPI, MPR and VR values, suggest biodegraded and thermally matured OM which has undergone hydrothermal alteration under anoxic to sub-anoxic conditions. Considerably, high degree of OM oxidization occurred synchronously with the reduction of U6+ to U4+ by sulfate-reducing bacteria. The consistent loss of diaromatic PAHs is also noticed from older to younger rock-units. Further, scanty appearance of PAHs in the lower Gorakalan shale and their disappearance in the upper Chloritic and black shale units, indicate progressive maturation of sediments. The Low Molecular Weight (LMW)-PAHs predominate over the High Molecular Weight (HMW)-PAHs. Comparatively, high phenanthrene abundance is also noticed in the Rohini carbonate, Chloritic shale and -black shale (with high U content). The high proportion of LMW-PAHs and absence of HMW-PAHs (>6 rings) is pointing towards the presence of hydrothermally derived bitumen. Moreover, partial combustion of OM (pyrogenic) contributed to the formation of PAHs. The Chloritic shale and Rohini carbonate are coeval with the Bijawars of the Sonrai basin, representing almost similar organo-molecular records. Organo-molecular abundance and their structural attributes when plotted across the stratigraphic successions, revealed alternate humid conditions facilitated U4+oxidation and formation of U6+ rich solutions, although arid/semiarid climatic conditions assisted precipitation, sorption and absorption of U4+. Almost, similar clay mineral attributes for both the basins lend support to cyclic humid to arid/semiarid palaeoenvironmental conditions. Moreover, majority of the OM derived from the algal mats has played critical role in U mineralization by trapping and adsorption of tiny uraninite grains as well as U ions onto the OM.

Hydrochemistry and stable isotopes in a coastal lagoon affected by evaporation, Cabo de Gata (Almería)

The Salinas de Cabo de Gata are a natural coastal lagoon that has been anthropically transformed to favor the entry of seawater and its evaporation until saturation in sodium chloride. For this, it is compartmentalized in a series of ponds in which the seawater is guided by a circuit along which the salinity increases. Sediment samples have been taken at the bottom of these ponds and water samples to recognize which hydrogeochemical processes occur along the route. In the first ponds (evaporators) the suspended solids are decanted and carbonate precipitation occurs, along with the formation of pyrite linked to the high concentration of organic matter. On the other hand, in the last ponds (crystallizers) gypsum precipitation occurs when 70% evaporation is reached and, finally, halite when it reaches 90%. This precipitation notably changes the chemical composition of the waters, reducing the concentration of the ions present in the minerals that precipitate. From the isotopic point of view, gypsum precipitation also has its mark, reducing the proportions of 18O/16O and 2H/1H in the pond water. The study of these processes, in a mesoscale system, has great advantages for making palaeoenvironmental inferences at the basin scale, such as knowing what percentage of seawater must be evaporated so that gypsum or halite can precipitate in a basin.

Revisiting the Middle and Upper Palaeolithic archaeology of Gruta do Caldeirão (Tomar, Portugal).

Gruta do Caldeirão features a c. 6 m-thick archaeological stratification capped by Holocene layers ABC-D and Ea, which overlie layer Eb, a deposit of Magdalenian age that underwent significant disturbance, intrusion, and component mixing caused by funerary use of the cave during the Early Neolithic. Here, we provide an updated overview of the stratigraphy and archaeological content of the underlying Pleistocene succession, whose chronology we refine using radiocarbon and single-grain optically stimulated luminescence dating. We find a high degree of stratigraphic integrity. Dating anomalies exist in association with the succession’s two major discontinuities: between layer Eb and Upper Solutrean layer Fa, and between Early Upper Palaeolithic layer K and Middle Palaeolithic layer L. Mostly, the anomalies consist of older-than-expected radiocarbon ages and can be explained by bioturbation and palimpsest-forming sedimentation hiatuses. Combined with palaeoenvironmental inferences derived from magnetic susceptibility analyses, the dating shows that sedimentation rates varied in tandem with the oscillations in global climate revealed by the Greenland oxygen isotope record. A steep increase in sedimentation rate is observed through the Last Glacial Maximum, resulting in a c. 1.5 m-thick accumulation containing conspicuous remains of occupation by people of the Solutrean technocomplex, whose traditional subdivision is corroborated: the index fossils appear in the expected stratigraphic order; the diagnostics of the Protosolutrean and the Lower Solutrean predate 24,000 years ago; and the constraints on the Upper Solutrean place it after Greenland Interstadial 2.2. (23,220–23,340 years ago). Human usage of the site during the Early Upper and the Middle Palaeolithic is episodic and low-intensity: stone tools are few, and the faunal remains relate to carnivore activity. The Middle Palaeolithic is found to persist beyond 39,000 years ago, at least three millennia longer than in the Franco-Cantabrian region. This conclusion is upheld by Bayesian modelling and stands even if the radiocarbon ages for the Middle Palaeolithic levels are removed from consideration (on account of observed inversions and the method’s potential for underestimation when used close to its limit of applicability). A number of localities in Spain and Portugal reveal a similar persistence pattern. The key evidence comes from high-resolution fluviatile contexts spared by the site formation issues that our study of Caldeirão brings to light—palimpsest formation, post-depositional disturbance, and erosion. These processes. are ubiquitous in the cave and rock-shelter sites of Iberia, reflecting the impact on karst archives of the variation in climate and environments that occurred through the Upper Pleistocene, and especially at two key points in time: between 37,000 and 42,000 years ago, and after the Last Glacial Maximum. Such empirical difficulties go a long way towards explaining the controversies surrounding the associated cultural transitions: from the Middle to the Upper Palaeolithic, and from the Solutrean to the Magdalenian. Alongside potential dating error caused by incomplete decontamination, proper consideration of sample association issues is required if we are ever to fully understand what happened with the human settlement of Iberia during these critical intervals, and especially so with regards to the fate of Iberia’s last Neandertal populations.

An Early Pleistocene hippopotamus from Westbury Cave, Somerset, England: support for a previously unrecognized temperate interval in the British Quaternary record

ABSTRACTAlthough fossil assemblages from the late Early Pleistocene are very rare in Britain, the site of Westbury Cave in Somerset, England, has the potential to address this gap. The mammal fossils recovered previously from the Siliceous Member in Westbury Cave, though few in number, have hinted at an age for the deposits that is as yet unparalleled in Britain. Here, we describe the first bona fide occurrence of Hippopotamus in the British Early Pleistocene, discovered during recent reinvestigation of the Siliceous Member. The hippo fossil indicates a refined biochronological age of ca. 1.5–1.07 Ma for the Siliceous Member and a palaeoclimate that was warm and humid, which accords well with previous palaeoenvironmental inferences. A synthesis of late Early Pleistocene hippo occurrences suggests that the Siliceous Member hippo may have been part of an early colonization of north‐west Europe by these megaherbivores, possibly during MIS (Marine Oxygen Isotope Stage) 31. Alternatively, it evidences a currently cryptic northward migration during an even earlier temperate phase. In either case, the Siliceous Member is likely to represent a warm period that has not been recognized previously in the British Quaternary record.

First fossil record in Tambería formation (Neogene) in Bolsón de Fiambalá, Catamarca province, Argentina: Palaeoenvironmental inferences through Leguminosae woods

The aim of this study is to report the first fossil wood record of Leguminosae in miocene sediments from Tambería Formation outcropping in the center-west of Catamarca province, Argentina. This Leguminosae specimen was found on levels of multi-colored sandstones that alternated with dark brown pelites and gray conglomerates. It is characterized by the presence of: semi-ring porous wood with vestured ornamented pits, helicoidal thickenings on the vessel walls, paratracheal parenchyma, homogeneous and multiseriate rays, all of which justify its assignment to Gleditsioxylon Müller-Stoll and Mädel. Six species are known and distributed in: Argentina, the United States, China and Japan in Miocene sediments coetaneous with sediments from Tambería Formation. The fossil wood specimen documented in this study is assigned to Gleditsioxylon fiambalense nov. sp. taking into account the combination of its anatomical features. Vulnerability and mesomorphy indices reveal its subtropical environmental condition which is not only typical of Gleditsia amorphoides, the current species, but also coincides with the palaeoenvironmental inferences derived from sedimentological research. This first paleontological record promises interesting analyses to understand the paleobiological and paleoecological aspects of the Tambería Formation and adds another new evidence to show the diversity of the neogene Leguminosae lignofloras of northern Argentina.

The finalization of the modern drainage pattern of the Tarim Basin: Insights from petrology and detrital zircon geochronology of sediments from Lop Nur

The Tarim Basin is the largest arid inland-river basin in China. Although drainage patterns of the basin provide crucial information on the hinterland evolution, the basin-wide river network evolution in this arid region is still poorly understood. This contribution uses a detailed study of the petrology and zircon U-Pb geochronology of sediments from Lop Nur to reconstruct the late Quaternary drainage evolution and source-sink relations of the Tarim Basin. Results reveal a relatively constant and stable sediment supply from the Tianshan Mountains until the middle Pleistocene. Negligible contribution from the Pamirs and Kunlun Mountains, suggests coeval rivers draining the western basin were likely in a premature state with limited propagation toward the basin interior, despite Lop Nur as the rivers’ terminus of the Tarim Basin. This suggested drainage pattern is different from that observed in the historical past or today with rivers draining the western basin crossing the Taklamakan Desert and reaching Lop Nur either after converging into the Tarim River or following separate courses. Combined with reported modern river sediments, ages of river terraces, stratigraphic records and palaeoenvironmental inferences, we tentatively suggest that the modern drainage pattern of the Tarim Basin was likely finalized in the late early Pleistocene or even afterward. Therefore, the ranges along the western Tarim Basin must have experienced fast and strong erosion since the late early Pleistocene that resulted in the steep topography and deep incision of these rivers. Subsequent transport of large quantities of sediment materials into the basin formed the vast and thick deposits of the Taklamakan Desert in a relatively short period of time.

The contribution of functional traits to the understanding of palaeoenvironmental changes

Abstract Performance traits implicated in feeding interact directly with the environment and are consequently relevant ecological indicators. However, they have rarely been used to better understand palaeoenvironmental variation. Here, we evaluate the usefulness of a performance (i.e. functional) trait, estimated bite force, in reconstructing the palaeoecology of shrews. We investigate the relationships between mandible morphology, bite force estimates and the ecological context. We use geometric morphometrics to quantify mandible shape diversity in shrews of the archaeological site El Harhoura 2 (Rabat, Morocco), dated from the Late Pleistocene to the Holocene. Morphological groups were used instead of taxa as units of diversity. To explore how phenotypic traits are linked to their environment, they were compared with palaeoenvironmental inferences for the El Harhoura 2 site extracted from the literature. Morphological groups acted as phenotypic response units. Estimated bite force was related to palaeoenvironmental variation over the considered period, with a particular sensibility to arid/humid transitions. The complementarity of morphological and performance indicators allowed us to infer functional convergence and divergence among shrews. Our results suggest that functional traits may be relevant indicators of changes in palaeoenvironments. This approach opens up new possibilities to explore the impact of environmental changes on extinct organisms.

Early Neogene palaeoenvironmental variability along the margins of the eastern Caribbean plate

This paper is the first review of Early Neogene palaeoenvironmental variability along the eastern Caribbean plate margins. We present new benthic foraminiferal data from (1) a single Spring Garden Member sample, Montpelier Formation, Jamaica at the Pots and Pans exposure, and (2) an offshore Dominican Republic gravity core (LDEO Eastward EA46-67 005D). Regional comparisons are made between our new data, the Cipero-Brasso-Nariva facies-belt complex of Trinidad, and coeval formations with suitable benthic foraminiferal data in Jamaica, the Dominican Republic, and Venezuela. We call these sites ‘marginal regions’ with respect to the Caribbean tectonic plate.Planktonic Foraminifera were used for biostratigraphic control and benthic foraminifera for palaeoenvironmental inferences. Shannon's Diversity Function H, the Benthic Foraminiferal Oxygenation Index (BFOI), and a Nutrient Flux Index (NFI) are used to explore and quantify palaeoenvironmental variability. We also present an Open Sea Nutrient Flux Index (OSNFI), calculated from the summed log-transformed plus unity proportional abundances of Globocassidulina subglobosa, Pullenia bulloides, Oridorsalis umbonatus and Spheroidina bulloides, to quantify nutrient flux to the deep-sea.Planktonic Foraminifera placed our Spring Garden sample at the Middle Miocene (Zone M6), and Core EA46-67 005D in the Pliocene/Pleistocene. Dominant benthic foraminifera differed for each marginal regional exposure. The Spring Garden Member was dominated by Loxostomum applinae and Core EA46-67 005D by Siphonodosaria hispidula. Other Dominican Republic sections were dominated by Bolivina spp. Siphonodosaria insecta dominated many Cipero Formation exposures.The marginal regions experienced varying nutrient fluxes to the sea floor. The lower bathyal Sombrerito and middle bathyal Trinchera Formations, Dominican Republic, experienced an enhanced nutrient flux to the sea floor. This may have been due to local upwelling, or delivery of nutrient-rich water from an upwelling cell along the northern South American shelf by a northerly-flowing filament. The neritic to bathyal Brasso Formation also experienced upwelling, indicated by the development of a pronounced oxygen minimum zone (OMZ). The extent of the oxygen depletion differed between the Brasso and the Sombrerito and Trinchera Formations, Uvigerina spp. being abundant in the Brasso but rare in the Dominican Republic. In contrast, the deep-water Cipero and Jamaican Basins were nutrient deficient.Oxygen concentrations based on BFOI varied between the marginal regions. The Cipero and Jamaican Basins were generally well oxygenated. The Sombrerito Formation, within the Azua Basin, was also well oxygenated. The Azua Basin, however, became low oxic during deposition of the Trinchera Formation, and this persisted to the Pliocene/Pleistocene Core EA46-67 005D.

Análisis paleontológicos a través límite Ediacárico-Cámbrico, Grupo Alto Corumbá, Brasil

Se presenta en este trabajo el análisis paleontológico de 26 especies fósiles muestradas en cinco cortes de las Formaciones de Tamengo y Guaicurus en las regines de Corumbá y Ladário: canteras de Corcal y Laginha, Porto Sobramil, Porto Figueiras y Ecoparque Cacimba. Además, se añaden varias interpretaciones paleoecológicas y ambientales, basadas en el registro fósil. Cloudina carinata Cortijo et al., 2010, previamente citada en España y Siberia, aparece por primera vez en el continente Americano, concretamente en limolitas de la Formación Tamengo en el corte de Porto Figueiras, Corumbá, Estado de Mato Grosso do Sul, Brasil. La biota de la Formación Tamengo incluye tres metazoos mineralizados, que incluyen espículas de poríferos, posibles gémulas de esponjas y una colonia sésil de procaiotas epibentónicos. Este trabajo se centra en la taxonomía y distribución estratigráfica de cuatro icnoespecies y tres especies de vendoténidos que forman la fauna bentónica de la parte superior del Grupo de Corumbá. La biodiversidad de la Formación Tamengo ha sido completada con el registro de 16 especies microfósiles que representan posiblemente una asociación plantónica marina. Se ha identificado un cambio drástico en las condiciones ambientales de las Formaciones Tamengo y Guaicurus, que culminan en un evento de extincinón masiva posiblemente relacionado con la extincición en masa que marca el tránsito global Ediácarico- Cámbrico. Por otro lado, se han extraído microfósiles de pared orgánica de varios afloramientos: nueve especies de la Formación de Nomtsas (Namibia), cuatro de la Formación Tagatiya Guazu (Paraguay) y seis de la Formación Dengying (China). Se propone un marco bioestratigráfico para el Ediacárico terminal que incluye seis biozonas y una biozona para el Cámbrico basal.

δ18O-inferred salinity fromLittorina littorea(L.) gastropods in a Danish shell midden at the Mesolithic–Neolithic transition

Norsminde Fjord has received extensive geoarchaeological investigation, hosting one of the classic Stone Age shell midden sites in Denmark, and one of the best examples of the widespread oyster decline at the Mesolithic–Neolithic transition. Here, intra-shell δ18O (and δ13C) analyses from the common periwinkle Littorina littorea (L.) are used to infer inter-annual environmental changes at the Mesolithic–Neolithic transition (four from each period). This study utilises a modern δ18O L. littorea-salinity training set previously developed for the Limfjord, Denmark to quantify winter salinity. δ18O values range between +1.6% and +4.0% in the late Mesolithic and ‒6.3% to +2.0% in the early Neolithic. Using maximum δ18O values, winter salinity at the known temperature of growth cessation in L. littorea (i.e. +3.7 ± 1°C) for the first annual cycle of each shell ranges between 25.5 and 26.8 psu (standard deviation (SD): 0.56) for the late Mesolithic, with an average salinity of 26.1 psu. Early-Neolithic shells range between 19.4 and 28.2 psu (SD: 4.59) with an average salinity of 23.7 psu. No statistically significant change in salinity occurs between the late Mesolithic and early Neolithic. This result supports recent diatom/mollusc-based inferences that salinity was not the sole cause of the oyster decline, although some evidence is presented here for more variable seasonal salinity conditions in the early Neolithic, which (along sedimentary change and temperature deterioration) might have increased stress on oyster populations in some years. It is recommended here that for robust palaeoenvironmental inferences, where possible, multiple specimens should be used from the same time period in conjunction with multiproxy data.

Los restos de &lt;em&gt;Sus scrofa&lt;/em&gt; (Artiodactyla, Mammalia) del yacimiento Pleistoceno de Pinilla del Valle (Madrid, España)

Se ha llevado a cabo un estudio morfológico y biométrico de los restos fósiles de Suidos excavados en el yacimiento del Pleistoceno superior de la Cueva del Camino, en el término de Pinilla del Valle (Madrid), comparándolos con los restos de otros yacimientos y con especímenes actuales. El material extraído comprende 47 elementos pertenecientes a un mínimo de 6 individuos, destacando la presencia de restos craneales, muy poco frecuentes en los yacimientos europeos de esta época, y ausentes en yacimientos españoles. Se han comprobado en los restos los caracteres anatómicos típicos de Sus scrofa, confirmándose las condiciones paleoambientales obtenidas del conjunto de la fauna.

Amidst wind, sand and raptors. Small mammal bone remains recovered in open-air archaeological sites from the Monte Desert in Central Western Argentina: taphonomic and palaeoenvironmental implications

The distinctive characteristic of the Monte Desert, the most arid rangeland of Argentina, is reflected in the varied composition of its small mammal fauna. The present study analyses the taphonomic features and the palaeoenvironmental implications of small mammal bone and tooth accumulations recovered in open-air archaeological sites from the Monte Desert plains of northern Mendoza (Central Western Argentina) in the South American arid diagonal. In order to identify the agents responsible for such accumulations relative abundance trends, bone breakage patterns and digestive corrosion were evaluated. The action of postdepositional processes, like weathering and trampling, also were analysed. Taphonomic results allowed the detection of avian raptors—owls in particular—as the principal accumulating agents of small mammal bone and tooth accumulations of open-air archaeological sites from the Monte Desert. In order to make palaeoenvironmental inferences, the taxonomic structure of archaeological and modern small mammal assemblages was analysed and compared, added to the evaluation of taphonomic dynamics in the archaeological sites. The taxonomic composition of archaeological assemblages differed from that of the current assemblages from the study area. Thus, an extinct species (Holochilus lagigliai) and a little-known species highly adapted to desert environments (Tympanoctomys barrerae) were detected in the archaeological record. Recent pellet samples showed major proportions of opportunistic and generalist species as well as the presence of an exotic species (Mus musculus). The general impoverishment of current small mammal assemblages in comparison with past ones (e.g. richness, diversity and evenness) could be attributed to the deep impact of the anthropic perturbations generated by economic activities since the arrival of European conquerors ca. 500 years BP. Small mammal archaeological assemblages could indicate a scenario of greater environmental heterogeneity during the Late Holocene than in the present, and thus, greater availability of patch resources in the landscape.

Late Pleistocene climate of the northern Iberian Peninsula: New insights from palaeoglaciers at Fuentes Carrionas (Cantabrian Mountains)

ABSTRACTNew 10Be dates for glacial landforms in the Fuentes Carrionas area (Cantabrian Mountains, nothern Spain) are presented. Mapped and dated landforms in Fuentes Carrionas made possible a palaeoglacier reconstruction for four glacial stages. Results were compared to other nearby palaeoenvironmental proxies, so a final approximation on the mean annual temperature and annual precipitation that caused the four glacial advance stages is proposed. Glaciers reached their maximum extension at 36 ka, in a cold and dry environment. A second advance stage took place between 18.5 and 19.5 ka, during the Last Glacial Maximum (LGM), when glaciers advanced in a wet environment, with positive rainfall anomalies. A third glacial advance was dated during the Oldest Dryas, in which climate shifted to extremely cold and dry conditions. Finally, a last stage has been identified and proposed to the Younger Dryas, in which precipitation anomalies are negligible. Our results confirm some of the previously made palaeoglacial and palaeoenvironmental inferences for the Iberian Peninsula, as well as provide valuable and accurate anomalies, which are useful for climate modelling.

Pronival ramparts

Pronival ramparts are debris ridges formed at the downslope margins of perennial or semi-permanent snowbeds beneath bedrock cliffs. These landforms, also previously known as protalus ramparts, are located in periglacial environments, but the apparent simplicity of rampart formation made these landforms far less interesting than other modified forms of talus in cold environments. As a result, limited research, use of supposed relict examples and assumed formative mechanisms led to the misidentification of ramparts, circular arguments regarding genesis and inappropriate palaeo-environmental inferences. Several advances have, however, been made in the past few decades, particularly where actively-forming ramparts have been studied. Thus, this paper provides a review of research on pronival ramparts. In particular, focus is placed on the advances made in our understanding of rampart genesis, identification (diagnostic criteria) and palaeo-environmental significance. Notable advances include the development of a retrogressive model of rampart genesis to supplement the conventional downslope model of development, revised diagnostic criteria for field identification and the use of calibration equations during Schmidt-hammer exposure dating of pronival rampart. The use of pronival ramparts as palaeo-environmental indicators is also examined to determine what relict examples of these landforms may reveal about past climates.

The biotic crisis across the Oceanic Anoxic Event 2: Palaeoenvironmental inferences based on foraminifera and geochemical proxies from the South Iberian Palaeomargin

Open marine sediments deposited during the Cenomanian–Turonian transition are well exposed in the Spanish Baños de la Hedionda section (Betic Cordillera, South Iberian Palaeomargin). Analysis of foraminiferal assemblages and geochemical proxies allow inferences on the impact of the Oceanic Anoxic Event 2 (OAE2) in this area of the western Tethys. Three main intervals have been identified corresponding to different lithological units and biozones. (1) The top of the Capas Blancas Member (Rotalipora cushmani Biozone) represents the pre-extinction phase with diverse foraminiferal assemblages and well developed water-column tiering, well-oxygenated, oligotrophic deep-waters and oxygenated to poorly oxygenated, mesotrophic surface-waters. Foraminiferal opportunist species point to a minor event with dysoxic conditions preceding the OAE2. (2) The black radiolaritic shales (Whiteinella archaeocretacea Biozone) consist of a foraminiferal-barren interval, except for the lowermost centimetres where planktic surface-dweller opportunists are common. Redox sensitive elements (Cr/Al, V/Al, U/Th, MoEF, Moaut, UEF and Uaut) and increased TOC values reflect oxygen depleted conditions related to the OAE2. The increase in P/Ti values at the base of this stratigraphic interval indicates an abrupt increase in productivity. High concentrations of radiolarians are congruent with high surface productivity probably related to changes in oceanic circulation and enhanced upwelling currents, as well as subsequent shallowing of the oxygen-minimum zone. The increase in MoEF and Moaut towards the top of the black radiolaritic shales indicates temporal euxinic conditions. (3) A slow, bottom-up recovery of foraminiferal assemblages is inferred at the base of the Boquerón Member (Helvetoglobotruncana helvetica Biozone), with seafloor recolonization by benthic foraminifera being recorded previous to the water column colonization by planktic forms, mainly by intermediate-dwellers typical of mesotrophic waters. The subsequent proliferation of surface-dweller opportunists and deep-dweller opportunists adapted to mesotrophic to eutrophic conditions, and the decrease in planktic foraminiferal diversity, may indicate the persistence of poorly oxygenated conditions in the water column towards the lower-middle part of the H. helvetica Biozone.

Mineral Chemistry of Clays Associated with the Late Cretaceous-Early Palaeogene Succession of the Um-Sohryngkew River Section of Meghalaya, India: Palaeoenvironmental Inferences and K/Pg Transition

Abstract A unique, continuous, shallow marine succession within the Langpar Formation in the Um-Sohryngkew river section of Meghalaya contains late Maastrichtian through early Danian planktonic foraminiferal biozones (CF4-P1a) and the K/Pg boundary (between CF1 and P0). To resolve compositional overlap [in the three-fold clay mineral based sub-divisions of the section (include 1-2 mm thick yellowish brown clay layer in biozone CF3)] and to understand paleoenvironmental conditions prevalent at the time of K/Pg transition, micro-structural and compositional studies were carried out. The paper discusses accurate compositional limits of solid solubility in smectite and illite. Clay morphological attributes distinctly vary with the changes in the biozonation. Major oxide data plots for the litho-units (samples JP1-16) over binary diagrams, show clustering of plots within the illite compositional field. Plots based on structural formulae and layer charges of illite and kaolinite rich clays (from CF4 to Pla biozones), show closeness with the clay data fields of Agost, Caravaca, Petriccio and El-Kef K/T boundary sections as their charge occupancies at tetrahedral (Zt), octahedral (Zo) and interlayer (Zi) sites are similar. Thermodynamic data plots over ternary [AR23+Si3O10 (OH)2 - R23+SiO4O10(OH)2 - A3AlSi4O10(OH)2] diagram, clustered within the illite compositional fields. Majority of illites shows high K values. They represent occasionally higher Altet. and lower Aloct. layer charges. Calculated palaeotemperature values for illite (from the CF4 to Pla zones) vary from 68 - 232°C. Sudden rise in the temperature (&amp;gt;140°C) of illite formation noticed in the upper part of the biozone CF3 (sample JP-12) is comparable to the K/T boundary layer of Caravaca section. Wide variation in the humid tropical to arid-semiarid climatic and thermal (diagenetic to low grade metamorphic) conditions noticed across the succession is possiby linked with the contemporaneous Abor / Deccan volcanic activities (at the time of their deposition) as also reflected in their clay layer [Si (2.95-3.68)] and interlayer [K+Na (0.4-4.61)] charges.

First record of Microscapha LeConte from Baltic amber with description of a new species and list of fossil Melandryidae (Coleoptera: Tenebrionoidea).

Microscapha andrzeji sp. nov., the first fossil representative of the genus is described from Eocene Baltic amber. An updated list of fossil Melandryidae (Coleoptera: Tenebrionoidea) is provided. The presence of Microscapha within Baltic amber suggests some potential for palaeoenvironmental inferences based on the melandryid assemblage within the deposit.