Humid Episodes Research Articles

Palaeoenvironmental changes in the Late Triassic lacustrine facies of the Ordos Basin of Northwest China were driven by multistage volcanic activity: Implications for the understanding the Carnian Pluvial Event

The Carnian Pluvial Event (CPE) induced an intense carbon-cycle disturbance and biological crisis at a global scale. The eruption of the Wrangellia Large Igneous Province (W-LIP) is considered a possible triggering mechanism; however, this cannot fully explain the significant differences in environmental perturbations across different regions. In this paper, we present detailed records of petrography, mercury geochemistry, carbon and sulfur isotopes, trace elements, and provenance data for the Triassic lacustrine facies of the Ordos Basin in the North China Plate, which provide insights into the important effects of volcanic activities, other than the W-LIP, on palaeoenvironment during the CPE interval. Massive emissions of SO2, CO2, and pyroclastic deposits resulting from these volcanic activities triggered four humid episodes, each characterized by lake-level rise, negative δ13Corg excursion, a transition from mudstones to organic-rich shales facies, as well as algal bloom within a time span of 180 kyrs. The establishment of an age framework in the Ordos Basin enables comparative analyses of environmental evolution during the Carnian age across the North China Plate, the western Tethys domain, and the South China Plate. During the period of global climate perturbation driven by the W-LIP eruption, we conclude that short-term localized volcanic activities may have further induced high frequentcy environmental perturbations, which influenced biological shifts and increase organic carbon burial. These short-term volcanic activities with different occurrence times and frequencies complicate local-scale palaeoenvironmental evolutions, which may be an important reason contributing to significant differences in environmental perturbations during the CPE interval across different regions of the globe.

COBERTURA VEGETAL, AÇÃO ANTROPOGÊNICA E PALEOCLIMAS NA CAATINGA

The Caatinga is dominated by a semiarid climate and a high plant biodiversity dealing with anthropogenic disturbance and climate change. Previous studies suggest that Caatinga became a completely soil‐water pulse-dominated forest in response to reduced water availability at the end of the last ice age, around 10 cal kyr BP. This work aimed to identify vegetative and climatic evolution, and the human influence in the Cariri region, one of the driest parts of Brazil. We sampled soil in a temporal pond to identify pollen. The testimony is 170 cm in lenght and achieves 6,216 cal yr BP at the base. Pollen analysis indicates the presence of taxa representative of humid climates, between 6,216 and ca. 5000 cal yr BP, like Azolla, followed by implantation of Caatinga's modern configuration from ca. 4,900 cal yrs BP. After 2,700 cal yr BP, humid episodes occurred, possibly related to the El Niño - La Niña variation across the region, marked by increased algae and aquatic herbs concentrations. The occurrence of human activity species like Caryocar, Dioscorea, Spondias, and Licania suggest possibly landscape manipulation by pre – Columbian populations, and exotic Pinus and Prosopis reveal changes in the tree cover caused by European colonization in the Caatinga. Keywords: Anthropocene; Dry Forest; Paleogeography; Semiarid Region; Sedimentology, Lakes, Lagoons & Swamps.

Four volcanically driven climatic perturbations led to enhanced continental weathering during the Late Triassic Carnian Pluvial Episode

The arid climate of the Late Triassic was interrupted by a particularly humid episode known as the Carnian Pluvial Episode (CPE; ca. 234–232 million years ago). The CPE is often linked to eruptions in the Wrangellia Large Igneous Province (LIP), and is assumed to have led to global warming, enhanced weathering, water deoxygenation, and biotic changes. However, direct evidence for a temporal link between volcanic activity and chemical weathering has not yet been established due to the lack of comprehensive records across the CPE. In this study, geochemical and mineralogical analyses are applied to a lacustrine stratigraphic succession of the Jiyuan Basin (North China) that captures the CPE in high resolution. We identify four distinct pulses of enhanced continental chemical weathering characterized by elevated Chemical Index of Alteration values and kaolinite contents. These peaks in continental weathering coincide with Hg/TOC enrichments and negative organic carbon isotope excursions that mark four short (∼400 kyr) but intense pulses of Wrangellia LIP volcanism. In combination with signs of increased humidity, our findings provide direct and independent evidence that Wrangellia LIP eruptions significantly altered CPE chemical weathering rates in response to global warming and wetting. The lake experienced eutrophication and water deoxygenation after each volcanic pulse but the swift recovery of carbon isotopes suggests that the system rapidly returned to conditions prior to the volcanic perturbation. Organic carbon burial facilitated by widespread dysoxic and anoxic waters, and CO2 consumption via enhanced weathering likely played crucial roles in the rapid climatic recovery after each volcanic pulse.

Palaeoenvironmental evolution of the Badain Jaran Desert hinterland during the Early to Middle Holocene: A multi-proxy reconstruction on Taoerlegetu paleolake, northwest China

In this paper, we examine the Early to Middle Holocene evolution of a prominent group of ground-water fed lakes in the southeastern hinterland of the Badain Jaran Desert (BJD) of northwest China. Specifically, we describe a sediment profile record from the Taoerlegetu (TR) palaeolake basin using multiple proxies of total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ13Corg, grain size and mineral composition based on a well-dated trench profile. As C/N values suggest that sedimentary organic matter mainly originated from aquatic plants, δ13Corg values can be used as a qualitative proxy for water level because aquatic plants in different biotopes (water depth) have different δ13C values. Our results show that from 10.9 to 9.1 cal kyr B.P., water level rose slowly, and aquatic macrophytes occupied the lake basin. From 9.1 to 5.5 cal kyr B.P., water level reached an even higher level and phytoplankton replaced macrophytes as the major contributor to organic matter. The humid episode of the lakes in the hinterland of the BJD in the early Holocene might be related to the increased groundwater supply from the northeast region of the Tibet Plateau. These findings are consistent with earlier studies of lacustrine and peat sediments found in periphery of the modern lake group, which indicate that their geographic extent may have been larger in the past. A relative drought period recorded in the studied succession from 8.5 to 8.0 cal kyr B.P. marks an interval of reduced ground-water transport from the Tibet Plateau. This interval probably corresponds to the “8.2 ka cold event” and provides evidence that this widespread climate episode influenced groundwater processes across inland Asia.

Intensive ocean anoxia and large δ13Ccarb perturbations during the Carnian Humid Episode (Late Triassic) in Southwest China

The Carnian Humid Episode (CHE) represents a dramatic dry to wet climate transition in the Late Triassic. Manifestations of this climate shift and its associated biological and environmental responses are not fully understood. Here, we carried out carbonate carbon isotope, trace metal, and pyrite framboid analyses at Wolonggang in southwest China to trace palaeoenvironmental changes during this critical interval. The CHE at Wolonggang is marked by the development of fine laminated carbonaceous siltstones and black shales overlying the intensely bioturbated Zhuganpo limestone deposited in the latest Julian 1. This lithological change is accompanied by two negative δ 13 C carb excursions, a strong enrichment of redox-sensitive trace metals U and Mo, and the development of abundant small pyrite framboids with an average diameter < 5 μm. The sedimentary and geochemical evidence collectively suggest a sharp decrease in carbonate production and a major carbon cycle disturbance, coinciding with the onset of intense ocean anoxia and the mass mortality of burrowing faunas. Unlike other areas in the western Tethys, the aftermath of the CHE at Wolonggang is characterized by long-lasting ocean anoxia, with weak carbonate production persisting at least to the late Tuvalian. This is evidenced by the deposition of finely laminated silty carbonates, marls, and carbonaceous siltstones with rare benthic fossils in the Wayao Formation. Our study suggests that anoxic-euxinic environments widely developed along the southwest margins of the Yangtze Platform and in the Nanpanjiang Basin, probably contributing to the loss of marine faunas during the CHE. • Sedimentary and bio-chemostratigraphic investigations were carried out in a key Carnian section in SW China. • Carbon cycle instability was seen during the Carnian Humid Episode. • Anoxia was basin-wide and long-lasting during the CHE and its aftermath. • Warming and anoxia played key roles in the loss of marine faunas during Carnian.

The Enzonalasporites group of Triassic pollen genera and species: New morphological and ultrastructural data, revised taxonomy and paleobiogeographical aspects

The ‘Enzonalasporites group’ comprises Enzonalasporites, Patinasporites, Vallasporites, Pseudenzonalasporites, Tulesporites, Daughertyspora and Zonalasporites pro parte, and their described species. There is little consensus on the taxonomy of this widely distributed group of mainly Late Triassic pollen despite their importance in biostratigraphy, paleoecology and conifer evolution. Last revised over forty years ago, their taxonomy is plagued by inadequate diagnoses and emendations, inconsistent or inaccurate terminology, and intergrading morphological attributes. In this paper we present new data and interpretations on the morphology, ornamentation and ultrastructure of key species, and use them together with analysis of published images and data to underpin a major review of the group's taxonomy and position in conifer evolution. Confocal laser scanning microscopy (CLSM) shows the raised ridges of rugulae on the proximal face of some pollen grains are impression marks, not trilete marks. Focused ion beam scanning electron microscope (FIBSEM) sectioning of some E. vigens and Patinasporites densus pollen grains shows that overlapping and intertwined rugulae create alveoli in a slightly inflated lateral exinal envelope, or “saccoid”. Dimensions of the corpus, saccoid and rugulae were measured using both SEM and transmitted light microscopy (LM) images. The challenge of intergrading attributes was managed by selecting morphologically stable criteria that can be used with routine LM, an approach which enables most specimens to be assigned taxonomically with confidence, while acknowledging that some may remain problematic. The hierarchy of criteria used in revising the taxonomy were: (1) corpus diameter/total width ratio, (2) dominant sculptural element, (3) presence or absence of impression marks, and (4) saccoid width and characteristics. The first two criteria help discriminate between genera, and the second two between species. After applying these criteria, emending diagnoses and synonymizing or transferring several species, three genera and seven species remain: E. vigens, E. ignacii, E. antonii n.c., Patinasporites densus, Pseudenzonalasporites cinctus n.c., Pseudenzonalasporites leschikii n.c., and Pseudenzonalasporites summus. The Enzonalasporites group reached maximum diversity, abundance and distribution during the Carnian, a stage characterized by several humid episodes, but the details of their paleobiogeographic distribution are complex. E. vigens and E. ignacii seem to have preferred xerophytic or halophytic conditions with occasional wetter episodes (e.g. monsoons), while Patinasporites densus seems to have preferred more hygrophytic conditions. The common thread between these species is their requirement for moisture during germination which required a pollination drop. Paleoenvironmental changes during the latest Triassic may have favored conifers which germinated using siphonogamy.

Biospeleothems Formed by Fungal Activity During the Early Holocene in the “Salar de Uyuni”

The Chiquini and Galaxias caves contain speleothems that are templated by long fungal structures. They have been associated with the carbonate lacustrine deposits in the margins of the Coipasa and Uyuni Salar basins. During a wetter episode, such carbonates formed at the end of the last glaciation raising the lake level to more than 100 m in the Tauca events (15–12 ky). Such an event flooded the caves that eventually became a cryptic habitat in the lake. The caves show bizarre speleothems framed by large (>1 m) fungal buildings covering the older algal mineralized structures. Although the origin of the caves is not fully understood, the occurrence of two carbonatic units with very distinctive fabric suggests that they formed in two separated humid events. In this regard, the mineralized algal structures, showing the same features as the lacustrine carbonates, likely formed during the Tauca flooding events in the terminal Pleistocene that inundated older caves. The different caves were exposed to the atmosphere after a drop in the lake level that promoted alluvial erosion by <12–10 ky (Ticaña episode) under arid conditions. A last humid episode rising the lake surface 10 m above the Salar level, which was not enough to inundate the caves a second time, drove the formation of the biospeleothems by fungi biomineralization. The abundance and size of the preserved fungal structures suggest that they were sustained by a stable hydrological activity plus a constant organic supply. While nutrients could have been primarily sourced from the vegetal communities that occupied the exhumated lake margins, they might have also been released from the lacustrine carbonatic unit. The combination of hydrology and biological activities were likely determinants for a fast rock dissolution and mineralization ending in the construction of the fungal biospeleothems.

An exceptional record of millennial-scale climate variability in the southern Iberian Margin during MIS 6: Impact on the formation of sapropel S6

The study of planktic and benthic δ18O at site U1389 in the Gulf of Cadiz allowed us to reconstruct climate variability during the penultimate glacial period at an unprecedented millennial scale resolution. Hereby, a sequence of interstadial-stadial episodes similar to the Dansgaard-Oeschger events recorded during Marine Isotope Stage (MIS)3, were recognized in MIS6. After a detailed correlation with millennial-scale variability recorded along the Iberian margin and the North Atlantic we were able to link the millennial changes next to the Iberian Peninsula with Antarctic climate variability due to the interhemispheric seesaw response of the Atlantic circulation. The straight coupling at site U1389 of a) the planktic δ18O that reflects climate change in the Atlantic with b) the benthic δ18O, which records the temperature and oxygen isotope composition of the mixture of Mediterranean Outflow and Atlantic intermediate water, indicates that millennial climate variability also had a strong impact on the eastern Mediterranean. The detailed analysis of the benthic δ13C and the fine sand content in the sediments from site U1389 led us to recognize the response of the Mediterranean overflow water (MOW) to millennial scale changes in Mediterranean overturning circulation during the penultimate glaciation. Both Mediterranean Overturning Circulation and MOW strength increased at times of cool and arid climates and weakened during warm and more humid episodes, similar to what has been described for MIS3. The tuning of MOW weakening events occurring at times of precession minima with eastern Mediterranean sapropels and enhanced Asian monsoon allowed the elaboration of a new chronology for MIS6. It was compared with the Epica Dome C time scale, which was also based on the tuning of atmospheric δ18O with Asian Monsoons speleothem records.Mediterranean overturning during MIS6 was also strongly affected by freshwater perturbations occurring at times of insolation maxima, leading to the formation of the “glacial sapropel” S6. Two major drops in seawater δ18O centered at 175 and 150 ky were observed near the entrance of the Mediterranean that were related to meltwater released from the ice sheets, coinciding with periods of insolation maxima. The entry of this meltwater anomaly through the Strait of Gibraltar is clearly registered in the western and eastern Mediterranean, especially at the onset of sapropel S6, suggesting that it was a major component of the freshwater that initiated the buoyancy gain preceding deep water stagnation.

Speleogenesis in a lens of metamorphosed limestone and ankerite: Ochtiná Aragonite Cave, Slovakia

The Ochtiná Aragonite Cave (Western Carpathians) represents an unique natural phenomenon. It originated under particular lithological and hydrogeological conditions of the Ochtiná Karst in which several isolated lenses of Paleozoic crystalline limestone (marbles), partly metasomatically altered to ankerite, are enclosed by phyllites. Meteoric water seepage through non-carbonate rocks dissolved limestone and caused the oxidation of ankerite to Fe oxyhydroxides. Carbon dioxide produced during ankerite oxidation enhanced limestone dissolution. The maze cave consists of parallel fault-controlled linear passages and chambers interconnected by transverse horizontal passages. Phreatic and epiphreatic solution morphologies resulted from slowly moving or standing water. These include flat ceilings (Laugdecken), facets (planes of repose, Facetten), lateral notches, convection ceiling cupola-shaped depressions, and spongework-like hollows. Flat ceilings were developed in several altitude positions, each of them probably closely below the slightly oscillated water table. Primary phreatic cupola-shaped depressions, truncated by flat ceilings, represent relics of the oldest cavities (pre-Quaternary? to Early Pleistocene). Inward-sloping smooth facets were not developed only in passages with flat ceilings, but also in the passages and halls with a vaulted ceiling. The asymmetrical shape of cusped depressions above the facets were documented in detail by a high-resolution cave topography with terrestrial laser scanning and digital photogrammetry. Middle–Late Pleistocene accumulation phases, identified by magnetostratigraphy of cave sediments and U-series dating of speleothems, are associated with phreatic and later epiphreatic development. The deposition on the bottom bedrock began before 1.8 Ma. The Brunhes/Matuyama boundary (0.773 Ma) and Jaramillo magnetozone (0.990–1.071 Ma) were recorded in the profile in the Oválna chodba Passage. Slow depositional rate (~0.09 cm/kyr) calculated from magnetostratigraphy resulted from slow water movement in confined conditions in marbles completely enclosed by phyllites and no direct relation to the surface. Only occasionally turbid water was loaded in extremely fine-grained infiltration material and autochthonous Fe oxyhydroxides. The depositional rate in Mn-rich layer was much slower (~0.03 cm/kyr). Additional U-series dating confirmed that old aragonite generations (with ages about 500–450 ka and 143–121 ka) were partly corroded by repeated floods during Late Pleistocene humid episodes. Aragonite younger than 13.5 ka is not corroded.

Environmental significance of benthic foraminifera and microfacies of central Tethyan Upper Triassic strata, central Iran

ABSTRACT: The evolution of the Late TriassicNaybandBasin in central Iranwas influenced by climatic changes and tectonic events. An increase in siliciclastic input and a corresponding carbonate productivity crisis in theQhrogchi area in central Iranwere initiated by the onset of a relatively humid episode in the Carnian, followed by arid to semi-arid conditions in the Norian and Rhaetian. Carbonate sediments of theNayband Formationwere deposited in a range of environments, from outer ramp to marginal marine environments. The rich benthic fauna is predominantly restricted to the limestone bedswithin the upper part of succession. Bivalves, hydrozoans (Heterastridium), calcareous algae, corals and sclerosponges are recorded. The latter two groups form patch reefs on the middle ramp. Benthic foraminifera show strong affinities with assemblages reported from the central Tethys, whereas others are also well-known from the Alpine region and from the eastern Tethys.

Geochemical constraints on the middle Triassic Kani Zarrineh karst bauxite deposit, Irano–Himalayan belt, NW Iran: Implications for elemental fractionation and parental affinity

The middle Triassic Kani Zarrineh bauxite deposit, in the Irano–Himalayan belt, located 20 km northwest of Saqqez city in northwestern Iran, occurs in depressions of the early Triassic bedrock carbonates of the Elika Formation. The ores formed during the Carnian Pluvial Event under high atmospheric pCO2 conditions and humid episodes. Powder-XRD analyses revealed that the Kani Zarrineh bauxite is mainly composed of diaspore, hematite, and kaolinite. There is a broad inverse relationship between hematite abundance and diaspore abundance in the profile with a downward increase of hematite and an upward increase of diaspore. Among minor constituents, single crystals rich in high field strength elements, such as florencite, monazite-(Ce), xenotime-(Y), and zircon were detected by SEM-EDS analyses. R-mode factor analysis indicates that most of the variance of the dataset is explained by a factor accounting for the competition between the Al2O3–TiO2–Ga–HFSE pool and the SiO2–Fe2O3–U–first row transition metals pool, and related to the coupled effect of a change of redox conditions and climatic regime. The other two factors are related to the importance of phosphate minerals (e.g., florencite and monazite) in hosting LREE, and to the influence that the chemistry of the soil solutions, especially pH, exerted in promoting the preferential mobility of HREE. Both these factors contribute to explaining LREE/HREE fractionation in the Kani Zarrineh bauxite ores. A negative correlation between the Ce/Ce* and the TOC (r = –0.91) corroborates the fact that bauxitization occurred in an environment characterized by a progressive increase in Eh upward. The coupled Ce/Ce* increase and TOC decrease upward are likely related to soil aeration, a progressive increase in soil temperature, and a reduction in soil moisture. An upward decrease of soil moisture is also consistent with an increase in the abundance of Al hydroxides that require drier conditions than those necessary for the formation of Fe oxyhydroxides. Finally, the evaluation of elemental mobility and results of the R-mode factor analysis indicate that, in addition to Al, high field strength elements Nb and Ta can be used confidently for assessing parental affinity of the Kani Zarrineh bauxite ores. The Al/Ta and Nb/Ta ratios and the Sm/Nd and Eu/Eu* provenance proxies reveal that mafic rocks interbedded in the early Triassic bedrock carbonates of the Elika Formation are likely protoliths of the Kani Zarrineh bauxite ores. This finding is consistent with what is observed for some bauxite deposits from the Mediterranean-type karst bauxite belt, especially from northwestern Iran of different ages that basalt rocks were the parent rock of these deposits.

The Rhaetian flora of Wüstenwelsberg, Bavaria, Germany: Description of selected gymnosperms (Ginkgoales, Cycadales, Coniferales) together with an ecological assessment of the locally prevailing vegetation

This paper describes the ginkgoaleans (Ginkgoites) and conifers (Palissya, Stachyotaxus, Schizolepis) of the Rhaetian flora from Wüstenwelsberg, as well as a new species of the cycad Becklesia. The ginkgophyte leaf fragments are very abundant in certain levels (‘Blätterkohle‘) whereas conifers are common in the main fossiliferous bed. The Wüstenwelsberg specimens extend the range for Ginkgoites taeniatus from the Hettangian to the Rhaetian and for the genus Becklesia from the Cretaceous to the Rhaetian. The other elements are typical for the Rhaetian floras of Bavaria and often also of the Northern Hemisphere. A comparison with other Northern Hemisphere plant assemblages demonstrates a high similarity with the Rhaetian floras from Jameson Land (Greenland) and Scania (Sweden) but significant differences to the Hettangian floras from adjacent areas in Franconia, especially at species and sometimes at generic level. A comparison with the microflora from the same sections shows a hidden diversity that is highest in small herbaceous plants (mosses, lycophytes, ferns) and in the conifers. Wüstenwelsberg reflects, thus, an articulated landscape with a high water and nutrients availability (stagnant water bodies and/or river systems) covered by a complex and multi-storeyed vegetation shown, among others, by the general abundance in hygrophytic spores and high diversity among the various plant groups. This must have corresponded to one of the humid episodes that characterized the generally warm and arid climate of the Rhaetian of Europe.

Paleorecords of Domesticated and Wild Grapevine in Romania: a Review

This paper reviews the, so far available, paleorecords of Vitis sylvestris C.C. Gmel and Vitis vinifera L. from Romania. The study takes into consideration the presence of Vitis pollen from Holocene peat sediment sequences and archaeological context, but also the presence of macrorests from various archaeological sites that date from Neolithic, Chalcolithic, Bronze Age, and La Tène. Both paleobotanical arguments and archaeological discoveries support the theory that places the beggining of viticulture in Romania a few millenia ago, in Neolithic period. Also, written evidences (works of classical authors, epigraphical sources) confirm, indirectly, the presence of grapevine in La Tène period. Occurrences of Vitis vinifera and those of Vitis sylvestris manifest independently of the climate oscillations, being present both through colder and more humid episodes, as well as through drier and warmer events. Probably prehistoric communities have made a constant and deliberate effort, all along the Holocene, to maintain grapevine crops.

Dark Side Archaeology: Climate Change and Mid-Holocene Saharan Pastoral Adaptation.

High-resolution paleoenvironmental research allows us to pinpoint the tempo and amplitude of past climate changes. Abrupt climate events have axiomatically triggered cascades of adjustments, in vegetation, fauna, humans, and pathogens. This essay focuses on the abrupt end of the African Humid Episode (9000–6000 cal BP), ca. 5000 cal BP in the Sahara. Neolithic pastoralists, practicing transhumance between sandy lowlands and Saharan mountains, adopted new cultural practices: cattle burials and livestock bone deposits in built installations. Their ritual nature is indisputable. But ritual for what? If considered from the perspective of livestock zoonoses, such practices may point to the “dark side” of cultural adjustments—strategies to counter human and livestock diseases. Livestock zoonoses are constant sources of emerging infectious diseases (EID) in the present, as they were in the past. Sustained research on livestock and human health are of paramount importance given the accelerating rate of world urbanization.

Record of the Carnian Pluvial Episode in the Polish microflora

The dry climate that prevailed during the Triassic period in the eastern part of the Central European Basin was interrupted by several humid episodes of varying durations. One of them was the Carnian Pluvial Episode (CPE), which took place in the late Julian (early Carnian age) and is confined to Camerosporites secatus and Aulisporites astigmosus palynological zones. CPE is marked by a significant change in the qualitative and quantitative composition of spore-pollen assemblages from mostly xerophytic species preserved in the upper part of the Grabfeld Formation (“Lower Gipskeuper”) to hygrophytic forms, which dominate in the Stuttgart Formation (“Schilfsandstein”). Changes in climate towards more humid conditions have been documented palynologically and sedimentologically, and analyzed utilizing quantitative spore-pollen analysis and Principal Component Analysis (PCA) of miospores occurring in core material from Poland. In all the studied boreholes, a shift from dry to wet climate is observed at the boundary between the Grabfeld Formation and the Stuttgart Formation, which matches the data from other European regions.

Climate and environmental response to the break-up of Pangea during the Early Jurassic (Hettangian-Pliensbachian); the Dorset coast (UK) revisited

Abstract Between the end-Triassic mass extinction and the Toarcian Oceanic Anoxic Event, the Early Jurassic witnessed important changes in carbon burial, palaeogeography and paleoceanography, which were linked to the initial breakup of Pangaea. In order to better understand the climate and environmental impact of this phase of major tectonic rearrangement we revisited a key section along the Dorset coast (UK) and used a multi-proxy geochemical approach for its analysis. Carbon isotopes (δ13C) measured on organic matter were corrected for the influence of changes in the type of organic matter. The thus obtained δ13C-HI index and an additional δ13Ccarb record measured on bulk carbonate indicate a suite of carbon-isotope excursions (CIEs) including the negative main CIE (Triassic-Jurassic boundary to early Sinemurian) the negative Sinemurian-Pliensbachian boundary CIE and the positive margaritatus Zone (late Pliensbachian) CIE. Based on elevated hydrogen index values and enrichments in Mo, U, V, total organic carbon (TOC) and pyrite, the Hettangian-Sinemurian interval was interpreted to have been characterised by high productivity conditions and strong oxygen depletion of the basin. The chemical alteration index (CIA), clay mineralogy, and δ18O data provide independent evidence for increased continental runoff triggered by humid climate conditions on the adjacent continent during this time period. The strongest oxygen-depleted conditions were inferred for the lowermost Hettangian interval, coincident with the onset of the main negative CIE. A further less strongly oxygen-depleted interval was recorded through the negative CIE near the Sinemurian-Pliensbachian boundary (jamesoni and ibex Zones). This interval was characterised by drier conditions and possibly cooler water temperatures (e.g. CIA, δ18Ocarb and kaolinite/illite ratio). Based on low CIA values and kaolinite/illite ratios, the Pliensbachian climate is considered to have been generally drier, superimposed by more humid episodes restricted to the davoei and margaritatus Zones. The long-term trend to drier conditions is explained by: (1) diminished atmospheric CO2 contents due to a reduction in emissions of volcanogenic greenhouse gases, and/or; (2) changes in the palaeogeography and current patterns related to the break-up of Pangaea and more specifically to the opening of the Hispanic corridor.

Palynology and weathering proxies reveal climatic fluctuations during the Carnian Pluvial Episode (CPE) (Late Triassic) from marine successions in the Transdanubian Range (western Hungary)

Abstract In the early Late Triassic, the Carnian Pluvial Episode (CPE) is a phase with increased siliciclastic influx into the marine-carbonate dominated depositional setting of the Western Tethys assumingly caused by a shift to more humid climatic conditions and increased continental runoff. Here, vegetation changes inferred from the palynological assemblages and weathering proxies (αAli) have been studied from the Transdanubian Range (TR), western Hungary to reveal climate variations and detect episodes with hygrophytic vegetation and enhanced continental hydrolysis. Palynostratigraphy has been applied to correlate the clastic pulses known from elsewhere in the Western Tethys. The quantitative palynological analysis indicates a shift towards hygrophytic elements in the Julian 2, and return to xerophytic associations in the Tuvalian. The increase in the hygrophytic vegetation elements is coincident with elevated kaolinite and partially with the increase of α-values indicating strong terrestrial runoff, enhanced continental hydrolysis and more humid climate in the lower part of the Veszprem Formation in the early Julian 2. The wetter conditions in the Julian 2 were periodically interrupted by shorter periods of drier climate manifested in the progradation of carbonate platforms and the deposition of carbonate series and breccias interbedded between the marl units. In the late Julian 2 the high amount of hygrophytes points to another humid episode, but the decrease of kaolinite in the clay mineral profile and the weathering indices might suggest stronger seasonality. Although, the multiple clastic pulses in the western Tethys were related primarily to more humid climate during the CPE, the comparison to clay mineralogy and weathering proxies suggest a more complicated scenario in the TR. The enhanced continental weathering related to a more humid climate is only suggested for the lower part of the Veszprem Formation in the early stages of the CPE in the Julian 2.

NORIAN AMMONOIDS FROM THE NAYBAND FORMATION (IRAN) AND THEIR BEARING ON LATE TRIASSIC SEDIMENTARY AND GEODYNAMIC HISTORY OF THE IRAN PLATE

A Middle Norian (Alaunian 2) ammonoid assemblage from north of Esfahan (Central Iran) is described and chronostratigraphically evaluated. Formerly known as Distichites fauna, it represents a geographically widely distributed and stratigraphically important fossil level in the lower part of the Upper Triassic Nayband Formation. The new distichitid ammonoid genus Mesodistichites with the new species M. evolutus are introduced; additional faunal members are Noridiscites nodosus n. sp. and the leiostracean Stenarcestes diogenis and Pinacoceras cf. imperator. The Nayband Formation of the Esfahan region, belonging to the Zefreh-Soh Facies, is lithostratigraphically emended to contain three formally introduced members (Parsefid, Venher and Niazmargh members), which are all of Norian age, whereas Rhaetian sediments are missing. These members are correlated with Norian lithostratigraphic units of the type sequence of the formation in Nayband, eastern Iran. Integration of all Iranian Nayband data allows the recognition of three 3rd order sequences within this formation and the proof of a major pre- or syn-Jurassic unconformity across Central Iran and the Central-East Iranian Microcontinent (CEIM) related to the Main-Cimmerian event. Because of the latter and of major lithostratigraphic and facial differences, we propose to exclude the Nayband Formation from the Shemshak Group. A careful review of the available biostratigraphic data from northern and southern Iran let us further assume that the collision of the Iran Plate with Eurasia occurred in the later Early Carnian and was concurrent to the onset of the Carnian Humid Episode.

Onshore and offshore evidences for four abrupt “warming” episodes during MIS 6 at the westernmost tip of continental Europe: did they control the migrations of Neanderthals?

The total shell production typical of the Pupilla association in the onshore site of Nantois (Brittany, France) evidenced for the first time four brief, abrupt, warm and humid episodes during the Upper Saalian (MIS 6) loess deposition. These “warming” events were also found in the marine deposits of the Celtic Sea (MD03-2692 core). Comparison with the variations of the sea-level, show that the “warming” episodes were not only of regional interest but corresponded to global events ruled by precession and insolation cycles. Other comparisons with biomarker records (mollusсs, charcoal and rodents) of the Paris Basin (Villiers-Adam) and Jersey Island (La Cotte de Saint Brolade) confirm the existence of these warmer events. Tentative correlations with the discontinuous Neanderthal dwelling phases recorded in Brittany suggest that these populations were mainly (only?) present in Westernmost Europe during the warmer episodes.

El registro paleoambiental del Pleistoceno tardío al presente en la Laguna de Lobos, Buenos Aires, Argentina

Se caracterizó el medio físico del ambiente, la fisiografía, régimen hidrológico y la historia geológica de la cubeta lagunar. La geología superficial está representada por seis unidades litoestratigráficas y dos pedoestratigráficas, que abarcan del Pleistoceno temprano al tardío y del Holoceno medio al presente. La más antigua, la Formación Ensenada, constituye el sustrato regional, sobre el cual se ubican cuatro unidades eólicas, las Formaciones Buenos Aires, La Postrera I, III y IV, los Geosuelos Sin Nombre y Puesto Berrondo y el Aluvio reciente. Los sedimentos colmatantes fueron obtenidos mediante perforaciones, reconociéndose siete unidades litoestratigráficas (cinco subácueas y dos subaéreas). Las subácueas corresponden a la Formación Luján, Miembros La Chumbiada, Lobos, Río Salado y Monte (Pleistoceno tardío al Holoceno tardío) y al Aluvio reciente. Los depósitos subaéreos a las Formaciones La Postrera I y IV del Pleistoceno tardío y Holoceno tardío-tardío, respectivamente. La excavación de la cubeta se inició en la etapa seca del ?Bonaerense?, la posterior alternancia climática: seco-húmedo facilitó la evolución. Las etapas secas se caracterizaron por deflación, generación de cubetas, sabkhas o lagos salados, precipitación de sales y acumulación de depósitos eólicos. En las húmedas predominó la sedimentación y la pedogénesis. De esta manera, el conjunto de depósitos posteriores a la Formación Ensenada está representado por cinco episodios de clima seco, que abarcan del Glacial Temprano a la Pequeña Edad de Hielo y cinco húmedos, cuyas acumulaciones límnicas conforman los cuatro miembros de la Formación Luján, el aluvio actual y los suelos sincrónicos S4, S1 y S0.