Major Paleoenvironmental Changes Research Articles

Discovery of the Callovian Oceanic Anoxic Event in the Qiangtang Basin, eastern Tethys: Insights from in situ calcite U[sbnd]Pb dating

Oceanic anoxic events (OAE) are global carbon-cycle perturbations and major paleoenvironmental changes documented by deposition of black shales rich in organic matter. Jurassic black shales exposed in the Biluo Co Section of the Qiangtang Basin (central Tibet) display a ∼ 3 % negative carbon isotope excursion (CIE) previously regarded as documenting the Toarcian T-OAE based on poorly preserved ammonites and one detrital zircon age. New biostratigraphic data on diagnostic calcareous nannofossils and ammonite assemblages have suggested a younger, Middle Jurassic age, thus raising doubts about the presence of the T-OAE in the Qiangtang Basin. We here present the first accurate in situ LA-ICPMS calcite UPb ages for carbonate layers intercalated in the Biluo Co section. Ages of 165.6 ± 3.7 Ma, 166 ± 16 Ma, and 164.0 ± 7.2 Ma obtained from two samples analyzed in two different laboratories indicate the Late Bathonian to mid-Callovian age, which is consistent with recent age assignments based on calcareous nannofossils and ammonites. Petrographic, geochemical, and C–O isotope analyses testify to only minor diagenetic effects, indicating that geochronological data do reflect the original timing of carbonate deposition. Therefore, the new age assignment does not document the T-OAE in the Qiangtang Basin, but possibly a younger, Callovian global-warming event.

Late Guadalupian–early Lopingian marine geochemical records from the Upper Yangtze, South China: Implications for climate-biocrisis events

Major paleoenvironmental changes occurred during the Guadalupian-Lopingian boundary (GLB) transition, but the causative linkages among the Emeishan Large Igneous Province (LIP), end-Guadalupian crisis and climatic fluctuations are still in dispute. Variation of geochemical proxies preserved in the sedimentary records is important evidence in examining potential links between volcanisms and environmental changes. Herein, we carried out a comprehensive study of carbon/strontium isotope and trace element geochemistry at the Dukou section, northern margin of the Upper Yangtze. During the Late Guadalupian, the carbon isotope showed a negative drift, the marine primary productivity declined simultaneously, and redox proxies indicate the enhancement of ocean oxidation. It is worth noting that the δ13Ccarb turns into a rapid negative drift from a slow decline at approximately 260.55 Ma, which was almost synchronized with the latest reported eruption ages of Emeishan Large Igneous Province. This coincidence suggests that global volcanic-tectonic activity during the Late Guadalupian might have been the important factor in carbon-cycle perturbation. Subsequently, the δ13Ccarb presents a rapid positive shift at approximately 259.4 Ma, and climate transformed from interglacial to P4 glacial, indicating that the climate rapidly cooled before the Emeishan LIP completely ended, which may be due to carbon sinks caused by weathering of mafic rocks, and may also be associated with a significant reduction in global volcanic activity. Accompanied by sudden weathering attenuation, the 87Sr/86Sr ratios show a significant increase instead from the previous long-time low value, which only can be explained reasonably by the rapid decline in mantle-derived Sr flux associated with the weakening of volcanic activity and mafic weathering. Intergrated geochemical indices in this interval shows that there is a rapid climate perturbation associated with a significant δ13Ccarb negative shift at approximately 260.55 Ma ∼ 259.10 Ma, which may be related to the eruption surge of the Emeishan LIP, active volcanic arcs, and triggered the end-Guadalupian biocrisis.

Quantitative Biostratigraphic Analysis and Age Estimates of Middle Cretaceous Sequences in The Baltimore Canyon Trough, Offshore Mid-Atlantic U.S. Margin

ABSTRACT We applied quantitative methods to previously published biostratigraphic data from the Baltimore Canyon Trough (offshore of the Mid-Atlantic U.S.A.) to provide an improved chronostratigraphic framework for Cretaceous sequences. Here, we successfully used graphic correlation of 228 planktonic foraminifera, nannofossil, and palynological events spanning 22 wells to define assemblage and interval zones as well as major paleoenvironmental changes in the Dawson Canyon, Logan Canyon (three sequences), and Missisauga Formations (two sequences, undifferentiated here). Ranking and scaling techniques were not successful because of the of the limited number of usable biostratigraphic markers. The ages of the sequences previously identified using well logs and seismic profiles were temporally constrained based on chronostratigraphically significant biostratigraphic markers that we identified: the late Cenomanian to Turonian DCx sequence (Rotalipora cushmani and Thalmanninella greenhornensis); the early Cenomanian LC1 sequence; the middle and late Albian LC2 sequence (Braarudosphaera africana, Planomalina buxtorfi, and Spinidinium vestitum); the late Aptian LC3 sequence (Cyclonephelium tabulatum); and the early Aptian to Barremian Missisauga sequences (Aptea anaphrissa, Pseudoceratium pelliferum, and Muderongia simplex). These five biostratigraphic associations are correlated with six prominent seismic reflectors and sequence boundaries that can be traced across the basin. Duration of hiatuses associated with these sequence boundaries are uncertain, though our Monte Carlo analysis allows extraction of age estimates from broad and sometimes contradictory ranges and suggests correlation of hiatuses with global sea-level falls. Together, these seismic and biostratigraphic interpretations can be applied (1) to evaluate reservoir continuity and the viability of offshore carbon storage reservoirs in the Baltimore Canyon Trough, (2) to better define the tectonostratigraphic evolution of the basin, and (3) to contribute to the understanding of regional and global variations in Cretaceous sea level.

Estimating the Drivers of Diversification of Stoneflies Through Time and the Limits of Their Fossil Record

AbstractDeciphering the timing of lineage diversification and extinction has greatly benefited in the last decade from methodological developments in fossil-based analyses. If these advances are increasingly used to study the past dynamics of vertebrates, other taxa such as insects remain relatively neglected. Our understanding of how insect clades waxed and waned or of the impact of major paleoenvironmental changes during their periods of diversification and extinction (mass extinction) are rarely investigated. Here, we compile and analyze the fossil record of Plecoptera (1,742 vetted occurrences) to investigate their genus-level diversification and diversity dynamics using a Bayesian process-based model that incorporates temporal preservation biases. We found that the Permian-Triassic mass extinction has drastically impacted Plecoptera, while the Cretaceous Terrestrial Revolution corresponds with a turnover of plecopteran fauna. We also unveiled three major gaps in the plecopteran fossil record: the Carboniferous-Permian transition, the late Early Cretaceous, and the late Cenomanian to Bartonian, which will need to be further investigated. Based on the life history of extant Plecoptera, we investigate the correlations between their past dynamic and a series of biotic (Red Queen hypothesis) and abiotic (Court Jester hypothesis) factors. These analyses highlight the major role of continental fragmentation in the evolutionary history of stoneflies, which is in line with phylogeny-based biogeographic analyses showing how vicariance drove their diversification. Our study advocates analyzing the fossil record with caution, while attempting to unveil the diversification and extinction periods plus the likely triggers of these past dynamics of diversification.

Middle Jurassic - Early Cretaceous drastic paleoenvironmental changes in the Ordos Basin: Constraints on sandstone-type uranium mineralization

Middle Jurassic - Early Cretaceous paleoenvironmental evolution is fundamental to U (Uranium) migration and U-enrichment in the Ordos Basin. However, the detailed long-term terrestrial climate evolution across the Jurassic/Cretaceous (J/K) transition is still lacking. This study presents a comprehensive geochemical element analysis of 88 fine-grained sediments from Well Pengyang-SDI to verify the major paleoenvironmental changes including the changes in paleoclimate, paleoweathering, paleosalinity, and paleo-redox conditions. Various paleoweathering proxies (e.g., CIA) suggest that the sediments in the source area experienced a stronger chemical weathering process during the Jurassic than during the Early Cretaceous. The paleoclimate proxies (e.g., C–value, Rb/Sr, and Sr/Cu ratios) and the sharp increase in the salinity of the Luohandong Formation (LHDF) in the Ordos Basin may provide strong evidence for the continuous aridification since the Early Cretaceous. In the Lower Cretaceous non-uranium mineralization section in the basin, large U primary enrichments (high U/Th ratio) may be related to the rise in atmospheric oxygen levels during the Cretaceous. This remarkable paleoenvironmental transition controls the spatial–temporal collocation of the coal and oil in deep strata and the uranium in upper host rocks. The large-scale hydrocarbon migration from the deep strata transformed the Cretaceous aeolian sandstones into favorable uranium reservoirs. Core alteration observation and iron content testing shows that the large-scale oxygen-containing uranium surface fluid came from the western margin of the Tianhuan Depression. Finally, based on the analysis of the genetic relationships among uranium, coal, hydrocarbons, and alteration this study proposes that regions adjacent to the western margin of the Changqing oilfield with large faded alteration in the Lower Cretaceous strata are new ideal target areas for further uranium exploration.

A 14,000 year peatland record of environmental change in the southern Gutland region, Luxembourg

A Late Pleistocene/Holocene paleoenvironmental record was obtained from the Rouer peatland (5°54′E, 49°45′N; 270 m a.s.l.), located in the Gutland area of southern Luxembourg. A total of six sediment samples were AMS radiocarbon-dated to obtain an age-depth model. XRF analyses and analyses of geochemical proxies of organic matter (TOC, TN, δ13C, δ15N) were conducted to identify major paleoenvironmental changes in the record. Pollen analysis reveals insights into the vegetation history throughout the last 14,000 cal. yr BP. The record offers unique insights into the evolution of local organic sediment/peat accumulation, as well as into the environmental history of the Gutland region and beyond. The accumulation of organic sediment and peat started at about 13,800 cal. yr BP before present. Until about 6000 cal. yr BP, periods of apparently stable climatic conditions had been interrupted repeatedly by pronounced episodes with increased input of minerogenic matter into the peat matrix (12,700–11,800 cal. yr BP; 11,500–11,300 cal. yr BP; 11,100–10,800 cal. yr BP; 9300 cal. yr BP; 8200 cal. yr BP), indicated by sudden increases of Ti/coh values. After 6000 cal. yr BP, environmental conditions stabilized. Between 4200 and 2800 cal. yr BP, during the Bronze Age, changes in the pollen spectrum indicate an increasing clearance of woodlands. Since the Roman period, an ongoing intensification of grassland farming and agriculture is evidenced. Lowest tree species abundances are witnessed during the Middle Ages. The Modern Era is characterized by enhanced sediment input due to soil erosion. In short, this record complements the Late Pleistocene/Holocene climatic history of the Gutland area and demonstrates that fen peat deposits can be valuable high-resolution paleoclimate archives.

Response of the western proto-North Atlantic margin to the early Aptian oceanic anoxic event (OAE) 1a: an example from the Cupido platform margin-Gulf of Mexico, NE Mexico

Integrated microfacies and geochemical analyses conducted on five stratigraphic sections in northeastern Mexico (ancentral western margin of the proto-North Atlantic) reveal major paleoenvironmental changes in shallow water and pelagic environments in the prelude and run-up of the early Aptian oceanic anoxic event (OAE) 1a. During the Barremian–Aptian transition, the replacement of photozoan rudist-coral by mesotrophic/eutrophic orbitolinid-miliolid communities in the Cupido platform occurred in association with increased nutrient input. Thereafter, oligotrophic, photozoan, green algal communities repopulated briefly the carbonate ramp. Microbial-dominated ecosystems and peloidal carbonates with scarce fossils flourished before and during the onset of the OAE 1a, attesting carbonate crisis and highly stressed conditions. Organic-rich sediments deposited under weak reducing conditions in some parts of the platform. Carbonate sedimentation at the end of OAE 1a was characterized by photozoan ooid-dominated facies documenting a recovery phase of marine alkalinity. The studied carbonate platform shows a response mode to OAE 1a marked by continuous carbonate production, presumably protected by the “kettle effect”, but accompanied by significant ecological perturbations and incipient drowning. The documented change shares attributes of both central/southern and northern Tethyan platforms response modes. The OAE 1a deposits in the pelagic setting are characterized by organic-rich, radiolarian-dominated carbonates accumulated under oxygen-restricted bottom water conditions and during enhanced nutrient input linked to intense chemical weathering. The intensity of the trace metal anomalies suggests that volcanic-hydrothermal activity associated with the construction phases of the Ontong Java LIP also influenced the elemental abundance in the proto-Atlantic water mass.

Population genetic structure of the bank vole Myodes glareolus within its glacial refugium in peninsular Italy

It is now well established that Southern European peninsulas have been major glacial refugia for temperate species during Pleistocene climatic oscillations. However, substantial environmental changes occurred also within these peninsulas throughout the Pleistocene, rising questions about the role and interplay of various of micro-evolutionary processes in shaping patterns of intraspecific diversity within these areas. Here, we investigate the patterns of genetic variation in the bank vole Myodes glareolus within the Italian peninsula. By using a panel of 13 microsatellite loci, we found more intra-specific variation than expected based on previous assessments. Indeed, both Bayesian and ordination-based clustering analyses of variation recovered five main geographic/genetic clusters along the peninsula, with three clusters geographically restricted to the southern portion of the study area. This pattern supports the occurrence of multiple sub-refugia for the bank vole in peninsular Italy, likely promoted by the major paleo-environmental changes which affected forested habitats within this area during the Pleistocene. Thus, our results support a scenario whereby the high levels of intraspecific diversity observed within major glacial refugia are better explained by dynamic micro-evolutionary processes occurred within these areas, rather than by long-term demographic stability of refugial population. Finally, the narrow and isolated distribution of some of the identified lineages, suggest the need for future assessments of their conservation and taxonomic status.

Late Holocene environmental changes reconstructed from stable isotope and geochemical records from a cushion‐plant peatland in the Chilean Central Andes (27°S)

ABSTRACTA Late Holocene paleoenvironmental record was obtained from the Lagunillas cushion peatland (LP, 27°12′S, 69°17′W), located in the dry Puna of the western Central Andes. Ten radiocarbon dates build the chronology for the last 1800 cal a BP. Analyses of stable isotopes on cellulose (δ18Ocell, δ13Ccell) and geochemical proxies on organic matter (δ13COM, δ15Nbulk, TOC, TN, LOI, T535) were conducted to identify major paleoenvironmental changes in this record. Simultaneously, ambient water (δ18O, δ2H) and plant samples of the dominant species Oxychloe andina (δ18Ocell, δ13Ccell) reveal insights into modern conditions. The record reveals distinct multi‐centennial oscillations of peat layer thickness and δ18Ocell. Decomposition, changes in the dominating plant species as well as in plant parts (leaves/roots) can be excluded as driving factors for these oscillations. Thus, δ18Ocell seems to be externally forced and reflects humidity changes. Around 470 cal a BP a distinct change towards increased humidity occurred, lasting during the Little Ice Age until about 70 cal a BP. Humid conditions prevailed between 1530 and 1270 cal a BP. Increasing δ18Ocell values since 30 cal a BP mark a trend towards again increased aridity.

Paleocommunity mixing increases with marine transgression in Dinosaur Park Formation (Upper Cretaceous) vertebrate microfossil assemblages

AbstractVertebrate microfossil assemblages in a stratigraphic sequence often yield similar assortments of taxa but at different relative abundances, potentially indicative of marginal paleocommunity changes driven by paleoenvironmental change over time. For example, stratigraphically younger assemblages in the Dinosaur Park Formation (DPF) yield proportionally more aquatic taxa, consistent with marine transgression. However, individual deposits may have received specimens from multiple source paleocommunities over time, limiting our ability to confidently identify ecologically significant, paleocommunity differences through direct assemblage comparisons. We adapted a three-source, two-tracer Bayesian mixing model to quantify proportional contributions from different source habitats to DPF microfossil assemblages. Prior information about the compositions of separate, relatively unmixed terrestrial, freshwater, and marine assemblages from the Belly River Group allowed us to define expected taxon percent abundances for the end-member habitats likely contributing specimens to the mixed deposits. We compared the mixed assemblage and end-member distributions using 21 different combinations of vertebrate taxa. Chondrichthyan, dinosaur, and amphibian occurrence patterns ultimately allowed us to parse the contributions from the potential sources to 14 of the 15 mixed assemblages. The results confirmed a significant decline in terrestrial contributions at younger DPF sites, driven primarily by increased freshwater specimen inputs—not incursions from the adjacent marine paleocommunity. A rising base level likely increased lateral channel migration and the prevalence of freshwater habitats on the landscape, factors that contributed to increased paleocommunity mixing at younger channel deposit sites. Bayesian methods can account for source-mixing bias, which may be common in assemblages associated with major paleoenvironmental changes.

Middle Miocene paleoenvironmental crises in Central Eurasia caused by changes in marine gateway configuration

Marine gateways prove to be important factors for changes in the ecology and biochemistry of marginal seas. Changes in gateway configuration played a dominant role in the Middle Miocene paleogeographic evolution of the Paratethys Sea that covered Central Eurasia. Here, we focus on the connection between the Central (CP) and Eastern Paratethys (EP) to understand the paleoenvironmental changes caused by the evolution of this marine gateway. We first construct an integrated magneto-biostratigraphic framework for the late Langhian-Serravallian (Chokrakian-Karaganian-Konkian-Volhynian) sedimentary record of the eastern domain, which allows a correlation to the well-dated successions west of the gateway. The magneto-biostratigraphic results from the Zelensky-Panagia section on the Black Sea coast of Russia show that the Chokrakian/Karaganian boundary has an age of 13.8Ma, the Karaganian/Konkian boundary is dated at 13.4Ma, and the Konkian/Volhynian boundary at 12.65Ma. We identify three major phases on gateway functioning that are reflected in specific environmental changes. During the Karaganian, the EP turned into a lake-sea that supplied a unidirectional flow of low-salinity waters to the west, where the CP sea experienced its Badenian Salinity Crisis. This configuration is remarkably similar to the Mediterranean during its Messinian Salinity Crisis. The second phase is marked by a marine transgression from the west, reinstalling open-marine conditions in the CP and causing marine incursions in the EP during the Konkian. The Volhynian is characterized by a new gateway configuration that allows exchange between CP and EP, creating unified conditions all over the Paratethys. We hypothesize that a density driven pumping mechanism is triggered by the increase in connectivity at the Konkian/Volhynian boundary, which simultaneously caused major paleoenvironmental changes at both sides of the gateway and led to the Badenian-Sarmatian extinction event in the CP.

Soil erosion in relation to land-use changes in the sediments of Amik Lake near Antioch antique city during the last 4 kyr

The Amik Basin in the Eastern Mediterranean region occupied since 6000–7000 BC has sustained a highly variable anthropic pressure culminating during the late Roman Period when the Antioch city reached its golden age. The present 6-m-long sedimentary record of the Amik Lake occupying the central part of the Basin constrains major paleoenvironmental changes over the past 4000 years using multi-proxy analyses (grain size, magnetic susceptibility, and x-ray fluorescence (XRF) geochemistry). An age model is provided by combining short-lived radionuclides with radiocarbon dating. A lake/marsh prevailed during the last 4 kyr with a level increase at the beginning of the Roman Period possibly related to optimum climatic condition and water channeling. The Bronze/Iron Ages are characterized by a strong terrigenous input linked to deforestation, exploitation of mineral resources, and the beginning of upland cultivation. The Bronze/Iron Age transition marked by the collapse of the Hittite Empire is clearly documented. Erosion continued during the Roman Period and nearly stopped during the early Islamic Period in conjunction with a decreasing population and soil depletion on the calcareous highland. The soil-stripped limestone outcrops triggered an increase in CaO in the lake water and a general decrease in ZrO2 released in the landscape that lasts until the present day. During the Islamic Period, pastoralism on the highland sustained continued soil erosion of the ophiolitic Amanus Mountains. The Modern Period is characterized by a higher pressure particularly on the Amanus Mountains linked to deforestation, road construction, ore exploitation, and drying of the lake for agriculture practices.

Paleomagnetism and integrated stratigraphy of the Upper Berriasian hemipelagic succession in the Barlya section Western Balkan, Bulgaria: Implications for lithogenic input and paleoredox variations

A continuous Late Berriasian sedimentary and stratigraphic record is here presented from a hemipelagic succession from the Western Balkan (Barlya section, Bulgaria). The section, 39-m-thick, was stratigraphically calibrated using a variety of methods: biostratigraphy (calpionellids, calcareous nannofossils and calcareous dinocysts), magnetostratigraphy and carbon isotope stratigraphy. Additionally, chemostratigraphy and rock magnetic stratigraphy were applied in order to identify major paleoenvironmental changes: lithogenic input and paleoredox variations. Polarity zones from M17r to M14r were identified from the uppermost Lower Berriasian up to the Berriasian/Valanginian boundary (Elliptica to Darderi calpionellid subzones and NK-1 to NK-3 nannofossil zones). Late Berriasian calcareous dinocyst zones of Stomiosphaerina proxima, Stomiosphaera wanneri and Colomisphaera conferta were correlated with magnetostratigraphy for the first time. A carbon isotope profile correlates very well with the δ13C records from SE France and the Western Atlantic, documenting some well-resolved minima and maxima in a generally decreasing trend. Magnetic susceptibility (MS) reveals a very good positive correlation with lithogenic elements (e.g., Al, Ti, Zr, Th and others) and is regarded as a reliable proxy of detrital input. Influx of fine grained terrigenous material increases in the Upper Berriasian up to the Berriasian/Valanginian boundary. A prominent MS increase takes place in the lowermost part of polarity zone M16n (close to the Simplex/Oblonga subzonal boundary). The MS event can be traced in the Central Carpathian, Apennine and SE France sections, exactly in the same stratigraphic position. It is coeval with an important climatic turnover in Western Tethys; however, it might have been strengthened by a general regression and regional tectonic events in the Carpatho–Balkan area. Two oxygen deficient intervals were documented: the first in the Lower Berriasian (M17r to M16r); the second one in the uppermost Upper Berriasian up to the boundary with Valanginian (M15r to M14r). Both intervals correlate with an elevated sea-level in the Western Tethys.

The Badenian–Sarmatian Extinction Event in the Carpathian foredeep basin of Romania: Paleogeographic changes in the Paratethys domain

The Badenian–Sarmatian boundary interval is marked by a major extinction event of marine species in the Central Paratethys. The exact age of the boundary is debated because many successions in marginal basins show erosional features and fauna reworking at the boundary level. Here, we selected the Tisa section in the Carpathian foredeep basin of Romania, which is continuous across this Badenian–Sarmatian Extinction Event (BSEE). Quantitative biostratigraphic records of planktic and benthic foraminifera and calcareous nannofossils allow to accurately locate the Badenian–Sarmatian boundary and indicate a major paleoenvironmental change from open marine to brackish water conditions. Magnetostratigraphic results reveal a polarity pattern that uniquely correlates to the time interval between 12.8 and 12.2Ma. Interpolation of constant sedimentation rates determines the age of the BSEE in the Carpathian foredeep at 12.65±0.01Ma, in good agreement with several earlier estimates. We conclude that the extinction event took place in less than 10kyr, and that it was most likely synchronous across the Central Paratethys. It corresponds to a major paleogeographic change in basin connectivity with the Eastern Paratethys, during which the nature of the Barlad gateway switched from a passive to a full connection.

Diatom-based reconstruction of Middle to Late Holocene paleoenvironments in Lake Lonkoy, southern Pampas, Argentina

Diatoms recovered from shallow Lake Lonkoy sediment core in southern Pampas, Argentina, were studied in order to assess past environmental conditions. A total of 47 samples were selected from a 1.42-m long core that spans the last 4840 cal. years. Diatoms were extracted by chemical cleaning and studied under light and scanning electron microscopy. A total of 89 diatom taxa were recorded, including 36 taxa that reached>2% relative abundance and were used in statistical analyses. A cluster analysis allowed five significant diatom association zones (DAZ) to be defined. DAZ I (142–92 cm) was dominated by Cyclotella meneghiniana Kützing, Cocconeis placentula Ehrenberg and Nitzschia hustedtiana Salah, and a low abundance of aerophilic taxa, indicating brackish water conditions probably related to the Holocene sea-level high stand. DAZ II (90–48.5 cm) was dominated by C. meneghiniana and Aulacoseira granulata (Ehrenberg) Simonsen, representing a period of high nutrient loading and turbid conditions in the lake, associated with higher water levels and lower salinities than the environmental conditions in DAZ I. The upper 50 cm of the core (DAZ III to V) showed an increase in the dominance of brackish epiphytic and hypereutrophic benthic taxa, indicating an increase in nutrient concentrations associated with agricultural human impacts in the basin. Overall, diatoms allowed major paleoenvironmental changes to be inferred for the lake during the Holocene.

Evidence for Changes in Paleoenvironments along the Lower Cap-Rouge River, Québec (Canada), in Relation to a High Water Stand during the Mid-Holocene Laurentian Transgression

ABSTRACT Verville, J.-F.; Filion, L., and Lajeunesse, P., 2014. Evidence for changes in paleoenvironments along the lower Cap–Rouge River, Quebec (Canada), in relation to a high water stand during the mid-Holocene Laurentian transgression. At the outlet of the Cap-Rouge River, upstream of the Quebec sound on the St. Lawrence north shore, a 5-m-high stratigraphic section was excavated within an urban area, specifically, in a schoolyard located on the 14 m terrace on the east side of the river. Our stratigraphic and high-resolution macrofossil data show that major paleoenvironmental changes occurred along the lower Cap-Rouge River during the mid-Holocene. Macrofossil assemblages indicate that during a low water stand between 6320 and 6230 cal YBP, eastern hemlock (Tsuga canadensis [L.] Carr.) and white pine (Pinus strobus L.) formed mixed stands on the sandy terraces flanking the river. They also indicate that these mesophytic forests shifted to hydrophytic plant communities (eastern larch and aquatic plant...

Paleo-environmental controls on cold seep carbonate authigenesis in the Sea of Marmara

The factors controlling fluid emission dynamics at ocean margins are poorly understood. In particular, there are significant uncertainties on how fluid seepage at cold seeps may have responded to abrupt environmental changes in the geological past. This study reports on a detailed geochemical investigation of seafloor carbonate crusts sampled at cold seeps along the submerged part of the North Anatolian Fault system in the Sea of Marmara – an inland sea, which has experienced major paleo-environmental changes over the last deglaciation period. We also analyzed a series of authigenic carbonate concretions recovered from two sediment cores at the Western-High ridge, an active fluid venting area.The ages of seafloor carbonate crusts derived from isochron U–Th dating cover the last 7 kyr, suggesting that fluid activity along the fault system remained continuous over that time interval. In the sediment cores, carbonate concretions are concentrated at the lacustrine-to-marine transition, which corresponds to the period when Mediterranean waters flowed into the Marmara Basin about 12–14 kyr ago. U–Th isotopic data indicate that most of these concretions formed later during the Holocene, around 9–10 kyr ago, a period coinciding with an important anoxic event that led to the deposition of a sapropel layer in the Sea of Marmara.Based upon these results, we suggest that the absence of carbonate concretions in the lacustrine sediment unit indicates that dissolved sulfate concentrations in the Marmara lake pore waters during glacial time were too low to promote significant anaerobic methane oxidation, thereby preventing sedimentary carbonate authigenesis. In contrast, the progressive inflow of Mediterranean waters into the glacial Marmara lake after 15 ka provided a source of dissolved sulfate that allowed anaerobic oxidation of methane to proceed within the anoxic sediment. Importantly, the synchronism between the main phase of authigenic carbonate precipitation at the studied sites (average 9.4±1.8 ka, n=16) and the regional anoxic sapropel event support the idea that the drop in bottom water dissolved oxygen content was probably a key factor to enhance microbial activity and associated carbonate precipitation at that time. Overall, these results provide straightforward evidence that fluid emission dynamics and hydrocarbon oxidation at cold seeps can be directly related to changing environmental conditions through time.

Paleoenvironmental changes at the lower Pleistocene Montalbano Jonico section (southern Italy): Global versus regional signals

Integrated high resolution data from calcareous plankton assemblages (foraminifera and nannofossils) together with geochemical and mineralogical investigations have been collected at the on-land Montalbano Jonico section (southern Italy) in order to reconstruct the paleoenvironmental changes through Marine Isotope Stages (MIS) 23–37. Time-series analysis on Globigerina bulloides and Cassidulina carinata δ18O records and on selected calcareous plankton proxies mainly revealed the occurrence of precession and obliquity forcing. The deposition of sapropel layers, which are interbedded in the Montalbano Jonico section, was driven by water column stratification (insolation cycle i-104) and enhanced sea surface water productivity (insolation cycle i-112, i-102 and i-86). Different paleoenvironmental conditions mark the sedimentary evolution of the section. From 1240 to 1082ka (MIS 37–MIS 32), high percentage abundances of warm and oligotrophic planktonic foraminifera and calcareous nannofossil taxa indicate the establishment of oligotrophic and stratified surface water conditions. A key paleoenvironmental change occurred during MIS 31 (from about 1080 to 1065ka), which was a very warm interglacial characterized by an increase of tropical–subtropical (Globigerinoides ruber group and Globigerinoides trilobus) and low salinity (Braarudosphaera bigelowii) sea surface water taxa. During this interval, more humid climate conditions coupled with changes in local paleomorphology may have triggered a higher and unusual freshwater input and the creation of a new entry point for sediment supply into the basin from a different drainage area. From about 1065 to 1010ka (MIS 30–MIS 29), a cool and dry climate prevailed in the circum-Mediterranean area during a time of precession maxima. This favored lowered sea surface temperatures and an increase of polar-water Neogloboquadrina pachyderma left coiling. There are also indications of a reduction of the terrigenous input from the new source area. From 1010ka upward (MIS 28–MIS 23), the higher abundances of Globigerina bulloides, Turborotalita quinqueloba and Calciosolenia spp. indicate enhanced productivity conditions probably related to high turbidity of sea surface waters triggered by a more conspicuous sediment input from land. Analysis of the long-term trends in the multiproxy patterns suggests that the major paleoenvironmental changes occurred as a consequence of the combined effect of orbitally-controlled global climate and regional processes.

Bound forms, compositional features, major sources and diagenesis of long chain, alkyl mid-chain diols in Lake Baikal sediments over the past 28,000 years

To elucidate the possibility of long chain, alkyl mid-chain diols (hereafter, mid-chain diols) in Lake Baikal sediments over the past 28 ka being paleoproxies, we studied their: (i) bound forms and compositional features, (ii) major sources and (iii) diagenesis during sedimentation. Of the seven bound forms investigated, i.e. free form (free type), three base-hydrolysable types (base-1, base-2, and base-3) and acid-hydrolysable type (acid-1 type) in solvent extractable lipids and base hydrolysable (NB) and acid hydrolysable (NA) types in non-solvent extractable (NONEX) lipids, only three, viz. free, NB, and base-3 types, were found. The relative compositions of the three types were 70–100%, 0–30% and 0–8%, respectively. The most abundant component of the free-type diols was the C 32 1,15-diol, whereas that of the base-3 and NB types was the C 30 1,13-diol. The average chain length, ratio of total amount of even chain lengths to that of odd chain lengths, the relative composition of positional isomers for each carbon number, and the diol index, obtained using the equation [C 30 1,15-diol]/([C 30 1,15-diol] + [C 32 1,15-diol]) × 100, hardly responded to reported major paleoenvironmental changes around the Lake Baikal region over the last 28 ka. Comparison of mid-chain diol compositions and their bound forms with those in possible sources suggested that the major biological source of all mid-chain diols in the sediments might be the Eustigmatophyceae class of algae. In the alga, the occurrence of mid-chain diols in the five bound forms, free, base-3, acid-1, NB and NA types, was suggested, while the acid-1 and NA types were not found in the sediments. Under the oxic depositional conditions of Lake Baikal, most of the acid-1 and NA type diols and part of the base-3 and NB type diols might be degraded and/or released free-type diols. In the anoxic sediments of the lake, the base-3 and NB diols seem to be resistant to diagenesis. All investigated parameters for the free, base-3 and NB diols in the sediments did not provide any information on paleoenvironments around the lake. On the other hand, among the fluxes of the three diol types, the base-3 type diol flux seems to have responded to the climatic events around the lake, especially over the last 15 ka. Hence, this flux might be a potential paleoproxy for the productivity of the biological source(s) and associated environmental factors.

Chad Basin: Paleoenvironments of the Sahara since the Late Miocene

Since the mid 1990s, the Mission paléoanthropologique francotchadienne (MPFT) conducts yearly paleontological field investigations of the Miocene-Pliocene of the Chad Basin. This article synthesizes some of the results of the MPFT, with focus on the Chad Basin development during the Neogene. We propose an overview of the depositional paleoenvironments of this part of Africa at different scales of time and space, based on a multidisciplinary approach (sedimentary geology, geomorphology, geophysic, numerical simulations and geochronology). The Miocene-Pliocene paleoenvironments are examined through the sedimentary archives of the early hominids levels and the Holocene Lake Mega-Chad episode illustrates the last major paleoenvironmental change in this area. The sedimentary record of the Chad Basin since the Late Miocene can be schematized as the result of recurrent interactions from lake to desert environments.