Variations In Sedimentation Rate Research Articles

Late Miocene to Present Paleoclimatic and Paleoenvironmental Evolution of the South China Sea Recorded in the Magneto‐Cyclostratigraphy of IODP Site U1505

AbstractThe continuous sedimentary cores recovered at the International Ocean Discovery Program (IODP) Site U1505, Expedition 368, provide an opportunity for paleoceanography and paleoclimate reconstruction in the continental margin of the northern South China Sea (SCS). In this study, we conducted detailed rock‐ and paleomagnetic studies on 420 discrete samples from the top ∼200 m of the synthetic records of Holes U1505C and U1505D. Rock magnetic analyses indicate that low‐coercivity pseudosingle domain magnetite dominates as the primary ferromagnetic mineral of Site U1505. The magnetostratigraphic age model was constructed by correlating the interpreted polarity sequence with the Geomagnetic Polarity Time Scale 2020 with the constraints of the biostratigraphic data and the distribution probability of the age of each polarity zone provided by a Dynamic Time Warping algorithm. The Milankovitch cycles of the short eccentricity, obliquity, and precession cycles were identified in the magnetic susceptibility (MS) and natural gamma radiation (NGR) series based on paleomagnetic results. We established an ∼9 Myr high‐resolution astronomical time scale by tuning the MS and NGR records to the global oxygen isotope curves, the obliquity, and the eccentricity curves of the La2004 astronomical solution. Our new age model reveals detailed sedimentation rate variations and a ∼500 kyr hiatus across the Brunhes‐Matuyama boundary related to local tectonic activity. These results lay the foundation for understanding the paleoceanography and paleoclimate evolution of the SCS.

Persistence of trace metal contamination in a fluvial system: Lahn River, central Germany

To monitor short-term changes in trace metal concentrations (Cu, Pb, Zn) at geomorphically sensitive floodplain locations and examine the persistence of contaminants in the fluvial environment, near-channel sites along the Lahn River, central Germany, that were sampled in 2007 were revisited in 2019. Thirty-three cores were extracted from sites <5 m from the active channel along a 75-km reach of the river. The median concentrations of Cu and Zn in 2019 were statistically unchanged from concentrations in 2007, but median concentrations of Pb in 2019 were statistically higher than in 2007. Concentration of all three trace metals remain above the background concentrations, but only Zn concentrations exceed the 2ϭ background upper limit. On an individual sample site basis, the Cu concentration increased at 48 % of the sites and the Zn concentration increased at 45 % of the sites between 2007 and 2019. Pb concentration increased at 70 % of the sites. Concentrations of trace metals generally increased with distance downstream; the lowermost reach of the Lahn River continues to have the highest concentration of trace metals. Between 2007 and 2019, the concentrations (mean and median) of all three metals increased in the uppermost and lowermost sections of the study area whereas in the middle section the mean and median concentrations of Cu and Zn and the median concentration of Pb decreased (the mean concentration of Pb increased in the middle reach). Changes in metal concentrations between 2007 and 2019 do not appear to be caused by factors such as changes in substrate of samples, variable sedimentation rates and flood history, or the percentage of clay and organic matter content. Elevated concentrations of trace metals persist in near-channel sediments and will continue to pose a risk of future downstream heavy metal pollution in the study reach, especially along the lowermost reach of the Lahn River where the most contaminated sediments are located. Trace metal concentrations in the study reach appear to have become “uncoupled” from overall decreases in metal releases to the environment.

Aluminium-normalised trace-element paleoredox proxies and their application to the study of the conditions of Burgess Shale-type preservation

The paleo-ecological settings of Burgess Shale-type (BST) fossils have been the subject of extensive investigations, particularly with regard to the role of anoxia in their exceptional preservation. Our understanding of the complexity of both paleontological and geochemical environmental proxies has evolved with increased knowledge of niche communities and marine geochemical and biogeochemical processes. Accordingly, dated approaches should be reevaluated. The commonly applied paleoredox proxies V/Cr, Ni/Co, and V/(V + Ni), as well as the redox proxy V/Al2O3 and productivity proxy Ba/Al2O3, were all tested on the Wheeler Formation (Utah, USA) for which a fluctuating oxycline environment has been well established based on paleontological features. Subsequently, these proxies were applied to three additional BST fossil-bearing deposits: the Emigsville Member of the Kinzers Formation (Pennsylvania, USA), the Burgess Shale (British Columbia, CA) and the Emu Bay Shale (South Australia, AU). Their host shales lack perceptible V of marine origin, indicative of oxic conditions, in contrast to the Wheeler and brine-related strata from the Burgess Shale which include additional marine input of V in some beds, consistent with varying redox conditions. The black shales of the Longs Park Member (Kinzers) have elevated V/Al2O3 indicative of anoxic conditions. Molybdenum concentrations are relatively low in most samples, but minor variations tend to correlate with V/Al2O3 patterns. Ba/Al2O3 indicates high productivity with deposition of BST fossils in the Wheeler Formation, and diagenetic remobilisation of Ba owing to sediment anoxia in the Burgess Shale. Our findings show that redox proxy V/Al2O3 can be effectively applied to BST samples, whereas Ba/Al is a reliable proxy for low to moderate paleoproductivity levels and may be useful as a secondary or tangential proxy for redox conditions. Taphonomic processes leading to BST preservation occur in a variety of environments characterised by oxyclines, matgrounds, variable sedimentation rates, hypersalinity and/or anoxia. KEY POINTS V/Al2O3 and Ba/Al2O3 are effective proxies for anoxia and productivity in BST deposits. BST preservation can occur in a variety of depositional environments. Marine anoxia is not required for BST preservation.

High-resolution magnetostratigraphic records of the pliocene sedimentary successions in Yengisar section, NW China, and its tectonic implications

The Neogene strata upward-coarsening sandstone and conglomerate sequences at the periphery of the Northeastern Pamir record the intense uplift of the paleosurface of the building mountains. To further improve our knowledge of source-sink processes, a detailed magnetostratigraphic investigation was carried out along the Yengisar section, which is located at the southwestern margin of the Tarim Basin. The new high-resolution magnetostratigraphic data revealed that the Artux Formation was deposited from 4.9 Ma to 1.9 Ma with three sedimentation rates changes. The variations in sedimentation rate may be due to the pulsating exhumation of the Western Kunlun Mountain, caused by the northward motion of the Pamir salient. By integrating the evidences from the seismic reflection profile and other magnetostratigraphic investigations in this region, the basal age of the Xiyu Formation and the early stages of growth strata deposition were estimated at ∼1.9 and 1.45 Ma, respectively. Based on the data, we propose that the progradation of the Xiyu Formation and the migration of the deformation front are the two independent responses of the sink region to the uplift events of the source region.

Comparative Phylogeography of Birds Across the Tocantins–Araguaia Interfluve Reveals a New Biogeographic Suture in the Amazon Far East

Few phylogeographic studies have focused on understanding the role of the Tocantins–Araguaia Interfluve (TAI) in the diversification of Amazonian biodiversity. Herein we evaluate the phylogeographic relationships of 14 avian lineages present in the TAI and its two neighboring Amazonian Areas of Endemism: the Xingu (XAE) and Belém (BAE). Four alternative scenarios coupling degree of genetic differentiation and area relationships were tested: (1) populations distributed in TAI, BAE, and XAE are not genetically differentiated from each other (assumed as the null hypothesis); (2) populations from TAI are more closely related to those from BAE; (3) populations from TAI are more closely related to those from XAE; and (4) TAI populations represent independent or endemic lineages not present in either the BAE or XAE. Molecular analyses considered Bayesian Inference methods and Bayesian Information Criterion (BIC) evolutionary models, haplotype sharing and genetic differentiation estimates. We found three distinct phylogeographic patterns: (i) four lineages presented no population structure across XAE, TAI and BAE; (ii) six lineages were represented in the TAI with distinct phylogroups replacing each other between XAE and BAE, but with varying degrees of contact and evidence of gene-flow within the TAI; and (iii) for four lineages, the Tocantins River acted as a barrier isolating BAE phylogroups from those inhabiting both TAI and XAE. These different patterns demonstrate a heterogeneous response to the barrier effects posed by both the Tocantins and Araguaia rivers on the local fauna. Historical geomorphological and hydromorphological factors, such as the presence and absence of paleochannels and anastomosed channel stretches and variations in sedimentation rates support a dynamic history for the Araguaia-Tocantins floodplains, likely accounting for the observed heterogeneity in species’ specific responses. Finally, the scenario of phylogeographic breaks and population subdivision recovered herein along the Tocantins and Araguaia rivers, associated with the existence of contact zones and the occurrence of gene flow, define the TAI as hitherto unknown biogeographic suture zone, localized in southeasternmost Amazonia.

A framework for 210Pb model selection and its application to 37 cores from Eastern Canada to identify the dynamics and drivers of lake sedimentation rates

AbstractLake sedimentation rate represents a synthetic metric of ecosystem functioning. Many localized studies have reported a significant association between land use/land cover changes and lake sediment mass accumulation rates, with a few global syntheses echoing these findings at larger scales. In the literature, studies evaluating lead‐210 (210Pb) for establishing sediment chronologies will report at least one of three dating models, but the constant rate of supply (CRS) model is the most widely used. However, it is often unclear how or why this model is selected, despite its influence on the interpretation of many subsequent analyses about ecosystem dynamics and functioning. It would thus be advantageous to design an objective and semi‐automated way of choosing among dating models. We measured radioisotopic activities in 37 sediment cores across four ecozones of Eastern Canada and developed an approach to assess model fit for the three commonly applied dating models. The derived chronologies were then used to evaluate the spatial and temporal variation in sedimentation rates across four ecozones in Canada (covering a surface area of 2.2 × 106 km2). We observed a recent increase in lake sedimentation rates across most lakes, as has been observed globally, albeit with significant differences in the magnitude of sedimentation rates across ecozones. Across all lakes, we found that regional human population counts and mean annual air temperatures were significant temporal predictors of variation in mass accumulation rates. Overall, this analytical framework offers an objective approach for assessing fit and selecting among sediment age models, which contributes to a more robust quantification of sedimentation rates. With this first application, we provide a quantitative assessment of how lake sedimentation rates have varied across a northern lake‐rich region and have responded to environmental change.

Regulation of sedimentation rate shapes the evolution of multicellularity in a close unicellular relative of animals.

Significant increases in sedimentation rate accompany the evolution of multicellularity. These increases should lead to rapid changes in ecological distribution, thereby affecting the costs and benefits of multicellularity and its likelihood to evolve. However, how genetic and cellular traits control this process, their likelihood of emergence over evolutionary timescales, and the variation in these traits as multicellularity evolves are still poorly understood. Here, using isolates of the ichthyosporean genus Sphaeroforma-close unicellular relatives of animals with brief transient multicellular life stages-we demonstrate that sedimentation rate is a highly variable and evolvable trait affected by at least 2 distinct physical mechanisms. First, we find extensive (>300×) variation in sedimentation rates for different Sphaeroforma species, mainly driven by size and density during the unicellular-to-multicellular life cycle transition. Second, using experimental evolution with sedimentation rate as a focal trait, we readily obtained, for the first time, fast settling and multicellular Sphaeroforma arctica isolates. Quantitative microscopy showed that increased sedimentation rates most often arose by incomplete cellular separation after cell division, leading to clonal “clumping” multicellular variants with increased size and density. Strikingly, density increases also arose by an acceleration of the nuclear doubling time relative to cell size. Similar size- and density-affecting phenotypes were observed in 4 additional species from the Sphaeroforma genus, suggesting that variation in these traits might be widespread in the marine habitat. By resequencing evolved isolates to high genomic coverage, we identified mutations in regulators of cytokinesis, plasma membrane remodeling, and chromatin condensation that may contribute to both clump formation and the increase in the nuclear number-to-volume ratio. Taken together, this study illustrates how extensive cellular control of density and size drive sedimentation rate variation, likely shaping the onset and further evolution of multicellularity.

Impact of sedimentation, climate and sea level on marine sedimentary pyrite sulfur isotopes: Insights from the Valle di Manche section (Lower-Middle Pleistocene, southern Italy)

Variations in the isotopic composition of sulfur in sedimentary pyrite (δ34Spyr) are often used to reconstruct global sulfur biogeochemical cycling and Earth's surface oxidation state over Earth history. Recent work, however, has shown that δ34Spyr is strongly impacted by local depositional conditions, which both confounds attempts to reconstruct global sulfur cycling and provides a new proxy for investigating local paleoenvironmental conditions. We present a chemostratigraphic record of δ34Spyr in a detailed paleoenvironmental and sequence stratigraphic framework spanning the Early-Mid Pleistocene transition from the Crotone Basin (Calabria, Southern Italy). Bulk δ34Spyr data parallel transgressive-regressive cycles and enable the differentiation of progradational and retrogradational stacking patterns, where δ34Spyr values decrease toward −50‰ in outer shelf deposits during late transgression and become more positive and variable in prograding sedimentary units accumulated in shallower environments. In parallel with the observed variations in δ34Spyr, complementary data on organic carbon abundance and isotopic composition and total nitrogen abundance document changes in terrestrial delivery of sediment to the basin, as a consequence of glacial-interglacial eustatic sea-level changes, regional climate and local tectonics. The chemostratigraphic record of δ34Spyr appears sensitive to variations in sedimentation rates and local erosional surfaces and therefore may represent a powerful tool to assess stratal stacking patterns for sequence stratigraphic interpretations of siliciclastic successions. These results highlight the role of local conditions in controlling sedimentary δ34Spyr records and illustrate how isotopic data can be used to reconstruct key parameters of the sedimentary environment that might not otherwise be accessible, especially in deep-time strata.

The Medial Offshore Record of Explosive Volcanism Along the Central to Eastern Aegean Volcanic Arc: 2. Tephra Ages and Volumes, Eruption Magnitudes and Marine Sedimentation Rate Variations

AbstractWe use the tephrostratigraphic framework along the Aegean Volcanic Arc established in Part 1 of this contribution to determine hemipelagic sedimentation rates, calculate new tephra ages, and constrain the minimum magnitudes of (sub)plinian eruptions of the last 200 kyrs. Hemipelagic sedimentation rates range from ∼0.5 cm/kyr up to ∼40 cm/kyr and vary laterally as well as over time. Interpolation between dated tephras yields an eruption age of ∼37 ka for the Firiplaka tephra, showing that explosive volcanism on Milos is ∼24 kyrs younger than previously thought. The four marine Nisyros tephras (N1 to N4) identified in Part 1 (including the Upper (N1) and Lower (N4) Pumice) have ages of ∼57 ka, ∼63 ka, ∼69 ka, and ∼76 ka, respectively. Eruption ages for the Yali‐1 and Yali‐2 tephras are ∼55 ka and ∼34 ka, respectively. The Yali‐2 tephra comprises two geochemically and laterally distinct marine facies. The southern facies is identical to the Yali‐2 fall deposit on land but the western facies has slightly less evolved glass compositions. Overall, erupted plinian and co‐ignimbrite fall tephra volumes range from &lt;1 to 56 km3 (excluding possible caldera fillings and ignimbrite volumes), and 80% of the eruptions had magnitude 5.5 &lt; M ≤ 7.2 (M = log(m)‐7; m = erupted magma mass in kg). Twenty percent of the tephras represent 3.2 &lt; M &lt; 5.5 eruptions. The long‐term average tephra magma mass flux through highly explosive eruptions of Santorini is estimated at ∼40 kg/s. The analogous data for the Kos‐Yali‐Nisyros volcanic complex is less‐well constrained but similar to Santorini.

Sedimentation rates by the 210Pb chronological method in Itanhaém river watershed, southeast Brazil.

The historical variation of sedimentation rate was investigated in five cores collected from the Itanhaém watershed main rivers, the second largest coastal watershed of the São Paulo state, Brazil, using the lead-210 radioisotope as a geochronometer. The main characteristics of the rivers' waters and sediments were determined in order to support the geochronological analysis results and associate sediments with possible source areas. In this context, the fluvial waters' general classification indicated the facies sulfated or chlorinated sodium in the winter and summer seasons, except for the Branco river waters in summer, which were classified as calcium or magnesium bicarbonate. A longitudinal salinity gradient was found in the downstream river courses, under greater marine influence, with the ions Cl-, Na+, SO42+, Mg2+, Ca2+, and K+ being most common in the waters. Silica is the predominant constituent in the sediment cores and is inversely related to the organic matter (OM) presence. Inverse correlations were also found between silica and other constituents. The watershed sedimentation rates were determined in the range of 0.31 up to 3.97g/cm2/year and 0.30 up to 3.40cm/year, highlighting the core extracted from Branco river, which showed the highest sedimentation rate. The profiles corresponding to Preto and Aguapeú rivers presented discontinuities in the sedimentation rates. The discontinuities were dated and would probably be related to the anthropic activities, which intensified in the municipality of Itanhaém around the middle of the twentieth century.

Integrated stratigraphy of the middle-upper Eocene Souar Formation (Tunisian dorsal): Implications for the Middle Eocene Climatic Optimum (MECO) in the SW Neo-Tethys

Calcareous nannofossil biostratigraphy and carbon-isotope stratigraphy on bulk organics of the middle-upper Eocene Souar Formation (Tunisia) allow for a refined stratigraphy of this interval in the southwestern Neo-Tethys margin. The Souar Formation represents the deepest sedimentary deposits of the central northern Tunisian Basin and was only dated previously by coarse data on planktonic foraminifera. Together with our new data, a correlation is proposed to previous Tunisian records of the Halk El Menzal carbonate platform to the NE and shallow-water deposits of central Tunisia to the SW, which leads us to the erection of a synthetic stratigraphic chart of the middle-upper Eocene in central and northeastern Tunisia. Our results allow for a review of the accurate position of the Lutetian / Bartonian and the Bartonian / Priabonian stage boundaries in Tunisia relative to calcareous nannofossil biohorizons. We apply Bayesian statistics to build our age-depth model which points to a hiatus in the Lutetian (CNE12 Zone) that we relate to the middle Lutetian regressive sequence leading to the Lu-4 M-cycle. Radiolarian-rich sediments and cherts of the late Lutetian and early Bartonian are interpreted as a response to an increase in productivity, tied to the seasonal upwelling of nutrient-rich waters. Correlation to other sections in Tunisia highlights the strong contrast in facies between the carbonate-rich sequences of the edges of the dorsal and the silica-rich deposition in the Souar Formation. This contrast is particularly pronounced in the interval before and across the Middle Eocene Climatic Optimum (MECO) characterized by a maximum of nummulitic carbonate production on the platform and a minimum of carbonate production in the deep basinal parts of the Tunisian dorsal, rather dominated by silica-rich sediments. • Middle-Late Eocene calcareous nannofossil biostratigraphy in the SW Neo-Tethys. • The MECO corresponds to the Reneiche member in the Tunisian stratigraphic chart. • The MECO is characterized by a δ 13Corg excursion and biosiliceous productivity. • Increase in terrigenous flux to the Tunisian dorsale during the MECO. • Major sedimentation rate variations due to changes in the on-land weathering.

Impact of Upward Oxygen Diffusion From the Oceanic Crust on the Magnetostratigraphy and Iron Biomineralization of East Pacific Ridge-Flank Sediments

Recent measurements of pore-water oxygen profiles in ridge flank sediments of the East Pacific Rise revealed an upward-directed diffusive oxygen flux from the hydrothermally active crust into the overlying sediment. This double-sided oxygenation from above and below results in a dual redox transition from an oxic sedimentary environment near the seabed through suboxic conditions at sediment mid-depth back to oxic conditions in the deeper basal sediment. The potential impact of this redox reversal on the paleo- and rock magnetic record was analyzed for three sediment cores from the Clarion-Clipperton-Zone (low-latitude eastern North Pacific). We found that the upward-directed crustal oxygen flux does not impede high quality reversal-based and relative paleointensity-refined magnetostratigraphic dating. Despite low and variable sedimentation rates of 0.1–0.8 cm/kyr, robust magnetostratigraphic core chronologies comprising the past 3.4 resp. 5.2 million years could be established. These age-models support previous findings of significant local sedimentation rate variations that are probably related to the bottom current interactions with the topographic roughness of the young ridge flanks. However, we observed some obvious paleomagnetic irregularities localized at the lower oxic/suboxic redox boundaries of the investigated sediments. When analyzing these apparently remagnetized sections in detail, we found no evidence of physical disturbance or chemical alteration. A sharp increase in single-domain magnetite concentration just below the present lower oxic/suboxic redox boundary suggests secondary magnetite biomineralization by microaerophilic magnetotactic bacteria living as a separate community in the lower, upward oxygenated part of the sediment column. We therefore postulate a two-phased post-depositional remanent magnetization of ridge flank sediments, first by a shallow and later by a deep-living community of magnetotactic bacteria. These findings are the first evidence of a second, deep population of probably inversely oriented magnetotactic bacteria residing in the inverse oxygen gradient zone of ridge flank sediments.

Orbital‐ and Millennial‐Scale Changes in Lake‐Levels Facilitate Earthquake‐Triggered Mass Failures in the Dead Sea Basin

AbstractThe possible link between the occurrence of submarine mass failure and climate‐driven factors is highly disputed. This is due largely to the lack of comprehensive records of mass failures in the geologic record for which ages, triggers, and preconditioning factors can be reliably constrained. Such controls would allow accurate testing of cause‐and‐effect relationships. We present a record that comprises 490 earthquake‐triggered mass failure deposits from the Dead Sea depocenter over the past 220 kyr that permits a robust statistical evaluation and correlation with potential preconditioning factors. Our data set reveals that (a) at the orbital‐ and millennial‐scale, variable sedimentation rates are not a preconditioning factor for these mass failure deposits; (b) at the centennial‐to decadal‐scale, earthquake‐triggered mass failures can occur at any lake‐level state; (c) at the orbital‐ and millennial‐scale, the mass failures are more frequent when lake‐levels were high and punctuated by large‐amplitude fluctuations.

Spatio-temporal differences of sediment accumulation rate in the Lake Gościąż (Central Poland) as a response of meteorological conditions and lake basin morphometry

Weather conditions and lake basin morphometry are of key importance in the study of sediment accumulation rate in lakes. This study aims to determine how these factors affect spatial and seasonal variations in sedimentation rate in the epilimnion and hypolimnion of Lake Gościąż. To determine sedimentation rates, six sedimentation traps were set up at different locations and depths in the lake. Weather data were obtained from a meteorological station near the lake. Furthermore, temperature in the lake water column was measured continuously, and during field work oxygenation and transparency were also measured. Seasonal changes in sediment composition were analyzed on smear slides under microscope. The study showed that sedimentation rate increased as bottom steepness increased, and that there was more sediment in the hypolimnion than the epilimnion, especially in spring and autumn. There was a clear seasonal variation in early-spring and autumn peaks in sedimentation. The obtained results were significantly dependent on bottom relief, wind and air temperature through these factors’ influence on water temperature. The results show that the sediment accumulation rate in Lake Gościąż depends on the hydrodynamic conditions, which are determined by wind speed, wind direction, water temperature, and the shape and steepness of the lake basin. The relief features of the lake bottom and its orientation relative to the prevailing wind are significant factors in the spatial differentiation in sediment accumulation rate and composition of sedimenting material. It has been shown that the lake’s shallow-water zone (littoral and sublittoral) is an important source of the material accumulated in the profundal zone. The patterns and mechanisms of the course of contemporary sedimentation in Lake Gościąż, as determined based on the conducted investigations, can be applied in the study of other lakes and in assessing the representativeness of sampling sites for laminated bottom sediments to be used in palaeo-environmental studies.

Evaluating Holocene natural hazards in the French Massif Central from a regional lake sediment approach

Geophysical surveys in the Lakes Tazenat, Aydat, Chambon and Lacassou combined with a multiproxy study of sediment cores highlight Late Holocene abrupt environmental changes in the northern part of the French Massif Central (FMC). Dating landslide-induced dust layers and subaqueous slope failures impacting lake basin sedimentary fills suggest regional triggering by palaeo-earthquakes (cluster of events) either in the Puy-de-Sancy volcano area, or along the regional Limagne fault. In the present study, a cluster of palaeo-earthquakes occurring in the Sancy area between AD 1243 and 1270 are documented in the Lakes Montcineyre, Chauvet, Pavin and Guéry, as well as by the formation of Lake Lacassou following the last emplacement of the Dent du Marais landslide in the Chaudefour glacial valley around AD 1250 ± 30. Former cluster of earthquakes occurring near the Limagne fault between AD 580 and 650 are evidenced in Lake Tazenat and in maar Lake Pavin. Lake Pavin present lake-level was similarly favoured by the cluster of earthquakes between AD 1243 and 1270 and the occurrence of a slump and an outburst flood event resulting in the bypassing of a palaeo-outlet. Holocene earthquakes near the Limagne fault are suggested in maar Lake Tazenat by coeval mass wasting deposits (MWDs) around 2250 ± 50 cal. BP and around 2730 ± 30 cal. BP. A landslide-induced dust layer dated between 2760 and 2520 cal. BP at the transition from paludal to lacustrine deposits in the Chaudefour glacial valley is suggesting that the formation of Lake Chambon resulted from a first emplacement of the Dent du Marais landslide. Radionuclides and radiocarbon dating in Lake Tazenat suggest variable sedimentation rates over the last millennia due to: (i) floods during the Little Ice Age, (ii) coeval MWDs at the basin edges and an erosive turbidite in the central basin between AD 575 and 625, and (iii) lake eutrophication since AD 1945. More gravity cores are needed to directly sample and date the youngest generation of coeval MWDs detected on seismic profiles in order to test the impact in this lake of the cluster of major historical earthquakes in the FMC between AD 1450 and 1490 near the Limagne fault.

A Continuous Seismostratigraphic Framework for the Western Svalbard-Barents Sea Margin Over the Last 2.7 Ma: Implications for the Late Cenozoic Glacial History of the Svalbard-Barents Sea Ice Sheet

Here we present a high-resolution, continuous seismostratigraphic framework that for the first time, connects the over 1,000 km long western Svalbard-Barents Sea margin and covers the last ∼2.7 million years (Ma). By exploiting recent improvements in chronology, we establish a set of reliable age fix-points from available boreholes along the margin. We then use a large 2-D seismic database to extend this consistent chronology from the Yermak Plateau and offshore western Svalbard, southwards to the Bear Island Trough-Mouth Fan. Based on this new stratigraphic framework we divide the seismic stratigraphy along the continental margin into three seismic units, and 12 regionally correlated seismic reflections, each with an estimated age assignment. We demonstrate one potential application of this framework by reconstructing the Svalbard-Barents Sea Ice Sheet evolution from the intensification of the northern hemisphere glaciation at ∼2.7 Ma to the Weichselian glaciations. Through seismic facies distribution and sedimentation rate fluctuations along the margin we distinguish three phases of glacial development. The higher temporal resolution provided by this new framework, allows us to document a clear two-step onset to glacial intensification in the region during phase 1, between ∼2.7 and 1.5 Ma. The initial step, between ∼2.7 and 2.58 Ma shows glacial expansion across Svalbard. The first indication of shelf-edge glaciation is on the Sjubrebanken Trough-Mouth Fan, northwestern Barents Sea after ∼2.58 Ma; whilst the second step, between ∼1.95 and 1.78 Ma shows glacial advances beyond Svalbard to the northwestern Barents Sea. Phase 2 is characterized by variations in sedimentation rates and the seismic facies are indicative for a regional glacial intensification for the whole Barents Sea-Svalbard region with widespread shelf-edge glaciations recorded at around ∼1.5 Ma. During Phase 3, the western Barents Sea margin is characterized by a dramatic increase in sedimentation rates, inferring once again a regional glacial intensification. Our new stratigraphic framework allows for the first time differentiation of the sediments deposited on the slope during Early Saalian (∼0.4 and 0.2 Ma), Late Saalian (∼0.2 and 0.13 Ma), and Weichselian (&amp;lt;∼0.123 Ma) periods, providing new insights into the Barents Sea glaciations over the last ∼0.42 Ma.

Geologically constrained evolutionary geomechanical modelling of diapir and basin evolution: A case study from the Tarfaya basin, West African coast

AbstractWe systematically incorporate burial history, sea floor geometry and tectonic loads from a sequential kinematic restoration model into a 2D evolutionary geomechanical model that simulates the formation of the Sandia salt diapir, Tarfaya basin, NW African Coast. We use a poro‐elastoplastic description for the sediment behaviour and a viscoplastic description for the salt. Sedimentation is coupled with salt flow and regional shortening to determine the sediment porosity and strength and to capture the interaction between salt and sediments. We find that temporal and spatial variation in sedimentation rate is a key control on the kinematic evolution of the salt system. Incorporation of sedimentation rates from the kinematic restoration at a location east of Sandia leads to a final geomechanical model geometry very similar to that observed in seismic reflection data. We also find that changes in the variation of shortening rates can significantly affect the present‐day stress state above salt. Overall, incorporating kinematic restoration data into evolutionary models provides insights into the key parameters that control the evolution of geologic systems. Furthermore, it enables more realistic evolutionary geomechanical models, which, in turn, provide insights into sediment stress and porosity.

Aeolian dust dynamics in the Fergana Valley, Central Asia, since ~30 ka inferred from loess deposits

Knowledge of the interactions among atmospheric dynamics, dust emissions and climate system is essential to understand the physical mechanisms for the dust lifecycle, their role in loess formation as well as the predictions of future dust concentration. However, these issues still remain relatively poorly known in Central Asia (CA). The extensive loess deposits on the CA pediments provide a promising archive to explore atmospheric dust dynamics and climatic conditions in the past and their association with loess formation. This study investigates the granulometric and magnetic properties of a loess section (named Osh section) in the Fergana Valley, which provides a sensitive record of atmospheric dust dynamics since 30 ka based on radiometric (AMS 14C) dating. The frequency-dependent magnetic susceptibility (χfd) and the mean grain size are used to reconstruct the broad-scale effective moisture and summer atmospheric dynamics pattern in CA, respectively. The results show that the precession forcing exerts a huge influence on the wind-regime variabilities in CA, but with different physical processes under the impact of the Northern Hemisphere ice sheet (NHIS) before and after 15 ka. The origin of the sedimentation rate variations in the Osh loess is also linked to the NHIS-modulated changes of the atmospheric circulation patterns. Either the strengthened westerlies or the increased surface roughness from higher vegetation cover in loess-deposition areas have significantly accelerated the loess accumulation. As a result, these complicated influence factors of sedimentation rate change in the Osh loess section, especially during the Holocene epoch, may hamper accessibility of the authentic dust emission flux and atmospheric dust concentration in CA.

The evolution of early diagenetic processes at the Mozambique margin during the last glacial-interglacial transition

The Mozambique continental margin experienced large variations in sedimentation rates, primarily due to re-routing of sediment deposition from the Zambezi River during the last glacial-Holocene transition. As changes in sediment accumulation and organic matter deposition impose a strong control on the formation of authigenic minerals in the sediment, the distribution of these minerals may reflect the regional paleoenvironmental and paleoclimatic evolution. Combining geochemical analyses of porewaters and sediments with a reactive transport modeling approach, we reconstruct the depositional history and its effect on pyrite formation and other biogeochemical transformations at a site on the Mozambique margin over the past 27 kyr. Fitting the model to match the observed geochemical patterns, most importantly authigenic pyrite, allowed for the reconstruction of past sulfate-methane transition zone depth, which migrated in response to changes in the sediment accumulation and organic matter deposition. Changes in sediment deposition quickly affected organoclastic sulfate reduction and associated pyrite formation, but the effect on anaerobic methane oxidation and subsequent pyrite formation occurred with a lag on the order of thousands of years. Model results reveal a transition from high diagenetic reaction rates representative of near-shore depositional environments during the late glacial maximum, to a setting typical of offshore sediments with low reaction rates at the present day. Notably, the remnants of methane and dissolved iron pools produced in the past still shape the diagenetic processes at and below the sulfate-methane transition zone today. Since deglacial shelf-flooding and corresponding changes in sediment deposition occurred along continental margins worldwide, our analysis highlights the important role of non-steady state diagenesis in continental margin sediments and its relevance for paleoceanographic interpretation of sediment cores experiencing strong variations in sediment input.

INCORPORATING INFORMATION ON VARYING SEDIMENTATION RATES INTO PALEONTOLOGICAL ANALYSES

ABSTRACTStratigraphic changes in the clustering of first or last taxon occurrences are a joint expression of evolutionary, ecological, taphonomic, and sedimentological processes. Sedimentation rates control the degree of sedimentary dilution and condensation and thus alter the time contained in a given thickness of sediment. However, it remains poorly explored quantitatively how distinct the stratigraphic patterns in the first and last occurrences can be under different deposition models with a constant thickness of accumulated sediment. Here, I present an algorithm that translates ecological or evolutionary signals between time and stratigraphic height. It is implemented for R Software as the package DAIME and complemented by tools to quantify the uncertainties associated with the construction of deposition models. By modeling the stratigraphic expression of the K/Pg extinction and an earlier extinction pulse potentially linked to Deccan volcanism on Seymour Island under varying sedimentation rates, I show that (1) clustering of last occurrences ∼ 250 kyr prior to the K/Pg boundary can be equally explained by a stronger earlier extinction pulse or prolonged intervals with reduced sediment accumulation rate, but (2) when the temporal variability in sedimentation rate is known, the most plausible extinction dynamics can still be identified. The approach is applicable for any type of information transported as a part of the sedimentary record (e.g., fossils or trace elements) or data derived from it (e.g., isotope ratios and rates of morphological evolution).