Sedimentary Record Research Articles

Assessment of the level of heavy metals contamination via sediments quality indices of the Koudiet Medouar Dam and its tributary (Batna, Algeria)

The present study assesses the level of heavy metals concerning sediment from the Koudiet Medouar dam. This dam is intended for the production of drinking water and irrigation. In order to assess the level of contamination of the dam by toxic metals, 216 sediment samples were taken at nine stations upstream and downstream of the dam from 2012 to 2014. At the same time, the physical characteristics of the water and the physicochemical parameters of the sediments were determined. The results, expressed by the mean ± standard deviation, are for water: temperature, 15.5 ± 7 °C; potential of hydrogen, 8.05 ± 0.36; conductivity, 1125 ± 228 μS/cm. For sediments the values are potential of hydrogen, 8.55 ± 0.22; conductivity, 730 ± 347 μS/cm; carbonates, 49.18 ± 18.1%; fraction less than 63 μm 27.06 ± 6.95%; organic matter 3.02 ± 1.2%. Trace metal concentrations followed the order: Mn > Zn > Cr > Cu > Co > Ni > Pb > Cd. The strong correlation among trace metal indicates that these elements have common sources suggesting their association with silted sands. The geo-accumulation index, contamination factors, degree of contamination, and sediment pollution index reveal a polymetallic contamination dominated by two or more elements in which Cd, Cr, and Cu are of greatest concern. The levels of trace metals in the sediments record high concentrations upstream of the dam, especially in the second station of the village, near the dam. Our results reflect the footprint of anthropogenic inputs of cadmium, chromium, and copper resulting from agricultural activities by runoff water and soil erosion as well as domestic water discharges.

Full-waveform inversion reveals diverse origins of lower mantle positive wave speed anomalies

Determining Earth’s structure is paramount to unravel its interior dynamics. Seismic tomography reveals positive wave speed anomalies throughout the mantle that spatially correlate with the expected locations of subducted slabs. This correlation has been widely applied in plate reconstructions and geodynamic modelling. However, global travel-time tomography typically incorporates only a limited number of easily identifiable body wave phases and is therefore strongly dependent on the source-receiver geometry. Here, we show how global full-waveform inversion is less sensitive to source-receiver geometry and reveals numerous previously undetected positive wave speed anomalies in the lower mantle. Many of these previously undetected anomalies are situated below major oceans and continental interiors, with no geologic record of subduction, such as beneath the western Pacific Ocean. Moreover, we find no statistically significant correlation positive anomalies as imaged using full-waveform inversion and past subduction. These findings suggest more diverse origins for these anomalies in Earth’s lower mantle, unlocking full-waveform inversion as an indispensable tool for mantle exploration.

A Northgrippian sedimentary magnetic enhancement along the western margin of India

Sedimentary magnetic records of shelf region contains complex environmental evolution information, necessitating records from various global regions to accurately interpret its significance. A sediment core (SSD-39/GC-01) retrieved from the eastern Arabian Sea was analyzed to elucidate the geologic and climatic controls on the sediment rock magnetic and grain size properties. We report the first record of high energy sediment deposits linked with intense monsoon phases, sea level variations, and extreme natural events during the Northgrippian period (8.27 ka to 4.20 ka). The compilation of magnetic susceptibility profiles of six sediment cores from the western margin of India revealed the presence of multiple sedimentary intervals of enhanced magnetic susceptibility and most likely reflect periods of high sedimentation events controlled by the regional geologic and climatic processes. We identified two anomalous sedimentary magnetic zones (Z-II, Z-IV) marked by an elevated magnetite content and sediment grain size, which reflect the periods of high-sedimentation events on the shelf off Goa. A shift in the magnetic mineral composition, clastic grain size, calcium carbonate, and organic carbon content at ~1.8 ka (Z-I) indicate a abrupt change in monsoon intensity. The elevated organic content within Z-I indicate efficient preservation of labile organic matter which survived oxidation due to rapid sediment deposition. End-member modeling of rock magnetic and grain size properties enabled us to discriminate and quantify the contributions of terrigenous fluxes and post-depositional mineral phases to the bulk magnetic mineral assemblage. We demonstrate that rapid scanning of magnetic susceptibility of sediment cores has the potential to precisely detect the periods of increased continental (magnetic flux) inputs into the marine shelf system. The proposed magnetic mineralogical approach has wider scope to constrain the understanding of how shelf sedimentation responded to past geological and climatic conditions globally.

Mid to late Holocene Indian monsoon variability, aridification and civilization changes in the Deccan Plateau, India

Climate change has been a key driver throughout human history and has frequently been associated with the rise and fall of civilizations. Holocene settlement changes or population displacements were almost always preceded by changes in climate. A high-resolution sedimentary record from the western Bay of Bengal offers insights to centennial-scale mid- to late-Holocene Indian summer monsoon (ISM) variability and its role in the decline of chalcolithic human settlements on India's Deccan Plateau. Increased erosion in the Indian peninsula during the mid to late Holocene, due to aridification and agricultural expansion, is evidenced by higher sedimentation, more magnetic mineral content, coarser magnetic grain size, and increased sand content. The results from mineral magnetic and textural analyses reveal centennial-scale abrupt weak ISM during the Bond events in the core monsoon zone of India. The Deccan Chalcolithic civilizations flourished between ~4.0–3.0 ka BP owing to the favorable climatic conditions, but most of the settlements were deserted after ~3.0 ka BP. We argue that the abrupt weakening of ISM during Bond event 2 (~3.1–2.8 ka BP) caused this collapse of Deccan Chalcolithic. The results from this study together with the published records of number of settlements and summed radiocarbon dates suggest a climate-culture link in the Deccan Plateau. The weak ISM periods in this study are coherent with the records of total solar irradiance record and the percentage of hematite-stained grains from the North Atlantic and suggest solar control on these abrupt climatic events.

Astronomical Calibration of the Ocean Anoxic Event 1b and Its Implications for the Cause of Mid‐Cretaceous Events: A Multiproxy Record

AbstractThe timing and duration of oceanic disturbances linked to Oceanic Anoxic Event (OAE) 1b, as well as the mechanisms driving anoxia and carbon burial during this period, remain subjects of debate. We conducted cyclostratigraphic analyses on magnetic susceptibility (MS) and elemental Ti and Fe series within the upper Aptian‐lower Albian interval of the Poggio le Guaine core in the Umbria‐Marche Basin, Italy. This interval provides a detailed sedimentary record, supported by variations in magnetic mineral content, Ti, Fe, and significant global shifts in the δ13C curve. Orbital control of MS, Ti, and Fe suggests a duration of 2.84 Myr for the OAE 1b event. Our chronostratigraphic analysis reveals ages of 114.07 ± 0.12 Ma for 113/Jacob, 113.28 ± 0.12 Ma for Kilian, 112.49 ± 0.12 Ma for the central age of the Monte Nerone cluster, 111.70 ± 0.12 Ma for Urbino, and 111.28 ± 0.12 Ma for Leenhardt sub‐events. Stable δ13C chemostratigraphy correlations enable the transfer of tiepoints across various sedimentary basins. Key features of the carbon isotope curves were identified, named, and dated using astrochronology. Our findings suggest that the organic‐rich layers associated with the OAE 1b event exhibit distinct characteristics influenced by several factors, including a warm climate driven by volcanic CO2 emissions, heightened precipitation, intense weathering, and marine transgressions. These factors amplify orbital forcings on paleoclimate changes, leading to oceanic‐atmospheric disturbances that promote deoxygenation and carbon burial during OAE 1b.

Sourcing of the Oligocene to Pliocene sediments of the Ningnan Basin: Evidence for Tibetan Plateau growth and local faulting unravelled by detrital apatite fission‐track and U–Pb double dating

AbstractThe Cenozoic topographic growth of the Tibetan Plateau is a pulsed, polyphase process that still requires more constraints. The Cenozoic sedimentary record of the Ningnan Basin, a continental basin located adjacent to the northeastern margin of the Tibetan Plateau, is a key archive for recording the surface evolution of the Tibetan Plateau. This work reports new provenance data (apatite fission‐track, apatite U–Pb dating, and trace element analysis on the same individual grains) from the Oligocene–Pliocene sedimentary sequence that filled the Ningnan Basin. The data set shows variations in provenance patterns through the Miocene which are related to the tectonic evolution of the northeastern margin of the Tibetan Plateau. In contrast to a primary provenance from the Western Ordos Block (WOB) during the Oligocene, the Miocene sediments were mostly derived from the recycling of Mesozoic successions that occur along the northwestern Haiyuan Fault, documenting it was active in the last ca. 15 Myr. These sediments, in turn, were derived from different orogenic blocks but mainly from different segments of the Qilian Mountains. We show that the Late Miocene–Pliocene sediments were primarily derived from transpressional uplift along the Haiyuan Fault, which affected regions such as the Liupan Mountains. Progressive northeastward migration of tectonic stress since the Middle Miocene has induced extensive regional deformation in the northeastern Tibetan Plateau, particularly along the Haiyuan Fault. The provenance record of the neighbouring Cenozoic basins is a key archive for deciphering this tectonic evolution.

Geochemical signatures of forearc serpentinites from oceanic to continental subduction

In subduction systems, the forearc (FA) serpentinized mantle plays a key role as a reservoir for fluid-mobile elements, especially those prone to early mobilisation from the slab. FA serpentinites therefore provide an indication of the fluid characteristics that have been steamed out of the slab, and allow better quantification of elemental recycling and fluid flow. FA serpentinites outcropping along the Indus Suture Zone are formed by hydration of mantle peridotites by fluids derived from the Indian slab, providing a geochemical record of fluid-rock interactions during the India-Eurasia convergence. Systematic trace and multi-isotope (Sr and Pb) analyses of serpentinites from three major sites, namely Shergol-Tingdo, Kargil and Tso Morari, along the Indus Suture Zone in Ladakh (NW Himalaya) show that these rocks record a major change in the origin of metasomatic agents, from oceanic to continental subduction. The Shergol-Tingdo and Kargil FA serpentinites, formed under low temperature and pressure conditions, are characterised by high B enrichment and As and Sb depletion, high alkali/U ratios and relatively unradiogenic Sr and Pb isotope ratios. These geochemical characteristics are identical to those reported for modern oceanic subduction zones (e.g., Mariana forearc) and are consistent with input by fluids derived from subducted oceanic crust. In contrast, FA serpentinites from the Tso Morari ultra-high pressure unit show enrichment in fluid mobile elements such as As, Sb and U, low alkali/U ratios and radiogenic Sr and Pb isotopic compositions. These features suggest a change in the metasomatizing agent with a strong influence from subducted continental material. Consistent with this scenario, the Sr-Pb isotopic composition of the Kargil FA serpentinites can be reproduced by mixing between an Indian MORB-depleted mantle source and fluids derived from dewatering of blueschist facies oceanic metasediments, whereas in the case of Tso Morari a fluid end-member derived from various eclogitic continental metasediments is required. We propose that the observed geochemical signature of the Indus Suture Zone FA serpentinites can be used to reconstruct the geochemical exchanges between the slab and the overlying mantle from intra-oceanic to continental subduction. This successful systematic approach could be applied to other collisional contexts

Estimating Primary Magmas From Mars With PRIMARSMELT: Implications for the Petrogenesis of Some Martian Rocks and the Thermal Evolution of Mars

AbstractPrimary magmas form by partial melting in the mantle of a terrestrial planet and represent the starting material for building its crust. The compositions of primary magmas are critical for understanding the thermal history of planetary interiors, as they can be used to estimate mantle potential temperatures (TP) and track changes in the conditions of mantle partial melting over time. Here, we introduce PRIMARSMELT, a new member of the PRIMELT software family, calibrated to estimate the composition of Martian primary magmas and their formation conditions. We applied PRIMARSMELT to a comprehensive database of basaltic compositions from Mars. Our results are consistent with their petrology, requiring olivine addition to restore fractionated compositions to their primary parents and olivine subtraction from cumulate rocks. Individual primary magma solutions provide insights into the petrogenesis of specific Martian meteorites, with implications for the near‐primary nature of some primitive meteorites and the relationship between lithologies A and B in meteorite EETA 79001. Taken together, our results suggest nearly constant or potentially increasing mantle potential temperatures throughout the geological history of Mars. The average TP for young shergottite meteorites is ∼1,442 ± 40°C, similar to ambient mantle temperatures inferred from geophysical models. In contrast, older basaltic rocks record potential temperatures as low as ∼1,320 ± 48°C for igneous clasts in meteorites NWA 7034/7533. We suggest that, rather than plume‐related magmatism, shergottite meteorites record ambient mantle temperatures, with the thermal evolution trend possibly resulting from inefficient heat loss, as expected for a planet in stagnant‐lid mode.

Rmacrostrat : An R package for accessing and retrieving data from the Macrostrat geological database

The geological record is a vast archive of information that provides the only empirical data about the evolution of the Earth. In recent years, concentrated efforts have been made to compile macrostratigraphic data into the online centralized database Macrostrat. Macrostrat is a global stratigraphic database containing information regarding surface and subsurface rock units and their respective ages, lithologies, geographic extents, and various other associated metadata. However, these raw data are currently directly accessible only through the Macrostrat application programming interface, which is a barrier to potential users that are less familiar with such services. This data accessibility hurdle currently prevents full capitalization of the value offered by Macrostrat, particularly its potential to improve understanding of the geological and biological evolution of the Earth. Here, we introduce rmacrostrat, an R package that interfaces with the Macrostrat database to access and retrieve a variety of geological, paleontological, and economic data directly into the R programming environment. In this article, we provide details about how the package can be installed, its implementation, and potential use cases. For the latter, we showcase how rmacrostrat can be used to visualize regional stratigraphic columns, produce regional geologic outcrop maps, and investigate temporal trends in macrostratigraphic units. We hope that this package will make geological data more readily accessible and in turn will facilitate new research utilizing Earth system data.

Alternative climatic steady states near the Permian-Triassic Boundary.

Due to spatial scarcity and uncertainties in sediment data, initial and boundary conditions in deep-time climate simulations are not well constrained. On the other hand, depending on these conditions, feedback mechanisms in the climate system compete and balance differently. This opens up the possibility to obtain multiple steady states in numerical experiments. Here, we use the MIT general circulation model to explore the existence of such alternative steady states around the Permian-Triassic Boundary (PTB). We construct the corresponding bifurcation diagram, taking into account processes on a timescale of thousands of years, in order to identify the stability range of the steady states and tipping points as the atmospheric CO2 content is varied. We find three alternative steady states with a difference in global mean surface air temperature of about 10°C. We also examine how these climatic steady states are modified when feedbacks operating on comparable or longer time scales are included, namely vegetation dynamics and air-sea carbon exchanges. Our findings on multistability provide a useful framework for explaining the climatic variations observed in the Early Triassic geological record, as well as some discrepancies between numerical simulations in the literature and geological data at PTB and its aftermath.

Twentieth century extreme precipitation detected in a high-resolution, coastal lake-sediment record from California

AbstractCalifornia faces increasing economic and societal risks from extreme precipitation and flooding associated with atmospheric rivers (ARs) under projected twenty-first century climate warming. Lake sediments can retain signals of past extreme precipitation events, allowing reconstructions beyond the period of instrumental records. Here, we calibrate AR-related extreme precipitation from the last century to proxy data from lake sediments collected in the latitudinal zone of the highest frequency landfall for modern ARs in California. Excursions in erosional proxy data (Ti/Al) are positively and significantly correlated (rmedian = 0.45, pmedian = 0.04) with modern records of integrated vapor transport (IVT, kg m−1 s−1), a key metric of AR intensity, using correlations that incorporate age-model uncertainty. Despite the land-use change near the study site, the data suggest intense and long-lasting AR storms are identifiable in this sedimentary record. These results allow conservative inferences concerning past extreme hydrology at this site.

Rapid India–Asia Initial Collision Between 50 and 48 Ma Along the Western Margin of the Indian Plate: Detrital Zircon Provenance Evidence

Constraining the collision timing of India and Asia requires reliable information from the coeval geological record along the ~2400 km long collisional margin. This study provides insights into the India–Asia collision at the westernmost margin of the Indian Plate using combined U-Pb geochronological data and sandstone petrography. The study area is situated in the vicinity of Fort Munro, Pakistan, along the western margin of the Indian Plate, and consists of the Paleocene Dunghan Formation and Eocene Ghazij Formation. The U-Pb ages of detrital zircons from the Dunghan Formation are mainly clustered between ~453 and 1100 Ma with a second minor cluster between ~1600 and 2600 Ma. These ages suggest that the major source contributing to the Dunghan Formation was likely derived from basement rocks and the cover sequence exposed mainly in Tethyan Himalaya (TH), Lesser Himalaya (LH), and Higher Himalayan (HH). Petrographic results suggest that the quartz-rich samples from the Dunghan Formation are mineralogically mature and have likely experienced log-distance transportation, which is possible in the case of an already established and well-developed river system delivering the sediments from the Craton Interior provenance. Samples of the overlying Ghazij Formation show a major detrital zircon age clustered at ~272–600 Ma in the lower part of the formation, comparable to the TH. In the middle part, the major cluster is at ~400–1100 Ma, and a minor cluster at ~1600–2600 Ma similar to the age patterns of TH, LH, and HH. However, in the uppermost part of the Ghazij Formation, ages of <100 Ma are recorded along with 110–166 Ma, ~400–1100 Ma, and ~1600–2600 Ma clusters. The <100 Ma ages were mainly attributed to the northern source, which was the Kohistan-Ladakh arc (KLA). The ~110–166 Ma ages are possibly associated with the TH volcanic rocks, ophiolitic source, and Karakoram block (KB). The Paleozoic to Archean-aged zircons in the Ghazij Formation represent an Indian source. This contrasting provenance shift from India to Asia is also reflected in the sandstone petrography, where the sample KZ-09 is plotted in a dissected arc field. By combining the U-Pb ages of the detrital zircons with sandstone petrography, we attribute this provenance change to the Asia–India collision that caused the provenance shift from the southern (Indian Craton) provenance to the northern (KLA and KB) provenance. In view of the upper age limit of the Ghazij Formation, we suggest the onset of Asian–Indian collision along its western part occurred at ca. 50–48 Ma, which is younger than the collision ages reported from central and northwestern segments of the Indian plate margin with 70–59 Ma and 56 Ma, respectively.

The influence of weathering and pedogenesis on the geochemical record of Miocene marls and Plio-Quaternary sediments, Medvednica Mt., Croatia

The geochemical signature of weathering and pedogenesis in a temperate humid climate on two parent material types in the foothills of Medvednica Mt. was studied. Five soil profiles on Miocene marls and three sections of Plio-Quaternary (PlQ) proluvial sediments with overlying soil and weathered material were analyzed. The (clay) mineralogy of all profiles and sections had been determined in previous studies. The chemical composition of the samples was determined by inductively coupled plasma emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectroscopy (ICP-MS). Poorly ordered Fe and Mn oxides were determined in the PlQ sediment and overlying soil samples by atomic absorption spectroscopy (AAS), after oxalate dissolution in the dark. The concentrations and element ratios were used to determine element enrichment/mobility and intensity of chemical weathering, material provenance, and to compare the geochemical signatures with previously obtained clay mineralogy results. Trace elements in the Miocene marls, including rare earth elements (REE), indicate the continental origin of the marl siliciclastic component, while more scattered geochemical data of the PlQ sediments reflect their proluvial/torrential nature. The mass transfer coefficient (τ) for major elements and element ratios of the Miocene marl profiles indicate chemical weathering and pedogenesis of lower intensity. The geochemistry of these samples shows homogeneity within the profiles. In the geochemical signature of the PlQ sections, a chaotic proluvial deposition of the material is visible, as well as the heterogeneity with the overlying soil and weathered material. Overall, the geochemistry results largely support the clay mineralogy of the samples and demonstrate how a multiproxy approach can help test hypotheses about past environments and provide valuable additional information for complex paleoenvironmental studies.

Quantifying Pleistocene loess provenance in midcontinental North America using a mixing model: Implications for glacial lobe evolution along the southern Laurentide ice sheet

Quaternary glaciations have significantly impacted the midcontinental North American landscape, leaving behind a proglacial sediment record of glacial lake deposits, glacio-fluvial sand and gravel, and windblown loess. This paper aims to expand upon a previous study using detrital zircon provenance analysis to investigate midcontinental North American loess provenance in relation to the glacial history of the southern Laurentide ice sheet during the middle to late Pleistocene. The study incorporates previously published detrital zircon data from last glacial tills (representing the Huron-Erie Lobe, Lake Michigan Lobe, Green Bay Lobe, Superior Lobe, Des Moines Lobe, and James Lobe), middle to late Pleistocene loess from several sites along the Illinois and Mississippi River valleys, and suspended sediment load inputs from the Missouri River and Arkansas River. A statistical mixing model (DzMix version 2.2) was used to estimate the relative proportions of glacial and nonglacial sources to Wisconsin Episode, Illinois Episode, and pre–Illinois Episode age loess. We show that mixing models that include the modern suspended sediment loads of the Missouri and Arkansas Rivers significantly improve (up to 23% increase in cross-correlation value) the source characterization of Wisconsin Episode (last glacial) and Illinois Episode (penultimate glacial) loess deposits within the Mississippi River drainage basin. These river sources are dominant inputs for certain loess sites (as much as 51%), but their relative contributions are not static across time and space, which has implications for temporal and spatial differences in relative sediment source estimates and glacial and fluvial sediment transport evolution. Specifically, differences in relative sediment proportion estimates among Wisconsin, Illinois, and pre–Illinois Episode loess support previous evidence for the persistence of a Quebec-Labrador ice dome source through multiple glacial cycles, even with the inclusion of river sources in updated mixing models. Illinois and pre–Illinois Episode loess in the southern portion of our study area received ~20% detrital zircon input from sources similar to the present-day Missouri and Arkansas Rivers, suggesting that these river systems were contributing a significant amount of detritus to the lower Mississippi River valley region during the middle Pleistocene.

Marsh topography reveals the signature of storm-surge-driven sedimentation

Salt marshes are valuable tidal landforms threatened by drowning due to increasing sea levels. Marsh accretion supported by sediment settling during repeated flooding potentially offsets the relative elevation loss. Although tidal flooding is commonly depicted as the main mechanism delivering the sediment to marshes, storm surges and waves may deeply affect tidal flow conditions and sediment reworking in shallow tidal systems, thus raising questions on the relative contribution of these processes to salt-marsh accretion. Here we show that storm surges substantially sustain the marsh sediment budget, locally contributing up to 90% of sedimentation, and critically influence depositional patterns by analyzing a 3-yr-long measurement record of sedimentation on the marshes in the Venice Lagoon (Italy). Surge-enhanced water levels promote wind-wave-driven sediment fluxes directly across the tidal flat-marsh transition, altering tidal sedimentation patterns and, thus, affecting marsh topographic elevation and morphology. By comparing sedimentation patterns and topographic profiles, we show that the signature of storm-surge sedimentation can be found in marsh topography, which we suggest therefore as an easily detectable indicator of the relative contribution of the different physical processes driving marsh vertical evolution. The comparison with other marshes worldwide, characterized by different tidal ranges and wave exposure, consistently supports the link between the salt-marsh topographic profile and the physical processes controlling marsh evolution.

Sediment Accumulation Rates and High-Resolution Age-Depth Models

Sediment accumulation rates are a powerful tool for interpreting the rock record, offering insight into the depositional environment of a given locality and the (in)completeness of a given stratigraphic record. Classic approaches to sediment accumulation rate characterization required large data compilations, but the advent of high-resolution age models enables the use of individual sections and regional composite records to generate a large enough sample size of accumulation rates to estimate stratigraphic completeness. Because of these prior limitations, it is unclear how precisely accumulation rates are known for many stratigraphic sections, with rare and discrete horizon-horizon accumulation rates potentially biasing results. Here, I explore how to leverage high-resolution age-depth models to reveal accumulation rate-duration trends for individual sections and to better understand depositional histories by calculating accumulation rates for every horizon in a given section. First, I demonstrate these analyses on three synthetic age-depth models. I then examine regional composite carbon isotope records from the Ediacaran to test the effectiveness of my method on real data. Based on the accumulation rate–duration relationship, I estimate that the Ediacaran Oman and China stratigraphies are ~22% and ~37% complete at a 1-Myr interval, respectively. I find that accumulation rates drop following the Gaskiers glaciation and are relatively low during the Shuram carbon isotope excursion. Furthermore, the Oman carbon isotope stratigraphy demonstrates increasing accumulation rates across the Ediacaran, peaking near the Ediacaran–Cambrian boundary. Using an iterative technique, I estimate mean accumulation rates and durations, with uncertainty, and demonstrate how iterative-style Sadler plots can be used to interrogate depositional histories. In an effort to facilitate this approach and further quantitative developments across the stratigraphy community, I provide an open-source function that generates the plots herein for any stratigraphic record with an accompanying age-depth model.

Cicada nymph trace fossils from South American Maastrichtian paleosols

The Cretaceous was a pivotal Period in the evolution of major insect groups, including cicadas. Insect diversification led to an increased complexity in the paleosol ichnofabrics due to the emergence of chambers associated with reproductive and feeding behaviors. Therefore, any new record of trace fossils attributed to cicadas from the Cretaceous period represent a significant advancement in understanding the diversification of this group and the emergence of insect feeding chambers, throughout the geological record. This work describes the record of the ichnogenus Feoichnus attributed to feeding chambers of cicada nymphs (Hemiptera: Cicadidae) from Maastrichtian paleosols developed in floodplain deposits of The Marília Formation (Bauru Basin, Brazil). The described Feoichnus chambers are elongated, hemispherical, and upwardly concave, with a lining covering the inner surface of the wall. The inner surface exhibits thin, irregular ridges and grooves, likely associated with fine roots. Feoichnus occurs in association with Beaconites antarcticus and root traces found within the feeding chamber, it could be indicating the movement of the trace maker and the feeding chamber from one root to another. These characteristics indicate the xylem-feeding behavior of Feoichnus trace maker in accordance with extant cicada nymph ecology. The presence of Beaconites antarcticus associated with Feoichnus and rhizoliths probably represents the foraging behavior of cicada nymphs and the displacement of feeding chambers in well-drained, rooted soils. Therefore, the cicada nymph could be the trace maker of both traces representing feeding and locomotion behavior. This contribution expands the knowledge about plant–insect interactions and insect groups that compose the Cretaceous paleosols ichnofabrics from South America.

Precipitation variability and environmental change across late Quaternary glacial-interglacial cycles in lowland Central America: Insights from Lake Petén Itzá (Guatemala) sediments

Lowland Central America, a biodiversity hotspot in the northern Neotropics, is a region where the climate is influenced by the location and expansion-contraction of the Intertropical Convergence Zone (ITCZ) on seasonal to millennial timescales. Paleo-records from the Caribbean Sea and the eastern equatorial and subtropical Pacific Ocean illustrate the response of regional precipitation to fluctuations in global temperature, driven by glacial-interglacial cyclicity over the past 500 kyr. Here, we present a paleoclimate and paleoenvironment record from Lake Petén Itzá, lowland Guatemala, which spans the last ∼413 kyr. Sediment in the lake recorded lacustrine and terrestrial ecosystem responses to large-scale climate variability. Precipitation patterns during MIS11-9 (∼413-304 ka BP) align with the latitudinal position of the ITCZ, with superimposed effects from the strength of the Caribbean Low-Level Jet (CLLJ). A sediment hiatus, likely attributable to mass removal processes in the lake's shallower areas, spans the period from MIS8 (starting at 304 ka BP) to the end of MIS6 (at 149 ka BP). MIS6 was characterized by humid conditions, perhaps ascribable to a more southerly extension of cold fronts and intensification of the CLLJ. During MIS5, pronounced fluctuations among all sediment variables, accompanied by an abrupt decline in precipitation, may correspond with cold events inferred from North Atlantic Ocean sediment cores. Although discontinuous, the Lake Petén Itzá sediment record provides a window into late Quaternary climate and environmental change in lowland Central America.

Facies variations in gravelly cyclic steps deposited from turbidity currents: Miocene fan delta front deposits compared with a modern active fan delta, central Japan

AbstractGravelly cyclic steps formed by turbidity currents have recently been widely recognised in the geological record. However, the comparison between modern and ancient gravelly cyclic steps remains challenging. In this study, the facies variations of gravelly cyclic steps deposited from turbidity currents in an outcrop of Miocene fan delta front deposits in central Japan are compared with the geomorphic evolution of analogous cyclic steps on the active fan delta front in modern geological systems. These cyclic steps share common characteristics in setting, grain size and dimensions, allowing direct comparison between ancient and modern examples. Repeat bathymetric surveys of the modern Kurobe River fan delta have revealed various types of upslope migrating bedforms interpreted as cyclic steps. Most of these are short‐lived due to erosion of thalwegs by powerful surge‐type turbidity currents triggered by slope failures or burial of thalwegs by deposition, possibly from river‐fed hyperpycnal flows. Such erosion and burial events occur annually on the fan delta front, resulting in compensational cycles. Sedimentary facies of the Miocene fan delta front deposits include conglomerate with a gently upslope dipping erosional base, backset‐stratified sandstone and foreset‐stratified sandstone, which are interpreted as deposits of hydraulic jumps in high‐density turbidity currents in scours on the stoss sides of cyclic steps. Parallel‐stratified conglomerate sandstone is an additional component. Although previous facies models of gravelly cyclic steps have focussed on deposits on stoss sides, a comparison of modern and ancient examples suggests that facies on the lee sides could be parallel‐stratified conglomerate sandstone and undulating bedforms, reflecting supercritical flow conditions. The present study also suggests that hyperpycnal and surge‐type high‐density turbidity currents may deposit different types of facies and play different roles in the construction and destruction of cyclic steps. The present study has significant implications for facies models of gravelly cyclic steps.

Tracking orbital and suborbital climate variability in the westernmost Mediterranean over the past 13,000 years: New insights from paleoperspectives on marine productivity responses

This study presents a comprehensive analysis of a sediment record from the Western Alboran Basin (core GP04PC), utilizing palynological and geochemical tools to investigate marine productivity responses to orbital and suborbital climate variability over the past 13,000 years. High productivity during the Younger Dryas humid phase (∼12.4–11.7 ka) and the Holocene humidity optimum (∼10.5–8.5 ka) was driven by increased local river discharges resulting from rapid mountain glaciers melting and enhanced regional precipitation. During the late Holocene, frequent flood events linked to negative North Atlantic Oscillation (NAO) incursions potentially led to multicentennial-scale productivity increases. The findings indicate that periods characterized by wet regional conditions and increased river run-off, influenced by orbital (e.g., insolation cycles) and suborbital factors (e.g., NAO and Atlantic Meridional Overturning Circulation changes), consistently enhanced marine productivity in the Western Alboran Basin. The study also reveals that the current high productivity and carbon export in the Western Alboran Basin are maintained by active upwelling and downwelling systems driven by a persistent positive NAO phase following the southward migration of the Intertropical Convergence Zone (ITCZ) that occurred around 6.5 ka. Furthermore, geochemical proxies support a strong detrital influence on trace metal concentrations, including barium (Ba), in deep Western Alboran sediments during the Holocene. This limits the use of Ba/Al ratios for accurately reconstructing productivity changes and highlights the importance of dinocyst analysis as a complementary tool for robust marine productivity reconstructions in this region. These observations provide valuable paleoperspectives on marine ecosystem responses to climate variability, contributing to the development of robust long-term productivity models essential for adapting to ongoing environmental changes in the region, and demonstrating the strong influence of North Atlantic climate and ocean dynamics on centennial-scale productivity oscillations in this region.