Sedimentary Record Research Articles

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.

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.

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.

Surges of the Black Rapids Glacier tracked climate over the last 600 years

Deposits of surge-type glaciers are widespread in the glacial geologic record; however, it is unclear how climate changes occurring at time scales of decades to centuries affect surge-type glaciers. Here we reconstruct the history of the Black Rapids Glacier (BRG) in the eastern Alaska Range since AD 1400 using a combination of geomorphology, stratigraphy, lichenometry, radiocarbon dating, and dendrochronology. Moraines in the glacier's foreland record four advances, all of which left deposits typical of surging glaciers. A surge in the AD 1600s dammed a lake which drained in an outburst flood ca. AD 1703-04. Another outburst flood from a larger glacier-dammed lake occurred in the AD 1400s. Based on the BRG's observed glaciology and its history over the last several centuries, its surge cycles have varied between 80 and 120 years. Between AD 1400 and 1900, the most extensive surges of the BRG coincided with minima in the Seuss / de Vries solar cycle when non-surging glaciers in the region also advanced. Synchroneity between the BRG, solar minima, and non-surging glaciers is surprising given that the terminus of the BRG was largely unresponsive to climate for 80–120 years between surges. One explanation is that the BRG's surge cycle shortened during the Little Ice Age (LIA, ca. AD 1300–1900) to the point that its climate-response lag resembled that of neighboring, non-surging glaciers. Although the reconstructed chronology of the BRG shows no indication of the surge cycle decreasing during the LIA, fading of the record with time makes it difficult to exclude this possibility. Another explanation is that the BRG's 80- to 120-year cycle is the result of tuning by the solar cycle over the course of millennia. Tuning occurred when quiescent phases that coincided with solar minima were shortened because of faster replenishment of the glacier's reservoir zone. The opposite occurred when the glacier's quiescent phases coincided with solar maxima. The net result was to align the surge cycle of the BRG with solar minima. Some combination of shortened surge cycles during the LIA and tuning by the solar cycle may be why the glacial-geologic record of this particular surge-type glacier provides a surprisingly dependable record of regional climate over the past 600 years.

Microplastics deposition in Arctic sediments of Greenland increases significantly after 1950

Marine sediments are archives of environmental change with pollutants potentially acting as chronographic markers of the Anthropocene. Particularly, the vertical transport and burial, as well as slow degradation rate of microplastics, indicate an eventual incorporation into the geological record. A high-resolution reconstruction of microplastics records requires high sedimentation rates, and in Disko Bay (Greenland), this quality coincides with a need for plastic pollution data. Here, a Greenlandic sediment core dated back to 1930 ± 2 was reconstructed for microplastics accumulation via micro-Fourier transform infrared spectroscopy. We show 85 years of fluctuating microplastics accumulation (987 − 16,645 particles Kg−1) down to 20 µm and diversified into eight polymers. Polyethylene (47%) and polypropylene (32%) were more abundantly present through time. Microplastics accumulation increases significantly after 1950 along with major socio-economic development in the area, suggesting an influence from regional stressors. Regional microplastics reconstructions must therefore be considered in the pursuit of an Anthropocene global plastic horizon.

Fluvial-lacustrine influences on linear dune erosion at Lake Caroline in the Simpson Desert of Australia

Linear dunes are frequently examined with regard to their formation and maintenance; however, erosion or degradation of these landforms is less commonly addressed, due in part to the lack of observable changes in the geologic record. This study investigates the significant erosion of linear dunes along Lake Caroline, a playa in the northern Simpson Desert of central Australia. Field observations, laboratory analyses, and remote sensing imagery document recent fluvial and lacustrine interactions at Lake Caroline. Compositional and geochemical sediment analyses from three ∼2 m deep hand-augured sample sites indicate that the playa is primarily filled with sand from linear dunes, but also contains evaporite minerals and weathered local bedrock. Satellite images show that the playa has flooded at least 58 times since 2001. Our results indicate that present-day aeolian processes are sufficient to mobilize and transport sediment but are dominated by fluvial-lacustrine processes, resulting in the playa-adjacent dunes becoming isolated and starved of local sediment. As a result, the dunes are currently eroding into the playa which supports the conclusion that long-distance sediment transport is not responsible for the formation or maintenance of linear dunes as suggested by the linear due extension hypothesis. Burial dates from optically stimulated luminescence (OSL) indicate the linear dunes have been eroding for as much as 24 ka, and sediment samples from the playa near one linear dune suggest an onset of dune formation in the area before 58 ka. This work documents an instance in geologic time during the late Quaternary when aeolian, fluvial, and lacustrine processes are competing with one another, offering new insights into the dynamics of linear dunes in the arid Simpson Desert.

Conditions for formation and preservation of andesite-hosted mafic enclaves during the 2018 Lower East Rift Zone eruption of Kīlauea

Andesites erupted at Kīlauea in 2018 in the Lower East Rift Zone for the first time in the known geological record. The evolved lavas erupted at Fissure 17 of the 2018 eruption, ranging from andesites to basaltic andesites, contain abundant mafic enclaves both in the lava flows and the ejecta, which are unusual at Kīlauea and in Hawai'i in general. Textural observations indicate that the enclaves originate from incomplete mixing of two magmas rather than the incorporation of cold basaltic wall rock. We suggest, on the basis of bulk and mineral compositions, that the source of the mafic enclaves is the early 2018 evolved basalt magma (phase 1b) that erupted concomitantly at adjacent fissures, which mixed with the andesite to produce the range of basaltic andesite compositions observed at Fissure 17. The coexistence of homogenized basaltic andesites and mafic enclaves within the same magma require a mixing mechanism resulting in both complete homogenization and preservation of enclaves. We propose that the range of mixing and mingling processes may be explained by spatial and temporal variability in the mixing percentages of the phase 1b basalt and the andesite within the andesite magma chamber. Field observations, chemical compositions, and 2D thermal conduction models suggest that enclaves are preserved where the basalt contribution to mixing is less than roughly 40 %, as a result of microlite crystallization leading to rigidification of the enclave magma. Above this threshold, the mixed magmas became largely homogenized. The scarcity of mafic enclaves at Kīlauea and in the Hawai'i igneous record is likely explained by mixing between magmas that lack sufficient compositional and rheological contrasts to preserve them.

Detrital zircon tales between the Rodinia and Pangea supercontinents – Exploring connections between Avalonia, Cadomia and Central Asia

The Rodinia to Pangea supercontinent cycle represents the most recent complete cycle in the geological record and thus informs models on the processes involved in supercontinent dispersal and assembly. The terranes and/or micro-continents of the Avalonian, Cadomian and Central Asian Orogenic Belts are witnesses to this complete cycle but their relationships to Rodinia, each other, and an intermediate stage in this supercontinent cycle represented by the formation of a large (but not supercontinent) landmass, Gondwana, are at time ambiguous. One method for testing these relationships is detrital zircon geochronology; zircons are a highly resistant and easily dateable mineral and thanks to rapid instrumental advances a huge number of detrital zircon datasets are now available. These data can provide a fingerprint whereby suspect terranes and micro-continental fragments can be linked to each other and their parental continent. Nonetheless, in order to develop coherent and testable geological hypotheses from these data it is necessary to integrate the data into a consistent framework. The presented work explores the possibilities and limitations of using detrital zircon data to better understand the position of the Avalonian, Cadomian, and Central Asian terranes in Rodinia and their journey from there to Pangea.

Sedimentary record of primary productivity changes in a crater lake in Northeast China since the Last Glacial Maximum

High-resolution primary productivity records are valuable for identifying lacustrine ecosystem degradation in the context of long-term climatic variability. In this paper, we analyse primary productivity changes in a seasonally ice-covered crater lake (Lake Tuofengling) in northeast China since the Last Glacial Maximum using biogenic silica content and the carbon preference index of short-chain n-alkanes as proxies. Results show that primary productivity was lower during the cold and dry glacial period, whereas it was higher during the warm and humid Holocene. During the last deglaciation, primary productivity experienced a ∼ 1.5-kyr lagged response to Bølling-Allerød warming, and multiple oscillations during the Younger Dryas. Additionally, the peak productivity of the entire profile also occurred during this period. These fluctuations and the highest primary productivity are suggested to be the result of the combined influences of increased summer temperatures and regional permafrost melting. The current state of primary productivity in Lake Tuofengling is moderate but has been increasing since the abrupt increase in diatom productivity after ∼3 ka B.P. This stage is associated with increased dust deposition and longer ice-free periods under winter-warming conditions. We suggest that longer seasonal stratification under the current warmer winters and increased nutrient concentrations caused by decreased lake level will increase the risk of lake ecosystem degradation in the future.

Fire in Feces: Bats Reliably Record Fire History in Their Guano

AbstractNew approaches are needed to resolve persistent geographic gaps and biases in paleofire research. Most sedimentary paleofire research relies on lake and peat sediments. We present an unconventional sedimentary charcoal record preserved in a modern, post‐bomb bat guano deposit and compare its accumulation to historical fire data. We find strong correlations between charcoal accumulation rates (CHAR) and non‐winter prescribed burns. CHAR in bat guano is more strongly correlated with prescribed fire than wildfire or total area burned, likely due to bats seeking out areas burned by prescribed fire for better foraging opportunities and/or bats avoiding wildfire. We attribute the CHAR in guano being a better recorder of area burned during non‐winter months to winter bat hibernation. Our analyses show that charcoal preserved in bat guano is a reliable paleofire proxy system, which has important implications for the paleofire field and encourages future research using bat guano as a viable archive.

Variable preservation of the 1991 Hudson tephra in small lakes and on land

Volcanic ash (tephra) preserved in terrestrial environments and lake sediments contains information about volcanic processes and can be used to infer eruptive parameters and frequency of past eruptions, contributing to the understanding of volcanic hazards. However, tephra deposits can undergo transformation from their initial fallout sedimentation to being preserved as a tephra layer in the sedimentary record. The process is likely to be different in lakes and in terrestrial (soil) sequences. Here we compare the thickness, mass loading and grain size of tephra layers from the 1991 eruption of Cerro Hudson, Chile, from small lakes and adjacent terrestrial settings to measurements of the tephra made shortly after the eruption. We analysed samples from 35 cores in total from six small lakes (<0.25 km2), located 76 and 109 km from the volcano in two contrasting climatic areas (cool and humid northern site, and warm and dry southern site), and made 73 measurements of tephra thickness and 11 measurements of grain size in adjacent terrestrial areas. The major element geochemistry of our samples confirmed they were from the 1991 Hudson eruption. We found that some of the measured characteristics of the preserved tephra layers were comparable to those recorded in 1991 shortly after initial deposition, but that there was considerable variability within and between locations. This variability was not predictable and lake sediments did not preserve a notably more accurate record of the fallout than terrestrial sites. However, in aggregate the characteristics of the preserved tephra was similar to those recorded at the time of deposition, suggesting that, for palaeotephra research, a sampling strategy involving a wide range of environments is more robust than one that relies on a single sedimentary record or a single type of sedimentary environment.

Variscan basement tectonics and Alpine shear zones in the external Balkanides: Structural data from the Vezhen Massif, Central Stara Planina Mts., Bulgaria

The Alpine Balkanides in Bulgaria are developed over Variscan orogenic fragments, which are variously affected by late-stage thick-skinned thrust tectonics. Often, these fragments hold both Variscan and Alpine structural records. А key area to shed light on important aspects of the tectonic evolution of the external parts of the Alpine Balkanide orogen is the Vezhen Massif in the Central Stara Planina Mountains. Although it is built exclusively of Paleozoic crystalline rocks, its structure was long considered as an example of intense mid Eocene to early Oligocene (Late Alpine) shortening. Detailed fieldwork in the area shows a more complicated tectonic framework and provides evidence of a polyphase structural evolution, involving an important stage of Variscan metamorphism and deformation and two stages of north-vergent Alpine shortening. The Stargel-Boluvanya Tectonic Zone that affects the western Vezhen Massif is one of the most important Variscan structures in the Balkan fold-and-thrust belt. Structural data indicate that the metamorphic basement records initial top-to-north thrusting, followed by further shortening, which led to folding and localized strike-slip deformation. The Variscan syn-metamorphic fabric is cross-cut by several post-kinematic igneous bodies of late Carboniferous to Permian ages. The tectonic history continues with a development of a network of greenschist facies north-vergent mylonitic zones for which an Early Alpine (post-late Permian but pre-Late Cretaceous) age is assumed. Late Alpine north-vergent thrusting is evident only on the eastern and northern flanks of the Vezhen Massif. In a broad structural context, the documented record in the basement rocks of the Vezhen Massif is comparable with those of the external massifs of the Alps and Iberia.

Paleostorm redeposition and post-glacial coastal chronology in the eastern Baltic Sea, Latvia

The 494 km long Latvian coast consists of sandy sediments, which serve as an excellent proxy for past coastal events and environment. Our study explores these understudied sediments along the western coast of the Gulf of Riga and combines two sand quartz-wise methods: optically stimulated luminescence (OSL) dating and grain microtextures. We provide a new chronology and microsedimentary results to trace post-glacial storm events and discuss correlations within the Baltic Sea region and elsewhere in Europe. OSL ages reveal a wide time span between 10.38 ± 0.61 ka and 1.04 ± 0.05 ka BP, but their inconsistency in the profiles along with the onshore position of landforms and gravelly horizons argues for sediment relocation due to storm action. A first paleostorm phase is dated to between 7.6 ± 1.2 ka and 4.63 ± 0.27 ka, corresponding with a transgression of the Littorina Sea and the Holocene Thermal Maximum, and with a roughly estimated vertical sediment redeposition above 5 m similar with the recent storms in the region. Sedimentary record from microstudy supports intense storm activity, especially in sediments redeposited after 6.07 ± 0.51 ka, and it is seen through an increased number of cracked quartz grains, shiny grains and fresh surfaces combined with a limited number of V-shaped marks. Weaker storm action, recorded by a lower share of cracked grains in the sediments, occurred between 7.6 ± 1.2 ka and 6.07 ± 0.51 ka.A second storm phase occurred at 1.44 ± 0.21 ka, corresponding with the post-Littorina, again with a performance of a weaker storm. Apart from the palaeostorm records, the beach ridges developed between 5.16 ± 0.33 ka and 4.47 ± 0.31 ka along with drier conditions when aeolian deposition took place twice: at 4.63 ± 0.27 ka and 1.55 ± 0.10 ka.

INDIVIDUAL FORAMINIFERAL ANALYSES: A REVIEW OF CURRENT AND EMERGING GEOCHEMICAL TECHNIQUES

Abstract The trace element (TE) and isotopic composition of calcareous foraminifera has been invaluable in advancing our understanding of environmental change throughout the geological record. Whereas “bulk” geochemical techniques, typically requiring the dissolution of tens to hundreds of foraminiferal tests for a single analysis, have been used for decades to reconstruct past ocean-climate conditions, recent technological advances have increased our ability to investigate foraminiferal geochemistry from an individual test to a micron-scale domain level. Here we review current and emerging techniques and approaches to studying the trace element and stable isotope geochemistry of individual foraminifera (i.e., individual foraminiferal analyses or “IFA”), covering spatial scales including whole-test analysis, intratest spot analysis, and cross-sectional chemical mapping techniques. Our discussion of each technique provides an overview of how the specific analytical tool works, the history of its usage in foraminiferal studies, its applications, considerations, and limitations, and potential directions for future study. Lastly, we describe potential applications of combining multiple IFA techniques to resolve key questions related to paleoceanography, (paleo)ecology, and biomineralization, and provide recommendations for the storage, dissemination, and transparency of the vast amounts of data produced through these methods. This review serves as a resource for budding and experienced foraminiferal geochemists to explore the wide array of cutting-edge approaches being used to study the geochemical composition of modern and fossil foraminifera.