Sedimentary Record Research Articles

ABSTRACT A new fossil diatom species of Encyonema Kützing was collected from the Pleistocene sediments of Colônia basin, State of São Paulo, Southeast Brazil, as part of an ongoing survey of its sedimentary record, aiming at exploring the long-term evolution of the Southern Hemisphere lowland rainforest. Morphology of the new species was examined using both light and scanning electron microscopy, and compared with the morphologically closest species in the genus, Encyonema latum Krammer and E. macedonicum Z.Levkov, D.Metzeltin and S.Krstic. The new species is characterized by a distinctly dorsiventral valve outline, a nearly straight ventral margin, and a relatively low length-to-width ratio, along with a higher areolae number. Preliminary diatom analysis of the Colônia basin sedimentary record indicates that the new species occurred associated with high organic matter input and shallow lake conditions, during a cold and humid period. The study contributes to the understanding of the Colônia basin biodiversity and will assist future ecological and evolutionary studies in the region.

ABSTRACT The southwestern Cape of South Africa experiences a complex and dynamic climate, shaped by the interplay between the temperate Southern Hemisphere westerly winds and the subtropical easterlies. Despite the climatic sensitivity of the region, relatively few studies have examined how conditions have varied since the last deglaciation in response to significant changes in global boundary conditions. Here, we present a 30 000‐year sedimentary record from a coastal wetland at Pearly Beach on the southern Cape coast, focusing on climatic changes that occurred during the last glacial–interglacial transition. Downcore variations in grain size and inorganic geochemical composition provide evidence for a period of heightened storm activity between ~18.5 and 14.0 cal ka BP, which we interpret to reflect intensified westerly wind‐driven activity. This period of increased storminess coincides with a slowdown in Atlantic meridional overturning circulation (AMOC) during Heinrich Stadial 1 (HS1: ∼18–14.6 ka) and subsequent warming in the southeast Atlantic Ocean. We propose that this warming enhances moisture uptake by westerly frontal systems, leading to stronger storms in the southern Cape. The intensification of westerly‐driven storms occurred concurrently with a broader cooling trend across South Africa, suggesting that AMOC variability during HS1 may have influenced climate across much of the region.

Most extant facies models depict the internal architecture of fluvial point bars as large-scale, inclined beds formed by the lateral migration of channel bends. However, recent studies have revealed that discharge variability can significantly influence these architectures, highlighting that the genetic processes governing their formation remain poorly understood. This study examines point-bar deposits along the meandering Powder River in Montana, USA, to understand how a highly variable hydrological regime impacts bar depositional architecture. Sedimentological data reveal that the bars consist of amalgamated beds and lack well-preserved, large-scale, inclined (macroform) bedding. By integrating architectural data with 27 years of hydrological and geomorphological records, we linked distinct beds to specific water discharge conditions, highlighting that major floods play a crucial role in constructing and reshaping point-bar architecture, whereas minor floods have marginal impacts. Bar-scale sedimentation occurs briefly during early flood-waning stages, forming limited bar-scale, inclined beds, which are later disrupted by localized scouring from subsidiary flood pulses. The preservation of these deposits is primarily controlled by the frequency of subsidiary peaks during the waning phase, rather than by intermittency or total duration of the waning stage. Consequently, the complex bedding in the Powder River point bars reflects autogenic intraflood reworking rather than interflood reworking. Major floods produce both slope-scale and localized deposits, with subsidiary peaks during waning stages driving macroform-bedding disruption. These results provide valuable insights for interpreting hydroclimatic environments and refining interpretations of past depositional processes from the rock record, and they emphasize the need to explicitly account for discharge variability in fluvial facies models.

Abstract The Chicxulub impact ∼66 Ma ago formed a large basin on the Yucatán platform, filled by sediments that provide a record of carbonate deposition, sea level and climate changes in the Gulf of Mexico. We study the post-impact sequence drilled in the Yaxcopoil-1 borehole in the crater terrace zone. The post-impact section is 792 m thick, overlying the impactites and Cretaceous carbonates. Section analyzed is between 400 and 792 m, formed by twelve units of limestones, dolomites, argillaceous/silicified limestones and calcarenites. Carbonates show cross-lamination, flow-currents, parallel lamination, cyclic graded bedding and styolitic structures. Study is based on core analyses, logging, petrography, digital scanned images, magnetic properties and X-ray diffraction and X-ray fluorescence geochemistry. The basal units U1–U4 represent low-energy deep bathyal environments and fine-grained facies varying from mudstone to wackestone. Sediment deposits, reworked and transported from the platform and crater rim, show textural and grain size changes from grainstone to packstone. Geochemical and magnetic susceptibility logs record effects of hydrothermal alteration, with secondary mineral assemblages. The SiO 2 and CaO contents display wide ranges, negatively correlated. Fe 2 O 3 , TiO 2 , Al 2 O 3 and K 2 O oxides show similar patterns downhole. The Sr and MgO show a positive correlation, except for the basal sediments. Paleocene units U1–U3 show increasing density, increasing seismic velocity and upward decreasing porosity. Upper units U5–U12 are characterized by laminated black shales and marls with microfacies varying from wackestone to packstone, with planktic and benthic foraminifera and bioclasts. Unit U9 shows low density and seismic velocity and increased porosity. Depositional environments vary from low-energy deep bathyal inside the basin to shallow neritic outside the crater rim. Sediments of the internal carbonate ramp to external neritic environments record sea level changes and platform subsidence/uplift.

Portable luminescence for rapidly identifying tsunami dynamics and responses in saltmarshes.

A sedimentary record of fire evolution history and its response to climate change and human activities during the last 7000 years from Lake Qionghai, southeastern Tibetan Plateau

Experimental and theoretical study on the seismic performance of an earthquake-resilient rocking column with a steel slit damper

Toolik Lake Sediment Record as a PAHs and Other Pollution Accumulation Proxy in Permafrost Region of Alaska

Continuous sedimentary drill cores provide crucial data for deciphering past climate variations and characterizing the subsurface for the energy industry (e.g., coal, petroleum, CO2 storage, geothermal energy). The Norwegian High-Arctic archipelago of Svalbard offers a diverse geological record that has been investigated by geoscientists for both scientific and applied projects, with hundreds of boreholes drilled over the past century. Unfortunately, much crucial data, including physical material from the boreholes, have been lost. The Svalbard Rock Vault project aims to safeguard drill cores, cuttings and hand samples from Svalbard and facilitate their scientific reuse. We aim to establish a physical core storage repository in, or near, Longyearbyen, Svalbard. In parallel, ongoing digitization and data integration efforts are improving access to complementary non-physical material, including hard-to-access reports, wireline logs and interpretations. In this contribution, we report on the motivation and background of the Svalbard Rock Vault project, synthesize current knowledge about physical subsurface material from Svalbard, and present a vision of an improved physical core storage facility near Longyearbyen.

Microbial fermentation facilitates the initial breakdown of organic matter into small molecules and is thought to be the rate-limiting step of anoxic organic mineralization. However, fermentation is understudied in modern and ancient biogeochemistry due to a lack of environmental biomarkers. It has long been assumed that fermentation, like respiration, does not express significant carbon isotope fractionations, precluding isotopic signals as a means of studying it in nature. Here, we tested this idea by growing pure cultures of four fermenting bacteria on glucose and measuring the carbon isotope compositions of the organic acids and alcohols produced. We found that fermentation exhibits a strong carbon isotope fractionation, ranging from [Formula: see text]6‰ to [Formula: see text]16‰, depending on the fermentation product. With bioisotopic models that track site-specific isotope enrichments through metabolism, we constrained the enzymes responsible for these fractionations. Our models reproduced in vivo organic acid [Formula: see text] values in all four organisms. These findings demonstrate that acetate 13C-enrichment is likely a widespread signature of fermentation. They also challenge traditional notions of controls on the isotope composition of lipids. Finally, our study suggests that fermentation imposes a trophic carbon isotope fractionation as organic carbon is passed from fermenters to secondary degraders like sulfate reducers. Looking to the geologic past, this trophic fractionation could have imprinted isotopic signals on the three billion year record of sedimentary organic carbon, specifically the inverse [Formula: see text] pattern of Precambrian acyclic isoprenoid and n-alkane biomarkers. Pervasive evidence of fermentation in the rock record would suggest its underappreciated role in biogeochemical cycles throughout Earth history.

Interactions between the parasitic larvae of digenean trematodes (mainly gymnophallids) and bivalves often produce characteristic pit-like malformations on shells. Tracking these traces in past and modern marine death assemblages has provided valuable insights into parasite-host responses to natural and anthropogenic environmental changes. Despite major breakthroughs, empirical explorations of parasite-host dynamics in the geological record are primarily based on trace occurrence data, overlooking the ecological information embedded in the spatial distribution of these traces (e.g. infective behavior, association with specific host anatomy, spatial relationships of traces with different size classes). Spatial Point Pattern Analysis of Traces (SPPAT), increasingly used to study predatory traces on mollusks, offers a promising approach to address this gap. However, its application to trematode-host interactions requires careful consideration of assumptions and caveats, such as the minimum number of traces required to accurately capture parasite-host dynamics and the reliability of point patterns constructed from data across multiple host skeletons. Here, we present a spatially explicit framework for extracting information from spatial patterns of trematode-induced pits on bivalve shells using SPPAT. We address methodological questions involved in assembling a point pattern of traces from multiple host specimens, and discuss critical issues related to drawing inferences from pooled point data. Our approach is illustrated using Late-Holocene samples of Chamelea gallina from the Northern Adriatic Sea (Italy), a species of commercial importance and a key model in climate change research. Our findings indicate that trematode-induced traces on C. gallina are non-randomly distributed, forming aggregated patterns. Notably, we detect no significant spatial differences between the two size classes of traces retrieved. This study extends the methodological toolkit for analyzing parasite-host interactions and highlights the potential of spatial trace patterns to enhance our understanding of their ecological and temporal dynamics.

ABSTRACTA variety of soft‐sediment deformation structures (SSDs) and mass flows of varying rheology are present in the Paleoproterozoic argillaceous Chakrata Formation, Lesser Himalaya. SSD structures (intra‐ and inter‐bed) include contorted/convoluted beds, deformed laminations, load casts, and flame structures, pseudonodules, and sand dykes. Deposits of high‐ and low‐density turbidity currents and sandy debris flows represent mass flows that are included in the Chakrata shelf shale succession. The lateral continuity and recurrent incidence of SSD‐bearing disturbed layers through the Chakrata lithopackage indicate a seismogenic origin. The disturbed bed thickness and nature of SSD structures suggest the earthquake shock magnitudes (Mz) of 5 to in excess of 8. It is ascertained that besides generating SSDs, the seismic shocks, at times, caused extreme liquefaction and fluidisation that caused sediment failure and generation of gravity flows. Though from rock record establishment of synchronicity between SSD formation and mass flow generation always remains a challenge in the absence of historical data or adjoining fault systems, the physical association of SSDs and mass flows in the Chakrata Formation allows identification of their co‐genetic nature related to seismic activity.

High pore pressure in faults is invoked as a weakening mechanism essential for fault slip, earthquake triggering, heat transport, and fluid and chemical cycling. Eighty years ago, the long-standing paradox surrounding the mechanical behavior of low-angle thrusts in tectonics and fault mechanics was resolved by invoking the effects of high pore pressure on reducing sliding resistance. However, observational structural criteria for past pore-pressure anomalies in natural fault rocks can be controversial because there is no agreement on how to interpret the rock record. The Muddy Mountain thrust in southern Nevada, USA, is part of the regional middle to Late Cretaceous Sevier orogenic front and preserves evidence of paleoseismic slip. The thrust juxtaposed an imbricated Paleozoic carbonate succession above Jurassic and Cretaceous sandstone, molasse, and conglomerate. Multiple crosscutting relations between principal slip surfaces and fault-rock injections record repeated coseismic pressurization events. Abundant ≤10-m-high injections containing centimeter-scale clasts of footwall and fault-core rock provide conclusive evidence of transient high pore pressure in the Muddy Mountain thrust during seismic slip. The injections have grain structures consistent with rapid emplacement by turbulent flow that transitions to laminar flow along the injections. These structures preserve evidence of transient fluid pressure gradients associated with fault zone pressurization. Coseismic pressurization allowed the Muddy Mountain thrust to slip at a low dip-angle in large earthquakes.

The nature of Archean tectonics and the associated geodynamic regimes are much debated in modern geoscience, despite decades of research. In this study, we present a geophysical model to show that, by the Neoarchean, convective forces from rising mantle plumes or early forms of plate subduction caused widespread extension, creating linear zones of crustal growth. These regimes can be identified as Archean rifts in the ancient rock record by the topography of the Moho, i.e., a shallowing of the boundary between the crust and the lithospheric mantle. Gravity data collected over the Abitibi greenstone belt, a particularly well-preserved portion of Neoarchean crust located in Canada’s Superior Province, was modeled to produce a topographic map of the Moho. The model shows corridors of shallow Moho surrounding islands of thick, intrusion-filled crust and is interpreted to be a snap-shot of microplate growth and breakup between 2.75 to 2.69 Ga. The connectivity of the interpreted relict rifts is possible evidence for the existence of Neoarchean plate boundaries and triple junctions and supports a model of at least local mobile-lid tectonics during this stage of Earth’s history.

Abstract Rocks at various lithospheric depths commonly display a fabric, resulting in mechanical anisotropy. The mechanical response of such anisotropic rocks depends on both the intensity of the anisotropy and the orientation of the fabric relative to the applied stress. Despite its potential significance, the role of mechanical anisotropy in governing lithospheric strength and deformation style during extension remains poorly constrained. Here, we investigate how mechanical anisotropy influences the deformation of the lithosphere under tectonic extension. We use two‐dimensional numerical models of lithospheric deformation that incorporate a non‐linear, transversely isotropic model. Both viscous and plastic rheologies are direction‐dependent, and fabric orientations evolve using the director‐vector approach. We perform simulations of continental extension and show that mechanical anisotropy is a major factor in the development of continental rifts. It influences the architecture of rift basins and reduces the driving force required for rifting. We explore the role of extensional velocity and find that it has only a second‐order influence on the evolution of rift systems. Furthermore, we investigate the relative contributions of crustal and mantle anisotropy, and highlight that mantle anisotropy plays a more significant role. The driving forces required for continental rifting are quantified and systematically analyzed. Compared to isotropic models, the required driving force is reduced by up to a factor of three when mechanical anisotropy is included. As a result, forces below 10 TN/m can be achieved, which is consistent with estimates from the geological record.

Abstract Environmental magnetism is widely employed for sediment provenance study, particularly in detrital‐dominated marine and lake systems. However, magnetofossils can complicate magnetic signals for accurate reconstructions of source‐to‐sink processes, yet their impact remains underexplored. The Bengal Fan, the largest submarine fan in the world, provides an ideal setting for studying sediment transport for its diverse sediment sources and transport pathways. Here, we combine magnetic and electron microscope analyses on a large set of surface sediments from the central and lower Bengal Fan to characterize magnetofossil contributions to magnetic properties. Results demonstrate widespread magnetofossil occurrence. Quantitative unmixing of isothermal remanent acquisition curves and first‐order reversal curve‐principal component analysis, assisted with direct transmission electron microscopic imaging of magnetofossils reveal that the southernmost region contains the highest magnetofossil contribution. Total organic carbon influences the magnetofossil abundance, while the magnetofossil morphology compositions are likely modulated by redox conditions impacting the diversity of magnetotactic bacteria species. Fuzzy c‐means clustering analysis identifies four sediment clusters. Cluster 1 derives from Indian Peninsula. Cluster 2 represents Himalayan–Burma–Indian mixtures, transported by the active channel with fining downstream. Cluster 4 and the southern part of cluster 3 show anomalous magnetic grain size trends linked to high magnetofossil contributions. The magnetofossil presence alters detrital magnetic records, showing high correlation between magnetofossil magnetization and bulk magnetic grain size parameter, thus complicates provenance interpretations. We demonstrate the combined use of rock magnetism and electron microscopy to quantify magnetofossil contributions for robust magnetic interpretation, especially in high detrital input regions where magnetofossils are often overlooked.

Abstract The India‐Asia collision generated the high topography of the northeastern Tibetan Plateau; yet the timing of its uplift remains debated. Reconstructing the deformation and uplift history of the Qilian Shan (northeastern margin of plateau) is therefore crucial for understanding the region's growth patterns and tectonic processes of the plateau. The well‐exposed, continuous Cenozoic sedimentary record in this area provides a detailed archive of the evolution of these active orogenic belts. This study presents new magnetostratigraphic data from the Baiyanghe section in the Jiuxi basin to constrain the timing of deformation and growth of the Qilian Shan. Our results date the depositional age of the Baiyanghe formation to ∼30–21.8 Ma (early Oligocene to early Miocene). Integrated stratigraphic analysis, paleocurrent data, and provenance results indicate that the Jiuquan basin likely initiated as a foreland basin and began receiving sediments from the Central Qilian Shan by the early Oligocene (∼30 Ma). Synthesizing these findings with prior research, we propose that the Qilian Shan has undergone three phases of tectonic deformation since the early Oligocene: initial uplift in the early Oligocene, northward propagation in the early Miocene, and intense uplift with outward expansion during the middle to late Miocene. Collectively, these findings elucidate the northward expansion of the Tibetan Plateau since the Oligocene.

A geological record of highly explosive eruptions from Sumatra (Indonesia)

Records of human activities in sediments from the old Yellow River estuary, China: Concentrations, sources, and ecological risks of organochlorine pesticides.

Environmental shifts and CaCO₃ variations in the sediment record of a dome-shaped alkaline fen in NE Poland: unravelling the timing and drivers of tufa onset, peak and decline