The Cenomanian–Turonian Greenhouse-Hothouse interval, encompassing Oceanic Anoxic Event 2 (OAE-2), represents one of the most intensively studied episodes of global environmental change in Earth History. However, despite extensive research, nitrogen isotope records from this interval remain geographically limited with a recent compilation highlighting that some continental margins were under-represented (e.g. one location and/or limited stratigraphic coverage per margin). This prevents a comprehensive understanding of the local and regional variability in nitrogen cycling in these Greenhouse to Hothouse conditions. This study provides new nitrogen isotope data, integrated with an extensive multidisciplinary dataset from multiple cores and outcrops across a single margin to provide new insights into the spatial and temporal variability in marine nitrogen cycling and marine primary producer community response. This study demonstrates that nitrogen isotope depletion in the Cretaceous Western Interior Seaway began in the Early Cenomanian (approx 97-98 Ma) , significantly earlier than previously recognized. The occurrence of δ15N-depleted organic matter, coupled with biomarker and palynological evidence for abundant (cyano-) bacteria, indicates enhanced diazotrophy in oxygen-deficient surface waters resulting in ammonium as the dominant form of fixed nitrogen in the photic zone. These conditions favoured low diversity eukaryote communities dominated by blooms in Prasinophyceae and Peridiniales (Dinophaceae), likely due to their ability to more efficiently assimilate ammonium through alternative nitrogenases enzymes. However, the observed δ15N values, even under broadly similar environmental conditions impacted by periodic volcanic events, can vary significantly over relatively short distances suggesting that, despite large-scale controls, local physiographic conditions significantly influenced the nitrogen cycle and related biological responses. This highlights the need to integrate data from multiple stratigraphic sections across a basin to fully capture the complexity of nitrogen cycle dynamics and associated ecological feedback during extreme climate events.
The Mazon Creek fossil beds of northern Illinois are famous for producing some of the world’s best-preserved fossils from the Pennsylvanian Period, about 307 million years ago. These fossils are found inside ironstone (siderite) concretions that formed rapidly around plants and animals as they were buried. Because of this unusual style of preservation, even soft-bodied creatures—like jellyfish, worms, and the mysterious “Tully Monster”—survive in remarkable detail. For decades, the Mazon Creek has been known for two distinct fossil communities: the plant-rich Braidwood association from nearshore environments, and the more marine Essex association full of jellyfish, shrimps, and other sea life. This study brings together the largest systematic sampling effort ever conducted at Mazon Creek—over 300 000 concretions collected from more than 350 sites—and compares them with new fossil discoveries from similar rocks across Illinois, Indiana, Missouri, and Oklahoma. We combine detailed descriptions of the preserved fossil assemblages, and show them to represent real, repetitive ecological groupings shaped by ancient environmental gradients. Our work also demonstrates that Mazon Creek-style fossil deposits are not unique to Illinois: similar environments and fossil communities occurred widely across the ancient U.S. Midcontinent as well as in Europe. These findings help us understand how rapid sea-level rise, coastal flooding, and tidal currents created the conditions that allowed such exceptional fossil preservation, offering a window into ancient ecosystems rarely preserved in the rock record.
The current economic and geopolitical scenario, once again, indicates straits as the focus of international headlines. These narrow passageways have an impact on the global economy, but foremost they are ecological, environmental and geological elements fundamental for the future of Earth and its environments. A better understanding of their role, evolution and peculiarities is needed.
Investigating the origins of large submarine landslides along seismically inactive continental margins is crucial in assessing tsunami risks in coastal regions. In this study, we use a combination of multi-channel seismic, seismic tomographic, oceanographic, expendable bathythermograph and remote sensing data along the eastern Demerara Plateau, located offshore French Guiana and Surinam. We aimed to image the deep-water processes responsible for the repeated landslides originating from a 350 km continuous head-wall scarp located along the plateau. Our comprehensive dataset enables us to expand the spatio-temporal coverage of water column observations, allowing the identification of a strong pycnocline between the Antarctic Intermediate Water and the North Atlantic Deep-Water. We also image a North Brazil Current associated eddy along the Demerara Plateau slopes. Within the seismically inactive context of the plateau, we propose that the interactions between water masses and sedimentary layers may trigger submarine landslides identified along the margin.
Outcrop exposures of sedimentary rocks preserve vital records of depositional processes and offer key insights into Earth's depositional history. Traditional field-based techniques, such as measuring bed orientations, sketches, and field photography, have long been used to document stratigraphic patterns, while modern approaches now leverage high-resolution panoramas and drone-based photogrammetry to quantify and geolocate measurements. Although Digital Outcrop Models (DOMs) derived from UAVs (drones) markedly improve our ability to capture and interpret spatial details, these modern approaches, when used to generate 2-D stratigraphic correlation panels, are still challenged by distortions caused by outcrop perspective and structural deformation. To accurately constrain stratigraphic reconstructions derived from DOMs, calibrated field data is necessary to corroborate these observations with thicknesses, length scales, and lithologies. Here, we present a method to correct stratigraphic interpretations from DOMs for structural overprint and outcrop perspective using field-based paleocurrent and strike-and-dip measurements to produce geometrically accurate surface length, height, and dip in stratigraphic correlation panels. We demonstrate this method on Cerro Cazador, a 15 km-long outcrop transect in Patagonia, Chile, recognized as containing continental shelf and shelf-margin sedimentary deposits. By systematically comparing three data projection strategies: no correction, a single correction, and a novel multi-correction workflow that applies localized adjustments to distinct structural regions, we show that the multi-correction method yields depositional geometries consistent with expected stratigraphic patterns (e.g., flat topset and bottomset deposits, sloping foresets, shelf-edge trajectories). These findings underscore the need for incorporating field-based calibrations into drone-derived models to accurately capture depositional patterns in geologically complex settings and highlight important implications for quantitative sedimentary analysis across diverse outcrop environments.
This study aims to quantify the response of carbonate producers to eustasy, tectonics and climate changes in intracontinental basins. We examined Middle to Late Jurassic carbonate systems (Aalenian to Oxfordian, c. 175 to 155 Ma) of the northern Aquitaine Basin (France). The detailed description of 67 outcrops and the large-scale correlation of 21 transgressive-regressive cycles allows for reconstruction of various evolving depositional environments. A westward dipping carbonate ramp developed from the Aalenian to Early Oxfordian, replaced by a rimmed-platform during the Middle to Late Oxfordian. Accommodation space indicates long wavelength flexures, locally disrupted by normal fault activity, that could relate to the extension of the western Tethys margin or the opening of the North Atlantic Ocean. The Aalenian and Callovian to Early Oxfordian display low carbonate accumulation rates (≈ 10 m Myr−1) that result from (1) limited accommodation space during the Aalenian, possibly caused by the “Mid Cimmerian” uplift, and (2) the development of a wet climate during the Callovian to Early Oxfordian, which enhanced continental weathering and siliciclastic input. The Late Bajocian, Bathonian and Middle to Late Oxfordian are stages of high neritic carbonate production, ranging from 25 to 70 m Myr−1 on the shallow platform. The thriving of ooid, photozoan and ‘Micrite and Microbial’ (M)-factories was favored by a dry climate disturbed by short episodes of intense precipitation in the Tethyan realm, leading to oligo-mesotrophic waters and calcium carbonate supersaturation. The M-factory flourished in lagoons throughout the Middle Jurassic and Oxfordian, independent of climate and tectonic upheavals.
Pre-salt carbonate reservoirs of the Santos Basin, eastern Brazilian margin, contain giant hydrocarbon accumulations, with reworked deposits constituting the highest-quality reservoirs across several oilfields. Despite their importance, the diagenetic evolution of the lacustrine reworked deposits remains poorly understood. This study investigates the diagenetic patterns and controls on reservoir quality of the reworked deposits of the Aptian Barra Velha Formation through integrated petrography, fluid inclusions, petrophysical, and micro-computed tomography (µCT) analyses. Reservoir petrofacies were characterized according to the main controls on porosity evolution, which comprised: dolomitization, silicification, and compaction. Dolomite and silica precipitation took place in a multi-phase scheme, as evidenced by paragenetic relations, and by fluid inclusions data showing heterogeneous entrapment with wide homogenization temperature ranges. Blocky dolomite precipitated both before and after compaction, while late saddle dolomite formed during deeper burial. At least two eodiagenetic silicification phases occurred, followed by late diagenetic coarse quartz precipitation. The relative timing between compaction and eodiagenetic dolomite, silica and calcite precipitation fundamentally controls reservoir quality in the reworked rocks. Mesodiagenetic and hydrothermal processes had subordinate influence on porosity evolution. Reworked rocks show greater susceptibility to compaction than in situ rocks, owing to the more stable crystalline framework of the latter. This study provided essential insights to improve the reservoir characterization and optimize the development strategies for the pre-salt accumulations, as well as for understanding the diagenetic evolution of intraclastic lacustrine carbonates worldwide.
Traditional sequence stratigraphy has largely linked submarine fan formation to relative sea-level changes during lowstand conditions. However, these interpretations may oversimplify the system's complexity by overlooking the contributions of other external and internal controls, such as sediment supply variability, tectonics, and autogenic dynamics. This study employs Lobyte3D, a reduced-complexity stratigraphic forward model, combined with genetic algorithm optimization, to systematically explore the impact of extrinsic factors, including sediment input, basin confinement, and oscillation periodicity on fan development. The results demonstrate that similar depositional architectures can emerge under diverse conditions. Sensitivity analyses reveal that depositional features traditionally linked to lowstands, such as lobate geometries and channelized sediment pathways, can also form under highstand or transgressive conditions. These findings challenge the single-cause scenario interpretative paradigms in sequence stratigraphy by demonstrating the equifinality of depositional processes, emphasizing the need for multivariate and probabilistic approaches in practical predictions of fan development.
Mixed carbonate-siliciclastic depositional systems are enigmatic with unique stratal patterns that are poorly understood and poorly represented in models that do not adequately represent complex tectonic, glacioeustatic, and sediment sourcing and routing controls. The Pennsylvanian Strawn Group, Eastern Shelf, Permian Basin, Texas, USA, is composed of a highly heterogeneous mixed ramp to proximal-shelf deltaic strata ideal for investigation of mixed system evolution in an icehouse regime. Analyses of Upper Strawn wireline logs and drill cores along a transect spanning three oil and gas fields in King County reveal a wide variety of facies attributed to many depositional environments, including ripple to trough cross-bedded, sand-dominated to heterolithic, commonly bioturbated sandstones (tidally modified delta and associated subenvironments), ooid grainstones (shallow marine shoal), phylloid algal bafflestones/boundstones (bioherm buildup), skeletal-peloidal wackestones/packstones (carbonate-dominated shallow marine low-energy), shaly carbonate and siliciclastic mudstones (offshore/deepwater), and paleosols (terrestrial). The facies and their stacking patterns have few shared characteristics between the fields, and elements of each field challenge traditional models for mixed systems. This heterogeneity can be explained with a modified depositional model ICCE-T (icehouse carbonate-clastic evolution in tectonically influenced systems model), which is tuned for icehouse mixed systems deposited in tectonically active regions. The ICCE-T model invokes differential topography, incompletely filled highstand accommodation, and high-amplitude, high-frequency sea level oscillations as mechanisms producing increasingly convoluted bathymetry through time. As sediments do not fill all accommodation within a sequence across the study area, complex topography is maintained, and positive topographic features are abandoned, reused, or reactivated at different relative sea levels. This model allows for significant spatial variation in depositional systems and better explains patterns observed in the study area.
The area now known as the Barents Shelf region was strongly impacted by the End-Permian Mass Extinction and a fundamental reorganisation of source-to-sink systems along the northern margin of Pangaea. Here we integrate new sedimentological, ichnological, chemostratigraphic, and provenance data from western Spitsbergen, collected at Festningen, Reinodden, and the Sørkapp-Hornsund High (Hornsundneset, southern Spitsbergen), to reconstruct the timing and drivers of Early Triassic basin evolution. At Festningen and Reinodden, the sharp but conformable transition from Permian spiculitic Kapp Starostin Formation strata to siliciclastic mudstones and sandstones of the Lower Triassic Vardebukta Formation coincides with the onset of the negative δ13Corg excursion. The Vardebukta Formation preserves seven stacked transgressive–regressive packages within an Induan-age interval of ca 1.2 to 1.6 Myr. Individual cycle durations (ca 177 to 225 kyr) are incompatible with a single dominant Milankovitch component and instead suggest bundling of orbital frequencies and/or strong autogenic modulation of accommodation and sediment supply. On the Sørkapp-Hornsund High, a 75 Myr hiatus above Mississippian continental deposits is terminated by a 10 to 15 cm thick bentonitic tephra bed linked to the Siberian Traps Large Igneous Province. This is overlain by Induan-age polymictic alluvial-fan and ephemeral braided-river conglomerates (Brevassfjellet Beds), on which limited but recurrent vegetation cover developed. Detrital-zircon age spectra from the conglomerates closely match published data from the Vardebukta Formation at Festningen and the Induan-age Parish Bjerg Formation in Greenland, indicating a shared north Greenland Caledonian source and direct sediment routing during the latest Permian and earliest Triassic. These continental conglomerates are capped by fossiliferous shallow-marine limestones of Dienerian age, which are then overlain by the coarsening-upward shelfal succession of the Vardbukta Formation. The timing of Dienerian flooding of the Sørkapp-Hornsund High is not aligned with any individual transgressive-regressive package in the Vardebukta Formation, implying that local tectonic subsidence of a promontory-like high, rather than eustatic rise, governed its transgression. This research refines the palaeogeographical and tectonostratigraphical evolution of the northern margin of Pangaea during the latest Permian and earliest Triassic.
In recent decades, the academic publishing world has aimed to transition from a paywall-dominated system to Open Access (OA). While OA seeks to make scientific knowledge freely available, the sustainability of current models remains debated. This article examines the three main OA publishing routes (Green, Gold and Diamond) and argues that, while Green OA offers short-term accessibility benefits, it perpetuates dependence upon for-profit publishers and fails to address systemic inequities. Gold OA shifts financial responsibility to authors through high article processing charges (APC), further exacerbating disparities. In contrast, Diamond OA, driven by community-led initiatives and supported by open infrastructures, eliminates APC, ensures equitable access, and allows authors to share their work freely. We highlight successful examples in geosciences and discuss the cultural and structural barriers that still hinder adoption, despite Diamond OA representing the most sustainable, fair and accessible long-term model for scholarly publishing.
This study provides new insights into the Siderolithic Group, a 158 m -thick sedimentary succession deposited within a regionally extensive karstified unconformity spanning tens of square kilometres. This unconformity marks the Cretaceous-Paleogene boundary, with a stratigraphic gap of about 94 Myr, ranging from the Lower Cretaceous (Barremian–Aptian) to (likely) the Bartonian (Eocene). Using borehole data from the GEo-02 geothermal exploration well in the Geneva Basin, our study integrates petrography, mineralogy, geochemistry, and petrophysical analyses of 139 samples to reconstruct the evolution of this complex depositional system. Six sedimentological subunits were identified, representing distinct phases of karst evolution, from initial formation to infill and subsequent diagenesis. Variations in gamma ray values suggest fluctuating water levels within the karst system, while the heterogeneous distribution of quartz grains indicates detrital sediment input from both aeolian and fluvial sources. The mineral assemblage, dominated by siderite, chlorite, and kaolinite, reflects diagenetic processes under reducing conditions, with siderite facilitating kaolinite chloritisation in the presence of quartz. Geochemical data and clay mineral data indicate humid climatic conditions during deposition. The Siderolithic Group is inferred to be of Bartonian age based on biostratigraphic constraints from analogue deposits on the Swiss Plateau, suggesting its deposition during the Middle Eocene Climatic Optimum (MECO). This study provides one of the few continental records of the MECO in Western Europe, recording high mercury content possibly related to the flare-up in Neotethys subduction zone volcanism.
Normal fault growth models are largely based on the geometric relationship between fault displacement and length, and the seismically imaged record of accommodation development contained within syn-rift strata. However, it is possible to infer variations in the style of normal fault growth across poorly exposed faulted margins through the analysis of the sedimentology and stratigraphic architecture of the associated syn-rift deposits. Here, we analyze the stratigraphic and along-strike variability of normal-fault controlled deltaic systems to infer the evolution of their related basin-margin fault system, for which the geometry and displacement patterns are poorly constrained. The Crati Basin (southern Italy) contains Pleistocene syn-rift deposits exposed in the hangingwall of a c. 45 km-long normal fault system. We show that during an early extensional phase, shelf-type deltas were deposited along the entire strike length of the fault system, suggestive of relatively shallow water depths and early establishment of fault length. In contrast, a later extensional phase resulted in the deposition of Gilbert-type deltas at the center and towards the northern end of the fault system, whereas shelf-type deltas persisted near the system southern tip; this stratigraphic evolution records the transition to a period when the fault system growth was characterized by displacement accumulation rather than lengthening. We show that the detailed sedimentological and stratigraphic analysis of exposed ancient deltaic systems can be used to discriminate between models for normal fault growth and that, conversely, displacement and accommodation variations along normal faults control the styles and depositional architecture of deltaic systems in extensional settings.
Detailed knowledge of the lithostratigraphy of unconsolidated sediments is essential for many scientific and industrial applications. Although drill cores provide lithological and petrophysical information (e.g., lithofacies, permeability, consolidation), core recovery is time- and resource-intensive. In contrast, flush drillings are faster and less expensive but lack detailed geological context. Therefore, combining the advantages of both methods can significantly enhance subsurface investigations while reducing reliance on costly core drillings. This study explores the use of unsupervised machine learning to build data-driven stratigraphic models from standard petrophysical and geochemical wireline logging data. Specifically, it applies dimensionality reduction (UMAP) and hierarchical clustering to identify distinct lithofacies types. The method was tested on datasets from the former Rhine Glacier area in Germany, including one core-controlled well and a nearby flush-drilled borehole. The developed workflow predicted the lithofacies of the core-controlled well with ~76% accuracy, capturing both major stratigraphic units and finer internal features, directly linking them with the geology identified at the drilled site. This allows linking the reconstructed lithology of the core-controlled well with the flush-drilled well. The results demonstrate that unsupervised machine learning can significantly improve stratigraphic models of unconsolidated Quaternary sediments using wireline logs, with minimal dependence on core data.
Mountain areas are very sensitive to climate change, which has led to changes in natural hazards that are often linked to disturbances in the cryosphere. In this context, changes in snowfall characteristics and snow cover affect avalanche hazards. Long-term variability can be reconstructed by using historical archives, tree rings and, more rarely, lake sediments. The latter approach is based on the identification of lake sediment consisting of poorly sorted, coarse sediments in a fine matrix, which are often associated with terrestrial organic debris. This sediment is generally brought to the lake within large amounts of wet snow, or via ‘drop stones’ when the ice melts if the avalanche takes place on a frozen surface. Here, we study two high-altitude lakes (Melu and Capitellu) in the Restonica Valley in Corsica, an area where systematic records are lacking, to reconstruct signals related to such large wet snow flows on a millennial scale. The analysis of several sedimentological and geochemical markers enables the characterization of wet avalanche deposits in the two lakes, as well as turbidite-type facies linked to historical earthquakes in Corsica. Age models based on short-lived radionuclides and radiocarbon also make it possible to reconstruct two avalanche chronologies covering 600 and 1750 years in Melu and Capitellu Lakes, respectively, which show similar temporal variations. A comparison with the only long-term chronology available in the Alps (Lake Muzelle, Ecrins) also reveals synchronicity in the secular variability of avalanches, suggesting a common forcing between Corsica and the Alps. Human observations and accident records from recent decades, and snow and weather release conditions reconstructed from a hydrological modeling scheme confirm the ability of the lacustrine avalanche sedimentary method to document local wet snow avalanche activity. The proposed methodology, which is based on paleolimnological studies, may therefore be useful, alone or combined with other avalanche data sources, for tracking changes in avalanche activity and related risks in mountainous areas.
Sequence stratigraphy in fine-grained successions is often challenging with traditional datasets, and in such intervals, chemostratigraphy is increasingly used to facilitate interpretations. In this study, we present an example from mudstone units of the Horn River Group (Northwest Territories, Canada), which provide a local record of Middle to Late Devonian marine conditions. The dataset comprises geochemical composition data from X-ray fluorescence (XRF), mineralogical data from X-ray diffraction (XRD), wireline logs, total organic carbon (TOC) profiles, and lithological core and thin section descriptions. We first focus on a mudstone core with high-resolution thin-section and geochemical results, enabling the evaluation of chemostratigraphic signatures associated with surfaces and systems tracts in the Horn River Group. By employing chemostratigraphic proxies for terrigenous sediment supply and proportion of biogenic silica, sequence stratigraphic analysis is extended to three cores and five outcrops lacking extensive thin section coverage. Six complete transgressive–regressive (T–R) sequences are identified and correlated in the Horn River Group, comprising higher-resolution cycles in relative sea-level and sediment supply, which are superimposed on previously identified larger-scale sequences. The sequence stratigraphic framework presented illustrates the local balance between relative sea-level rise and sediment supply along the northwestern margin of Laurentia during the Eifelian to the Frasnian. Moreover, this study demonstrates the utility of integrating chemostratigraphic proxies with sedimentological results as a means of sequence stratigraphic interpretation and correlation in mudstone intervals.
Grain size and shape significantly influence sediment transport and deposition, so accurate characterization is essential for understanding depositional dynamics. Biogenic carbonate grains, such as skeletal fragments, exhibit irregular morphologies that challenge traditional, single-diameter-based size estimates. To better characterize these non-spherical grains, two- or three-dimensional analyses are required. Micro-computed tomography (micro-CT) offers high-resolution, three-dimensional models of individual grains, enabling accurate quantification of volume, projection area, and shape. However, the high cost and limited accessibility of micro-CT in standard sedimentology labs hinder its widespread use. This study compares caliper measurements, sieve analysis, static image analysis (SIA), and dynamic image analysis (DIA) against a micro-CT reference dataset for sand-sized skeletal carbonate grains. We assess the accuracy of each method in capturing key grain properties relevant for hydrodynamic and geomechanical modeling, including volume, maximum projection area, nominal diameter, and Corey shape factor. We also evaluate the potential of predicting a grain’s third dimension based on its maximum projection dimension, as measured through SIA of loose grains and thin sections. A regression model comparing SIA to known micro-CT values yields 72–78% accuracy. Results show that methods relying on axial dimensions systematically overestimate volume and maximum projection area. DIA tends to oversimplify grains as spherical, while SIA on thin sections may underestimate grain size due to slicing orientation effects. This study highlights the advantages and limitations of various measurement techniques and underscores the importance of selecting appropriate grain measurement techniques in sedimentological research.
Removing carbon dioxide from the atmosphere is important in minimising the impact of anthropogenically-induced climate change. Anthropogenic geomaterials, such as slag and cement, can be utilised in an engineered context for mineralising CO2. However, such anthropogenic geomaterials, typically waste products, were usually deposited on the land surface and left to passively mineralise CO2, resulting in the formation of anthropogenic carbonates. In this study, we document anthropogenic carbonates from a suite of locations across Scotland and Northern England, and use stable carbon and oxygen isotopes to show that they are formed from atmospheric CO2. Carbonates which formed in subaqueous settings recorded δ13C values of -25 to -28 ‰ and δ18O values of -15 to -20 ‰, which indicate rapid precipitation from atmospheric CO2. Subaerially-formed samples recorded slightly higher delta values, indicating partial re-equilibration of the dissolved atmospheric CO2 towards expected equilibrium values with ambient conditions before precipitation. The broad suite of samples from multiple locations across Scotland and Northern England show anthropogenic carbonates are more common than previously realised, which demonstrates their effectiveness in passive drawdown of atmospheric CO2.
Earthquakes along the Ring of Fire are considered among the most destructive on Earth. In Indonesia, 19 earthquakes with a magnitude greater than 7.5 have been recorded in the last 20 years, all causing devastating catastrophes. As witnessed by the 2018 magnitude 7.5 Palu earthquake, extensive areas on the island of Sulawesi are particularly prone to seismic hazards due to the converging Australian, Eurasian, Pacific, and Philippine tectonic plates. However, instrumental records show that extensive areas in the central part of the island appear to be seismically quiet in the last century regarding larger magnitude ≥ 7 earthquakes. Lake sediments are excellent sentinels for environmental changes occurring in its near surroundings, hence they serve as a natural archive for events, including seismicity, thus allowing the investigation of the notion of absence of large-magnitude earthquakes. In 2022, we conducted a geophysical and high-resolution bathymetric survey at Lake Poso to provide insight into seismic activity in Central Sulawesi beyond the instrumental record. The survey allowed us to image large subaquatic slides and lake-bottom offsets, which indicate high-intensity earthquakes, possibly related to the presence of an active local fault system. Our paleoseismological assessment suggests a recurrence of large-magnitude earthquakes every 1600 ± 1450 years over the last 11,000 years. Based on our subsurface observations, the evolution of the tectonic Poso basin indicates that large-magnitude earthquakes are also possible in this region. The consequences of such an event may have devastating consequences for local populations and infrastructures in Sulawesi.
Conventionally, geologists have regarded mudstones as deposits formed through suspension settling in environments located at the terminus of sediment transport pathways, with the sediment sourced from a mix of detrital inputs into the basin and in situ production within the basin. However, mudstones are sedimentologically enigmatic as they are characterized by intricate small-scale features. Analysing mudstones with the typical techniques used for coarse grained siliciclastics does a disservice to the intricacies of these deposits. Grains, pores, and depositional fabrics within these rocks are not visible in hand sample, and often not even at the petrographic scale. Study of these features, at appropriate scales, can generate valuable insights into the physical and chemical conditions of their deposition. Along with analytical techniques, the conventionally held interpretations of these rocks are out of date. New insights into the origins and composition of grain components reveal significant variability, indicating these deposits are much more complex than traditionally understood. As a result, historical nomenclature and interpretation paradigms have undergone significant revision. However, there is still more research needed to fully address the challenges of mudstone description, classification and interpretation. This paper presents digestible discussions of changes in mudstone paradigms, the most effective practices consistent with modern understandings of mudstones, and considers areas that merit further consideration. Ideas presented herein are aimed at all those interested in mudstones, but is primarily meant for those new to the challenge of conducting mudstone analyses. Herein we recognize several preferred practices that have gained consensus in the literature, these include: (1) clearly defining common historical terms such as ‘clay’, ‘silt’, ‘bed’, and ‘shale’ depending on modern chosen usage; (2) outlining the transportational (i.e., functional) grain size of the deposit, as many constituents may be transported as amalgamated clasts; (3) clearly defining if reported mudstone composition is based on transported or apparent grain size (i.e., individual grain measurements); (4) thin section preparation methods and their integration with other complementary analytical techniques. As well, we discuss: (1) the use of both petrographic trace fossil analysis and microfacies analysis; (2) complex depositional mechanisms, beyond suspension settling, that lead to the accumulation of fine-grained deposits; and, (3) the interaction of several variables involved in accumulating organic-rich deposits. Ultimately, when embarking on mudstone analysis, one must first decide what question they are trying to answer. This will dictate the approach used, and if the focus is on the intricacies of grain size, composition, or depositional fabric.
