Depositional setting and facies of the late Holocene sediments at the Atrato River Delta, Colombia

Provenance and uranium source of the lower cretaceous sedimentary rocks in Northern Sichuan Basin: evidence from sedimentary facies analysis and detrital zircon U-Pb geochronology

The timing and sedimentary facies of the early Khvalynian stage in the Lower Volga Region (Northern Caspian Lowland)

Crushed oyster shells reduce mud shrimp (Upogebia major) populations and enhance Manila clam (Ruditapes philippinarum) recruitment in Korean tidal flats.

The impact of volcanic eruptions on the sedimentary filling process of a rift basin is not only the premise for reasonably explaining the binary filling characteristics of volcanic and sedimentary rocks in a rift basin, but also the key geological basis for hydrocarbon reservoir prediction. Based on a large amount of three-dimensional seismic, logging and lithology data, we estimated the volcanic eruption period, volcano distribution and sedimentary facies distribution in the Changling faulted depression in the Songliao Basin. Then we assessed the influence of volcanic eruptions on the type of sedimentary fill, the distribution of sedimentary facies and the spatial stacking of sedimentary strata. This study revealed that during the rapid rifting stage, the Changling faulted depression experienced four phases of volcanic eruptions. The lithology, scale and spatial distribution of volcanoes were directly related to the activity and location of the basement faults in this area, reflecting the control that basement fault activity had on the volcanic eruptions. The stacking form and eruption scale of volcanic rocks played a substantial role in the paleogeomorphology of the basin, which in turn affected the form of the source channel in the basin, causing changes in the sedimentary facies type, spatial distribution and changes in spatial overlapping patterns of sediments. Moreover, the differences in location and delivery methods of volcanic debris complicate the structure and reservoir properties of the sandstone.

Sedimentary facies of the Upper Jurassic Kolar Dungar Member of the Bhadasar Formation, Jaisalmer Basin, Western India

Abstract Biological productivity, shaped by climate and environmental factors, is critical to climate feedback mechanisms and the global carbon cycle. This study investigates the measurement of six phytosterols (β‐sitosterol, stigmasterol, campesterol, dinosterol, epi‐brassicasterol, and 24‐methylene cholesterol) from core MD01‐2414 in the central Okhotsk Sea, covering the past 1.5 million years (Ma). These sterols serve as proxies for terrestrial and marine productivity in the central Okhotsk Sea and northeast Siberia. Sterol concentrations reflect global glacial/interglacial cycles between 1.2 and 0.6 Ma, with higher and lower values during interglacial and glacials intervals, respectively. X‐ray fluorescence (Ba/Ti) and total organic carbon/total nitrogen (TOC/TN) ratios indicate shifts in marine and terrestrial sources, confirming biological productivity as a key driver of sterol deposition. Sterol fluxes, combined with sea surface temperature records from the northwest Pacific and sea ice proxies from the Bering Sea, reveal an extreme cold interglacial (Marine Isotope Stage, MIS 23) and prolonged glacial conditions during MIS 22, which stressed both terrestrial and marine ecosystems. Increased sea ice expansion during this period likely fostered North Pacific Intermediate Water formation, reducing upwelling and CO 2 exchange between bottom waters and the atmosphere. Integration of sterol data with regional records, including pollen, temperature, and sedimentary facies from Lake El'gygytgyn, highlights a warming event at the onset of MIS 32, peaking in late MIS 32. This warming precedes the “super‐interglacial” MIS 31 and coincides with maxima in boreal and austral summer insolation, underscoring its significance in regional climate evolution.

ABSTRACT The Lower Cretaceous Yamama Formation of southern Iraq represents a key carbonate reservoir within Iraq and the Middle East, yet its complex depositional facies architecture and diagenetic alterations present challenges for predicting reservoir quality. This study integrates well‐log interpretation, detailed description of about 400 m of core intervals, petrographic analysis, fluid‐inclusion microthermometry, and stable‐isotope (δ 13 C, δ 18 O) geochemistry from several oilfields to determine the controls on reservoir heterogeneity. Fourteen depositional facies are recognized across a W–E‐trending, slightly steepening homoclinal ramp. These vary into four reservoir (YRA–YRD) and four nonreservoir (B0–B3) units. Reservoir intervals consist mainly of shoal grain‐supported peloids and ooids and Lithocodium–Bacinella reefal facies, whereas mud‐supported lagoonal and middle‐ramp facies form permeability barriers. Diagenetic processes exerted strong control on reservoir quality evolution. Early marine rim and scattered calcite cements preserved interparticle pores in the grain‐supported limestone facies, whereas burial equant calcite sourced by stylolitization of the host limestones reduced porosity. The precipitation of pore‐filling kaolin and saponite in the mud‐supported limestone facies limited porosity. Saponite is suggested to have been formed from alkaline brines developed under restricted, evaporative conditions. The formation of kaolin is attributed to the migration of Al 3 ⁺‐bearing brines charged with organic acids along stylolites, during tectonic compression of the basin. The presence of framboidal and euhedral pyrite indicates a diagenetic shift from microbial to thermochemical sulfate reduction. TSR suggests that brines were thermally evolved and migrated upward from the underlying, hotter evaporitic formation, such as the Upper Jurassic Gotnia. Fluid‐inclusion microthermometry in blocky calcite in moldic/vuggy pores indicates homogenization temperatures of 85°C–140°C (exceeding the maximum burial temperature, ∼116°C) from brines composed of NaCl–KCl–H 2 O, with total salinity of 10 wt.% NaCl eq. and δ 18 O_VSMOW values of +4‰ to +8‰. These values, along with depleted δ 18 O_VPDB (−6.9‰ to −5.6‰), suggest precipitation from evolved basinal fluids related to stylolitization. The occurrence of saddle dolomite in close association with euhedral pyrite suggests precipitation from brines that were affected by TSR. Four third‐order depositional sequences bounded by Type 2 sequence boundaries are recognized; regressive shoal and reefal facies formed the reservoir units, whereas transgressive, mud‐dominated facies are impervious. The integration of depositional facies, diagenesis, and sequence stratigraphy indicates that depositional facies architecture and fluid migration allow better understanding of the reservoir heterogeneity in the Yamama Formation.

Abstract Planamandibulus nevadensis n. gen n. sp. is a newly discovered exceptionally preserved Laurentian phosphatocopid crustacean described from the upper Windfall Formation (Furongian, Stage 10) in Nevada. Planamandibulus nevadensis has closest affinity with the Baltic and Avalonian taxon Cyclotron. Its occurrence in sedimentary facies associated with dysoxia on the Laurentian paleocontinent fills in a gap in the global distribution of phosphatocopid crustaceans, facilitating a paleoenvironmental synthesis of this Cambrian group. We assess 75 taxa from nine paleocontinental areas spanning Cambrian stages 3 to 10 (~521–486.9 Ma). Comparison of these data with paleoclimate model simulations suggests that phosphatocopid distribution is explained partly by biogeography and ocean temperature patterns. Dabashanella species (e.g., D. hemicyclica Huo et al., 1983) are found across the low paleolatitude (<35°) paleocontinents of East Gondwanan (Australia), South China, and the central Asian terranes, spanning marine shelf carbonates to deeper marine black shale lithofacies, but are absent from mid- and high-paleolatitude sites, suggesting a warmer water preference. A similar warm-water preference is inferred for endemic taxa (e.g., Ulopsis , Parashergoldopsis ) of East Gondwana, and perhaps for the newly described Laurentian Planamandibulus. By contrast, the mid- to high-paleolatitude paleocontinents Baltica and Avalonia are characterized by Veldotron , Cyclotron , Bidimorpha , Waldoria , Vestrogothia , Falites , and Trapezilites species, which occur in deep-shelf, cooler-water settings, typically below storm wave base. Hesslandona species sensu lato occur in mid-depth (likely above storm-wave base) warm tropical marine waters but are more typically found in deeper shelf and cooler waters in mid to high paleolatitudes. Phosphatocopids are also associated with sedimentary deposits characteristic of low environmental oxygen concentrations; this is emphasized by a peak in occurrences in the Guzhangian (Miaolingian) and Paibian (Furongian) stages, around the interval of the Steptoean Positive Carbon Isotope Excursion (SPICE) and its associated expansion of anoxic water masses onto shallow marine shelves. Our data compilation and data–model comparison support the environmental preference of phosphatocopids for low-oxygen, but not anoxic, water masses, and the new occurrence of Planamandibulus is consistent with this pattern. UUID: http://zoobank.org/f136f8bf-1ccf-46b0-8980-b88be8f9603d

Abstract. This study investigates the lithostratigraphy and palaeoenvironmental conditions of Holocene sediments from five boreholes in the Lower Central Plain of Thailand, with a focus on ostracod assemblages and sedimentary facies. Lithostratigraphic analyses identified five lithologic units belonging to two distinct facies representing tidal–intertidal and prodelta environments. Ostracod analysis identified 15 species, representing genera found in the Indo-Pacific and South China regions, including Neocyprideis, Sinocytheridea, Propontocypris, Hemicytheridea, Keijella, Neomonoceratina, Aglaiocypris, Lankacythere, Cytherella, and Stigmatocythere. Ostracods recovered from tidal–intertidal facies suggest transportation from shallow marine environments to tidal channels, while the greater diversity in prodelta facies indicates a more stable and favourable environment. Neocyprideis agilis was found abundantly in the samples, marking the oldest known record of this species in the South China Sea during the Late Holocene. The facies succession is characterised by a fining-upward trend, reflecting a shift from Lower–Middle Holocene tidal channels and intertidal flats to a Late Holocene prodelta system. These findings clarify the depositional history of the Lower Central Plain, demonstrating how tidal and marine processes shaped a dynamic, tide-dominated palaeoenvironment throughout the Holocene.

Abstract. Sedimentary rocks can provide information about the Earth paleoenvironment and are studied extensively to understand the causes and consequences of global climate changes in deep time. They facilitate long-time perspectives that constrain climate models and provide analogues for how Earth systems may respond to, and recover from, intervals of profound environmental change, including projected anthropogenic change. The Norwegian Svalbard archipelago offers an extensive Phanerozoic stratigraphic record that reflects the geological evolution of the northern flanks of continental assemblages that include Laurentia, Eurasia, and Pangea. Svalbard's Phanerozoic sedimentary and paleoclimatic archive is controlled largely by Svalbard's overall northward plate-tectonic motion from equatorial to high latitudes but also by regional to local formation of topography and basins in response to long-term plate reorganization, as well as the near- and far-field influence of large igneous province activity on the tectono-stratigraphic and paleoclimatic development. Various sedimentary and geochemical proxies, such as bentonite beds and carbon isotope excursions associated with the far-reaching environmental effects of the Siberian Traps, the High Arctic Large Igneous Province, and the North Atlantic Igneous Province, are present in Svalbard's near complete geological record. As such, Svalbard is unique in that these and numerous other global environmental perturbations are recorded within a relatively restricted study area, with most of the key events preserved and recorded in easily accessible drill cores and well-exposed outcrop sections. Here we review deep-time paleoenvironmental and paleoclimate research in Svalbard by summarizing 148 peer-reviewed scientific articles. The review builds on the well-established tectono-stratigraphic and lithostratigraphic framework, as well as state-of-the art environmental reconstructions, to provide insights into the Earth system during the Phanerozoic northward drift of Svalbard and the many major biotic crises in the geological past. We focus on globally significant events including (i) the expansion of Devonian vegetation, (ii) the Carboniferous–Permian response to icehouse conditions during the Late Paleozoic Ice Age (LPIA), (iii) the End-Permian Mass Extinction (EPME) and the subsequent Triassic recovery, the (iv) Carnian Pluvial Episode, (v) Jurassic–Early Cretaceous climate perturbations including the Volgian Isotopic Carbon Excursion (VOICE) and the Aptian Ocean Anoxic Event 1a (OAE1a), and (vi) the Paleocene–Eocene Thermal Maximum (PETM). We present and synthesize existing core and outcrop data that preserve biological and geochemical proxies and climate-sensitive sedimentary facies that reflect environmental change in terrestrial and marine settings. Finally, we discuss the Phanerozoic climate recorded in Svalbard and its role in providing high-latitude calibration points for several global paleoclimate events to provide a higher-latitude perspective to complement the dominance of mid- and low-latitude locations and datasets in the literature.

Organic pores serve as crucial storage spaces for shale gas, whose morphology and structure vary significantly among different types of organic matter, directly influencing the storage and seepage capacity of shale gas. The Upper Permian shale in the Western Hubei Trough formed in diverse sedimentary facies and has undergone multiple geological activities, resulting in strong heterogeneity of organic pores across different strata and regions. To figure out the heterogeneous characteristics of organic pores and the forming reason, the occurrence state of organic matter, pore morphology, and structural parameters (pore size, specific surface area, pore volume, and fractal dimension) of the Upper Permian shale in Western Hubei, have been discussed in detail, based on the data of field emission scanning electron microscopy and low-temperature nitrogen adsorption experiments conducted on the extracted organic matter. On this basis, fractal dimension theory was applied to discuss the heterogeneity of organic pores in different layers, and the reason for heterogeneity has been analyzed in detail. The results indicate that the occurrence mode of organic matter in different layers presents various characteristics: in the Gufeng Formation, the organic matters distribute primarily dispersed in flocculent state; at the bottom of Wujiaping Formation, they occur as isolated individuals, while the organic matters turn into discontinuous laminated distribution in the middle and upper Wujiaping Formation; in the Dalong Formation, the organic matters show continuous parallel banded distribution. Moreover, the morphology and structural parameters of organic pores exhibit obvious changes from the Gufeng Formation to the Dalong Formation: (a) the pore morphology shows the changed trend as extremely complex-simple-complex; (b) the specific surface area and pore volume follow the trend as large-small-large; (c) the pore size distribution displays in the pattern of bimodal-unimodal-bimodal; (d) the data of fractal dimension show the variation of high–low–high. Overall, the various sedimentary environments during the Upper Permian shale depositional period determined the differences in organic sources, which dominated the heterogeneity of organic pores in shale. These data clarify the development and variation characteristics of organic matter pores under different depositional environments, providing a theoretical basis for shale gas exploration and development during the transition from marine to marine–continental facies.

Accurate prediction of reservoir porosity is fundamental for hydrocarbon resource evaluation and development planning, yet traditional methods struggle with spatial heterogeneity and complex geological structures. This study proposes a hybrid deep learning framework that integrates U-Net++ with an attention-guided graph neural network to simultaneously capture multiscale well logging data features and non-Euclidean spatial dependencies. The model incorporates dense skip connections, deep supervision, and dual-channel attention mechanisms to enhance both local feature extraction and global topological modeling. Experiments on a real-world continental sedimentary basin dataset (26 wells, ~40 km2) demonstrated that the proposed method achieved a mean squared error (MSE) of 4.62, mean absolute error of 1.24, coefficient of determination (R2) of 0.912, and structural similarity index measure of 0.831, representing a 14.9–38.7% reduction in prediction errors relative to widely used deep learning and graph-based baselines. Statistical tests (p<0.05) confirmed the significance of the improvements. The model was particularly robust in extreme porosity ranges (>16% or <8%), reducing errors by 23.1–42.6% compared to U-Net++. Ablation studies highlighted the contribution of graph structure (19.0% MSE reduction), attention mechanism (15.0%), and deep supervision (12.5%). Beyond predictive accuracy, attention-weight analysis revealed strong alignment with geologically meaningful features, such as faults and sedimentary facies boundaries, thereby enhancing interpretability. The proposed framework offers a scalable and interpretable solution for reservoir characterization, with broad potential applications in heterogeneous and faulted reservoirs.

ABSTRACT The Early Cambrian was a crucial transition for Earth's environment and life evolution. The Early Cambrian Yuertusi Formation black shale in the Tarim Basin, a typical organic‐rich black rock series, records regional sedimentary and paleo‐oceanographic information. Integrating outcrop, logging, core, seismic and litho‐geochemical data, this study documents the Yuertusi Formation's sedimentary features and organic‐rich deposit controls. Comprising lower black shale and upper carbonate, it divides into three sequences (Sq1–3). Three sedimentary facies (outer ramp, mid ramp, and inner ramp) formed in a ramp setting. Geochemical analysis shows the outer ramp had higher paleoproductivity. Oxygen isotopes and siliceous rock lithofacies suggest hydrothermal activities were in the outer ramp during Sq1. Cross‐plots and shale phosphorus indicate upwellings were active in mid‐outer ramps during Sq1–3, stronger in the mid ramp. Redox proxies show outer ramp Sq1 organic‐rich shales were anoxic, mid ramp Sq2–3 organic‐lean carbonates were oxic. Terrigenous influx (Al, Ti) didn’t correlate with TOC. In summary, the most organic‐rich deposits (TOC > 5%) in the outer ramp along the northern basin margin were controlled by hydrothermal‐induced high productivity and anoxic preservation, with siliceous, phosphate rocks and abundant trace elements.

This paper identifies and discusses the paleoenvironmental characteristics of the Quadrilátero Ferrífero based on studies of unconsolidated alluvial fans and the chronological organization of their respective sedimentary facies. These alluvial fans were submitted to stratigraphic survey and dating by Optically Stimulated Luminescence (OSL) and, subsequently, their ages and faciological characteristics were compared with the paleoclimatic and paleotectonic data available for the region. The description and interpretation of the sedimentary facies evidenced a lack of aggradationalprocesses, which are inactive. About 40% of the identified facies are plastic (Gmm) and pseudoplastic (Gcm) debris flows interspersed with occasional channel-filling facies (Gt), hyper- concentrated (Sm), and mud (Fm) flows. The unconsolidated alluvial fans of the Quadrilátero Ferrífero had their genesis throughout the Pleistocene, mainly in a dry climate, with vegetation retraction and sedimentary filling of river valleys. Climatic oscillations to establish a humid environment increased the flow of drainage courses and, consequently, erosion of the deposits. However, it was cenozoic tectonics that acted most strongly in the dismantling of the fans through strong fluvial incision in the Holocene, caused by uplifts of the Brazilian continental shelf.

During the early Jurassic, arid and thermally intense greenhouse climate conditions led to dominantly oxidizing environments, resulting in the widespread development of purple-red mudstone. However, under this climatic backdrop, a lacustrine transgression occurred in the Sichuan Basin, China, leading to the formation of a distinctive lithological assemblage comprising purple-red mudstone interbedded with grey sandstone. The sedimentary facies and origin of sandbodies from this period remain insufficiently understood. This study focuses on the Zhenzhuchong Member of the Lower Jurassic Ziliujing Formation in the Guanyin–Data area, located in the southern Sichuan Basin. Due to the absence of drilling cores, samples were collected from four field outcrop sections. A combination of lithological description, petrographic identification, cathodoluminescence measurement, geochemical profiling, X-ray diffraction were employed to interpret the depositional environment of the Zhenzhuchong Member. The results reveal that the Zhenzhuchong Member is primarily composed of lithic quartz sandstones, with quartz content ranging from 80.7% to 93.4%. Geochemical proxies (e.g., Sr/Cu, Sr/Ba, Ni/Co ratios) indicate a warm to hot, freshwater-influenced, oxic setting. Sedimentary structures and stratigraphic sequences suggest deposition in a delta front to shallow lacustrine environment, including features such as distributary channels, mouth bars, shallow lake deposits. With ongoing lake transgression, distributary channels gradually retreated, giving way to an expansion of shallow lacustrine conditions. Sedimentation patterns during this phase were mainly driven by localized variations in water level. The characteristics purple-red coloration of mudstone is attributed to oxidizing conditions under the prevailing greenhouse climate. Subsurface data from well logs and seismic interpretation identify three sandbody units, with the 1# and 2# sandbodies displaying good lateral continuity, with branch shape. Favorable hydrocarbon shows within these sandstones suggest promising potential for natural gas exploration.

No relevant studies have been conducted on sedimentary organic facies (SOF) in the Linhe Depression. This study investigates the characteristics of SOF from the Linhe and Guyang formations using geochemical methods. The analysis results indicate that the Linhe Formation can be divided into two facies zones: A (littoral-shallow lake SOF) and B (delta front SOF). Among these, facies A exhibits the best organic matter (OM) type and hydrocarbon generation potential, as well as the most extensive distribution area. The Guyang Formation is divided into three facies zones: C (semi-deep lake SOF), D (littoral-shallow lake SOF), and E (delta front SOF). Among these, facies C exhibits the highest quality of source rocks and is primarily distributed in the basin’s southern. Facies D and E are of lower quality, with Total organic carbon less than 1.0%. The contribution of aquatic organisms provides a substantial material foundation, and the reducing saline environment facilitates the enrichment and preservation of OM. These factors collectively contribute to the formation of high-quality source rocks in facies A, C, and D. The deployment of future oil and gas exploration is based on the extensive distribution of source rocks, so this research has certain guiding significance for practical exploration.

Abstract Conditional sedimentary facies modeling enables accurate characterization of the spatial architecture of sedimentary facies, providing crucial support for the fine evaluation and efficient development of natural resources. However, traditional conditional generative adversarial networks (CGANs) often require extensive training data and trade‐offs in conditional loss, making it difficult to maintain both diversity and geological consistency in data‐scarce geological scenarios. To address this issue, this study proposes a conditional simulation method integrating a training network and a post‐constraint network (CMS‐PCSinGAN). The training network adopts a concurrent multi‐stage SinGAN architecture based on a single training image to accelerate model convergence. The post‐constraint network progressively incorporates sparse well facies data through multi‐scale image editing to enhance the geological consistency of the generated realizations. To validate the effectiveness of the proposed method, experiments were conducted on multiple fluvial sedimentary facies models, and the results were systematically evaluated using facies proportion analysis, variogram analysis, and connectivity analysis. The results demonstrate that the CMS‐PCSinGAN method can satisfy sparse conditional constraints while maintaining strong diversity and geological consistency. Compared with commonly used multiple‐point statistics (MPS) methods, the proposed approach shows significant advantages in both applicability and reproduction of statistical characteristics.

This paper focuses on the problems of unclear oil and gas enrichment laws and difficult prediction of favorable zones in the tight reservoir of the Chang-7 member in the southwest of Wuqi Oilfield. It conducts research on reservoir characteristics and main controlling factors to provide a geological basis for efficient exploration in this area. By comprehensively applying technical methods such as detailed core observation, cast thin sections, scanning electron microscopy, high-pressure mercury intrusion, and basin simulation, the petrology, pore structure, and physical properties of the reservoir are systematically analyzed, and the controlling mechanisms of tectonism, sedimentation, and diagenesis are deeply discussed. The results show that the Chang-7 reservoir in the study area is an ultra-low porosity and ultra-low permeability lithic arkose sandstone, with intergranular pores and feldspar dissolution pores as the main pore types. The reservoir quality is controlled by multiple factors: sedimentary facies zones control the distribution of high-quality reservoirs such as sandy debris flows and turbidite sand bodies; in diagenesis, strong compaction and cementation lead to reservoir densification, while dissolution effectively improves the reservoir space; most importantly, the tectonic uplift and denudation since the Late Cretaceous have significantly improved the seepage capacity of the reservoir through elastic rebound and pressure reduction expansion mechanisms. Tectonic uplift is the key acquired constructive factor for improving the physical properties of the reservoir in the study area, and the paleotectonic high areas and areas with strong uplift and denudation are the favorable targets for further oil and gas exploration.

The Lower Cretaceous Tuxen and Sola formations in the Danish Central Graben (North Sea) constitute pelagic chalks and marlstones, which locally are hydrocarbon-bearing. Based on previous identification of 21 sedimentary facies in the cored Boje-2C well of the Boje Field, 66 samples were analysed through back scattered electron microscopy to delineate how the microscopic character reflects the macroscopic sedimentary facies and to identify indications of diagenesis. For most samples, microscopic characters can clearly be related to the previously identified sedimentary facies. Bioturbation and shear deformation, however, were not consistently reflected in the microscopic character. In all samples, the microtexture is characterised by massive or laminated calcareous mudstone with varying content of mainly kaolinitic clay and only sparse remains of microfossils or shell fragments, whereas particles of quartz silt and kaolinitic claystone silt are common. Porosity is mainly interparticular, typically reaching 25% in the Sola and upper Tuxen formations, and declining with depth to ca. 17% in the lower Tuxen and upper Valhall formations. Diagenesis is reflected in the occurrence of calcite cementation, pyrite and calcite-rimmed dolomite, and some pores may represent moulds after silicious microfossil fragments, which probably sourced the locally observed silicification of the sediment. Further, in clay-poor intervals below the oil zone, a significant diagenetic feature constitutes biogenic calcite mud particles that become increasingly recrystallized and euhedral with depth. It is therefore possible that burial-related crystal ripening was delayed in the oil zone represented by the upper part of the core. In the underlying transition zone, which in the Boje-2C well comprises most of the Tuxen Formation, the degree of recrystallization increases with depth as water saturation increases. Pressure dissolution features were noted in clay-rich intervals, but proper stylolites were not encountered, reflecting the generally high clay content of these marly chalks.