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The composition of marine authigenic iron silicates bears subtle evidence of paleo-oceanographic and paleoclimatic conditions. This study focuses on the compositionally unique glauconite within the Early Cretaceous Pariwar and Habur formations in the Jaisalmer Basin and discusses its implications. The Al-glauconite is enriched in TFe 2 O 3 (> 18 wt%), and is considered as Fe-rich Al-glauconite. The X-ray diffraction parameters, the micro-texture, and the K 2 O content reveal an evolved to highly evolved structure of the glauconite. It is abundant in shallow subtidal and tidal- and wave-influenced shoreface facies, and it forms either by the alteration of fecal pellets or as bioclast infillings. Micropaleontological and ichnological proxies confirm the glauconitization in an oxygen-depleted, shallow marine depositional setting. Small-sized (< 1 cm) fodinichnial, pascichnial, domichnial, and repichnial traces, and agglutinated foraminifera ( Bathysiphon) corroborate the oxygen-depleted seawater. The landward expansion of the oxygen minimum zone, leading to oxygen depletion in coastal settings, facilitates the glauconitization in a marginal marine setting. Kaolinite and Fe-Al-smectite react in the presence of excess Fe, forming Fe-rich Al-glauconite on the seafloor. Therefore, the compositionally unique glauconite reflects atypical seawater chemistry with increased elemental influx of Al, Fe, and Mg related to intense continental weathering, kaolinite substrate, and mobilization of Fe 2+ in oxygen-depleted seawater.

Modern oceanographic studies demonstrate that marginal seas and semi-restricted marine environments, including epicontinental seas and carbonate platforms, are highly sensitive to changes in circulation, freshwater input, stratification, and redox conditions, allowing climatic perturbations to be recorded with high fidelity. Understanding the behavior of such systems under icehouse conditions is therefore important for interpreting climate variability in both ancient and modern oceans. The Late Paleozoic Ice Age was a prolonged icehouse interval characterized by repeated glacial and interglacial oscillations, yet its climate dynamics are still mainly constrained by Gondwanan glacigenic records and low-latitude carbonate successions. High-resolution climate information from mid-latitude regions remains limited. The purpose of this study is to obtain high-resolution mid-latitude geochemical constraints on climate variability during the Late Paleozoic Ice Age using a semi-restricted marine carbonate succession. Specifically, this study aims to (1) establish high-resolution carbon and oxygen isotope records from well-preserved carbonate samples spanning the Visean to Asselian interval; (2) identify and characterize major glacial to interglacial cycles recorded in the succession; (3) evaluate the extent to which semi-restricted paleogeography amplifies isotopic responses relative to coeval low-latitude open-marine settings and (4) assess the climatic significance of a short-lived negative carbon isotope excursion during the middle Bashkirian. Here we present high-resolution carbon and oxygen isotope records from a Visean to Asselian marine carbonate succession deposited in a semi-restricted basin. Stable isotope analyses of well-preserved carbonate samples document temporal variations in carbonate carbon and oxygen isotopes. The records resolve at least three major glacial to interglacial cycles, with isotope shifts substantially larger than those reported from coeval low-latitude open-marine settings. Carbon isotope variations reach up to 7.7‰, while oxygen isotope variations reach up to 9.2‰. These pronounced responses are attributed to semi-restricted paleogeography, facies heterogeneity, and the sensitivity of marine carbonate systems to stratification, redox variability, and organic carbon cycling. A short-lived negative carbon isotope excursion during the middle Bashkirian may record a Northern Hemisphere deglaciation event superimposed on the broader Gondwanan icehouse background, a signal that is not clearly expressed in other regions. Overall, this study describes new mid-latitude geochemical constraints on Late Paleozoic climate variability and offers valuable analogs for understanding climate responses in modern marginal marine systems.

Sedimentological and palynostratigraphy studies were used to evaluate sediment-stacking patterns in a depth range between 400 and 50 m in the Kemar-1 well section, Bornu (Chad) Basin, Nigeria. The greyish-sandy claystone, rich micaceous, lithified, and unlithified greyish claystone, dark well sorted micaceous sandstone, and poorly sorted and heterolithic clayey sandstones are the major facies components recognised in the well sections. The lithofacies characteristics were used to delineate and assign depositional environments ranging from lacustrine to fluvial settings. Paleoecological results revealed that the dominant palynofloral associations are angiosperm pollen and pteridophytic spores and they were tentatively grouped under three ecological groups which include freshwater, mangrove/brackish and savannah depositional environments in wet to dry climatic conditions during sediment formation. The presence of Echitricolporites spinosus was used to define the Echitricolporites spinosus palynological zone. The basal section at 390–385 m interval in the well shows the dominance of Psilatricolporites crassus, Verrucastosporites usmensis, and Monoporites annulatus, which marked the Eocene boundary from the overlying Miocene marker bed species of Echitricolporites spinosus, Grimsdalea magnaclavata, Anthocerus sp., Nymphaea lotus, and Retistephanocolpites gracilis. The palynomorph data and lithological characteristics from the studied well section have been used to establish that the Chad Formation is of late Eocene to early Miocene age, and that it unconformably overlies the Kerri–Kerri Formation that was deposited in varying lacustrine, fluvial and prograding shoreface and deltaic settings. This study has resolved the controversy surrounding the age of the Chad Formation, the challenge in depositional environment reconstruction. Finally, the stratigraphic framework of the Chad Formation in the study area is presented.

The influence of marine components in the study area is attributed to seafloor spreading and opening in the Indian Ocean during the Aptian, coupled with eustatic sea-level rise throughout the Aptian–Albian period. The present investigation delineates a marine incursion in the Chintalapudi sub-basin of the Godavari Valley Coalfield based on the occurrence of dinocysts, acritarchs and prasinophytes. Noteworthy stratigraphic marker taxa are recognized as key components in the age assignment of the sedimentary rocks. Sum total of four zones have been recognised in the studied part of the sequence. The oldest zone in the deepest set of sedimentation is identified as Cicatricosisporites australiensis Zone. This zone is assigned based on the first occurrence (FO) of Cicatricosisporites australiensis and Biretisporites eneabbaensis . The next zone, further above in the sequence is Foraminisporis wonthaggiensis Zone. The FO of Foraminisporis wonthaggiensis attested to the initiation of this zone. The third zone is Cyclosporites hughesii Zone recognised by the FO of Foraminisporis asymmetricus . The accessory palynotaxa comprised of Retimonocolpites sp. , Tricolpites confessus, Tricolpites sp., Tricolporites sp . and Triporites sp. in the recognition of this zone . The youngest zone of this sequence is recognised at the top of the sequence named Crybelosporites striatus zone based on the FO of Crybelosporites striatus . Palynological analysis places the studied part of succession between the Berriasian to early Albian. The primary objective of this investigation is to explicate the characteristics of sedimentation and paleoenvironmental contexts, with a specific emphasis on utilizing palynofacies and Botryococcus morphotypes as distinct benchmarks. Based on the palynofacies investigation three different depositional regimes have been assigned, which are distinguished as follows: (a) continental (384.30–203.75 m) dysoxic–anoxic basin; (b) shallowest nearshore–inner shelf, marginal marine/brackish water settings; and (c) heterolithic proximal shelf deposition with significant sea transgression (94.50–36.50 m). Unpredictable morphotaxonomical responses across diverse habitats with varying pH levels are projected to enhance comprehension of the palaeoecological and palaeoenvironmental significance of fossil Botryococcus colonies. The uppermost marine part of the sequence denotes the least abundance, reduced size, and ill-defined amorphous forms of fossil Botryococcus colonies. The continental part displays the less abundant but well-defined and fully grown sporadic distribution of fossil Botryococcus colonies; the middle part records its presence with a well-diversified, sturdy structural framework and cellular cup-like structures. The investigation of the Cretaceous strata reveals a dynamic geological history influenced by tectonic activities, including plate drifting and rifting. Present investigation enhances our comprehension of palynostratigraphy, and paleoenvironmental history and facilitates the formulation of models elucidating environmental processes during the Early Cretaceous. In addition, the lipid-rich composition of Botryococcus renders it promising for biofuel production, attracting attention in biotechnology and renewable energy research endeavors.

Twenty-five species of Podocopida are reported in seven localities in the São Paulo State, Brazil, corresponding to the Serra Alta and Teresina formations (Middle to Upper Permian). The specimens are mostly preserved as steinkerns (internal molds), except some carbonitids and cytherocopines which are predominantly recrystallized. The results indicate marginal marine environments influenced by influxes of nonmarine waters, as suggested by the occurrence of Velatomorpha, Gutschickia, Carbonita and Darwinuloidea. Velatomorpha rochacamposi sp. nov. is described, and evidences of prédation are reported for the first time in Paleozoic ostracods. This study contributes to the understanding of the ecology and evolution of nonmarine ostracods during the Late Paleozoic.

The sandstone-shale-coal succession of the Barakar Formation (early Permian) of the Raniganj Basin, India hosts low-diversity ichnoassemblages, containing ichnogenera Arenicolites , Chondrites , Diplocraterion , Monocraterion , Ophiomorpha , Palaeophycus , Planolites , Skolithos , Taenidium, and Thalassinoides , produced by shallow marine infaunal invertebrates. Sedimentary facies architecture depicts a transgressive, fluvio-tidal (with a minor wave) interactive estuarine depositional setting. The fluvial deposits, lying beyond the zone of tidal encroachments, record absence of trace fossils, which is attributed to a low colonization window caused by high fluvial discharge and frequent channel migrations. Tidal interactions with high fluvial discharge led to bay-head deltas in the inner-middle estuary with the dominance of suspension-feeding and deposit-feeding ichnotaxa in coarser- and finer-dominated sediments, respectively, suggesting a mixed Skolithos–Cruziana ichnofacies. Increasing tidal influence with very less fluvial input allowed opportunistic colonizers and deposit feeders of the Cruziana ichnofacies to flourish in the central estuarine setting. Intermittent low-oxygenated restricted conditions marked by the chemosymbiotic ichnoassemblages of the Zoophycos ichnofacies indicate very low energy conditions. The outer estuary with increasing wave dominance is inhabited by suspension-feeding, domicile ichnotaxa of Skolithos ichnofacies, frequently mixed with the ichnotaxa of the Cruziana ichnofacies. The recurrent juxtaposition and lateral distribution of the Seilacherian marginal marine ichnofacies is attributed to complex sediment–organism interaction patterns in response to prevalent energy conditions, sediment discharge and substrate conditions in different zones of the fluvio-tidal estuarine setting. The integrated sedimentological-ichnological model signifies marine transgressions that affected the palaeogeography of the Permian continental Gondwanaland. Research Highlights Sedimentological–ichnological analysis signifies marine encroachment in Barakar Formation in peninsular India. Ichnoassemblages point to complex pattern of sediment–organism interactions with gross energy distribution. Sustained marine transgression event within the continental Gondwanaland during early Permian is visualized.

The Brsnina Permian–Triassic nearshore marine sediments were deposited on the Adria carbonate platform in tropical latitudes at the western end of the Neotethys Ocean. Continuous channel samples across the boundary show no consistent change in element or element/Al ratios, except that most element/Al ratios increase in the top 0.5 m of the Permian strata. Though there are sporadic higher values of some element/element ratios, such as Ti/Zr, Th/Sc, Zr/Sc, Cr/Ni, Y/Ni, Co/Th, Cu/Zn, and Nb/Ta, La/Sc, the overall geochemistry indicates that the sediments were derived from dominantly silica-rich continental rather than silica-poor sources though with some more silica-poor inputs at times. Sporadic high Ti/Zr ratios indicate periods of increased aridity, but no overall increase across the boundary. Various geochemical redox proxies suggest mainly oxic depositional conditions, with episodes of anoxia, but with little systematic variation across the boundary. Geochemical proxies for productivity indicate little change up the section with values two orders of magnitude less than elsewhere. The lack of consistent element geochemical changes across the boundary accompanied by significant C, S, and other isotopic changes suggests that atmospheric and oceanic chemical variations drove the Permian–Triassic boundary environmental changes at least on the sabkha environments of the tropical Adria platform.

Numerous karst dolines have been formed along the Croatian coast and many have been submerged during the Late Glacial and Holocene sea level rise. The coastal area of Cres Island in the Northern Adriatic is a typical example of this geomorphological setting, where transitional forms from subaerial to submerged dolines are present. Once dolines are formed they can accumulate soil, water and sediments due to their morphology. Sediments are an especially valuable source of environmental data. This paper presents the results of the study of foraminiferal assemblages and sediment geochemistry, supplemented with grain-size and mineralogical data, from the marine ponds developed in the karst dolines on Cres Island. Obtained data is correlated with the sediment core record from submerged dolines in the present-day embayments along the coastal zone of Cres Island. In total, 3 sediment cores were collected in the marine ponds Marinska, Arcij and Podbrajde, while 2 longer sediment cores have been extracted from the Jaz and Sonte embayments. The Marinska, Arcij and Podbrajde marine ponds have distinct geochemical and mineralogical sediment compositions, with monospecific foraminiferal assemblages and generally differ from each other. The common characteristics are their high N and P concentrations and the algal origin of organic matter. Agglutinated foraminiferal taxa (Haplophragmoides canariensis and Trochammina inflata), typical for intertidal environments, are abundant in the brackish-water Marinska pond, while stress-tolerant species Ammonia tepida has been identified in the Arcij marine pond. Environmental conditions in the Podbrajde marine pond did not facilitate the development of a rich foraminiferal fauna. Results from the present-day marine ponds enabled recognition of similar environments in the sediment cores collected in the Jaz and Sonte embayments that were progressively inundated during the Holocene sea level rise. A palaeo-marine pond existed in the Sonte embayment until 6610 cal BP, when the sea flooded the investigated area. A marine pond in the Jaz embayment was formed at 711 cal BP. Low-diversity foraminiferal assemblages in these palaeo-ponds are similar to those recognized in the present-day Arcij marine pond on Cres Island. However, differences in the geochemical composition of palaeo-marine ponds, in comparison to the present-day ponds, exist. They might be attributed to climate variability oVer time and Variations in the geological setting of each environment. High Mo concentrations and abundant organic matter content are the main sediment characteristics of the recognized palaeo-marine ponds in the Jaz and Sonte embayments.

Trilobites have traditionally been considered fully marine. Through the integration of ichnological, palaeobiological and sedimentological datasets within a sequence-stratigraphic and strati­graphic palaeobiology framework, we challenge this assumption. This analysis is based on the study of incised fluvio-estuarine valley deposits from the Furongian Tilcara Member (TM) and the latest Furongian Pico de Halcón Member (PHM) of the Santa Rosita Formation, the early late Tremadocian Cardonal Formation (CF), and the Dapingian–Darriwilian Alto del Cóndor Formation (ACF), from Cordillera Oriental of northwest Argentina. These valleys were incised into wave-dominated shallow-marine strata and filled with transgressive deposits that accumulated in tide-dominated estuaries. Whereas the TM lacks any body or trace fossil evidence of the presence of trilobites in estuarine settings, the other three units reveal that trilobites were able to inhabit these settings. The PHM and CF are host to trilobite trace fossils in outer estuarine facies, both containing various ichnospecies of Cruziana (e.g., C. omanica and C. semiplicata in the TM) and Rusophycus (e.g., R. latus in both units). In addition, the PHM also contains body fossils of the olenid trilobite Neoparabolina frequens argentina in the same deposits in which the trace fossils are preserved, as well as from middle estuarine facies. The ACF displays trilobite trace fossils of the C. rugosa group in inner, middle, and outer estuarine deposits, illustrating further landward incursions. This unit also contains body fossils of the asaphid trilobite Ogyginus sp. Accordingly, our data indicate two attempts of landward exploration via brackish water: phase 1 in which the outer to middle portion of estuaries were colonized by olenids (Furongian–early late Tremadocian) and phase 2 involving exploration of the inner, middle, and outer estuarine zones by asaphids (Dapingian–Darriwilian). Our study indicates that these trilobites were tolerant to salinity stress and able to make use of the ecological advantages offered by marginal-marine environments migrating up-estuary, following salt wedges either reflecting amphidromy or as euryhaline marine wanderers. It is suggested that tolerance to salinity stress arose independently among different trilobite groups as a result of the broad array of behaviors and adaptations of trilobites during the Ordovician radiation. We speculate that the assumption that all trilobites were stenohaline may have resulted in the misinterpretation of some tide-dominated estuarine deposits as fully marine.

Reservoir quality prediction in deeply buried reservoirs represents a complex challenge to geoscientists. In sandstones, reservoir quality is determined by the extent of compaction and cementation during burial. During compaction, porosity is lost through the rearrangement and fracture of rigid grains and the deformation of ductile grains. During cementation, porosity is predominantly lost through the growth of quartz cement, although carbonate and clay mineral growth can be locally important. The degree of quartz cementation is influenced by the surface area of quartz available for overgrowth nucleation and thermal history. Clay grain coats can significantly reduce the surface area of quartz available for overgrowth nucleation, preventing extensive cementation. Using a coupled-effect compaction and cementation model, we have forward-modelled porosity evolution of surface sediments from the modern Ravenglass Estuary under different maximum burial conditions, between 2000 and 5000 m depth, to aid the understanding of reservoir quality distribution in a marginal marine setting. Seven sand-dominated sub-depositional environments were subject to five burial models to assess porosity-preservation in sedimentary facies. Under relatively shallow burial conditions (<3000 m), modelled porosity is highest (34 to 36%) in medium to coarse-grained outer-estuary sediments due to moderate sorting and minimal fine-grained matrix material. Fine-grained tidal flat sediments (mixed flats) experience a higher degree of porosity loss due to elevated matrix volumes (20 to 31%). Sediments subjected to deep burial (>4000 m) experience a significant reduction in porosity due to extensive quartz cementation. Porosity is reduced to 1% in outer estuary sediments that lack grain-coating clays. However, in tidal flat sediments with continuous clay grain coats, porosity values of up to 30% are maintained due to quartz cement inhibition. The modelling approach powerfully emphasises the value of collecting quantitative data from modern analogue sedimentary environments to reveal how optimum reservoir quality is not always in the coarsest or cleanest clastic sediments.