Based on an integrated dataset, the biostratigraphy of the late Cenomanian-Turonian ammonites and benthic fauna from northern Egypt is evaluated. The Cenomanian-Turonian successions were measured from six stratigraphic sections in north Eastern Desert and Sinai, represented by the mixed siliciclastic-carbonate sediments, comprising intertidal, shallow subtidal, and deep subtidal facies associations. A quantitative biochronological analysis is performed on the dataset by means of the unitary association method (UAM), using the Past software. This led to the recognition of a sequence of 5 ammonite unitary associations (maximal sets of actually or virtually coexisting taxa). The ammonite taxonomic richness is also illustrated, with respect to the Oceanic Anoxic Event 2 (OAE2). The regional correlation using UAZ is more straightforward and presents fewer boundary contradictions than classical interval zones. Furthermore, the unitary association method was performed on the benthic fauna. Consequently, twelve benthic unitary associations were constructed, and merged into 5 more geographically reproducible unitary association zones.
Rat’s Nest Cave in western Alberta, Canada, has six moonmilk accumulations on cave walls varying from 2 to 3 m2 to 100 m2 in area with thicknesses of 1–2 mm to > 15 cm. The compositions of the moonmilk deposits differ, consisting of low-Mg calcite needle-fibre crystals or aggregates of tabular euhedral crystals of hydromagnesite, but commonly mixtures. The needle-fibre crystals of calcite-type moonmilk are draped by a meshwork of thread-like filaments of extracellular polymeric substances (EPS), commonly calcified, and similar to other documented moonmilk deposits. In contrast, hydromagnesite-type deposits lack these nanofibres. Controls on the needle-fibre crystal morphogenesis include the adsorption of EPS organic molecules, Mg2+ ions from groundwater seeping into the cave, and other environmental factors that constrained the growth of crystal faces oriented in the a-axis direction while enhancing elongation in the c-axis direction. This interference on the structure of the cell lattice resulted in the needle-fibre habit as a type of skeletal crystal characterised by smooth well-defined surfaces of length-long grooves forming 120° Bravais-Miller junctions between the ±a1 and ±a2 axes and the suppression of crystal faces in the direction of the ±a3 axis. Epitaxial overgrowths on the needle-fibre crystals record the cessation of organic molecules and Mg2+ ion adsorptions on the surfaces of the underlying skeletal crystals, permitting the development of dendritic arrays of rhombic crystallites. This alternative model for the origin of the longitudinal grooves on needle-fibre calcite crystals in moonmilk contrasts with biogenic hypotheses that attribute groove formation to the earliest nanoscale growth stage generated by two adjoined rod-shaped precursors developed within organic sleeves of bacteria or fungal hyphae.
The late Cambrian is known for global biogeochemical perturbations to the marine carbonate system whose timing, extent, and duration remain unresolved, highlighting the need for high-resolution facies analyses to assess the nature of carbonate deposition. We investigate the dominant processes contributing to carbonate deposition using lithologic, microfacies, petrographic point count, and stable isotope analyses at a previously undescribed section at Rendezvous Peak, western Wyoming. The lower Pilgrim Limestone of the Gallatin Group represents deposition in an offshore storm-dominated carbonate platform composed of flat pebble conglomerates and laminated glauconitic and micropeloidal carbonate mudstones. Facies shift to middle and platform edge packstone/grainstone units that include two microbialite horizons. The upper Pilgrim Limestone returns to offshore flat pebble conglomerates and laminated micropeloidal carbonate mudstones during the continued interpreted marine transgression. Point count data indicate consistently low skeletal contributions (2.9
Hitherto undescribed fine-grained carbonate deposits of inferred microbial origin unconformably rest atop a truncated basement complex along the western coastline of northwestern Saudi Arabia. These carbonates form drapes on the basement complex as well as mounds aligned along a dominant fracture direction (ENE-WSW strike). They are directly overlain by uppermost Burdigalian to Langhian strata of the Wadi Waqb Member (Jabal Kibrit Formation), which feature the earliest coral bioherms associated with the nascent Red Sea, suggesting an early to middle Miocene age for the underlying putative microbialites. Outcrop geometries reveal that the carbonate unit has undergone no significant post-depositional tilting and is largely preserved at its original depositional angle (up to 35°). Thin-section petrography and X-ray diffraction (XRD) analysis confirm that the carbonates are predominantly composed of dolomite. Micromorphological features, including textures consistent with mineralized extracellular polymeric substances (EPS), and capsule-like forms reminiscent of bacterial remains, closely resemble those found in microbialites from modern hypersaline or highly alkaline lacustrine environments. Similarly, crystal splays resemble occurrence in the fossil record that have been interpreted to be indicative of high-alkalinity conditions. Taken together, the observations suggest a restricted environment characterized by elevated levels of salinity and/or alkalinity during the early stages of Red Sea rifting and underline that microorganisms played a significant role in carbonate deposition during this stage. The stratigraphic relationship between the microbialites and the overlying coral-bearing deposits indicates that the basin evolved into a fully marine environment in the late Burdigalian.
Fossil echinoderm ossicles are often occluded by syntaxial overgrowths which obscure stereom. Phosphatized ossicles from insoluble residues show fine microstructure. We investigated phosphatized stereom in Cincinnaticrinus columnals in insoluble residues from the Ordovician around Cincinnati, Ohio USA. Microstructures appeared to be stereom micromolds. We tested this hypothesis by examining residue and thin sections of undissolved sample using light microscopy, SEM and EDS, resulting in these observations: (1) calcite within phosphatized ossicles is optically aligned and parallel to stem; (2) phosphate deposited centripetally from calcite surfaces, often incompletely filling cavities, leaving a central vug; (3) while calcite is inclusion-free, phosphate contains siliciclastic inclusions from surrounding sediments. These observations suggest that calcite is original, and phosphate was deposited as micromolds. To confirm the phosphatic micromold hypothesis, we compared internodal columnals from the extant isocrinid Endoxocrinus from the Florida Straits using fracture surfaces and epoxy-impregnated thin sections. We then dissolved the thin section calcite, leaving epoxy micromolds for comparison. Schematic 3-D models summarize our reconstructions of structure of the crinoids in both original calcite and micromolds. Through-going solid cylinders are present in Cincinnaticrinus phosphate and Endoxocrinus epoxy molds. In Endoxocrinus, these are molds of stereomic galleries complete with ligaments, confirming Cincinnaticrinus phosphate is also moldic. Galleried stereom of the two crinoids differs in structural details, a divergence that is consistent with phylogenetic evidence of through-going ligaments in an early common ancestor. Preservation by phosphatic micro-molding, interpreted as preserved negative space, facilitates study of stereomic features supporting crinoid soft tissues.
Karst lakes, often sustained by groundwater, feature unique opportunities to investigate lake formation and depositional processes reflecting their dynamic hydrological and geological settings. Located in an arid environment in the centre of the Arabian Peninsula, the recently dried out Layla Lakes reveal a unique history of their formation and contain sediments resulting from complex interlinked depositional processes controlled by seasonal climatic, biological and chemical processes. The region’s gypsum-anhydrite karst formation is interacting with carbonate and sulfate (co-)precipitation processes and is accompanied by caves and sinkhole development. This study employs a combined approach of fieldwork, lithofacies analysis, digital elevation analysis, and digital photogrammetry as well as radiocarbon dating to explore lake-forming processes and the combination of depositional environments that define a distinct evaporitic and biotic sediment inventory. The findings reveal that the collapse of the karst features leading to the formation of groundwater-filled sinkholes within the Layla Lakes could be explained by swelling of anhydrite and the aggradation of a sabkha environment at the surface. Within these sinkholes, laminated lake sediments developed, recording diverse lithofacies produced by subaqueous deposition of biogenic and biotically induced components, together with carbonate–sulfate co-precipitation controlled by water chemistry. Continuous evaporative pumping promoted progressive accumulation of haloturbated and crystalline precipitates within and around the lakes. This study provides a detailed characterization of mixed evaporative sediment associations composed of sulfates, carbonates, and microbial structures, and presents a semi-quantitative facies model over time that may serve as a pilot study for further investigations in similar locations.
The presence of fossilised fungi within deep crustal rock formations has been established based on fossil evidence from 400 Ma continental crust and 81 Ma oceanic basaltic crust. Moreover, the Palaeoproterozoic Ongeluk Formation contains putative fungal remains reaching 2.4 Ga. The resulting gap of 2 billion years raises questions regarding the history of fungi in marine subsurface environments, in particular the lack of bona fide fossils in ophiolites, sections of layered basalts from mid-ocean ridges. Devonian examples of cryptoendolithic microorganisms preserved in marine pillow basalt stem from the Arnstein locality, Rheinisches Schiefergebirge, and the Kahlleite locality, Thüringer Wald, Germany, and have previously been described as filaments of microorganisms with uncertain biological affinity. The filamentous fossils were investigated using environmental scanning electron microscopy, Raman spectroscopy, confocal microscopy, widefield microscopy, and optical light microscopy. Energy dispersive spectroscopy analyses of several of the inferred microfossils revealed a presence of clay minerals, pointing to a mode of mineralisation in association with organic matter and agreeing with a biological origin. Raman spectroscopy showed carbon localised within the studied filaments and revealed that particularly iron oxide minerals are associated with carbon. Element compositions similar to younger mineralised fungal remains and morphologies resembling sporophores and hyphae agree with the interpretation of the Arnstein and Kahlleite fossils as marine fungi, shedding new light on many of the previously undetermined fossils and plausibly narrowing the fossil gap of oceanic deep subsurface fungi by at least 300 million years.
Coral reefs are highly diverse ecosystems comprising a wide range of organisms that build and inhabit them. Understanding the ecological complexity and evolutionary dynamics of these ecosystems necessitates data of both the reef-building and reef-associated fauna. However, a comprehensive understanding of the structure and composition of coral reefs and associated fauna across space and time remains limited, even from the highly diverse Western Indo-Pacific (WIP) biogeographic region. In this study, we reconstruct the paleoecology and paleoenvironment of a Late Pleistocene tropical coral reef, exposed along western India of the WIP Realm, by analyzing the reef’s geomorphological architecture and paleoecology of the reef-building corals and associated fauna. Our results reveal that the Indian fossil reef was a fringing reef, dominated primarily by non-acroporid, massive, and encrusting merulinid corals, and lacked vertical and/or ecological succession, unlike other Pleistocene reefal ecosystems globally. The ARM reef was spatially patchy and was short-lived (i.e., 200–1000 years) which led to a depauperate faunal assemblage compared to coeval coral reefs that spanned longer times. Reefal diversity was also constrained as the reef developed under a high-energy and low-to-moderate detritus setting. We finally estimate the regional sea level fluctuations, using various lithological, faunal, and archaeological proxies, and infer that the lowstand associated with the Last Glacial Maximum at 20 kyr contributed to the reef's short-lived nature and eventual demise.
This study presents integrated microfacies, biostratigraphic, and sedimentological analyses of five previously undocumented Upper Triassic reefal/fore-reefal to basin carbonate sections from far-travelled nappes situated today in northern Montenegro (Outer Dinarides/East Bosnian-Durmitor megaunit). The achieved data offer new insights into the evolution of shallow-water reef systems within the Dachstein Carbonate Platform during a time of pronounced global geological disturbances (intense tectonic activity, volcanism, bolide impacts, and climatic shifts). The sections studied reveal a relatively cyclic deposition of reef-derived sediments (framestone blocks and shallow-water sediments with turbiditic character) into an open marine, slope to basin environment defined by thin-shelled bivalves (“filament”)-rich/siliceous packstone facies dated by conodont faunas. The analysed reef facies contain a wide range of well-preserved reef-building organisms, including microproblematica: Baccanella floriformis Pantić, Microtubus communis Flügel, Tubiphytes obscurus Maslov, Radiomura cautica Senowbari-Daryan Schäfer, Actinotubella gusici Senowbari-Daryan, Muranella sphaerica Borza, ?Porferitubus buseri Senowbari-Daryan; calcified sponges: Cryptocoelia sp., Uvanella sp., Celyphia sp., and various corals of the Late Triassic Dachstein reef habitat. The conodont assemblages prove a latest Carnian (higher Tuvalian) to early Rhaetian age interval for the development of the studied sections. Importantly, three distinct reef-influenced depositional cycles with rapid reef progradation are identified, each disrupted by different events that directly influenced the carbonate production throughout this roughly 20 million years long time interval. These cycles challenge the notion of an undisrupted Late Triassic shallow-water carbonate factory, also highlighting the vulnerability of reef ecosystems to large-scale environmental disturbances and the difficulties to establish sequence stratigraphy cyclicity on biological controlled sedimentary systems.
In view of their porosity, coquinas are excellent hydrocarbon reservoirs worldwide. This work presents a taphonomic and stratigraphic study of Pleistocene shell accumulations from Moreno Bay (Mejillones Peninsula, Chile) and Pleistocene-Holocene deposits from San Antonio Bay (Villarino Peninsula, Argentina). The Mejillones Formation records a transgressive to falling stage systems tract, and is the topmost sedimentary unit deposited in a half-graben preserved in the Mejillones Peninsula (northern Chile). The Villarino Peninsula deposits record a series of prograding beach ridges, mostly composed of shells and gravelly sediments. Taphofacies and lithofacies interpretation of stratigraphic profiles from both sites indicate high-energy subaqueous depositional environments, allowing their use as analogues for coquina reservoirs. The comparative analysis of taphofacies also revealed different levels of similarity between the fossil assemblages, based on characteristics such as packing, orientation and the degree of shell fragmentation. Although morphologically similar, the deposits resulted from distinct geological controls and processes: active tectonic uplift on the Mejillones Peninsula and tectonic stability episodes on the Villarino Peninsula. The main difference lies in the sediment composition: the Pleistocene profiles of San Antonio Bay (Argentina) are predominantly siliciclastic (clasts), whereas Moreno Bay (Chile) is dominated by bioclastic material (shells). The different tectonic and climatic contexts, hyperarid in Chile versus glacial fluvial input in Argentina, explain the compositional differences. The presented data demonstrate that similar coastal features can be generated by unique combinations of tectonic, eustatic and climatic controls, reinforcing the need for an integrated approach for the correct interpretation of palaeoenvironments.
Stromatoporoids are hypercalcified sponges and were major reef-building and reef-associated organisms in the middle Palaeozoic Era, but their skeletons are poorly preserved and continue to challenge interpretations of their original nature. In view of the very low amount of organic matter in the skeletons, fluorescence (FL) imaging has rarely been applied for the study of stromatoporoid skeletal structure. Since the Silurian rocks on Gotland are well preserved, the stromatoporoids there contain enough organic material to examine the microstructure of the skeletons using FL microscopy. FL highlights the presence of small amounts of organic matter in stromatoporoids by green-coloured light emission. By using this method, it is possible to visualize potentially original or near-original skeletal microstructures, which commonly appear extensively altered under transmitted light, particularly under cross-polarised light. Such alteration results from early-diagenetic neomorphism of stromatoporoid skeletons, in particular the formation of fabric-retentive irregular calcite (FRIC) crystals. FRIC permeates the entire skeleton, including its skeletal elements and cement-filled internal spaces. However, the FRIC formation did not redistribute the organic material in the skeleton, so that FL microscopy enables the visualization of the porosity of the galleries and, in certain genera, also the microporosity within the skeletons (microgalleries), demonstrating that many stromatoporoid skeletons originally had extremely high porosity and thus presumably also very high permeability. A systematic investigation of stromatoporoids from other periods and regions using FL microscopy could therefore not only provide valuable insights into the lifestyles of stromatoporoids, but also contribute to the systematics of this group, which remain problematic.
Carbonate platforms are subject to falls of the sea level registered in the sedimentary sequences. Traces of these exposures are represented by paleokarst features such as red paleosols, speleothems, breccias and fissures filled by sediment. All these features were recognized in the Eocene–Oligocene deposits of the Salento region (Italy) applying a combination of outcrop observations, cement fabric, cathodoluminescence, stable isotopes (δ18O and δ13C) and trace element analyses. A red paleosol on an epikarst and associated fissure fills are of Pleistocene age based on the fossil content. Speleothems are related to the sea level fall of the Eocene–Oligocene transition, based on stratigraphic contacts. Breccias that fill caves and relatively thin fissures filled by sediment were found in correspondence to the Eocene–Oligocene transition and are related to the sea level drop linked the Oi-1 Event. Stable isotopes and trace elements applied on either the bulk rock or cements allowed us to discern marine and meteoric diagenesis. The paleokarst related to the Eocene–Oligocene transition could precipitate cement at one site, and was purely erosive at another location. The proposed multi-proxy approach was successful in determining the age of the paleokarstic events, identifying the specific paleokarstic environment (epikarst vs. vadose zone), and improving knowledge on the dominant diagenetic processes (precipitation vs. physico-chemical erosion). The success of our approach can be repeated worldwide in other carbonate ramps affected by exposure to weathering and groundwater flow.
To characterize the paleoenvironments of the Cenomanian in northeastern Algeria, 74 samples from the Ras El mers section (Aurès Mountains) were quantitatively analyzed. Based on planktic foraminifera and ammonites, substages of the Cenomanian were identified. The lower Cenomanian age was indicated by the Thalmanninella globotruncanoides Zone, supported by Mantelliceras ammonites. The Thalmanninella greenhornensis Zone ending with the FO of Whiteinella baltica, indicates a middle Cenomanian age, confirmed by the ammonite Acanthoceras rhotomagense. Although the Rotalipora cushmani Zone is missing, Dicarinella hagni and related species suggested an upper Cenomanian age for the top part of the section. Non-Metric Multidimensional Scaling (NMDS) and Permutational MANOVA (PERMANOVA) tests indicated a significant difference between the lower and the middle Cenomanian association, while middle and upper Cenomanian associations are non-significantly different. The biotic attributes of the benthic foraminifera indicated that during early Cenomanian, stable, deeper marine conditions prevailed. The middle Cenomanian saw a shift to a shallower setting, characterized by slightly higher water energy and harder substrates, indicating moderate stress levels (more epifauna and lower diversity). By the late Cenomanian, the environment transitioned to shallower, low-energy conditions dominated by soft substrates, with moderate stress persisting. This progression reflects gradual tectonic-influenced shallowing trend and growing environmental variability throughout the Cenomanian. The muddy and pelagic nature of the sediments, the dominance of infaunal echinoids and planktic foraminifera indicates deep, soft substrates, outer ramp setting, and the general lower diversity values of all associations point to environmental stress associated with eutrophic dysoxic/poikiloaerobic regime. The diversity patterns and key biotic indices provide valuable insights for identifying depositional sequences and complementing stratigraphic interpretation.
Research on the sedimentary facies of the Middle Permian Maokou Formation in the Sichuan Basin has predominantly concentrated on inner-platform settings, with the evolution of its platform-margin facies belts being less well understood. This study, utilizing integrated well-log, core and seismic data from the Jiange-Yuanba area, employs sequence stratigraphy, sedimentology and seismic geomorphology to delineate sequence architecture, interpret depositional environments and characterize platform-margin development. Key findings include: (1) The Maokou Formation comprises three third-order sequences (SQ1–SQ3); SQ1 features subdued palaeotopography, whereas SQ2–SQ3 exhibit pronounced south-thick/north-thin differential subsidence. (2) Deposition evolved from an early gentle carbonate ramp to a progradational, rimmed carbonate platform during its middle–late stages. (3) Whereas SQ1 contains sporadic, low-energy shoals on subtle palaeo-highs, SQ2–SQ3 developed NW–SE-trending, vertically stacked platform-margin shoal complexes. These shoals constitute potential large-scale, high-quality reservoirs and represent key exploration targets. This work refines the sedimentary model for the northwestern Sichuan Basin and provides insights for hydrocarbon exploration in the Maokou Formation.
The evolutionary history of the Deyang–Anyue depression (DAD) during the Sinian and Cambrian periods in the Sichuan Basin (SB) remains unclear, and the lithofacies palaeogeography during key stages is poorly understood. To address these gaps, this study integrates data from core samples, thin sections, well logs, seismic records, and previous research. The analysis focuses on the tectonic–sedimentary background shaped by the evolution of the DAD in the SB. Using 2D and 3D continuous seismic data, the study reconstructs the evolutionary process of the DAD, reconstructs lithofacies palaeogeography for critical periods, analyses the temporal and spatial distribution patterns of reservoir variations within the context of DAD evolution, and identifies the reservoir development zones of the Dengying Formation (DY). The research reveals that the inherited geomorphic pattern of the DY during its depositional and karst exposure stages—characterized by lower elevations in the west and north and higher elevations in the east and south—controlled the deposition and filling patterns of the DY across different periods. Consequently, the formation is thicker in the west and north and thinner in the east and south. The scale and morphology of the DAD were shaped by the combined effects of negative geomorphology, regional extensional forces, and sea-level fluctuations prior to DY deposition. The DAD underwent four major evolutionary stages: initial embryonic formation, progressive development, structural stabilization, and eventual infill and demise. Controlled by the tectonic and sedimentary evolution of the DAD, the DY platform evolved from a ramp platform depositional system to a rimmed-platform depositional system. Constrained by seismic facies, the mound–shoal complexes of each stage display a sequential evolutionary pattern, characterized by both inherited construction and a consistent ring-shaped distribution around structural highs. The DAD governs the differential reservoir-forming processes of the DY and the development of high-quality source rocks. The Intraplatform karst-reworked slope reservoir zone of the fourth member of the Dengying Formation (D4) represents a key future exploration target, owing to its favorable reservoir development potential and excellent hydrocarbon source configuration.
Phylloid algae are the dominant reef-building organisms during the Pennsylvanian, and they have a widespread distribution. However, the construction model and the controlling factors of the phylloid algal reef during this period were not well understood. In this study, a well-developed Kasimovian triple hybrid carbonate reef is reported for the first time from the Houchang area, southern Guizhou Province, South China. The reef is primarily composed of phylloid algal cementstones and phylloid algal-cement-microbial framestones. The reef developed in a platform margin setting within the photic zone under well-circulated marine conditions, likely around the fair-weather water base. Phylloid algae, abiotic cements and microbially mediated cements were dominant contributors to the studied reef. Phylloid algae could build simple frameworks. Early marine cement stabilized the reef framework and filled almost half of primary cavities. Microbial carbonates occurred in the upper part of the reef, as subordinate framework stabilizer. This phylloid algal-cement-microbial reef is classified as a triple hybrid carbonate in the tropical region of eastern Paleo-Tethys. It was controlled by long-term and regionally universal factors throughout the Pennsylvanian, including eustatic fluctuations, atmospheric pCO2 levels, and seawater chemistry (specifically the Mg2+/Ca2+ ratio). The studied reef provides insight for the triple hybrid carbonates in the Late Pennsylvanian.
The Romualdo Formation, located in the Araripe Basin (NE, Brazil), represents an important sedimentary record of the late Aptian/early Albian transition, evidencing the establishment of a mixed siliciclastic–carbonate platform influenced by eustatic oscillations and marine ingressions associated with the breakup of Gondwana. Detailed analysis of thin sections from the Santo Antônio, Cedro, and Sobradinho sections revealed eight main microfacies: Packstone with ostracod (Po), Bioclastic Packstone with intraclasts (BPi), Bioclastic Wackestone with foraminifera (BWf), Wackestone with bioclasts and peloids (Wbp), Microbialite (Mb), Shale with ostracods (So), Massive sandstone with glauconite (Smg), and Lithic Sandstone (LS) which record the transition from restricted inner shelf environments to open marine conditions. Micropaleontological data described in thin sections reveal a high diversity of microfossils, including foraminiferal genera (Spirosigmoilina sp., Quinqueloculina sp., Neoconorbina sp., Sigmoilinita sp., Microhedbergella sp., among others) and ostracod genera (Pattersoncypris sp., Damonella sp., Mongolianella sp., and Dicrorygma sp.). The dasycladacean green algae Neomeris cretacea and Brasiliporella sp. were also identified, representing new records for the south-central margin of the basin and expanding the paleogeographic distribution of these organisms. Biostratigraphic data and the Oceanic Anoxic Event (OAE1b) was used as a chronostratigraphic datum for correlation between the studied sections, marking the upper Aptian/lower Albian boundary. The event OAE1b corresponds to a major transgressive pulse, enabling the integration of local facies successions into the global paleoceanographic framework. Overall, the integration of microfacies, microfossil, and geochemical data reveals the development of a heterogeneous shallow-marine system, composed of third-order transgressive–regressive cycles controlled by eustatic oscillations and marine connections of Tethyan affinity during the late Aptian/early Albian.
This study investigates the Upper Cretaceous Muti Formation, exposed in isolated outcrops around the Jabal Akhdar Dome, which was deposited within a tectonically active marine foreland basin along the northeastern margin of the Arabian Plate during syn-obduction. Detailed sedimentological analyses were carried out using measured stratigraphic sections, lithofacies and microfacies analysis, and petrographic examination of carbonate and siliciclastic components from ten sections across the northern, northeastern and southern parts of the dome. The Muti Formation comprises four lithofacies associations; (1) limestone, (2) conglomerate-breccia, (3) claystone and (4) ferruginous claystone, encompassing ten lithofacies and ten carbonate microfacies ranging from mudstone to packstone. Facies assemblages indicate deposition in mid- to outer-shelf, slope and basinal marine environments, dominated by pelagic to hemipelagic carbonate sedimentation. Detrital components, chiefly quartz with subordinate clay minerals and heavy minerals, record sustained siliciclastic input from mixed continental and platform sources, with an upward increase reflecting progressive basin evolution. Spatial facies variations and thickness changes document asymmetric foreland basin development controlled by thrust loading, differential subsidence and syndepositional faulting. Initial sedimentation was concentrated along the northeastern margin of the basin, whereas southern sections record deeper-water deposition during later stages. Collectively, the results demonstrate that the Muti Formation preserves a facies-based record of Late Cretaceous foreland basin evolution, marking the transition from carbonate-dominated sedimentation to a mixed carbonate-siliciclastic system driven by syn-obduction tectonics and high sea level.
An unusual type of encrusted bubble froth accumulated within hyperthermophile biofilms along the waterline and splash zones of the Dewar Creek geothermal spring in southeastern British Columbia area of the Canadian Cordillera. Two tiers of adjoined bubbles resulted as the froth was progressively encrusted on the unconsolidated bottom sediment and an overlying crust. The calcium carbonate phase of the encrusted bubbles remains uncertain, but the depositional environment of the sediments accumulated along the geothermal spring includes innumerable amorphous calcium carbonate (ACC) spheroids, many with partial to complete transformation into larger calcite spherules. This depositional environment would be consistent with ACC nanoparticles precipitated on the bubble surfaces. Rapidly nucleated ACC or other calcium carbonate nanoparticles were responsive to electrostatic forces and resulted in their monodispersal on the 0.5 to 1.5 µm diameter bubble surfaces. The nanoparticles were mobilized downward toward the basal attachment area of each bubble, resulting in a circular rim of nanoparticles at the top surface of the bubble. This process formed a circular zone without nanoparticles as the join site for the attachment of an overlying bubble and a nonoccluded conduit for connectivity between the gaseous interiors of the adjacent bubbles. Upon the removal of the protective biofilm cover, gas migrated upward between the interiors of the adjoined bubbles and outward into the water, bursting the upper tier bubbles. Infilling of the bubble interiors with water prevented collapse and complete obliteration. The fragmentary basal portions of the burst upper bubbles were preserved as bell-shaped fluid escape structures attached to the intact portions of the underlying encrusted bubbles. These fragile bell-shaped burst-nanobubble structures have not been previously documented in other hot spring deposits.
