Shallow-water Sediments Research Articles

Estimation of gas saturated sediments parameters in shallow water using vector receiver

A scheme for estimating parameters of gas-saturated sediments in shallow waters based on signals from moving noise source is proposed and tested on experimental data. Advantages of joint use of information about pressure and vertical component of particle velocity in solving the considered problem are discussed.

Paleo-redox conditions during the demise of a carbonate platform in the Tethyan ocean: Evidence from phosphatized and metals (Mn and Fe) rich hardgrounds

Phosphatized Mn and Fe rich hardgrounds and condensed pelagic deposits in carbonate platform successions are precious archives of abrupt climate and environmental changes (redox conditions and phosphorous availability) in the past shallow-water marine environment. While numerous examples have been documented in the Cretaceous successions of the Northern Tethys, the scarcity of similar descriptions from the southern margins suggests differences in sedimentary processes or preservation conditions.In this work we study three phosphatized Mn and Fe rich hardgrounds and pelagic condensed deposits that mark the repetitive demise of the Panormide carbonate platform developed in the Southern Tethyan margin during the Cretaceous. The integration of SEM-EDS, PXRD, and Micro-Raman spectroscopy data shows that these hardgrounds consist of fine-grained Fe (goethite and hematite) and Mn (birnessite and/or vernadite) oxides dispersed in a calcite and apatite matrix. Micro-Raman spectroscopy shows the presence of oxidized Mn species: Mn3+ and Mn4+. The oxidation of Mn2+ → Mn3+/4+ and/or Fe2+ → Fe3+ occurred at the sediment-seawater interface under oxic conditions (where both Mn and Fe oxidize) or suboxic conditions (where only Fe oxidizes). The paleoenvironmental perturbations that triggered the formation of both hardgrounds and condensed pelagic deposits were likely related to pCO2 cycle, upwelling of P-Mn-Fe-rich water masses, eutrophication and phosphatization related to the Cretaceous climate oscillations during the main Oceanic Anoxic Events. These perturbations were likely enhanced by tectonic activity. Moreover, we show that the formation of the phosphatized metals-rich hardgrounds and the recovery of shallow-water sedimentation occurred after long-term periods (6–12 Ma). Thus, the Panormide serves as a remarkable example of resilience amidst significant climatic changes.

Grain-size distribution characteristics of sediments in coastal shallow waters from Van Don to Tien Yen - Ha Coi, Northwest Gulf of Tonkin, Vietnam, according to End-member modelling analysis

The study involved the collection of eighteen surface sediment samples from the coastal shallow water area from Van Don to Tien Yen - Ha Coi in the Northwestern section of the Gulf of Tonkin to analyze their particle size composition. Utilizing the EMMAgeo end-member analysis model, four characteristic particle sizes (4EM) of 0.34, 7.7, 130, and 230 µm, corresponding to clay, fine silt, and fine sand of varying sizes were identified. In conjunction with the sedimentary environment, the spatial distribution analysis of these end members allowed a detailed determination of the formation conditions and distribution of the sediment components. Clay deposits (EM1) are primarily intercalated between the islands. At the same time, fine silt (EM2) is concentrated in the northern part of the study area, transported by flows, and deposited in a low-energy environment. Fine sand sediments (EM3 and EM4) are distributed along the coast of the Van Don peninsula in the Southern part of the study area and likely formed in association with tidal-wave processes under higher energy conditions compared to the North.

Pyritic stromatolites from the Paleoarchean Dresser Formation, Pilbara Craton: Resolving biogenicity and hydrothermally influenced ecosystem dynamics.

This study investigates the paleobiological significance of pyritic stromatolites from the 3.48 billion-year-old Dresser Formation, Pilbara Craton. By combining paleoenvironmental analyses with observations from well-preserved stromatolites in newly obtained drill cores, the research reveals stratiform and columnar to domal pyritic structures with wavy to wrinkly laminations and crest thickening, hosted within facies variably influenced by syn-depositional hydrothermal activity. The columnar and domal stromatolites occur in strata with clearly distinguishable primary depositional textures. Mineralogical variability and fine-scale interference textures between the microbialites and the enclosing sediment highlight interplays between microbial and depositional processes. The stromatolites consist of organomineralization - nanoporous pyrite and microspherulitic barite - hosting significant thermally mature organic matter (OM). This includes filamentous organic microstructures encased within nanoporous pyrite, resembling the extracellular polymeric substance (EPS) of microbes. These findings imply biogenicity and support the activity of microbial life in a volcano-sedimentary environment with hydrothermal activity and evaporative cycles. Coupled changes in stromatolite morphology and host facies suggest growth in diverse niches, from dynamic, hydrothermally influenced shallow-water environments to restricted brine pools strongly enriched in from seawater and hydrothermal activity. These observations, along with S stable isotope data indicating influence by S metabolisms, and accumulations of biologically significant metals and metalloids (Ni and As) within the microbialites, help constrain microbial processes. Columnar to domal stromatolites in dynamic, hydrothermally influenced shallow water deposits likely formed by microbial communities dominated by phototrophs. Stratiform pyritic structures within barite-rich strata may reflect the prevalence of chemotrophs near hydrothermal venting, where hydrothermal activity and microbial processes influenced barite precipitation. Rapid pyrite precipitation, a putative taphonomic process for preserving microbial remnants, is attributed to microbial sulfate reduction and reduced S sourced from hydrothermal activity. In conclusion, this research underscores the biogenicity of the Dresser stromatolites and advances our understanding of microbial ecosystems in Earth's early history.

Deep-water first occurrences of Ediacara biota prior to the Shuram carbon isotope excursion in the Wernecke Mountains, Yukon, Canada.

Ediacara-type macrofossils appear as early as ~575 Ma in deep-water facies of the Drook Formation of the Avalon Peninsula, Newfoundland, and the Nadaleen Formation of Yukon and Northwest Territories, Canada. Our ability to assess whether a deep-water origination of the Ediacara biota is a genuine reflection of evolutionary succession, an artifact of an incomplete stratigraphic record, or a bathymetrically controlled biotope is limited by a lack of geochronological constraints and detailed shelf-to-slope transects of Ediacaran continental margins. The Ediacaran Rackla Group of the Wernecke Mountains, NW Canada, represents an ideal shelf-to-slope depositional system to understand the spatiotemporal and environmental context of Ediacara-type organisms' stratigraphic occurrence. New sedimentological and paleontological data presented herein from the Wernecke Mountains establish a stratigraphic framework relating shelfal strata in the Goz/Corn Creek area to lower slope deposits in the Nadaleen River area. We report new discoveries of numerous Aspidella hold-fast discs, indicative of frondose Ediacara organisms, from deep-water slope deposits of the Nadaleen Formation stratigraphically below the Shuram carbon isotope excursion (CIE) in the Nadaleen River area. Such fossils are notably absent in coeval shallow-water strata in the Goz/Corn Creek region despite appropriate facies for potential preservation. The presence of pre-Shuram CIE Ediacara-type fossils occurring only in deep-water facies within a basin that has equivalent well-preserved shallow-water facies provides the first stratigraphic paleobiological support for a deep-water origination of the Ediacara biota. In contrast, new occurrences of Ediacara-type fossils (including juvenile fronds, Beltanelliformis, Aspidella, annulated tubes, and multiple ichnotaxa) are found above the Shuram CIE in both deep- and shallow-water deposits of the Blueflower Formation. Given existing age constraints on the Shuram CIE, it appears that Ediacaran organisms may have originated in the deeper ocean and lived there for up to ~15 million years before migrating into shelfal environments in the terminal Ediacaran. This indicates unique ecophysiological constraints likely shaped the initial habitat preference and later environmental expansion of the Ediacara biota.

Geomorphological features along the shelf of the southern Brazilian margin: Implications for shallow-water sediment transport induced by ocean currents

Chirp profiles collected on the southern Brazilian shelf were combined with sedimentological and hydrodynamic data to characterize shelf geomorphology, focusing on the development of outer shelf bedforms and their genetic links with major oceanic currents. Outer shelf sediment accumulations are interpreted as two scales of bedforms, such as dunes and sand ridges. In the São Paulo Bight, cuspate bedforms are bounded landward by a geomorphological scarp. The sector between Florianopolis and Mostardas also exhibits frequent asymmetric bedforms, whereas the inner- middle shelf is covered by semitransparent sheets. The southern Rio Grande Cone is characterized by stratified deposits covering vast outer shelf areas. Surficial sediment samples reveal a dominantly muddy composition and relatively high carbonate contents. Hydrodynamic data indicate a major influence of the Brazil Current over the São Paulo Bight. The prolific bedform outer-shelf environment is assumed to be mostly relict formed in a transgressive shallow-water setting. The sand ridges are believed to have evolved from a moribund stage characterized by morphological degradation to a relict stage, with preservation enhanced by fine-grained winnowing, coarse sediment armoring, and early cementation. Bedform migration seems to be occurring on the São Paulo Bight due to the presence of a nearly permanent meander of the Brazil Current. Over most of the inner shelf, the northward advection of sediments mainly led by the Brazilian Coastal Current has formed extensive fine-grained deposits. The occurrence of a relict shelf scarp may have conditioned the formation of the outer-shelf bedform environment. The vast spatial distribution of bedforms over most of the outer shelf seems comparable with other shelf areas, such as the south African shelf, dominated by the influence of unidirectional oceanic currents. Dune dimensions are lower on the Brazilian shelf, due to their relict character, the geomorphological configuration of the margin, and the scarcity of sand sources.

Mixed siliciclastic-carbonate-tuffaceous sedimentation in a rift lacustrine basin: A case study of the Lower Cretaceous Jiufotang Formation in the Luxi sag, Songliao basin

The Lower Cretaceous Jiufotang Formation lacustrine successions in the rift Luxi sag, Songliao Basin are characterized by mixed siliciclastic-carbonate-tuffaceous and organic-rich deposits. Ten facies were recognized and were formed in fan delta, delta, littoral-sublittoral lacustrine and deep lacustrine environments. A depositional sequence characterized by significant changes in facies and lake regime has been defined, and is divided into lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST) that are separated by sequence boundaries, initial flooding surfaces, and maximum flooding surfaces, respectively. During the LST, the delta and fan delta deposits covered the marginal area and extended into littoral-sublittoral lacustrine and deep lacustrine environments, respectively. During the TST, the areas of delta and fan delta decreased and lake areas increased, and the carbonate-dominated shoals and mixed siliciclastic-carbonate shorelines occupied the edge of the Majiapu highland belt. During the HST, the lake areas further expanded, and the fan delta deposits extended into deep lacustrine environments and formed deposits of underflows and turbidites. A depositional model in the rift lacustrine Luxi sag is proposed, incorporating the effects of tectonics and sediment supply, climate and carbonate production, hydrodynamic conditions, and lake-level fluctuations. During the LST, the active tectonic movement, high input of siliciclastic sediments, and subaerial volcanic eruptions resulted in the wide distribution of mixed siliciclastic-tuffaceous sedimentation. During the TST, the brackish lake water controlled by periodic dry and hot climate facilitated the carbonate deposition in shallow water, and tractional currents onto the lake shore carried sediments to form the mixed siliciclastic-carbonate-tuffaceous facies. During the HST, more humid climate and increased runoff allowed formation of widely distributed, mostly oil shale-rich deposits, and the gravity flows carried the sediments into the deeper part of basin to form the mixed siliciclastic-carbonate-tuffaceous facies. The depositional model of mixed deposits in this rift lacustrine basin has been proposed here in order to encourage comparison with other similar basins.

SEDIMENTATION CONDITIONS OF THE LOWER CRETACEOUS DEPOSITS OF THE NORTHERN CASPIAN

This research identifies sedimentation settings of Lower Cretaceous (Aptian-Albian) terrigenous sediments of the North Caspian, which are oil and gas reservoirs. These rocks are characterized by irregular distri- bution of pelitic and silty fractions, which leads to ambiguous results of petrophysical analyses. In order to correctly interpret the geophysical data, a detailed lithologic analysis of the rocks was carried out. In the studied area in the Early Cretaceous time marine conditions prevailed: coastal, shallow-marine, relatively shallow shelf lithofacies with signs of active hydrodynamics, as well as relatively deep-water shelf lithofacies of low hydrodynamics. The study of sections reveals a change from shallow-water sediments to deeper-water sediments and vice versa, which allows us to conclude that the sea level fluctuates periodically. Lithologic analysis also showed the predominance of shallow-water and coastal sediments in the Aptian time and deeper-water, shelf sediments in the Albian time. Consequently, we can assume the presence of local sea transgression in this study area during the Lower Cretaceous.

Stepwise astronomical tuning of obliquity-driven evaporite cycles in an Eocene salt lake (Jianghan Basin, Hubei Province, China): Implications for middle Eocene East Asian monsoon-like climate evolution

The rhythmic evaporation cycle is an ideal recorder of astronomical cycle signals, but studies on cyclostratigraphy have yet to be directly conducted on halite-rich strata. The Qianjiang Depression of the Jianghan Basin is a representative Eocene East Asian halite-rich basin, and the salt rhythmites that developed therein are important recorders of climate evolution in East Asia. This study selected five wells for basin-scale cyclostratigraphy analysis, taking the Lower Qian 4 member of the Qianjiang Formation as the research object. This study found that the basinal salt lake facies were dominated by obliquity cycles, whereas the shallow-water deposits mainly recorded short eccentricity cycles. The study also found that s3−s6 obliquity cycles could be detected throughout the salt lake sedimentary record. Therefore, a stepwise astronomical tuning scheme was adopted. First, the target intervals in different sedimentary areas were preliminarily tuned to s3−s6 obliquity cycles, and stratigraphic correlation was performed. Then, the tuned data were further adjusted using obliquity cycles to reveal the impact of obliquity on the development of salt rhythmites and establish a floating astronomical time scale (ATS). Sedimentary noise models and pollen analysis further demonstrated that obliquity amplitude modulation cycles drove periodic changes in hydrology and climate. Based on the spatiotemporal distribution of salt rhythmite−rich strata in Paleogene East Asia, this study proposes that the development of rhythmic evaporites can reveal the existence of a monsoon-like climate. Astronomical influence was an important driving force for developing the middle Eocene East Asian monsoon.

Stratigraphical and sedimentological controls on the distribution of Cloudina bioclastic accumulations in the terminal Ediacaran Tamengo Formation (Corumbá Group), Brazil

The appearance of the early biomineralized skeletons during the latest Ediacaran was one of the most important evolutionary gains for the ancient animals' lineage. This evolutionary innovation likely represents a pivotal shift in ecology and the interactions between the geosphere and biosphere. Among these fossils, Cloudina stands out as the oldest macroscopic biomineralized metazoan that achieved widespread distribution. However, the complex interplay between sedimentation, preservation, and the vertical distribution of bioclastic accumulations in the Ediacaran strata remains unexplored. The Ediacaran Tamengo Formation (Western Brazil) records thick shallow water deposits and preserves several stratigraphic intervals that contain bioclastic-rich beds formed by Cloudina remains. This unit represents a window for investigating the role of the earliest truly and their impact on Ediacaran marine environments. Our investigation aims to examine the sedimentology and taphonomy of Cloudina within the Tamengo Formation in Brazil to test the hypothesis that the emergence of skeletal hard parts influenced sedimentary depositional processes. To achieve this goal, we combine bioclastic remains and facies/microfacies analysis, taphonomy, and sequence stratigraphy. Our approach involves analyzing the distribution of bioclasts in correlation with stratigraphy and microfacies. By doing so, we aim to forecast the presence of bioclastic accumulations across a mixed siliciclastic–carbonate ramp section. Our findings reveal variability in bioclast sizes among different sites, suggesting a correlation with environmental factors. Furthermore, our study underscores the significance of comparing bioclast accumulations between Precambrian and Phanerozoic deposits, emphasizing their broad utility in understanding evolutionary and environmental shifts over time.

Estimating Parameters of Gas-Saturated Sediments in Shallow Water Using a Vector Receiver

Estimating Parameters of Gas-Saturated Sediments in Shallow Water Using a Vector Receiver

A new species of the larger porcelaneous foraminifer Borelis provides novel insights into Neogene to Recent western Pacific palaeobiogeographical dispersal patterns

Only three species of alveolinoidean larger foraminifera occur in present-day tropical shallow-water marine settings. Alveolinella quoyi thrives in the Central Indo-Pacific and Eastern Indo-Pacific, Borelis pulchra in the Central and Eastern Indo-Pacific and in the central Atlantic, whereas Borelis schlumbergeri inhabits the Indo-Pacific Ocean. The northernmost record is that of Alveolinella quoyi from the shallow-water settings in Okinawa (central Ryukyu Islands, Japan). A new porcelaneous larger foraminiferal species, Borelis matsudai sp. nov. (Alveolinoidea, Borelinae), is established herein, based on specimens discovered in present-day shallow-water sediments from Sekisei Lagoon, southern Ryukyu Islands (Japan). This is the northernmost record of the genus in the western Indo-Pacific Warm Pool. The architectural characters of this species suggest its phylogenetic relationship with the Borelis pulchra group. A comprehensive literature survey of fossil and modern records of Borelis pulchra over the past 30 million years shows that the Middle Miocene constriction of the Indonesian Seaway and the Late Miocene–Early Pliocene restriction of the Indonesian Throughflow impacted the species-level dispersal of this species in the Indo-Australian Archipelago. Driven by the Kuroshio dispersal route Borelis matsudai sp. nov. likely appeared in the southern and central Ryukyu Islands at least from the Chibanian (Middle Pleistocene). This species represents a marginal part of a population in significant contact with its ancestor (B. pulchra), which is widespread southward since the Oligocene (Philippines). With ongoing global warming possible occurrences of Borelis matsudai sp. nov. in the northern Ryukyu Islands, where it has not yet been found, are expected. The Sekisei Lagoon represents, therefore, a biogeographical stepping stone relay station in northward migration of the shallow-water benthic organisms along the Kuroshio dispersal route.

Litho-bio-stratigraphy model and palaeoenvironments of the Babouri-Figuil Basin (NE Cameroon): A lacustrine/fluvial/deltaic setting associated to the Benue Trough (Nigeria)

This paper focuses on the lithostratigraphy and the palaeoenvironmental evolutions of the Babouri-Figuil Basin depositional system. Facies analysis, palynology and organic geochemistry were investigated to propose a 2D sedimentary model of the basin. The study reveals that, this basin is made up of four main facies (sandstones, siltstone, claystone/shale and marls) resting on the granite-gneissic basement. The general trend of the beds is E-W; they dip to the S (SW or SE) and NE, with angles ranging between 4 and 30°. The sedimentary analysis indicates an arid to semi-arid climate. The pollen assemblage strongly suggests a Cenomanian-Turonian age for the sedimentary interval which contains the black shale formations. The presence of the mixture of marine and terrestrial organic matter (type II, I and III) in the same interval indicates a possible marine shallow-water deposit in the basin. The deposits were also influenced by volcanic events and hydrothermal fluid circulation during diagenesis, which are the source of carbonate enrichment in the sediments. The analysis of the sedimentary bodies, the encountered palynology assemblage and the 2D reconstruction show that the sedimentary formations of the Babouri-Figuil Basin were deposited in a lacustrine/fluvial/deltaic sedimentary environment.

Holocene extreme palaeofloods recorded by slackwater deposits along the Jiacha Gorge of the Yarlung Tsangpo River valley, southern Tibetan Plateau

Natural archives of past larger floods provide insights for assessment of future extreme flood events and climate variability in High Asian rivers. However, the sedimentary characteristics and ages of palaeoflood slackwater deposits (SWDs) still remain unclear in the Yarlung Tsangpo River (YTR), the largest river around the Tibetan Plateau. In this study, three palaeoflood SWD benches along the Jiacha Gorge were systemically analyzed. The SWDs are characterized by very fine and fine sand with parallel-bedding climbing ripples. High-resolution grain-size variation from bottom to end-point part of SWD layers, as well as the C–M technique and hydrodynamic model indicates a past suspension sand deposition (as graded and uniform beds) in shallow water and at lower velocity during high flood discharges. Geochemical data and heavy-mineral analysis suggest the SWDs to have experienced only a weak weathering process, and identify the assemblage to be derived from local felsic bedrocks in the Lhasa Terrane. At least two periods of palaeoflood events, 6.3–4.7 and 3.7–3.0 ka, were identified by using the optically stimulated luminescence (OSL) dating. The minimum palaeoflood discharges were estimated to be 31,600 m3/s in the one-dimensional model, varying from 28,500 m3/s to 45,000 m3/s within a 25% variation in roughness values. The palaeoflood chronology and magnitude documented herein are obviously different from earlier work in the area, do not supporting to establish a direct linkage with palaeo-lakes and outburst floods along the middle YTR valley. These extreme palaeoflood records exhibit good consistency with strengthened monsoon and glacier meltwater during the Middle and Late Holocene in the southern Tibetan Plateau.

Middle Visean (Mississippian) conodonts from shallow-water deposits in the Yashui section, Guizhou, South China, and their stratigraphic significance

AbstractThe typical Mississippian shallow-water deposits of the Jiusi and Shangsi formations are well exposed in the Yashui section in southern Guizhou, South China. The strata are composed mainly of platform limestones intercalated with shales and sandstones. Conodonts obtained from the limestones are dominated by two assemblages of cavusgnathids: the Cavusgnathus aff. Cav. unicornis and Clydagnathus windsorensis assemblage from the upper Jiusi Formation and the Cavusgnathus unicornis assemblage from the lowest Shangsi Formation. Vogelgnathus campbelli (Rexroad, 1957) is reported for the first time in Eastern Paleotethys and is characterized by small lateral denticles. The evolutionary first occurrence of Cavusgnathus unicornis Youngquist and Miller, 1949 is recognized as a marker for the regional Shangsian stage. This biostratigraphic datum is interpreted to be correlative with other shallow-water conodont zones marked by Cavusgnathus unicornis s.l. and similar species from North America and Europe.

Morphology, seismic stratigraphy, and tectonic control of the Yitong submarine canyons – fan apron system in the northern South China Sea

Submarine fans are ubiquitous in modern deep-water environments. Such systems reported in the literature are largely fed by shelf-indented canyons receiving ample fluvial or longshore drift sediment inputs, whereas those nourished by slope-confined canyons far away from terrigenous sediment sources remain poorly understood. Herein, we report such a system, the Yitong submarine canyons – fan apron system (YCFS), from the northern South China Sea. This system was studied using multibeam bathymetric and two-dimensional multichannel seismic data, combined with geological constraints from nearby International Ocean Discovery Program drilling sites. YCFS consists of approximately 12 submarine canyons confined in the lower continental slope of >1200 m water depth, which feed a fan apron in the connecting abyssal plain. The canyons are erosion-dominated, as evidenced by their V-shaped cross-sections with up to 708 m deep incisions. Canyon infillings comprise mass transport deposits and turbidites, and interfluves exhibit features such as landslides, creep-typed sediment waves, and gullies, indicating the canyons and interfluves are dominated by mass transport and turbidity-current processes. The fan apron is generally depositional, in which channels and channel-levee complexes, turbidite lobes, and mass transport deposits comprise the main depositional elements. In the canyon-to-fan transitions, supercritical turbidity current features and bedforms, including plunge pools and connected sediment mounds, cyclic steps, and antidunes, are developed, which are linked to the deceleration and hydraulic-jump effects of the high-velocity turbidity currents shedding off the canyons. Seismic stratigraphic analysis revealed that YCFS was initiated in Late Miocene. The formation and maintenance of YCFS are linked to the long-term existence of an upslope margin-parallel basement high. The latter could have maintained a steep slope condition (up to 6.5°) that favors the development of canyons and supercritical turbidity currents. Because of the blocking effect of the basement high, YCFS receives limited supply of the shallow-water sediments.

Stable Barium Isotope Fractionation in Pore Waters of Estuarine Sediments

AbstractThe development of stable barium (Ba) isotope measurements provides a novel tool to investigate the geochemical cycling of Ba in the ocean and its sediments. In sediment pore waters, gradients of dissolved Ba concentrations result from various diagenetic processes. The distribution and fractionation of Ba isotopes in the pore waters are expected to further improve our understanding of these early diagenetic control mechanisms. Here, we present pore water profiles of dissolved stable Ba isotopic signatures (δ138Bapw) from shallow water sediments covering the entire Pearl River Estuary (PRE) in Southern China. We find pronounced depth‐dependent Ba isotope variations generally showing a shift from heavy to light δ138Bapw signatures from the sediment surface down to 15 cm depth. These gradients are well reproduced by a diffusion‐reaction model, which generates an apparent fractionation factor (138ε) of −0.60 ± 0.10‰ pointing to preferential removal of low‐mass Ba isotopes from the pore water during solution‐solid phase interactions. Consequently, the combined diagenetic processes induce the highest δ138Bapw values of +0.5 to +0.7‰ in the pore waters of the topmost sediment layer. Although the detrital fraction dominates the Ba content in the PRE surface sediments, the determined gradients of pore water Ba isotopes, together with concentration variations of Ba and other redox‐sensitive elements such as manganese (Mn), show that non‐detrital excess Ba carriers including Mn oxides and authigenic barite clearly affect the post‐depositional Ba dynamics. Stable Ba isotopes are thus a potentially powerful tracer of Ba geochemistry during early sediment diagenesis in estuarine depositional environments.

The first record of a Konservat-Lagerstätten in which early post-settlement stages of fossil archaeobalanids (Cirripedia: Balanomorpha) are preserved.

A diverse sessile barnacle fauna from a Miocene shallow-water deposit at Dolnja Stara vas in Slovenia is described. It includes the first descriptions of early post settlement juveniles of Actinobalanus sloveniensis attached to mangrove leaves. These represent three distinct growth phases, the earliest being interpreted as being less than 24 h post settlement, the others being 1 to 2 days post settlement. An assessment of their taphonomy is provided. Associated adult balanomorphs are attached to a variety of organic substrates, including mangrove leaves and branches, fragments of the conifers ?Taxodioxylon, Carapoxylon, pine cones, molluscs, and cetacean bones. The barnacles include A. sloveniensis, Amphibalanus venustus, and Perforatus perforatus-many with opercula retained within the shells. A. venustus retains some of the original shell color. This is the second record of barnacle-plant associations from the Central Paratethys from Kamnik and Trbovlje. The paleoecology and paleogeography of the site are discussed.

Carbonate sedimentation and reservoirs associated with a volcanic mound in an open-marine, deep-water, drowned platform setting, Elaine field area, Upper Cretaceous Anacacho Formation, South Texas U.S.A.

In the Upper Cretaceous Balcones Igneous Province in South and Central Texas, numerous small volcanoes developed during Austin Chalk and Anacacho deposition that are similar to the recent Surtsey volcano offshore of Iceland. The volcanoes formed topographic highs on the deep-water (500–900 ft [150–275 m]), earlier-drowned Comanche Platform. The Elaine field in South Texas is associated with one of these relict volcanic highs and integration of a 3D-seismic dataset and cores permitted a detailed analysis of the deeper-water carbonate depositional systems of the field and associated carbonate reservoir development. This reservoir description extends the understanding of petroleum systems associated with relict, open-marine, deep-water, volcanic highs. In the shallow water at the top of the volcanic topographic highs, a carbonate factory developed that produced coarser-grained carbonate sediments that sourced the deeper-water flanks and toe-of-slope of the mound. Finer-grained carbonate chalk was deposited in the open-marine, deep-water environment adjacent to the volcanic mound. The coarser-grained carbonate sediments sourced from the mound top were transported downslope by gravity-flow processes that formed debrites and hyperconcentrated density-flow deposits. The gravity-flow deposits are composed of a mixture of shallow- and open-marine, deep-water biota indicating they are not shallow-water deposits, but are deeper-water mound-flank and toe-of-slope deposits.In the Anacacho Elaine field, the coarser-grained carbonates (i.e., skeletal packstones and grainstones) associated with the volcanic mound are the oil-producing reservoirs. The Elaine volcanic mound itself is tight and not productive. The Anacacho chalk immediately above the mound are also tight and form the top seal for the Elaine field.Associated with the relict volcanic mounds in the Balcones Igneous Province are a spectrum of carbonate plays. The relict volcano can be a reservoir, but not all the relict volcanic mounds are porous. The coarser-grain carbonates on the top, flanks, and at the base of the volcanic mounds are reservoirs in the area of the Balcones Igneous Province. The chalks deposited penecontemporaneously on the open-marine, deep-water platform can also be tight carbonate reservoirs.

The mesoglea buffers the physico-chemical microenvironment of photosymbionts in the upside-down jellyfish Cassiopea sp.

IntroductionThe jellyfish Cassiopea has a conspicuous lifestyle, positioning itself upside-down on sediments in shallow waters thereby exposing its photosynthetic endosymbionts (Symbiodiniaceae) to light. Several studies have shown how the photosymbionts benefit the jellyfish host in terms of nutrition and O2 availability, but little is known about the internal physico-chemical microenvironment of Cassiopea during light–dark periods.MethodsHere, we used fiber-optic sensors to investigate how light is modulated at the water-tissue interface of Cassiopea sp. and how light is scattered inside host tissue. We additionally used electrochemical and fiber-optic microsensors to investigate the dynamics of O2 and pH in response to changes in the light availability in intact living specimens of Cassiopea sp.Results and discussionMapping of photon scalar irradiance revealed a distinct spatial heterogeneity over different anatomical structures of the host, where oral arms and the manubrium had overall higher light availability, while shaded parts underneath the oral arms and the bell had less light available. White host pigmentation, especially in the bell tissue, showed higher light availability relative to similar bell tissue without white pigmentation. Microprofiles of scalar irradiance into white pigmented bell tissue showed intense light scattering and enhanced light penetration, while light was rapidly attenuated over the upper 0.5 mm in tissue with symbionts only. Depth profiles of O2 concentration into bell tissue of live jellyfish showed increasing concentration with depth into the mesoglea, with no apparent saturation point during light periods. O2 was slowly depleted in the mesoglea in darkness, and O2 concentration remained higher than ambient water in large (> 6 cm diameter) individuals, even after 50 min in darkness. Light–dark shifts in large medusae showed that the mesoglea slowly turns from a net sink during photoperiods into a net source of O2 during darkness. In contrast, small medusae showed a more dramatic change in O2 concentration, with rapid O2 buildup/consumption in response to light–dark shifts; in a manner similar to corals. These effects on O2 production/consumption were also reflected in moderate pH fluctuations within the mesoglea. The mesoglea thus buffers O2 and pH dynamics during dark-periods.