Platform Geometry Research Articles

Measurements of K-edge and L-edge extended x-ray absorption fine structure at the national ignition facility (invited).

High-energy-density laser facilities and advances in dynamic compression techniques have expanded access to material states in the Terapascal regime relevant to inertial confinement fusion, planetary science, and geophysics. However, experimentally determining the material temperature in these extreme conditions has remained a difficult challenge. Extended X-ray Absorption Fine Structure (EXAFS), referring to the modulations in x-ray absorption above an absorption edge from photoelectrons' interactions with neighboring atoms, has proven to be a versatile and robust technique for probing material temperature and density for mid-to-high Z elements under dynamic compression. The current platform at the National Ignition Facility has developed six configurations for EXAFS measurements between 7 and 18keV for different absorption edges (Fe K, Co K, Cu K, Ta L3, Pb L3, and Zr K) using a curved-crystal spectrometer and a bright, continuum foil x-ray source. In this work, we describe the platform geometry, x-ray source performance, spectrometer resolution and throughput, design considerations, and data in ambient and dynamic-compression conditions.

Geometry optimization of a floating platform with an integrated system of wave energy converters using a genetic algorithm

This study uses a genetic algorithm(GA) to investigate the practicality of optimizing the geometry and dimensions of a floating platform, which houses pitching wave energy converters (WEC). Using frequency-domain analysis, sensitivity tests for the search start point, choice of optimized variable, number of iterations, simulation time, and contents of the search space are made. Results show that the required number of iterations to convergence increases with an increased number of optimized variables. Furthermore, for the studied platform geometry, no single global optimum exists. Instead, various combinations of characteristic features can lead to comparable performances of the integrated wave absorber. Finally, it is observed that when the solution space is controlled and made to contain a subset of potential solutions known to improve the system performance, computation time, absorption efficiency and range are observed to improve. Additionally, the GA optimum tends towards platform geometries for which the wave absorber’s resonance response corresponds to the dominating wave climate frequencies. A key contribution of this study is the controlled manipulation of the solution space to contain a subset of potential solutions that enhance system performance. This controlled approach leads to improvements in computation time, absorption efficiency, and range of the system.

X-Ray Diffraction Measurements for Inconel 718 Alloy Elements Created by Incremental Methods

Abstract The work presented is the result of the implementation of diffraction measurements: phase composition and stresses resulting from additive manufacturing process of nickel superalloy Inconel 718 components print. With the help of diffraction methodologies, the key parameters from the point of view of the quality of prints and their strength were determined. The existence of individual phases in the material after printing was demonstrated, and the surface variation of the stress values was presented, showing its dependence on the geometry of the printed part – measurements were made at various points on the surface of samples with different geometries. In addition, the variation of the stress level was shown depending on the distance of the measurement point from the build platform on which the additive manufacturing process was carried out. Components were printed on the surface of a single build plate in order to study the effect of printing differently oriented samples with respect to the platform geometry, as well as the mutual effect of the temperature of samples printed first on the stress state of elements printed in subsequent steps of the procedure, and the effect of the temperature of elements printed later on the rate of temperature decrease, and consequently on the stress state, of elements printed first.

Local and global controls on carbon and sulfur isotope records in the Middle Ordovician Epeiric sea successions of the Taebaeksan Basin, Korea

Although the sedimentary carbonate carbon isotope record is generally considered a reliable archive of long-term changes in the global carbon cycle, the influences of local variability in carbon cycling and diagenesis frequently overwhelm its global controls, particularly in shallow platform environments. During the Middle Ordovician period, the middle Darriwilian isotopic carbon excursion (MDICE) has been identified worldwide, including the Taebaeksan Basin in the Sino-Korean Block. However, in the eastern part of the Taebaeksan Basin, the positive δ13Ccarb trend associated with the MDICE was disrupted by negative δ13Ccarb anomalies, indicating the alternating prevalence between local and global controls. By comparing paired carbon and sulfur isotope signatures, we demonstrate the involvement of two distinct mechanisms in this local event: a gradual decrease in δ13Ccarb closely parallels that of organic carbon, and a negative δ13Ccarb peak, superimposed on the long-term δ13Ccarb decrease, coincides with the positive sulfur isotope shift in pyrite, without a corresponding change in δ13Corg. The latter indicates the formation of 13C-depleted authigenic carbonate during early diagenesis, associated with microbial sulfate consumption, whereas post-depositional processes cannot fully account for the coupled negative shifts in δ13Ccarb and δ13Corg values. Instead, this simultaneous divergence from the MDICE event may be due to limited exchange of dissolved inorganic carbon with open ocean water, coupled to an increase in terrestrial runoff, as shown by changes in the clay mineral assemblage. While generally aligning with sedimentological and paleontological investigations regarding the formation of restricted environments in the eastern part of the Taebaeksan basin, this interpretation challenges the previously presumed timing and duration of platform restriction. Our findings highlight that the spatial variability of isotopic records may compromise their fidelity as global proxies but offer valuable insights into the evolution of depositional environments and platform geometry, often obscured by sporadic outcrop exposure.

Numerical Simulation of the Plant Shelterbelt Configuration Based on Porous Media Model

Low-coverage line-belt-pattern protective forests offer significant advantages in terms of wind and sand control measures. It is important to study the windbreak effectiveness of sand-fixing forests with different spacing for the construction and optimization of plant shelterbelt configurations. The effect of plant spacing on the flow field around a row of trees was investigated using the k-ε turbulence model coupled with the porous media model. In order to accurately simplify the complex and stochastic plant constitutive features, we simplify the plant canopy to a circular platform geometry, which introduces a porous media model, and the plant trunk is simulated as a solid cylinder. The simulation results show that windbreaks only affect wind profiles up to 1.25-times the height of the tree; on the leeward side of the canopy, large-spaced shelterbelts provide greater protection in the near-wake zone, while small-spaced shelterbelts are more effective at reducing velocity in the re-equilibration zone. The flow field recovery properties of the trunk and canopy indicate that the canopy wake zone is longer. In this study, we also quantitatively analyze the relationship between average wind protection effectiveness as a function of plant spacing and streamwise distance from the leeward side of the canopy, and the given parameterized scheme shows a power exponential relationship between wind protection effectiveness and plant spacing and a logarithmic relationship with streamwise distance. This scheme can provide a predictive assessment of the effects during the implementation of the plant shelterbelt.

Modeling future cliff-front waves during sea level rise and implications for coastal cliff retreat rates

It is often assumed that future coastal cliff retreat rates will accelerate as global sea level rises, but few studies have investigated how SLR (sea level rise) might change cliff-front wave dynamics. Using a new simple numerical model, this study simulates the number and type (breaking, broken, or unbroken) of cliff-front waves under future SLR scenarios. Previous research shows breaking waves deliver more energy to cliffs than broken waves, and unbroken waves generate minimal impact. Here, we investigated six cliff-platform profiles from three regions (USA, New Zealand, and UK) with varied tidal ranges and wave climates. Model inputs included 2013–2100 hindcast/forecast incident wave height and tidal water level, and three future SLR scenarios. Results show the number of both cliff-front breaking and broken waves generally increase for a high-elevation (relative to tide) cliff-platform junction. In contrast, breaking/broken wave occurrence decrease by 38–92% for a near-horizontal shore platform with a low-elevation cliff-platform junction under a high SRL scenario, leading to high (96–97%) unbroken wave occurrence. Overall, results suggest the response of cliff-front waves to future SLR is complex and depends on shore platform geometries and SLR scenarios, indicating that future cliff retreat rates may not homogeneously accelerate under SLR.

Methodology to assess scour development around complex structures

Accurate prediction of scour evolution around fixed offshore foundations is a key parameter for selecting the most appropriate scour mitigation strategy. Various formulations can be used to estimate scour around monopiles. However, non-specific formulations have been developed for more complex foundations. In the case of jacketed offshore substations (OSS), the geometry can be one of the most complex. This paper describes a hybrid methodology (numerical model simulations, semi-empirical approaches and physical experiments) to estimate the scour evolution around OSS. The application of this methodology allows the selection of the most appropriate mitigation strategy from an early stage of the project to the final decision. The methodology is accompanied by some examples. In general, the results obtained from the semi-empirical approaches show quite good agreement with the measurements from the physical experiments. Nevertheless, considering the complex geometry of the OSS and the potential non-linearities associated with the platform geometry, physical experiments are required to ensure the correct estimation of the maximum scour (local and global).

Dielectric Waveguide-Based Sensors with Enhanced Evanescent Field: Unveiling the Dynamic Interaction with the Ambient Medium for Biosensing and Gas-Sensing Applications—A Review

Photonic sensors utilize light–matter interaction to detect physical parameters accurately and efficiently. They exploit the interaction between photons and matter, with light propagating through an optical waveguide, creating an evanescent field beyond its surface. This field interacts with the surrounding medium, enabling the sensitive detection of changes in the refractive index or nearby substances. By modulating light properties like intensity, wavelength, or phase, these sensors detect target substances or environmental changes. Advancements in this technology enhance sensitivity, selectivity, and miniaturization, making photonic sensors invaluable across industries. Their ability to facilitate sensitive, non-intrusive, and remote monitoring fosters the development of smart, connected systems. This overview delves into the material platforms and waveguide structures crucial for developing highly sensitive photonic devices tailored for gas and biosensing applications. It is emphasized that both the material platform and waveguide geometry significantly impact the sensitivity of these devices. For instance, utilizing a slot waveguide geometry on silicon-on-insulator substrates not only enhances sensitivity but also reduces the device’s footprint. This configuration proves particularly promising for applications in biosensing and gas sensing due to its superior performance characteristics.

A computational framework for the co-optimization of platform hydrodynamic and passive structural control of floating offshore wind turbines

Floating offshore wind turbines extract rich and stable wind energy in the deep sea. However, they face severe sea conditions and high maintenance costs, and a promising method is needed to generate a high-performing, reliable, and robust design. Traditional sequential methods overlook the coupling between sub-systems and may miss the global optimum. The control co-design method, in contrast, focuses on the integrated optimization of the whole system. However, implementing co-simulation and co-optimization for co-design is challenging. In this study, a control co-design framework is developed and validated to couple the platform hydrodynamics with multi-physical wind turbines for integrated simulations and optimization. Based on this framework, the floating platform and tuned mass damper are co-optimized by establishing an efficient Kriging-enhanced Genetic algorithm. A case study is conducted using a 10 MW floating offshore wind turbine for demonstration. The platform shape and tuned mass dampers are parameterized by five and three design variables, respectively. To minimize platform mass, two formulations are proposed, that is, multi- and single-objective, for scenarios with and without consideration of structural loads. These formulas are solved under pre-defined turbulent wind and irregular wave conditions. Compared to the baseline model, the optimal design significantly reduces platform mass, enhancing both power generation and platform motion stability. After involving structural load in optimization, the optimal platform mass, energy production, and platform motion stability are degraded. These findings demonstrate the effectiveness of the co-design framework in optimizing platform geometry and passive structural control.

Investigating the mineralogical and geochemical composition of fluvial sediments of Watari river system, Kano, Nigeria

A key objective of this research is to conduct a mineralogical and geochemical screening of the fluvial sediments in Watari river. Data collected from this study can be used to further enhance scientific understanding of the fluvial processes in the Watari basin as well as the larger Hadejia-Jama' are basin. The geological data can also be used as input information for the prediction of sedimentation rates in the Watari dam, Kano. An intensive field was conducted to explore thebedforms (sand bars, ripples, and sand filled channel or dunes) of the proximal channel environments, platform geometry and sinuosity.X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses were used to study the mineralogy and chemical composition of the collected samples, respectively. The Watari river can be considered as braided due to the presence of smaller multi-threaded channels, braid or channel bars. The lithology of exposures observed at the river bank show a series of depositional cycles that comprise mudrocks (light and dark), sandstone, conglomerate and a basal quartzitic gravel deposit. The wacke and sub-litheranite rocks were sourced from mafic and intermediate igneous rocks. The relatively high La and Ce in the mudrocks can be attributed mainly to the adsorption of Ce onto Fe-oxides which are abundant in the fluvial sediments eroded from lateritic soils. From the bivariate plot of Al2O3/SiO2 against Fe2O3+MgO, the sandstone facies fall under the passive continental margin, while the quartzite and conglomerate facies are grouped under the foreland basin, and the light mudrock facies is classified under the continental island arc. In addition, the plot of Al2O3/(CaO + Na2O) against Fe2O3+MgO shows the sandstone and quartzite facies fall under the foreland basin. The relatively high concentration of feldspar and muscovite mica in the siliciclastic facies is indicative of close proximity to parent material, and low degree of weathering and diagenesis. The variability in the mineral composition points toward different cycles of fluvial sedimentation, diverse provenance, and wide range of source materials.The geochemical data further buttresses the variability in provenance, wider geographic area of the sediments or re-deposition and reworking by fluvial actions.

A tale of two Arabian Cenozoic ooids: Factors controlling the differential growth of ooids across the Arabian Plate

Ooids are a critical yet enigmatic carbonate grains in the geological record. Previous studies have focused their efforts on studying the mode of ooid formation throughout the Phanerozoic via experimental, numerical simulations, and field studies. To date, however, there is little discussion around factors governing the texture, mineralogy, structure, size, and geometry of Cenozoic ooids, particularly in Saudi Arabia. The present article aims to provide insights on key factors controlling the differential growth of Cenozoic ooids in Saudi Arabia by comparing two contrasting carbonate environments and tectonic settings. Here, we studied the Holocene (0.4–2 kya) ooids developed in the tidally dominated carbonate ramp of the Arabian Gulf under a passive margin setting and the Miocene (15–21 mya) ooids from the Red Sea that were developed in a tectonically active, wave-dominated fault-bounded carbonate platform. The Holocene ooids were characterized by aragonitic, heavily micritized and small (max:550 μm) ooids with bioclast-dominated nuclei. In contrast, the Miocene ooids were replaced by dolomite, larger in size (max:820 μm) and significantly less micritized with variable nuclei compositions, such as rock fragments and bioclasts. The variation in the intensity of bioerosion and micritization suggest the Miocene ooids experienced lesser resting stage time than the Holocene ooids developed under the tide regime due to active wave actions. In addition, the Miocene ooids were developed in a fault-bounded margin allowing a higher carbonate saturation state to concentrate in that zone while the Holocene ooids were developed under a widespread distribution of carbonate saturation state in a vast carbonate ramp setting. These findings indicate that original platform geometry and depositional system (tide-vs wave-dominated) are substantial in dictating the duration of ooid resting stage and distribution of carbonate saturation state across the platforms. All these combined, allows the Miocene ooids to grow larger and reaching its equilibrium size faster. This study highlights the importance of coupling platform architecture and other key environmental parameters (wave actions, sediment supply, and tectonic activities) in understanding the formation of Cenozoic ooids.

Reduced-order models for array structures mounted on platforms with parameters variations

A hybrid model order reduction (MOR) method is developed to calculate the electromagnetic characteristic of array structures mounted on platforms with parameters variations. The reduced-order model (ROM) of the platform is generated as a reduced-order input-output matrix during the offline stage. Using the equivalence principle algorithm (EPA), the ROM of array is generated by transferring the unknowns on the elements to equivalence surfaces. The frequency and material independent reactions (FMIR) method is applied to support the sweep of array material parameters. In the online stage, when the array positions vary in the input region, both of the array and platform ROMs can be used repeatedly. When the array materials vary in the input region, the platform ROM and geometry dependent matrices of EPA are reusable. Therefore, the computational cost can be reduced significantly. Comparing the proposed method to commercial solver, two numerical results are given to show the efficiency.

Hydrodynamic characteristics of a 15 MW semi-submersible floating offshore wind turbine in freak waves

Dynamics of the floating offshore wind turbines (FOWTs) in harsh ocean environments gains increasing attention due to the high maintenance costs in case of structural damage. The freak wave occurring more frequently than believed poses a threat to FOWTs, but mechanism and influencing factors of the wave-structure interaction problem have not been fully explained. In this paper, dynamics of the VolturnUS-S semi-submersible platform designed for the IEA 15 MW wind turbine under freak waves is studied using a coupled computational fluid dynamics and finite element mooring line model. First, the hydrodynamic model is validated using the DeepCwind semi-submersible platform. Then, the validated model is employed for the analysis of the VolturnUS-S semi-submersible platform under freak waves described as a focused group of waves. Hydrodynamic behaviors of the semi-submersible FOWT are described in detail, and parametric analysis of the problem including the effects of focusing crest amplitude, focusing location, incident angle, gravity center location is conducted. Important results include the dramatic surge motion of the platform and fairlead tension of the upstream mooring line, and alleviation of these responses by varying the wave angle to 30° and moving the gravity center to the centroid of the platform geometry.

Carbonate factories and their critical control on the geometry of carbonate platforms (mid-Cretaceous, southern Iran)

Tropical rimmed platforms represent a much more efficient protection from coastal erosion than carbonate ramps. Understanding the controlling factors of platform geometry is therefore crucial to predict the fate of rimmed platforms under global-warming conditions. Here, we present detailed biostratigraphic, sedimentological, geochemical, and high-resolution carbon-isotope analyses of mid-Cretaceous (Albian-Cenomanian) carbonate rocks well exposed in the Khormoj section located in the Zagros Mountains of southern Iran. Sixteen microfacies were identified, allowing us to define the superposition of different platform geometries, a carbonate ramp in the Albian and a rimmed platform in the Cenomanian. Biostratigraphic and carbon-isotope analyses allowed us to identify the OAE1b, OAE1d, and Middle Cenomanian events in the Khormoj section. The paleodepth changes documented by carbonate microfacies testify to two transgressive events that can be correlated with long-term eustatic curves during the ramp stage. The Albian ramp was formed by orbitolinids under high siliciclastic input whereas the Cenomanian rimmed platform was built by rudists during clear water conditions. These two carbonate factories have drastic different carbonate sedimentation modes. The orbitolinid factory is characterized by a low carbonate production rate and fine carbonate grains resulting in ramp geometry, whereas the rudist factory is characterized by a high carbonate production rate and coarse carbonate grains leading to a rimmed platform geometry.

Modelica‐AeroDyn: Development, benchmark, and application of a comprehensive object‐oriented tool for dynamic analysis of non‐conventional horizontal‐axis floating wind turbines

AbstractThe exploitation of offshore wind energy by means of floating wind turbines is gaining traction as a suitable option to produce sustainable energy. Multi‐rotor floating wind turbines have been proposed as an appealing option to reduce the costs associated with manufacturing, logistics, offshore installations, and operation and maintenance of large wind turbine components. The development of such systems is forestalled by the lack of a dedicated tool for dynamics and load analysis. Standard codes, such as FAST by NREL, offer the desired fidelity level but are not able to accommodate multi‐rotor configurations. A few experimental codes have been also proposed, which may accommodate multi‐rotor systems, but low flexibility makes them impractical to study a vast range of innovative multi‐rotor FWTs concepts. To close the gap, this work presents the development and comprehensive benchmark of a fully coupled aero‐hydro‐servo‐elastic tool able to easily accommodate arbitrary platform and tower geometries and the number of wind turbines employed. Development is carried out in Modelica, which allows for the employment of the same code functionality in a virtually unlimited number of physical configurations. Full blade‐element momentum capabilities are achieved by integrating into Modelica the well‐established NREL aerodynamic module AeroDyn v15 within FAST v8. Structural dynamics of tower and blades are implemented through a lumped‐element approach. Hydrodynamic loads are computed by employing the DNV software SESAM WADAM. Thorough benchmark is performed against FAST, and positive results are obtained. The dynamic performance of a two‐rotor floating wind turbine is finally assessed considering different turbulence spectrums.

Warm, not cold temperatures contributed to a Late Miocene reef decline in the Coral Sea

Evidence shows that in the modern ocean, coral reefs are disappearing, and these losses are tied to climate change. However, research also shows that coral reefs can adapt rapidly to changing conditions leading some researchers to suggest that some reef systems will survive future climate change through adaptation. It is known that there were changes in the area covered by coral reefs in the past. Therefore, it is important to investigate the long-term response of coral reefs to environmental changes and high sea-surface temperatures (SSTs). However, because of diagenetic issues with SST proxies in neritic, metastable carbonate-rich environments, there is an incomplete and sometimes even incorrect understanding of how changes in SSTs affect carbonate reef systems. A good example is the Queensland Plateau offshore northeast Australia next to the threatened Great Barrier Reef. In the Late Miocene, between 11 and 7 Ma, a partial drowning caused the reef area on the Queensland Plateau to decline by ~ 50% leading to a Late Miocene change in platform geometry from a reef rimmed platform to a carbonate ramp. This reef decline was interpreted to be the result of SSTs at the lower limit of the modern reef growth window (20–18 °C). This article presents a new Late Miocene—ased SST record from the Coral Sea based on the TEX86H molecular paleothermometer, challenging this long held view. Our new record indicates warm tropical SSTs (27–32 °C) at the upper end of the modern reef growth window. We suggest that the observed temperatures potentially exceeded the optimal calcification temperatures of corals. In combination with a low aragonite supersaturation in the ocean, this could have reduced coral growth rates and ultimately lowered the aggradation potential of the reef system. These sub-optimal growth rates could have made the coral reefs more susceptible to other stressors, such as relative sea-level rise and/or changes in currents leading to reef drowning. Given that these changes affected coral reefs that were likely adapted to high temperature/low aragonite saturation conditions suggests that reefs that have adapted to non-ideal conditions may still be susceptible to future climate changes due to the interaction of multiple stressors associated with climate change.

Experimental Investigation of a High-Speed Turbine With Rainbow Rotor and Rim Seal Purge Flow

AbstractThe present paper addresses the experimental and numerical study of the unsteady flow established in a high-pressure turbine stage with rim seal purge. The HPT test section, operated at engine-relevant flow conditions in the high-speed turbine rig of the von Karman Institute, is heavily instrumented for high-resolution, high-bandwidth aerothermal measurements. A rainbow rotor setup allows the simultaneous testing of six different sectors, each hosting a specific tip and platform geometry optimized for enhanced aerodynamic performance. This paper focuses on the flow over the baseline sector, equipped with an axisymmetric hub platform and a squealer tip, with a purge flowrate matching 1.74% and 1% of the stage mass flow. The numerical study relies on Reynolds-averaged Navier–Stokes (RANS) computations with test-calibrated boundary conditions. Unsteady pressure and heat transfer measurements are performed at the rotor shroud. The maximum heat transfer is achieved along the front pressure side rim, whereas the squealer cavity generates a region of uniformly low static pressure and heat flux. The experimental adiabatic wall temperature is derived to quantify the thermal contribution to the global heat flux, demonstrating an increase in over-tip gas temperature up to 1.2 T01 above the pressure side rim. A Euler-based model is proposed to evaluate the temperature-driving work-exchange mechanism in the tip gap. The peak in casing heat transfer coefficient (750 W/m2K) is found at the tip leading edge. Time-resolved measurements of outlet total pressure, Mach number, and flow angle confirm the predicted phase and intensity of the tip leakage and upper passage vortex in the near-casing region. At 20% hr, the total pressure minimum is highly underpredicted by the RANS, indicating an inaccurate modeling of the interaction between rim seal purge and main flow. The measured impact of the purge flow variation is more significant than predicted by the RANS computations, with a negative offset of about 0.5% P01 in the lower 50% hr at lower purge flowrate.

Cramér–Rao Lower Bounds on 3D Position and Orientation Estimation in Distributed Ranging Systems

As radio frequency (RF) hardware continues to improve, many technologies that were traditionally impractical have suddenly become viable alternatives to legacy systems. Two-way ranging (TWR) is often considered a poor positioning solution for airborne and other vehicular navigation systems due to its low precision, poor angular resolution, and precise timing requirements. With the advent of modern RF hardware and advanced processing techniques, however, modern studies have experimentally demonstrated TWR systems with an unprecedented, sub-centimeter ranging precision with low size, weight, power, and cost (SWaP-C) consumer-grade hardware. This technique enables a new class of positioning, navigation, and timing (PNT) capabilities for urban and commercial aircraft but also instigates new system design challenges such as antenna placement, installation of new electronics, and design of supporting infrastructure. To inform these aircraft design decisions, we derive 2D and 3D Cramér–Rao lower bounds (CRLBs) on position and orientation estimation in a multi-antenna TWR system. We specifically formulate these bounds as a function of the number of antennas, platform geometry, and geometric dilution of precision (GDoP) to inform aircraft design decisions under different mission requirements. We simulate the performance of several classic position and orientation estimators in this context to validate these bounds and to graphically depict the expected performance with respect to these design considerations. To improve the accessibility of these highly theoretical results, we also present a simplified discussion of how these bounds may be applied to common airborne applications and suggest best practices for using them to inform aircraft design decisions.

Depositional processes of the mixed siliciclastic-carbonate system in the Lower Cambrian Xiannüdong Formation in the northern Sichuan Basin, South China

Mixed siliciclastic-carbonate systems contain significant heterogeneity of facies associations which complicates the interpretation of depositional environments and platform evolution. The Lower Cambrian Xiannüdong Formation in the northern Sichuan Basin was deposited in a mixed system which is characterized by the non-skeleton grain (ooids and microbialites) dominated carbonates mixed with siliciclastic sediments. Such a depositional system provides a template to decipher the facies variability of mixed depositional systems and the evolution of platform geometry. Based on the facies analysis in outcrops and drilling wells, seventeen lithofacies were identified and grouped into seven lithofacies associations which represents a shallow-marine environment dominated by wave and storm activities. The vertical stacking pattern of lithofacies in the Xiannüdong Formation archives a regressive cycle which can be subdivided into four sub-cycles (i.e., S1 to S4). All the four sub-cycles exhibit the characteristic of the shallowing-upward successions, which are overlain by a flooding unit. The spatial distribution of lithofacies suggests an eastward-inclined platform. The migrating ooid shoals together with the storm activities may prevent the platform from evolving into a rimmed shelf. The lateral and vetical distribution of the terrigenous materials indicates that the provenance of terrigenous sediments were mainly sourced from the Kangdian and Bikou massifs, which indicates that the mixed system and the provenance area were separated by the Mianyang-Changning trough. Therefore, the transport of siliciclastic materials was related to the available accommodation space on the shelf, and was controlled by the eustatic sea-level fluctuation, with increased input of siliciclastic material occurred during phases of relative sea-level rise. The input of siliciclastic sediments brings nutrition for the growth of algal–archaeocyathan mounds, and therefore the mounds were mainly developed in the lower part of Xiannüdong Formation. Moreover, high siliciclastic sediments influx would also influence the growth of ooids by serving nuclei and promoting abrasion, which resulted in smaller ooid size compared to those of the relatively pure oolite. This study provides clues to understanding the facies variability in mixed systems and servers as a valuable reference for studies of other similar platforms.

Carbonate platform architecture and carbon isotope stratigraphy from the neoproterozoic Narji limestone formation, Kurnool Group, India: Decoding clues of relative sea level fluctuations

From a detail process-based facies and facies association analysis in a spatio-temporal framework, a rimmed shelf platform geometry is proposed for the Neoproterozoic Narji Limestone Formation, Kurnool Group, India. Ten carbonate facies types were delineated and clubbed under seven facies associations belonging to four different paleogeographic settings viz. Forereef (intertidal to shallow subtidal and shallow to deep subtidal), peritidal reef and back-reef lagoon. Whereas crinkly microbial laminites with subordinate domal stromatolites constitute the reef part, the fore slope deposition in the platform largely remained tide-and storm-dominated. Grey to black colored pyrite bearing bedded limestone-shale alternation without any current or wave imprint represents the back-reef lagoon deposition. A high carbonate saturation and productivity in the Narji inner and mid shelf is suggested from an overall dominance of microalgal laminite and microdigitate stromatolites over columnar stromatolites. From documentation of decimeter-to meter-thick shallowing-upward depositional hemicycles, embedded within an overall aggradational Narji lithosuccession, a combined control of sea level and carbonate productivity is inferred in course of Narji sedimentation. A short-duration medium-to large-scale rise in the base level led to the aggradation in shallow water rim of the Narji platform margin; interruption of this overall motif by short thickening- and shallowing-upward progradational hemicycles bear testimony for higher productivity in the Narji mid-to inner shelf areas. The present study intends to correlate shallowing-upward hemicycles with keep-up to catch-up depositional cycles with signature of apparent sea level fall. The control of relative base level variation in Narji depositional history is strengthened with multiple signatures including secular δ13C composition, total organic carbon (TOC) content and siliciclastic content documented from the entire Narji litho-succession.