Pinnacle Reefs Research Articles

Comparing rapid assessment methodologies in response to widespread epibiosis by Haliclona sp. (Porifera) on coral reef pinnacles in the Gulf of Thailand

Increasing documentation of coral-competing sponges have been made across the Indo-Pacific in recent years, utilising a variety of in-situ survey methods to quantify and classify the competitive capacity of these sponges. Estimating the abundance and comparative abundances of sponges in marine environments is made challenging due to the number of variables that can be assessed and the cost/benefit analysis of differing survey methods that may be used. Regular monitoring surveys at two adjacent submerged pinnacle sites in the Gulf of Thailand revealed colonisation and rapid proliferation of a previously undocumented coral-competing sponge at one pinnacle but not the other. To investigate the influence of survey methodology on the abundance and substrate specificity of the sponge, tentatively identified as Haliclona sp., we conducted point-intercept (PIT) and quadrat surveys along transect lines, alongside roving diver assessments. Qualitative assessments unsurprisingly found roving-diver surveys as documenting the greatest diversity of Anthozoa colonised by the sponge, with quadrat surveys generally classifying a similar or greater diversity colonised than PIT surveys. Quantitative analyses however revealed that, despite broadly similar substrate compositions, PIT surveys tended to find higher substrate coverage of certain biotic substrates than quadrat surveys. We discuss the merits and flaws of different survey methodologies, and possible applications of each, in the context of our findings.

Impact of palaeokarsts on the pinnacle reef reservoirs in the Sirt Basin, Libya

More than 20 pinnacle reefs have been discovered in the SE of the Ajdabiya Trough within Paleocene carbonate sediments, most of which are oil-bearing. However, detailed reservoir characterization and conditions governing oil fill-up in this reef have remained unresolved. The major faults provide paths for significant vertical movement of fluids at the edges of the Intisar reef reservoirs. At the same time, the ongoing karst solution collapse also creates vertical zones for fluid encroachment both outside of and within the productive area of the Intisar reef reservoirs. The seismic data show numerous karst-collapse features up to 300 m in diameter that developed shortly after the final drowning of the Intisar ‘B’ and ‘C’ reefs. These karst-collapse features may be the main contributing factor in the escape of hydrocarbons within these reefs, which could explain the high water cuts in the Intisar ‘B’ and ‘C’ reefs. However, the porosity of the southeastern part of the Intisar ‘A’ reef has been significantly improved by fracturing and dissolution, as faults associated with fractures are very common in this part of this reef.

Types and Evolution of the Miocene Reefs Based on Seismic Data in the Beikang Basin, South China Sea

During the Miocene, several reefs formed in the Beikang Basin, South China Sea, which may be potential targets for hydrocarbon exploration. This is due to the environment that developed as a result of the collision, splitting, and splicing of the Nansha Block, which was influenced by the Neogene expansion of the area. However, studies on the types, distribution, controlling factors, and evolution stages of these reefs are scarce. In this study, we used high-resolution seismic data and extensive well-drilling records to gain insights into the evolution of reefs in this particular area. Six distinct types of reefs, namely, the point reef, the platform-edge reef, the block reef, the bedded reef, the pinnacle reef, and the atoll reef, were identified based on our data. These reefs underwent four stages of development. During the initial stage, a few small-sized point reefs emerged in the basin and experienced significant growth during the early Middle Miocene. In the flourishing stage, the reefs predominantly thrived around the Central Uplift and Eastern Uplift areas. In the recession stage, the reefs began to deteriorate during the late Middle Miocene period as a result of the rapid increase in relative sea level caused by tectonic subsidence. In the submerged stage, since the Late Miocene, as the relative sea level continued to rise steadily over time, many reefs that had previously flourished surrounding the Central Uplift and Eastern Uplift areas became submerged underwater, with only a handful of atoll reefs surviving near islands located on the Eastern Uplift. This study indicated the presence of a significant number of well-preserved reefs in the Beikang Basin that have experienced minimal subsequent diagenesis and therefore exhibit high potential as reservoirs for oil and gas exploration.

An efficient deep learning-based workflow for CO2 plume imaging considering model uncertainties with distributed pressure and temperature measurements

Monitoring CO2 plumes throughout the operation of geologic CO2 sequestration projects is essential to environmental safety. The evolution of underground CO2 saturation can be predicted using high-fidelity numerical simulations. However, high-fidelity simulations can be prohibitively expensive to compute. As a result of recent developments in data-driven models, rapid predictions of the CO2 plume can now be made using readily available pressure and temperature measurements. This study presents a novel deep learning-based workflow for efficiently visualizing CO2 plumes in near real-time while considering their uncertainties.In our deep learning workflow, we visualize the CO2 plume images in the reservoir as a propagating saturation front, represented by ‘onset time’, using field measurements, including downhole pressure and temperature. At a given location, the ‘onset time’ is the calendar time when the CO2 saturation exceeds a certain threshold. Therefore, a single image of the CO2 front propagation is captured using the ‘onset time’ rather than storing multiple CO2 saturation images at different time steps. The use of ‘onset time’ significantly reduces memory and computational cost of deep learning-based framework, enabling large-scale field applications.We use a variational autoencoder-decoder (VAE) network to compress high dimensional ‘onset time’ images into low dimensional latent variables while considering uncertainties of the predicted images. The use of VAE and onset time, simplifies the overall neural network architecture and significantly enhances the training efficiency. To estimate the latent variables of the VAE network, we train a feed forward neural network model that incorporates available monitoring data such as downhole pressure and temperature measurements. The estimated latent variables are then fed into a trained decoder network to generate 3D onset time images, visualizing the propagation of CO2 plume in near real time.The proposed workflow is applied to both synthetic and field cases, where the field application is a large-scale geological carbon storage project in a carbonate reef reservoir in the Northern Niagaran Pinnacle Reef Trend in Michigan, USA. The field measurements include distributed temperature sensing (DTS) and distributed pressure responses from down-hole gauges along the monitoring well. The predicted CO2 plume images provided by the proposed workflow are shown to be consistent with the simulation results of traditional history matched model using genetic algorithm. Our deep learning-based framework can predict the CO2 front propagation in terms of onset time in seconds, making it well-suited for real time decision-making and operational optimization.

Strong hydrodynamic drivers of coral reef fish biodiversity on submerged pinnacle coral reefs

AbstractHydrodynamic processes are important in all marine environments and on coral reefs drive patterns of habitat zonation, community structure, and biodiversity. Abrupt geomorphological features like pinnacles and seamounts often possess distinct localized currents and these habitats are also often characterized by high abundance and biomass of fishes. However, differences in fish community structure between pinnacles and emergent reefs, and their key drivers are poorly understood. In this study, we compared fish communities among emergent fringing and offshore coral reefs, and submerged pinnacle reefs in Papua New Guinea. Submerged pinnacles possessed higher fish biomass, abundance, and species richness than both fringing and offshore emergent reefs. We collected in‐situ current speed and temperature data over a full year at each reef and used random forest analysis to investigate the relative influence of hydrodynamics compared to other well‐established drivers of reef fish biodiversity, including habitat and biogeographic factors. Environmental variables explained 70%, 52%, and 5% of variability in models for species richness, abundance and biomass respectively. In all models, average current speed, current speed variability, and reef area were consistently among the most influential variables. Models examining relationships between fish biodiversity metrics and current speed did not yield conclusive results but did highlight the association of distinct hydrodynamic regimes on pinnacles with high fish richness, abundance, and biomass. Our study highlights the strong influence of reef‐scale hydrodynamics on fish biodiversity and demonstrates the ecological value of small, submerged coral reefs, which are globally numerous yet remain understudied in coral reef ecology.

Using Biofacies Analysis of a Tertiary Algal Reef (Pinnacle Reef - Middle Eocene IIA), at Burton Guyot (IODP Site U1376) to Determine Transition from Greenhouse to Icehouse

Twenty-five samples were collected at 30 cm intervals from the studied cored interval within the limestone unit (AII) reported at IODP Site U1376 on Burton Guyot. The purpose of this research is to examine and identify the coral and algae suites in the studied core concerning sea level fluctuation during the Eocene time. This reef is isolated by being between two volcanic units in the Southwest Pacific Ocean. Eleven biofacies units have been established based on the fabric of the grains. The biofacies units are as follows; Algal-coral grainstone, foraminiferal algal-coral grainstone (Alabaminabed), foraminiferal algal-coral packstone to grainstone (Heterostegina bed), algal-coral grainstone, foraminiferal algal boundstone, foraminiferal algal grainstone (Lagena bed), foraminiferal algal grainstone (Cibicidoides micrus-bed), foraminiferal algal boundstone to grainstone, foraminiferal algal-coral grainstone, algal echionoidal packstone, and foraminiferal algal coral wacke-packstone. This is the first study to use both algae and coral in differentiating the units mentioned above. The only coralline red algae recognized in the samples is Lithothamnion camarasae. This species is a good indicator of the warm climatic conditions during the middle-late Eocene. The only species of coral found in these units is Isopora togianensis, a scleractinian reef builder. The high percentage of algae compared to coral indicates a climatic change from a greenhouse to an icehouse climate. The faunal trend during this time also indicates a tectonic change.

Coral reef pinnacles act as ecological magnets for the abundance, diversity and biomass of predatory fishes

Predation is a key ecological process regulating the structure and diversity of biological communities, yet predators do not exist homogeneously in nature. Coral reefs possess diverse assemblages of predatory fishes, the distribution and abundance of which is well documented for coastal and emergent reefs. However, for remote, isolated and submerged reefs, such as those found on pinnacles and seamounts, our understanding of predatory fish communities is limited. These features are ubiquitous in the world’s oceans and frequently targeted by fishers for their presumed fish aggregation properties. Here we describe communities of predatory fishes on a series of pinnacle reefs and contrast these to regional coastal and offshore emergent reefs. Pinnacles supported 2-4× higher abundance, biomass and diversity of predatory fishes compared to emergent reefs. They also supported unique communities, with 32 out of the 63 predator species in our study found only on pinnacle reefs. For species found on all 3 reef types, all were most abundant on pinnacles and the 6 taxa driving differences in community structure were most abundant on pinnacles. Together, our results show that predatory fishes are strongly attracted to pinnacles, although the mechanisms are still unclear. Prioritising the selection of these small ecological magnets in conservation planning would be an effective approach to target the protection of regional reef fish biodiversity.

Seismic-based paleoenvironmental analysis of the Paleocene carbonate shelf in Ajdabiya Trough, north-central of Libya

Abstract The results of the seismic and well logs interpretation, together with previous literature, were used to construct a generalized model of the development of the Paleocene reefs, and a depositional model for the Paleocene carbonate shelf in Ajdabiya Trough that focuses on the initiation, growth, and demise of the reefs in this basin. The Intisar reefs began as algal-foraminiferal banks. Growth of the reefs was halted by a short-lived transgression that drowned reefs and led to shale deposition of Kheir shales. The inversion of 3-D seismic data to acoustic impedance has allowed for a better determination of the main facies in Intisar reefs. These facies reflect different depositional conditions and different ages. They are: 1) algal-foraminiferal packstone/grainstone; 2) bioclastic grainstone/packstone; 3) coralline floatstone/bindstone; 4) reefal boundstone and; 5) bio-lithoclastic talus. The Upper Sabil consists of a prograding carbonate shelf with ramp platform morphology, and its differentiated deposits indicate four main depositional facies tracts: 1) inner shelf margin; 2) barrier reefs; 3) pinnacle reefs and; 4) outer shelf margin. The proposed model for the growth of the Paleocene reefs in the Ajdabiya Trough represents consecutive stages of development: 1) the Lower Sabil Carbonate was deposited during the very early Upper Paleocene time; 2) the influx of the Sheterat Shale during the major marine transgression; 3) the sea-level began a very slow fall due to variable subsidence of the underlying strata (a deposition of micrite over the Sheterat Shale, the lower part of the Upper Sabil Carbonate); 4) the rise in sea level is evident from an increase in foraminifera and algae constituents over the high areas of the lower part of the Upper Sabil Carbonate; 5) the isolated Intisar reefs were born under the proper local circumstances. The rate of subsidence was very slow, and the coral reef had significant upward growth and; 6) a major transgression happened at the end of the Paleocene, and the consequent deepening of the water in the area drowned and killed the Intisar reefs and capped it with Kheir Shale.

Evaluation of the Microbial Community and Geochemistry in Produced Waters Collected from CO2 EOR in the Niagaran Pinnacle Reef

Evaluation of the Microbial Community and Geochemistry in Produced Waters Collected from CO₂ EOR in the Niagaran Pinnacle Reef

Porosity estimation of a geothermal carbonate reservoir in the German Molasse Basin based on seismic amplitude inversion

The Molasse Basin is one of the most promising areas for deep geothermal exploitation in Germany and the target horizon is the aquifer in the Upper Jurassic carbonates. Carbonate deposits can be very heterogeneous even over a small area due to diagenetic processes and varying depositional environments. The preferential targets for geothermal exploitation in carbonate deposits are fault zones, reef facies and karstified areas, since they are expected to act as hydraulically permeable zones due to high porosity and high permeability. Therefore, identifying these structures and characterizing, e.g., their internal porosity distribution are of high importance. This can be accomplished using 3D reflection seismic data. Besides structural information, 3D seismic surveys provide important reservoir properties, such as acoustic impedance, from which a porosity model can be derived. In our study area in Munich we carried out a seismic amplitude inversion to get an acoustic impedance model of the Upper Jurassic carbonate reservoir using a 3D seismic data set, a corresponding structural geological model, and logging data from six wells at the ‘Schäftlarnstraße’ geothermal site. The impedance model and porosity logs were than used to calculate a porosity model. The model shows a wide porosity range from 0 to 20% for the entire reservoir zone and the lithology along the wells reveals that dolomitic limestone has the highest porosities and calcareous dolomite has the lowest porosities. The study area is cut by a large W–E striking fault, the Munich Fault, and the footwall north of it shows higher porosities and more intense karstification than the hanging wall to the south. Considering the entire study area, an increase in porosity from east to west is observed. Furthermore, we identified a complex porosity distribution in reef buildups and pinnacle reefs. The reef cores have mostly low porosities of, e.g., < 3% and the highest porosities of up to 7 to 14% are observed at the reef caps and on the reef slopes. The reef slopes show a characteristic interfingering of the reef facies with the surrounding bedded facies, which indicates a syn-sedimentary reef development with slightly varying build up growth rates. We also assessed the reservoir quality with regard to porosity distribution and determined areas with moderate to good quality for geothermal exploitation by defining porosity evaluation levels. The porosity evaluation maps show that the carbonate rocks of Berriasian to Malm zeta1 are preferential targets for exploitation, especially in the footwall of the Munich Fault and to the west of the hanging wall, because these areas are characterized by high porosities due to intense karstification of bedded and massive facies, although the latter is mainly restricted to reef caps and reef slopes.

Habitat-specific fish fauna responses to different management regimes in the largest coral reef complex in the South Atlantic

While marine protected areas (MPAs) are increasing worldwide, it is still needed to assess the effectiveness of those already consolidated. Methods and ecological assessments to understanding integrated and habitat-specific management regimes are still scarce and insufficient for policy implications and biodiversity conservation. Through Baited Remote Underwater Video (BRUV), we used fish assemblages as proxy of ecological and managerial status in two reef habitat types along three protection levels at Abrolhos Bank - the largest and most biodiverse coral reef complex of the South Atlantic. We found completely distinct responses in the fish fauna between the top (shallow) and bottom (deep) habitats of the unique “chapeirões” pinnacle reef formations. In the most protected zone (no-take), higher richness and abundance of commercial fish and more diverse trophic structure was observed. Particularly, large (sharks and groupers) and small carnivores (snappers) were more abundant and distributed more homogeneously over both reef habitats in the strictly enforced no-take zone. Abundance of these top-predators decreased from the low enforcement no-take zone to the multiple use area, where they were often absent while their typical preys (primary and secondary consumers) were thriving, notably in the top habitats. These outcomes highlight the importance to focus investigations not selectively on a single habitat type or depth zone in order to properly assess MPA effectiveness. Consequently, the monitoring and protection of fish species supported by marine spatial planning may benefit from an improved understanding of ecological functioning provided by MPA performance.

Controls on Early Miocene carbonate and siliciclastic deposition in eastern Java and south Makassar Straits, Indonesia

The Early Miocene stratigraphy of NE Java and the southern Makassar Straits is examined in the context of siliciclastic sediment supply and subsidence (creation of accommodation space), as indicated by biohermal carbonate growth. Stratigraphic variation is examined geographically and assessed quantitatively, using geohistory analysis. During the Oligocene through to basal Miocene times, basin development had been dominated by extension with local transtension. This changed within the Early Miocene to regional compression, increasing in magnitude with time. Three tectonic events, at about 24 Ma (base of section studied), at 21 Ma, and roughly 16 Ma are described in terms of the influence they had on stratigraphy. Most significant was the concentration of siliciclastics on the proximal side of the Oligo-Miocene axis of subsidence, which caused isostatic loading and nearby pinnacle reefs to achieve high relief, but ultimately an acceleration in siliciclastic input at about 16 Ma caused simultaneous reef extinction. Carbonates of Early Miocene age are important hydrocarbon reservoirs, and the siliciclastics are a geographically variable part of the overburden and seal, as well as causing the thermal maturation of hydrocarbon source rocks. The stratigraphic framework described here will have implications for facies and exploration risk prediction into under-explored regions around the study area. The tectono-stratigraphic framework is carefully constrained for age and facies inputs, and the resulting palaeogeographic history indicates a new model of basin development. This dynamic framework correlates to coeval tectonic processes over a large region and has important implications for Sundaland plate tectonics.

A highly diverse dromioid crab assemblage (Decapoda, Brachyura) associated with pinnacle reefs in the lower Eocene of Spain

AbstractA highly diverse fauna of dromioid brachyurans from the Serraduy Formation (lower Eocene) in the western Pyrenees (Huesca, Spain) is described and illustrated. Recorded taxa areMclaynotopus longispinosusnew genus new species,Torodromia elongatan. gen. n. sp.,Basidromilites glaessnerin. gen. n. sp., ?Basidromilitessp.,Sierradromia gladiatorn. gen. n. sp.,Kromtitis isabenensisn. sp., and ?Basinotopussp. Other European outcrops have yielded dromioids in association with specific environments, likely coral and sponge reef and siliciclastic soft bottoms; but the present material constitutes the most diverse dromioid assemblage from the lower Eocene worldwide. These dromioids co-occurred with a rich invertebrate fauna and lived near coral–algal reef mounds. Sedimentological data suggest that most of the fauna accumulated in fore reef settings as a result of storm activity. The present material greatly increases the diversity of known dromioid crabs associated with Eocene reef environments.UUID:http://zoobank.org/aed8cafa-7c64-4e70-bd45-9f357fc37a28

Manoel Luiz Reefs morphology unveiled by high resolution satellite images (North Brazilian Continental Shelf)

The reefs of Manoel Luiz are located 100 nautical miles N from the city of Sao Luis, capital of the State of Maranhao - Brazil. The region is practically unconquerable, due to the great concentration of shallow reef pinnacles; it has never been possible to map the area by traditional methods, due to the dangers to navigate. The images acquired in June 2018, by programmed WorldView-3 satellite (30 cm resolution), revealed for the first time the real and exuberant reef formation with innumerable constructions, predominantly individual with circular, or linear and coalescent format. The reefs of Manoel Luiz are not constructed by corals. Drop-camera videos shows that sparse colonies of corals are fixed on hard structures formed (covered) by superimposed crusts of calcareous algae. The location of Manoel Luiz reefs remained almost 300 years unknown to navigators, since the year 1500, attributed to the discovery of Brazil, until 1820, when it was described by the French hydrographer Adm. Baron de Roussin, and another 198 years to be precisely georeferenced and mapped.

Dynamic modeling to understand pressure response from oil production and CO2 injection in a depleted pinnacle reef reservoir: Manual calibration using simplified resolution of reservoir heterogeneity

The Midwest Regional Carbon Sequestration Partnership has been investigating various reservoir characterization and modeling technologies as part of its commercial-scale implementation of carbon dioxide injection for geologic storage in multiple Silurian carbonate pinnacle reefs in northern Michigan, USA. This paper presents a discussion of the reservoir modeling study that was conducted for history-matching oil production and CO2 injection responses, forecasting CO2 plume migration and estimating associated storage to characterize the closed, depleted Dover-33 reef which has undergone extensive primary and secondary production. Dynamic modeling using equivalent simplified descriptions of reservoir heterogeneity were found to be numerically efficient and successfully explained the observed pressure buildup in the reef during the MRCSP CO2 injection phase. The validated history matched models are extremely useful for potential predictive modeling for considering operational optimization and evaluating subsequent production scenarios relevant to the reef.

Enhancing Paleoreef Reservoir Characterization through Machine Learning and Multi-Attribute Seismic Analysis: Silurian Reef Examples from the Michigan Basin

Historically, Silurian pinnacle reef complexes in the Michigan Basin have been largely identified using 2D seismic with very little research on the reservoir characterization of these reefs using 3D seismic data. By incorporating a high-resolution 3D dataset constrained by a well-studied and data-rich paleoreef reservoir, the Puttygut reef, seismic attributes were correlated to petrophysical properties through machine learning and self-organizing maps (SOMs). A suite of structural and frequency-based attributes was calculated from pre-stack time migrated (PSTM) seismic data, with only a subset of them selected as SOM inputs. Structural attributes enhanced details in the reef but frequency attributes were overall more useful for correlating with reservoir quality. A strong relationship between certain combination percentages of attributes and certain sections of the reef with porosity and permeability was found after the SOM results were compared to wireline log and core analysis data. Areas with high permeability and porosity correlated with the average frequency and spectral decomposition at 29 and 81 Hz. Areas with high porosity and varying permeability correlated with the average frequency and spectral decomposition at 29, 57, and 81 Hz. Areas with intermediate porosity correlated with the average frequency and spectral decomposition at 29 and 57 Hz. The efficacy of the procedure was then demonstrated on two nearby reefs with very similar results.

A comprehensive analysis of transient pressure and rate data from CO2 storage projects in a depleted pinnacle reef oil field complex, Michigan, USA

Pressure and rate data are commonly recorded as part of a basic monitoring program in CCS projects. This paper discusses the application of multiple analytical techniques to interpret pressure and rate transient data from CO2 injection and storage operations. The techniques of interest, i.e., injection-falloff analysis, injectivity/productivity index analysis and pressure pulse arrival time analysis, are commonly used in the oil and gas industry to assess reservoir properties, but not well known in the CCS literature (especially the last two). Injection-falloff analysis involves log-log pressure derivative plotting for the falloff data and history-matching of the entire injection-falloff sequence to determine permeability. In the injectivity/productivity index analysis, rate-normalized pressure buildup is plotted against material balance time or ratio of cumulative injection to injection rate to determine the injectivity index (ratio of injection rate to stabilized pressure buildup) which can be related to the permeability-thickness product. The arrival time analysis identifies the arrival of a pressure disturbance (∼0.1 psi change from ambient) to determine the hydraulic diffusivity from which permeability can be estimated. The applicability of these techniques is demonstrated via illustrative examples from multiple wells in different pinnacle carbonate reefs undergoing CO2-EOR in Northern Michigan. The paper ends with a discussion of the relative merits of each interpretive technique, as well as recommendations that could be useful for other field projects.

Geological Interpretation and Hydrocarbon Exploration Potential of Three Types of Mound‐shaped Reflectors in the Meishan Formation, Southern Qiongdongnan Basin

AbstractMany mound‐shaped reflectors with different features and shapes are evident in the Upper Member of the Meishan Formation from seismic profiles taken in the deep‐water area of the Southern Qiongdongnan Basin. Based on the drilling, 2D and 3D seismic data from the study area, descriptions of the seismic reflection characteristics as well as the geometric shape, wave impedance inversion, analogy and comparative analyses are carried out. Taken in conjunction with research on the paleostructure and paleosedimentary background, we consider that the mound‐shaped seismic reflectors are distributed in the Southern Slop belt and the Southern High‐rise of the Qiongdongnan Basin, which can be subdivided into three types: reefs, contourite mounds and magmatic diapirs. The first type, reefs, includes patch reefs, platform marginal reefs and pinnacle reefs. Patch reefs present mound‐shaped seismic facies with medium frequency and a moderately strong amplitude, being distributed at the uplift of the fault control platform on the Southern Slop belt. The platform marginal reefs have flat mound‐shaped seismic facies with strong amplitude and medium frequency, developing at the margin of the carbonate platform in the Southern High‐rise. The pinnacle reefs have mound‐shaped seismic facies with strong amplitude and medium frequency and are developed on an isolated volcanic cone. The boundaries between individual reefs are clear on the seismic section, with reef ridge and reef ditch developed, the phenomenon of ‘front product’ being visible within, two‐way superelevation between wings is developed and they exist visibly as mounds in any viewed direction of the cross‐section. They are slightly asymmetrical in the direction perpendicular to the paleodepth, the reef body being steep near the deep‐water side, while being gentle near the shallow water side. The wave impedance of a patch reef is about 7 kg/m3×m/s, while the wave impedance of a platform marginal reef is about 7.5 kg/m3×m/s. The second type ‐ contourite mounds ‐ are mainly developed under the slope break of the southern slope fault control platform's edge. They are subdivided into two types: conical and flat. The former has mound‐shaped seismic facies with medium‐strong amplitude and low frequency, the latter having mound‐shaped seismic facies with medium amplitude and low frequency. The internal texture of the mounds is not clear on the seismic section, with the boundaries between contourite mounds being blurred. They are mound‐shaped only in cross‐section, being banded in the extending direction. The upper surface of a single contourite mound is relatively gentle near the deep‐water side, while being steep near the shallow water area. The wave impedance of contourite mounds is about 5.8 kg/m3×m/s, which is speculated to represent a marly to calcareous clastic deposit. The third type is the magmatic diapir, which has ‘roots’. They have a dome‐shaped upper boundary, are bottomless, with a chaotic interior. They penetrated multiple formations, opening towards the base. There are two major accumulation assemblages of reefs, one is the platform margin reef accumulation assemblage with distant source rocks and long‐distance migration through an unconformity surface in the Southern High‐rise, the other is the patch reef accumulation assemblage with twin sources and short distance migration through faults in the Southern Slop belt near the Central Depression zone. The latter is the main exploration targets at present. There are contourite mound accumulation assemblages with nearby source rocks and short distance vertical migration through faults, which are potentially important targets. The magmatic diapirs pierce the overlying strata and form good hydrocarbon traps and migration pathways, thus representing potential prospecting targets.

An Assessment of Monitoring Technologies Deployed in Multiple Carbonate Reef Reservoirs at the MRCSP Large-Scale CO2-EOR Site Michigan

The Midwest Regional Carbon Sequestration Partnership (MRCSP) is one of seven regional partnerships established in October 2003 as part of the U.S. Department of Energy’s (DOE’s) Regional Carbon Sequestration Partnership (RCSP) program to assess the technical and economic viability and public acceptability of carbon sequestration in the U.S. The MRCSP Phase III project injected over 1 million metric tons (MT) of CO2 into a group of Silurian (Niagaran)-age pinnacle reef reservoirs in Otsego County, Michigan (USA) that are operated by Core Energy, LLC [1]. There are over 800 pinnacle reefs in northern Michigan, and collectively, these geologic features have enough capacity to store several hundred million MT of CO2. Moreover, most of the reefs are depleted oil- or gas-reservoirs having previously undergone primary production in the 1970s and 1980s; therefore, they offer the opportunity to achieve CO2 storage through enhanced oil recovery (CO2-EOR) (associated storage) and via geologic sequestration (injection alone without production). A key objective of the MRCSP Phase III project was to evaluate the effectiveness of various monitoring technologies for use in associated storage or sequestration projects in the Niagaran pinnacle reefs. Over the period 2013 to 2020, the MRCSP Phase III project conducted monitoring using eleven different technologies for their effectiveness for CO2 plume delineation, assessing geochemical interactions, well integrity, leak detection, induced seismicity, land deformation, and mass balance accounting in the group of study reefs operated by Core Energy. This paper discusses the effectiveness of selected monitoring technologies that had the goal of detecting/delineating the extent of CO2 in the subsurface. The results are relevant to others planning or currently conducting CO2 sequestration or associated storage projects in similar carbonate reef reservoirs.

High diversity, abundance and distinct fish assemblages on submerged coral reef pinnacles compared to shallow emergent reefs

Coral reefs exhibit consistent patterns in biodiversity across multiple spatial scales, from local to global clines in species richness, abundance and community structure. Knowledge of fundamental processes driving these patterns is largely derived from studies of shallow, emergent and nearshore reefs. Although research efforts are expanding to deeper mesophotic coral reef ecology, distinct and isolated reef morphologies like submerged pinnacles or seamounts have received scant attention. Despite being potentially important for connectivity and as refugia, the extent to which established patterns and processes in coral reef ecology apply to these systems is unknown. Here we examine the fish and benthic communities associated with coral reefs found on submerged pinnacles in Kimbe Bay, Papua New Guinea. Community structure and diversity metrics are compared with emergent reefs at the same depth in both near and offshore settings. We then explicitly test whether benthic complexity variables known to influence reef fish communities exhibit similar patterns at each reef type. Pinnacles were characterised by 3.70 times the mean fish abundance and 1.98 times the species richness recorded at the same depths on emergent reefs. Fish community structure showed distinct separation across reef morphologies, with pinnacles most similar to offshore reefs. Benthic habitat complexity did not vary across reef types while fish assemblages were weakly related to benthic habitat variables, with reef morphology the most consistent predictor of fish community metrics. The pinnacles in our study support high coral reef fish biodiversity despite their small habitat area and relative isolation by depth and offshore setting. Our results suggest that habitat-specific environmental conditions are generated by the distinct geomorphology of pinnacles. As coastal reefs become more increasingly disturbed, understanding ecological patterns on deep patch reef habitats like pinnacles will be useful to provide a more holistic understanding of coral reef seascapes and their resilience.