Shoal System Research Articles

Co‐existence of skeletal and ooid shoals as a result of antecedent topography—Cat cay shoal complex, Bahamas

AbstractHigh‐resolution seismic data reveal an unexpected Pleistocene topography underneath the Cat Cay shoal complex along the western margin of Great Bahama Bank, illustrating how Pleistocene topography focuses tidal flow to create different types of grainstone shoals. The 1–3 km wide and 35 km long shoal complex is composed of the Cat Cay ooid shoal that is a laterally continuous 8 m thick ooid shoal and a sequence of 300–600 m wide and less than 6 m thick skeletal‐dominated tidal deltas south of Ocean Cay. The skeletal tidal deltas overlie an irregular Pleistocene surface, while the Cat Cay ooid shoal is situated on a flat Pleistocene surface east of a Pleistocene rock ridge. This finding challenges the assumption that an antecedent high is needed for ooid shoal initiation. The base of the Cat Cay ooid shoal is an up to 4 m thick skeletal‐peloidal unit that is similar in composition to the skeletal tidal deltas south of Ocean Cay but their deposition was followed by an up to 4 m thick accumulation of ooids. The Pleistocene ridge west of the Cat Cay ooid shoal allowed accumulation of mud and peloids (the nucleus source), while to the south, muddy sediment was winnowed away and no ooids formed. The evolution of the two shoal types is ultimately the result of the presence and absence of antecedent topography adjacent to the shoal system, resulting in variations of mud accumulations and the formation of the nucleus in the ooid shoal. The coeval occurrence of ooid and skeletal shoals in the same complex implies that in the rock record, a vertical succession from oolitic to skeletal shoals does not indicate an environmental change such as climate or an anoxic event but rather a change in flow conditions created by antecedent topography.

Statistical pattern analysis of surficial karst in the Pleistocene Miami oolite of South Florida

A robust airborne light detection and ranging digital terrain model (LiDAR DTM) and select outcrops are used to examine the extent and characteristics of the surficial karst overprint of the late Pleistocene Miami oolite in South Florida. Subaerial exposure of the Miami oolite barrier bar and shoals to a meteoric diagenetic environment, lasting ca. 120 kyr from the end of the last interglacial highstand MIS 5e until today, has resulted in diagenetic alteration including surface and shallow subsurface dissolution producing extensive dolines and a few small stratiform caves.Analysis of the LiDAR DTM suggests that >50% of the dolines in the Miami oolite have been obscured/lost to urbanization, though a large number of depressions remain apparent and can be examined for trends and spatial patterns. The verified dolines are analyzed for their size and depth, their lateral distribution and relation to depositional topography, and the separation distance between them. Statistical pattern analysis shows that the average separation distance and average density of dolines on the strike-oriented barrier bar versus dip-oriented shoals is statistically inseparable. Doline distribution on the barrier bar is clustered because of the control exerted on dissolution by the depositional topography of the shoal system, whereas patterning of dolines in the more platform-ward lower-relief shoals is statistically indistinguishable from random. The areal extent and depth of dissolution of the dolines are well described by simple mathematical functions, and the depth of the dolines increases as a function of their size. The separation and density results from the Miami oolite are compared to results from other carbonate terrains. Near-surface, stratiform caves in the Miami oolite occur in sites where the largest and deepest dolines are present, and sit at, or near, the top of the present water table.

Geology: In All Modesty

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Cloud services for the Fermilab scientific stakeholders

As part of the Fermilab/KISTI cooperative research project, Fermilab has successfully run an experimental simulation workflow at scale on a federation of Amazon Web Services (AWS), FermiCloud, and local FermiGrid resources. We used the CernVM-FS (CVMFS) file system to deliver the application software. We established Squid caching servers in AWS as well, using the Shoal system to let each individual virtual machine find the closest squid server. We also developed an automatic virtual machine conversion system so that we could transition virtual machines made on FermiCloud to Amazon Web Services. We used this system to successfully run a cosmic ray simulation of the NOvA detector at Fermilab, making use of both AWS spot pricing and network bandwidth discounts to minimize the cost. On FermiCloud we also were able to run the workflow at the scale of 1000 virtual machines, using a private network routable inside of Fermilab. We present in detail the technological improvements that were used to make this work a reality.

Simulating sediment transport processes in San Pablo Bay using coupled hydrodynamic, wave, and sediment transport models

Abstract San Pablo Bay is a tidal sub-embayment of the San Francisco Estuary which is dominated by broad shallow shoals bisected by a deep channel. Under the conceptual model of sediment transport in San Pablo Bay proposed by Krone (1979) , sediment typically enters San Pablo Bay during large winter and spring flows and is redistributed during summer conditions through wind wave resuspension and transport by tidal currents. Numerical simulations of sediment resuspension due to wind waves and the subsequent transport of this sediment by tidal currents show that sediment concentrations and fluxes throughout the channel–shoal system result from a complex temporal and spatial interaction of the waves and tides. The three-dimensional UnTRIM San Francisco Bay-Delta Model was coupled with the Simulating WAves Nearshore (SWAN) wave model and the SediMorph morphological model, to develop a three-dimensional (3D) hydrodynamic, wind wave, and sediment transport model of San Francisco Bay and the Sacramento–San Joaquin Delta. The coupled model was validated using water level, velocity, wind waves and suspended sediment data collected in San Pablo Bay, and then used to quantify the spatial and temporal variability of sediment fluxes on the extensive shoals in San Pablo Bay under a range of tidal and wind conditions. The model validation shows this modeling system can accurately predict hydrodynamics, waves, and suspended sediment concentration in San Pablo Bay. The predicted bottom orbital velocities are elevated across the shoals during large wave events regardless of tidal stage, but near low tide orbital velocities are increased even under low to moderate waves. Sediment fluxes between the shoals and the deeper channel are highest during spring tides, and are elevated for up to a week following wave events, even though the greatest influence of the wave event occurs abruptly.

Relations between geomorphic form and sedimentologic-stratigraphic variability: Holocene ooid sand shoal, Lily Bank, Bahamas

Although the linkages among surface sediments, geomorphic forms, and hydrodynamics in Holocene ooid tidal sand shoals have been evaluated recently, how these factors are reflected in the geomorphic evolution and stratigraphic record of shoals is less constrained. Yet, such understanding is essential to developing meaningful predictive conceptual models of three-dimensional architecture of ancient reservoir analogs. Integrating remote-sensing imagery, high-frequency seismic data, and core characterization from Lily Bank, a modern tidally dominated Bahamian ooid shoal in which sedimentologic processes are well documented, reveals the stratigraphic record of geomorphic change. An irregular, gently dipping rocky surface (interpreted as the top Pleistocene) with no pronounced topographic high underlies the Holocene oolitic succession. A 6-m (20-ft)–thick poorly sorted, gravelly muddy sand with few ooids overlies this basal surface. This lower interval is overlain by sand with an upward increase in proportion of ooids, sorting, and grain size. The uppermost unit, present only under active bar forms, is well-sorted oolitic medium sand with accretionary foresets. Sediments vary stratigraphically and geomorphically; the lower unit is finer and less well sorted than the upper units, and in the oolitic upper unit, sediment size and sorting on bar crests are distinct from bar flanks. Collectively, these results suggest that a marked antecedent bump is not necessary for occurrence of ooid shoals and that the stratigraphic record of analogous ooid shoal systems may preserve clues of geomorphic position, as well as geobody size and orientation.

Addressing an Optimal Schedule for Inlet Bypassing

Abstract St. Augustine Inlet is located on the NE coast of Florida, connecting the Atlantic Ocean to the Tolomato and Matanzas rivers. The inlet is unique because it was relocated in the 1940s, resulting in considerable perturbations to the adjacent coastal system, especially the downdrift (southern) shoreline. The relatively low, permeable, and short north jetty has allowed sediment to move around, through, and over the jetty, resulting in deposits on the interior lagoon/bay and on the ebb shoal system. Since 2001, dredging has occurred on the ebb shoal and bypassed to the downdrift side of the inlet on St. Augustine Beach. At present, dredging and bypassing have occurred on an irregular schedule, although questions remain about what a reasonable schedule would be to prevent excessive problems on both the updrift and downdrift beaches. This article presents an evaluation of a potential approach for use in addressing the dredging and bypassing schedules to assess how various intervals of dredging/bypassin...

Pressure-gradient-driven nearshore circulation on a beach influenced by a large inlet-tidal shoal system

[1] The nearshore circulation induced by a focused pattern of surface gravity waves is studied at a beach adjacent to a major inlet with a large ebb tidal shoal. Using a coupled wave and wave-averaged nearshore circulation model, it is found that the nearshore circulation is significantly affected by the heterogeneous wave patterns caused by wave refraction over the ebb tidal shoal. The model is used to predict waves and currents during field experiments conducted near the mouth of San Francisco Bay and nearby Ocean Beach. The field measurements indicate strong spatial variations in current magnitude and direction and in wave height and direction along Ocean Beach and across the ebb tidal shoal. Numerical simulations suggest that wave refraction over the ebb tidal shoal causes wave focusing toward a narrow region at Ocean Beach. Due to the resulting spatial variation in nearshore wave height, wave-induced setup exhibits a strong alongshore nonuniformity, resulting in a dramatic change in the pressure field compared to a simulation with only tidal forcing. The analysis of momentum balances inside the surf zone shows that, under wave conditions with intensive wave focusing, the alongshore pressure gradient associated with alongshore nonuniform wave setup can be a dominant force driving circulation, inducing heterogeneous alongshore currents. Pressure-gradient-forced alongshore currents can exhibit flow reversals and flow convergence or divergence, in contrast to the uniform alongshore currents typically caused by tides or homogeneous waves.

Controls on morphology and sedimentology of carbonate tidal deltas, Abacos, Bahamas

Although the physical processes controlling siliciclastic shoal bodies are reasonably well-understood, the sedimentary processes that shape carbonate tidal shoal systems are poorly constrained. The tidal deltas of the northwestern Abaco Islands, Bahamas, provide a unique opportunity to explore the relationships between physical and sedimentary processes in a variety of sizes and shapes of tidal deltas. The length of tidal deltas range in size from ~ 350 m to 2 km (from the inlet to the termination of the delta lobe) and shoal crests consist primarily of well-sorted ooid sands (mean grain size between 400 and 500 μm; McManus sorting factor ≤ 0.70). Coated grains are rare off the shoals, and sorting decreases with distance from the shoal crests. Velocities in the rocky inlets can exceed 2 m/s in the daily tidal cycles, and the systematic distribution of grain types reflects tidal velocity variations. Areas with the highest velocities (≥ 0.80 m/s) correspond to hard, rocky bottoms with some skeletal grains. These regions of elevated velocities are focused within the inlets, where jets of high velocity currents form during each tidal cycle. These current jets extend outward from the inlet throat, and velocities decrease outwards as the flow disperses. Velocities between 40 and 80 cm/s occur in the regions with abundant ooids, and peloids are most abundant in the lowest velocity regions (< 0.40 m/s) in the tidal delta system. At a larger scale, inlet tidal prism and delta size are closely correlated in these tidal deltas, as in their siliciclastic counterparts. The results of this study illustrate a clear relationship between quotidian physical processes and their geomorphic and sedimentologic products in a carbonate system. In this context, carbonates appear to share many geomorphic similarities with siliciclastic analogs. The results represent an important step beyond qualitative facies interpretations and towards quantitative, specified environmental and sedimentologic characterizations for carbonate systems.

The Bay of Mont-Saint-Michel northeastern littoral: an illustrative case of coastal sedimentary body evolution and stratigraphic organization in a transgressive/highstand context

Abstract The aim of the present paper is primarily of pedagogic order. It presents the landscapes of the northeastern littoral of the Bay of Mont-Saint-Michel and explains how these landscapes can be understood in terms of stratigraphic organization and evolution. The northeastern coast of the Bay displays contrasted landscapes and morphodynamic processes along a restricted area. This coast consists in an elongated sandy barrier made of beaches and aeolian dunes, and back barrier tidal flats. A wide estuarine channel-and shoal system migrates in front of the beaches. Because of direct wave attack, the barrier experiences a severe retreat in the north whereas in the south, due to sufficient sediment supply, beaches and dunes tend to prograde. These contrasted processes give rise to different sedimentary bodies and surfaces, the nature, geometry, extension, and time-scale of which are described and discussed through examination of the landscapes. The present-day depositional system can be thus used to illustrate and test sequence stratigraphic concepts such as system tracts, ravinement surfaces and process time-scales.

Paleogeographic Setting and Depositional Architecture of a Sand-Dominated Shelf Depositional System, Miocene Utsira Formation, North Sea Basin

ABSTRACT The middle-late Miocene Utsira sandstone of the North Sea Basin contains a fully preserved, regional marine sand deposit that records a stable paleogeographic setting of shelf sand transport and accumulation within an epeiric shelf sea which persisted for ca. 8 Myr. The sediment dispersal system was defined by (1) sediment input through a prograding strandplain platform, coast-to-shelf bypass, and regional basin-centered transport and deposition within an elongate seaway; (2) a high-energy marine regime; (3) very low rates of sediment supply and accumulation in the accommodation-dominated seaway; (4) high sediment reworking ratio and consequent abundance of autochthonous sediment; (5) regional along-strike sediment transport; and (6) local to subregional landward sediment transport. Shelf systems were primarily nourished by sediment reworked from the Shetland strandplain, which prograded eastward into the central Viking Trough. The Viking strait lay between the constructional platform and the nondepositional Horda Platform. Southward longshore transport on the high-energy shoreface and shallow shelf platform constructed the mounded south Viking shelf shoal. Southward-building sandy banner banks that formed along the recurved arc of the platform margin nourished the shoal system. Low-angle sigmoid clinoforms with downstepping, aggradational tops are distinctive architectures of the strike-fed sand bodies. The combination of strong marine currents and slow but continual sand supply from the Shetland strandplain created regional, sandy shelf depositional systems that individually covered 3500 to 6000 sq. km. of basin floor. Defining elements of the shelf shoal systems include their location within the basin axis, mounded morphology, stratal architecture, and construction by amalgamated marine sand facies.

Seismic expressions of deep-shelf depositional and erosional morphologies, Miocene Utsira formation, North Sea Basin

The Middle–Late Miocene Utsira Formation of the North Sea Basin contains a fully preserved, regional marine sand deposit that records a stable paleogeographic setting of sand transport and accumulation within a deep, epeiric seaway which persisted for >8 Ma. The sediment dispersal system was defined by (1) input through a marginal prograding strandplain platform, coast-to-basin bypass, transport along a narrow strait, and accumulation in strait-mouth shoal complexes within a shelf sea; (2) a high-energy marine regime; (3) very low time-averaged rates of sediment supply and accumulation; and (4) consequent high sediment reworking ratio. Sand distribution and stratal architectures reflect regional along-strike sediment transport and local to sub-regional landward sediment transport. Plume-shaped, south-building, submarine sand shoals that formed along the recurved arc of the strandplain margin nourished the shoal system. Very low-angle sigmoid clinoforms and down-stepping, aggradational top sets are distinctive architectures of these strike-fed sand bodies. The combination of strong marine currents and slow but long-lived sand supply from the Shetland strandplain created regional, sandy shelf shoal depositional systems that individually covered 3,500 to 6,000 km2 of the basin floor. Defining attributes of the shelf shoal systems include their location within the basin axis, abundance of autochthonous sediment, and sandy marine facies composition. Diagnostic depositional architectures include the along-strike-dipping sigmoidal clinoforms, poly-directional low-angle accretionary bedding at both regional and local scales, and mounded depositional topography. Erosional features include regional hummocky, low-relief shelf deflation surfaces, broad, elongate scours and sub-circular scour pits.

Scanning laser mapping of the coastal zone: the SHOALS system

The SHOALS system uses lidar technology to remotely measure bathymetry and topography in the coastal zone. During five years of survey operations, SHOALS has demonstrated airborne lidar bathymetry's benefits to the coastal community by providing a cost-effective tool for comprehensive assessment of coastal projects. This paper discusses the application of lidar technology for water-depth measurement, specifically outlining the SHOALS system and introducing a SHOALS survey from Saco River, ME.

高海水面期堆積体中を前進するバリアーショール堆積システム

高海水面期堆積体中を前進するバリアーショール堆積システム

シーケンス層序学 アブダビ海域Ｎｅｅｗａｔ Ａｌ Ｇｈａｌａｎ （ＧＡ）油田におけるＡｒａｂ・Ｈｉｔｈ層（ジュラ系）中のＨＳＴとＴＳＴ ＧＡ油田における堆積サイクルと積み重なりパターン

The depositional sequence in the Upper Jurassic Arab•Hith Formations, which is main reservoir zone of the Neewat Al Ghalan (GA) field, offshore Abu Dhabi, is composed of sabkha-nearshore deposits and divided into two systems tracts (transgressive systems tract (TST) and highstand systems tract (HST)) based on the characteristics of parasequence stacking patterns.Each parasequence in TST shows a shallowing upward cycle which commences from barrier shoal grainstone and terminates in lagoonal mudstone or sabkha anhydrite. Vertical stacking patterns of these parasequences within TST indicate thinning upward cycle and retrogradational/aggradational pattern.The parasequences in HST are characterized by a shallowing upward cycle from tidal channel grainstone or lagoonal mudstone to sabkha anhydrite. Stacking patterns of both bedsets parasequences within HST show overall thickening upward cycles and progradational pattern.The stacking patterns in the depositional sequence reflect various orders of sea level fluctuations. During TST deposition the barrier shoal systems accompanied by shoreface erosion developed in the field. In the succeeding HST deposition, the barrier shoal (strand plain) systems were migrating basinward, and the tidal flat-sabkha systems, in turn, were prograding to the field. These environmental changes due to the sea level fluctuations are considered to have affected the reservoir quality (cementation or dolomitization) of the field.

Sand Shoal Development on Muddy Mississippi River Delta Shelf: ABSTRACT

Trinity and Ship Shoals are transgressive sand bodies on the Louisiana inner continental shelf, and they represent the reworked sands of the abandoned Holocene Teche and Maringouin deltas. The development of these shoals is initiated by an episode of delta abandonment followed by subsidence-enhanced sea level rise. Through the process of shoreface retreat, the abandoned delta lobe evolves from an erosional headland with flanking barrier islands to a barrier-island arc and finally into a submerged inner-shelf shoal system. Trinity and Ship Shoals represent the final stage in the Mississippi River delta barrier shoreline cycle and provide a possible modern analogue for some Cretaceous shelf sandstones of the Western Interior. More than 1,000 km (620 mi) of high-resolution s ismic profiles correlated with cores provide the data base for interpretation of the depositional history of sand-body development on the muddy Louisiana shelf. Ship Shoal is the oldest inner-shelf shoal associated with the abandonment and subsequent reworking of the Maringouin delta 6,150 y.B.P. Located 25 km (16 mi) south of the Isles Dernieres, the Ship Shoal transgressive sands lie disconformably over the Maringouin deltaic muds. The Ship Shoal sand body is shore parallel, 32 km (20 mi) long and 2-4 km (1-2 mi) wide. The inner-shelf relief ranges (east to west) from 2-6 m (7-20 ft) with a corresponding decrease (east to west) in the water depth over the shoal crest from -6 to -3 m (-20 to -10 ft). The shoal profile is asymmetric landward. The Ship Shoal sand body is composed of an upward-coarsening sequence of well-sorted fine-grained sand with a median size of 125µ. Trinity Shoal is associated with the Teche delta, abandoned 3,500 y.B.P., and it is located 20 km (12 mi) south of Marsh Island. The base of Trinity shoal lies unconformably over the Teche deltaic sediments. Trinity shoal is a shore-parallel lunate sand body, 36 km (22 mi) long and 5-10 km (3-6 mi) wide. The inner-shelf relief ranges (east to west) 2-3 m (7-10 ft), with a corresponding decrease (east to west) in the water depth over the shoal crest 5-2 m (16-7 ft). The Trinity Shoal sand body is 5-7 m (16-23 ft) thick. End_of_Article - Last_Page 515------------