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Ss Flint - One of the best experts on this subject based on the ideXlab platform.

  • Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles
    'Geological Society of America', 2018
    Co-Authors: Hl Brooks, Dm Hodgson, Rl Brunt, Peakall J, Poyatos-moré M, Ss Flint
    Abstract:

    The effects of abrupt changes in slope angle and orientation on turbidity current behavior have been investigated in numerous physical and numerical experiments and examined in outcrop, subsurface, and modern systems. However, the long-term impact of subtle and evolving Seabed Topography on the stratigraphic architecture of deep-water systems requires fine-scale observations and extensive 3-D constraints. This study focuses on the Permian Laingsburg and Fort Brown formations, where multiple large sand-rich systems (Units A–F) have been mapped from entrenched slope valleys, through channel-levee systems, to basin-floor lobe complexes over a 2500 km2 area. Here, we investigate three thinner (typically

  • Aggradational lobe fringes: The influence of subtle intrabasinal Seabed Topography on sediment gravity flow processes and lobe stacking patterns
    'Wiley', 2017
    Co-Authors: Yt Spychala, Dm Hodgson, Cj Stevenson, Ss Flint
    Abstract:

    Seabed Topography is ubiquitous across basin-floor environments, and influences sediment gravity flows and sediment dispersal patterns. The impact of steep (several degrees) confining slopes on sedimentary facies and depositional architecture has been widely documented. However, the influence of gentle (fraction of a degree) confining slopes is less well-documented, largely due to outcrop limitations. Here, exceptional outcrop and research borehole data from Unit A of the Permian Laingsburg Formation, South Africa, provides the means to examine the influence of subtle lateral confinement on flow behaviour and lobe stacking patterns. The dataset describes the detailed architecture of subunits A.1 to A.6, a succession of stacked lobe complexes, over a palinspastically restored 22 km across-strike transect. Facies distributions, stacking patterns, thickness and palaeoflow trends indicate the presence of a south-east facing low angle (fraction of a degree) lateral intrabasinal slope. Interaction between stratified turbidity currents with a thin basal sand-prone part and a thick mud-prone part and the confining slope result in facies transition from thick-bedded sandstones to thin-bedded heterolithic lobe fringe-type deposits. Slope angle dictates the distance over which the facies transition occurs (hundreds of metres to kilometres). These deposits are stacked vertically over tens of metres in successive lobe complexes to form an aggradational succession of lobe fringe. Extensive slides and debrites are present at the base of lobe complexes, and are associated with steeper restored slope gradients. The persistent facies transition across multiple lobe complexes, and the mass flow deposits, suggests that the intrabasinal slope was dynamic and was never healed by deposition during Unit A times. This study demonstrates the significant influence that even subtle basin-floor Topography has on flow behaviour and depositional architecture in the Laingsburg depocentre, Karoo Basin; presenting a new aggradational lobe fringe facies association and recognition criteria for subtle confinement in less well-exposed and subsurface basin fills

Stephen S Flint - One of the best experts on this subject based on the ideXlab platform.

  • disconnected submarine lobes as a record of stepped slope evolution over multiple sea level cycles
    Geosphere, 2018
    Co-Authors: Hannah L Brooks, Rufus L Brunt, David M. Hodgson, Jeff Peakall, Miquel Poyatosmore, Stephen S Flint
    Abstract:

    The effects of abrupt changes in slope angle and orientation on turbidity current behavior have been investigated in numerous physical and numerical experiments and examined in outcrop, subsurface, and modern systems. However, the long-term impact of subtle and evolving Seabed Topography on the stratigraphic architecture of deep-water systems requires fine-scale observations and extensive 3-D constraints. This study focuses on the Permian Laingsburg and Fort Brown formations, where multiple large sand-rich systems (Units A–F) have been mapped from entrenched slope valleys, through channel-levee systems, to basin-floor lobe complexes over a 2500 km2 area. Here, we investigate three thinner (typically <5 m in thickness) and less extensive sand-rich packages, Units A/B, B/C, and D/E, between the large-scale systems. Typically, these sand-rich units are sharp-based and topped, and contain scours and mudstone clast conglomerates that indicate deposition from high-energy turbidity currents. The mapped thickness and facies distribution suggest a lobate form. These distinctive units were deposited in similar spatial positions within the basin-fill and suggest similar accommodation patterns on the slope and basin floor prior to the larger systems (B, C, and E). Stratigraphically, these thin units represent the first sand deposition following ­major periods of shut-down in sediment supply, and are interpreted as marking a partial re-establishment of sand delivery pathways creating “disconnected lobes” that are fed mainly by flows sourced from failures on the shelf and upper slope rather than major feeder channel-levee systems. Thickness and facies patterns throughout the deep-water stratigraphy suggest Seabed Topography was present early in the basin formation and maintained persistently in a similar area to ultimately form a stepped slope profile. The stepped slope profile evolved through three key stages of development: Phase 1, where sediment supply exceeds deformation rate (likely caused by differential subsidence); Phase 2, where sediment supply is on average equal to deformation rate; and Phase 3, where deformation rate outpaces sediment supply. This study demonstrates that smaller systems are a sensitive record of evolving Seabed Topography and they can consequently be used to recreate more accurate paleotopographic profiles.

  • stratigraphic evolution of fine grained submarine fan systems tanqua depocenter karoo basin south africa
    Journal of Sedimentary Research, 2006
    Co-Authors: David M. Hodgson, Nicholas J. Drinkwater, David Hodgetts, Erik P Johannessen, Stephen S Flint, Stefan M Luthi
    Abstract:

    Abstract The integration of correlated outcrop and newly acquired core and wireline logs, extensive paleocurrent data, and accurately mapped surfaces has enabled a common model of the stratigraphic evolution to be developed of four Permian fine-grained submarine fan systems (Fans 1–4) from the Tanqua depocenter, SW Karoo Basin, South Africa. Additionally, this data has revealed the influence of subtle Seabed Topography on the fan systems' boundaries, internal facies architecture, and paleocurrent directions. Furthermore, the internal stratigraphy of individual fan systems are now known to be more complex than first believed. Mapping high-frequency intrafan units reveals a progradational–aggradational–retrogradational stacking pattern common to each submarine fan, which allows the geographic and stratigraphic distribution of lithofacies and architectural elements to be predicted. Basinward of the main feeder system, fan axes are dominated architecturally by sheet turbidites with discrete zones of high amalgamation during progradational and aggradational phases, whereas isolated channel forms that cut thin-bedded turbidites are more common in the retrogradational phase. This change is interpreted to be due to local increase in the lower slope gradient through sediment aggradation increasing the potential for channel avulsion and the development of splay lobes during decreasing sediment supply. The progradational, aggradational, and retrogradational phases are assigned to the early, middle, and late lowstand systems tract of a fifth-order sequence respectively. Each phase is built of higher-frequency (sixth-order) sequences so that each fan is a composite sequence. The overall basinward-to-landward stepping of the individual fans means that moving down dip in any basin-floor fan system, the lowermost sandstone preserved is progressively younger, whilst the uppermost sandstone is progressively older. This stacking pattern imparts an important predictable control on reservoir and seal geometries. This study aids the development of predictive models for fine-grained submarine fan initiation, growth, and abandonment, and lithofacies and architectural element distributions in space and time.

Hongmei Zhang - One of the best experts on this subject based on the ideXlab platform.

  • side scan sonar image mosaic using couple feature points with constraint of track line positions
    Remote Sensing, 2018
    Co-Authors: Jianhu Zhao, Xiaodong Shang, Hongmei Zhang
    Abstract:

    To obtain large-scale Seabed surface image, this paper proposes a side-scan sonar (SSS) image mosaic method using couple feature points (CFPs) with constraint of track line positions. The SSS geocoded images are firstly used to form a coarsely mosaicked one and the overlapping areas between adjacent strip images can be determined based on geographic information. Inside the overlapping areas, the feature point (FP) detection and registration operation are adopted for both strips. According to the detected CFPs and track line positions, an adjustment model is established to accommodate complex local distortions as well as ensure the global stability. This proposed method effectively solves the problem of target ghosting or dislocation and no accumulated errors arise in the mosaicking process. Experimental results show that the finally mosaicked image correctly reflects the object distribution, which is meaningful for understanding and interpreting Seabed Topography.

  • reconstructing Seabed Topography from side scan sonar images with self constraint
    Remote Sensing, 2018
    Co-Authors: Jianhu Zhao, Xiaodong Shang, Hongmei Zhang
    Abstract:

    To obtain the high-resolution Seabed Topography and overcome the limitations of existing Topography reconstruction methods in requiring external bathymetric data and ignoring the effects of sediment variations and Side-Scan Sonar (SSS) image quality, this study proposes a method of reconstructing Seabed Topography from SSS images with a self-constraint condition. A reconstruction model is deduced by Lambert’s law and the Seabed scattering model. A bottom tracking method is put forward to get the along-track SSS towfish heights and the initial Seabed Topography in the SSS measuring area is established by combining the along-track towfish heights, towfish depths and tidal levels obtained from Global Navigation Satellite System (GNSS). The complete process of reconstructing Seabed Topography is given by taking the initial Topography as self-constraint and the high-resolution Seabed Topography is finally obtained. Experiments verified the proposed method by the data measured in Zhujiang River, China. The standard deviation of less than 15 cm is achieved and the resolution of the reconstructed Topography is about 60 times higher than that of the Digital Elevation Model (DEM) established by bathymetric data. The effects of noise, suspended bodies, refraction of wave in water column, sediment variation, the determination of iteration termination condition as well as the performance of the proposed method under these effects are discussed. Finally, the conclusions are drawn out according to the experiments and discussions. The proposed method provides a simple and efficient way to obtain high-resolution Seabed Topography from SSS images and is a supplement but not substitution for the existing bathymetric methods.

  • A New Method for Acquisition of High-Resolution Seabed Topography by Matching Seabed Classification Images
    MDPI AG, 2017
    Co-Authors: Jianhu Zhao, Hongmei Zhang, Junxia Meng, Jun Yan
    Abstract:

    The multibeam echo sounders (MBES) can acquire accurate positional but low-resolution Seabed terrain and images, whereas side scan sonars (SSS) can only acquire inaccurate positional but high-resolution Seabed images. In this study, a new method for superimposing corrected-positional SSS images on multibeam bathymetric terrain is proposed to obtain high-resolution and accurate-positional Seabed Topography using traditional MBES and SSS. Three steps, including the normalization by the z-score, sediment classification by the k-means++ algorithm, and denoising processing using morphological operations, are processed for both MBES and SSS images to obtain the corresponding sediment images. Next, a segmented matching method is given based on the common sediment distributions and features of MBES and SSS sediment images. The two kinds of sediment images are matched segmentally using the speeded up robust features algorithm and random sample consensus algorithm. Then, the positions of SSS images are corrected segmentally using thin plate splines based on matching points. Finally, the corrected SSS image is superimposed on MBES bathymetric terrain, based on positional relationship. The proposed method was verified through experiments, and high image resolution and high position accuracy Seabed Topography were obtained. Moreover, the performances of the method are discussed, and some conclusions are drawn according to the experiments and discussions

  • Determination of time delay for precise bathymetric survey
    OCEANS 2008, 2008
    Co-Authors: Hongmei Zhang, Jianhu Zhao, Fengnian Zhou
    Abstract:

    Now tide- independent bathymetric system is widely used in hydrographic survey and improves effectively single-beam bathymetric accuracy relative to the traditional bathymetric method. While time delay (TD), which exists between GPS RTK and single-beam sounding system, often leads to the positioning and sounding solution non synchronization and decreases the accuracy of final result. TD mainly originates from the lingering output of GPS RTK solution due to its interior algorithm, satellites number, radio signal processing mode and logging data model. Large numbers of experiments have proved that time delay may reach 0.2 second at least and 1.2 second at most. Generally, TD is determined by comparing sounding solutions with positioning solutions measured as vessel going by an anchored buoy in a to-and-fro surveying way with different velocities. However, this method may bring obvious error in the determination due to buoy movement. Therefore the following three methods are studied and presented in the paper. We first study method of characteristic point pairs. Looking for a characteristic inshore Seabed, we implemented a to-and-fro measurement along a planning line. The characteristic terrain of the Seabed can be found easily in the two profiles. For a characteristic aim on Seabed, we can find a pair of characteristic points in the two profiles. According to the two horizontal positions, depths and time of the characteristic point pair, we can calculate the TD. For different characteristic points, we can also determine their time delays. Then the TD of the system is the mean of TDs of all point pairs. Determined TD by the above method needs to choose characteristic point pairs manually. In the following, we will study an automatic determination method, which is method of maximum similarity of profiles. High-sampling rate makes the to-and-fro profiles present Seabed Topography subtly and continuously. If we think the two profiles are two curves of A and B, we can determine TD in virtue of similarity coefficient R of them. If we fix profile A and move profile B, we can get a series of similarity coefficient R(d). If we move a displacement of d, R reaches maximum or is close to 1, then the d is the displacement resulted from TD. If vA and vB are mean vessel velocity in to-and- fro measurements, then TD can be acquired through the calculating of d divided by the sum of vA and vB. The method can automatically calculate TD, while we must implement a fro-and- to measurement. In the following, we present a more convenient method which is Method of Consistent Vertical Motion of Vessel. Both of heave derived from MRU and GPS height from GPS RTK take the same role in monitoring the vessel vertical motion. If we correct the two signals to the same position, such as reference point(RP) in vessel frame system(VFS), we can get two time series dhheave-RP and hGPS-RP. Taking similar method shown in method of maximum similarity of profiles, we can acquire TD by fixing time series dhheave-RP and moving time series hGPS-RP in time scale. If we move a time ? and make similarity coefficient R(?) reach maximum, then the ? is also time delay of the system. The method of time delay determination can be implemented at any time and by any way. While an important mention, which time length [0T] of the time series used for determining time delay is not the whole time length of dhheave-RP or hGPS-RP, but only part of it, needs to be clarified. As concerning frequency characters of the two time series, time series hGPS-RP , veritably reflects entire- frequency vertical motion, while dhheave-RP is only valid in presenting high-frequency vertical motion. Thus, the time length of both time series should be within 60 second of their common period. we used the three methods in an experiment of time delay detection, and acquire very consistent time delay and high accuracy of time delay determination. Finally, we analyze the characters of the three methods. Method of characteristic point pairs and method of maximum similarity of profiles need to implement to-and-fro profile measurements in data sampling. The two methods are simple in calculation, while accuracy of the determination of TD will become weak with the decreasing of sampling density and point- pair correlative degree. Method of consistent motion has simplicity in implement and high accuracy in the determination of time delay. Thus we recommend it as an optimum method for determining TD.

Dm Hodgson - One of the best experts on this subject based on the ideXlab platform.

  • Quantification of basin-floor fan pinchouts: examples from the Karoo Basin, South Africa
    'Frontiers Media SA', 2019
    Co-Authors: Hansen Las, Dm Hodgson, Ponten A, Bell D, Flint S
    Abstract:

    The Topography of the Seabed (orientation and gradient) and rheology of the flows greatly influences the character of basin-floor turbidity current deposits. Therefore, submarine fan pinchouts can help to constrain Seabed Topography and flow behavior at the time of deposition. Although the depositional architecture of submarine lobe pinchouts has been documented in various basin-fills, the quantification of the rates of change at pinchouts in different paleogeographic positions and basin configurations has not been attempted previously. Here, we utilize extensive outcrops and research boreholes from the oblique up-dip pinchout of Fans 3 and 4 and the lateral pinchout of Fan 3 in the Tanqua depocenter, Karoo Basin, South Africa, to compare sedimentary facies and to quantify the rates of change in gross interval thickness. At the oblique up-dip pinchout, Fan 3 thins abruptly at a rate of 12 m/km, while Fan 4 thins at a rate of 4 m/km. Marked differences between Fans 3 and 4 in sedimentary facies and architecture toward the up-dip pinchout, with termination of lobes in Fan 3 and a channel-lobe transition zone and external levee in Fan 4, suggests progradation of the system. The thinning rate of the lateral pinchout of Fan 3 is 2 m/km, with the presence of hybrid beds in the lower part of Fan 3, while the upper part is dominated by structured sandstones and thin-bedded heterolithics. The variations in facies suggest that lobe-scale frontal and lateral pinchouts are stacked at the lobe complex-scale lateral pinchout of Fan 3, highlighting the importance of a hierarchical understanding when studying basin-floor fan pinchouts. The quantified rates of change in fan thickness and sedimentology on the oblique up-dip and lateral fan pinchouts are markedly different. Contrasting pinchout architecture above slopes with subtle differences in gradient and orientation cautions against the simple definition of reservoir input parameters for stratigraphic traps in submarine fan systems

  • Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles
    'Geological Society of America', 2018
    Co-Authors: Hl Brooks, Dm Hodgson, Rl Brunt, Peakall J, Poyatos-moré M, Ss Flint
    Abstract:

    The effects of abrupt changes in slope angle and orientation on turbidity current behavior have been investigated in numerous physical and numerical experiments and examined in outcrop, subsurface, and modern systems. However, the long-term impact of subtle and evolving Seabed Topography on the stratigraphic architecture of deep-water systems requires fine-scale observations and extensive 3-D constraints. This study focuses on the Permian Laingsburg and Fort Brown formations, where multiple large sand-rich systems (Units A–F) have been mapped from entrenched slope valleys, through channel-levee systems, to basin-floor lobe complexes over a 2500 km2 area. Here, we investigate three thinner (typically

  • Aggradational lobe fringes: The influence of subtle intrabasinal Seabed Topography on sediment gravity flow processes and lobe stacking patterns
    'Wiley', 2017
    Co-Authors: Yt Spychala, Dm Hodgson, Cj Stevenson, Ss Flint
    Abstract:

    Seabed Topography is ubiquitous across basin-floor environments, and influences sediment gravity flows and sediment dispersal patterns. The impact of steep (several degrees) confining slopes on sedimentary facies and depositional architecture has been widely documented. However, the influence of gentle (fraction of a degree) confining slopes is less well-documented, largely due to outcrop limitations. Here, exceptional outcrop and research borehole data from Unit A of the Permian Laingsburg Formation, South Africa, provides the means to examine the influence of subtle lateral confinement on flow behaviour and lobe stacking patterns. The dataset describes the detailed architecture of subunits A.1 to A.6, a succession of stacked lobe complexes, over a palinspastically restored 22 km across-strike transect. Facies distributions, stacking patterns, thickness and palaeoflow trends indicate the presence of a south-east facing low angle (fraction of a degree) lateral intrabasinal slope. Interaction between stratified turbidity currents with a thin basal sand-prone part and a thick mud-prone part and the confining slope result in facies transition from thick-bedded sandstones to thin-bedded heterolithic lobe fringe-type deposits. Slope angle dictates the distance over which the facies transition occurs (hundreds of metres to kilometres). These deposits are stacked vertically over tens of metres in successive lobe complexes to form an aggradational succession of lobe fringe. Extensive slides and debrites are present at the base of lobe complexes, and are associated with steeper restored slope gradients. The persistent facies transition across multiple lobe complexes, and the mass flow deposits, suggests that the intrabasinal slope was dynamic and was never healed by deposition during Unit A times. This study demonstrates the significant influence that even subtle basin-floor Topography has on flow behaviour and depositional architecture in the Laingsburg depocentre, Karoo Basin; presenting a new aggradational lobe fringe facies association and recognition criteria for subtle confinement in less well-exposed and subsurface basin fills

Ji Cai - One of the best experts on this subject based on the ideXlab platform.

  • Effects of the sea floor Topography on the 1D inversion of time-domain marine controlled source electromagnetic data
    Geophysical Prospecting, 2018
    Co-Authors: Ji Cai, Bülent Tezkan, Yuguo Li
    Abstract:

    Time-domain marine controlled source electromagnetic methods have been used successfully for the detection of resistive targets such as hydrocarbons, gas hydrate, or marine groundwater aquifers. As the application of time-domain marine controlled source electromagnetic methods increases, surveys in areas with a strong Seabed Topography are inevitable. In these cases, an important question is whether bathymetry information should be included in the interpretation of the measured electromagnetic field or not. Since multi-dimensional inversion is still not common in time-domain marine controlled source electromagnetic methods, bathymetry effects on the 1D inversion of single-offset and multi-offset joint inversions of time-domain controlled source electromagnetic methods data are investigated. We firstly used an adaptive finite element algorithm to calculate the time-domain controlled source electromagnetic methods responses of 2D resistivity models with seafloor Topography. Then, 1D inversions are applied on the synthetic data derived from marine resistivity models, including the Topography in order to study the possible Topography effects on the 1D interpretation. To evaluate the effects of Topography with various steepness, the slope angle of the Seabed Topography is varied in the synthetic modelling studies for deep water (air interaction is absent or very weak) and shallow water (air interaction is dominant), respectively. Several different patterns of measuring configurations are considered, such as the systems adopting nodal receivers and the bottom-towed system. According to the modelling results for deep water when air interaction is absent, the 2D Topography can distort the measured electric field. The distortion of the data increases gradually with the enlarging of the Topography’s slope angle. In our test, depending on the configuration, the Seabed Topography does not affect the 1D interpretation significantly if the slope angle is less or around 10°. However, if the slope angle increases to 30° or more, it is possible that significant artificial layers occur in inversion results and lead to a wrong interpretation. In a shallow water environment with Seabed Topography, where the air interaction dominates, it is possible to uncover the true subsurface resistivity structure if the water depth for the 1D inversion is properly chosen. In our synthetic modelling, this scheme can always present a satisfactory data fit in the 1D inversion if only one offset is used in the inversion process. However, the determination of the optimal water depth for a multi-offset joint inversion is challenging due to the various air interaction for different offsets.

  • Effects of the sea floor Topography on the 1D inversion of time-domain marine controlled source electromagnetic data
    'Wiley', 2018
    Co-Authors: Ji Cai, Tezkan Buelent, Li Yuguo
    Abstract:

    Time-domain marine controlled source electromagnetic methods have been used successfully for the detection of resistive targets such as hydrocarbons, gas hydrate, or marine groundwater aquifers. As the application of time-domain marine controlled source electromagnetic methods increases, surveys in areas with a strong Seabed Topography are inevitable. In these cases, an important question is whether bathymetry information should be included in the interpretation of the measured electromagnetic field or not. Since multi-dimensional inversion is still not common in time-domain marine controlled source electromagnetic methods, bathymetry effects on the 1D inversion of single-offset and multi-offset joint inversions of time-domain controlled source electromagnetic methods data are investigated. We firstly used an adaptive finite element algorithm to calculate the time-domain controlled source electromagnetic methods responses of 2D resistivity models with seafloor Topography. Then, 1D inversions are applied on the synthetic data derived from marine resistivity models, including the Topography in order to study the possible Topography effects on the 1D interpretation. To evaluate the effects of Topography with various steepness, the slope angle of the Seabed Topography is varied in the synthetic modelling studies for deep water (air interaction is absent or very weak) and shallow water (air interaction is dominant), respectively. Several different patterns of measuring configurations are considered, such as the systems adopting nodal receivers and the bottom-towed system. According to the modelling results for deep water when air interaction is absent, the 2D Topography can distort the measured electric field. The distortion of the data increases gradually with the enlarging of the Topography's slope angle. In our test, depending on the configuration, the Seabed Topography does not affect the 1D interpretation significantly if the slope angle is less or around 10 degrees. However, if the slope angle increases to 30 degrees or more, it is possible that significant artificial layers occur in inversion results and lead to a wrong interpretation. In a shallow water environment with Seabed Topography, where the air interaction dominates, it is possible to uncover the true subsurface resistivity structure if the water depth for the 1D inversion is properly chosen. In our synthetic modelling, this scheme can always present a satisfactory data fit in the 1D inversion if only one offset is used in the inversion process. However, the determination of the optimal water depth for a multi-offset joint inversion is challenging due to the various air interaction for different offsets