The Ogooue Fan (offshore Gabon): a modern example of deep-sea fan on a complex slope profile

Abstract. The effects of changes in slope gradient on deposition processes and architecture have been investigated in different deep-sea systems both in modern and ancient environments. However, the impact of subtle gradient changes (< 0.3∘) on sedimentary processes along deep-sea fans still needs to be clarified. The Ogooue Fan, located in the northeastern part of the Gulf of Guinea, extends over more than 550 km westwards of the Gabonese shelf and passes through the Cameroon volcanic line. Here, we present the first study of acoustic data (multibeam echosounder and 3.5 kHz, very high-resolution seismic data) and piston cores covering the deep-sea part of this West African system. This study documents the architecture and sedimentary facies distribution along the fan. Detailed mapping of near-seafloor seismic-reflection data reveals the influence of subtle slope gradient changes (< 0.2∘) along the fan morphology. The overall system corresponds to a well-developed deep-sea fan, fed by the Ogooue River sedimentary load, with tributary canyons, distributary channel–levee complexes and lobe elements. However, variations in the slope gradient due to inherited salt-related structures and the presence of several seamounts, including volcanic islands, result in a topographically complex slope profile including several ramps and steps. In particular, turbidity currents derived from the Gabonese shelf deposit cross several interconnected intra-slope basins located on the low gradient segments of the margin (< 0.3∘). On a higher gradient segment of the slope (0.6∘), a large mid-system valley developed connecting an intermediate sedimentary basin to the more distal lobe area. Distribution and thickness of turbidite sands is highly variable along the system. However, turbidite sands are preferentially deposited on the floor of the channel and the most proximal depositional areas. Core description indicates that the upper parts of the turbidity flows, mainly composed of fine-grained sediments, are found in the most distal depocenters.

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The Ogooue Fan (Gabon): a modern example of deep-sea system on a complex sea-floor topography

10.5194/se-2018-99 ◽

2018 ◽

Author(s):

Salomé Mignard ◽

Thierry Mulder ◽

Philippe Martinez ◽

Thierry Garlan

Keyword(s):

Sea Level ◽

Deep Sea ◽

Sedimentary Facies ◽

Turbidity Currents ◽

Acoustic Data ◽

Fine Grained ◽

Longshore Drift ◽

Volcanic Islands ◽

Sea Fan ◽

Channel Levees

Abstract. The Ogooue deep-sea Fan located in the northeastern part of the Gulf of Guinea expands over more than 550 km westwards of the Gabonese shelf and passes through the Cameroun volcanic line. Here are presented the first study of acoustic data (multibeam echosounder and 3.5 kHz seismic data) and piston cores covering the deep-sea part of this West African system. This study led to the construction of the sedimentary processes map of this area. The overall system corresponds to a well-developed mud-sand rich deep-sea fan, fed by the Ogooue River 'sedimentary load. This system presents the typical morphological elements of clastic slope apron: tributary canyons, distributary channel-levees systems and lobes elements. However, variations on the slope gradient cumulated with the presence of numerous seamounts, including volcanic islands and mud volcanoes, led to a more complex fan architecture and sedimentary facies distribution. In particular, turbidity currents derived from the Gabonese shelf deposit across several interconnected sedimentary sub-basins located on the low gradient segments of the margin. The repeated spill-overs of the most energetic turbidite flows have notably led to the incision of a large distal valley connecting an intermediate sedimentary basin to the more distal lobe area. The sedimentary facies repartition over the fan indicates that pelagic to hemipelagic sedimentation is dominant across the area. Distribution and thickness of turbidite sand beds is highly variable along the system, however turbidite sands preferentially deposit in the bottom of channel-levee systems and on the most proximal depositional areas. The most distal depocenters receive only the upper parts of the flows, which are composed of fine-grained sediments. The Ogooue deep-sea system is predominantly active during periods of low sea-level because canyon heads are separated from terrestrial sediment sources by the broad shelf. However, the northern part of this system appears active during sea-level highstands. This feature is one deeply incised canyon, the Cape Lopez canyon, located on a narrower part of the continental shelf has a different behaviour and receives sediments transported by the longshore drift.

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An improved method to estimate Q based on the logarithmic spectrum of moving peak points

Interpretation ◽

10.1190/int-2017-0234.1 ◽

2019 ◽

Vol 7 (2) ◽

pp. T255-T263 ◽

Cited By ~ 4

Author(s):

Yanli Liu ◽

Zhenchun Li ◽

Guoquan Yang ◽

Qiang Liu

Keyword(s):

Seismic Waves ◽

Wave Attenuation ◽

Real Data ◽

Peak Frequency ◽

Seismic Reflection Data ◽

The Real ◽

Time Frequency ◽

Reflection Data ◽

Text Filtering ◽

The Impact

The quality factor ([Formula: see text]) is an important parameter for measuring the attenuation of seismic waves. Reliable [Formula: see text] estimation and stable inverse [Formula: see text] filtering are expected to improve the resolution of seismic data and deep-layer energy. Many methods of estimating [Formula: see text] are based on an individual wavelet. However, it is difficult to extract the individual wavelet precisely from seismic reflection data. To avoid this problem, we have developed a method of directly estimating [Formula: see text] from reflection data. The core of the methodology is selecting the peak-frequency points to linear fit their logarithmic spectrum and time-frequency product. Then, we calculated [Formula: see text] according to the relationship between [Formula: see text] and the optimized slope. First, to get the peak frequency points at different times, we use the generalized S transform to produce the 2D high-precision time-frequency spectrum. According to the seismic wave attenuation mechanism, the logarithmic spectrum attenuates linearly with the product of frequency and time. Thus, the second step of the method is transforming a 2D spectrum into 1D by variable substitution. In the process of transformation, we only selected the peak frequency points to participate in the fitting process, which can reduce the impact of the interference on the spectrum. Third, we obtain the optimized slope by least-squares fitting. To demonstrate the reliability of our method, we applied it to a constant [Formula: see text] model and the real data of a work area. For the real data, we calculated the [Formula: see text] curve of the seismic trace near a well and we get the high-resolution section by using stable inverse [Formula: see text] filtering. The model and real data indicate that our method is effective and reliable for estimating the [Formula: see text] value.

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Tsunami hazard from lacustrine mass wasting in Lake Tekapo, New Zealand

Geological Society London Special Publications ◽

10.1144/sp477.21 ◽

2018 ◽

Vol 477 (1) ◽

pp. 413-426 ◽

Cited By ~ 5

Author(s):

Joshu J. Mountjoy ◽

Xiaoming Wang ◽

Susi Woelz ◽

Sean Fitzsimons ◽

Jamie D. Howarth ◽

...

Keyword(s):

High Resolution ◽

Sediment Cores ◽

Lake Basin ◽

Diverse Range ◽

Seismic Reflection Data ◽

Reflection Data ◽

Tectonically Active ◽

Tsunami Risk ◽

Western Shore ◽

The Impact

AbstractLacustrine-tsunami risk from landslides can be significant yet for most locations globally the hazard remains unquantified. Lake Tekapo, in the tectonically active mountain belt of New Zealand's South Island, has been chosen to develop surveying and modelling techniques to assess the hazard from landslide tsunamis. Lake Tekapo is ideal for this study due to the high sedimentation rates, steep surrounds and the proximity to active faulting that indicate a high landslide potential. The shoreline tourist settlement and hydropower infrastructure mean the impact of any tsunami could be significant. In 2016 a survey was carried out to collect high-resolution (1 m grid) EM2040 multibeam bathymetry, high-resolution seismic reflection data (Boomer and chirp) and 6 m long sediment cores. These data reveal a diverse range of sedimentary processes in response to high sediment input and numerous landslides with varied styles of emplacement. For example, a one-off landslide initiated 40 m above the shoreline with debris deposits that have runout onto the lake floor to 100 m water depth contrasts with the Cass River delta on the western shore that has failed multiple times during the lake-basin infilling history. Landslide-generated tsunami scenarios are used to determine the relative hazard at different regions of the lake to guide development of a probabilistic tsunami model.

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Hydrocarbon Prospect of Block VI, East Gobi Basin

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.827.148 ◽

2013 ◽

Vol 827 ◽

pp. 148-152

Author(s):

Lian Jin Wang ◽

Yan Jun Chen ◽

Chou Chou Yang

Keyword(s):

Fault Zone ◽

Oil And Gas ◽

Facies Analysis ◽

Gravity Data ◽

Sedimentary Facies ◽

Western Slope ◽

Seismic Reflection Data ◽

Reflection Data ◽

Stratigraphic Sequences ◽

Electrical Data

2D seismic reflection data and magnetism data, gravity data and electrical data together define the overall subsurface structure of the East Gobi basin (EGB), and reflect Jurassic-Cretaceous intracontinental rift evolution through deposition of at least five distinct stratigraphic sequences. Three major NE-SW trending fault zones divide the basin[. In the paper, through strata sequence description and sedimentary facies analysis, as well as zone appraisal for the oil and gas in the study area, we conclude that western step-fault zone of the block VI of EGB was most favorable pay, then the reverse faulted-nose structure in the east, while in the western slope and eastern fault zone, their hydrocarbon prospect need further proved.

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How do tectonics influence the initiation and evolution of submarine canyons A case study from the Otway Basin, SE Australia

10.31223/x57043 ◽

2021 ◽

Author(s):

Nan Wu ◽

Harya Nugraha ◽

Michael Steventon ◽

Fa Zhong

Keyword(s):

Late Miocene ◽

Submarine Canyon ◽

Turbidity Currents ◽

Submarine Canyons ◽

Seismic Reflection Data ◽

Reflection Data ◽

Depositional Processes ◽

Seabed Topography ◽

Gravity Driven ◽

Unconformity Surface

The architecture of canyon-fills can provide a valuable record of the link between tectonics, sedimentation, and depositional processes in submarine settings. We integrate 3D and 2D seismic reflection data to investigate the dominant tectonics and sedimentary processes involved in the formation of two deeply buried (c. 500 m below seafloor), and large (c. 3-6 km wide, >35 km long) Late Miocene submarine canyons. We found the plate tectonic-scale events (i.e. continental breakup and shortening) have a first-order influence on the submarine canyon initiation and evolution. Initially, the Late Cretaceous (c. 65 Ma) separation of Australia and Antarctica resulted in extensional fault systems, which then formed stair-shaped paleo-seabed. This inherited seabed topography allowed gravity-driven processes (i.e. turbidity currents and mass-transport complexes) to occur. Subsequently, the Late Miocene (c. 5 Ma) collision of Australia and Eurasia, and the resulting uplift and exhumation, have resulted in a prominent unconformity surface that coincides with the base of the canyons. We suggest that the Late Miocene intensive tectonics and associated seismicity have resulted in instability in the upper slope that consequently gave rise to emplacement of MTCs, initiating the canyons formation. Therefore, we indicate that regional tectonics play a key role in the initiation and development of submarine canyons.

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