Stratigraphic Organization and Predictability of Mixed Coarse- and Fine-grained Lithofacies Successions in a Lower Miocene Deep-water Slope-channel System, Angola Block 15

Distinguishing among deep-water sedimentary facies has been a difficult task. This is possibly due to the process continuum in deep water, in which sediments occur in complex associations. The lack of definite sedimentological features among the different facies between hemipelagites and contourites presented a great challenge. In this study, we present detailed mudrock characteristics of the three main deep-water facies based on sedimentological characteristics, laser diffraction granulometry, high-resolution, large area scanning electron microscopy (SEM), and the synchrotron X-ray diffraction technique. Our results show that the deep-water microstructure is mainly process controlled, and that the controlling factor on their grain size is much more complex than previously envisaged. Retarding current velocity, as well as the lower carrying capacity of the current, has an impact on the mean size and sorting for the contourite and turbidite facies, whereas hemipelagite grain size is impacted by the natural heterogeneity of the system caused by bioturbation. Based on the microfabric analysis, there is a disparate pattern observed among the sedimentary facies; turbidites are generally bedding parallel due to strong currents resulting in shear flow, contourites are random to semi-random as they are impacted by a weak current, while hemipelagites are random to oblique since they are impacted by bioturbation.

Download Full-text

Mud prone entrenched deep-water slope channel complexes from the Eocene of eastern Turkey

Geological Society London Special Publications ◽

10.1144/gsl.sp.2005.244.01.10 ◽

2005 ◽

Vol 244 (1) ◽

pp. 155-180 ◽

Cited By ~ 5

Author(s):

Bryan T. Cronin ◽

Hasan Çelik ◽

Andrew Hurst ◽

Ibrahim Turkmen

Keyword(s):

Deep Water ◽

Eastern Turkey ◽

Slope Channel

Download Full-text

Modelling the embedment process during offshore pipe-laying on fine-grained soils

Canadian Geotechnical Journal ◽

10.1139/cgj-2012-0185 ◽

2013 ◽

Vol 50 (1) ◽

pp. 15-27 ◽

Cited By ~ 20

Author(s):

Z.J. Westgate ◽

D.J. White ◽

M.F. Randolph

Keyword(s):

Deep Water ◽

Small Amplitude ◽

Model Tests ◽

Soil Parameters ◽

Sea State ◽

Field Surveys ◽

Centrifuge Model ◽

Fine Grained ◽

Displacement Patterns ◽

Centrifuge Model Tests

Subsea pipelines are becoming an increasingly significant element of offshore hydrocarbon developments as exploration moves into deep-water environments further from shore. During the lay process, pipelines are subject to small amplitude vertical and horizontal oscillations, driven by the sea state and lay vessel motions. Centrifuge model tests have been used to simulate these small-amplitude lay effects, with varying degrees of idealization relative to the real lay process. In the soft soils found in deep water, pipe embedment can exceed a diameter or more, thus significantly affecting the lateral pipe–soil interaction, axial resistance, and thermal insulation. In this paper, results from centrifuge model tests are used to calibrate a model for calculating the dynamic embedment of a subsea pipeline. The model uses elements of plasticity theory to capture the effects of combined vertical and horizontal loading, and incorporates the softening of the surrounding soil as it is remoulded due to the pipeline motions. Influences from the lay rate, lay geometry, and sea state are included in the calculation process. The model is compared with observed as-laid pipeline embedment data from field surveys at three different offshore sites. Using site-specific soil parameters obtained from in situ testing and idealized pipe loads and motions to represent the load and displacement patterns during offshore pipe-laying, respectively, the model is shown to capture well the final as-laid embedment measured in the field surveys.

Download Full-text

High-frequency sea-level changes recorded in deep-water carbonates of the Upper Cretaceous Dol Formation (island of Brač, Croatia)

Geologica Carpathica ◽

10.2478/v10096-009-0042-z ◽

2010 ◽

Vol 61 (1) ◽

pp. 29-38

Author(s):

Damir Bucković ◽

Maja Martinuš ◽

Duje Kukoč ◽

Blanka Tešović ◽

Ivan Gušić

Keyword(s):

Sea Level ◽

Deep Water ◽

High Frequency ◽

Upper Cretaceous ◽

Distal Part ◽

Preferential Orientation ◽

Sea Level Changes ◽

Carbonate Production ◽

Fine Grained ◽

Platform Margin

High-frequency sea-level changes recorded in deep-water carbonates of the Upper Cretaceous Dol Formation (island of Brač, Croatia)The upper part of the Middle Coniacian/Santonian-Middle Campanian deep-water Dol Formation of the island of Brač is composed of countless fine-grained allodapic intercalations deposited in an intraplatform trough. Within the studied section 13 beds can be distinguished, each defined by its lower part built up of dark grey limestone with abundance of branched, horizontally to subhorizontally oriented burrows, and the upper part, in which the light grey to white limestone contains larger burrows, rarely branched, showing no preferential orientation. The lower, dark grey, intensively bioturbated levels are interpreted as intervals formed during high-frequency sea-level highstands, while the upper, light grey-to-white levels are interpreted as intervals formed during the high-frequency sea-level lowstands. Cyclic alternation of these two intervals within the fine-grained allodapic beds is interpreted as the interaction between the amount of carbonate production on the platform margin and the periodicity and intensity of shedding and deposition in the distal part of toe-of-slope environment, which is governed by Milankovitch-band high frequency sea-level changes.

Download Full-text

Field-Scale Stratigraphy and Depositional Elements of a Slope Channel System and Implications for Reservoir Dynamics; A Case Study from the Angolan Margin

New Understanding of the Petroleum Systems of Continental Margins of the World: 32nd Annual ◽

10.5724/gcs.12.32.0469 ◽

2012 ◽

pp. 469-493

Author(s):

Luz Sophia Cobos ◽

Mike Mayall ◽

Tim Primmer ◽

Rosa Osvaldo

Keyword(s):

Field Scale ◽

Channel System ◽

Slope Channel ◽

Depositional Elements

Download Full-text

Distinguishing between Fine-Grained Turbidites and Contourites on the Nova Scotian Deep-Water Margin

Deep-Water Turbidite Systems ◽

10.1002/9781444304473.ch12 ◽

2009 ◽

pp. 149-165 ◽

Cited By ~ 1

Author(s):

Dorrik A. V. Stow

Keyword(s):

Deep Water ◽

Fine Grained ◽

Water Margin ◽

Nova Scotian

Download Full-text

The Alikayasi Canyon–Channel System (Miocene, Southeast Turkey) Compared with the South Brae Fan System (Upper Jurassic, North Sea); Characterizing Sand and Gravel-Filled Channel Complexes in Coarse-Grained Deep-water Systems Without Gravel Cone Geometries

10.1306/13652194m1153311 ◽

2018 ◽

pp. 595-618

Keyword(s):

North Sea ◽

Deep Water ◽

Upper Jurassic ◽

Water Systems ◽

Coarse Grained ◽

The South ◽

Channel System ◽

Sand And Gravel

Download Full-text

Architecture, process, and environmental diversity in a late Cretaceous slope channel system

Journal of Sedimentary Research ◽

10.2110/jsr.2020.1 ◽

2020 ◽

Vol 90 (1) ◽

pp. 1-26 ◽

Cited By ~ 3

Author(s):

Benjamin Kneller ◽

Guilherme Bozetti ◽

Richard Callow ◽

Mason Dykstra ◽

Larissa Hansen ◽

...

Keyword(s):

Building Blocks ◽

Heavy Minerals ◽

Coarse Grained ◽

Turbidity Currents ◽

Axial Region ◽

Sedimentary Process ◽

Channel System ◽

Environmental Diversity ◽

Channel Belt ◽

Slope Channel

ABSTRACT Arroyo San Fernando, on the Pacific coast of Baja California, Mexico, provides a superb view of the architecture of a Maastrichtian active margin slope channel system and the record of its evolution through a third-order sea-level cycle. The succession is organized into architectural building blocks (channel-complex sets) consisting of a channel belt with an axial region and a channel-belt margin of terraces and internal levees. The channel belt is confined by an external levee on one side and by an erosion surface into the slope on the other. Each channel-complex set can be subdivided into three stages of evolution: Stage I consists of highly amalgamated coarse-grained channel complexes, Stage II consists of gravelly meander belts with marginal and stratigraphically intervening thin-bedded turbidites, and Stage III consists of mudstones representing abandonment. This succession is associated with repeated and therefore predictable changes in architecture, facies distribution, inferred seafloor morphology, and sedimentary process. We describe variability in the sedimentology, ichnology, palynology, provenance, and inferred sedimentary processes between and within these architectural elements. Channel formation and fill are attributed to erosion, sediment transport, and deposition by turbidity currents and lesser debris flows. Ichnology indicates enhanced oxygenation and supply of organic material, substrate type, and turbidity within the channel belt; the axial region can be differentiated from the terraces by differing response to turbidity-current intensity. Levee environments show ichnological gradients away from the channel towards background slope. Palynology reflects confinement of the supply of terrigenous material to the channel belt, but is also indicative of stratification within the turbidity-currents, as is the distribution of heavy minerals. Provenance is from the extinct part of the continental-margin arc to the east, via high-gradient gravelly streams and across a steep shoreline, with direct supply of coastal material to deep water. Architectural hierarchy bears comparison with other slope channel systems, but in common with them the fill represents only a small fraction of the time that the system was active.

Download Full-text