1,721,263 research outputs found
Submarine slope degradation and aggradation and the stratigraphic evolution of channel-levee systems
Full text linkTwo seismic-scale submarine channel–levee systems exposed in the Karoo Basin, South Africa provide insights into slope conduit evolution. Component channel fills in a levee-confined channel system (Unit C) and an entrenched channel system (Unit D) follow common stacking patterns; initial horizontal stacking (lateral migration) is followed by vertical stacking (aggradation). This architecture is a response to an equilibrium profile shift from low accommodation (slope degradation, composite erosion surface formation, external levee development, sediment bypass) through at-grade conditions (horizontal stacking and widening) to high accommodation (slope aggradation, vertical stacking, internal levee development). This architecture is likely common to other channel–levee systems
Intrinsic controls on the range of volumes, morphologies, and dimensions of submarine lobes
No full textSLOPE Phase 2: sponsors’ third field workshop, Laingsburg Karoo, South Africa
No full textOutcrops of the Permian ecca Group in the southwestern Karoo basin are outstandingly well exposed and easily accessible. Present day erosion allows viewing of laterally continuous (tens of kilometres) outcrops in the Tanqua and Laingsburg depocentres. Key objectives of this report are:
-To illustrate the downdip and across-strike changes in facies, incisional styles, channel dimensions,in-complex and out-of-complex net:gross variations and the internal stratigraphy of Unit C and D;
-Discussion of seismically resolvable surfaces, geometries and volumes and uncertainties in estimating facies, net:gross and reservoir quality from seismic alone;
to build further on the Vischkuil story, variability of MTDs, run out distances, etc. and to discuss the effects of depositional vs tectonic topography on facies, geometries and thichness of lower Fan A;
-Examination of different types of channel, channel complex, and channel complex set, related to different profile positions. Discussion on the relative amounts of lateral spill vs bypass vs in-channel aggradation and the implications for axis to margin to overbank sand connectivity;
-To introduce and debate a sequence stratigraphic hierarchy for the slope succession
SLOPE 2 Project Final Report (sponsors only)
No full textThis report details the results from Phase 2 of the SLOPE research project undertaken by the Stratigraphy Group of the Earth and Ocean Sciences Department of the University of Liverpool. Slope Phase 2 was an outcrop-based study that lasted for 3 years and was conducted in the exceptionally well exposed Permian deepwater reservoir analogue deposits of the Karoo basin, South Africa. The project team involved 2 full-time Post-Doctoral researchers (Rufus Brunt and Claudio Di Celma), a PhD student (Willem van der Merwe) and several graduate research assistants, supervised by David Hodgson and Stephen Flint. PhD students Carlos Oliveira, Jorge Figueiredo and Amandine Prélat also assisted in the field, alongside their own research.
The purpose of the research was to develop predictive models for the sub-seismic scale architecture, net:gross distribution and connectivity of submarine slope deposits, within a hierarchical structure that could be applied to subsurface datasets. The starting point was that in many deepwater plays, 3-D seismic allows good imaging of the larger scale channel complexes, external levees and overall systems but not adequate description of lithologies and connectivity. In other plays such as the ultra-deep Gulf of Mexico and sub-basalt Atlantic margin, seismic quality is inadequate for good definition of larger geometries, requiring more reliance on well data and 3-D architectural scenarios derived from outcrop analogues.
This project built on aspects of Phase 1 and focuses on the slope channel/interchannel successions in the Laingsburg depocentre. A unique aspect of the Laingsburg study area is the potential to trace and document different slope channel and marginal architectural elements within a single stratigraphic unit downslope, from bypass-dominated upper slope to depositional lower slope/basin floor positions (Fig 1.1.3). The analysis has been based on detailed sedimentology coupled with the interpretation of key surfaces and stacking patterns in order to understand the spatial/temporal variability in geometry, architecture and connectivity in slope channel complexes and between these and the deposits lateral to them. A hierarchical approach has been adopted through the study. A database has been developed for shale types, bed lengths and connectivity of sands, channel dimensions and trends in thickness, facies and net:gross, both locally and semi-regionally. The 3-D architecture of a high net:gross and a low net:gross slope channel complex set have been captured in PETREL static reservoir models.
Full analysis of the Vischkuil Formation, the deepwater initiation unit, has been a major aim of Phase 2 because it provides a powerful outcrop analogue to similar debrite/MTC complex initiation phases recognized in West Africa and other subsurface examples. We have analysed the down-slope translation of the MTDs into turbidites, to capture their runout distances. Our current understanding of the Vischkuil system is detailed in this report but sponsors will also receive an electronic copy of the PhD thesis of Willem van der Merwe in approximately 1 year’s time (Dec 2008).
Deliverables
1) A facies scheme and a hierarchical classification of the building blocks of reservoir and non-reservoir deposits in interpreted high to low gradient, mid to base of slope settings. Detailed examples are given of different styles of channel, channel complex and complex set and associated inner and outer levee, overbank and distributive frontal lobe deposits from different positions along and across the slope profile.
2) Capture of specific architectural changes within selected stratigraphic intervals traceable for 30 km plus downslope.
3) A high resolution sequence stratigraphic framework for the deepwater systems.
4) A quantitative database of geometries and architecture, within the hierarchical scheme and sequence stratigraphy.
5) Detailed study of the early muddy basin floor, emplacement of early debrites and associated deformation deposits. Capturing the effect of these mass transport deposits on the architecture of overlying sands in Fan A.
6) PETREL model of a high net:gross channel complex
Age control on the Tanqua and Laingsburg deep-water systems: New insights on the evolution and sedimentary fill of the Karoo basin, South Africa
No full textU-Pb zircons ages from the southwestern Karoo Basin, South Africa – Implications for the Permian-Triassic boundary
No full textSLOPE Phase 2: sponsors’ second field workshop, Laingsburg Karoo, South Africa
No full textOutcrops of the Permian ecca Group in the southwestern Karoo basin are outstandingly well exposed and easily accessible. Present day erosion allows viewing of laterally continuous (tens of kilometres) outcrops in the Tanqua and Laingsburg depocentres. Key objectives of this report are:
-Discussion of seismically resolvable surfaces, geometries and volumes and uncertainties in estimating facies, net:gross and reservoir quality from seismic alone;
-Assesment of the role of depositional topography (related to mass-transport deposits) compared to active growth of topography during episodic deformation of the seabed;
-Differentiation of lower slope from basin floor settings and characterisation of lower and middle slope channel-overbank complexes;
-development of criteria to recognise and assess bypass processes in slope settings and implications for down-dip sand supply;
-Examination of different types of channel, channel complex, and channel complex set, related to different profile positions. Discussion on the relative amounts of lateral spill vs bypass vs in-channel aggradation and the implications for axis to margin to overbank sand connectivity;
-Recognition of facies and facies associations, based on depositional processes, vertical succession and geometry, using outcrop, core and wireline logs;
-Appreciation of the strong stratigraphic control on distribution of reservoir permeability extremes and their capture in reservoir models;
-Discussion of approaches to building reservoir models of deep-water systems
U-PB zircon tuff geochronology from the Karoo Basin, South Africa: implications of zircon recycling on stratigraphic age controls
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