--> Abstract: Fine-Grained Submarine Fan Growth and the Distribution of Architectural Elements: An Example from the Skoorsteenberg Formation (Fan 4), Southwest Karoo Basin, South Africa, by David M. Hodgson, Nick Drinkwater, Stephen Flint, David Hodgetts, and Erik Johannessen; #90039 (2005)

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Fine-Grained Submarine Fan Growth and the Distribution of Architectural Elements: An Example from the Skoorsteenberg Formation (Fan 4), Southwest Karoo Basin, South Africa

David M. Hodgson1, Nick Drinkwater2, Stephen Flint1, David Hodgetts3, and Erik Johannessen4
1 University of Liverpool, Liverpool, United Kingdom
2 ChevronTexaco, Bellaire, TX
3 The University of Manchester, Manchester, United Kingdom
4 Statoil, Stavanger, Norway

Integration of correlated outcrop, core and wireline logs, an extensive palaeocurrent dataset, and Differential Global Positioning surveyed fan surfaces has enabled a progradational-aggradational-retrogradational growth history to be identified in a fine-grained submarine fan system. Fan 4 of the Tanqua depocentre was deposited during an interpreted 5th order lowstand and is built of higher frequency (6th order) sequences (alternating sand- and silt-prone intervals). Feeder channels filled by basal mudstone clast conglomerates, cross-bedded and structureless sandstones occur in the most proximal areas, but the majority of Fan 4 is dominated by sheet turbidites containing discrete zones of complete vertical bed amalgamation. The 6th order cycles stack in a progradational to aggradational to retrogradational pattern, which is expressed in strike section as a fan expansion, build and contraction geometry. The expansion phase geometry may be also influenced by pre-existing topography such as older fans. Moving down dip (and across strike from fan axis to margin) the lowermost sandstone preserved is progressively younger, whilst the uppermost sandstone is progressively older. This stacking pattern imparts an important and predictable control on reservoir and seal geometries and the distribution of lithofacies and architectural elements at reservoir scale, and emphasises the need to discriminate between the lithologic and stratigraphic bases and tops of fan systems in subsurface datasets. Vertical connectivity is increased locally through amalgamation of sand-prone zones, especially in those areas immediately down dip of feeder complexes. This study aids the development of predictive models for submarine fan reservoir and seal distributions in space and time.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005