Depositional architecture and sequence stratigraphy of the Karoo basin floor to shelf edge succession, Laingsburg depocentre, South Africa

The Laingsburg depocentre of the SW Karoo Basin, South Africa preserves a well-exposed 1200 m thick succession of upper Permian strata that record the early filling of a basin during an icehouse climate. Uniformly fine-grained sandstones were derived from far-field granitic sources, possibly in Pata...

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Bibliographic Details
Published in:Marine and petroleum geology 2011-03, Vol.28 (3), p.658-674
Main Authors: Flint, S.S., Hodgson, D.M., Sprague, A.R., Brunt, R.L., Van der Merwe, W.C., Figueiredo, J., Prélat, A., Box, D., Di Celma, C., Kavanagh, J.P.
Format: Article
Language:English
Subjects:
Basins
Deepwater sequence stratigraphy
Delivery systems
Deposition
Earth sciences
Earth, ocean, space
Exact sciences and technology
Hydrocarbons
Karoo basin
Lobes
Marine
Marine geology
Sand
Sandstones
Sedimentary rocks
Stacking
Stratigraphy
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Summary:The Laingsburg depocentre of the SW Karoo Basin, South Africa preserves a well-exposed 1200 m thick succession of upper Permian strata that record the early filling of a basin during an icehouse climate. Uniformly fine-grained sandstones were derived from far-field granitic sources, possibly in Patagonia, although the coeval staging and delivery systems are not preserved. Early condensed shallow marine deposits are overlain by distal basin plain siltstone-prone turbidites and volcanic ashes. An order of magnitude increase in siliciclastic input to the basin plain is represented by up to 270 m of siltstone with thin sandstone turbidites (Vischkuil Formation). The upper Vischkuil Formation comprises three depositional sequences, each bounded by a regionally developed zone of soft sediment deformation and associated 20–45 m thick debrite that represent the initiation of a major sand delivery system. The overlying 300 m thick sandy basin-floor fan system (Unit A) is divisible into three composite sequences arranged in a progradational–aggradational–retrogradational stacking pattern, followed by up to 40 m of basin-wide hemipelagic claystone. This claystone contains Interfan A/B, a distributive lobe system that lies 10 m beneath Unit B, a sandstone-dominated succession that averages 150 m thickness and is interpreted to represent a toe of slope channelized lobe system. Unit B and the A/B interfan together comprise 4 depositional sequences in a composite sequence with an overall basinward-stepping stacking pattern, overlain by 30 m of hemipelagic claystone. The overlying 400 m thick submarine slope succession (Fort Brown Formation) is characterized by 10–120 m thick sand-prone to heterolithic packages separated by 30–70 m thick claystone units. On the largest scale the slope stratigraphy is defined by two major cycles interpreted as composite sequence sets. The lower cycle comprises lithostratigraphic Units B/C, C and D while the upper cycle includes lithostratigraphic Units D/E, E and F. In each case a sandy basal composite sequence is represented by an intraslope lobe (Units B/C and D/E respectively). The second composite sequence in each cycle (Units C and E respectively) is characterized by slope channel-levee systems with distributive lobes 20–30 km down dip. The uppermost composite sequence in each cycle (Units D and F respectively) are characterised by deeply entrenched slope valley systems. Most composite sequences comprise three sequences separated by t
ISSN:0264-8172
1873-4073
DOI:10.1016/j.marpetgeo.2010.06.008