Depositional history and stratigraphical evolution of the Sakoa Group (Lower Karoo Supergroup) in the southern Morondava Basin, Madagascar

Wescott, William A.; Diggens, J. N.

doi:10.1016/s0899-5362(97)00082-1

Cited by 28 publications

(23 citation statements)

References 8 publications

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“…9b). The higher velocities observed in the eastern parts of the basins can be explained by the fact that the Karoo facies, which are mainly sandstones, outcrop only in the eastern parts of the basin (Wescott & Diggens 1997, suggesting that the shearwave velocities in the western part of the basin are influenced by the younger deposits overlying the Karoo sequence.…”

Section: Discussionmentioning

confidence: 96%

The structure of the crust and uppermost mantle beneath Madagascar

Andriampenomanana

Nyblade

Wysession

et al. 2017

Geophysical Journal International

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S U M M A R YThe lithosphere of Madagascar was initially amalgamated during the Pan-African events in the Neoproterozoic. It has subsequently been reshaped by extensional processes associated with the separation from Africa and India in the Jurassic and Cretaceous, respectively, and been subjected to several magmatic events in the late Cretaceous and the Cenozoic. In this study, the crust and uppermost mantle have been investigated to gain insights into the present-day structure and tectonic evolution of Madagascar. We analysed receiver functions, computed from data recorded on 37 broad-band seismic stations, using the H-κ stacking method and a joint inversion with Rayleigh-wave phase-velocity measurements. The thickness of the Malagasy crust ranges between 18 and 46 km. It is generally thick beneath the spine of mountains in the centre part (up to 46 km thick) and decreases in thickness towards the edges of the island. The shallowest Moho is found beneath the western sedimentary basins (18 km thick), which formed during both the Permo-Triassic Karro rifting in Gondwana and the Jurassic rifting of Madagascar from eastern Africa. The crust below the sedimentary basin thickens towards the north and east, reflecting the progressive development of the basins. In contrast, in the east there was no major rifting episode. Instead, the slight thinning of the crust along the east coast (31-36 km thick) may have been caused by crustal uplift and erosion when Madagascar moved over the Marion hotspot and India broke away from it. The parameters describing the crustal structure of Archean and Proterozoic terranes, including average thickness (40 km versus 35 km), Poisson's ratio (0.25 versus 0.26), average shear-wave velocity (both 3.7 km s -1 ), and thickness of mafic lower crust (7 km versus 4 km), show weak evidence of secular variation. The uppermost mantle beneath Madagascar is generally characterized by shear-wave velocities typical of stable lithosphere (∼4.5 km s -1 ). However, markedly slow shear-wave velocities (4.2-4.3 km s -1 ) are observed beneath the northern tip, central part and southwestern region of the island where the major Cenozoic volcanic provinces are located, implying the lithosphere has been significantly modified in these places.

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Section: Discussionmentioning

confidence: 96%

The structure of the crust and uppermost mantle beneath Madagascar

Andriampenomanana

Nyblade

Wysession

et al. 2017

Geophysical Journal International

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“…1a). A number of authors have suggested that most of the Gondwana supercontinent (including large parts of Australia and India) was characterised by large-scale uplift that may have affected or caused the Late Carboniferous-Early Permian glaciation (Veevers and Powell, 1994;Visser and Praekelt, 1996;Wescott and Diggens, 1997). This uplift has been interpreted to be related to subduction along the Palaeo-Pacific Ocean and a change in stress regime during the development of the Permo-Triassic Cape Fold Belt in South Africa (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Sediments initially accumulated on an irregular basement surface with several small pullapart basins formed due to east-west extension and leftlateral strike slip movements along reactivation zones (Wescott and Diggens, 1997). The early extensional basin evolution was possibly related to north-south directed compression in the south African Cape Fold Belt (de Wit and Ransome, 1992).…”

Section: Geological Framework Of Madagascarmentioning

confidence: 99%

“…The Middle and Upper Sakoa deposits represent the evolution of the syn-rift phase. Many small rift initiation faults became inactive and extension focussed on a few large faults (Wescott and Diggens, 1997). The Sakamena Group, which unconformably overlies the Sakoa Group, comprises Late Permian continental sandstones and conglomerates overlain by Early Triassic marine shales and sandstones.…”

Section: Geological Framework Of Madagascarmentioning

confidence: 99%

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Titanite and apatite fission track analyses on basement rocks of central-southern Madagascar: constraints on exhumation and denudation rates along the eastern rift shoulder of the Morondava basin

Emmel

Jacobs

Razakamanana

2004

Journal of African Earth Sciences

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“…The base of the sequence was formerly interpreted as being of glacial origin and probably equivalent to the Dwyka glacials of Southern Africa. This interpretation was subsequently rejected in favour of an alluvial fan and debris flow origin (Wescott and Diggens, 1997). However, new observations suggest the basal Sakoa Group does indeed have characteristics strongly supportive of a glaciogenic origin, including massive diamictites with floating clasts, stratified diamictites with probable dropstones and metre-scale folds which do not affect adjacent beds (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Source Rock and Reservoir Evaluation in Madagascar: Insights from New Fieldwork And Outcrop Analyses

O’Neill¹

2017

Proceedings

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SummaryIn frontier areas geological fieldwork remains a basic but essential and highly valued tool for evaluating under explored regions. Compared with more sophisticated exploration techniques, fieldwork is a cost effective method that can reduce exploration risk and provide a deeper understanding of complex geology. In the summer/autumn of 2016 Robertson CGG geological teams collected 590 samples from 403 locations in the Morondava, Majunga and Diego Ambilobe basins as well as along the east coast of Madagascar. Seeps were also sampled at various locations. Field traverses covering a cumulative distance of ~12,000 km, often with poor road conditions in remote areas were overcome to complete this work in an eleven week period. The sampling and analytical programme primarily targeted source rock and reservoir horizons in the Karoo and younger Mesozoic and Tertiary intervals. The results of new biostratigraphy, sedimentology and geochemistry studies will assist in refining the stratigraphy, understanding the proven and potential source rocks and gaining a deeper insight into the quality of both clastic and carbonate reservoirs.

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Depositional history and stratigraphical evolution of the Sakoa Group (Lower Karoo Supergroup) in the southern Morondava Basin, Madagascar

Cited by 28 publications

References 8 publications

The structure of the crust and uppermost mantle beneath Madagascar

The structure of the crust and uppermost mantle beneath Madagascar

Titanite and apatite fission track analyses on basement rocks of central-southern Madagascar: constraints on exhumation and denudation rates along the eastern rift shoulder of the Morondava basin

Source Rock and Reservoir Evaluation in Madagascar: Insights from New Fieldwork And Outcrop Analyses

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