Coarse-grained, deep-water sedimentation along a border fault margin of Lake Malawi, Africa; seismic stratigraphic analysis

Soreghan, Michael J.; Scholz, Christopher A.; Wells, John T.

doi:10.2110/jsr.69.832

Cited by 94 publications

(97 citation statements)

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“…Existing structures of significance are the Ubendian Proterozoic mobile belt, known to have exerted strong influence on the location and orientation of the northern (Karonga) basin of the Malawi Rift (Rosendahl, 1987;King, 1994), and later Permian Karoo extensional basins onto which many basin separating accommodation zones are juxtaposed (e.g., Versfelt and Rosendahl, 1989) . There are significant occurrences of Karoo sediments in a SW-NE graben to the east of the central basin of the Malawi Rift, and some deposits to the west suggesting this graben continues into the region occupied by Lake Nyasa (Figure 1b The north and central segments have been recognised by previous interpretations (e.g., Ebinger et al, 1987;Scholz, 1989;Soreghan et al, 1999;Contreras et al, 2000), separated by a relay ramp (Chilumba 'platform' Scholz, 1989) that is dissected by normal, preferentially SW-dipping faults (e.g., Soreghan et al, 1999). The south fault segment was first interpreted by Contreras at al., (2000) based upon PROBE data, however, the greater resolution of our data indicates that it does not continue so far north into the basin as they proposed.…”

Section: Nkhata Basin Setting and Architecturementioning

confidence: 60%

“…This leads to a highly compartmentalized depocentres adjacent to the transfer fault. Soreghan et al (1999) have well documented the distribution of sediments along the western part of the central basin. They record a channel network both through the relay zone (Rukwa River) and an additional channel from the Ruhuhu graben into the central part of the basin (Figure 7).…”

Section: Sediment Distribution and Hydrocarbon Implicationsmentioning

confidence: 99%

“…They record a channel network both through the relay zone (Rukwa River) and an additional channel from the Ruhuhu graben into the central part of the basin (Figure 7). Wells et al (1995) and Soreghan et al (1999) show that coarse-grained material deposited dominantly in gravity driven flows accumulate on the relay ramp during highstands but otherwise are transported through canyons to the offshore area adjacent to the tips of the overlapping fault segment . The systems in the intra-basin region are confined by the western margin of the horst structures defined in our study.…”

Section: Sediment Distribution and Hydrocarbon Implicationsmentioning

confidence: 99%

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Implications of structural inheritance in oblique rift zones for basin compartmentalization: Nkhata Basin, Malawi Rift (EARS)

Mortimer

Paton

Scholz

et al. 2016

Marine and Petroleum Geology

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The Cenozoic East African Rift System (EARS) is an exceptional example of active continental extension, providing opportunities for furthering our understanding of hydrocarbon plays within rifts. It is divided into structurally distinct western and eastern branches. The western branch comprises deep rift basins separated by transfer zones, commonly localised onto pre-existing structures, offering good regional scale hydrocarbon traps. At a basin-scale, local discrete inherited structures might also play an important role on fault localisation and hydrocarbon distribution. Here, we consider the evolution of the Central basin of the Malawi Rift, in particular the influence of pre-existing structural fabrics.Integrating basin-scale multichannel 2D, and high resolution seismic datasets we constrain the border, Mlowe-Nkhata, fault system (MNF) to the west of the basin and smaller Mbamba fault (MF) to the east and document their evolution. Intra basin structures define a series of horsts, which initiated as convergent transfers, along the basin axis. The horsts are offset along a NE-SW striking transfer fault parallel to and along strike of the onshore Karoo 2 (Permo-Triassic) Ruhuhu graben. Discrete pre-existing structures probably determined its location and, oriented obliquely to the extension orientation it accommodated predominantly strike-slip deformation, with more slowly accrued dip-slip.To the north of this transfer fault, the overall basin architecture is asymmetric, thickening to the west throughout; while to the south, an initially symmetric graben architecture became increasingly asymmetric in sediment distribution as strain localised onto the western MNF. The presence of the axial horst increasingly focussed sediment supply to the west. As the transfer fault increased its displacement, so this axial supply was interrupted, effectively starving the south-east while ponding sediments between the western horst margin and the transfer fault. This asymmetric bathymetry and partitioned sedimentation continues to the present-day, overprinting the early basin symmetry and configuration. Sediments deposited earlier become increasingly dissected and fault juxtapositions changed at a small (10-100 m) scale. The observed influence of basin-scale transfer faults on sediment dispersal and fault compartmentalisation due to pre-existing structures oblique to the extension orientation is relevant to analogous exploration settings.

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Section: Nkhata Basin Setting and Architecturementioning

confidence: 60%

Section: Sediment Distribution and Hydrocarbon Implicationsmentioning

confidence: 99%

Section: Sediment Distribution and Hydrocarbon Implicationsmentioning

confidence: 99%

See 1 more Smart Citation

Implications of structural inheritance in oblique rift zones for basin compartmentalization: Nkhata Basin, Malawi Rift (EARS)

Mortimer

Paton

Scholz

et al. 2016

Marine and Petroleum Geology

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“…In most depositional settings (deltaic, deep-water, fluvial) sedimentation is always made up of stratigraphic cycles characterized primarily by the alternation of fine suspended-load deposit (settling out of suspension load) and coarser bedload deposit which produce typical sand-shale alternations (Damuth, 1994;Edwards, 1995;Cross and Lessenger, 1998;Soreghan et al, 1999;Hiscott, 2001). The different processes record in different ways the differential subsidence due to growth faulting.…”

Section: Determining Fault Kinematics From Growth Strata: An Overviewmentioning

confidence: 99%

High-resolution record of tectonic and sedimentary processes in growth strata

Pochat

Castelltort

Choblet

et al. 2009

Marine and Petroleum Geology

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a b s t r a c tGrowth strata are used to determine the kinematics of synsedimentary structures such as faults. Classical methods of analysis such as thickness versus throw plot consider that the available space created by fault slip in the hanging wall of faults is instantaneously filled up by sediments. This has lead many previous works to identify a cyclic activity for growth faults. Here we perform a careful analysis of the variation of strata thicknesses on each side of a very well documented normal growth fault in the Niger delta. We show that these thickness variations are induced by the alternation of sedimentary processes during continuous fault slip. Suspended-load processes induce either uniform or slightly variable thickness of a large majority of mudstone layers. Bedload processes result in a preferential thickening of sand layers in the hanging wall. These high quality data thus provide strong grounds for doubting the polycyclic growth diagnosed for some faults at the scale of sedimentary cycles and supports the notion that fault displacement rates can be very well behaved. Our study emphasizes the important conclusion that stable fault growth, and related displacement rates, can appear to be punctuated when viewed at the scale of sedimentary cycles. It follows that care should be taken when attempting to derive displacement rates on temporal scales equivalent to those of alternating sedimentological cycles.

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“…Bornhauser, 1959;Edwards, 1976;Thornburg et al, 1990;Ravnas and Steel, 1997;Morris et al, 1998;Soreghan et al, 1999;Anderson et al, 2000;Hodgetts et al, 2001;Hooper et al, 2002;Shaw et al, 2003). This means that fault-generated topographies occur at the depositional surface, and that the fill-to-the-top assumption may not always be valid.…”

Section: Introductionmentioning

confidence: 99%

Using T–Z plots as a graphical method to infer lithological variations from growth strata

Castelltort

Pochat

Driessche

2004

Journal of Structural Geology

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The 'T-Z plot' method consists of plotting the throw of sedimentary horizons across a growth fault versus their depth in the hanging wall. This method has been initially developed for the analysis of growth fault kinematics from seismic data. A brief analytical examination of such plots shows that they can also provide valuable information about the evolution of fault topography. When growth is a continuous process, stages of topography creation (fault scarp) and filling (of the space available in the hanging-wall) are related to non-dynamic (draping, mud-prone pelagic settling) and dynamic (sand-prone, dynamically deposited) sedimentation, respectively. In this case, the T -Z plot analysis becomes a powerful tool to predict major lithological variations on seismic profiles in faulted settings. q

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Coarse-grained, deep-water sedimentation along a border fault margin of Lake Malawi, Africa; seismic stratigraphic analysis

Cited by 94 publications

References 0 publications

Implications of structural inheritance in oblique rift zones for basin compartmentalization: Nkhata Basin, Malawi Rift (EARS)

Implications of structural inheritance in oblique rift zones for basin compartmentalization: Nkhata Basin, Malawi Rift (EARS)

High-resolution record of tectonic and sedimentary processes in growth strata

Using T–Z plots as a graphical method to infer lithological variations from growth strata

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