Mapping the complexity of transform margins

Markwick, Paul J.; Paton, Douglas; Mortimer, Estelle

doi:10.1144/sp524-2021-82

Cited by 3 publications

(1 citation statement)

References 133 publications

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“…The Central and South Atlantic Oceans then connected through initially isolated “oceanic crust basin” patches (e.g., Blarez & Mascle, 1988; Ye et al., 2017). In the Late Albian, the African Equatorial rifted margin had acquired its segmentation with alternating transform and divergent segments formed along former strike‐slip and normal faults, respectively (e.g., Markwick et al., 2021; Ye et al., 2019) (Figure 1). After the continental break‐up, the tectono‐stratigraphic evolution of the rifted margin was predominantly driven by thermal subsidence, allowing for the preservation of thick Upper Cretaceous‐Cenozoic siliciclastic deposits including limited amounts of carbonates (e.g., Bennett & Rusk, 2002; Brownfield & Charpentier, 2006; Ye et al., 2019).…”

Section: Geological Outline and Earlier Workmentioning

confidence: 99%

Source‐To‐Sink Sedimentary Budget of the African Equatorial Atlantic Rifted Margin

Rouby,

Ye,

Chardon

et al. 2023

Geochem Geophys Geosyst

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Despite their very low relief and erosion rates, non‐orogenic (i.e., cratonic) continental domains account for over 60% of the Earth's exposed lands. Therefore, they contribute significantly to the clastic sediments and solutes exported to the ocean and should be accounted for in global studies. Nonetheless, they have been much less studied than orogenic domains. In this study, we establish the source‐to‐sink sedimentary budget of the sub‐saharan West African cratonic domain and its Equatorial Atlantic rifted margin using published low‐temperature thermochronological data to estimate onshore denudation and regional geological cross‐sections to estimate offshore accumulation. We show that during and immediately following rifting (130‐94 Ma), the build‐up and subsequent erosion of rift‐related relief resulted in a transient, 100–200 km wide strip along the margin recording high denudation rates (>50 m/Myr), while the inland domain underwent steady and very low denudation (<10 m/Myr). Afterward, the whole onshore domain underwent very low and steady denudation. Thus, the changes in post‐rift accumulation rates documented along the rifted margin were caused by changes in the climate and/or drainage network. During the Late Cretaceous, we document a regional rise in accumulation rates caused by the enlargement of drainage areas feeding the basins by a hinterlandward migration of the continental divide. During the Paleogene, we document a general drop in accumulation rates in all the basins of the African Atlantic margins caused by the global greenhouse climate, which enhanced the development of lateritic weathering mantles, storing clastic sediments on the continent and favoring solute exports to the ocean.

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Section: Geological Outline and Earlier Workmentioning

confidence: 99%

Source‐To‐Sink Sedimentary Budget of the African Equatorial Atlantic Rifted Margin

Rouby,

Ye,

Chardon

et al. 2023

Geochem Geophys Geosyst

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Coeval development of extensional and contractional features along transform margins: insights from the Diaz Marginal Ridge

Paton¹,

Mortimer

Markwick

et al. 2022

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The Diaz Marginal Ridge (DMR), on the southern transform margin of South Africa, is a bathymetric feature parallel to the Agulhas Falkland Fracture Zone (AFFZ) that has long been considered an archetype marginal ridge; and yet its origin and evolution remains unconstrained. Using recently acquired seismic data we present a new structural interpretation of the DMR and its association with the evolution of both the AFFZ and the Southern Outeniqua Basin. In contrast to previous scenarios invoking thermo-mechanical explanations for its evolution, we observe a more straightforward structural model in which the genesis of the DMR results from the structural inversion of a Jurassic rift basin. This inversion resulted in the progressive onlap of latest Valanginian-Hauterivian aged stratigraphic units, important for the formation of stratigraphic plays of the recent Brulpadda discovery.Paradoxically, this contraction is contemporaneous with renewed extension observed in the inboard normal faults. The orientation of the DMR and inboard structures have been demonstrated to be controlled by the underlying Cape Fold Belt (CFB) fabric. The onset of motion across the AFFZ shear system led to east-west orientated maximum stress and north-south orientated minimum stress. We propose this stress re-orientation resulted in strain partitioning across existing structures whereby in addition to strike-slip on the AFFZ there was coeval extension and contraction, the nature of which was determined by fault orientation. The fault orientation in turn was controlled by a change in orientation of the underlying CFB. Our model provides new insights into the interplay of changes in regional stress orientation with basement fabric and localised magmatism along an evolving transform. The application of horizontal strain partitioning can provide an explanation of similar features observed on other transform margins.

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Mapping deformation: the map representation of geological structure

Markwick,

Paton,

Cavalcanti de Araújo

2024

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Faults and folds are the clearest expressions of deformation we can observe directly in the rock record. This is visualised on 2D maps through the geometry of outcrop patterns and lines or polygons with marker symbols indicating different kinematics. But the record of deformation is 4D, and faults and folds represent only the products of deformation, not the processes responsible. Understanding the evolution of the 3D structural framework through time is fundamental for all forms of subsurface exploration across the energy transition. The aim of this paper is to show how 2D geospatial databases can represent the 4D deformational record. This is by capturing the three components of deformation: the initial state of the crustal architecture to be deformed (the pre-deformational crustal facies and structural framework), the processes responsible for the deformation (geodynamics), and the products of the deformation (folds, faults, magmatism, and crustal facies). Deformation is not limited to a single tectonic cycle. Within each cycle, it is time-transgressive and highly variable spatially. By evolving these 2D geospatial databases through time using restoration and plate modelling, we can better understand the 4D complexity of deformation and how this impacts exploration.

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Mapping the complexity of transform margins

Cited by 3 publications

References 133 publications

Source‐To‐Sink Sedimentary Budget of the African Equatorial Atlantic Rifted Margin

Source‐To‐Sink Sedimentary Budget of the African Equatorial Atlantic Rifted Margin

Coeval development of extensional and contractional features along transform margins: insights from the Diaz Marginal Ridge

Mapping deformation: the map representation of geological structure

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