Browsing by Author "Jackson, M. P. A."
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- Can the South Atlantic Opening Model be Applied to the India Margins?Publication . Cramez, Carlos; Talwani, Manik; Jackson, M. P. A.The presence of SDRs (seawrd dipping reflectors) on the regional lines around the Indian continent strongly suggest the breakup of the lithosphere and the onset of the sea-floor spreading were similar to those proposed and described for the South Atlantic, which, in fact, is quite similar to the opening of the North Atlantic.
- Contractional Cornucopia on Offshore AngolaPublication . Cramez, Carlos; Jackson, M. P. A.; Sikkema, W.; Fraenkl, R.Three main contractional tectonic regimes are recognized: (1) Late Cretaceous gravity spreading, (2) Mid-Tertiary uplift, and (3) Neogene transpression. Tilting of the young continental margin created the first tectonic regime, the ultimate cause of this was thermal subsidence after continental breakup. The second regime was the direct cause of the uplift of the Angolan coast, mostly in the Oligo-Miocene but continuing into the Plio- Pleistocene, while the late tectonic regime was probably the differential movement of reactivated crustal blocks, whose slip directions depended on their orientation.
- Raft tectonics in the Kwanza Basin, AngolaPublication . Duval, Bernard; Cramez, Carlos; Jackson, M. P. A.Raft tectonics (tectonique en radeaux) allows the extreme thin-skinned extension of overburden over a dêcollement of thin salt or other evaporites.
- Role of salt tectonics in the petroleum systems of Angola and Gulf of MexicoPublication . Fonck, Jean-Michel; Cramez, Carlos; Jackson, M. P. A.
- Role of subaerial volcanic rocks and mantle plumes in creation of South Atlantic margins: implications for salt tectonics and source rocksPublication . Jackson, M. P. A.; Cramez, Carlos; Fonck, Jean-MichelSeaward-dipping re¯ectors (SDRs) represent ¯ood basalts rapidly extruded during either rifting or initially subaerial sea-¯oor spreading. Evaporites can form on this basaltic proto-oceanic crust, as in the Afar Triangle today. Evidence for SDRs in South Atlantic deep-water regions comes from proximity to the uniquely large Paranaà ±Etendeka volcanic province onshore, the Tristan and Gough hot spots, drilled volcanic rocks, and seismic pro®les showing SDR provinces more than 100 km wide, as much as 7 km thick, and thousands of kilometers long. SDRs are clearest adjoining the Aptian salt basins. However, we speculate that SDRs are also present but seismically obscured below the salt basins. We argue that the conjugate Aptian salt basins are post-breakup, not pre-breakup; they were separated from the start by a mid-oceanic ridge; distal salt accumulated on proto-oceanic crust, not rift basins. This hypothesis is supported by: seismic stratigraphy and structure; magnetic anomalies; plate reconstructions; and hydrothermal potash evaporites. An important implication for exploration is that thick basalts, rather than rift-age source rocks, may underlie distal parts of the salt basins.
- Role of subaerial volcanic rocks and mantle plumes in creation of South Atlantic margins: implications for salt tectonics and source rocksPublication . Jackson, M. P. A.; Cramez, Carlos; Fonck, Jean-Michel
- Superposed deformation straddling the continental-oceanic transition in deep-water AngolaPublication . Cramez, Carlos; Jackson, M. P. A.The Angolan margin is the type area for raft tectonics. New seismic data reveal the contractional buffer for this thin-skinned extension. A 200-km-long composite section from the Lower Congo Basin and Kwanza Basin illustrates a complex history of superposed deformation caused by: (1) progradation of the margin; and (2) episodic Tertiary epeirogenic uplift. Late Cretaceous tectonics was driven by a gentle slope created by thermal subsidence; extensional rafting took place updip, contractional thrusting and buckling downdip; some distal folds were possibly unroofed to form massive salt walls. Oligocene deformation was triggered by gentle kinking of the Atlantic Hinge Zone as the shelf and coastal plain rose by 2 or 3 km; relative uplift stripped Paleogene cover off the shelf, provided space for Miocene progradation, and steepened the continental slope, triggering more extension and buckling. In the Neogene, a subsalt half graben was inverted or reactivated, creating keystone faults that may have controlled the Congo Canyon; a thrust duplex of seaward-displaced salt jacked up the former abyssal plain, creating a plateau of salt 3–4 km thick on the present lower slope. The Angola Escarpment may be the toe of the Angola thrust nappe, in which a largely Cretaceous roof of gently buckled strata, was transported seawards above the thickened salt by up to ,20 km. q 2001 Elsevier Science Ltd. All rights reserved.