Geodynamic, sedimentary and volcanic evolution of the Cape Bojador continental margin; Northwest Africa

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doi: 10.1029/ME003p0187
Author(s): von Rad, U.; Arthur, M. A.
Author Affiliation(s): Primary:
Scripps Inst. Oceanogr., Deep Sea Drill. Proj., La Jolla, Calif., United States
Volume Title: Deep drilling results in the Atlantic Ocean; continental margins and paleoenvironment
Volume Author(s): Talwani, M., editor; Hay, W.; Ryan, W. B. F.
Source: Maurice Ewing Series, 3, p.187-203; Deep drilling results in the Atlantic Ocean; continental margins and paleoenvironment, Harriman, N.Y., March 19-25, 1978, edited by M. Talwani, W. Hay and W. B. F. Ryan. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0197-6346. ISBN: 978-1-118-66583-1 CODEN: MEWSDN
Note: In English. 60 refs.; illus. incl. sects., block diag., geol. sketch maps
Summary: The geodynamic and sedimentary evolution of the Northwest African continental margin at Cape Bojador is well documented by a transect of DSDP sites, commercial wells, and seismic surveys (Fig.1-3). This evolution is mainly influenced by vertical tectonics (subsidence), sediment supply from the continent, volcanism of the Canary Islands, and global fluctuations of sea level, climate, and surface or deep-water circulation. Jurassic shallow-water carbonates deposited on a steadily subsiding shelf are overlain by a very-thick Cretaceous Wealden-type deltaic sequence with an upward and seaward facies transition from continental elastics to lagoonal/intertidal deposits, delta front sediments, and laminated prodelta muds (Fig.5). Distal turbidites reached the Moroccan Basin and the deep-sea fan recorded in the flysch-type sediments of Fuerteventura. Many similar "Wealden-type" deltas were built out along the narrow Neocomian North Atlantic (Fig.4). A conspicuous unconformity with a 100 m.y. hiatus cuts 1-3 km deep into the upper continental rise. This is the result of a major erosional event which removed about 7,500-15,000 km3 of lower slope and upper rise sediments (erosion rate >100 m/m.y.) and may have destroyed evidence of several previous hiatuses. The mid-Cenozoic slope rejuvenation was probably caused by the coincidence of a major regression with intensified bottom water circulation during late Oligocene to earliest Miocene times. The oversteepened escarpment was rapidly covered by early to middle Miocene gravitative sediments (debris flows, turbidites, slumps), derived primarily from the Cape Bojador margin and partly from more distant source areas (Fig.7). The slope was gradually stabilized and equilibrium conditions ensued (Fig.6). This thick flysch-type sediment sequence occurs in a "passive" margin setting with no obvious local tectonic deformation. Early to middle Miocene debris flow deposited volcaniclastic sandstones and hyaloclastites evidence the evolution of the Canary Island uplift and volcanism from a submarine to a subaerial shield stage. Air-fall ash layers record the post-middle Miocene volcanic history of the individual islands (Fig.8). In the uniformly subsiding, 12-15 km thick "Cape Bojador marginal basin" below the present shelf, slope and upper rise, the Jurassic subsidence rates were high (80-120 m/m.y.); they increased slightly during the Early Cretaceous (130-140 m/m.y.) and decreased more or less exponentially during the Late Cretaceous and Cenozoic to about 15 m/m.y. After mid-Cretaceous times, the accumulation rates lagged behind subsidence rates, causing a gradual deepening of the outer margin from a few hundred meters to its present depth. Abstract Copyright 1979 by the American Geophysical Union.
Year of Publication: 1979
Research Program: DSDP Deep Sea Drilling Project
Key Words: 18 Geophysics, Solid-Earth; Africa; Atlantic Ocean; Cape Bojador; Cenozoic; Clastic rocks; Continental margin; Cretaceous; Deep Sea Drilling Project; Deformation; Deltas; Environment; Evolution; Faults; Jurassic; Lagoons; Mesozoic; Morocco; North Africa; Oceanography; Plate tectonics; Regression; Research; Sea-level changes; Sedimentary rocks; Sedimentation; Shore features; Stratigraphy; Structural geology; Structure; Tectonics; Tectonophysics; Turbidite
Coordinates: N200000 N310000 E0190000 E0080000
Record ID: 1980017759
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