Wagner, Thomas and Pletsch, Thomas (1999): Tectono-sedimentary controls on Cretaceous black shale deposition along the opening Equatorial Atlantic gateway (ODP Leg 159)

Leg/Site/Hole:
ODP 159
ODP 159 959
Identifier:
2000-002394
georefid

Creator:
Wagner, Thomas
Universitaet Bremen, Geowissenschaften, Bremen, Federal Republic of Germany
author

Pletsch, Thomas
Lacustrine Basin Research, United Kingdom
author

Identification:
Tectono-sedimentary controls on Cretaceous black shale deposition along the opening Equatorial Atlantic gateway (ODP Leg 159)
1999
In: Cameron, Nick R. (editor), Bate, Raymond H. (editor), Clure, Val S. (editor), The oil and gas habitats of the South Atlantic
Geological Society of London, London, United Kingdom
153
241-265
The Cretaceous Equatorial Atlantic Gateway between the Central and South Atlantic basins is of interest not only for palaeoceanographic and palaeoclimatic studies, but also because it provided particularly favourable conditions for the accumulation and preservation of organic-rich sediments. Deposition of carbonaceous sediments along the Cote d'Ivoire-Ghana Transform Margin (Ocean Drilling Program Leg 159) was intimately linked to the plate tectonic and palaeoceanographic evolution of this gateway. Notably, the formation of a marginal basement ridge on the southeastern border of the transform margin provided an efficient shelter of the landward Deep Ivorian Basin against erosive and potentially oxidizing currents. Different subsidence histories across the transform margin were responsible for the development of distinct depositional settings on the crest and on both sides of the basement ridge. Whereas the southern, oceanward flank of the basement ridge was characterized by rapid, continuous deepening since the latest Albian-early Cenomanian, marine sedimentation on the northern, landward flank was interrupted by a period of uplift and erosion in the late Albian, and rapid subsidence started after the early Coniacian. Organic-rich sediments occur throughout almost the entire Cretaceous section, but hydrogen-rich marine black shales were exclusively recovered from core sections above an uplift-related unconformity. These black shales formed when separation of Africa and South America was sufficient to allow permanent oceanic midwater exchange after the late Albian. Four periods of black shale accumulation are recorded, some of them are correlated with the global oceanic anoxic events: in the latest Albian-earliest Cenomanian, at the Cenomanian-Turonian boundary, during the middle Coniacian-early Campanian, and in the mid-Maastrichtian. These periods were characterized by increased carbon fluxes to the seafloor, induced by enhanced palaeoproductivity and intensified supply of terrestrial organic matter. Black shale deposition appears to be intimately linked to periods of rising or maximum eustatic sea level and to the expansion of the oxygen minimum zone, as indicated by foraminiferal biofacies. Intervals between black shale units, in contrast, indicate a shrinking oxygen minimum zone and enhanced detrital flux rates, probably related to lowering sea level. Upper Cretaceous detrital limestones with high porosities may provide excellent hydrocarbon reservoirs, although their areal extent appears to be limited. Palaeogene porcellanites, capped by Neogene pelagic marls and clays, extend over a wider area and may provide another target for hydrocarbon exploration.
English
Serial
Coverage:Geographic coordinates:
North:3.3740
West:-3.1056East: -2.4359
South:3.1503

Economic geology, geology of energy sources; Stratigraphy; Africa; Atlantic Ocean; biofacies; biostratigraphy; black shale; carbon; carbonate rocks; Cenozoic; clastic rocks; clay mineralogy; Cretaceous; deposition; Equatorial Atlantic; geophysical methods; geophysical profiles; geophysical surveys; Ghana; hydrocarbon indicators; hydrogen; IGCP; Ivory Coast; Leg 159; limestone; lithofacies; marl; Mesozoic; microfossils; Ocean Drilling Program; ODP Site 959; organic carbon; paleo-oceanography; paleoenvironment; Paleogene; palynomorphs; petroleum; petroleum exploration; porosity; productivity; reconstruction; reservoir rocks; sedimentary rocks; sedimentation; seismic methods; seismic profiles; SEM data; source rocks; structural controls; surveys; Tertiary; thermal maturity; traps; West Africa;

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