Turbidity current transport of organic-rich sediments: Alpine and Mediterranean examples
Analyses of facies at the outcrop and petrological examination of cores provide a supplement to the geochemical study of deep-sea organic-rich layers, particularly those on margins and in basins likely to be affected by turbidity currents. Base-of-slope, including submarine fan, deposits of the Anno...
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Veröffentlicht in: | Marine geology 1986-02, Vol.70 (1), p.85-101 |
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Zusammenfassung: | Analyses of facies at the outcrop and petrological examination of cores provide a supplement to the geochemical study of deep-sea organic-rich layers, particularly those on margins and in basins likely to be affected by turbidity currents. Base-of-slope, including submarine fan, deposits of the Annot Sandstone Formation in the Maritime Alps display excellent examples of terrestrial plant-rich layers which accumulated in oxic basins. Preservation of this organic debris was enhanced by a frequent succession of downslope transport events, rapid basinward transport, and flows carrying sufficiently large volumes of sediment to insure rapid burial. Preferential concentration in overbank channel levee and interchannel sequences and also in more distal fan deposits is largely a result of hydraulic equivalent effects, i.e. delayed settling of low-density platy particles from flows of reduced concentration and velocity in a direction away from channels.
Turbidity current and related sediment gravity flows can also considerably modify the development of dark organic layers (commonly termed “black shales”) in anoxic basins as demonstrated by the diversity of sapropel types which accumulated in the eastern Mediterranean during the Quaternary. The incursion of turbidites during periods of organic-rich layer formation expands organic layer thickness, dilutes the organic matter content and also produces local modification (repetition or even removal) of these distinct stratigraphic horizons. Focus on the role of redeposition can help facilitate, and give greater accuracy to, the interpretation of organic layers deposited in settings such as the once much narrower and tectonically more active Cretaceous Atlantic basins. |
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ISSN: | 0025-3227 1872-6151 |
DOI: | 10.1016/0025-3227(86)90090-3 |