Importance of submarine landslides for non-steady state conditions in pore water systems — lower Zaire (Congo) deep-sea fan
✍ Scribed by Matthias Zabel; Horst D Schulz
- Book ID
- 104156982
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 635 KB
- Volume
- 176
- Category
- Article
- ISSN
- 0025-3227
No coin nor oath required. For personal study only.
✦ Synopsis
Most concentration pro®les of sulfate in continental margin sediments show constant or continuously increasing gradients from the benthic boundary layer down to the deep sulfate reduction zone. However, a very marked change in this gradient has been observed several meters below the surface at many locations, which has been attributed to anoxic sul®de oxidation or to non-local transport mechanisms of pore waters. The subject of this study is to investigate whether this feature could be better explained by non-steady state conditions in the pore-water system. To this end, data are presented from two gravity cores recovered from the Zaire deep-sea fan. The sediments at this location can be subdivided into two sections. The upper layer, about 10 m thick, consists of strati®ed pelagic deposits representing a period of continuous sedimentation over the last 190 kyr. It is underlain by a turbidite sequence measuring several meters in thickness, which contains large crystals of authigenic calcium carbonate (ikaite: CaCO 3 ´6H 2 O). Ikaite d 13 C values are indicative of a methane carbon contribution to the CO 2 pool. Radiocarbon ages of these minerals, as well as of the adjacent bulk sediments, provide strong evidence that the pelagic sediments have overthrust the lower section as a coherent block. Therefore, the emplacement of a relatively undisturbed sediment package is postulated. Pore-water pro®les show the depth of the sulfate±methane transition zone within the turbiditic sediments. By the adaptation of a simple transport-reaction model, it is shown that the change in the geochemical environmental conditions, resulting from this slide emplacement, and the development towards a new steady state are fully suf®cient to explain all features related to the pore-water pro®les, particularly, SO 22 4 and dissolved inorganic carbon (DIC). The model shows that the downslope transport took place about 300 yr ago.