Modern sandy contourites: conceptual and economic implications. / De Castro Santos, Sandra.

2021. 231 p.

Research output: ThesisDoctoral Thesis

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  • de Castro (2021)_PhDthesis_Modern Sandy Contourites

    Final published version, 93.7 MB, PDF document

    Embargo ends: 12/07/24

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Abstract

Bottom currents are common sedimentary and oceanographic processes in deep-marine settings that affect continental margins worldwide. Contourites are defined as sediments deposited or substantially reworked by the persistent action of bottom currents. Despite numerous efforts to differentiate between contourites and other deep-water deposits in cores, reliable diagnostic criteria are still lacking. This Thesis presents a multidisciplinary study based on grain size and geochemistry of sedimentary facies —reinforced by micro- and ichnofacies— in the Gulf of Cadiz Contourite Depositional System, in the upper continental slope of the Mozambican margin and the eastern flank of the Corsica Trough. Discrimination criteria are put forth for hemipelagites, silty contourites, sandy contourites, bottom current reworked sands, fine-grained turbidites, hyperpycnites and debrites in sediment cores. The stacked vertical variability of these deposits evidences that the contourite drifts, contourite channels and contourite terraces were influenced by the interrelation of hemipelagic, gravitational and bottom current induced depositional processes. The interrelation of sedimentary processes is tied to intermittency in bottom current velocity, observed at different scales. In the Gulf of Cadiz, the intermittency is a consequence of precession-driven changes related to Mediterranean climate variability, punctuated by millennial-scale variability. In the Corsica contourite depositional system, bioclastic sands would have been transported to the slope during sea level lowstands, probably during isolated episodes of reworking and transport of sediments from the shelf. In contrast, the Mozambique contourite terrace occupies shallower locations and lies directly offshore the Zambezi delta, meaning it was continuously supplied from the adjacent continent and shelf and by along-slope currents, especially during sea level highstands. At bed scale, the variability in ichnodiversity, abundance and distribution of bioturbation is linked to intermittent interactions between bottom currents and sediment supply, hence different environmental conditions for tracemakers. Such intermittency reflects brief changes in hydrodynamic conditions during its deposition: shorter-term (centennial) yet higher accumulation rates, lower bioturbation rates, and flow variability. This new model could therefore provide support for basic sedimentological interpretation and petroleum exploration strategies.
Original languageEnglish
QualificationPh.D.
Awarding Institution
Supervisors/Advisors
Thesis sponsors
  • JIP - Contourites
Award date1 Aug 2021
Publication statusPublished - 2021

ID: 42683484