From confined to unconfined: the processes and stratigraphic record of submarine channel-mouth lobes

Turbidity currents exiting the mouths of submarine channels can experience an abrupt change from confined to unconfined conditions, which has a profound impact on the capacity of flows to transport sediment farther into the basin. The spatial transition from channels (and levees) to lobes, is commonly referred to as the channel-lobe transition zone (CTLZ). In modern settings, the CLTZ varies in character and 'detachment length', and can be characterized by scours and erosional lineations separated by patchily distributed sands (e.g. Wynn et al., 2002). How the CTLZ is recorded stratigraphically is a background question to this studentship.

This studentship forms part of Phase 2 of the Lobe project, which is jointly funded by 12 companies, and builds on the results of Phase 1 that focussed on exceptionally large, continuous exposures in the Karoo Basin, South Africa (Prélat et al., 2009, 2010; Groenenberg et al. 2010). Phase 1 of the LOBE project intentionally focused on areas of Fan 3 stratigraphy where the amount of erosion was minimal, to allow the documentation of the shapes and dimensions of complete elements. This was successful, however the approach resulted in a natural bias towards the more distal and axial parts of this system. In Phase 2, we will correlate the internal stratigraphy of lobe complexes up-dip toward the channelized parts of the lobe complex in order to document the transition from lobes to channels around lobe apices, and closer to interpreted points of feeder channel avulsion.

The project will involve the drilling of and collection of data from behind-outcrop research boreholes to complement outcrop datasets. We hypothesise that the change in confinement is more abrupt in proximal locations, whereas 'terminal lobes' are connected to small low-relief distributary channels where downstream changes in flow character are more gradual. This abrupt physiological change can lead to the deposition of submarine lobes at channel mouths that may involve significantly different processes, and therefore depositional character.

In addition, Units A and B, exposed in the Laingsburg area, provide an opportunity to document 2D ‘postcard’ examples of lobes and their stratigraphic relationship to up-dip and adjacent feeder channel-fills, and the influence this spatial relationship has on sedimentary facies distributions, the stacking patterns in lobes, and the stratigraphic record of proximal avulsion processes. Sedimentary sections will be logged at the cm-scale in select locations with an emphasis on interpretation of facies and facies associations in order to establish sedimentological criteria for discriminating between proximal vs. distal lobe settings in both outcrop and well data.

As this is an interdisciplinary studentship, the student will benefit from a variety of research training in particular field-based deep-water sedimentology/stratigraphy, and will be required to spend field seasons in remote locations. The student will fully participate in the School and University postgraduate training programme and will present work at national and international conferences, as well as interacting with geoscientists at several a major hydrocarbon companies. In addition, the supervisors expect that the thesis will be written as a collection of journal papers.