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Unravelling the architecture of turbidite sheets vs. lobes in confined settings: the Lauzanier system, Maritime Alps

Prof Bill McCaffrey (SEE), Dr Marco Patacci (SEE), Dr Luca Baruffini (ENI), Dr Marco Fonnesu (ENI)

Project partner(s): ENI (CASE)

Contact email: w.d.mccaffrey@leeds.ac.uk

Summary

Deep marine clastic systems are volumetrically the most important sedimentary environment on the surface of the earth. Built by particulate gravity currents (turbidity currents, debris flows, hybrid flows), they can develop a bewilderingly complex array of depositional landforms, such as canyons, channels, levees and semi- or unconfined depositional lobes, and the transitions between them. Depositing flows often traverse sedimentary basins where they may be fully or partly confined, depending on the magnitude of the flow and the size of the basin. In the present state of knowledge, the organisational style of such deposits is difficult to predict. If the flows are unconfined, then autogenic processes of lobe deposition and compensational stacking may prevail - yet the rules governing this style of deposition remain a matter of debate; if fully confined, the present paradigm is that tabular, non-compensating sheet-form deposits prevail, albeit possibly tapering distally - yet this understanding is currently being challenged.

This project will assess the relative roles of autogenic forcing vs. forcing due to lateral confinement in the development of sheet-form turbidite sandstones, principally through a field study in the Annot turbidite system (Maritime Alps). A secondary approach will be to exploit large dataset analysis to better understand lobe and sheet architecture development.  As well as developing fundamental new understanding, the work will also find practical application in the hydrocarbon industry by enabling prediction and characterisation of turbidite sheet and lobe architectures based on prior knowledge of their boundary conditions of formation and/or their outline geometrical configuration.

Aim and objectives

The immediate goal of this project is to assess the relative roles of internal (autogenic) forcing vs. that of external (allogenic) forcing - as expressed by the ratio size of flow to size of basin, in the development of sheet-form turbidite sandstone. This goal will be achieved through a field study in a spectacular and well exposed setting spanning the French-Italian border in the Maritime Alps in the Annot turbidite system: the Lauzanier Basin.  The basin fill is exposed across four high-Alpine valleys. A prior study in the three valleys on the French side of the Franco-Italian border (Mulder et al., 2010) has established a good stratigraphic framework, and an initial architectural interpretation; a fourth valley on the Italian side of the border was not considered by Mulder et al. The stratigraphy can be divided into two units: a lower interval comprises a mixture of coarse-grained tabular sands that can be traced without significant thickness change across the outcrop and tapering sands that are laterally impersistent. A coarser grained (conglomeratic) upper interval erodes via an intraformational angular unconformity into the underlying unit. In this project the sedimentary succession of the lower Unit will be studied across all four valleys with a combination of techniques including as logging and analysis of high-resolution photopanels and 3D models; reconnaissance work has shown that the fourth valley may hold the key to unravelling the story of system development. Particular attention will be paid to facies associations of those beds that taper vs. those that are tabular, including the facies characteristic of bed termination.  The analysis will focus on differentiation of the vertical organisational styles of intervals characterised by tapering beds vs. those characterised by tabular beds, to assess what mechanisms of compensational stacking may occur. Statistical evaluation of vertical and lateral facies trends will be used to test approaches to predict the geometry and architectures of lobe and sheet bodies at different hierarchical scales in subsurface settings. The role of tabular beds in re-setting instantaneous lateral bathymetric gradients will also be assessed.

A related field goal is to develop new models to understand the wider development of Lauzanier system: a lower package is succeeded a coarser-grained upper package in which correlation lengths are apparently rather low, yet it forms a compound interval that is rather wide – the transition and contrast between packages can be examined to investigate broader implications for system development.

 Fig. 1. Eo-Oligocene fill of the Lauzanier Basin, Alpine Tertiary foreland basin, Maritime Alps. A lower unit of tabular and tapering sheets (dipping into the lake) is succeed by higher net-to-gross upper unit (forming the top cliff) via an intraformational unconformity.

A final goal will be to exploit large dataset analysis to better understand lobe and sheet architecture development, based upon a combination of prior submarine studies, the new field data and new analysis of seismic data. This work package will exploit the Deep-Marine Architecture Knowledge Store (DMAKS), a relational database designed and populated by members of TRG at Leeds. Data uploaded to DMAKS will be derived from the field study, from the peer-reviewed literature and possibly from a seismic study.

Both fundamental and applied research themes fall within the project remit, and the project scope can evolve depending on the interests and aptitudes of the student.

Eligibility

Applicants should have a BSc degree (or equivalent) in geology, earth sciences, geophysics or a similar discipline. An MSc or MGeol in applied geoscience or petroleum geoscience (or similar) would be an advantage. Skills in field-based geological data collection and field sedimentology and stratigraphy are desirable. Experience of using GIS software would be useful, though is not essential.

Training

The successful applicant will work within the inter-disciplinary Turbidites Research Group, which is part of the wider Sedimentology Group at the School of Earth and Environment, University of Leeds. The TRG has a number of on-going research projects related to deep-marine clastic sedimentology via field studies, physical and numerical modelling and seismic studies. The project will provide specialist scientific training, as appropriate, in: (i) field-based techniques for the sedimentological and architectural analysis of clastic successions; (ii) relational-database theory and practice; (iii) statistical analysis; (iv) geological interpretation of seismic datasets. The mixed pure- and applied-science nature of this research project will enable the student to consider a future career in either academia or industry. In addition, the student will have access to a broad spectrum of training workshops provided by the Faculty that include an extensive range of training workshops in statistics, through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk). The successful candidate will be strongly encouraged and supported to publish the outcomes of their research in leading international journals.

The project will be run as a CASE award, supported by ENI spa; as well as a £1k pa research funding enhancement, there will also be an opportunities for the appointed applicant to undertaken an internship with ENI in Milan. Such placements will involve working embedded in a team of applied geology professionals.

References

Mulder, T., Callec, Y., Parize, O., Joseph, P., Schneider, J. L., Robin, C., Dujoncquoy, E., Salles, T., Allard, J., Bonnel, C., Ducassou, E., Etienne, S., Ferger, B., Gaudin, M., Hanquiez, V., Linares, F., Marches, E., Toucanne, S. and Zaragosi, S. (2010). High-resolution analysis of submarine lobes deposits: Seismic-scale outcrops of the Lauzanier area (SE Alps, France). Sedimentary Geology 229(3), 160-191.

Further Information

For more information about this project and other TRG activities contact:

Bill McCaffrey, w.d.mccaffrey@leeds.ac.uk, http://trg.leeds.ac.uk/

Related undergraduate subjects:

  • Earth science