Distal flow transformations and architecture of turbidite lobe systems


PhD Candidate: Marco Fonnesu

Supervisor: P.D.W. Haughton, W.D. McCaffrey

Funded by: Turbidites Research Group (http://trg.leeds.ac.uk/)



This Ph.D project is concentrated on the investigation of some of the outstanding issues associated with hybrid event bed (HEBs) deposition (see Haughton et al., 2003; 2009, Talling, 2013) in distributive deep-water lobe and basin plain settings. Hybrid event beds are a type of deep-water sediment gravity flow deposit that generally comprise a basal clean sandstone overlain by a variety of muddier and less-permeable sandy facies (H3 division of Haughton et al., 2009) thought to be emplaced as part of the same transport event. Their recognition, interpretation and prediction are crucial for oil company exploration and reservoir quality assessment, as the reservoir proprieties of these event beds are compromised by high-matrix clay concentration. For this reason is important to develop facies models to better predict the occurrence and character of this bed type.

The project aims to investigate the HEBs character at different scales:

1 - To document the internal structure and vertical organization within hybrid event beds in very well exposed outcrops, distinguishing various bed types and textures of the “debritic” internal division and the relationships with the cleaner sandstone base.

2 – To describe and account for short-distance (10s to 100s meters) lateral variability in hybrid event bed make-up and investigate the implications for correlation and production efficiency in subsurface reservoirs.

3 – Have a better understanding of the mechanisms of turbulence damping in depositing flows, focusing in particular on the role of mudclast entrainment and disaggregation with the study of the basal scour features where the muddy material is possibly bulked into the flow.

4 – To investigate the occurrence and characteristics of hybrid event beds in different fan “sub- environments” such as channel-lobe transition zones and proximal inner-fan lobes in addition to the better-known outer-fan and fan fringe settings.

5 - Study the wider stratigraphic occurrence and typical stacking patterns of lobes and fans dominated by hybrid flows and compare these with existing models for “classic” turbidite lobes and fan systems, in order to constrain predictive triggers for their deposition in the basin.

In order to investigate in detail some of these problematics the work has been approached in several field areas as the Pennsylvanian Ross Formation in Western Ireland and Miocene Cilento Flysch in Southern Apennines, but the bulk of the project has been carried out in the Cretaceous-Paleocene Gottero Sandstone in Northern Apennines. The extensive fieldwork, with more than 5000 m of detailed sedimentary logs measured along the entire basin, but in particularly around the outstanding exposure of M.Ramaceto, reconstructs the general system stratigraphy and is focused on the characterisation, geometrical reconstruction, facies tract definition and process interpretation of different types of hybrid event beds in the proximal and distal part of the system.



Fonnesu, M., Haughton, P.D.W., Felletti, F., and McCaffrey, W.D, 2015. Short-length scale variability of hybrid event beds and its applied significance. Marine and Petroleum Geology 67, 583-603. Awarded of the HARLOLD READING MEDAL by BSRG for the best article published by a current or recent postgraduate student in 2015.

Fonnesu, M., Patacci, M., Haughton, P.D.W., Felletti, F., and McCaffrey, W.D., (in press.). Hybrid event beds generated by local substrate delamination on a confined basin floor. Journal of Sedimentary Research.



Haughton, P.D.W., Barker, S.P. and McCaffrey, W.D., 2003. “Linked” debrites in sand-rich turbidite systems – origin and significance. Sedimentology 50, 459-482

Haughton, P.D.W., Davis, C.E. and McCaffrey, W.D., 2009. Hybrid sediment gravity flow deposits – Classification, origin and significance. Marine and Petroleum Geology 26, 1900-1918

Talling, P.J. 2013. Hybrid submarine flows comprising turbidity current and cohesive debris flow: Deposits, theoretical and experimental analyses, and generalized models. Geosphere 9, 1-28