Submarine Slope Systems
Imaging submarine channel bedforms and internal architecture on seismic: a quantitative analysis of the geophysical variables based on detailed outcrop/ experimental rock analysis: A case study of channels in the Numidian Flysch, Sicily.
PhD research by Myron Thomas, Supervised by Dr Jonathan redfern and Dr Duncan Irving
Introduction:
The projects main aim will be to relate the detailed sedimentology of selected submarine channels to the experimentally modeled seismic response. In order to do this, core samples will be taken from outcrops, and pressure confined 3D velocity analysis undertaken in the seismic laboratories in Manchester University, This will allow generation of accurate synthetics of the seismic response, and sensitivity analyses of the seismic response for known sedimentological bodies at depth to be computed. In conjunction with LiDAR models of various submarine system elements, a powerful 3D synthetic seismic model can be constructed that provides insight into how industry standard seismic is viewed.
Overview:
Current understanding of seismic response of submarine channels is often limited to geometrical and descriptive terms (ie Peakall et al., 2000), so this project will allow for a greater, quantative understanding of how channel morphology and architecture is imaged on 3D seismic data sets, and may aid in understanding what seismic attributes are highlighting in terms of lithology, sedimentary architecture and geometry. While a case study of the Numidian flysch of Sicily will be used, it is hoped that this technique can be applied to a range of systems.
The work will be carried out on the Numidian Flysch (Figures 1) of Sicily and Tunisia (See Johansen et al., 1998) (representing a high energy proximal system), and this will be compared with and linked directly with Numidian Flysch deposits from offshore Tunisia using industry 2D and possibly 3D seismic surveys from that region.
The Numidian Flysch is a potential hydrocarbon reservoir offshore Tunisia, which displays seismic anomalies (Direct Hydrocarbon indicators) offshore Tunisia. The Flysch is found offshore Northern Tunisia, below a gently sloping continental shelf and water depths of 200-400m. The Numidian Flysch is defined as one of 3 principle Hydrocarbon producing systems; the Albuan/Cenomanian/Maastrichtian fractured Carbonates; the Ypresian Marine Limestones; and the Oligocene-Miocene Numidian Flysch. The Flysch is a proven play in Sicily, and exploration is commencing offshore Tunisia.
Rationale:
The industry interest in submarine channels as hydrocarbon reservoirs has generated a considerable volume of research (Nile Delta, Niger Delta, Mississippi Fan etc) including attempts to group submarine channels in categorised systems (ie
Baas et al., 2005). Submarine channels are important sediment delivery pathways, which can effectively bypass the continental shelf, depositing continental/marine sediments on the continental slope and abyssal floor. Recent academic work has looked at, among other things, the similarity (or lack of) of submarine channels to subaqeous river channels (Peakall 2000), and the geohazard effect of fast moving and erosive turbidity currents utilising the submarine channel system on deep sea communication cables etc. High resolution 3D seismic surveys have allowed a greater understanding of morphologies of submarine channels and the deposits that fill them (Cronin et al., 2005, Armentrout et al., 2000 etc). 3D seismic has allowed submarine channels to be examined in context to their tectonic and morphological environments, including placing them within a sequence stratigraphic framework. Ultra high resolution surveys processed with steep dip migrated algorithms are now allowing small scale lateral variations in turbidite facies to be mapped (ie Hackbarth et al. 1994), often with the use of cores and wireline well log data.
Weimer 2000 suggests that the future of 3D seismic will be linking core and logs to seismic, which will improve out understanding of facies, architecture and depositional processes in slope systems. The aims of this project will enable a level of detail to be added to seismic examples of submarine channel systems in terms of lithology, petrology and morphology by quantative examination of seismic attributes, and a high resolution sedimentological framework.
The Numidian Flysch deposits:
The Numidian Flysch represent a late Oligocene to early Miocene foreland basin deposit. They represent a tectonically evolving submarine slope system with associates hemipelagics, channel systems (see figure 3), turbidites, and mass transport deposits (slumps, slides etc) (see figure 2).
As hard collision occurred between the African and European plates (starting around the upper Eocene) a complex subduction zone was developed. The collision generated thrust and fold belts which represent the accretionary prism, can be traced from the Betic and Riff sectors of south Spain and Morocco, through the Tellian Atlas sector of Algeria and Tunisia, across the Sicily strait, and forming the southern and northern Apennines of Italy. In north Italy the belt turns east in to the Alpine chain, and from there in to the Carpathian mountains and the Balkans (Guerrera et al 2005, Wezel 1970). Oucrops of Numidian Flysch follow the orogenic belt, and are seen within southward verging nappes (figure 1).
figure 3: Channel outcrops within the Numidian in northern Sicily. The palaeo-environment is difficult to recreate due to dissection from the south eastwards migrating Mahgrebide-Sicillide fold and thrust belt. Classic examples of foreland basins however envisage a long trough basin parallel to the approaching/encroaching accretionary Prism, with multiple input sources producing fan systems. The floor of the basin, whose geometry is controlled by the tectonics and geodynamics of the subduction zone (rather than eustacy and climate), may contain a main axial sediment transport flux, reworking distal basin fan deposits. Most work on the Numidian flysch describes how deposition occurred in a west-north west to east-south east trending thin foreland basin, which splits in the south east in to the northeast trending Lucanian ocean, and the south east trending Ionian ocean.
The Numidian Flysch deposits were caught in the migrating thrust belt from the Miocene onwards, and tectonically transported south east. In Sicily, the Mahgrebian/Sicillide belt was superceded by a Pleiocene-Pleistocene foreland, which in turn was superceded by the present day foreland basin, both of which can be seen in the south east of Sicily. The Ragusa Plateau,
made from platform carbonates represents the most northerly piece of African plate, and this is directly abutted to its north by the present foreland basin which cuts across the southern part of Sicily. The presently active portion of accretionary prism lies across the northern half of Sicily, accounting for the active seismicity observed.
Key references:
Cronin, BT. Akhmetzhanov, AM. Mazzini, A. Akhmanov, G. Ivanov, M. Kenyon, NH. TTR-10 Shipboard scientists. 2005: Morphology, evolution and fill: Implications for sand and mud distribution in filling deep-water canyons and slope channel complexes. Sedimentary Geology 179 (2005) pp 71-97.
Guerrera, F. Martin-Martin, M. Perrone, V. Tramontana, M 2005: Tectono-sedimentary evolution of the southern branch of the Western Tethys (Maghrebian Flysch Basin and Lucanian Ocean): consequences for Western Mediterranean geodynamics. Terra Nova, 17. pp 358-367.
Hackbarth, CJ. Shew, RD. 1994: Morphology and Stratigraphy of a mid-Pleistocene Turbidite Leveed Channel from Seismic, Core and Log data, Northeastern Gulf of Mexico. GCSSEPM Foundation 15th annual Research conference; Submarine fans and Turbidite systems, December 4-7th 1994.
Johansson , M. Braakenburg, N E. Stow, D A V. Faugeres, JC. 1998: Deep-water massive sands: facies, processes and channel geometry in the Numidian Flysch, Sicily. Sedimentary Geology volume 115 (1998) pp 233-265.
Khazanehdari, J. Rutter, EH. Brodie, KH. 2000: High-pressure-high-temperature seismic velocity structure of the midcrustal and lower crustal rocks of the Ivrea-verbano zone and Serie dei Laghi, NW Italy. Journal of Geophysical Research, Volume 105, Issue B6, pp 13843-13858.
Peakall, J. McCaffrey, W. Kneller, B. 2000: A Process Model for the Evolution, Morphology, and Architecture of Sinuous Submarine Channels. Journal of Sedimentary Research, May 2000, vol 70. no 3. pp 434-448.
Weimer, P. 2000: Interpreting turbidite systems with 2-D and 3-D seismic data: an overview in A H. Bouma and C. E. Stone, eds. Fine-grained submarine fans: AAPG Memoir 72, pp 89-91.
Werff, W van der. Johanson, S. 2003: High resolution stratigraphic analysis of a Turbidite system, Tanqua Karoo Basin, South Africa. Marine and Petroleum Geology, vol 20 (2003) pp 45-69.
Wezel, F.C. 1970: Numidian FLysch: an Oligocene-early Miocene Continental Rise Deposit off the African Platform. Nature Vol. 228, October 17th 1970. pp 275-276