TURBIDITES: MODE OF FORMATION AND ITS ECONOMIC IMPORTANCE

OLOMO, JAMES OPEMIPO

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PRESENTATION OUTLINE Introduction Aims and Objectives What are turbidites? What is turbidity current? Formation of turbidity current Formation of turbidites from turbidity current Bouma sequence in a turbidite succession Idealized Bouma sequence Economic importance of turbidites Turbidites in hydrocarbon exploration Conclusion

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INTRODUCTIONTurbidites are deposits resulting from turbidity currents and are

deposited when the current loses its energy

The deposit has been described by the Bouma sequence which delineates five major lithologies A-E

It has been established that these deposits help to host important economic resources such as hydrocarbon. Hence, the need to understand their formation for exploration success

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AIMS AND OBJECTIVES

The aim is to understand how turbidites develop and why these deposits are important

The Objectives include studying: Impact of turbidity current in the formation of turbidites

Characterization of turbidites using the idealized Bouma sequence

Economic importance of turbidites

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WHAT ARE TURBIDITES ? Turbidites are deposits resulting

from turbidity currents and are deposited when the current loses its energy

Turbidites was first described by Arnold H. Bouma (1962) studying Deepwater sedimentation

Turbidites are special deposits which help to host important economic resources such as hydrocarbon and most recent success in Deep water exploration has been linked with them

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WHAT ARE TURBIDITY CURRENT ? Turbidity current are fast

flowing current driven downslope by its high density from suspended load

Motion imparts turbulence which then maintains the turbidity

They are characteristic of

areas where there is seismic instability and an underwater slope

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FORMATION OF TURBIDITY CURRENT

Triggers of turbidity current can be Earthquakes Slope failure Landslides Major storm

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FORMATION OF TURBIDITES BY TURBIDITY CURRENT

Sediment load transported by turbidity current are gradually dropped as current slackers and water comes to rest

Distance covered is determined by the turbulence and velocity of the current

Resulting sediment deposits are referred to as TURBIDITES

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BOUMA SEQUENCE IN A TURBIDITE SUCCESSION The Bouma sequence specifically describes the ideal vertical succession of structures

deposited by low-density turbidity currents. An alternate classification scheme called, Lowe sequence exists

Bouma sequence is deposited during waning flow as turbidity currents move

downslope; flows lose energy as they react to changes in the slope of the surface

The sequence is divided into 5 distinct layers; A through E. Each layer described has a specific set of sedimentary structures and a specific lithology with a fining-upward sequence.

22 April 2016This is an idealized case; most turbidities don’t contain all the lithology

IDEALIZED BOUMA SEQUENCE

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Turbidites provide a mechanism for assigning tectonic and depositional setting to ancient sedimentary sequences

Turbidites from lakes also provide chronologic evidence of the frequency of landslides/ earthquakes that form them

They are hosts of lode gold deposits e.g in Victoria, Australia (where over 2600 tons of gold have been extracted from shale sequences in the turbidite succession)

Lithified accumulations of turbidites may become hydrocarbon reservoirs; hence the effort in exploring turbidites sequences

ECONOMIC IMPORTANCE OF TURBIDITES

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TURBIDITES IN HYDROCARBON EXPLORATION About 80% of the major discoveries in

recent exploration has been in DW (Bob Fryklund, 2015)

90% of DW reserves have been found in turbidites (Henry Pettingill, 1989)

Turbidites contain large reserves compared to shallow water fields for comparable trap size

Example of places where turbidite plays have been discovered:West Africa( Angola, Gabon, Congo, Nigeria; Bonga, Erna, Ogo, Agbami), Gulf of Mexico, California Basins, North Sea Basin, NW Australia, Brazil(Campos Basin)

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Turbidity current aid in the formation of turbidites

The Bouma sequence serve to characterize a turbiditic succession

Turbidites host economic resources such as gold and hydrocarbon

Ancient turbidites – are highly prospective in hydrocarbon especially if deposits coalesce into extensive sand bodies

90% of Deep water resources have been found in turbidites. Hence the need for the petroleum explorationist to identify, study their formation and development

Present campaign in deep offshore Nigeria is targeting such prospects, & has scored successes – Bonga, Agbami, Ogo, Akpo, Egina etc

CONCLUSION

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REFERENCESBouma, Arnold H. (1962). Sedimentology of some Flysch deposits: A graphic approach to facies interpretation. Elsevier. p. 168 p.

Arnold H. Bouma, Charles G. Stone, ed. (2000). Fine-Grained Turbidite Systems. American Association of Petroleum Geologists.

Bob Fryklund, (2015). Deep-water the future of exploration . American Association of Petroleum Geologists Bulletin 2015 (4)

Lowe, D.R. (1982). Sediment gravity flows: II. Depositional models with special reference to the deposits of high-density turbidity currents, Journal of Sedimentology, Society of Economic Paleontologists and Mineralogists, v. 52, p. 279-297.

Pettingill, H.S. (1999). Historical look at worldwide turbidite production: The importance of stratigraphic traps in predicting play reserves, paper presented at AAPG International convention, Sept. 7-10, 1999

Pettingill, H. S., 2001. Giant discoveries of the decade 1990–1999: Atlas of deep-water outcrops : AAPG Studies in Geology 56

S. A. Lomas, P. Joseph, ed. (2004). Confined Turbidite Systems. Geological Society of London.

Walker, R.G. (1978). Deep-water sandstone facies and ancient submarine fans: model for exploration for stratigraphic traps. American Association of Petroleum Geologists Bulletin, 62 (6), p. 932-966.

Weimer, P., and Link, M.H., Global petroleum occurrences in submarine fans and turbidite systems, in Weimer, P., and Link, M.H., eds., Seismic facies and sedimentary processes of submarine fans and turbidite systems, Springer-Verlag, New York, 1991, pp. 9-67