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Abstract

(Begin page 1499)

AAPG Bulletin, V. 85, No. 8 (August 2001), P. 1499-1521.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.

Sandy submarine braid plains: Potential deep-water reservoirs

Reinhard Hesse,1 Ingo Klaucke,2 Saeed Khodabakhsh,3 David J. W. Piper,4 William B. F. Ryan,5 NAMOC Study Group6

1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada; [email protected]; current address: Institut fuer Geologie, Ruhr-Universitaet Bochum, Universitaetsstr. 150, D-44 801, Bochum, Germany; email: [email protected]
2GEOMAR, Wischofstr. 1-3, D-24148 Kiel, Germany; email: [email protected]
3Geology Department, Bu-Ali-Sina University, Hamedan, Iran, 65174; email: [email protected]
4Geological Survey of Canada (Atlantic), Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada; email: [email protected]
5Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, 10964; email: [email protected]

AUTHORS

Reinhard Hesse obtained his Diplom (M.Sc. degree), Dr. rer. nat. (Ph.D.), and Habilitation (D.Sc. degree) from the Technical University of Munich, Germany. In 1969 he joined the Department of Geological Sciences of McGill University, Montreal, Canada, as assistant professor; he retired in 1996 and is now professor (postretirement). He is Honorar Professor at the Ludwig Maximilians University of Munich and currently visiting professor at the Ruhr-University, Bochum, Germany. His scientific interests include modern and ancient deep-sea sedimentation, clastic diagenesis, and plate tectonics.

Ingo Klaucke is currently a research fellow at GEOMAR, Kiel, Germany. He studied geology at the universities of Freiburg (Germany), Lyon (France), and McGill (Canada), where he received his Ph.D. in 1995. His main research interests focus on the modes and pathways of sediment transfer from the continent to the deep sea and on the facies distribution of clastic deep-sea deposits.

Saeed Khodabakhsh received his B.Sc. degree from Shahid Beheshti University, Iran, in 1986 and his M.Sc. degree from Tehran University, Iran, in 1990. During 1987-1991 he worked for the Geological Survey of Iran and the National Iranian Oil Company. In 1992 he went to McGill University, Montreal, Canada, where he obtained his Ph.D. in 1997. He is currently assistant professor in the Geology Department, Bu-Ali Sina University, Hamedan, Iran. His research interest is clastic depositional environments.

David Piper is a research scientist with the Geological Survey of Canada at Bedford Institute of Oceanography. He gained his B.A. degree and Ph.D. from Cambridge University, England. His interests include modern and ancient turbidites, marine Quaternary of eastern Canada, neotectonics and sedimentation in Greece, and sediment instability constraints to hydrocarbon development offshore eastern Canada.

Bill Ryan is a Doherty Senior Scholar at the Lamont-Doherty Earth Observatory. His current research has taken him to the Gulf of Lyon in the Mediterranean to study the cutting and filling of submarine canyons related to sea level cycles. He has also been investigating a very rapid Holocene transgression on the Black Sea shelf. Bill received his Ph.D. in geological sciences from Columbia University in 1971 and the Shepard Medal from SEPM in 1993.

ACKNOWLEDGMENTS

Reviews of this article by Keith W. Shanley, L. G. Kessler II, and particularly by Carlos Pirmez, as well as the cooperation of Captain Lewis, officers and crew of CSS Hudson cruise 93-025, major funding from NSERC, Ottawa, Ontario, and NSF, Washington, D.C., and a major contribution of AAPG to the printing costs of the foldout, are gratefully acknowledged.

ABSTRACT

Sandy submarine braid plains, like their fluvial counterparts on land, are sand-rich depositional environments that may display excellent reservoir characteristics in terms of sediment volume, porosity, and permeability. The submarine examples may be laterally associated with potential source rocks such as the fine-grained levee deposits of deep-sea channels. A side-scan sonar study of the central Labrador Sea revealed the existence of a more than 700 km long and up to 120 km wide submarine sand and gravel plain that has been supplied with sediment by high-density turbidity currents, possibly resulting from subglacial lake outburst flooding in the Hudson Strait. The side-scan imagery of parts of the plain displays a conspicuous streaky pattern of alternating high and low backscatter intensity. High-resolution 3.5 kHz seismic profiles and 12 kHz bathymetric profiles show that the pattern represents a furrow-and-ridge (erosional) or channel-and-bar (depositional) topography, similar to a braided alluvial plain. The furrows or channels have low acoustic backscatter, are less than 10 m deep, and are separated by ridges or bars having high backscatter. Some channels terminate in depositional lobes. Individual channels and bars (or furrows and ridges) are less than 100 m wide and can be followed up to 40 km downcurrent. On sleeve-gun seismic profiles, the total sand thickness appears to be between 200 m (proximal) and 100 m (distal). Piston cores from the plain recovered massive sand layers up to 4 m thick, buried under 1 m of Holocene hemipelagic ooze. Texturally, the sands and gravelly sands display a trend of improving sorting with increasing mean grain size. Some very coarse grained samples are moderately well sorted and almost matrix free.

The flooding events that deposited the sands might be the submarine counterpart of Heinrich events but need not be restricted to such events. Radiocarbon ages of about 10 k.y. from the base of the ooze overlying the youngest sand gave a minimum age for the sand that is similar to the age of Heinrich event 0. Estimates for the discharge volume of individual events are poorly constrained and range from 103 to 105 km3. Braided channel patterns in deep-water (Begin page 1500) sandy depositional environments are not restricted to high latitudes but also have been identified in various submarine fan settings in the lower latitudes, for example, the Orinoco, Var, and Monterey deep-sea fans and in the Santa Monica Basin. The largest examples, however, are known from high latitudes, suggesting that melt-water discharge from continental ice sheets may favor the formation of this habitat of giant sands in the deep sea. The occurrence of sandy braided deep-water environments having favorable reservoir characteristics in a variety of tectonic settings makes this type of environment a potentially interesting deep-water target.

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