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Book Chapter

Eolian Deposits of the Younghusband Carbonate Barrier, South Australia: Analog for Ancient Eolian Petroleum Reservoirs

By
Steven G. Fryberger
Steven G. Fryberger
Shell UK Exploration and Production, 1 Altens Farm Road, Nigg, Aberdeen AB12 3FY, Scotland, UK
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Brett Walker
Brett Walker
Woodside Petroleum Limited, 1 Adelaide Terrace, Perth, Western Australia 6000, Australia
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Rob Rutherford
Rob Rutherford
Reservoir Consultants Pty Ltd, 22 Kershaw Street, Subiaco, 6008, Western Australia, Australia
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Published:
January 01, 2001

Abstract

The Holocene eolian barrier of the Younghusband peninsula, South Australia, is an accessible and well-studied modern analog for ancient eolian carbonate and mixed quartz-carbonate barriers, as well as the associated suites of sedimentary structures that might be expected in such settings. The barrier has formed from the shoreward drift of Lacepede Shelf biogenic carbonate fragments as well as the longshore drift of quartz sand from the Murray River.

The Younghusband barrier carbonate content increases from roughly 12 percent at the mouth of the Murray River southeastward to nearly 75 percent at Lacepede Bay, near Kingston. The barrier consists mainly of eolian dune and sand-sheet deposits. Dune bedforms consist of parabolic, blowout, coppice, and various subtypes of transverse dunes including barchan, barchanoid ridge, and transverse ridge dunes. There is a low foredune along the shore, landward of which lies a narrow sabkha mat separates this foredune from the main barrier. Where vegetation has been destroyed or thinned, deflation forms large blowouts, parabolic dunes, and transverse dunes, whose advance is causing the barrier to shift northeastward into the Coorong Lagoon.

The abundant carbonate material within the barrier includes transported bryozoans and coralline algae that originated on the cool-water Lacepede Shelf. These materials, along with broken shells of lagoonal and nearshore fauna such as gastropods and mollusks, have been incorporated into the cross stratification. This process has produced such coarse, shelly textures in the eolian barrier sediments, particularly the sand-sheet deposits, that it would be difficult to identify these sediments as eolian in the ancient record. This is not merely because of the presence of shell debris but also because of unusual sedimentary structures. Nevertheless, common eolian sedimentary features are present and identifiable, and provide a key to proper interpretation of this group of sediments in ancient rocks. The Holocene Younghusband barrier and the landward Pleistocene carbonate barriers are viable analogues for subsurface petroleum reservoirs. The Younghusband barrier, if buried and preserved, would be a very narrow but elongate sand lens about a kilometer wide at maximum, and up to 30 meters thick, with enormous reservoir volume because of its great length. It would consist mainly of clean eolian sands, composed dominantly of either quartz or carbonate depending upon position along the barrier. These sediments would be interbedded with nearshore and lagoonal facies (potential source rocks).

Recognition of the eolian nature of such a barrier-originated petroleum reservoir would allow correct paleogeographic placement of the sediments, and would facilitate both development drilling and further exploration for new barriers or extensions of the current field. Further, the knowledge that the modern barriers exist in trends controlled by sea-level stands would suggest that petroleum reservoirs in such ancient systems might occur in multiple fields parallel to bathymetric contours of an ancient marine shelf. The current preservation of eolian parts of older barriers in the South Australia region onshore but below sea level (observed in shallow-drilling programs) and offshore as subsea “ranges” proves that such preservation of the eolian component of barriers is not only possible but should be expected in the ancient record.

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SEPM Special Publication

Modern and Ancient Carbonate Eolianites: Sedimentology, Sequence Stratigraphy, and Diagenesis

F. E. (Rick) Abegg
F. E. (Rick) Abegg
Chevron USA Production Company, 935 Gravier St., New Orleans, Louisiana 70112, U.S.A.
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David B. Loope
David B. Loope
University of Nebraska, Lincoln, Nebraska 68588, U.S.A.
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Paul M. (Mitch) Harris
Paul M. (Mitch) Harris
Chevron Petroleum Technology Company, Houston, Texas, U.S.A.
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SEPM Society for Sedimentary Geology
Volume
71
ISBN electronic:
9781565761933
Publication date:
January 01, 2001

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