--> Abstract: Significance of Reef-Bearing Upper Jurassic Ramp Types for Basin Analysis and Hydrocarbon Exploration, by Reinhold Leinfelder, Martin Nose, Rainer Zuehlke, Ernest Mancini, and Geraint Wyn Hughes; #90039 (2005)

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Significance of Reef-Bearing Upper Jurassic Ramp Types for Basin Analysis and Hydrocarbon Exploration

Reinhold Leinfelder1, Martin Nose2, Rainer Zuehlke3, Ernest Mancini4, and Geraint Wyn Hughes5
1 GeoBio-Center at Ludwig-Maximilians-University of Munich, D-80333 Munich, Germany
2 Bavarian State Collection of Palaeontology and Geology, D-80333 Munchen, Germany
3 Ruprecht Karl University, D-69120 Heidelberg, Germany
4 University of Alabama, Northport, AL
5 Saudi Aramco, Dhahran, Saudi Arabia

Upper Jurassic, reef-associated ramps comprise three categories:

(1) Ramps with high accomodation space are largely muddy and exhibit a simple facies pattern. Mound growth in the deeper water is boosted by, in the shallower water restricted to, transgressive intervals. String-of-pearl arranged pinnacles are aggradational and are largely buried during regressive intervals. Examples: southern Germany, southern Portugal, eastern Spain, US East Coast. Source rocks may be available. Strongly compartmentalized reservoirs include dolomitized microbialites.

(2) Ramps with subcritical accomodation space exhibit complex architecture. They may be strongly progradational being punctuated by aggradational and retrogradational events. Small keep-up or catch-up reefs develop during major flooding events. Progradational highstand carbonate sands bury and blanket such ramps. Lowstand events may cause exposure, improving reservoir potential which is highest in encasing highstand sands. Type 2 ramps may develop on the flat top of progradational slope-basin systems with source rock potential. Examples: northern Germany , Lusitanian Basin, Agadir Basin.

(3) Ramps with critical accomodation space may be termed 'shaved' tropical ramps. They exhibit high biogenic carbonate productivity on the proximal ramp. Reef thickets grew during flooding events but under insufficient accomodation space. This results in abrasive 'shaving' by annual or perennial storms and continuous redistribution and export of material towards more distal settings with an improved accomodation space, causing ‚facies leveling'. Subaerial leaching may be widespread, in part causing enormous reservoir potential. Examples are from southern Germanya and the Arabian Peninsula.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005