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Using Quaternary Reefs and Platforms as a Comparative Tool*

By

William F. Precht1 and Paul M. (Mitch) Harris2

 

Search and Discovery Article #50082 (2008)

Posted June 3, 2008

 

*Adapted from oral presentation at AAPG Annual Convention, Calgary, Alberta, June 16-19, 2005

Click to view list of articles adapted from presentations by P.M. (Mitch) Harris or by his co-workers and him at AAPG meetings from 2000 to 2008.

 

1PBS&J, Miami, FL

2ChevronTexaco Energy Technology Company, San Ramon, CA ([email protected])

 

Abstract 

Exposures of Quaternary reefal limestones provide an excellent opportunity to evaluate carbonate platform history relative to high-frequency sea-level change. Detailed comparative studies of these reef systems from localities worldwide reveal a distinct and similar relationship between relative sea level history, sedimentary sequences, internal facies mosaics, and subsequent overprinting by fabric specific diagenetic alteration.  

Reef complexes generally consist of discrete depositional stages (cycles or parasequences) that can be correlated within and between complexes. The complex stacking patterns observed between the individual cycles and systems tracts put facies with very different petrophysical properties in both temporal and spatial contact. Understanding the spatial context of facies within the sequences is essential to predicting porosity and permeability distributions across ancient carbonate platforms. Further analysis indicates that the diagenetic potential of the various facies and their position relative to sequence boundaries also control the heterogeneous reservoir properties observed throughout these reef complexes.  

The exploitation history of many hydrocarbon bearing reef complexes of various ages from around the world underscores the significance of discerning reservoir continuity relative to individual cycles of deposition. Because of the ability to unravel relative sea level history in Quaternary reefs, their use as a counterpart for comparative studies makes them an invaluable tool for developing sound models for reefs through time and space.

 

 

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Selected Figures

Plot of sea-level changes with respect to present sea level during the past 140,000 years.

Temporally, Quaternary reef systems exposed for examination are composed of numerous, parasequence-scale, shallowing-upwards packages.

Relationships of sea-level changes to GRIP (Greenland Ice-Core Project) data (after GRIP, 1993).

Generally, the bases of the individual sequences are characterized by a transgressive surface. Vertical (temporal) changes reveal an initial rapid deepening, related to flooding of the platform.

 

Conclusions 

  • By studying reef communities through the Quaternary and their changes over time, it is possible to understand more fully the history of development, structure and function of modern reef systems.

  • Conversely, modern reefs form the foundation for understanding the multiscale processes behind the preserved sedimentary architecture and biofacies of the fossil reef sequences.

  • Stage 5e consists of as many as three discrete millennial-scale parasequences.

  • These parasequences are regionally and globally coherent.

  • The exploitation history of many hydrocarbon bearing reef complexes underscores the significance of discerning reservoir continuity relative to individual cycles of deposition.

  • Because of the ability to unravel relative sea level history in Quaternary reefs, their use as a counterpart for comparative studies makes them an invaluable tool for developing sound models for the development of hydrocarbon resources.

 

References 

GRIP (GREENLAND ICE-CORE PROJECT) Members, 1993, Climate instability during the last interglacial recorded in the GRlP ice core: Nature, v. 364, p. 203-207.

Maslin, M., 2002, The Coming Storm: Quarto Publishing, also published by Barron's Educational Series, 144p.

Maslin, M., J. Pike, C. Stickley, and V. Ettwein, 2003, Evidence of Holocene climate variability in marine sediments: in Global Change in the Holocene, p. 185-209.

 

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