Insights from Quantitative Sequence Stratigraphic Analysis of Cyclic Peritidal Carbonates: Triassic, Sultanate of Oman

Obermaier, Michael ¹; Aigner, Thomas ¹; Al-Kindy, Suleiman ²
(1)Department of Geosciences, Sedimentary Geology, University of Tuebingen, Tuebingen, Germany. (2) Petroleum Development Oman, Muscat, Oman.

The Triassic in the Northern Oman mountains constitutes largely peritidal dolomites of a flat epeiric carbonate ramp. To unravel the sequence stratigraphic framework, different quantitative sequence stratigraphic analyses were applied:

(1) A rooting index, quantifying the severity of rooting, was used to identify the order of a cycle boundary. High-order sequence boundaries (3rd/2nd-order) tend to be heavier rooted and (karst-)brecciated than low-order cycle boundaries (5th/4th-order).

(2) Facies proportion curves were applied in combination with gamma-ray trends to establish a 3-fold cycle hierarchy. Since proximal facies in this peritidal environment typically show higher natural gamma radiation (K, Th), they can clearly be differentiated from distal grain-dominated facies of rather low GR values.

(3) Stacking pattern diagrams visually accentuate facies changes through time and highlight high-frequency fluctuations in relative sea-level. Interpreted medium-scale cycles (< 10 m) show lateral facies changes and occasionally pinch-outs on a scale of several kilometers.

(4) Fischer plots provide a proxy for accommodation space. Pronounced peaks depict high accommodation space and therefore maximum flooding events, low peaks sequence boundaries. Fischer plots were also compared regionally revealing different behavior of the plots in different parts of the study area. These patterns are most likely due to locally varying subsidence and presumably indicate paleo-high or paleo-low structures.

Techniques of quantitative sequence stratigraphy are thus useful for establishing a solid high-frequency sequence stratigraphic framework. They complement each other and help to verify or falsify different scenarios of cycle picks, cycle hierarchies and regional correlation. In some cases they can even be used as first-pass indicators for regional paleotectonic relationships. This has several implications for reservoir occurrence and quality, relevant for both regional exploration and field development.

The authors would like to thank Petroleum Development Oman and the Sultanate of Oman Ministry of Oil and Gas for permission to present this work.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.