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Houston Geological Society Bulletin

Abstract


The Houston Geological Society Bulletin
Vol. 60 (2018), No. 7. (March), Page 26

Abstract: Tectonic Forcing and Sedimentary Cyclicity: Impact on Petroleum System Elements

Kurt Rudolph1

Sequence stratigraphy is an observationally-based method for interpreting sedimentary cyclicity. Stacking patterns of progradation, retrogradation, aggradation and degradation are related to the balance of sediment accommodation versus sediment supply. While often related to eustasy, accommodation is also controlled by tectono-subsidence (Figure 1). Based on over 50 global examples, regional subsidence and uplift rates are usually greater than rates of sea level rise / fall for durations greater than about one million years. Thus, the larger scale patterns of sedimentary cyclicity are related to tectonics in many basins.

hgs600026-fg1.jpg (2,441 bytes)Figure 1.  

Another important aspect of active tectonics is, unlike eustasy, it is spatially variable. For example, while basins may be subsiding adjacent areas may be uplifted (such as rift flanks in extensional basins or orogenic belts in foreland basins). This often drives basin differentiation, variations in sediment supply, development of silling / interior drainage and steepening of the depositional profile (Figure 2).

hgs600026-fg2.jpg (2,584 bytes)Figure 2.  

Tectono-subsidence controls on large sequence development and petroleum system play elements are illustrated by examples in the Western Interior U.S., North Slope Alaska, Western Siberia Basin, North Sea and East Natuna-Sarawak Basin.

Many of the world's most important petroleum source rocks (and regional seals) are associated with tectonic events which differentiated the basin and increased subsidence rates. This can result in marine transgressions (leading to condensed intervals / concentration of organic matter), steepening of the profile (enhancing upwelling / productivity), and basin restriction (enhancing the potential for anoxia / preservation). Another important aspect is tectonic steepening of the depositional profile created by differential subsidence and/or uplift. This enhances the potential for submarine fan development, especially as subsidence wanes. Periods of decreased subsidence (or uplift) are associated with strongly progradational / degradational stratigraphic intervals. The resultant lowstands are a means of bypassing sands into the basin and are potentially reservoir-prone intervals (Figure 3).

hgs600026-fg3.jpg (2,404 bytes)Figure 3.  

Biographical Sketch

Kurt Rudolph received a BS in Geology from Rensselaer Polytechnic Institute and an MA in Geology from the University of Texas. He began his career as an Exploration Geologist with Unocal in 1978, then joined Exxon Production Research in 1981. Kurt held a variety of positions in Exxon/ExxonMobil, including Chief Geoscientist from 2002-2015, retiring in April 2015. He was a co-recipient of the Wallace Pratt Award for the best AAPG Bulletin paper for 1992 and the AAPG-SEG Previous HitDistinguishedNext Hit Previous HitLecturerNext Hit for 2001-2002. Kurt was the AAPG Michael Halbouty Previous HitLecturerTop for 2007 and received best paper award from the Rock Mountain Association of Geologists in 2015. He is currently an Adjunct Professor at Rice University and the University of Houston. His interests include stratigraphy, seismic interpretation, and regional geology.

Acknowledgments and Associated Footnotes

1 Kurt Rudolph: Rice University and University of Houston

Copyright © 2018 by HGS (Houston Geological Society)