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Luo, Hongjun, and Dag Nummedal, 2012, Forebulge migration: A three-dimensionalflexural numerical modeling and subsurface study of southwestern Wyoming, in D. Gao, eds., Tectonics and sedimentation: Implications for petroleum systems: AAPG Memoir 100, p. 377395.


Copyright copy2012 by The American Association of Petroleum Geologists.

Forebulge Migration: A Three-dimensional Flexural Numerical Modeling and Subsurface Study of Southwestern Wyoming

Hongjun Luo,1 Dag Nummedal2

1BP Exploration, Chertsey Rd., Sunbury-on-Thames, TW16 7LN, United Kingdom (e-mail: [email protected])
2Colorado Energy Research Institute, Colorado School of Mines, 1500 Illinois St., Golden, Colorado, 80401, U.S.A. (e-mail: [email protected])


We thank Ronald Steel, Paul Heller, Art Snoke, Shaofeng Liu, Peigui Yin, Randi Martinsen and James Steidtmann for discussions. We also thank James Drever for his help. This project was part of Hongjun Luo's dissertation funded by the Institute for Energy Research-Enhanced Oil Recovery Institute (IER–EORI) and the Department of Geology and Geophysics at the University of Wyoming during 2001 to 2005. Additional financial support came from the 2003 to 2005 Walter and Constance Spears Memorial Scholarship, the Phillips Geology Scholarship, the 2004 Weimer Family AAPG grant, and a 2004 SEPM travel grant. We thank peer reviewers Frank Ettensohn and John Londono for the constructive suggestions to improve this paper.


The recognition of a forebulge in the subsurface is difficult because of its low amplitude and wide extent. It is further complicated by the subsequent tectonic modification (by the Laramide orogeny in this case) that may have overprinted the forebulge with complex younger structural patterns. Three-dimensional (3-D) flexural numerical modeling provides a strong supportive tool to help predict forebulge locations and focus subsurface search on their subtle isopach expression. Based on detailed well-log correlations and good outcrop control, three regional cross sections were established to identify Late Cretaceous forebulges in southwestern Wyoming. Along these sections in the Greater Green River Basin (two east–west and one northwest–southeast), the existence of forebulges was only recognized in the southern section. In response to the progressive eastward movement of the Crawford, early Absaroka, and late Absaroka thrusts, the forebulge migrated eastward to the Moxa Arch, the Rock Springs Uplift, and the Washakie Basin, respectively. The 3-D flexural modeling indicates that the forebulge was limited in its extent only to the southern part of the basin because of the distribution of thrust loads. The forebulge shifted southeastward over time because of the migration of these loads. The 3-D flexural modeling is critical to understanding Late Cretaceous forebulge migration across southwestern Wyoming.

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