Modeling of Strain Partitioning During Gravity-Driven Deformation of Multilayered Evaporites and Overburden

Tim P. Dooley¹, Martin P. Jackson¹, Joe A. Cartwright², and Michael R. Hudec^1
1Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX
²School of Earth, Ocean and Planetary Sciences, Cardiff University, Cardiff, United Kingdom

As seismic imaging improves, deformed layering is now clearly visible in evaporite source layers once thought to comprise homogeneous rock salt. Recognizing multilayered evaporites prompts questions: can strain in the salt be much higher than in its overburden; if so, is there a strain discontinuity, such as a roof thrust? To explore this topic, our physical models simulated high strains during gravity-driven deformation of a 7-layer evaporite sequence based on Messinian stratigraphy in the eastern Mediterranean. The models show how widely different strains can develop within the evaporite sequence and its overburden. In the model evaporites, a wide extensional zone comprised thinned mobile layers separated by boudinaged competent layers. Preferential expulsion of the mobile units produced nonuniform thinning within the evaporites. The contractional zone comprised thickened mobile units and intensely buckled, thrusted and duplexed competent interlayers. Strain intensity in the evaporite sequence was 2-3 times that in the prekinematic overburden illustrating how strain can be markedly partitioned even without a roof thrust along the top of the salt. This major contrast in strain intensity corroborates speculation that oblique reflectors in thick salt in some basins are the seismic signature of intensely imbricated thrusts or isoclinal folds beneath an overburden that is only mildly shortened.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas