--> Abstract: Structural Styles In A Deformed Turbidite Basin - Champsaur SE France; #90063 (2007)

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Structural Styles In A Deformed Turbidite Basin - Champsaur SE France

 

Butler, Robert W.H.1, Henry Lickorish2, William D. McCaffrey1, Jake Lockley3, Jamie Vinnels1 (1) University of Leeds, Leeds, United Kingdom (2) Rock Deformation Research, Calgery (3) School of Earth and Environment, University of Leeds, Leeds, United Kingdom

 

Thrust zones are notoriously difficult to image seismically. Does the transparency of such zones result from inadequate seismic resolution of simple, discrete faults or does it represent complex structure? Here we present a field study using seismic scale outcrops (km x km) to explore the nature of contractional deformation developed in multilayer turbidite sandstones. Our examples come from the Champsaur sandstones of the French Alps. These late Eocene-early Oligocene tubidites lie in the footwall to a major detachment thrust sheet (Embrunnais-Ubaye Nappe). They are in turn involved in the thrusting. Yet in all cases deformation includes folding. The importance of folding vs thrusting varies from site to site. In the eastern part of the area there are almost no thrusts within the turbidite sequence. Deformation is accomplished by asymmetric folding. This style generates km-long panels of gently dipping strata, connected by forelimbs of greater structural complexity. Given the problems of imaging forelimbs such structures are likely to be (mis) interpreted in the subsurface as narrow fault zones. At outcrop, the macroscopic forelimbs themselves contain trains of subsidiary folds that vary in tightness, frequency and wavelength depending up on the stacking pattern of turbidite sandstones. In general, short wave-length folds and correspondingly greater structural complexity relate to thinner bed packages. These studies indicate that folding, related to stratigraphic variations, may be a significant component of subsurface structural styles. While fold interpretations may be difficult to resolve from seismic data alone, dip-metre logs from well penetrations offer useful indicators. Correct assessment of fold styles is important for predicting reservoir connectivity in the subsurface, especially for contractional systems in deep water settings.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California