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Structure and Kinematics of a Syndepositional Paired Detachment Previous HitSystemNext Hit, Triassic Ischigualasto Basin, NW Argentina*

By

Brian S. Currie1 and Tony Albrecht2

 

Search and Discovery Article #30059 (2008)

Posted July 15, 2008

 

 

*Adapted from oral presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008

 

1Department of Geology, Miami University, Oxford, OH ([email protected])

2North America Gas Reserves and Renewal, BP America, Inc., Houston, TX

 

Abstract

In the Ischigualasto basin of NW Argentina, lacustrine/fluvial deposits exhibit both extensional and contractional deformation features. Extensional structures consist of north-striking listric normal faults that are concentrated in an ~100 meter-wide zone at the eastern edge of the deformed area. Contractional structures are concentrated along an ~250 m wide zone at the western side of the deformed area.

The primary structure in this area is a west-vergent thrust Previous HitsystemNext Hit that contains two primary imbricates and carries upright to overturned folds with fault bend, fault propagation, and detachment geometries. Faults in both eastern and western areas have similar magnitudes of displacement (~80 m) and sole into a sub-horizontal detachment surface, below which deposits are undeformed. All deformed strata are overlain by undeformed fluvial deposits. Observed structures are consistent with deformation associated with syndepositional gravity-induced displacement above an overpressured detachment horizon.

The contractional frontal part of the Previous HitsystemNext Hit was driven by extension produced by gravity spreading / Previous HitdepositionalNext Hit loading of lacustrine delta platform and fluvial deposits, with lateral translation occurring above an overpressured shale décollement. Deformation occurred at shallow depths (<30 m) in relatively shallow water (<15 m) environments. Although 2-3 orders of magnitude smaller, the overall geometry of the Ischigualasto detachment Previous HitsystemNext Hit is comparable to passive margin detachment systems. Based on these similarities, the deformation features, internal geometry, and reconstructed kinematics of the Ischigualasto detachment Previous HitsystemNext Hit may serve as a small-scale analogue for passive-margin paired extensional-contractional systems.

 

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uAbstract

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uAbstract

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uSignificance

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Selected Figures

 
Figure 1 Location map for Ischigualasto Basin
Figure 2 Cross-section, Triassic central Ischigualasto Basin
Figure 3 Stratigraphic column for the Triassic section
Figure 4

Outcrop in which there is ~ 70 m combined displacement on extensional zone normal faults

 
Figure 5

Outcrop in which the frontal thrust Previous HitsystemNext Hit between HW/FW cutoffs indicate ~ 70 m displacement

 

Significance

 

  • Deformation features associated with unrecognized lacustrine paired extensional-contractional detachment systems may result in misinterpretations of basin tectonic histories.
  • Fluid expulsion may produce elevated pore-fluid pressures that facilitate the development of shallow paired detachment systems.
  • Scale-independent nature of compressional wedge may produce early development of reservoir-scale traps in rocks that contain both source and reservoir lithologies.

 

Conclusions

 

  • Triassic-aged deformation near Agua de la Peña canyon exhibits the characteristics of a paired extensional-contractional detachment Previous HitsystemNext Hit.
  • Deformation was driven by lacustrine delta/fluvial channel deposition and resulting gravity spreading above a shale detachment horizon.
  • The Agua de la Peña detachment Previous HitsystemTop may serve as a small-scale analogue to paired extensional-contractional deformation systems developed along passive margins.

 

References

 

Bilotti, Frank, and John H. Shaw, 2005, Deep-water Niger Delta fold and thrust belt modeled as a critical-taper wedge: The influence of elevated basal fluid pressure on structural styles: AAPG Bulletin, v. 89, p. 1475-1491.

 

Bhattacharya, Janok P., and Russell K. Davies, 2004, Sedimentology and Structure of Growth Faults at the Base of the Ferron Sandstone Member Along Muddy Creek, Utah, in AAPG Studies in Geology No. 50, p. 278 – 304.

 

Acknowledgements

 

Appreciation is expressed to Carina Colombi, Museo de Ciencias Naturales, San Juan, and to the Staff of the Ischigualasto Provincial Park, San Juan.

 

Appreciation is also expressed for grants from:

AAPG Foundation Grants-in-Aid Program

GSA Student Research Grant Program

National Geographic Society

Miami University Department of Geology

Miami University Hampton Fund for International Studies

SOLE Environmental Research Fund.

 

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