--> Abstract: Evolution and Style of Complex Relay Ramps in Nature and Analog Models, by Nathan M. Franklin, David A. Ferrill, Darrell W. Sims, and Alan P. Morris; #90039 (2005)

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Evolution and Style of Complex Relay Ramps in Nature and Analog Models

Nathan M. Franklin1, David A. Ferrill1, Darrell W. Sims1, and Alan P. Morris2
1 CNWRA, Southwest Research Institute, San Antonio, TX
2 University of Texas San Antonio, San Antonio, TX

Relay ramps, a common feature of extensional fault systems, accommodate the transfer of displacement from the neighboring tips of overlapping and similarly dipping faults. These structures can act as fluid traps or as pathways for fluid migration depending on their stage of development and the characteristics of the deforming rocks. In the conventional model, these faults link by either formation of a connecting fault across the ramp or by the propagation of curving fault tips. Once connected, the relict fault tips are generally assumed to become inactive while displacement accrues on the throughgoing fault. Here, we analyze relay ramps found in natural fault systems and developed in analog models (using dynamic structured light 3D imagery). Although many relay ramps appear to reflect the “typical” evolution, others are more complex and involve interaction of multiple parallel faults. We find ramps in models and nature (e.g., Canyonlands National Park, Utah and Sierra Del Carmen, Texas) that contain smaller parallel faults and relay ramps within a larger ramp. These nested relay ramps appear to occur with increased spacing of the larger faults. The breaching process in these complex relay ramps is complicated by interaction of the multiple faults, the requirement of breaching of nested ramps, and consequently, greater total displacement on the fault system before breaching occurs. The potential of these complex ramps to be fluid pathways or traps is affected by elaborate juxtaposition of reservoir and reservoir seal layers and higher fault and fracture densities.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005