--> ABSTRACT: Controls on the Development of Clay Smearing Fault Seals Along Synsedimentary Faults in Unconsolidated Sediments: a Field Example from the Calabacillas Fault, New Mexico, by P. Ted Doughty, Douglas K. McCarty, and Jean Hsieh; #90906(2001)
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P. Ted Doughty1, Douglas K. McCarty2, Jean Hsieh2

(1) Eastern Washington University, Cheney, WA
(2) Texaco Upstream Technology, Houston, TX

ABSTRACT: Controls on the Development of Clay Smearing Previous HitFaultNext Hit Seals Along Synsedimentary Faults in Unconsolidated Sediments: a Field Example from the Calabacillas Previous HitFaultNext Hit, New Mexico

New geologic mapping and measurements of Previous HitfaultNext Hit zone materials along the Calabacillas Previous HitfaultNext Hit provide new information on the development of clay smears and the Previous HitfaultNext Hit seal potential of synsedimentary normal faults. The Calabacillas Previous HitfaultNext Hit is a Quaternary growth Previous HitfaultNext Hit that offsets interbedded unconsolidated mud, sand, and gravel of Pliocene-Pleistocene age along the western margin of the Rio Grande Rift near Albuquerque, New Mexico. The Previous HitfaultNext Hit zone exhibits an external damage zone of small-throw faults that surround an internal zone where one or two slip surfaces have accommodated most of the Previous HitfaultNext Hit displacement and anastomose around large Previous HitfaultNext Hit bounded slivers. Such features are typical of more "brittle" faults formed in consolidated sediments. Clay gouge is present nearly everywhere along the 2,000 meter strike exposure of the Previous HitfaultNext Hit, ranging in thickness from 1 cm to 380 cm. Only eight holes (< 2-5 m in length) were observed. The clay gouge is developed in alternating bands of clay-rich and sand-rich gouge that formed by the attenuation of footwall lithologies; there is little evidence of wholesale mixing. Source beds with the highest smectite equivalent content have been injected and smeared along the Previous HitfaultNext Hit zone, whereas source beds with lower smectite equivalent content are truncated and do not contribute to the clay gouge. Thus the clay mineralogy and resulting ductility of the mud source beds controls the formation of clay smears. Current Previous HitfaultNext Hit seal algorithms will overestimate the potential for Previous HitfaultTop seal unless they can account for the presence of noncontributing low smectite source beds.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado