--> Abstract: Complex History of San Pedro Basin Fault and the Development of San Pedro Basin; Preliminary Results from High-Resolution Seismic Reflection Data, by R. D. Francis and M. R. Legg; #90088 (2009)
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Complex History of San Pedro Basin Previous HitFaultNext Hit and the Development of San Pedro Basin; Preliminary Results from High-Resolution Seismic Reflection Data

R. D. Francis1 and M. R. Legg2
1California State University, Long Beach, [email protected]
2Legg Geophysical, Huntington Beach, California, [email protected]

We mapped the San Pedro Basin Previous HitfaultNext Hit (SPBF) across San Pedro Basin. The Previous HitfaultNext Hit divides the basin into two parts with possibly different tectonic histories. The Previous HitfaultNext Hit has deformed sediments younger than 70 ka, suggesting activity into latest Pleistocene or Holocene time.

The stress Previous HitregimeNext Hit of the SPBF has varied over time and along strike. Dip discordance across the Previous HitfaultNext Hit occurs as deep as 2.5-3 km below the seafloor. In the southern part of the Basin strata dip toward the Previous HitfaultNext Hit on both sides forming a trough, suggesting a transtensional Previous HitregimeNext Hit in this area. This condition persisted until at least late Pleistocene time (70 to 300 ka). Very deep sediments (more than 1.5 km below the seafloor; age unknown) are poorly imaged, but apparently the transtensional Previous HitregimeNext Hit was weaker or non-existent when they were deposited.

In contrast, strata in the northern part of the Basin east of the SPBF dip away from the Previous HitfaultNext Hit, forming a large depocenter about 4 km to the northeast. This argues against transtension along the Previous HitfaultNext Hit in this area. Highly disturbed rocks associated with Redondo Knoll occur west of the Previous HitfaultNext Hit. Only the youngest sediments (about 70 ka) continue over the Previous HitfaultNext Hit and a subsurface projection of Knoll rocks southwest of the Previous HitfaultTop. This projection stops about 5 km southeast of the Knoll, southeast of which the trough previously described exists.

Sediment packages are found on some of the slopes surrounding San Pedro Basin, including Redondo Knoll, Catalina Ridge, and the slope south of San Pedro Sea Valley. These strata have divergent dips toward the Basin, and onlap up-slope, away from the Basin. This suggests uplift and tilting, particularly west of the SPBF. Ages of these sediments, and relationship of this uplift to the SPBF and formation of the Basin, are still to be determined.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009