Abstract

Reprocessed deep-penetration seismic reflection profiles across the offshore southern Santa Maria Basin suggest a complex history of tectonic deformation. The top of subducted oceanic crust, imaged at the north end of EDGE line RU-10, is disrupted and eventually disappears to the south. Farther south, a strong lower crustal reflection ramps up and may reflect a possible north-dipping low- angle detachment, or a change in crustal geometry associated with the subducted Morro Fracture Zone. Above a time-transgressive unconformity, Miocene and younger sediments onlap to the south and water bottom deepens, suggesting a major regional tilt reversal in post-Miocene time. Below the unconformity, basement is displaced by largely northwest-striking normal faults that we believe form tilted crustal blocks; it is possible that Cretaceous and Paleogene sections are preserved in resulting half-grabens. Some of these normal faults, including splays off the outer Santa Lucia Bank fault system, were reactivated as minor reverse faults in post-Miocene time. There is no evidence that requires any post-17.5 Ma tectonostratigraphic terrane boundary through this area; rather, much of the structure of the southern Santa Maria Basin appears to be continuous with the rotated Western Transverse Ranges and northern Channel Islands.

You do not currently have access to this article.