Fault-Controlled Turbidite Fairways, Late Miocene and Early Pliocene of Southern California
Gordon, Greg; Pyles, David; and Schwartz, Dan
The late Miocene and early Pliocene was a time of active tectonism in Southern California. Several deepwater basins located adjacent to the San Andreas fault underwent transtensional rifting or transpression-related thrusting. Normal faulting was prevalent in the Ventura and Los Angeles basins, whereas reverse faulting was common in the Southern San Joaquin basin. Some of the syndepositionally active faults formed half-grabens and troughs which guided sediment gravity flows downslope to deeper water, forming sand-rich fairways. The goal of this study is to use three outcrop examples of Mio-Pliocene fault-bounded turbidite fairways to document a relationship between the magnitude of dip-slip offset to reservoir architecture.
A continuum of stacking patterns and relative amounts of dip-slip motion along the associated faults are noted in the three outcrops. The Capistrano Formation at Dana Point Harbor (L.A. basin) contains channels that stack predominantly laterally resulting in abundant sand-on-sand contacts between stratigraphically adjacent channels. Normal dip-slip offset on the associated fault is interpreted to be relatively low. The Point Fermin sandstone at Palos Verdes (L.A. basin) contains channels that stack both laterally and vertically resulting in intermediate sand-on-sand contacts between stratigraphically adjacent channels. Normal dip-slip offset on the associated fault is interpreted to be moderate. The Modelo Formation near Devil Canyon (East Ventura basin) contains channels that are completely encased in mudstone, resulting in no sand-on-sand contacts between stratigraphically adjacent channels. Normal dip-slip motion along the Devil Canyon fault, and hence accommodation, is interpreted to be relatively high.
These patterns are important because fault-bounded fairways comprise oil and gas reservoirs in L.A. basin (e.g. Beta field) and Southern San Joaquin basin, where Upper Stevens (Monterey) turbidite sand fairways formed in troughs adjacent to east-west- or southeast-northwest-oriented thrust faults. These sand fairways are > 250’ thick in fields such as Yowlumne, Aqueduct, and Landslide.
AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013