15 November 2013
Friday fold: Ventura Avenue Anticline
Posted by Callan Bentley
A guest post today for the Friday fold from my former student Naseem Naghdi, who’s now in southern California:
The Ventura Avenue anticline is a fault-propogated fold and is located in the core of (Conoco’s) San Miguelito oil field, which is on the Ventura-Rincon anticlinorium. Carbon dating of seashells have indicated that the terraces range between 1800 – 5600 years old and it was deposited from deep marine turbidity currents. Sea level has remained relatively constant since then so it is suggested that this uplift has been caused by reoccurring earthquakes every ~600 years or so. The formation containing the most petroleum (reservoir rock) is the highly porous Pico Formation (Plio-Pleistocene), which is a blue-gray siltstone/fine-grained sandstone with a fossiliferous basal conglomerate. Most of the oil was generated from the Monterey Formation (source rock), an organic-rich siliceous shale. The fold itself and nearby faults both serve as structural petroleum traps.
The most significant thing about this anticline was that it was deposited, folded, and filled with oil all within a very short amount of time, geologically speaking. It’s also one of the fastest uplifting structures in the world with an uplift rate of 5mm/year and is underlain by the Ventura fault. And of course, it’s on a beautiful location–near the cliffs of the Pacific Coast Highway.
I pulled most of the information from these two articles below along with our field trip guidebook (Sylvester & Brown, 1988) in case you wanted more info:
Thanks, Naseem! And to everyone else: Happy Friday!
PS – I’m happy to feature YOUR fold photos here as part of the now three-year-old Friday fold series. Just shoot me an email if you have a cool fold worth sharing.
The prominent marine terrace seen in your photo to the left of the crest of the anticline is actually much older than the age range you quoted. It is estimated to be ~45ka (see, for example, Yerkes and Lee, 1987). Regardless, the relatively high elevation of this terrace still implies the high uplift rate you describe.
Thanks for the correction/addition/augmentation. Much obliged!