Sedimentary Facies and Depositional Environments of the Big Blue Formation Between Anticline Ridge and the Domengine Ranch
Matthew A. Bate, 1984. "Sedimentary Facies and Depositional Environments of the Big Blue Formation Between Anticline Ridge and the Domengine Ranch", 1984 Midyear Meeting San Jose, California, Ralph E. Hunter, H. Edward Clifton, N. Timothy Hall, John L. Chin
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The Big Blue Formation conformably overlies the Temblor Formation along the northeast flank of the Coalinga anticline, but is progressively truncated beneath the late Miocene Santa Margarita Formation. The near continuous exposures of yellow, orange, brown, red, and blue sediments are almost exclusively composed of detrital serpentinite. Several authors (Eckel and Myers, 1946; Cowan and Mansfield, 1970) noted the proximity of the thickest Big Blue exposures to the large (19 × 6 km) serpentine body atop San Joaquin Ridge, near the mining town of New Idria, and suggested a relationship between the two. This inferred, but poorly understood relationship between the technically emplaced serpenti nite mass at New Idria, exposed up-plunge from the San Joaquin-Coalinga anticline and the sedimentary serpentinite, was significantly clarified by Dickinson and Casey,(1976). They recognized the non-detrital character of much of the Big Blue Formation and distinguished a chaotic facies that represents protrusive serpentinite flows that resulted from massive protrusive emplacement of serpentine, associated with a major episode of diapiric movement. The major uplift occured in late middle Miocene (Luisian) time, depositing between 5 and 10 cubic miles of serpentinite debris (Eckel and Myers, 1946). Dickinson (1966) likewise called upon extrusive sheets of serpentine to explain similar deposits to the south on Table Mountain, west of Reef Ridge.
The upper Temblor Formation is grey-green silty claystone overlain by 22 m of an increasingly coarse sand and pebble interval. The lowest 5 m are very fine-grained sandstone, planar bedded with thin silt-stone layers. The next 3 m are generally medium-grained sandstone, with wel 1-cemented si Itstone inter-beds.