Geology of the Lake Pillsbury area, northern coast ranges, California
Thesis/Dissertation
·
OSTI ID:5375390
Rock units in the Lake Pillsbury area are Franciscan Complex and non-Franciscan (Great Valley Sequence-type) strata and surficial deposits. Franciscan units include relatively coherent sequences, broken-formations, and malanges comprising chiefly graywackes and mudstone, with variable abundances of both native and exotic blocks. Non-Franciscan units comprise generally mildly deformed coherent sequences of graywacke, shale, conglomerate, and limestone. A larger portion of the Lake Pillsbury area is underlain by non-Franciscan lithologies than had been indicated by previous mapping. Franciscan strata range in age from Mid-Jurassic or older to Late Cretaceous (Cenomanian .); non-Franciscan strata range from Jurassic (Tithonian) to Middle Tertiary. The distributions of metamorphic minerals in graywackes (chiefly lawsonite, aragonite, jadeitic pyroxene, glaucophane, pumpellyite, and laumontite) indicate that most Franciscan rocks have undergone high pressure - low temperature blue-schist metamorphism, and that non-Franciscan rocks have undergone lower pressure, zeolite metamorphism. Franciscan rocks are, on average, more dense than non-Franciscan rocks. Franciscan graywackes contain virtually no detrital K-feldspar; K-feldspar content of non-Franciscan sandstones increases with decreasing age and inferred depth of burial. Overall, compositions and physical properties of Lake Pillsbury non-Franciscan sandstones are similar to those of sandstones of the same age from Great Valley Sequence strata.
- Research Organization:
- Texas Univ., Austin (USA)
- OSTI ID:
- 5375390
- Country of Publication:
- United States
- Language:
- English
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