What are the principle rocks of the Franciscan Formation?
What are the principle rocks of the Franciscan Formation?
The Franciscan primarily consists of graywacke sandstone and argillite, but also contains lessor amounts of greenstone (altered submarine basalt), radiolarian ribbon chert, limestone, serpentinite (altered mantle material), and a variety of high-grade metamorphic rocks such as blueschist (high-pressure), amphibolite.
What are Franciscan rocks?
The Franciscan Complex is a jumbled mass of sandstone and shale, mixed with chert and volcanic rocks plus minor serpentine and scarce metamorphic rocks called blueschist.
What is the most common rock in the Franciscan Complex?
Sedimentary rocks are the most common Franciscan Complex units and consist of both clastic rocks, such as greywacke, and biogenic rocks, such as chert.
What is Franciscan chert?
Chert is a sedimentary rock rich in silica. Franciscan chert is formed from the tiny silica shells (0.5-1 mm) of marine plankton called Radiolaria. Radiolarian chert forms where two conditions are met.
What is the most common rock in the salinian block?
The Salinian Block is largely granitic, in accordance with its continental crustal origin. This composition contrasts sharply, and paradoxically, with much of the crust to its east, which is sedimentary and oceanic in origin.
What is argillite sedimentary rock?
Argillite is a sedimentary rock composed of fine silt and sand-sized particles mixed with finer volcanic ash.
How is green chert formed?
It was originally the name for chert found in chalk or marly limestone formations formed by a replacement of calcium carbonate with silica. Known Common chert is a variety of chert which forms in limestone formations by replacement of calcium carbonate with silica. This chert type is most abundant.
What is chert rock?
Chert is a sedimentary rock consisting almost entirely of silica (SiO 2), and can form in a variety of ways. Biochemical chert is formed when the siliceous skeletons of marine plankton are dissolved during diagenesis, with silica being precipitated from the resulting solution.
How did the Monterey shale formation originate?
The Monterey Formation is a bio-siliceous, very organic-rich deposit found in southern California. It was deposited between 17 and 5 million years ago during a time when tectonic forces were shifting, and localized subsidence during a time of high eustatic sea level, along with coastal upwelling, affected the area.
What kind of rock forms the Pinnacles in the Pinnacles National Monument?
The formation consists of rocks such as banded and massive rhyolite, some andesites and dacites, and various pyroclastic units. The High Peaks consists of a relatively strong, well-consolidated breccia.
