California Geology Harden Pdf File
Weathered, poorly sorted conglomerate from the lower member of the Sespe Formation, Santa Ynez Mountains, California. The range in size from boulders to small pebbles. Type sedimentary Underlies, Overlies ('Coldwater Sandstone', 'Coldwater Shale') Thickness 0-7,500 ft Lithology Primary, Other, occasional Location Region Southern and south central California Country United States Type section Named for Named by Watts (1897); redefined by Kew (1924) The Sespe Formation is a widespread geologic unit in southern and south central California in the United States. It is of nonmarine origin, consisting predominantly of and laid down in a, shoreline, and environment between the upper Epoch (around 40 million years ago) to the end of the Epoch (around 24 million years ago). It is often distinctive in appearance, with its sandstones weathering to reddish-brown, maroon, pinkish-gray, tan, and green. Since many of its sandstones are more resistant to erosion than many other regional sedimentary units it often forms dramatic outcrops and ridgelines in many local mountain ranges.
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Contents • • • • • • Type locality [ ] The of the Sespe is along in the, about four miles (6 km) north of, where it was first named in 1897 and redefined in 1924. Subunits [ ] The Sespe Formation has been divided into three clearly differentiable subunits, designed Lower, Middle, and Upper. Tera Term Serial Macro Example In C on this page. • The Lower Unit has a large proportion of conglomerate, as well as sandstone, and a smaller amount of mudstone and shale. Distinguishing this unit are the clasts within the conglomerate, which originated from a source with granitic and volcanic rocks, probably in the vicinity of the modern-day. • The Middle Unit also contains conglomerates and sandstones, but the clasts within the conglomerates include and sandstones of the.
• The Upper Unit of the Sespe Formation consists of interbedded sandstone, mudstone, and siltstones, without the conglomerates; the at this time no longer included the pebbles and boulders which result in conglomerate beds. Depositional environment and paleontology [ ] During the Oligocene Epoch, the and mountain ranges in the present-day vicinity of eroded over many millions of years, with their, ranging in size from microscopic particles to pebbles and even larger rocks, deposited in an extensive coastal floodplain intersected with rivers. The sedimentary rocks which resulted from the millions of years of deposition included,, and abundant sandstones and conglomerates.
During this time the seashore gradually regressed to the west, as the large mountains eroded and filled the floodplain with alluvium. Over time the depositional environment changed from continental to marine, due to changes in surface elevation and sea level; the marine sedimentary formation equivalent to the Sespe is known as the Alegria Formation, and is more often found to the west, for example in southwestern Santa Barbara County. A peculiarity of the Sespe Formation is the presence of an throughout much of the geographic distribution of the unit, representing a gap of millions of years and including most or all of the early; in the vicinity of, the gap corresponded to an erosional event lasting about 8 million years. The found in the Sespe are similar to those characteristic of the period, and the sudden occurrence of redbeds have been used – for example by Thomas Dibble – to demarcate the beginning of the Sespe from the end of the in the stratigraphic column. In the Oligocene the land subsided, creating a shallow, warm marine environment.