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The Juncal Formation (also Juncal Shale) ( or ) is a prominent sedimentary geologic unit of Eocene age found in and north of the Santa Ynez Mountain range in southern and central Santa Barbara County and central Ventura County, California. An enormously thick series of sediments deposited over millions of years in environments ranging from nearshore to deep water, it makes up much of the crest of the Santa Ynez range north of Montecito, as well as portions of the San Rafael Mountains in the interior of the county. Its softer shales weather to saddles and swales, supporting a dense growth of brush, and its sandstones form prominent outcrops.〔Dibblee (1966) 20-22〕 ==Type locality, description, and distribution== The type locality of the Juncal Formation is found north of the Santa Ynez River and east of Agua Caliente Canyon, near Juncal Campground in the Los Padres National Forest, where the unit is well-exposed. At the type locality the Juncal Formation is 3,360 feet thick, which is about average; elsewhere it is both thicker and thinner, reaching 5,400 feet thick near the Romero Saddle north of Carpinteria, and thinning to 1,500 feet north of the Santa Ynez Fault in Oso and Redrock Canyons.〔 The unit consists of shales and sandstones, with the shales being generally more abundant, particularly near the top of the stratigraphic column.〔Dibblee (1966) 22〕 Overall the unit shows a persistent alternation of shale and sandstone layers, of widely varying thickness, indicating frequent and erratic changes in water depth at the point of deposition. The lithologic characteristics of the unit are different north and south of the Santa Ynez River. South of the river, on the north slope and on the crest of the Santa Ynez Mountains, the shales are darker and a thick interior sandstone member can be mapped as a separate unit. Page, Marks, and Walker, in their 1951 report on the region mapped it as the "Camino Cielo Sandstone member."〔Page, B.M., Marks, J.G., Walker, G.W. Stratigraphy and structure of mountains northeast of Santa Barbara, California. Bulletin of the American Association of Petroleum Geologists, Vol. 35 No. 8. 1951. p. 1749〕 North of the river, the unit contains fossil oyster beds in a sandstone member at its base, and an interior sandstone member is massive and cliff-forming, unlike anything in the Juncal of the Santa Ynez Mountains.〔 Shales of the unit are micaceous and dark, usually gray or brown, weathering to various colors. Sandstones are arkosic, hard, and range from white to tan in color. The shale weathers readily, and supports a dense growth of chaparral, similar to the other shale units in the Santa Ynez Mountains, such as the Cozy Dell.〔Thomas M. Dibblee, 1986. Geologic Map of the Santa Barbara Quadrangle, Santa Barbara County, California. California Department of Conservation, Division of Mines and Geology. Dibblee Foundation Map DF#06.〕〔Dibblee (1966) 20-21, 24〕 The unit lies conformably on the Sierra Blanca Limestone, a relatively thin, separately-mapped limestone unit, in some areas. Where the Sierra Blanca is not present the unit lies unconformably on older units – including the Jalama Formation and Espada Formations, both of Cretaceous age; and in some places the Juncal lies unconformably on the Franciscan Formation, which is probably of Jurassic age.〔Norris, 77-80〕〔Dibblee (1966) 21-24〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Juncal Formation」の詳細全文を読む スポンサード リンク
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