The Entrada Sandstone is a formation in the San Rafael Group found in the U.S. states of Wyoming , Colorado , northwest New Mexico , northeast Arizona , and southeast Utah . Part of the Colorado Plateau , this formation was deposited during the Jurassic Period sometime between 180 and 140 million years ago in various environments, including tidal mudflats , beaches , and sand dunes . The Middle Jurassic San Rafael Group was dominantly deposited as ergs (sand seas) in a desert environment around the shallow Sundance Sea .
12-717: At its type section at Entrada Point , located in the northern part the San Rafael Swell in Emery County, Utah , the Entrada consists of red silty sandstone and lesser interbedded mudstone and is a slope-forming formation. This part of the Entrada is sometimes described as the "earthy facies ". Here the Entrada is overlain by the Curtis Formation , and overlies the Carmel Formation . To
24-406: A stratigraphic unit is nowhere fully exposed, the original type section may be supplemented with reference sections covering the full thickness of the unit. A reference section may also be defined when the original type section is poorly exposed, or for historical units which were designated without specifying a type section according to more modern standards. This palaeogeography article
36-416: Is a stub . You can help Misplaced Pages by expanding it . This article about stratigraphy is a stub . You can help Misplaced Pages by expanding it . Palaeogeography Palaeogeography (or paleogeography ) is the study of historical geography , generally physical landscapes . Palaeogeography can also include the study of human or cultural environments. When the focus is specifically on landforms ,
48-740: Is attributed to bleaching by organic-rich fluids from overlying beds. The formation rests on the Carmel Formation and is overlain by the Morrison Formation . In the Curtis Mountains region of northeastern Arizona, the Entrada is overlain by the Wanakah Formation . In the San Juan Basin of northwestern New Mexico , the Entrada consists of upper and lower sandy members and a medial silty member,
60-415: Is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the standard of reference for unlayered rocks is the type locality . Also it can be defined as "The particular sequence of strata chosen as standard of reference of a layered stratigraphic unit." When
72-504: The Earth 's surface are preserved in the stratigraphic record. Palaeogeographers also study the sedimentary environment associated with fossils for clues to the evolutionary development of extinct species. Palaeogeography is furthermore crucial to the understanding of palaeoclimatology , due to the impact of the positions of continents and oceans on influencing global and regional climates. Palaeogeographical evidence contributed to
84-537: The Kaiparowitz Basin, the Entrada is 314 meters (1,030 ft) thick and is divided into three informal members. The lower member is 113 meters (371 ft) of orange-red silty sandstone, with occasional beds of red mudstone, corresponding to the earthy facies. The middle member is 132 meters (433 ft) of red to green mudstone interbedded with red to white sandstone. The upper member is 69 meters (226 ft) of crossbedded white sandstone. The white color
96-669: The Rehoboth Member. The Curtis Formation is sometimes absent and the Entrada then overlies Chinle Formation . It is overlain by the Todilto Formation . Southeast of Fort Defiance, Arizona , the lower sandy beds are assigned to the Iyanbito Member. Total thickness is up to 37 meters (121 ft). In the Slick Rock, Colorado area, the Entrada is divided into a "middle sandstone", the Rehoboth Member, and
108-598: The Slick Rock Member, in ascending order. The Entrada has been dated to the early to middle Callovian stage of the latest Middle Jurassic . The Entrada Sandstone was named as one of the four formations of the San Rafael Group by James Gilluly and Reeside in 1928. Gregory and Moore worked out the geographic extent of the formation and gave an overview of it in 1931. The extent was revised several times afterwards (most recently in 1992 by Condon). It
120-482: The south and east, the Entrada transitions to cliff-forming red or white crossbedded sandstone, sometimes called the "slickrock facies". This is actually more typical of the Entrada as a whole, and a principal reference section including both facies was designated by Peterson in 1988 at Pine Creek, 5 kilometers (3.1 mi) north of Escalante, Utah , in the Kaiparowits Basin . At the reference section in
132-419: The term paleogeomorphology is sometimes used instead. Paleomagnetism , paleobiogeography , and tectonic history are among its main tools. Palaeogeography yields information that is crucial to scientific understanding in a variety of contexts. For example, palaeogeographical analysis of sedimentary basins plays a key role in the field of petroleum geology , because ancient geomorphological environments of
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#1732786650059144-515: Was divided into the Gunsight Butte, Cannonville, and Escalante members by Thompson and Stokes in 1970. The principal reference for the formation was written in 1988 by Peterson. Entrada members are (in alphabetical order): Entrada Sandstone is found in these geologic locations: Geologic province : Found in these parklands (incomplete list): Spatial distribution: Type section A stratotype or type section in geology
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