Entrada Sandstone Explained
| Entrada Sandstone |
| Type: | Geological formation |
| Period: | Middle Jurassic |
| Prilithology: | fluvial mudstone, siltstone, and eolian sandstone |
| Namedfor: | Entrada Point, northern San Rafael Swell |
| Namedby: | James Gilluly and J.B. Reeside, Jr. (1928) |
| Region: | Colorado Plateau |
| Country: | United States |
| Coordinates: | 39.261°N -110.543°W |
| Subunits: | Cannonville Member, Cow Springs Member, Dewey Bridge Member, Escalante Member, Henrieville Member, EExeter Member, Gunsight Butte Member, Iyanbito Member, Moab Member, Red Mesa Member, Slick Rock Member |
| Underlies: | Curtis Formation
Todilto Formation |
| Overlies: | Carmel Formation |
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.[1] The Middle Jurassic San Rafael Group was dominantly deposited as ergs (sand seas) in a desert environment around the shallow Sundance Sea.[2] [3]
Description
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 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, 5km (03miles) north of Escalante, Utah, in the Kaiparowits Basin.
At the reference section in the Kaiparowitz Basin, the Entrada is 314m (1,030feet) thick and is divided into three informal members. The lower member is 113m (371feet) of orange-red silty sandstone, with occasional beds of red mudstone, corresponding to the earthy facies. The middle member is 132m (433feet) of red to green mudstone interbedded with red to white sandstone. The upper member is 69m (226feet) of crossbedded white sandstone. The white color 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.[4]
In the San Juan Basin of northwestern New Mexico, the Entrada consists of upper and lower sandy members and a medial silty member, 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 37m (121feet).[4]
In the Slick Rock, Colorado area, the Entrada is divided into a "middle sandstone", the Rehoboth Member, and the Slick Rock Member, in ascending order.
The Entrada has been dated to the early to middle Callovian stage of the latest Middle Jurassic.[5]
History of investigation
The Entrada Sandstone was named as one of the four formations of the San Rafael Group by James Gilluly and Reeside in 1928.[6] Gregory and Moore worked out the geographic extent of the formation and gave an overview of it in 1931.[7] The extent was revised several times afterwards (most recently in 1992 by Condon).[8] It was divided into the Gunsight Butte, Cannonville, and Escalante members by Thompson and Stokes in 1970.[9] The principal reference for the formation was written in 1988 by Peterson.
Members
Entrada members are (in alphabetical order):
- Cannonville Member (UT)[9]
- Cow Springs Member (AZ); equivalent to the upper member at the reference section in southern Utah
- Dewey Bridge Member (CO, UT) - named after the type locality at Dewey Bridge. This brick-red layer has a blocky look to it.[10] Now assigned to the Carmel Formation.[4]
- Escalante Member (UT)[9]
- Henrieville Member (UT);[9] abandoned by Peterson in 1988.
- Exeter Member (NM)[11]
- Gunsight Butte Member (UT)[9]
- Iyanbito Member (NM)[12]
- Moab Member (CO, UT) or Moab Tongue (CO, UT) - named after the type locality of Moab, Utah. The whitish sands from inland dunes make up this "cap rock" layer, as seen atop Delicate Arch and Broken Arch in Arches National Park.[10]
- Red Mesa Member (AZ, NM, UT)
- Slick Rock Member (CO, UT) - named for the type locality at Slick Rock, Colorado; rounded beach sands were cemented together to create this uniform layer.[10]
Places found
Entrada Sandstone is found in these geologic locations:
Geologic province
Found in these parklands (incomplete list):
Spatial distribution:
- spatial distribution of Entrada Sandstone in Macrostrat
Further reading
External links
Notes and References
- Peterson . Fred . 1988 . Stratigraphy and nomenclature of Middle and Upper Jurassic rocks, western Colorado Plateau, Utah and Arizona . U.S. Geological Survey Bulletin . 1633-B . 27 . 10.3133/b1633AC. free .
- Lucas . S.G. . Anderson . O.J. . Spencer G. Lucas . The Jurassic San Rafael Group, Four Corners region . New Mexico Geological Society Guidebook . 1997 . 48 . 117-120 . 26 October 2021.
- Web site: The formation of the Entrada Sandstone: Tectonics, Accommodation space, Wind and lots of Sand . Written in Stone . 2011 . Share . Jack.
- O'Sullivan . Robert B. . 2003 . The Middle Jurassic Entrada Sandstone in northeastern Arizona and adjacent areas . New Mexico Geological Society Guidebook . 54 . 303-308 . 25 October 2021.
- Condon . S.M. . Huffman . A.C. Jr. . Peterson . F. . Aubrey . W.M. . Revisions to stratigraphic nomenclature of Jurassic and Cretaceous rocks of the Colorado Plateau . United States Geographical Survey Bulletin . 1988 . 1633-B . B13-56 . 10.3133/b1633AC. free .
- Gilluly . James . Reeside . J.B. Jr. . Sedimentary rocks of the San Rafael Swell and some adjacent areas in eastern Utah . U.S. Geological Survey Professional Paper . 1928 . 150-D . D61-110 . 10.3133/pp150. free .
- Gregory . H.E. . Moore . R.C. . 1931 . The Kaiparowits region, a geographic and geologic reconnaissance of parts of Utah and Arizona . U.S. Geological Survey Professional Paper . 164 . 10.3133/pp164. free .
- Condon . S.M. . 1992 . Geologic framework of pre-Cretaceous rocks in the Southern Ute Indian Reservation and adjacent areas, southwestern Colorado and northwestern New Mexico . U.S. Geological Survey Professional Paper . 1505-A . A1-A56 . 10.3133/pp1505A. free .
- Thompson . A.E. . Stokes . W.L. . 1970 . Stratigraphy of the San Rafael Group, southwest and south central Utah . Utah Geological and Mineral Survey Bulletin . 87.
- Wright . J.C. . Shawe . D.R. . Lohman . S.W. . Definition of Members of Jurassic Entrada Sandstone in East-Central Utah and West-Central Colorado . AAPG Bulletin . 1962 . 46 . 2057-2070 . 10.1306/BC74394B-16BE-11D7-8645000102C1865D.
- Lucas . S.G. . Spencer G. Lucas . Kietzke . K.K. . Hunt . A.P. . 1985 . The Jurassic System in east-central New Mexico . New Mexico Geological Society Field Conference Guidebook . 36 . 213-242 . 2 September 2020.
- Imlay . R.W. . Jurassic paleobiogeography of the conterminous United States in its continental setting . U.S. Geological Survey Professional Paper . 1980 . 1062 . 10.3133/pp1062. free .
- Mackin . J.H. . 1954 . Geology and iron ore deposits of the Granite Mountain area, Iron County, Utah . U.S. Geological Survey Miscellaneous Field Studies Map . MF-14 . 26 October 2021.
- Rowley . P.D. . Hansen . W.R. . Geologic map of the Plug Hat quadrangle, Moffat County, Colorado . U.S. Geological Survey Geologic Quadrangle Map . 1979 . GQ-1514 . 26 October 2021.
- Johnson . R.B. . Geology of the Huerfano Park area, Huerfano and Custer Counties, Colorado . U.S. Geological Survey Bulletin . 1959 . 1071-D . 10.3133/b1071D. free .
