• Source: Blackwater Draw Formation

The Blackwater Draw Formation is a geologic formation in the southern High Plains of eastern New Mexico and Texas. The formation was deposited between 1.8 million (Ma) and 300,000 years ago, corresponding to the early to middle Pleistocene epoch.




Description


The formation is a very fine to fine red aeolian sandstone that rests on the resistant caprock calcrete of the Ogallala Formation. The formation is highly variable, but has a maximum thickness of 27 meters (89 ft). The sediments generally are less coarse to the northeast, indicating that they had their source in the Pecos River valley.
The formation is interpreted as loess deposition on a grassland. Deposition was likely episodic, with peak deposition at times of more arid climate and soil formation during moister periods.
The lower part of the formation contains an ash bed of the Toledo eruption in the Jemez Mountains 1.61 million years ago (Ma). The formation also contains the 0.62 Ma Lava Creek B ash bed. The upper part of the formation has an infrared stimulated luminescence (IRSL) age of 300 to 350 thousand years (ka), corresponding to the middle Pleistocene epoch.




Fossils


Rhizoliths are locally abundant in paleosol beds and show features characteristic of small plants such as grasses.




History of investigation


The unit was first investigated by John C. Frye and A. Byron Leonard in 1957, who named it the "Cover Sands". The unit was formally named the Blackwater Draw Formation by C.C. Reeves, Jr., in 1976.




See also



List of fossiliferous stratigraphic units in New Mexico
Paleontology in New Mexico




Footnotes






References


Frye, John C.; Leonard, A. Byron (November 1957). "Studies of Cenozoic geology along eastern margins of Texas High Plains, Armstrong to Howard Counties". Texas Bureau of Economic Geology Report of Investigations. 32: 28–31. Retrieved 1 September 2020.
Gustavson, T. C.; Holliday, V. T. (1 May 1999). "Eolian sedimentation and soil development on a semiarid to subhumid grassland, Tertiary Ogallala and Quaternary Blackwater Draw formations, Texas and New Mexico High Plains". Journal of Sedimentary Research. 69 (3): 622–634. doi:10.2110/jsr.69.622.
Hall, Stephen A.; Goble, Ronald J. (Spring 2020). "Middle Pleistocene IRSL age of the upper Blackwater Draw Formation, Southern High Plains, Texas and New Mexico, USA" (PDF). New Mexico Geology. 42 (1): 31–38. Retrieved 1 September 2020.
Holliday, Vance T. (1 June 1988). "Mt. Blanco revisited: Soil-geomorphic implications for the ages of the upper Cenozoic Blanco and Blackwater Draw Formations". Geology. 16 (6): 505–508. doi:10.1130/0091-7613(1988)016<0505:MBRSGI>2.3.CO;2.
Holliday, Vance T. (1 December 1989). "The Blackwater Draw Formation (Quaternary): A 1-4-plus-m.y. record of eolian sedimentation and soil formation on the Southern High Plains". GSA Bulletin. 101 (12): 1598–1607. doi:10.1130/0016-7606(1989)101<1598:TBDFQA>2.3.CO;2.
Reeves, C.C. Jr. (1976). "Quaternary stratigraphy and geologic history of the southern High Plains, Texas and New Mexico". In Mahaney, W.C. (ed.). Quaternary stratigraphy of North America. Stroudsburg, Pennsylvania: Dowden, Hutchinson, and Ross, Inc. pp. 213–234.

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