Tahoka Formation
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| Tahoka Formation | |
|---|---|
| Stratigraphic range: | |
| Type | Formation |
| Unit of | Tule Group |
| Thickness | 3 m (10 ft) |
| Lithology | |
| Primary | Mudstone |
| Other | Conglomerate, gypsum |
| Location | |
| Coordinates | 33°09′50″N 101°47′38″W / 33.164°N 101.794°W |
| Region | Texas New Mexico |
| Country | United States |
| Type section | |
| Named for | Tahoka, Texas |
| Named by | Evans and Meade |
| Year defined | 1945 |
  Tahoka Formation (the United States)  Tahoka Formation (Texas) | |
The Tahoka Formation is a geological formation in Texas and New Mexico, which was emplaced in now-dry lakes during late Pleistocene wet periods.
A number of playa lakes occur on the Llano Estacado between Texas and New Mexico,[1] they are the easternmost such lakes in the United States.[2] These basins such as Double Lakes, Guthrie Lake, Tahoka Lake and Twin Lakes[3] apparently formed through fluvial erosion during wet and wind erosion during dry periods.[4]
The Tahoka Formation consists of lake sediments that cover most of these basins when not covered by younger lake and wind-transported sediments.[4] It is well preserved in the larger playas[5] but also occurs across thousands of small playa depressions in the Southern High Plains[6] and as far as Nall Playa in Oklahoma.[7] At Arch Lake in New Mexico, it may cover a surface of over 130 square kilometres (50 sq mi).[8] At Illusion Lake, Lamb County, wind-driven deflation of Tahoka Formation deposits has formed a new lake basin.[9]
It features clays deposited by river deltas and at shores but also muds deposited in the middle of lakes.[2] The clays are accompanied by sand and are bentonitic;[10] there is also gravel and gypsum.[11] The mineral finchite (Sr(UO2)2(V2O8)·(H2O)5) was discovered in the Tahoka Formation.[12] The Tahoka Formation was emplaced in perennial lakes. Limestones, later determined to be dolomite, have been used to correlate it across lake basins.[2] The deposits are usually thin; at Tahoka Lake they reach thicknesses of 3 meters (10 ft).[13] At at least one site, they are mined for gravel.[14] The Tahoka Formation rocks appear to be derived from Cretaceous shales that were redeposited.[15] After deposition, the Tahoka Formation rocks were tilted by differential subsidence.[16]
History of investigation
Initially, a "Tahoka clay" was defined in 1945 by G.L. Evans and G.E. Meade as clay deposits in former lakes, and named after Tahoka, Texas which is close to several of the lakes studied. A reference section was defined at Rich Lake, Lynn County.[2] Reeves proposed in 1976 that the layer underlying the dolomite be redefined as the "Double Lake Formation", but the proposal was not accepted by Hall 2001.[17]
Correlations
The Tahoka Formation has been correlated to the Gamerco Formation in Gallup, New Mexico, the Jeddito Formation in the Hopi Reservation of Arizona, and the Neville Formation in the Big Bend Region, Texas. The "High Terrace" in the Plains is also correlative to the Tahoka Formation.[18] A mudstone found in a pit at Blackwater Draw, Clovis, New Mexico, has also been related to the Tahoka Formation.[19] Together with older formations it constitutes the Tule Group, which consists in sediments deposited within basins.[20]