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Geologic formation in New Mexico From Wikipedia, the free encyclopedia
The Todilto Formation is a geologic formation in northern New Mexico and southeastern Colorado. It preserves fossils dating back to the Callovian stage of the middle Jurassic period.
| Todilto Formation | |
|---|---|
| Stratigraphic range: | |
Small hill capped with gypsum beds of the Todilto Formation | |
| Type | Formation |
| Sub-units | Luciano Mesa Member, Tonque Arroyo Member |
| Underlies | Beclabito Formation |
| Overlies | Entrada Formation |
| Thickness | 70 m (230 ft) |
| Lithology | |
| Primary | Gypsum |
| Other | Calcareous shale |
| Location | |
| Coordinates | 35.911°N 108.956°W |
| Region | New Mexico |
| Country | United States |
| Type section | |
| Named for | Todilto Park, San Juan Basin |
| Named by | Herbert E. Gregory |
  Todilto Formation (the United States)  Todilto Formation (New Mexico) | |
The formation consists of evaporites. It is divided into a lower calcareous shale (the Luciano Mesa Member) up to 6 meters (20 feet) thick, and an upper gypsum bed (the Tonque Arroyo Member).[1][2]
Based on varve counts in the Luciano Mesa Member, the formation was laid down in a geologically brief period of time,[3] likely in a salina (a coastal body of saline water) that was replenished both by rivers and by seepage or periodic flooding from the Sundance Sea.[2] The varves show a 10 to 13 year periodicity that is interpreted as the solar sunspot cycle, showing that this cycle has existed for at least 160 million years.[3] The contact with the underlying Entrada Formation is very sharp and may indicate the Todilto Sea formed catastrophically from a breach in a barrier between the basin and the Sundance Sea.[4] The presence of dasyclad algae in the Luciano Mesa Member indicates at least some marine flooding.[5]
Dasyclad algae have been found in the Luciano Mesa Member. Evidence has been found for stromatolites in the formation near Mesa Montañosa 35.3806°N 107.8763°W.[6]
The formation is mined for gypsum in the northern Albuquerque Basin, including along the La Bajada escarpment south of I-25, near San Felipe Pueblo, and at White Mesa near San Ysidro.[7] It has also yielded uranium ore.[8]
The formation was first described by H.E. Gregory in 1917 for exposures at Todilto Park in the San Juan Basin. He assigned it to his (now defunct) La Plata Group.[9] It has sometimes been included in the Morrison Formation.[10]
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