Overall Stratigraphy: major volcanic units of the Yellowstone Plateau volcanic field
The recognition of the three volcanic cycles provides a natural basis for dividing the volcanic rock layers in the Yellowstone area. The major ash-flow tuffs that erupted at the climax of each cycle are the primary rock units of Yellowstone in areas beyond the caldera complex. The table below represents the work of geologists who identified, described, and mapped the different volcanic rock deposits in the Yellowstone area and determined the order in which they erupted during each of the three cycles of activity. The units are shown in stratigraphic sequence (the youngest at the top of the table, oldest at the bottom). Table is from Christiansen (2001).
| Volcanic Cycle | Precaldera Rhyolite | Caldera-forming ash-flow tuff | Postcaldera rhyolite | Contemporaneous plateau-marginal basalts1 |
|---|---|---|---|---|
| Third | Plateau Rhyolite2 | Basalts of Snake River Group Osprey Basalt Madison River Basalt Basalt of Geode Creek Swan Lake Flat Basalt Basalt of Mariposa Lake |
||
|
Lava Creek Tuff |
||||
| Mount Jackson Rhyolite Lewis Canyon Rhyolite |
Undine Falls Basalt Basalt of Warm River Basalt of Shotgun Valley |
|||
| Second | Island Park Rhyolite | Basalt of the Narrows | ||
|
Mesa Falls Tuff |
||||
| Big Bend Ridge Rhyolite3 | ||||
| First | Big Bend Ridge Rhyolite3 | |||
|
Huckleberry Ridge Tuff |
||||
| Rhyolite of Snake River Butte | Junction Butte Basalt |
1 Plateau-marginal basaltic volcanism has
been intermittently active throughout the history of the Yellowstone area. The
basaltic volcanism is not inherently part of the rhyolitic cycles, but for
descriptive purposes they are discussed together.
2 The Plateau Rhyolite comprises
more than 20 individual flows ranging
in age from 70,000 to 160,000 years. Flows
of the contemporaneous basalts (Madison River basalt, etc.) range in age
from > 110,000 to < 640,000 years ago.
3 Part of the Big Bend Ridge Rhyolite comprises
postcaldera flows of the first cycle and part comprises precaldera
flows of the second cycle.
References
Christiansen, R.L., 2001, The Quaternary and Pliocene Yellowstone Plateau Volcanic Field of Wyoming, Idaho, and Montana: U.S. Geological Survey Professional Paper 729-G, 145 p., 3 plates.
