Grand Canyon Supergroup: Six unconformities make one 'Great Unconformity' - a record of supercontinent assembly and disassembly
Timmons JM, Karlstrom KE, Dehler CM. 1999. Grand Canyon Supergroup: Six unconformities make one 'Great Unconformity' - a record of supercontinent assembly and disassembly. Boatmans Quarterly Review: Grand Canyon River Guides. 12(1):28-33
You have all seen the Great Unconformity in the Grand Canyon, just as John Wesley Powell noticed it in 1869 on his pioneer voyage. This geologic feature is a dramatic break in the rock record. Below this feature are older (Paleoproterozoic) igneous and metamorphic "basement rocks;" above are younger (Phanerozoic) layered sedimentary rocks. In most parts of the Grand Canyon, and in fact, throughout much of the southwestern u.s., the Cambrian Tapeats Sandstone forms the layer just above the unconformity. One such place is Black tail Canyon, where the Great Unconformity represents about r.2 billion years of missing time (I.75 Ga (billion year old) gneiss is overlain directly by 0.5 Ga sandstone). This amount of time adds up to 25% of Earth's history! What went on in the Southwest during this vast time gap?
- Type
- Journal Article
- Authors
- Timmons, J; Karlstrom, K; Dehler, C
- Units
- GRCA
- Keywords
- Disassembly, Geology, Grand Canyon Supergroup, Great Unconformity, IAR, Precambrian, Rodinia, supercontinent