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South Rim October 20, 2008 |
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| Looking down there, is in fact looking back in time 1.5 billion years at the bottom stratum, the Vishnu Schist.
Above that, however, everything is much younger. The next layer, the Tapeats Sandstone is only 550 million years old.
This discontinuity is known as the Great Unconformity. In between there must have been a period of deposit, followed by a period
of erosion, erasing the record. The top layer, the Kaibab Limestone was formed 260 million years ago.
From top to bottom, the layers are (age in million years): Kaibab Limestone (262), Toroweap Formation (260) Coconino Sandstone (265), Hermit Shale (270) Supai Group (270-320), Redwall Limestone (340), Temple Butte Limestone (370), Muav Limestone (530), Bright Angel Shale (540), Tapeats Sandstone (550), Vishnu Schist (1,700 - 1,500). |
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