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The Grand Canyon Tells the Story of North America Knowing how and where rocks are formed allows us to read the story written in the rocks. A mile thickness of rocks of the Great Plains are exposed by uplift and erosion by the Colorado River. Rocks of the Grand Canyon Separate the larger puzzle into a series of smaller puzzles (I.e., each group of rocks) Metamorphic rocks (oldest) Intrusive igneous rocks Sedimentary rocks lying on an irregular metamorphic surface Sedimentary layering Erosion of the canyon (Youngest event) Rocks of the Grand Canyon Each group of rocks is separated by a gap in the geologic record (formations and contacts) Metamorphic rocks Metamorphism Granite Intrusion of silicic magma Eroded surface Uplift and erosion Sedimentary rocks Shallow inland seas Erosion of the Canyon Recent uplift Metamorphic and Igneous Rocks Metamorphism of sedimentary rocks Igneous intrusion during later stages of metamorphism (during mountain building) Uplift and erosion (during and after mountain building) (nonconformity) Sedimentary Rocks Deposition of sediments on eroded metamorphic and igneous rocks. Uplift and erosion exposing sedimentary layers and Eventually expose Igneous and metamorphic rocks again G Uplift and Renewed Erosion Erosion and Exposure Uplift and erosion exposing sedimentary layers and Eventually Igneous and metamorphic rocks again G Uplift and Renewed Erosion G Uplift and Renewed Erosion Formation of the Grand Canyon Sandstone Shale Limestone 350 380 450 Million Years Old 300 million years ago Formation of the Grand Canyon 1. Regional Uplift, Tilting (or folding), Erosion Erosion Sandstone Shale Limestone 350 380 450 280 million years ago Regional Uplift Tilting (or folding) Formation of the Grand Canyon 1. Regional Uplift, Tilting (or folding), Erosion Erosion Sandstone Shale Limestone 350 380 450 270 million years ago Regional Uplift Formation of the Grand Canyon 1. Regional Uplift, Tilting (or folding), Erosion Erosion Sandstone Shale Limestone 350 380 450 260 million years ago Regional Uplift Formation of the Grand Canyon 1. Regional Uplift, Tilting (or folding), Erosion Erosion Sandstone Shale Limestone 350 380 450 250 million years ago Regional Uplift 1. Regional Uplift, Tilting, or folding) causes Erosion 2. Erosion surface indicates gap in geologic record Formation of the Grand Canyon Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 240 million years ago 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation Formation of the Grand Canyon Sedimentation (e.g., clay) Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 220 million years ago 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation Formation of the Grand Canyon Sedimentation (e.g., lime mud) Shale (220) Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 210 million years ago 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation Formation of the Grand Canyon Sedimentation (e.g., quartz sand) Limestone (210) Shale (220) Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 200 million years ago 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation Formation of the Grand Canyon Quartz Sandstone (200) Limestone (210) Shale (220) Sedimentation (e.g., immature sand) Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 190 million years ago 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation Formation of the Grand Canyon Quartz Sandstone (200) Limestone (210) Shale (220) Arkose (190) Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 180 million years ago 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation 4. Sedimentation ceases Formation of the Grand Canyon Quartz Sandstone (200) Limestone (210) Shale (220) Arkose (190) Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 170 million years ago Formation of the 1. Erosion of horizontal beds Grand Canyon Quartz Sandstone (200) Limestone (210) Shale (220) Arkose (190) Erosion Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 160 million years ago Formation of the Grand Canyon Quartz Sandstone (200) Limestone (210) Shale (220) Arkose (190) 1. Erosion of horizontal beds 2. Loss of geologic record (i.e., Arkose) 3. Formation of a horizontal erosion surface Erosion Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 150 million years ago Formation of the Grand Canyon Quartz Sandstone (200) Limestone (210) Shale (220) 1. Erosion of horizontal beds 2. Loss of geologic record (i.e., Arkose) 3. Formation of a horizontal erosion surface 4. Renewed Sedimentation Arkose Sedimentation (e.g., reef) (190) Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 140 million years ago Formation of the Grand Canyon Quartz Sandstone (200) Limestone (210) Shale (220) 1. Erosion of horizontal beds 2. Loss of geologic record (i.e., Arkose) 3. Formation of a horizontal erosion surface 4. Renewed Sedimentation Arkose (190) Limestone (140) Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (280) Gabbro (790) 130 million years ago Formation of the Grand Canyon Quartz Sandstone (200) Limestone (210) Shale (220) 1. Erosion of horizontal beds 2. Loss of geologic record (i.e., Arkose) 3. Formation of a horizontal erosion surface 4. Renewed Sedimentation Arkose (190) Limestone (140) Sandstone 350 Shale 380 Limestone 450 Gneiss (1,500) Granite (290) Gabbro (790) 120 million years ago Formation of the Grand Canyon Deciphering Relative Ages Limestone Quartz Sandstone Limestone Shale Sandstone Shale Limestone Principles give sequences of geologic events Unconformities indicate gaps in the geologic record Disconformity Angular Unconformity Gneiss Granite Gabbro Nonconformities Uplift and Erosion As the land is lifted up by tectonic forces A stream will attempt to maintain its base level by Cutting down into the rocks due to accelerated erosion The Grand Staircase Eastern Zion National Park