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SUBMERGENCE and EMERGENCE of Rock Layers with Respect to Sea Level

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SUBMERGENCE and EMERGENCE of Rock Layers with Respect to Sea Level SUBMERGENCE AND EMERGENCE of Rock Layers With Respect to Sea Level The building up and wearing away of Earth's Crust. Follow the progression of illustrations to see the roles that submergence and emergence of rock layers play in both the addition of rock material to earth's surface as well as its removal. The Key: Be sure to look at the key before observing the Illustration 1: Sedimentary Rocks are typically layered series of illustrations. horizontally and the Law of Superposition dictates that, Notice that not only do symbols exist for sandstone, shale unless overturning of rock layers has occurred, the oldest and conglomerate, but also for the loose sediments that rock layers are towards the bottom of a rock column while will eventually lithify to become these rock types. the youngest layers are at the top. This illustration depicts layers of sedimentary shale, sandstone and limestone, exposed at earth's surface. Illustration 2: The rock layers have been submerged, Illustration 3: Over time the processes of compaction possibly due to crustal movement or to a rise in sea level. and cementation will lithify these loose sediments turning All rock layers are now underwater and there exists the them into sedimentary rocks. The newly lithified rock possibility for additional, loose sediments to be deposited layer will be on top of the original layers shown in on top of the preexisting layers. Illustration 1 and it will be the youngest layer by L. Immoor 2006 Geoteach.com 1 comparison. Notice the unconformity in this illustration. The unconformity is evidenced by the wavy, eroded top surface of a rock layer. An unconformity is a gap in the geologic record. Rocks are missing either because they were never deposited during a geologic time period or because they were eroded away. In the case of this illustration, rocks did exist but they were removed due to the processes of weathering and erosion. Unconformites exist when eroded rock layers have additional rocks on top of them. They are "buried erosional surfaces". We do not use the term unconformity to refer to rocks exposed at the earth's surface that are undergoing present-day erosion. Illustration 4: A lowering of sea level or crustal uplift Illustration 5: As weathering and erosion continues to may eventually cause the 4 layers to emerge above sea wear away at the rock layers over time, new landforms level exposing them to the earth's atmosphere and take shape. Large quantities of rock material have been making them vulnerable to the processes of weathering removed and one can see a valley flanked by plateaus and erosion. where there once existed flat, level rock layers. Illustration 6: Submergence below sea level occurs Illustration 7: The rock layers are still submerged and once again. The "valley" fills in with new unconsolidated the additional sediments have been lithified into sediment as rivers bring their bedload for deposition in sedimentary rock. There are now 2 unconformities the ocean. present between rock layers. L. Immoor 2006 Geoteach.com 2 They will be the basis for new layers of sedimentary rock. The clays will become shale, the sand will turn into sandstone and the larger, mixed pebbles, cobbles and boulders will become conglomerate. Illustration 8: Emergence takes place once again and Illustration 9: Present-day erosion of rocks exposed at now 7 rock layers are present. At this point, over time earth's surface continues, shaping the crust into rocks have submerged and emerged twice. Now exposed mountains, plateaus, valleys, etc.. at earth's surface and vulnerable to the atmospheric effects of wind, rain, temperature, etc., rock layers will Notice the 2 arrows pointing to the buried erosional weather and erode. The conglomerate, being at the top, is surfaces. These are unconformities. initially the most vulnerable to erosion. Notice the arrow pointing to "Present-Day Erosional Surface". This is not an unconformity since no additional rock layers were ever deposited on that particular conglomerate layer. Also, it is not a buried erosional surface, but rather an exposed rock layer undergoing erosion. NEXT PAGE Telling the Geologic Story of Illustration 9 This lesson and all graphic images are © L. Immoor Geoteach.Com, Geolor 2006 You may need to print this lesson using Landscape Orientation. L. Immoor 2006 Geoteach.com 3.
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