111-17 - GY 111 Lecture Notes D Haywick(2008-09 1 GY 111...

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GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111 Lecture Note Series Sediment, sedimentary rocks and sediment transport Lecture Goals A) Types of Sediment B) Sedimentary Rock Classification C) Sediment Transport Reference: Press et al., 2004, Chapter 8; Grotzinger et al., 2007, Chapter 5, p 111-120 GY 111 Lab manual Chapter 3 A) Types of sediment Last time we discussed weathering and the development of soil. Remember: soil is a product of weathering that occurs in situ (i.e., in place). Soils are mostly the product of chemical weathering and almost always contain significant organic material. If you have already committed the rock cycle cartoon to memory, you will remember that the sedimentary component involves several important processes: 1) weathering, 2) erosion/ transportation and 3) lithification. We have already dealt with weathering and will deal with lithification in an upcoming lecture. Today we will concentrate on the erosion and transportation of sediment, but not until we sort out the types of sediments that occur on the surface of the Earth and how geologists classify sedimentary rocks. There is a lot of different types of sediment. All that material derived from the weathering of bedrock is just one type. In general, geologists recognize 4 types of sediment: 1) siliciclastic 2) biochemical (also called bioclastic ) 3) chemical 4) organic Siliciclastic sediment is sediment that is dominated by silicate minerals like quartz, feldspar and clay minerals (the silic component of siliciclastic). That the sediment is usually derived from the break up of bedrock (weathering) is the reason why we classify it as silici clastic . Remember pyroclastic rocks from last week? Clastic means broken up bits of rock. Biochemical (or bioclastic) sediment is mostly produced from the remains of living animals. Shells and skeletons produced by many forms of marine life (e.g., clams, oysters, corals) produce hard body parts that are primarily composed of CaCO 3 . There are two polymorphs of this substance. One you have already seen in the lab ( calcite ). The other is aragonite . When sediment is dominated by aragonite and calcite, we classify it as biochemical or bioclastic ( bio- life; clastic broken up material). It should also be noted that CaCO 3 is not the only material used by beasties to produce skeletons or shells. Silica and various phosphate minerals are also used, just not as often. Note: Depending upon the semester, some of the material that is scheduled for this lecture (e.g., some aspects of sedimentary rock classification), may not be discussed today. Sometimes it is discussed during a lab lecture in place of a lecture lecture.
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