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Chapter 8: From Sediment to Sedimentary Rock Carbonate reef off coast of the Bahamas © 2012 John Wiley & Sons, Inc. All rights reserved. Learning Objectives Sediment • Describe the three major types of sediment and their formation. Transport and deposition of sediment • Describe the process of deposition, including where and how it takes place. Sedimentary rock • Discuss the lithification of sediment into different types of rock. How plate tectonics affects sedimentation • Contrast what happens to sediment in different plate tectonics settings. © 2012 John Wiley & Sons, Inc. All rights reserved. Sediment Sediment is separated into three broad categories: • Clastic • Chemical • Biogenic © 2012 John Wiley & Sons, Inc. All rights reserved. Sediment Figure 8.1 From clasts to rocks © 2012 John Wiley & Sons, Inc. All rights reserved. Sediment Clastic Sediment Clastic sediment • • • Sediment formed from fragmented rock and mineral debris Produced by weathering and erosion Described by particle shape, angularity, and size © 2012 John Wiley & Sons, Inc. All rights reserved. Sediment Figure 8.2a Sorting © 2012 John Wiley & Sons, Inc. All rights reserved. Sediment Figure 8.2b Roundness © 2012 John Wiley & Sons, Inc. All rights reserved. Sediment Figure 8.2c Till, poorly sorted Figure 8.2d Well-sorted quartz sand © 2012 John Wiley & Sons, Inc. All rights reserved. Sediment Clastic Sediment • • Clasts: grains of mineral or rock fragments Volcaniclastic sediments • Volcanic in origin • Pyroclasts are distinguished by size: • Bombs • Lapilli • Ash Figure 6.1 Volcanoclasts © 2012 John Wiley & Sons, Inc. All rights reserved. Sediment Chemical and Biogenic Sediment Chemical sediment • Sediment formed by the precipitation of minerals dissolved in lake water, river water, or sea water. • Plants and animals alter chemical balance: • Limestone deposits • Shallow sea water evaporation causes dissolved salts to precipitate. Figure 8.3a Chemical Sediment © 2012 John Wiley & Sons, Inc. All rights reserved. Sediment Chemical and Biogenic Sediment Biogenic sediment • Sediment that is primarily composed of plant or animal remains • Shells, bones, teeth • Wood, roots, leaves • Or, sediment precipitates as a result of biologic processes Figure 8.3b Biogenic sediments © 2012 John Wiley & Sons, Inc. All rights reserved. Transport and Deposition of Sediment Transportation of sediment by: • Water • Wind • Ice • Mass wasting Figure 8.4 Transport of sediment © 2012 John Wiley & Sons, Inc. All rights reserved. Transport and Deposition of Sediment Deposition • The laying down of sediment Figure 8.5 Depositional environments © 2012 John Wiley & Sons, Inc. All rights reserved. Transport and Deposition of Sediment Figure 8.5, part 3 Delta Figure 8.5, part 4 Playa © 2012 John Wiley & Sons, Inc. All rights reserved. Transport and Deposition of Sediment Figure 8.5, part 5 Sand dunes © 2012 John Wiley & Sons, Inc. All rights reserved. Transport and Deposition of Sediment Depositional Environments on Land Streams Lakes Glaciers Wind • Eolian sediment Figure 8.6 Soil from the last Ice Age © 2012 John Wiley & Sons, Inc. All rights reserved. Transport and Deposition of Sediment Depositional Environments in and Near the Ocean Deltas and estuaries • Estuary: Semi-enclosed body of coastal water, in which fresh water mixes with seawater Beaches Shelves Carbonate platforms and reefs © 2012 John Wiley & Sons, Inc. All rights reserved. Depositional Environments in and Near the Ocean Figure 8.7a Delta Figure 8.7b Beach © 2012 John Wiley & Sons, Inc. All rights reserved. Transport and Deposition of Sediment Depositional Environments in and Near the Ocean Turbidity current •A turbulent, gravity-driven flow consisting of a mixture of sediment and water •Conveys sediment from the continental shelf to the deep sea Seafloor is rich in nutrients: •Calcareous ooze •Siliceous ooze © 2012 John Wiley & Sons, Inc. All rights reserved. Depositional Environments in and Near the Ocean Figure 8.7c Carbonate reef Figure 8.7d Deep-sea turbidites © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Rock Beds Lithification • The processes by which loose sediment is transformed into sedimentary rock Bedding • The layered arrangement of strata in sediment/sedimentary rock Bedding surface • The top or bottom surface of a rock stratum or bed Figure 8.8 Layers of rock: bedding © 2012 John Wiley & Sons, Inc. All rights reserved. Rock Beds Figure 8.9 Clues to bed’s origin © 2012 John Wiley & Sons, Inc. All rights reserved. Rock Beds Figure 8.9 Clues to bed’s origin © 2012 John Wiley & Sons, Inc. All rights reserved. Rock Beds Ancient dunes © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Lithification Compaction • Reduction of pore space in a sediment as a result of the weight of overlying sediments Cementation • Substances dissolved in pore water precipitate out and form a matrix in which grains of sediments are joined together Figure 8.10 Lithification © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Lithification Recrystallization • The formation of new crystalline mineral grains Figure 8.10 Recrystallization © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Types of Sedimentary Rocks Clastic sedimentary rock • • • • Conglomerate has large fragments in a finer-grained matrix. Sandstone is medium-grained, where clasts are typically, but not necessarily, dominated by quartz grains. Mudstone is a very fine-grained sedimentary rock of the same composition as shale but without fissility. Shale is a very fine-grained fissile or laminated sedimentary rock, consisting primarily of clay-sized particles. © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary or Igneous? Sedimentary or Igneous? Sedimentary or Igneous? How do you know? How do you know? © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Types of Sedimentary Rocks Chemical sedimentary rocks • • Evaporite • Formed by the evaporation of lake water or sea water, followed by lithification of the resulting salt deposit Banded iron formation • A type of chemical sedimentary rock rich in iron minerals or silica © 2012 John Wiley & Sons, Inc. All rights reserved. Types of Sedimentary Rocks What a Geologist Sees: A Change in the Atmosphere © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Types of Sedimentary Rocks Biogenic sedimentary rocks •Limestone • A sedimentary rock that consists primarily of the mineral calcite •Peat • Formed from the accumulation and compaction of plant remains •Coal • A combustible rock formed from the lithification of plant-rich sediment © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Interpreting Environmental Clues Figure 8.12a Ripples Figure 8.12b Ripple marks © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Interpreting Environmental Clues Figure 8.12c Mudcracks Figure 8.12d Mudcracks preserved in rocks © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Interpreting Environmental Clues Figure 8.13 Seagull footprints Figure 8.13 Fossilized footprints © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Rock Interpreting Environmental Clues Figure 8.14 Fossil fern found in Greenland from the Triassic Period © 2012 John Wiley & Sons, Inc. All rights reserved. Sedimentary Facies Figure 8.15 One sedimentary environment changes over time © 2012 John Wiley & Sons, Inc. All rights reserved. How Plate Tectonics Affect Sedimentation Divergent plate boundaries • Rift valleys • A linear, fault-bounded valley along a divergent plate boundary or spreading center Convergent plate boundaries • Collisional type • Subduction type • Back-arc basin • Accretionary wedges • Ophiolites © 2012 John Wiley & Sons, Inc. All rights reserved. How Plate Tectonics Affects Sedimentation Figure 8.17 Accretionary wedge © 2012 John Wiley & Sons, Inc. All rights reserved. Critical Thinking • If oxygen from cyanobacteria caused iron to precipitate billions of years ago, then what is your hypothesis as to why silica precipitated? • Estuaries are generally shallow, yet there are thick accumulations of estuarine sediments in the geologic record. What hypothesis can you suggest to explain this? © 2012 John Wiley & Sons, Inc. All rights reserved.