Understanding Earth, Eighth Edition, Chapter 6 PDF

John Grotzinger Thomas H. Jordan Understanding Earth EIGHTH EDITION t Lecture Slides CHAPTER 6 Sedimentation: Rocks Formed by Surface Processes Copyright © 2020, W.H. Freeman and Company  About Sedimentation...

John Grotzinger Thomas H. Jordan Understanding Earth EIGHTH EDITION t Lecture Slides CHAPTER 6 Sedimentation: Rocks Formed by Surface Processes Copyright © 2020, W.H. Freeman and Company  About Sedimentation Sediments are produced on Earth’s surface as a result of weathering. Sediments are transported and become sedimentary rocks after they come to rest. Sedimentary rocks give evidence of ancient sedimentary environments where they formed.  Lecture Outline 1. Surface processes of the rock cycle 2. Sedimentary basins: the sinks for sediments 3. Sedimentary environments 4. Sedimentary structures 5. Burial and diagenesis: from sediment to rock 6. Classification of siliciclastic sediments and sedimentary rocks 7. Classification of chemical and biological sediments and sedimentary rocks 1. Surface Processes of the Rock Cycle (1 of 5) Processes forming sedimentary rock: Weathering Erosion Transportation Deposition (sedimentation) Burial and compaction Diagenesis 1. Surface Processes of the Rock Cycle (2 of 5) Weathering Physical weathering Chemical weathering  1. Surface Processes of the Rock Cycle (3 of 5) Figure 6.1 1. Surface Processes of the Rock Cycle (4 of 5) Classification of sediments Siliciclastic sediments Chemical sediments Biological sediments  1. Surface Processes of the Rock Cycle (5 of 5) Current strength and distance of transport affect: Size of clastic particles Sorting of clastic particles Rounding of clastic particles  Sorting of sand Well-sorted sand Poorly sorted sand Figure 6.6  Rounding of sand Figure 6.7  Derivation of sand TABLE 6.1 Minerals Present in Sediments Derived from a Granite Outcrop Under Varying Intensities of Weathering Intensity of Weathering: LOW Intensity of Weathering: MEDIUM Intensity of Weathering: HIGH Quartz Quartz Quartz Feldspar Feldspar Clay minerals Mica Mica Pyroxene Clay minerals Amphibole 1. Surface Processes of the Rock Cycle Chemical mixing vats: Oceans Lakes Thought questions for this chapter (1 of 5) A geologist is heard to say that a particular sandstone was derived from a granite. What information could she have gleaned from the sandstone to lead her to that conclusion? Weathering of the continents has been much more widespread and intense in the past 10 million years than it was in earlier times. How might this be borne out in the sediments that now cover Earth’s surface? Describe the beach sands that you would expect to be produced by the beating of waves on a coastal mountain range consisting largely of basalt.  2. Sedimentary Basins Sediments tend to accumulate in depressions in Earth’s crust. Depressions are formed by subsidence. Sedimentary basins are depressions filled with thick accumulations of sediment. They are sinks for sediment.  2. Sedimentary Basins – Types Types of sedimentary basins: Rift basins and thermal subsidence basins Flexural basins  Sedimentary basins form on rifted continental margins Figure 6.8  3. Sedimentary Environments – Continental Types of environments: Lake Alluvial Desert Glacier  3. Sedimentary Environments – Shoreline Types of environments: Delta Beach Tidal flats 3. Sedimentary Environments – Marine Types of environments: Deep sea Continental shelf Organic reef Continental margin and slope  Sedimentary Environments Figure 6.9  3. Sedimentary Environments – I Environments of siliciclastic sediments: Continental (alluvial, desert, lake, and glacial) Shoreline (deltas, beaches, and tidal flats) Marine (shelf, margin, slope, and deep sea)  3. Sedimentary Environments – II Environments of chemical and biological sediments: Carbonate deposits (organic reefs, beaches, shelves, and tidal flats) Siliceous environments (deep sea) Evaporite environments (lakes) TABLE 6.2 Major Chemical and Biological Sedimentary Environments ENVIRONMENT AGENT OF PRECIPITATION SEDIMENTS Shoreline and Marine Carbonate (reefs, Shelled organisms, some Carbonate sands and muds, platforms, deep sea, etc.) algae; inorganic precipitation reefs from seawater Evaporite Evaporation of seawater Gypsum, halite, other salts Siliceous (deep sea) Shelled organisms Silica Continental Evaporite Evaporation of lake water Halite, borates, nitrates, carbonates, other salts Wetland Vegetation Peat Thought questions for this chapter (2 of 5) From the base upward, a bedding sequence begins with a bioclastic limestone, passes upward into a dense carbonate rock made of carbonate-cementing organisms, and ends with beds of dolostone. Deduce the possible sedimentary environments represented by this sequence. In what sedimentary environment are carbonate muds? How can you use size and sorting of sediments to distinguish between sediments deposited in a glacial environment and those deposited in a desert? Where are reefs likely to be found?  4. Sedimentary Structures Sedimentary structures – all kinds of features in sediments formed at the time of deposition. Bedding (stratification) Cross-bedding Graded bedding Ripples Bioturbation structures  Cross-bedding Figure 6.11  Ripple marks Figure 6.13  Ripples – modern and ancient Figure 6.12  Bioturbation structures Figure 6.14  4. Sedimentary Structures – Bedding Bedding sequences – vertically stacked layers of sedimentary rock with different types of sedimentary structures in each layer.  Example of a bedding sequence Figure 6.15 Thought questions for this chapter (3 of 5) You are looking at a cross section of rippled sandstone. What sedimentary structure would tell you the direction of current that deposited the sand? You discover a bedding sequence that has a conglomerate at the base; grades upward into sandstone and then to a shale; and finally, at the top, grades to a limestone. What changes in the sediment source area would have been responsible for this sequence?  5. Burial and Diagenesis Burial is the preservation of sediments within a sedimentary basin. Diagenesis is the physical and chemical change that converts sediments to sedimentary rocks.  5. Burial and Diagenesis – Lithification Includes: Compaction Cementation  Process of diagenesis - I Figure 6.16  Process of diagenesis - II Figure 6.16  Process of diagenesis - III Figure 6.16 Figure 6.16 Thought questions for this chapter (4 of 5) If you drilled one oil well into the bottom of a sedimentary basin that is 1 km deep and another that is 5 km deep, which would have the higher pressures and temperatures? Oil turns into natural gas at high basin temperatures. In which well would you expect to find more natural gas?  6. Classification of Siliciclastic Sediments and Sedimentary Rocks Classification of sediments by particle size Classification of sedimentary rocks by texture and composition  6. Classification of Siliciclastic Sediments and Sedimentary Rocks – Common Rocks TABLE 6.3 Major Classes of Siliciclastic Sediments and Sedimentary Rocks PARTICLE SIZE SEDIMENT ROCK Coarse-Grained Gravel Larger than 256 mm Boulder 256–64 mm Cobble Conglomerate 64–2 mm Pebble Medium-Grained 2-0.062 mm Sand Sandstone Fine-Grained Mud 0.062–0.0039 mm Silt Siltstone Mudstone (blocky fracture) Finer than 0.0039 mm Clay Shale (breaks along bedding) Claystone Figure 6.19a Figure 6.19b Figure 6.19c 6. Classification of Siliciclastic Sediments and Sedimentary Rocks – Groups Four major compositional groups of siliciclastic sediments: Arkose Lithic Quartz arenite Graywacke  Mineralogy of sandstone groups Figure 6.20  7. Classification of Chemical and Biological Sediments, Sedimentary Rocks – Chemical Chemical sedimentary rocks: Limestone Chert Organics Phosphorite Figure 6.22a Figure 6.22b Figure 6.22c Figure 6.22d  7. Classification of Chemical and Biological Sediments, Sedimentary Rocks – Biological Biological sedimentary rocks: Dolostone Iron formation Evaporite  TABLE 6.4 Classification of Biological and Chemical Sediments and Sedimentary Rocks SEDIMENT ROCK CHEMICAL COMPOSITION MINERALS Biological Sand and mud (primarily bioclastic) Limestone Calcium carbonate (CaCO3) Calcite, aragonite Siliceous sediment Chert Silica (SiO2) Opal, chalcedony, quartz Peat, organic matter Organics Carbon compounds; carbon (Coal, oil, natural gas) compounded with oxygen and hydrogen No primary sediment (formed by Phosphorite Calcium phosphate (Ca3(PO4)2) Apatite diagenesis) Chemical No primary sediment (formed by Dolostone Calcium-magnesium carbonate Dolomite diagenesis) (CaMg(CO3)2) Iron oxide sediment Iron formation Iron silicate; oxide (Fe2O3); Hematite, siderite limonite, carbonate Evaporite sediment Evaporite Calcium sulfate (CaSO4); sodium Gypsum, anhydrite, halite, chloride (NaCI) other salts Marine organisms/carbonate platforms Figure 6.23  The reef at Bora Bora Box 6.1 7. Classification of Chemical and Biological Sediments, Sedimentary Rocks – Groups Carbonate sediments and rocks Evaporite sediments and rocks Other sediments and rocks  7. Classification of Chemical and Biological Sediments, Sedimentary Rocks – Carbonates Carbonate sediments and rocks: Limestones Dolostones  7. Classification of Chemical and Biological Sediments, Sedimentary Rocks – Evaporites Evaporite sediments and rocks: Marine Non-marine  Evaporite formation in the Mediterranean Sea Figure 6.25  7. Classification of Chemical and Biological Sediments, Sedimentary Rocks – Other Groups Other sediments and rocks: Siliceous Phosphorite Iron oxide Coal and peat Thought questions for this chapter (5 of 5) What role do organisms play in the origin of some types of limestone? Compare the sediments formed in shallow environments with those formed in deep sea environments. A bay is separated from the open ocean by a narrow, shallow inlet. What kind of sediment would you expect to find on the floor of the bay if the climate were warm and arid? What kind of sediment would you find if the climate were cool and humid? How are chert and limestone similar in origin? Discuss the roles of biological versus chemical processes.