Understanding Earth Fifth Edition

Transcription

1 Understanding Earth Fifth Edition Grotzinger Jordan Press Siever Chapter 5: SEDIMENTATION: Rocks Formed by Surface Processes Lecturer: H Mohammadzadeh Assistant professors, Department of Geology, FUM Copyright 2007 by W. H. Freeman and Company Chapter 5 Sedimentation: Rocks Formed by Surface Processes About Sedimentation Sediments are produced on the 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. 1

2 Lecture Outline 1. Sedimentary rocks; surface processes 2. Sedimentary basins 3. Sedimentary environments 4. Sedimentary structures 5. Burial and diagenesis 6. Siliciclastic classification 7. Chemical and biological classification 1. Sedimentary rocks are produced by surface processes in the rock cycle. Processes forming sedimentary rock Weathering (Physical and Chemical weathering) Erosion Transportation Deposition (sedimentation) Burial and compaction Diagenesis Some sedimentary environments Glacier River Delta Desert Lakes and playas Marine shelf 2

3 Sedimentary environments Glacier Delta Desert Playa lake Sedimentary rocks Metamorphic rocks Plutons Processes forming sedimentary rock Weathering breaks down rocks. Erosion carries away particles. Transportation moves particles downhill. Glacier Delta Desert Playa lake Deposition occurs when particles settle out or precipitate. Sedimentary rocks Metamorphic rocks Plutons Burial occurs as layers of sediment accumulate. Diagenesis causes lithification of the sediment, making sedimentary rocks. 3

4 1. Sedimentary rocks are produced by surface processes in the rock cycle. Classification of sediments (Siliciclastic, Chemical and Biological sediments) Current strength and distance of transport affect: Size, sorting and rounding of clastic particles. 4

5 2. Sedimentary basins Sediments tend to accumulate in depressions, which are formed bysubsidence in the Earth s crust. Sedimentary basins are depressions filled with thick accumulations of sediment. They are sinks for sediment. Types of sedimentary basins: Rift basins and thermal subsidence basins Flexural basins Sedimentary basins form on rifted continental margins 5

6 3. Sedimentary environments Types of environments: Continental Lake River (alluvial) Desert Glacier Shoreline Delta Tidal flat Beach Marine Continental shelf Organic reef Continental margin Continental slope Deep sea 6

7 3. Sedimentary environments 3. Sedimentary environments Environments of siliciclastic sediments: Continental (alluvial, desert, lake, and glacial) Shoreline (deltas, beaches, and tidal flats) Marine (shelf, margin, slope, and deep sea) Environments of chemical and biological sediments: Carbonate deposits (organic reefs, beaches, shelves, and tidal flats) Siliceous environments (deep sea) Evaporite environments (lakes) 7

8 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 8

9 Cross-bedding 9

10 Bioturbation structures Bedding sequences vertically stacked layers of sedimentary rock with different types of sedimentary structures in each layer. 10

11 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. 11

12 5. Burial and diagenesis Lithification includes: Compaction and Cementation 12

13 6. Classification of siliciclastic sediments and sedimentary rocks Classification of sediments by particle size Classification of sedimentary rocks by texture and composition 13

14 Four major compositional groups of siliciclastic sediments: Arkose, Lithic, Quartz arenite, Graywacke 7. Classification of chemical and biological sedimentary rocks Biological sedimentary rocks: Dolostone, Iron formation and Evaporite 14

15 Organic reef development 15

16 Key terms and concepts Iron formation Arkose Bedding Bedding sequence Bioclastic and biological sediment Bioturbation Carbonate environment Carbonate platform Carbonate sediment and rock Cementation and compaction Chemical and biological environment Chemical sediment Chemical weathering Chert Clastic sediment and clastic particle Clay and claystone Coal Conglomerate Cross-bedding Diagenesis Dolostone Evaporite rock and sediment Gas Graded bedding Gravel Graywacke Limestone Lithification Mud and mudstone Oil Organic sedimentary rock Peat Physical weathering Porosity Quartz arenite Reef Rift basin Ripple Salinity Sand and sandstone Sedimentary basin Sedimentary environment Sedimentary structure Shale Siliciclastic sediment Siliciclastic sedimentary environment Silt and siltstone Sorting Subsidence Weathering 16