Rocks Formed by Surface Processes Grotzinger • Jordan Understanding Earth Sixth Edition Chapter 5: SEDIMENTATION: Rocks Formed by Surface Processes © 2011 by W. H. Freeman and Company

Rocks Formed by Surface Processes 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.

Lecture Outline 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

Lecture Outline 6. Classification of siliciclastic sediments and sedimentary rocks 7. Classification of chemical and biological sediments and sedimentary rocks

Surface Processes and the Rock Cycle Weathering Physical weathering Chemical weathering

Surface Processes and the Rock Cycle Processes forming sedimentary rock: Weathering Erosion Transportation Deposition (sedimentation) Burial and compaction Diagenesis

Surface Processes and the Rock Cycle

Surface Processes and the Rock Cycle Classification of sediments Siliciclastic sediments Chemical sediments Biological sediments

Surface Processes and the Rock Cycle Current strength and distance of transport affect: Size of clastic particles Sorting of clastic particles Rounding of clastic particles

Surface Processes and the Rock Cycle Chemical mixing vats: Oceans Lakes

Thought questions for this chapter 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 support this? 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.

Sediments tend to accumulate in depressions in the Earth’s crust. 2. Sedimentary Basins Sediments tend to accumulate in depressions in the Earth’s crust. Depressions are formed by subsidence. 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

3. Sedimentary Environments Types of environments: 1. Continental Lake Alluvial Desert Glacier

3. Sedimentary Environments Types of environments: 2. Shoreline Delta Beach Tidal flats

3. Sedimentary Environments Types of environments: 3. Marine Deep sea Continental shelf Organic reef Continental margin Continental slope and slope

Sedimentary Environments

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)

3. Sedimentary Environments Environments of chemical and biological sediments: Carbonate deposits (organic reefs, beaches, shelves, and tidal flats) Siliceous environments (deep sea) Evaporite environments (lakes)

Thought questions for this chapter 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

Ripples – modern and ancient

Bioturbation Structures

4. Sedimentary Structures Bedding sequences – vertically stacked layers of sedimentary rock with different types of sedimentary structures in each layer.

Example of a Bedding Sequence

Thought questions for this chapter 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?

Burial is the preservation of sediments within a sedimentary basin. 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.

Lithification includes: Compaction Cementation 5. Burial and Diagenesis Lithification includes: Compaction Cementation

Thought questions for this chapter 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

6. Classification of Siliciclastic Sediments and Sedimentary Rocks Four major compositional groups of siliciclastic sediments: Arkose Lithic Quartz arenite Graywacke

7. Classification of Chemical and Biological Sediments, Sedimentary Rocks Chemical sedimentary rocks Limestone Chert Organics Phosphorite

7. Classification of Chemical and Biological Sediments, Sedimentary rocks Biological sedimentary rocks Dolostone Iron formation Evaporite

Organic Reef Development

Organic Reef Rock

7. Classification of Chemical and Biological Sediments, Sedimentary Rocks Carbonate sediments and rocks Evaporite sediments and rocks Other sediments and rocks

7. Classification of Chemical and Biological Sediments, Sedimentary Rocks Carbonate sediments and rocks Limestones Dolostones

7. Classification of Chemical and Biological Sediments, Sedimentary Rocks Evaporite sediments and rocks Marine Non-marine

7. Classification of Chemical and Biological Sediments, Sedimentary Rocks Other sediments and rocks Siliceous Phosphorite Iron oxide Coal and peat

Thought questions for this chapter What role do organisms play in the origin of some types of limestone? 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.

Key terms and concepts Bedding sequence Bioclastic sediment Arkose Bedding sequence Bioclastic sediment Biological sediment Bioturbation Carbonate rock Carbonate sediment Cementation Chemical sediment Chemical weathering Chert Clay Claystone Coal Compaction

Key terms and concepts Continental shelf Cross-bedding Crude oil Conglomerate Continental shelf Cross-bedding Crude oil Diagenesis Dolostone Evaporite rock Evaporite sediment Flexural basin Foraminifera Graded bedding Gravel Graywacke Iron formation Limestone

Key terms and concepts Lithification Mud Mudstone Natural gas Oil Lithic sandstone Lithification Mud Mudstone Natural gas Oil Organic sedimentary rock Peat Phosphorite Physical weathering Porosity Quartz arenite Reef Rift basin Ripple

Key terms and concepts Salinity Sand Sandstone Sedimentary basin Sedimentary environment Sedimentary structure Shale Siliciclastic sediments Silt Siltstone Sorting Subsidence Terrigenous sediment Thermal subsidence basin