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 produced on the Earth’s surface as a result of weathering. Sediments are transported and become sedimentary rocks after they come to rest. Sediments are transported and become sedimentary rocks after they come to rest. Sedimentary rocks give evidence of ancient sedimentary environments where they formed. 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
Lecture Outline 6. Classification of siliciclastic sediments and sedimentary rocks 7. Classification of chemical and biological sediments and sedimentary rocks
urface Processes and the Rock Cycle 1. Surface Processes and the Rock CycleWeathering Physical weathering Chemical weathering
Surface Processes and the Rock Cycle 1. Surface Processes and the Rock Cycle Processes forming sedimentary rock: WeatheringErosionTransportation Deposition (sedimentation) Burial and compaction Diagenesis
Surface Processes and the Rock Cycle 1. Surface Processes and the Rock Cycle
Classification of sediments Siliciclastic sediments Chemical sediments Biological sediments
Surface Processes and the Rock Cycle 1. 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 1. Surface Processes and the Rock Cycle Chemical mixing vats: OceansLakes
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.
2.Sedimentary Basins 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.
2.Sedimentary Basins 2. Sedimentary Basins Types of sedimentary basins: Rift basins and thermal subsidence basins Flexural basins
Sedimentary basins form on rifted continentalmargins
Environments of siliciclastic sediments: Continental (alluvial, desert, lake, and glacial) Shoreline (deltas, beaches, and tidal flats) Marine (shelf, margin, slope, and deep sea)
3.edimentary Environments 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
Ripples – modern and ancient
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?
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: CompactionCementation
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: ArkoseLithic Quartz arenite Graywacke
7. Classification of Chemical and Biological Sediments, Sedimentary Rocks Chemical sedimentary rocks LimestoneChertOrganicsPhosphorite
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, 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 LimestonesDolostones
7. Classification of Chemical and Biological Sediments, Sedimentary Rocks Evaporite sediments and rocks MarineNon-marine
7. Classification of Chemical and Biological Sediments, Sedimentary Rocks Other sediments and rocks SiliceousPhosphorite 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.
Arkose Bedding sequence Bioclastic sediment Biological sediment Bioturbation Carbonate rock Carbonate sediment Cementation Chemical sediment Chemical weathering ChertClayClaystoneCoalCompaction Key terms and concepts
Conglomerate Continental shelf Cross-bedding Crude oil DiagenesisDolostone Evaporite rock Evaporite sediment Flexural basin Foraminifera Graded bedding GravelGraywacke Iron formation Limestone Key terms and concepts
Lithic sandstone LithificationMudMudstone Natural gas Oil Organic sedimentary rock PeatPhosphorite Physical weathering Porosity Quartz arenite Reef Rift basin Ripple Key terms and concepts