2Rocks Formed by Surface Processes Chapter 5Sedimentation:Rocks Formed by Surface Processes
3About SedimentationSediments 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.
4Lecture Outline Surface processes of the rock cycle 2. Sedimentary basins: the sinks for sediments3. Sedimentary environments4. Sedimentary structures5. Burial and diagenesis: from sediment to rock
5Lecture Outline6. Classification of siliciclastic sediments and sedimentary rocks7. Classification of chemical and biological sediments and sedimentary rocks
6Surface Processes and the Rock Cycle WeatheringPhysical weatheringChemical weathering
7Surface Processes and the Rock Cycle Processes forming sedimentary rock:WeatheringErosionTransportationDeposition (sedimentation)Burial and compactionDiagenesis
13Surface Processes and the Rock Cycle Chemical mixing vats:OceansLakes
14Thought 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.
15Sediments tend to accumulate in depressions in the Earth’s crust. 2. Sedimentary BasinsSediments 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.
16Types of sedimentary basins: Rift basins and thermal subsidence basinsFlexural basins
17Sedimentary basinsform on riftedcontinentalmargins
253. 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)
263. Sedimentary Environments Environments of chemical and biological sediments:Carbonate deposits (organic reefs, beaches, shelves, and tidal flats)Siliceous environments (deep sea)Evaporite environments (lakes)
28Thought 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?
294. Sedimentary Structures Sedimentary structures – all kinds of features in sediments formed at the time of deposition.Bedding (stratification)Cross-beddingGraded beddingRipplesBioturbation structures
38Thought 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?
39Burial is the preservation of sediments within a sedimentary basin. 5. Burial and DiagenesisBurial is the preservation of sediments within a sedimentary basin.Diagenesis is the physical and chemical change that converts sediments to sedimentary rocks.
40Lithification includes: Compaction Cementation 5. Burial and DiagenesisLithification includes:CompactionCementation
46Thought 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?
476. Classification of Siliciclastic Sediments and Sedimentary RocksClassification of sediments by particle sizeClassification of sedimentary rocks by texture and composition
486. Classification of Siliciclastic Sediments and Sedimentary Rocks
697. Classification of Chemical and Biological Sediments, Sedimentary RocksOther sediments and rocksSiliceousPhosphoriteIron oxideCoal and peat
70Thought 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.