FROM SEDIMENT INTO SEDIMENTARY ROCK
Objectives
• Identify three types of sediments. • Explain where and how chemical and biogenic sediments form. • Explain three processes that lead to the lithification of sediments. • Explain how features such as ripples, cracks, and fossils tell geologists about the environment in which a rock originated. • Identify plate tectonics that are favorable for the accumulation of sediments.
Sediments and Sedimentation
• Deposition – The laying down of sediment • Sediment separated into three broad categories – Clastic – Chemical – Biogenic
1 Sediments and Sedimentation
Sediments and Sedimentation
• Clastic sediment – Sediment formed from fragmented rock and mineral debris – Produced by weathering and erosion – Described by particle shape, angularity, and size
• Clastic sediment – Volcaniclastic sediments • Volcanic in origin • Pyroclasts – Distinguished by size » Bombs » Lapilli » Ash
2 Clastic sediment
Clastic sediment
Clastic sediment
Glacial till: poorly sorted Well sorted, well rounded, quartz sand
3 Sediments and Sedimentation • Chemical sediment – Sediment formed by the precipitation of minerals dissolved in lake water, river water, or sea water – Plants and animals alter chemical balance • Limestone – Shallow sea water evaporation causes dissolved salts to precipitate
Sediments and Sedimentation
• Biogenic sediment – Sediment that is primarily composed of plant or animal remains • Shells, bones, teeth • Wood, roots, leaves – Or, precipitates as a result of biologic processes: foraminifer in the head of a pin
Sedimentary Rocks • Lithification – The processes by which loose sediment is transformed into sedimentary rock • Bedding – The layered arrangement of strata in sediment/sedimentary rock • Bedding surface – The top or bottom surface of a rock stratum or bed
4 Lithification Processes
Lithification Processes
Lithification Processes
• Compaction – Reduction of pore space in a sediment as a result of the weight of overlying sediments • Cementation – Substances dissolved in pore water precipitate out and form a matrix in which grains of sediments are joined together
5 Lithification Processes • Recrystallization – The formation of new crystalline mineral grains
What kind of sediment?
• How do you know? • How do you know?
Compare textures of a sedimentary rock with an igneous rock (granite)
6 Types of Sedimentary Rocks • Clastic sedimentary rock – Conglomerate • Has large fragments in a finer grained matrix – Sandstone • Medium grained, where clasts are typically, but not necessarily, dominated by quartz grains – Mudstone • A very fine grained sedimentary rock of the same composition as shale but without fissility – Shale • A very fine grained fissile or laminated sedimentary rock, consisting primarily of clay sized particles
Conglomerate
Figure 7.6
Quartz sandstone
Figure 7.4
7 Breccia
Figure 7.7
Shale with plant remains
Figure 7.2
Types of Sedimentary Rocks
• Chemical sedimentary rocks – Evaporite • Formed by the evaporation of lake water or sea water, followed by lithification of the resulting salt deposit – Banded iron formation • A type of chemical sedimentary rock rich in iron minerals or silica
Bedrock geology of Lower Michigan
http://www.deq.state.mi.us/documents/deq-glm-rcim-geology- 1987_Bedrock_Geology_Map.Pdf
9 Travertine-Mammoth Hot Springs, Yellowstone NP
Banded Iron Formation (BIF)
Types of Sedimentary Rocks
• Biogenic sedimentary rocks – Limestone • A sedimentary rock that consists primarily of the mineral calcite – Peat • Formed from the accumulation and compaction of plant remains – Coal • A combustible rock formed from the lithification of plant-rich sediment
10 Coquina
Figure 7.9
Chalk
White Cliffs of Dover
11 Depositional Environments
• Interpreting environmental clues – Patterns formed by air and water moving over sediments Ripple marks • Preserved and later exposed – Ripple marks – Fossils – Mud cracks
Characteristics-fossils
Fossiliferous limestone
12 Mud cracks
Depositional Environments on Land
Depositional Environments on Land • Streams • Lakes – Delta • A sedimentary deposit, commonly triangle shaped, that forms where a stream enters a standing body of water – Glacier – Wind • Eolian sediment – Sediments that are carried and deposited by the wind
13 Depositional Environments on Land
Delta Old Lake bed
Lacustrine sediments-Lake Michigan Bluffs
Depositional environments in and near the ocean • Delta • Estuary – Semi-enclosed body of coastal water, in which fresh water mixes with sea water • Beaches • Shelves • Carbonate platforms and reefs Green beach due to olivine
14 Chesapeake Bay: An Estuary
Depositional environments in and near the ocean
Carbonate platform in the Bahamas
16 Depositional environments in and near the ocean • Turbidites – A turbulent, gravity driven flow consisting of a mixture of sediment and water, – Conveys sediment from the continental shelf to the deep sea • http://www.youtube.com/watch?v=tfNLI2JW7mg&NR=1 • Seafloor – Rich in nutrients • Calcareous ooze • Siliceous ooze
Deep sea sediments deposited by turbidity current (turbidite)
How Plate Tectonics Affect Sedimentation
• Divergent plate boundaries – Rift valleys • A linear, fault-bounded valley along a divergent plate boundary or spreading center • Convergent plate boundaries – Collisional type – Subduction type • Back-arc basin • Accretionary wedges • Ophiolites (slabs of oceanic lithosphere)
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