FROM SEDIMENT INTO SEDIMENTARY ROCK. Objectives. Sediments and Sedimentation

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1 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

2 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

3 Clastic sediment Clastic sediment Clastic sediment Glacial till: poorly sorted Well sorted, well rounded, quartz sand 3

4 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

5 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

6 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

7 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

8 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 8

9 Evaporites Bedrock geology of Lower Michigan _Bedrock_Geology_Map.Pdf 9

10 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

11 Coquina Figure 7.9 Chalk White Cliffs of Dover 11

12 Depositional Environments Interpreting environmental clues Patterns formed by air and water moving over sediments Preserved and later exposed Ripple marks Fossils Mud cracks Ripple marks Characteristics-fossils Fossiliferous limestone 12

13 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

14 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

15 Chesapeake Bay: An Estuary 15

16 Great Barrier Reef Depositional environments in and near the ocean Carbonate platform in the Bahamas 16

17 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 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) 17