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Lecture 3 Geologic Time, Sediments, and Sedimentary Rocks CEE 437 Engineering Geology I Oct. 8, 2002.

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Presentation on theme: "Lecture 3 Geologic Time, Sediments, and Sedimentary Rocks CEE 437 Engineering Geology I Oct. 8, 2002."— Presentation transcript:

1 Lecture 3 Geologic Time, Sediments, and Sedimentary Rocks CEE 437 Engineering Geology I Oct. 8, 2002

2 Sedimentary Rocks and Geologic Time Geologic Time Scale and it Origins Sedimentary Rock Types Depositional Environments Engineering Properties

3 Relative Time Principle of Superposition Fossil Evidence Cross Cutting Relationships Unconformities Alteration Fracture Termination


5 Geologic Time Scale — Eras Precambrian — Minimal fossil record Era, Period, Epoch Based on major changes — extinctions, mountain building events

6 Paleozoic (Old Life) — Brachiopods, Trilobites, Fish Periods based on English Geology Cambrian for Latin Wales Ordovician and Silurian for ancient Welsh Tribes Devonian for Devon Carboniferous for Coal Measures (also Mississippian and Pennsylvanian in US) Permian for Perm Basin in Ukraine

7 Mesozoic (Middle Life) — Ammonites, Dinosaurs Triassic based on distinctive three-layer stratigraphy in southern Germany Jurassic based on Jura Mountains in France and Switzerland Cretaceous (Latin for Chalk) based on chalk unit that forms Dover’s cliffs

8 Cenozoic (Recent Life) — Mammals, Modern marine fauna (foraminifera) Periods are Tertiary (before Ice Ages) and Quaternary (ice ages) Primary and secondary have been long replaces Rocks of western Washington are primarily Tertiary and Quaternary in age

9 Age of the Earth Kelvin and a basis in heat flow (set at 20 million years) Problem of fitting all of evolution in this time Rutherford and the introduction radioactive decay Added a head source, pushed ages back to 4.5 billion years

10 Absolute Time Basis on radiometric dating Common dating tools – 14 C, K-Ar, Rb-Sr,Uranium decay series

11 Sedimentary Rocks Clastics, Siliciclastics, Carbonates, and Evaporites Clastic rocks, depositional medium, and energy Diagenesis — chemical changes after deposition

12 Clastic Sedimentary Rocks Clastic — broken like iconoclast) Often referred to as Siliciclastics as having Si based rock forming minerals Based on grain size and to a lesser extent composition Grain size related to energy of depositional environment –Relationship of medium velocity to maximum grain size)

13 Clastic Sedimentary Rocks Clay, muds  shales, mudstones, claystones (difference based on fissility) Silts  siltstones Sands  sandstones Gravels  Conglomerates (Breccia if angular, breccia may also be a term for tectonically fragmented rock)

14 Weathering Cycle

15 Clastic Sediments


17 Classification of Sedimentary Rocks (ex. evaporites and coal)

18 Clay Minerals Sheets of linked silica tetrahedra sandwiching octahedral layers of gibbsite composition, Al 2 (OH) 6, or brucite Mg 3 (OH) 6 Major Clay Groups –kaolinite: single gibbsite layer –montmorillonite:weak water bonding between layers, moderated by Ca, Na, or K (near-shore environments) –illite: K bonds between layers (off-shore environments) –bentonite: highly expansive, volcanic-derived, Na-rich montmorillonite

19 Clay Structure

20 Clay Structure Cont’d. Kaolinite Illite Montmorillonite

21 Clay Plasticity

22 Lithification Cementation –deposition of a material different from clasts Crystallization –crystal growth on clasts to fill pore space Compaction Diagenesis –Early post-depositional chemical transformation of sediments, e.g. calcite to dolomite

23 Carbonates Generally like siliciclastics — carbonate muds, sands, etc. Often deposited in reefs Major portion of world oil deposits Properties depend strongly on post- depositional pore chemistry –Cementation –Dissolution

24 Carbonate Environments

25 Evaporites Rock salt (NaCl), Gypsum-Anhydrite (CaSO 4 ), Sylvite (KCl) Deposition in regions where evaporation exceeds recharge –desert lakes –restricted seas (Mediterranean) –lagoons, back-reef areas Subject to flow and diapirism

26 Other Sedimentary Rocks Chert: finely crystalline silica –as replacement/diagenetic nodules –as bedded material from silica-shelled biota Coal –Derived from vegetation Banded Iron Formation –Likely bacteria derived, mainly Pre-Cambrian

27 Sedimentary Rocks and Rock Properties Properties for a given geologic description vary wildly based on cementation, porosity and other diagenetic factors. Properties can be strong anisotropic and heterogeneous based on bedding

28 Expanding Sedimentary Materials Expanding clays (especially bentonite) Gypsum-Anhydrite hydration (CaSO 4 )

29 Depositional Environments Synchronicity of deposition of different rock types Sedimentary facies –A rock unit is not everywhere the same age: Bright Angel Shale Related to energy of environment – (example channels and banks in fluvial systems) Energy related to topography, climate, and tectonic activity

30 Sediment Sorting

31 Sedimentary Structures — Load Casts, Rip-ups, etc.

32 Sedimentary Structure — Cross Bedding

33 Fluvial and Lacustrine Environments Fluvial –Channelization –Complex and close interrelationship of fine and course sediments –Challenge for characterization due to high variability –Special examples: glacial environments Lacustrine –Deltaic deposits at margins, finer materials in lake beds

34 Deltaic Environments Variability based on proximity to source Stratigraphy effected by progradation

35 Deltaic Development and Sedimentary Facies

36 Continental Slope Environments Turbidites and turbidity currents Graded bedding –poor sorting –vertical zonation with fining upwards

37 Turbidites and Turbidity Currents Formed by mobilization of sediments on slopes Graded bedding (coarse at bottom, fining upwards)

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