Geology G100 Quick review for Test #2

1. Geology G100 Quick review for Test #2 Dr. Isiorho, IPFW

2. Sedimentation and Sedimentary Rocks • What is a sedimentary rock? Dr. Isiorho, IPFW

3. Sediments Sediments are loose fragments of solid materials- pre-existing rocks, remains of organisms, and precipitation of minerals • Sediment textures- size, shape, and arrangement • are determined by transportation and depositional processes • Sorting • selecting particle based on size, shape and density • Shape • angular or irregular grains become rounded • longer travels lead to more rounding of grains Dr. Isiorho, IPFW

4. From Sediments to Sedimentary Rocks Pressure, heat, and underground circulating water produce changes in rocks- known as Diagenesis • Lithification- conversion of loose sediments into solid sedimentary rocks • Compaction- weight of overlying materials • Cementation- mineral precipitated in pore spaces • Recrystallization- less stable minerals change to new stable minerals Dr. Isiorho, IPFW

5. Sedimentary Structures Physical features that reflect condition of deposition (how and where?) • Beddings (stratification) • sediments in distinct layers- separate depositional environments • Graded beddings • deposition occurs in relatively quiet waters • Cross bedding • sedimentary layers at an angle to underlying layers • Ripple marks • small surface ridges- produced by water or wind • Symmetrical & Asymmetrical • Mud crack • muddy sediments that dry and contracts • Bioturbation • No drawing provided  Dr. Isiorho, IPFW

6. Classification of Sedimentary Rocks Detrital and Chemical • Detrital-based on grain size • Mudstone- clay and silt size- constitute > 50% of all detrital sedimentary rocks • Shale- clay and silt size particles- parallel layers- fissility • Siltstone- silt size particles • Sandstone- quartz arenite, arkose (with ~ 25% feldspar), graywacke (lithic, dark fragments & fines) • Breccia- angular gravel size particles • Conglomerate- rounded gravel size particles Dr. Isiorho, IPFW

7. Sed. rock Classification contd. • Chemical- organic and inorganic • Organic- derived from living organism/biogenic • Limestone and chert- composed of skeletal remains of animals • coal- carbon rich remains of terrestrial plants • Inorganic Sedimentary Rocks • Direct precipitation from water • e.g. Limestone, chert • Evaporation of saline water • evaporite- gypsum, halite, dolostone Dr. Isiorho, IPFW

8. Sedimentary Environments • Continental • rivers, lakes, caves, desert, glaciers- mostly detrital • Transitional- coastal- along ocean shores • estuaries and deltas • Marine • shallow-above continental shelf (< 200m (700’)) • deep- beyond the continental shelf • Sedimentary Facies- sediments deposits at the same time but in different environments as a horizontal continuum of distinct rock type Dr. Isiorho, IPFW

9. Metamorphic Rocks • Altered rocks Dr. Isiorho, IPFW

10. Definitions • Metamorphic rock is formed when existing rocks change due to subjection to pressure and or temperature • Any rock can undergo metamorphism • Metamorphism is the process by which heat, pressure, and chemical reactions deep within the earth alter the mineral content and or structure of existing rock without melting it down Dr. Isiorho, IPFW

11. What Drives Metamorphism • Heat • Accelerate pace of chemical reactions • Pressure • Lithostatic (confining)- rock becomes smaller and denser • Directed- minerals become aligned- Foliation • Circulating Fluids • Ions in water- change mineral composition • Parent Rocks • Original rock’s composition will affect the outcome of metamorphism Dr. Isiorho, IPFW

12. Types of Metamorphism • Contact • Heat is the dominant factor • Area affected generally smaller than regional metarmorphism • Regional are two types with extensive coverage • Burial- occurs in deep sedimentary basins- no plate tectonics involved • Dynamothermal- occurs where converging plates squeeze a rock caught between them • Others • Hydrothermal- involves hot water from magma • Fault-zone- rocks grinding past one another • Shock- meteorites strike • Pyrometamorphism- lightning Dr. Isiorho, IPFW

13. Metamorphic Rock Types • Foliated- based on type of foliation • Slate- fine grain • Phyllite- fine grain with sheen • Schist- has ‘split’ appearance • Gneiss- layers/bands of minerals • Non-foliated- based on mineral composition • Marble • Quartzite • Hornsfel • Mixed Rock • Migmatite- indicates partial melting Dr. Isiorho, IPFW

14. Metamorphism Temperature & Pressure Information about degree to which a metamorphic rock differs from its parent material • Metamorphic Grade- • low (200-400) slate • high (500-800) gneiss • Index minerals/metamorphic Zones are used to determine metamorphic condition of temperature and pressure • Chlorite, muscovite-low grade (low P/T) • Garnet, staurolite- intermediate • Sillimanite- high grade (high P/T) Dr. Isiorho, IPFW

15. How old is the Rock? • How can we tell the age of rocks? • Geochronology Dr. Isiorho, IPFW

16. Geochronology Geochronology is the study of time in relation to earth’s existence • Relative Dating • Determines how old a rock is in relation to its surrounding • Numerical Dating (Absolute Age?) • Determines actual age in years Dr. Isiorho, IPFW

17. Relative Dating Relies on Key Principles such as • Uniformitarianism- thepresent is key to the past • Original horizontality • Sediments deposited in horizontal layers • Superposition • Youngest rocks are on top (assuming no tectonic activity) • Cross-cutting relationships • Cut layer is older than ‘cutting’ rock • Faunal succession • Organisms succeed one another in recognizable reproducible pattern • Unconformity • Represents a break (gap) in the rock record Dr. Isiorho, IPFW

18. Numerical Age Isotope Dating relies on the rate of decay of radioactive isotopes within a rock • Radioactive isotopes have nuclei that spontaneously decay emitting or capturing a variety of subatomic particles • Decaying radioactive isotope- parent isotopes decay to form daughter isotopes • Half-life- is the time it takes for half the atoms of parent isotope to decay • Some radioactive isotopes with daughter products • U-238 => Pb-206; K-40 => Ar-40; C-14 => N-14 Dr. Isiorho, IPFW

19. Factors Affecting Isotope Dating Results • Isotope dating is more useful for igneous rocks • Clock is set when igneous rock crystallizes locking the radioactive isotopes within its crystal lattice • Rock/Mineral must be a closed system • Atoms of parent and daughter are still present in rock/mineral being dated • Condition of parent Material • Fracture, weathering and migrating ground water • Age of Substance • Enough measurable daughter isotope, use appropriate radioactive isotope Dr. Isiorho, IPFW

20. Other Numerical Dating Techniques • Fission Track • High speed particles emitted during radiation may pass through crystal leaving ‘tears’ within the crystal- the older the rock, the more fission tracks • Dendrochronology (Tree-Ring dating) • Annual growth rings • Varve- deposited layers of lake-bottom • Paired layers of sediments • Lichenometry • Lichens grow at a fairly constant rate • Cosmogenic isotopes • Used in dating land features Dr. Isiorho, IPFW

21. Geologic Time Scale Contrasting several dating techniques chronicling Earth’s history to produce a geologic Time Scale • Geologic Time Scale- divided into Eons, Eras, Periods, and Epoches • Phanerozoic Eon (evidence of life began) divided into three eras • Paleozoic (ancient life) dominated by marine invertebrates • Mesozoic (middle life) dominated by reptiles • Cenozoic (recent life) dominated by mammals Dr. Isiorho, IPFW

22. The Earth moves • It’s not an earthquake…but the earth materials Dr. Isiorho, IPFW

23. Mass Movement • Process that transports Earth’s materials downslope by the pull of gravity • Friction, strength, and cohesiveness of materials resist mass movement • Angle of slope (sloppiness), water content, lack of vegetation, and biological disturbances enhance mass wasting Dr. Isiorho, IPFW

24. Causes of Mass Movement • Steepness of Slope • Faulting, folding, river cut, glacial, coastal wave create steep slope • Composition of Material either promotes or resists mass wasting • Solid /Unconsolidated • Vegetation- lack of which promotes mass wasting • Water Content- increases weight of material and reduces friction between planes of weakness • Human/Other Disturbances Dr. Isiorho, IPFW

25. Triggers for Mass Movement Events • Natural Triggers • Climatic- torrential rains and snow melt • Geologic- earthquakes and volcanic eruptions • Human-Induced Triggers • Oversteeping of slopes- excavation • Overloading- excess water, building, and other construction • Deforestation/overgrazing of vegetation • Loud noise- trains, aircrafts, blasting Dr. Isiorho, IPFW

26. Mass Wasting Types Classification is based on composition and velocity • Creep- slowest form • Slides- move along a plane of weakness • Slumps- move along concave slip surfaces • Flows- rocks and soils have with excess water • Falls- fastest type Landslide is a general term for downslope movement Dr. Isiorho, IPFW

27. Reducing Mass Movement • Avoiding • Predicting mass movement • Terrain analysis, field visit, eye witness/recorded accounts • Vegetation- over grazing, harvesting • Preventing • Develop Prevention Plan • Enhance Forces that Resist or Reduce forces of mass wasting • Structural Approach- reduce slope • Non-Structural Approach- tree, chemical stability Dr. Isiorho, IPFW

28. Study for Test #2 • Use the class notes/textbook and the links provided in the syllabus. • It’s an open book test and the “Honor System” prevails…no help from any one, no collaboration Dr. Isiorho, IPFW

29. Some key words for Test #2 • Some key words for test #2 • Cementation, crystallization, Compaction • Transportation of sediments results in….. • Rock salt, sandstone, siltstone, coal, arkose, graywacke • Quartzite, marble, slate, schist, migmatite, order of metamorphism • Types of metamorphism, parent materials of some metamorphic rocks • Relative age and principles of Superposition, original horizontality, faunal succession, cross-cutting, unconformities, radiometric dating, half life.. Dr. Isiorho, IPFW