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 Sediment textures- size, shape, and arrangement Sorting
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 ( ) slate
high ( ) 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. Geochronology How old is the Rock? How can we tell the age of rocks?
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- the present 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
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