Geological Sciences 100

EARTH SYSTEM I:
GEOLOGICAL ENVIRONMENT

Lecture XVII. Breaking Rocks

A) Unconformities	B) Rock Fractures
C) Rock Faults

A) Unconformities

Figure 17.1 (1) Elements of an unconformity. (2) Disconformity. (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).
- disconformity
- nonconformity
  
  Figure 17.2 Nonconformity - Cambrian sedimentary rocks overlying Precambrian granite (MO).
- angular unconformity
  
  Figure 17.3 Origin of angular unconformity (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).
  
  Figure 17.4 Angular unconformity, nonconformity and disconformities of the Grand Canyon - looking downstream near the mouth of Shinamo Creck.
  
  Figure 17.5 Angular unconformity in Tennessee sandstone.
- Ohio unconformities beneath where we sit.
  
  Figure 17.6 Ohio unconformities.

B) Rock Fractures

joints ==> fractures along which no appreciable movement occurred

Figure 17.7 Modern mudcracks with imprinted raindrops (Lisbon Valley, UT).

Figure 17.8 Columar basalt dike with spheriodal weathering (Hatfield, WI).

Figure 17.9 Joints in sandstone along interstate 90 near Tomah, WI.
faults ==> fractures along which appreciable movement occurred

Figure 17.10 Right lateral strike slip faulting.

C) Rock Faults

nomenclature & movements

Figure 17.11 Fault nomenclature (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).

Figure 17.12 Fault movements (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).
normal (= tension) & reverse (= compression) faults

Figure 17.13 Dip-slip faults, normal and reverse.

Figure 17.14 Vertical fault in Precambrian slates (Wausau, WI).

Figure 17.15 Normal faulting of metamorphosed graded bedding (Metagreywacke Mbr, Lake Vermilion Fm near Tower, MN).

Figure 17.16 Reverse faulting of graded beds of Metagreywacke Mbr (Lake Vermilion Fm, Tower, MN).

Figure 17.17 Schematic of cliff formed during the Miro - Owari earthquake, Japan, in 1891.

Figure 17.18 Mexican earthquake offsets roadway and produces small fault scarp.

Figure 17.19 Major types of faults.

Figure 17.20 Right lateral strike slip movement of the San Andreas Fault.

Figure 17.21 Left lateral strike slip movement of the Trenuing Fault (Calexico, CA) revealed by an orange grove 30 years after it was planted.

Figure 17.22 Right lateral strike slip faulting.

Figure 17.23 Microfaulting in finely laminated siltstone (Carbondale Fm (Penn.), Montgomery Co., IL)
thrust faults

Figure 17.24 Chief Mountain (MT) - Precambrian rocks thrust from upper left over Cretaceous shales.

Figure 17.25 Stages in the development of an overthrust sheet as a result of folding and thrust faulting (from The Earth - An Introduction to Physical Geology (2nd ed.), by Tarbuck & Lutgens, Merrill Publishing Co., 1984).