News and information

1
News and information

• Partner list posted
• Gas up vans before tomorrow morning
• Leave some space in your notebook
• NIU students with yellow GPS come see me with
  your unit

2
Practical field procedures

• Estimate total thickness of section
• Graphical or trigonometric
• Determine level of detail for your description
• Depends on purpose
• Determine section starting and ending points
• Walk entire section if time permits
• Determine measurement method

3
Organizing your notebook

• Purpose for day
• What is the level of detail you are aiming for?
• Geographic location
• Method used
• Starting and ending point descriptions
• Scale for graphical column

4
Notebook layout
5
Denver, CO strat column

• Geologic ages along left
• Split columns for extra thick sections
• Weathering profile
• Capture lithologic variability within units

6
Phosphoria Fm.

• Graphical representation of thickness
• Text description of important lithological
  characteristics

7
Measuring stratigraphic sections

• Why measure sections?
• Acquire fundamental geologic information
• Needed for basic characterization of an area
• Assist in mapping
• Facilitate correlations
• Establish relative ages
• Facies and sedimentologic analyses

8
Where do we measure sections?

• Is there a need?
• Basic geological characterization, mapping,
  correlations, facies analysis
• Good exposure
• Easy access
• Others can duplicate or examine your work
• Structurally simple
• Low potential for tectonic thickness variations

9
Variables in section measurement

• True thickness (T)
• Perpendicular distance from top to bottom
• Slope distance (s or w)
• Distance from top to bottom measured along the
  surface
• Surface slope (s)
• Bedding dip (d)
• Traverse orientation (a)

10
Sources of error

• Surface slope
• 2-5 degrees?
• Bedding dip
• 2-5 degrees?
• Surface distance
• 1-2?
• Traverse orientation
• 2-5 degrees?
• Strive for lt 10 total thickness error

11
Simplest case of section measurement

• Horizontal land surface
• Traverse normal to strike
• Constant dip
• t w sin d

12
General case of section measurement

• Seven possibilities

13
Measurement techniques

• Compass and Tape
• Must know s, d, s, a

14
Measurement techniques

• Hewett (1920) method

E
d
d
T
d
No need to measure surface slope angle
or distance!
T E cos d
15
Hewett method procedure

• Determine eyeheight
• Measure strike and dip of section to be measured
• Design traverse
• If normal to strike
• Set inclinometer to measured dip
• If oblique to strike
• Set inclinometer to apparent dip in the direction
  a

16
Hewett method procedure

• For the measured dip or apparent dip, calculate
  how much section thickness is equal to one
  eyeheight
• T E cos d
• Stand at base of section
• Site to new position along traverse
• Move to newly cited position
• Record T of stratigraphic thickness
• Repeat the above steps until reaching the top of
  the section
• Estimate thickness of last fraction of section

17
Mertie method

• Allows for traverses that are not normal to
  bedding strike
• T s (sin d cos s sin a) /- s (sin s cos d)
• Use () when slope and bedding dip in opposite
  directions
• Use (-) when slope and bedding dip in the same
  direction
• When a 90, this equation reduces to one of the
  general cases previously discussed