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. 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 Measuring stratigraphic sections

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 (sorw) • 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 < 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 dcosssin a) +/- s (sin scosd) • 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