news and information partner list posted gas up vans before tomorrow morning leave some space in...
Post on 31-Dec-2015
213 Views
Preview:
TRANSCRIPT
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
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
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
Denver, CO strat column
Geologic ages along left Split columns for extra
thick sections Weathering profile Capture lithologic
variability within units
Phosphoria Fm.
Graphical representation of thickness
Text description of important lithological characteristics
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
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
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 () Bedding dip () Traverse orientation ()
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
Simplest case of section measurement
Horizontal land surface
Traverse normal to strike
Constant dip t = w sin
Measurement techniques
Hewett (1920) method
T
E
No need to measuresurface slope angle ordistance!
T = E cos
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
Hewett method procedure For the measured dip or apparent dip,
calculate how much section thickness is equal to one eyeheight
T = E cos 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
top related