Geologic Cross-Sections

Cross Sections are Based on Surface and Sub-Surface Data

Sub-Surface Interpretation (3-D)

Constructing a Cross-Section choose a line of section (perpendicular to structures)

Cross-Section Construction Cont… 2. transfer topographic data (topographic profile with no vertical exaggeration)

Structural Data – (Apparent) Dips 3. add structural data to the topographic profile

Add the Geology! 4. add geologic data (contacts) to the profile; dash in eroded structures above present-day topography

Apparent Dip

True Dip & Apparent Dip

Apparent to True Dip Trigonometry = apparent dip = angle between strike and apparent dip direction = true dip

Calculating Apparent Dip from True Dip ( )

Apparent Dip “Nomogram”

True Dip to Apparent Dip – the Easy Way!

Cross Section “Rules” calculate apparent dips of beds that are not perfectly perpendicular to your section line DO NOT use vertical exaggeration don’t extrapolate structural data too far from your section line dash in eroded structures above the present-day topography don’t extend dip data more than a few hundred meters in depth