Look at the block diagram below. Are there any unconformities below? Age? How old is layer B? How old is layer G? How many sets of faulting events are recorded above? What is the sense of shear of the faults? What is the age of the faulting event(s) Look at the block diagram below. Use it to talk about the answers to the questions with your neighbors

Are there any unconformities below? Age? How old is layer B? How old is layer G? How many sets of faulting events are recorded above? What is the sense of shear of the faults? What is the age of the faulting event(s)

Are there any unconformities below. Age Are there any unconformities below? Age? Angular unconformity, between 50 Ma and 22 Ma How old is layer B? How old is layer G? How many sets of faulting events are recorded above? What is the sense of shear of the faults? What is the age of the faulting event(s)

Are there any unconformities below. Age Are there any unconformities below? Age? Angular unconformity, between 50 Ma and 22 Ma How old is layer B? Between 60 Ma and 50 Ma How old is layer G? How many sets of faulting events are recorded above? What is the sense of shear of the faults? What is the age of the faulting event(s)

Are there any unconformities below. Age Are there any unconformities below? Age? Angular unconformity, between 50 Ma and 22 Ma How old is layer B? Between 60 Ma and 50 Ma How old is layer G? Between 70 Ma and 60 Ma How many sets of faulting events are recorded above? What is the sense of shear of the faults? What is the age of the faulting event(s)

Are there any unconformities below. Age Are there any unconformities below? Age? Angular unconformity, between 50 Ma and 22 Ma How old is layer B? Between 60 Ma and 50 Ma How old is layer G? Between 70 Ma and 60 Ma How many sets of faulting events are recorded above? 2 What is the sense of shear of the faults? What is the age of the faulting event(s)

Are there any unconformities below. Age Are there any unconformities below? Age? Angular unconformity, between 50 Ma and 22 Ma How old is layer B? Between 60 Ma and 50 Ma How old is layer G? Between 70 Ma and 60 Ma How many sets of faulting events are recorded above? 2 What is the sense of shear of the faults? First trust sense, then normal sense What is the age of the faulting event(s)

Are there any unconformities below. Age Are there any unconformities below? Age? Angular unconformity, between 50 Ma and 22 Ma How old is layer B? Between 60 Ma and 50 Ma How old is layer G? Between 70 Ma and 60 Ma How many sets of faulting events are recorded above? 2 What is the sense of shear of the faults? First trust sense, then normal sense What is the age of the faulting event(s) 1 – between 50 and 22 Ma, 2 – between 20 and 15 Ma

3-D geometry of geological layers True thickness versus apparent thickness of dipping beds The Folding Line: a graphical approach to solving 3-D problems with simple geological layers HW1 and Visible Geology

True vs Apparent thickness The two layers in the block diagram to the right have the exact same true thickness, but very different apparent thicknesses on the horizontal surface (map view). So, what if all you have is a geologic map and strike/dip of beds? Can you calculate the true thickness of those units? Why would you want to?

Clark Ls example problem The Clark limestone bed strikes N40°E and dips 30° SE. On a horizontal ground surface, the apparent thickness is 60 m. See attached map.   1. What is the true thickness of the limestone bed? 2. A driller suspects that there is water in the Clark limestone. A well site has been located 220 m due south of a surface exposure of the top of the limestone. At what depth will the limestone be hit in the drill hole? 3. In a different part of the map area, the Clark limestone bed crops out on the side of a hill, sloping down to the northwest. How will the apparent thickness of the bed in this area compare with that seen on the horizontal surface?

FL should be perpendicular to the strike

Draw layer contacts at the dip angle in the dip direction across the FL

Now measure off the true thickness with your ruler Now measure off the true thickness with your ruler. Convert cm to m using the known scale.

Draw well location on the map to scale

Well will be vertical at depth Well will be vertical at depth. Draw a line from well to bed that will represent this.

Measure “d”, the depth of the well to limestone.

Use folding line to imagine how the bed would look cut on a NW dipping slope

3-D block diagrams with Visible Geology http://app.visiblegeology.com/home.html