Solution Exercise 4
Although it can be difficult to observe every important feature at this scale, some obvious structures stand out. In the photograph below, many of the regularly spaced vertical striations on the cliff are the result of digging/quarrying and do not reflect natural features.
The photograph shows some excellent examples of normal faults (highlighted in orange), the offset of which can be observed by the displacement of several marker beds. On the left-hand side, some larger high-angle joints are visible, which may be important pathways for groundwater and recharge. Many more fractures exist but are not visible at this scale.
Sedimentary structures such as cross-beds are also visible as the diagonally dipping beds in the center of the exposure. These structures can provide insight into the flow direction and environment during deposition. They may also affect fracture orientations and propagations, and the mechanical properties of the rock sometimes change from bed to bed.
Finally, several sequence stratigraphic boundaries and erosional surfaces (angular unconformities and disconformities) can be observed in the photograph, such as the boundaries at the top and bottom of the cross-bedded unit. Some are highlighted in red. These surfaces can also introduce significant mechanical contrasts in the rock sequence that can impact fracture propagation and connectivity. They have also been linked to hydrogeological unit boundaries in other sedimentary rock aquifers (Meyer et al., 2016).