BIG THREE PART 2
Topography and Geology
Discussion begins from a hypothetical location on a mesa and describes the landscape leading to a river valley.
Geology vs. Topography:
While observably visible to the naked eye, topography is merely the surface features of the land.
Geologists seek to understand deeper geological formations beyond just the topographic features.
Geological Composition and Processes
The view of the river valley reveals layers of sedimentary rock units as the primary focus.
Geologists utilize various methods for examining geological strata:
Drilling: Bringing drill rigs to extract subsurface materials.
Road Cuts: Natural or man-made cuts through the earth expose geological layers.
Examination reveals that rock layers contain a complex sequence reflecting a series of geological events.
Rock Units Examination
Predominantly dealing with Sedimentary Rocks:
Rocks formed via deposition, lithification (hardening), and environment of deposition.
Examples include:
Sand deposited into Sandstone (unit h):
Represents high-energy environments like beaches.
Clay deposited into Claystone (shale):
Indicates low-energy depositional environments like lagoons.
Sequence of Events in Geological History
Unit H (Oldest):
Initial deposition of sand, forming sandstone.
Example: If located in San Diego, possibly named Torrey Sandstone.
Change in Depositional Environment:
Transition from sand deposition to clay, representing a lower energy environment (lagoon).
Unit E:
Further deposition, possibly of silty muds, on top of the clay from the lagoon environment.
Changing Conditions Again:
New layers accumulate, indicating further transitions in environmental conditions for different sediment deposits.
Folding and Faulting:
Units H, G, F, E, and D experienced geological forces resulting in folding (anticline formations) and faulting.
Importance to oil reserves, especially in areas like the LA Basin (Wilmington Oil Field).
Erosion and Unconformities
Evidence suggests that erosional events and unconformities occurred affecting the previous layers:
Erosion Surface: A period where sediments were removed, comprised of running water, glaciers, or other natural processes.
The existence of an unconformity:
Indicates gaps in geological history where deposition did not occur continuously.
Implications for Understanding Earth's Geological History
Gaps in the geologic record indicate periods where material was lost or that deposition was interrupted by erosion.
The complexity of layering, folding, and faulting must be understood to effectively interpret earth's history in relation to time.
Important to recognize that geological history cannot be represented by a singular column of continuous deposition.
Key Takeaways
Complex geological history requires competencies in understanding:
Stratigraphic layers, sediment types, environments of deposition, forces acting on rock units, and periods of erosion.
Geology is a science that uses logical deduction and observation to reconstruct Earth's history, rather than relying on isolated explanations.