Laboratory eight dating of rocks fossils and geologic events
Read the introduction and carefully review stratigraphic principles (superposition, original horizontality, cross cutting, inclusions, fossil and strata correlation) on Pages 207-216 plus figure 8.10, the Geological time & fossil (faunal) succession chart with range zones p.213. Learn to recognize the three different types of unconformity and be able to estimate the relative amount of missing geological time for each type. Disconformity – erosion or non-deposition generally lasting years to millions of years. Angular unconformity needs deformation & erosion, ~millions of years or more. Nonconformity marks erosion clear down to crystalline basement rocks below the sedimentary basin.
Often this is the basal unconformity for an entire sedimentary basin.
The angle means the underlying rocks not only had time to be deposited and lithified, but also time enough to become folded, uplifted and eroded.
In any place on Earth we tend to find less complete records, but segments of shorter duration that preserve more detail for that interval of the stratigraphic record.
The photo above on the right is of the “Amherst Clay” from de-glacial lake Hitchcock (~10 Ka).
The rocks below are deformed igneous and metamorphic that are hundreds of millions to billions of years older than the overlying sedimentary succession.
This requires uplift and erosion on land of much of the upper continental crust.