ENVS 1060 Lecture Notes - Lecture 10: Biostratigraphy, Radiometric Dating, Absolute Dating
Document Summary
Describe the three main stratigraphic principles and how they can be applied. (ans). Another way of putting it is that the present is the key to the past. Although the analogy between the present and the past is correct it should be applied with caution because in older times, conditions at the earth"s surface were much different. Principle of original horizontality of rock layers: most sedimentary layers deposited on basin floors are horizontal or have a very low angle of incline. Exceptions occur,, for instance, in sediments deposited against glaciers, or in steep deltas at the head of fjords. However, these sediments usually contain slump features attesting to the particular setting they were deposited in. Principle of superposition: this principle states that in an undisturbed sequence of sedimentary rocks, the bottom layer is the oldest and the uppermost one is the youngest.