12: Stratigraphy
Stratigraphy is the study of the geometric relationships, composition, origin, age, and relationships between stratified rocks deposited at the surface of the Earth. We will begin with an overview of different types of unconformities and geologic contacts and then move on to a discussion of the most common approaches to subdivide and classify sedimentary rocks. These schemes are based on lithology (lithostratigraphy), depositional trends (sequence stratigraphy), or seismic reflection data (seismic stratigraphy).
- Identify different types of contacts and unconformities and explain their implications for reconstructing the geologic history of an area.
- Identify and describe the different types of lithostratigraphic contacts and units.
- Describe a complete sea level cycle using sequence stratigraphic terminology and the concepts of accommodation and sediment supply.
Chapter thumbnail shows a relative sea level curve ( Page Quinton via Wikimedia Commons ; CC BY-SA 4.0 ).
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- 12.1: Review of unconformities and other types of contacts
- The three major types of unconformities are angular unconformities (angular discordance between layers), nonconformities (sedimentary deposited atop deep-formed crystalline rocks), and disconformities (sedimentary atop sedimentary with no obvious angular discordance). Recognition of contact metamorphism can help distinguish an intrusive contact from an unconformity.