Basic Stratigraphic Concepts (Chapter 2) Flashcards
Principle of Uniformitarianism
- present physical laws and geological processes occurring today also occurred in the past.
- Ex: gravity
Principle of Original Horizontality
most sediments or extrusive igneous rocks are deposited in horizontal layers
Principle of Lateral Continuity
rocks extends in all direction until they end allows for correlation of rock units across different areas
Principle of Superposition
- where a sequence of rocks is undisturbed:
- oldest sedimentary rock layer is at bottom
- youngest at top
- allows for relative dating of when the layer is formed compared to each other
Principle of Cross-Cutting
- when layers or geological features cut across layers of rocks or sediments, features are younger than rocks they cut
- ex: intrusive dike is younger than layers of rock it cuts
Principle of Inclusion
- rocks found within other rocks must be older than rocks that incorporate them
- ex: sandstone pieces that cut part of the mudstone are older than matrix
Principle of Fossil Succession
organisms existed on Earth change over time rock layer that contains older fossils is older than rock layer containing younger fossils
Correlation
- matching of rock units base on shared similarities
- similarities: lithology, fossils found, age, environment of deposition, or stratigraphic location
Lithostratigraphic unit
based on rock characteristics
e.g. mineralogy, grain size
time-stratigraphic unit
an interval of rock, based on the time it was created
unconformity
gaps in succession of rocks, older may have been folded & uplifted before younger layer
conformity
no apparent disruption in deposition of sediments appeared to have occurred