Basic Stratigraphic Concepts (Chapter 2)

Question 1

Principle of Uniformitarianism

Answer 1

• present physical laws and geological processes occurring today also occurred in the past.
• Ex: gravity

Question 2

Principle of Original Horizontality

Answer 2

most sediments or extrusive igneous rocks are deposited in horizontal layers

Question 3

Principle of Lateral Continuity

Answer 3

rocks extends in all direction until they end allows for correlation of rock units across different areas

Question 4

Principle of Superposition

Answer 4

• 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

Question 5

Principle of Cross-Cutting

Answer 5

• 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

Question 6

Principle of Inclusion

Answer 6

• 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

Question 7

Principle of Fossil Succession

Answer 7

organisms existed on Earth change over time rock layer that contains older fossils is older than rock layer containing younger fossils

Question 8

Correlation

Answer 8

• matching of rock units base on shared similarities
• similarities: lithology, fossils found, age, environment of deposition, or stratigraphic location

Question 9

Lithostratigraphic unit

Answer 9

based on rock characteristics

e.g. mineralogy, grain size

Question 10

time-stratigraphic unit

Answer 10

an interval of rock, based on the time it was created

Question 11

unconformity

Answer 11

gaps in succession of rocks, older may have been folded & uplifted before younger layer

Question 12

conformity

Answer 12

no apparent disruption in deposition of sediments appeared to have occurred