Historical Geology - Sedimentary environments - terrestrial

Question 1

What are depositional environments?

Answer 1

• The combination of biological, chemical, and physical processes associated with the deposition of particular types of sediment (and therefore rocks).
• Do not include all environments on Earth
• Need net sediment accumulation
• Vast majority are shaped and molded through actions of water

Question 2

What do we mean by sediment entrainment?

Answer 2

Movement of sediment in a current (usually water, but can be air or ice)

Question 3

What are continental depositional environments also refered to as?

Answer 3

nonmarine environments

Question 4

What determines soil type?

Answer 4

Mineral and organic content, along with water regime.

Question 5

Soil can be preserved in rock records as what?

Answer 5

paleosols

Question 6

What is the devil’s corkscrew?

Answer 6

burrows of the terrestrial beaver Paleocastor

Question 7

List the 5 major continental depositional environments and describe each.

Answer 7

• soil
  
  • a loose collection of sediments and organic matter accumulated at earths surface.
• Glacial environments
  
  • can entrain any size of sediment
  • does not sort sediments by grain size
  • referred to as glacial till
• Lake (Lacustrian) environments
  
  • tend to be low energy environments
  • Coarse sediments settle out of suspension as water slows down at lake shore
  • Fine-grained sediments (fine sands, muds, and silts) settle out of suspension further from shore
  • Planar laminations and varves are typical sedimentary structures
• Desert environment
  
  • both wind and water involved in sediment movement (water still primary driver)
  • playa lake - closed basin (lake doesn’t drain anywhere)
• River (fluvial) environments
  
  • exist in wide variety of environments
  • produce a wide variety of sedimentary structures

Question 8

What is a varve?

Answer 8

an annual layer of sediment or sedimentary rock

Question 9

What is a braided river?

Answer 9

• Multiple channels that shift regularly

- Usually found at the base of glaciers and alluvial fans

Question 10

What is a Meandering or anastamosing River?

Answer 10

• Better developed channel than braided systems

- Channel migrates laterally

Question 11

What is Walther’s Law?

Answer 11

as depositional environments migrate laterally, facies (rock with specific characteristics) from different parts of the environment come to lie on top of one another