Lecture Twenty Five - Sedimentary geology (basins)

Question 1

How do plate tectonics control surface processes?

Answer 1

Tectonic activity at plate margins produces significant topographic relief (highlands).

• Weathering and eroded by surface sedimentary processes.
• Largely based on topography, the Earths surface can be subdivided into distinct sedimentary environments.
• Tectonic/topographic features define sedimentary basins margins.

Therefore, plate tectonics is a fundamental influence on surface sedimentary systems on Earth.

Question 2

What is a basin?

Answer 2

A low area on the Earths surface relative to the surroundings.
Sediments tend to gravitate towards basins, and fill them - gravity.
E.g. a deep ocean or intramontane basin.
Mostly tectonic in origin (may be erosional in stable regions).
A ‘big bucket’ or receptacle for sedimentation.
May include multiple environments e.g. continental rift basins contain alluvial fan, river and lake environments.
Basins can be found in all tectonic settings (divergent, convergent, transform and intra-plate).

Question 3

Where do sediments come from?

Answer 3

Regions uplifted (via plate tectonics) are eroded by the motto of air and/or water and the influence of gravity.
These are transported to tractional and mass flow processes.
Most eroded sediments end up deposited and buttered in aqueous bodies (seas, lakes, oceans etc.).
The ‘Goldilocks zone:’
- Not too hot and not too cold = liquid water.
- Not too big and not too small = long term plate tectonics and retains a thick atmosphere.

Sedimentary geology starts where structural geology and climatology end.

Question 4

What is the hydrologic cycle?

Answer 4

Drives sedimentary transport.
Short circuited on a cold/dry planet.
Movement of water on Earth in relation to the land.

Question 5

What can a basin tell us?

Answer 5

Earths ancient surface environments are written in basin (sedentary) rocks.
The history of life on Earth.
Primary sources of todays energy reserves.
Extreme environmental conditions unlike todays conditions.

Question 6

Describe sedimentary environments.

Answer 6

Sedimentary environments are regions of sediment accumulation in sedimentary basins.
-> Most seminary basins contain several different environments.
These environments are distinct from adjacent environments by:
- Different environmental chemistry (water/soil/atmospheric etc.).
- Different styles of sediment transport and deposition (physical processes).
- And/or varying, ecologically sensitive faunal and floral (biological) assemblages.

Sedimentary environments leave distinctive sedimentary successions.

Question 7

What controls sedimentary environments?

Answer 7

What controls sedimentary environments?
Climate, tectonic activity volcanism, and human activity.

Tectonic processes: 
Topographic relief produced by tectonic processes. 
High relief promotes: 
- High erosion rates. 
- High sediment mass flux rates. 
- High energy erosional environments. 
Adjacent to mountains: 
- High energy depositional environments. 
E.g. Alluvial fans and braided rivers. 

Topographically low areas are tectonically stable.

• Low energy environments.
• -> meandering river systems, lakes, deltas, swamps, deep marine settings.
• -> E.g. the Mississippi, Amazon, Murray, Pacific basin.

Question 8

What are some sedimentary environments?

Answer 8

Continental: 
Mountains (erosional). 
Glacial environments. 
Alluvial fans and rivers (aka fluvial). 
Lakes (aka lacustrine). 
Deserts. 
Volcaic systems. 

Marine - aka 'paralic' environments  
Deltas. 
Lagoons. 
Tidal flats/intertidal. 
Beaches. 
Near shore - Littoral. 
Inner and outer shelf - Neritic. 
Reefs. 
Continental slope and rise - Pelagic. 
Abyssal plains - Pelagic. 
Volcanic systems - Pelagic.