Weeks 8 and 9: Sedimentary Basins

• Sedimentary Basin

  • A sedimentary basin is any topographic depression which receives or has received sediment
  • It can accumulate sediments 1km to 10’s of km thick
  • Accumulate over 10’s to 100’s of millions of years
  • Mostly occur on the margins of continents and within continents
• Basin Classifications

  • Basins are classified based on their formation mechanism
  • Subsidence is a key requirement for basin formation and basins are classified according to their formation mechanism
  • 3 main causes of subsidence:
  • Changes in thermal regime (heating and erosion): when rocks are heated, they expand and uplift (isostasy), the top of which is then eroded, making the crust thinner. Sediments then begin to deposit and push the crust further into the lithosphere
  • Lithospheric stretching or compression
  • Lithospheric flexure, when the weight of loading bends the crust
• Extensional Basins

  • Extensional “stretch” basins THERMAL / Rift basins EXTENSIONAL
  • Can be formed due to lithospheric stretching or changes in thermal regime depending on basin structure
  • Formation:

  1.     Rift phase – active extension and therefore active growth faults

  2.     Sag phase – stable period with no extension
• Flexural Basins

  • Flexure could be orogenic loading, sedimentary and volcanic loading or sub crustal loading
  • Foreland basins – flexure of the continental lithosphere adjacent to collisional zones
  • Oldest deposits are fine grained, turbidic sediments
  • With later deposits being dominantly shallow water or continental
  • Trench basins - flexure of oceanic lithosphere adjacent to subduction zones
  • Sharp, deep basins, often deformed due to gravitational forces on the down going slab and excess volcanic arc mass
  • E.g., Hawaiian Islands
• Back Arc Basins

  • Outward of subduction zones
  • Classification- dependant on tectonic setting, typically lithospheric contraction or extension
  • In areas where the lithosphere is contractional, extensional or stable.
• Continental Strike-Slip Basins

  • Subsidence occurs in fault bends (areas of transtension and transpression)
  • Can be very deep in a small surface area
  • Classification- can form as a response to any of the classifications
• Intraplate Basins

  • Often circular, form major sediment stores on all continents
  • Origins of this basin are still debated
• Intracratonic Basins


  • Basins occurring in areas of cratons, usually stable with little to no deformation
• Types of Basins

  • Extenstional basins
  • Rift basins
  • Foreland basins
  • Trench basins
  • Back arc basins
  • Continental strike-slip basins
  • Intraplate basins
  • Intracratonic basins