Weathering and Regolith

• What is Weathering

  • Weathering occurs on all scales in every landscape. Weathering creates clastic sediments via physical and chemical processes
  • All rocks weather but the rate of their weathering is affects by the rocks lithology and structure
  • Physical – the mechanical breakdown or disintegration of rocks
  • Chemical – the decomposition of rocks via reaction with water
  • CO2 is critical in increasing the weathering intensity of landscapes, therefore peaks in CO2 could provide knowledge of periods of higher weathering rates
• Weathering Fronts


  • As time progresses the weathering front moves deeper underground
  • This leads to a loss in mobile elements, leading to a higher concentration of Al, Fe, Ti as they cannot be dissolved as easily as elements such as Na
  • This weathering breaks down the bedrock and creates regolith
  • Regolith - Everything that sits above fresh bedrock, layer of loose, heterogeneous superficial deposits/material covering solid rock, such as dirt, dust, soil, broken rock, unconsolidated sediments
• Weathering Zones

  • 5 different weathering zones, however there is not always 5 zones present
  • 1. Upper zone- reworking, erosion, oxidation processes
  • 2. Transition into Mottled zone- dissolution and precipitation processes, ground water plays a big role
  • 3. Pallid zone - reprecipitation of material, affected by ground water year-round, less oxidation normally greyish in colour
  • 4. Saprolite zone - heavily weathered, almost powdery like substance
  • 5. Core stones - near the weathering front
• Weathering Example

  Example: Etchplains and inselbergs

  • Were thought of to developed in 2 major phases

  ·      1. Protracted deep weathering

  ·      2. Brief episode of stripping denudation

  • They typically indicate a transition from a tropical climate to a more arid one
  • The weathering front travels deep down the rock via pre-existing fractures and cracks
  •   Overtime the etchplain will erode away to reveal inselbergs

  - DRAW
• Australia and Weathering

  • Uluru is an Inselberg
  • There are different aged surfaces Australia wide, but in Central Australia there is a weathering rate of 0.17mm/Ma
  • Australia today have an average denudation rate of 0.2-7m/Ma, making the survival of very old surfaces (500Ma) unlikely, but this rate does vary spatially and temporally