Reading Question
1. What are the processes involved in the creation of sediments and sedimentary
rocks?
Sedimentary Rocks
• Processes
– Weathering = sediments and soils
– Erosion and transport
– Deposition
– Lithification and Diagensis
Weathering & Sediments
• Types of Weathering
– Mechanical & Chemical
• Types of Sediment
– Siliciclastic
– Chemical/Biochemical
– Carbonaceous
Weathering & Sediments
• Discuss the following question with the people next to you:
• What factors influence rates of weathering and where on earth are these
rates highest?
Weathering & Sediments
• Controlling Factors
• Source
• Climate
• Topography and latitude
• Sea level
• Tectonic Setting
Weathering Processes
• Mechanical - physical disintegration
• Processes
– Thermal Weathering
– Frost (ice) Wedging
Mechanical Weathering
• Processes
• Exfoliation - removal of overburden pressureMechanical Weathering
• Processes
• Wetting & Drying
• Salt
• Plants
Chemical Weathering
• Chemical weathering - alteration of chemistry and or mineralogy of source
rock
• most important agent of chemical weathering = water
– Atmospheric gasses
Chemical Weathering
• Processes
• Hydrolysis - reaction between silicate minerals and acids
– H+
– solution
– Aluminum silicates = clays
Chemical Weathering
• Processes
• Solution - soluble minerals exposed to meteoric water
• Carbonic acid
• karst
Chemical Weathering
• Oxidation - alteration of iron and manganese in silicate minerals
• Iron and manganese oxides
• Reduction - soluble ferrous iron (Fe2+)
Chemical and mechanical weathering enhance each other
• Mechanical - increases effective surface area
• Chemical - differential weathering
• Where is both types of weathering most intense?
Products of Weathering
• Source-rock residues - siliciclastics
• Secondary minerals - mudrocks
• Soluble constituents - evaporites, limestone, chert