Sediments and Sedimentary Rocks
• History of Earth
• Changing sea level, climate, life, etc.

I. Sedimentary Rocks
 - rocks derived from the weathering of older rocks
 - Earth’s recycled rocks
  - The result of surface processes….
  - weathering, erosion, transport, deposition

Mechanical Weathering

•  Physical breakdown of earth materials
 -> composition remains unchanged

• Types of processes
­ Creation of Joints
­ Removal of overburden = exfoliation
Mechanical Weathering
• Processes

•  freeze/thaw: frost wedging
Mechanical Weathering
• impact and abrasion

•  biological activity
Chemical Weathering
• Chemical reactions -> elements added or removed
• most important agent of chemical weathering = water

•  Types of reactions

­ Dissolution  - carbonic acid
Chemical Weathering
• Oxidation

• Hydrolosis - creation of clay minerals

Chemical and mechanical weathering enhance each other
• Mechanical - increases effective surface area

• Chemical - differential weathering

• Where is both types of weathering most intense?
 

The Regolith
• weathering - produces a layer
-> the regolith or pedosphere (unconsolidated sediments):

2 types of sediment
• Clastic - particles
• Chemical - ions

Erosion & Transport
what moves sediment?

4 agents = 1. Gravity, 2. Wind, 3. Water, and 4. Ice
Sediment Texture
• Reading the texture in sediments and sedimentary rocks

• Why do these rocks have different textures?

- Transport  - Depositional Environment

- Texture and Composition of sediment reflect agent and amount of transport.

a) composition  b) grain size

c) sorting

d) roundness

E. Deposition => occurs when transport ends

1. Sediments deposited within broad regional topographic low areas => Basins

2. Specific sites within basin =>Depositional Environments

 * 3 categories
  a) marine, b) transitional, and c) continental

=> sediment texture and composition - reflects transport & depositional environment

Sediment Texture
• Grain size, sorting, shape, & maturity

• Clues about depositional environment & transport

Sediment Components
• Mineral & Rock fragments
• Fossils
• Clues about origin & depositional environment

Lithification => converting loose sediment into solid rock

 => burial leads to

 a) compaction  b) cementation

Types of Sedimentary Rocks
 A. Clastic (siliciclastic) - clastic texture
   - rock fragments and mineral grains

  - subdivided on the basis of grain size.…

Chemical Sedimentary Rocks

  - chemical precipitates from solution - crystalline & 1 mineral
 
 evaporites => gypsum and rock salt (halite)
 

Biochemical
 1. Carbonates = limestone and dolostone

- can be considered -> clastic (bioclastic), organic, or chemical......…
- organisms secrete chemical sediments as skeletons
Organic - particle of plants and animals
 - lithified organic material (plant remains)
 
EX: coal
only forms in specific environments and climate

Stratification

 => sedimentary rock = layered = bedding

 => Why are sedimentary rocks layered?

Why are sedimentary rocks layered?
• Shifting depositional environments

• What causes environments to shift

• Changes in relative sea level
­ Transgression and regression

Reading sedimentary rocks
• Interpreting environments from rocks

• Components and Texture

• Fabric - sedimentary structures

Sedimentary Structures

Ripples -
Small-scale ridges that form in slow-moving fluids….

Moving sand
Cross-Bedding -

The result of the movement (by fluids) of large amounts of sand - dunes or bars

Sand Waves

Dessication = mud cracks
Activities of organisms = Trace Fossils