1. Sedimentary Rocks
The products of deposition and lithification of weathered and eroded debris and chemical precipitants.
BY FAR, most of the rocks exposed on the Colorado Plateau are sedimentary!

2. Weathering: the physical breakdown and chemical alteration of rock at or near the Earth’s surface.
Mechanical weathering: from physical forces
(e.g. frost wedging, thermal expansion)
Chemical weathering: chemical alteration of rock
(e.g. dissolution, oxidation)
Erosion: the physical removal and transportation of weathered material by water, wind or ice.

3. Weathering
Erosion

4. Types of sedimentary rocks:
Clastic (detrital): from deposits of detritus (loose sediment) Are lithified by compaction and cementation and tend to be more permeable with larger grain sizes Chemical: from reprecipitation (and recrystallization) of minerals Crystals grow until they fill all of the pore space, so these rocks tend to be relatively impermeable until they are exhumed (brought towards the surface) or fractured

5. Weathered material (sediment) has to go somewhere… So, Gravity carries the sediment down until it settles out of air or water Lithification: the process by which unconsolidated sediments are changed into solid sedimentary rock

6. Lithification Processes for clastic rocks:
Compaction: compression of sediment from the weight of the overlying material
Cementation: A chemical change that involves the precipitation of mineral among the original grains
Most common cement types:
Silica: creates a harder, more resistant sedimentary rock
Calcite: creates a softer rock and will effervesce with HCl
Iron oxides: causes a red color on weathered surfaces from oxidation

8. Common minerals in detrital rocks
Clay: most abundant product of chemical weathering from feldspars (clay is a mineral name and a size term)
Quartz: most resistant mineral –when granite is weathered, chemical weathering attacks the other minerals and the quartz grains are freed
Less common:
Feldspars: break down easily from chemical weathering processes
Micas: Soft, breaks down easily from mechanical weathering processes

9. Clastic (Detrital) Rocks
Conglomerate/Breccia
Sandstone/Arkose
Siltstone
Mudstone
Claystone
Grain Size

10. Grain Size: gives information about the energy of the depositional system

11. Sorting: The degree of similarity in particle size
Gives us information about the depositing current (e.g. wind blown sand = well sorted, mountain stream deposits = poorly sorted
Very well sorted
Well sorted
Moderately sorted
Poorly sorted
Very poorly sorted
0.35
0.5
0.7
2.0

12. Composition of detritus
Rounding
Tells you the distance material was transported
Composition of detritus
Tells us about rapidness of burial and length of transport, because less stable minerals will weather quickly at the surface

13. Classification by % matrix
Sediment size
Sediment Name
Sedimentary Rock
Less than cm
Clay
Shale
cm – cm
Silt
Siltstone
0.006 cm – 0.2 cm
Sand
Sandstone
Mixed
Conglomerate (rounded sediments)
Breccia (angular sediments)

15. Shale Most common sedimentary rock
Comprised of silt and clay sized particles
Form gradual in a relatively calm environment
Compaction: clay minerals wrap around silt particles
Darker= more organics
Low porosity from tightly packed parallel alignment of clay and silt

16. Quartz Sandstone Second most common sedimentary rock
Contains sand sized particles of quartz
Form gradually in a relatively calm environment
Often contains bedding
Grains cemented together
Greater permeability than shale

17. Conglomerate/ Breccia
Usually poorly sorted
Contains particles larger than sand size
Conglomerate has rounded clasts while breccia has angular ones
From a high energy system near the sediment source
Can be from glacial activity
Are rarer than Ss and Sh because they are usually deposited in a system that has not reached equilibrium
Breccia
Conglomerate

18. Carbonates Organic carbonates Inorganic Carbonates
Limestone makes up ~10% of all sedimentary rocks
Made up predominantly of calcite and dolomite
Can form by inorganic means or biochemically
Although they are produced under a variety of conditions, those with a marine, biochemical origin are the most common
Organic carbonates
Inorganic
Carbonates

19. Sedimentary Environments
Continental
Fluvial (stream)
Alluvial Fan
Eolian
Playa Lake
Marine
Shallow Marine
Deep Marine
Transitional
Beach
Tidal flat
Lagoon
Delta