Embed Size (px)
DESCRIPTION
White Sands Nat’l Monument, NM Molly Rogers. Dolomite Mountains Lea Korsmeyer. SEDIMENTATION AND SEDIMENTARY ROCKS. SEDIMENTARY STRUCTURES. CROSS-BEDDING. Consists of sedimentary layers deposited at an angle to the underlying set of beds. Navajo Sandstone Utah. Coconino Sandstone - PowerPoint PPT Presentation
Citation preview
White Sands Nat’l Monument, NMMolly Rogers
Dolomite MountainsLea Korsmeyer
SEDIMENTATION AND SEDIMENTARY ROCKS
SEDIMENTARY STRUCTURES
CROSS-BEDDINGConsists of sedimentary layers deposited at an angle to
the underlying set of beds.
Navajo SandstoneUtah
Coconino SandstoneArizona
SEDIMENTATION AND SEDIMENTARY ROCKS
SEDIMENTARY STRUCTURES
CROSS-BEDDING
Form when particles drop from a moving current, such as a flowing river or wind.
Cross beds always slope towards the down-currentdirection.
Consequently, they can be used to indicate direction offlow.
SEDIMENTATION AND SEDIMENTARY ROCKS
SEDIMENTARY STRUCTURES
CROSS-BEDDING
SEDIMENTATION AND SEDIMENTARY ROCKS
SURFACE SEDIMENTARY STRUCTURES
RIPPLE MARKS
Surface layers of sedimentary rocks also have structures.
Shallow, curving ridges produced by currents
SEDIMENTATION AND SEDIMENTARY ROCKS
SURFACE SEDIMENTARY STRUCTURES
RIPPLE MARKS
SEDIMENTATION AND SEDIMENTARY ROCKS
SURFACE SEDIMENTARY STRUCTURES
MUD CRACKSPolygonal cracks that form as mud is exposed to air
and then dries out.Occurs when lakes dry up or evaporate.
SEDIMENTATION AND SEDIMENTARY ROCKS
LITHIFICATION
When sediments are buried they retain heat.Some heat comes from buried radioactive grains.Some heat conducted from Earth’s interior.
Sediments are also compressed by overlying sediments.Sediments are invaded by groundwater carrying ions.
Heat, pressure and ions alter the physical and chemicalnature of the sediments by a processescollectively known as DIAGENESIS.
SEDIMENTATION AND SEDIMENTARY ROCKS
LITHIFICATION
DIAGENESIS can lead to LITHIFICATION.
LITHIFICATION is the conversion of loose sedimentsto solid sedimentary rocks.
Usually occurs in the upper few kilometers of crust.Temperatures are <200C and at low pressure.
Sediments are COMPACTED and often CEMENTED.
SEDIMENTATION AND SEDIMENTARY ROCKS
LITHIFICATION
COMPACTION - the process by which pressurereduces the volume of sediment during diagenesis.
Overlying sediment squeezes air and water out of sediments forcing grains closer together.
Clays have weak attractive forces which causes grainsto adhere and become SEDIMENTARY ROCK.
SEDIMENTATION AND SEDIMENTARY ROCKS
LITHIFICATION
CEMENTATION takes place as water circulatesbetween grains and compounds originally dissolved during chemical weathering areprecipitated and bind sediments together.
Types of cement:Calcium carbonate (CaCO3)Silica (SiO2)Iron oxides (Fe2O3, FeOOH)Iron sulfide (FeS2)Iron carbonate (FeCO3)
Organic fragments are also compacted and cemented.
SEDIMENTATION AND SEDIMENTARY ROCKS
LITHIFICATION
Increased heat and pressure can also causeRECRYSTALLIZATION.
Recrystallization is the development of stable mineralsfrom unstable varieties.
Many marine organisms secrete aragonite in skeletons.Aragonite recrystallizes to calcite upon the death of
the organism that produced it.This explains why there is no aragonite in ancient
carbonate rocks.
SEDIMENTATION AND SEDIMENTARY ROCKS
CLASSIFICATION OF SEDIMENTARY ROCKS
Grain-size forms the basis of clastic sedimentary rockclassification.
Sediment Size(mm)
Particle Name Rock Name
<0.004
64-256
4-64
2-4
0.063-2
0.004-0.063
>256 Boulder
Cobble
Pebble
Granule
Sand
Silt
Clay
Gravel
Mud
ConglomerateBreccia
Sandstone
Shale
SiltstoneMudstone
SEDIMENTATION AND SEDIMENTARY ROCKS
CLASSIFICATION OF SEDIMENTARY ROCKS
CONGLOMERATES AND BRECCIAS
Both have particles sizes > 2mm.Conglomerates have rounded grains.
Indicates greater weathering and erosion.
Breccias have angular grains.Indicates less weathering and erosion.
SEDIMENTATION AND SEDIMENTARY ROCKS
CLASSIFICATION OF SEDIMENTARY ROCKS
SANDSTONES
Clastic sedimentary rocks with a grain-size between0.063 (1/16) and 2 mm.
Represent 25% of all sedimentary rocks.Are usually cemented by carbonate (calcite) or silica.
>90% quartz grains = quartz sandstonewell sorted and rounded grains
>25% feldspar = arkosepoorly sorted and angular grains
>33 1/3 silt, clay and rock fragments = greywackepoorly sorted and angular grains
SEDIMENTATION AND SEDIMENTARY ROCKS
CLASSIFICATION OF SEDIMENTARY ROCKS
SANDSTONES
SEDIMENTATION AND SEDIMENTARY ROCKS
CLASSIFICATION OF SEDIMENTARY ROCKS
SANDSTONESSandstones are useful as building stones
contain oil, gas and groundwaterdue to high porosity and permeability
SEDIMENTATION AND SEDIMENTARY ROCKS
CLASSIFICATION OF SEDIMENTARY ROCKS
MUDSTONES
Grain-size is small, < 0.063 (1/16) mm.Mudstones with particles <0.004 mm in diameter
constitute >50% of all clastic sedimentary rocks.Usually extremely fine-grained.Settle out in very quiet waters.
Lakes, lagoons, floodplains and ocean floors.Generally composed of micas and clay minerals.
These can be oriented parallel to each other.
SEDIMENTATION AND SEDIMENTARY ROCKS
CLASSIFICATION OF SEDIMENTARY ROCKS
MUDSTONES
Parallel alignment of micas and clays is termedFISSILITY.
SHALE = FISSILE mudstone.
SEDIMENTATION AND SEDIMENTARY ROCKS
CLASSIFICATION OF SEDIMENTARY ROCKS
MUDSTONES
Color in MUDSTONES is variable.Color usually depends on depositional environment.
Black = High organic content Low oxygen content
Red = Oxidizing environment Terrestrial settings
Green = Reducing environment Marine settings with low O2
