Sedimentary Rocks. Biblical Reference When he makes all the altar stones to be like limestone...
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Transcript of Sedimentary Rocks. Biblical Reference When he makes all the altar stones to be like limestone...
Sedimentary Rocks
Biblical Reference
When he makes all the altar stones to be like limestone crushed to pieces, no Asherah poles or incense altars will be left standing. Isaiah 27:9
Top 5 Reasons to Study Sedimentary Rocks
5) Sedimentary Rocks are the most common rocks.
4) Sedimentary Rock features help decipher Earth’s history.
3) Fossils in Sedimentary Rocks give knowledge of pre-existent life.
2) Some sedimentary rocks contain resources (water, petroleum, natural gas).
Top 5 (Cont’d)1) Sedimentary Rocks are the most interesting
of the three types of rocks!
Sedimentary RocksHow They are Made
Wind and water break down the earth
Bits of earth settle in lakes and rivers
Layers are formed and build up
Pressure and time turn the layers to rock
Types of Sedimentary Rocks
Gypsum
Sandstone
Shale
Limestone
Conglomerate
Sedimentary Rocks are the principal repository for Information about the Earth’s past environment.
SedimentarySediments – Pieces of solid material that have been deposited on the Earth’s surface by:
– Wind– Water– Ice– Gravity– Precipitation
Weathering• Surface is being worn away• Breaks rocks into smaller pieces• Produces Clastic (broken) rocks• Minerals remain chemically unchanged
Erosion & Transport• 4 Main agents of Erosion
– Wind Gravity– Moving Water Glaciers
• Rocks are then transported to a new location.• Surface material is removed (eroded).
Deposition• When transported sediments are deposited
on the ground or sink to the bottom of a body of water.
• Often these are sorted with larger grains on the bottom and smaller grains on the top.
• Transportation Agents determine the method of sorting.– Example: Sand dunes = fine sand
• Wind too weak to carry large grains
Lithification• Sediments deposited in low areas (valleys
or ocean basins).• As sediment piles up, increased pressure
& temperature lithifies the sediment into Sedimentary Rock.– From the Greek word, lithos, which means
stone.
• Two Stages:– Compaction– Cementation
Compaction• The weight of the overlying sediment forces
the grains closer together.
– Mud goes from 50% - 60% to 10% - 20% water
• Sand grains maintain open spaces, which can trap:– Groundwater– Oil– Natural Gas
Cementation• Mineral growth glues the sediment grains
together into solid rock.
From Sediment to Sedimentary Rock
Environmental Clues• Grain Size• Rippling• Rounding• Sorting• Bedding• Fossils• Color• Chemistry
Grain Size• Power of Transport Medium
– Water• Large Particles – Fast Moving• Small Particles – Slow Moving
– Wind• Can only move small grains (sand
dunes)
– Glaciers• Can carry all sizes equally – Unsorted
particles
– Landslides• Sediment moves downhill in a
jumbled mess
Rippling• Sediment is moved into small ridges by wind
or waves.– Often a sign of flooding– Can be symmetrical or asymmetrical
Rounding• When rocks break apart, the edges are sharp.
– As they bump into each other or encounter weathering, the edges become rounded.
– Harder rocks (quartz sand) round better than softer rocks (carbonate sand).
– Sediment that travels far experiences more rounding.
Sorting• Sediments are “sorted” by grain size
– Indicates:• Energy, Rate and Duration of Deposition• Mode of Transportation
• Well-Sorted– Quartz Sandstones– Shales
• Poorly-Sorted– Conglomerates– Breccia
Rounding & Sorting
well-rounded, poor-sorted gravel angular, poor-sorted gravel
Bedding• Horizontal Layering
– Layers can be between a few millimeters to more than a meter thick.
• Two Types:– Graded Bedding
• Particle Sizes become progressively larger toward the bottom of the layer
– Cross-Bedding• Inclined layers across a horizontal surface
Fossils• Fossils are not Sedimentary Structures
– Remains or traces of ancient organisms• Salt Water - Corals, Echinoderms
– Heavy-Shelled Clams: Shallow, Turbulent Water
– Thin-Shelled Clams: Deep, Calm Water
– Filter-Feeding Organisms: Clear Seawater
• Fresh Water: Insects, Amphibians
• Terrestrial: Leaves, Land Animals
Color & Chemistry• Red Beds - Often Terrestrial • Black Shale - Often Deep Water• Dark or Black – Organic Material• Different layers can have very different colors• Oxygen Poor - Often Deep Water• Evaporites – Arid Climates• Iron-Rich – Red, Brown or Pink
Types of Sedimentary Rocks
Relative Abundance of Sediments
Formation of Sedimentary Rocks
Clastic Rocks• Made of Fragmentary
Material • Deposited by
– Water (Most Common) – Wind – Glacial Action – Gravity
Biochemical Rocks• Evaporation • Precipitation • Biogenic
Sediments
Clastic Sedimentary Rocks• Most Common Sedimentary Rocks
• Greek Word klastos – “broken”
• Made up of broken pieces of pre-existing rocks– Could be Igneous or Metamorphic in origin
• Three types categorized by grain size:– Coarse-Grained– Medium-Grained– Fine-Grained
Coarse-Grained Clastic Rocks• Usually gravel-sized rock & mineral fragments
– Rarely boulder-sized (see below)
• Two Main Types:– Conglomerates– Breccias
Conglomerates• Gravel Transported by High Energy Water
– Mountain Streams– Flooding Rivers– Ocean Waves
• Well-Rounded• Lithification Compacts & Cements these
fragments into Rocks
Conglomerate = rounded gravel (>2 mm)
Breccias• Angular, Gravel-Sized Particles• Particles transported short distances from
their sources– Did not have time to become rounded
Breccia = angular gravel
Medium-Grained Clastic Rocks• Sand-sized sediments in streams, rivers,
deserts and beaches
• Sandstone– Ripple Marks and Cross-Bedding indicate
direction of current flow
– High Porosity – Open spaces allow liquid to travel• Valuable as underground reservoirs of oil, natural gas,
and water
Sandstone• Sand-size (1/16 mm – 2 mm particles)• Classified by Minerology
– Most Common: Quartz Sandstone– Arkose Sandstone = 25% Feldspars
• Feels Rough & Gritty
Fine-Grained Clastic Rocks• Consist of Silt or Clay-sized particles
• Typically found near swamps or ponds– Still or slow-moving water
• Poor Porosity which forms a barrier to the movement of groundwater
• Three Main Types– Siltstone– Claystone– Shale
Fine-Grained Clastic Rocks• Siltstone
– Made from Silt• 1/256 mm to 1/16 mm
– Three times stronger than most bricks
• Claystone– Made from Clay
• < 1/256 mm
• Shale– Made from Fissile Clay– Splits along closely spaced planes
Clastic rocks
Sediment Sizes and Clastic Rock Types
Sedimentary rocks made of silt- and clay-sized particles are collectively called mudrocks, and are the most abundant sedimentary rocks.
Rock Type Sediment
Shale Clay
Siltstone Silt
Sandstone Sand
Conglomerate Gravel
Chemical Sedimentary Rocks• Ions are taken into solution by the parent
weathering material• Evaporation in arid locations leaves chemically
enriched crystals, which solidify into rock• Other conditions for Evaporites:
– Fresh water supply is low– No connect to an open sea
• Usually are light-colored
Common Chemical Rocks
• Dolostone– Magnesium ions bonded to
CaCO3
• Flint– Formed from Silica in Sea Beds
• Rock Gypsum– Sulfate-based– Very soft– Used to construct the Egyptian
pyramids
Bio-Chemical Sedimentary Rocks• Formed from remains of once-living organisms• Many contain fossils
– Evidence of their biological origins– Falls of the Ohio fossil beds are made of
limestone
Common Bio-Chemical Rocks• Limestone
– Predominately CaCO3
– Formed from skeletal fragments of marine invertebrates
• Chert– Silica-based– Layers of microscopic shells
• Coal– Carbon-based– Compressed, altered plant
remains from bogs & swamps
Francis John Turner
A. cementation
B. crystallization
C. compaction
D. evaporation
During which process does the weight from layers of sediment force out fluids and decrease the space between grains?
Pop Quiz
A. chemical
B. biochemical
C. fragmented
D. clastic
Which types of rocks are sedimentary rocks made up of broken pieces of minerals and rock fragments?
Pop Quiz
A. gas
B. water
C. sediment
D. magma
Chemical rocks form when minerals crystallize directly from which of these?
Pop Quiz