british virgin islands daria jones virgin gorda, bvi james o’brien
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SEDIMENTATION AND SEDIMENTARY ROCKS
DEPOSITIONAL or SEDIMENTARY ENVIRONMENTS
Analysis of sedimentary rock can provide clues to theirDEPOSITIONAL ENVIRONMENT.
Can then be used to interpret geologic history of a region.
Can includeContinental environmentsTransitional environmentsMarine environments
SEDIMENTATION AND SEDIMENTARY ROCKS
Continental EnvironmentsFound on landmasses.Most sediments are clastic.Include paleocurrent
direction or indicators.Plant and freshwater fossils
common.Includes rivers, lakes, caves,
deserts and glaciers.
DEPOSITIONAL or SEDIMENTARY ENVIRONMENTS
SEDIMENTATION AND SEDIMENTARY ROCKS
Transitional EnvironmentsOccur at boundary between
ocean and land.Some sediments are clastic,
some are organic.Influenced by tides, currents,
and breaking waves.Includes estuaries, deltas,
beaches and lagoons.
DEPOSITIONAL or SEDIMENTARY ENVIRONMENTS
SEDIMENTATION AND SEDIMENTARY ROCKS
Marine Environments
Entirely oceanic environments.Most sediments are clastic, some are organic.Vary according to depth of water.Shallow marine < 200 m.
Narrow band along continent.Sandstone, mudstone, limestone
Deep marine - offshore.Fine-grained wind blown claysand organic, calcareous or siliceous oozes.
DEPOSITIONAL or SEDIMENTARY ENVIRONMENTS
SEDIMENTATION AND SEDIMENTARY ROCKS
Shallow Marine Environments
DEPOSITIONAL or SEDIMENTARY ENVIRONMENTS
SEDIMENTATION AND SEDIMENTARY ROCKS
Deep Marine Environments
DEPOSITIONAL or SEDIMENTARY ENVIRONMENTS
SEDIMENTATION AND SEDIMENTARY ROCKS
DEPOSITIONAL or SEDIMENTARY ENVIRONMENTS
Deep Marine Environments
SEDIMENTATION AND SEDIMENTARY ROCKS
SEDIMENTARY FACIES
Adjacent sedimentary or depositional environmentsproduce different sediment and rock types.
While different, they are deposited at the same time.Represents a horizontal continuum.The horizontal changes demonstrate the variability of
the adjacent environments.Vertical changes reflect how environments have
changed over time.
SEDIMENTATION AND SEDIMENTARY ROCKS
SEDIMENTARY FACIES
Sedimentary facies move as environmental conditionschange.
Position of the beach will vary as position of sea levelchanges.Adjacent facies will stack up vertically over time.
Walther’s Law of Succession of Facies
SEDIMENTATION AND SEDIMENTARY ROCKS
DIFFERENCES IN CLIMATE AND WEATHERING
Arid RegionsSandstones and Limestones produce cliffs.Mudrocks make up slopes.
Humid RegionsSandstones produce cliffsMudrocks and limestones make up slopes
SEDIMENTATION AND SEDIMENTARY ROCKS
DIFFERENCES IN CLIMATE AND WEATHERING
Slopes in Humid Regions
Kope Formation, OH Showangunks, NY
METAMORPHISM AND METAMORPHIC ROCKS
All rocks are susceptible to metamorphism.Change occurs in response to conditions affecting them.
METAMORPHISM AND METAMORPHIC ROCKS
METAMORPHIC ROCKS
Generally form at conditions between those that formigneous and sedimentary rocks.
METAMORPHISM is the process by which heat, pressure, and chemical reactions deep in the Earth alter the mineralcontent and/or structure of pre-existing rock without melting it.
METAMORPHISM AND METAMORPHIC ROCKS
Most are buried beneath layers of sedimentary rocks.Processes take place deep in the Earth.Brought to the surface by tectonics and erosion.Most of what we know about metamorphism and
metamorphic rocks comes from lab experiments.
METAMORPHISM AND METAMORPHIC ROCKS
What Drives Metamorphism?
Rocks and minerals are most stable at the conditionsunder which they form.
Movement of rocks causes instabilities to exist.New minerals and rocks are formed in an
attempt to become stable.
Increase the amount of change, metamorphism occurs.Produce clays by weatheringWith metamorphism, clay are altered to become
micas with increasing heat and pressure.
METAMORPHISM AND METAMORPHIC ROCKS
Rocks remain solid during metamorphism.Minerals become unstable during metamorphism.
Bonds break in minerals allowing the creationof new minerals, stable at new conditions.
Not all the bonds break, that would be melting.
Circulation of ion-rich fluids enhances the movementwithin a rock undergoing metamorphism.The power of water strikes again.
Composition of the parent rock also influences the metamorphic rock that forms.
METAMORPHISM AND METAMORPHIC ROCKS
METAMORPHISM is the transformation of solidrock to form new minerals and textures.
Quartz will remain quartz, but size and shape may change.
Clays break down and elements and ions recombineto form new minerals.
With enough heat, atoms and ions can move within arock to form new minerals.
Composition of the rock may stay the same, but theminerals and texture may change.
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
HEAT
Most important factor in driving metamorphism.Accelerates the pace of most chemical reactions.
Heat increases with depth in the EarthThermal Gradient
20-30C/kilometer depth74 F/mile depth
Rocks at depth are always at higher temperature.Rocks and minerals that form there are stable.
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
HEAT
Moving rocks from the surface to depth causes increasein heat and metamorphic potential.
Sources for Increase in Heat
Tectonic activity pushes rock from surface to depth.Sediments get buried.Contact with magma.
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
HEAT
Heat in the crust is produced by:Decay of radioactive isotopesUpward conduction of heat from the mantleFriction from subduction
Heat necessary for metamorphism is not attained until a depth of 10 kilometers (6 miles).
To occur at the surface it requires contact withrising magma.