Formation of Stratified Rocks

• Stratified rocks, also known as sedimentary rocks
• Stratified rocks

  • are types of rocks that are formed by the deposition and cementation of mineral or organic particles on the floors of bodies of water
• Three types of rocks

  • igneous
  • sedimentary
  • metamorphic
• Most fossil appears in sedimentary
• Metamorphic rocks are formed when bits of rocks are layered and cemented together
• Gravel is NOT an example of sedimentary particles
• Rock cycle

  • series of processes that slowly changes rocks from one kind to another
• Compaction

  • layers upon layers of sediment build up and exert pressure on the layers below
• Erosion

  • moving of sediments
• Deposition

  • settling out sediments
• Cementation

  • sediments are glued together when minerals dissolve
• Law of Superposition

  • older layers are deeper than recent layers
• Stratification

  • process that leads to formation or deposition of rock layers
• Law of Lateral Continuity

  • all layers are continuous until they encounter solid bodies that block their deposition
• Igneous rocks form from cooling lava or magma
• Metamorphic rocks are formed under the surface of the earth from the metamorphosis that occurs due to intense heat and pressure
• These particles settle down at the bottom of the body of water, in a process called sedimentation
• These layers harden and turn into rock in a process called lithification
• Geologists can make educated guesses about what the Earth’s climate was like when each layer was formed and can even find fossils that tell us about life on Earth at different points in history
• Relative dating

  • method of arranging geological events based on the rock sequence
  • It does not provide actual numerical dates for the rocks
• Principle of Original Horizontality

  • Layers of rocks deposited from above, such as sediments and lava flows, are originally laid down horizontally
• Absolute Dating

  • called numerical dating
  • give rocks an actual date, or date range, in numbers of years
  • obtained with radiometric methods
• Uranium – Lead Dating

  • Used for dating rocks older than 1 million years
• Uranium – Thorium Dating

  • Another method used for dating very old rocks
• Potassium – Argon Dating

  • Used to date rocks older than 20,000 years
• Carbon Dating (Radiocarbon Dating)

  • Measures radioactive isotopes in once-living organic material instead of rock, using the decay of carbon-14 to nitrogen-14.
  • It can only be used on material up to about 60,000 years old
• Luminescence Dating

  • Used to date sediments up to 100,000 years old
• Fission Track Dating

  • Used to date tephra from 10,000 to 400 million years old
• Argon-Argon Dating

  • A variant of Potassium-Argon dating that allows much smaller samples to be measured
• Isotopes are important to geologists because each radioactive element decays at a constant rate, which is unique to that element.
• • Gravel- conglomerate
  • Sand- sandstone
  • Mud- shale or mudstone
• Uncomformity

  • gap in record when rock is eroded, exposing older rock and new rock forms on the older exposed rock
• Nicholas Steno studied the relative positions of sedimentary rocks
• Layering or bedding is a distinct quality of sedimentary rocks
• The layered rocks are also called strata
• • Geologic time scale shows the geologic time intervals based on the geologic rock records.
• Law of Superposition: the layers on the bottom are the oldest and layers above them are younger
• Principle of Lateral Continuity: strata are continuous in all directions until they thin out at the edge of that basin