Geologic Time Flashcards
Relative Dates
Sequence of Formation (non numerical dates)
Principle of Superposition
•In an undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below
Principle of Inclusiuon
Fragments of one rock unit enclosed within another rock unit; rock containing inclusion is younger
Unconfirmity
brteak in rock record produced by nodeposition and erosion of rock units
Angular Unconformity
Tiled rocks are overlain by flat-lying rocks
Isotope (2)
Different neutron number/mass number (total)
Disconformity
Sedimentary Strata at either side of the nonconformity are parallel
Nonconformity
Sedimentary Strata overlay metamorphic or igenous rock
Principles of Faunal Succession
so known as the law of faunal succession, is based on the observation that sedimentary rock strata contain fossilized flora and fauna, and that these fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances.
Index Fossils
Widespread geographically, limited to short period of geologic time
Fossil Assemblages
Can be used to identify a r rock bed that does not contain and index fossil
Metamorphic Grade
Degree to which parent rock changes: progress from low grade (temp, pressure) to high grade (temp, pressure)
Metamorphic rock Definition
transition of one rock to another by temperatures or pressures unlike those in which it was form. Changes in minerology from parent rock
Parent Rock->Metamorphic Rock (2)
Pressure/Heat
Foliation
Describes any planar arrangement of mineral grains or structural features within a rock
Correlation
Matching of rocks of similar ages from different regions: position of bed in a sequence of strata: match rocks of similar ages from different regions
Principle of Fossil Succession
states that fossils are arranged according to their age
Fossil Succession Examples
Age of Triboilites, Fishes, Repitiles, Mammals
Shells of Organisms
can be used to infer positions of ancient shorelines and seawater temperatures
Corals
can be used to indicate former temperature of the water
daughter products
Isotopes resulting from the decay of a parent are termed the
parent
unstable radioactive isotope
Parent:Daughter
The ratio between parent and daughter isotopes in a rock is used to determine its numerical age
PArent:Daughter = 1:1
Half life passed
Stable
Daughter Isotope
sedimentary rocks can rarely be dated by radiometric means so…
geologists must rely on igneous rocks in strata
Bracketing episodes in earth’s history
relative dating from igneous to sedimentary rocks
Disconformity between
horizontal sedimentary
Nonconfrmity between
younger sedimentary and older igenous/metamorphic
Principle of Cross Cutting
Faults/Intruions within (DIKES) are younger
Xenolith
•When magma intrudes a rock mass, blocks of that rock may become dislodged and incorporated into the magma
Uplift and Erosion followed by
angular unconformity (subsidence and renewed deposition)
Beta emssion
•beta particle ejected from the atom
Beta particle
election
Alpha Emission
alpha emmited
alpha particle
two protons/two neutrons
Electron Capture
electron captured combines with proton to become neutron
Conformable layers
no break in rock record
flat layers
not deformed
rock layers that are deformed
deformed after deposition
Principle of Lateral Continuity
- Beds originate as continuous layers that extend in all directions until they eventually thin out or grade into a different sediment type
- When a river carves a canyon, we can assume that similar strata on either side were once connected across the span of the canyon
