W2 - Stratigraphy Flashcards
Who was Clair Patterson?
In 1956, showed the Canyon Diablo Meteorite to be - established age of planetary formation in solar system
How old is the solar system?
4.55by +/- 70my
How was the age of the solar system formation estimated?
Determined by Clair Patterson who developed the first clean labs to measure lead isotopes
In 1956, determined the age of the Canyon Diablo Meteorite
What is absolute geologic age?
Understanding of when events actually happened
Asks how old it is
What is tephra?
Volcanic ash layer
Helpful for dating
What is relative geologic age?
Understanding when events occurred relative to one another
Asks what came first
What is stratigraphy?
Study of layered rocks in order to understand their composition, origin, and changes in space and time
What are layers of rock called?
Strata (pl.) or stratum (s.)
Sedimentary rocks are usually layered or “bedded”
Stratigraphic succession is the vertical sequence of layering
Who was Nicolas Steno?
Danish Catholic monk and famed renaissance anatomist
Tried to understand the connection between inorganic and organic material
What was Nicolas Steno’s big discovery?
Recognized that fossil shark’s teeth were entombed in sedimentary rock rather than grown within the rock
Reasoned that rock was originally fluidized and that crystals in igneous rocks formed in original liquid state - indicated that Earth’s geology recorded complex processes of sedimentation and transformation of sediments to rocks
Also invented the basic laws of stratigraphy
What is the Principle of Original Horizontality?
Sedimentary layers laid down in water are deposited nearly horizontal and parallel to the Earth’s surface
Layers now eroded were once continuous (ex: Tapeats sandstone layer in the Grand Canyon has been eroded by the Colorado River)
What is the Principle of Superposition?
In any undisturbed series of sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top
What is the Principle of Lateral Continuity?
Strata extend continuously in all directions until they are terminated by thinning at the edge of a basin, end abruptly at a barrier to sedimentation, or grade laterally into a different sediment type
Who was Charles Lyell?
Came up with the Principles of Geology
What is uniformitatianism?
The theory that present is key to the past
What is the Principle of Cross-Cutting Relationships?
States that a rock unit, sediment body, or fault that cuts another geologic unit is younger than the unit that was cut
What is the Principle of Included Fragment?
States the fragment of rock within a larger rock unit are older than the rock in which they are enclosed
What is a disconformity?
Layers above and below the unconformity are parallel to one another
What is an angular unconformity?
Younger beds overlie tilted or folded beds
What is a nonconformity?
Younger beds overlie much older metamorphic or plutonic rocks
What is stratigraphic correlation?
Matching of strata from one region to another
What is lithostratigraphy (lithology)?
Rock type
What is a formation?
Distinctive rock units that can be mapped over a large area
Usually named after a type locality where the rocks were first described
Sub-divided into members
Lumped together to form groups
What is biostratigraphy?
Zoning of stratigraphic layers, and arrangement of those layers according to relative time of deposition, using the ranges of fossils
What is the geological range of a fossil?
Time interval between first and last appearance of each species
What is a zone (biozone)?
Stratigraphic interval defined by its fossil content, and usually given the name of a characteristic fossil present in that interval
What is chemostratigraph?
Using ratios of chemical isotopes to arrange stratigraphic layers according to relative time of deposition
Excursions in chemical signatures (ex: isotopic ratios) can record global environmental changes
Carbonates contain carbon and thus are good for dating
Ex: C12/C13 show changes in burial/exhumation of carbon-bearing sediments
What is magnetostratigraphy
Stratigraphy on the basis of magnetic properties
Fine-grained magnetic minerals (magnetite) orient themselves when settling from suspension within earth’s magnetic field, recording the polarity of earth’s magnetic field at time of deposition
Applicable only in deep sea environments
