Chapters 16-18 Flashcards
(61 cards)
Uses various radioactive decay dating techniques to assign ages to rocks in years before the present.
Absolute dating
A principle holding that in a vertical sequence of undeformed sedimentary rocks, the relative ages of rocks can be determined by their sequence- oldest at the bottom , followed by successively younger layers.
Principle of superposition
The process of determining the age of an event as compared to other events; involves placing geologic events in their correct chronological order but does not involve the consideration of when the events occurred in number of years ago.
Relative dating
According to this principle, sediments are deposited in horizontal or nearly horizontal layers.
Principle of original horizontality
A principle holding that rock layers extend outward in all directions until they terminate.
Principle of lateral continuity
A principle holding that an igneous intrusion or fault must be younger than the rocks it intrudes or cuts across
Principle of cross-cutting relationships
A principle holding that inclusions or fragments in a rock unit are older than the rock unit itself; for example, granite inclusions in sandstone are older than the sandstone
Principle of inclusions
A principle holding that fossils, and especially groups or assemblages of fossils, succeed one another through time in a regular and predictable order.
Principle of fossil succession.
A break in the geologic record represented by an erosional surface separating younger strata from older rocks.
Unconformity
An unconformity in which the rock layers above and below are parallel.
Disconformity
An unconformity below with older rocks dip at a different angle (usually steeper) than overlaying strata.
Angular unconformity
An unconformity in which stratified sedimentary rocks overlie an erosion surface cut into igneous or metamorphic rocks.
nonconformity
Demonstration of the physical continuity of rock units or biostratigraphic units, or demonstration of time equivalence as in time-stratigraphic correlation.
Correlation
An easily identified fossil with an extensive geographic distribution and short geologic range useful for determining the relative ages of rocks in different areas.
Guide fossil
The spontaneous change of an atom to an atom of a different element by emission of a particle from its nucleus (alpha and beta decay) or by electron capture.
Radioactive decay
The time necessary for half of the original number of radioactive atoms of an element to decay to a new, and more stable daughter product; for example, the half-life for potassium 40 is 1.3 billion years.
Half-life
Absolute dating technique relying on the ratio of C14 to C12 in an organic substance; useful back to about 70,000 years ago.
Carbon-14 dating technique
A vast area of exposed ancient rocks on a continent; the exposed part of a craton.
Shield
The broad area extending from a shield, but covered by younger rocks; a platform and shield form a craton.
Platform
The relative stable part of a continent; consists of a shield and buried extension of a shield known as a platform; the ancient nucleus of a continent.
Craton
The exposed part of the North American craton; mostly in Canada but also in Minnesota, Wisconsin, Michigan, and New York.
Canadian Shield
A linear or podlike association of igneous and sedimentary rocks; typically synclinal and consists of lower and middle volcanic units and an upper sedimentary rock unit.
Greenstone Belt
A proterozoic continent composed mostly of North America, Greenland, and parts of Scotland and Scandinavia
Laurentia
A linear part of earth’s crust that was, or is, being deformed during an orogeny.
Orogen
