Geol 102 exam 2 part 2

relative dating

uses basic stratigraphic principles to determine the age of rocks and fossils in relation to one another.

absolute dating

uses natural radioactivity decay of isotopes in minerals to determine specific age

original horizontality

sediments are deposited horizontally, any folding or tilting happened after

superposition

in an undisturbed rock sequence, the oldest are on bottom, youngest on top

lateral continuity

layers of sediment extend horizontally in all directions

Cross cutting relationships

features that cut across rocks are younger than the rocks they cut

inclusions

rock fragments contained within another rock are older than the rock they’re in

radioactive decay

when an unstable atomic nuclei of one element changes into a different element

half life

the time needed for half the atoms to decay into daughter atoms

what rocks are most reliable for absolute dating?

igneous rocks as they contain few interferences

intrusive contacts

where magma intruded older rock

Fault contacts

rocks have moved on either side of the fault

depositional contacts

where volcanic or sed rocks are deposited on older rocks

erosional contacts (unconformities)

surface representing a period of time where deposition ceased or erosion occurred

disconformity

surface between two parallel SED layers

angular unconformity

two angled SED layers

Nonconformity

surface between SED rocks and ANY other rocks

formation

unit with distinct upper and lower boundaries, named after locations

Members

formations are divided into members

groups

set of several similar formations

vertical relationships

separating the columns of the vertical column, identifying the rock types and trans periods

lateral relationships

rock thicknesses can change laterally die to different depositional rates

stratigraphic correlation

matching rocks together across distances; uses fossils, key beds, sequences

pinch out

due to energy differences

intertonguing

layer being pinched out with an unfinished point, each point could signify sea level rising and falling

lateral gradation

change in layers

Transgression

sandstone, shale, limestone

Regression

limestone, shale, sandstone

Causes of Transgression/Regression

changes of polar ice cap sizes(melting = trans), rate of seafloor spreading(mid-ocean ridge causes swelling = trans), localized uplift(reg)

conditions for fossilization

hard parts, multiple body parts, high reproductive rate, low energy environment, buried quickly

Is the fossil record biased?

yes

index fossils

geographically widespread, easily identified, short time range zone