Magnetostratigraphy Flashcards
What does magnetostratigaphy deal with?
The chronology of magnetic reversal events and stratigraphic correlation by means of these events.
Earths magentic field lines vary in strength from being _____ at the equator to be _____ strongest at the pole
Weakest and Strongest
Inclination
Parallel at earths surface. 90 degrees at the magentic poles
Name the three hypothetical theories of how earths magnetic field is generated?
- The basic geodynamo model
- Two convection cell model
- Radical new theory suggests earths magnetism may be linked to movement of ocean currents
Basic geodynamo model
The earths outer core is composed of liquid iron. Some of this becomes ionized and charged electrically due to heat from the core. The movement of the charged outer core from earths rotation produces the magnetic field. This model predicts stable field and coincidence of magnetic and geograpic poles which is not true
Two Convection cell model
Liquid core consists of two convection cells, with opposite flow direction, driven by heat from the inner core
New theory
Ryskin suggests that earths magnetism is linked to ocean movements. The salt in seawater allows it to conduct electricity, meaning it generated electrical and magnetic field as it moves. This is controversial
How were paleo-magnetic fields recorded?
Fe rich minerals are natural minerals and align themselves according to polarity of geomagnetic field.
Remnant magnetism
Alignment of magnetic minerals and the magnetic induction that remains in minerals after removal of the magnetizing field
Currie point
Temperature at which magnetic mineral obtains its remnant magnetism (about 570 C for magnetite)
Magnetic clock reset
Recrystallization, oxidation, dehydration, and other alteration processes may produce magnetism in some minerals at low temperatures, much below the curie point. In this case the time of alteration is recorded not when the rock was formed
Relaxation
The primary magnetism of minerals will decrease in intensity over geological time
What Two parameters of the primary magnetism are measured?
Declination: with respect to geographic north
Inclination: with respect to horizontal in the original bed at the collection site
What is Magnetostratigraphy?
It deals with the classification and correlation of stratigraphic units based on the remnant paleomagnetic characteristics
What is a polarity zone?
A polarity zone is the fundamental unit characterized by some degree of internal homogeneity of its magnetic polaritymay contain rocks of entirely or predominantly one polarity or mixed polarities
