Paleomagnetism relative dating
As the earth rotates, these electric currents produce a magnetic field that extends outward into space.This process, in which the rotation of a planet with an iron core produces a magnetic field, is called a dynamo effect.The data have also been crucial for better understanding the problems of regional and local tectonics, geodynamics, and thermal history of our planet.The paleomagnetism of rocks of the ~1.1 billion year old North American Midcontinent Rift have been intensively studied since early 1960s (for example, see a review in Halls and Pesonen, 1982).This correlation process is called magnetostratigraphy. Lava, clay, lake and ocean sediments all contain microscopic iron particles.When lava and clay are heated, or lake and ocean sediments settle through the water, they acquire a magnetization parallel to the Earth's magnetic field. Selector .selector_input_interaction .selector_input. Selector .selector_input_interaction .selector_spinner. The record of the strength and direction of Earth’s magnetic field (paleomagnetism, or fossil magnetism) is an important source of our knowledge about the Earth’s evolution throughout the entire geological history.
The reversely magnetized lavas (the Siemens Creek formation of Powder Mill group, the lowermost part of North Shore volcanics, Osler volcanics, and the lower part of Mamainse Point formation) are found in many locations around Lake Superior (see figure from ) during the normal polarity interval.During this interval, a sequence of Portage Lake lava flows erupted within a two to three million year interval around 1095 million years ago.