Contrasting studies in paleomagnetism : Quaternary magnetostratigraphy and early Proterozoic plate motion analysis
Date
1992
Authors
Cioppa, Maria Thérèse
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Abstract
Two projects involving different aspects of paleomagnetism were completed for this thesis.
The magnetostratigraphy of stacked sequences of pre-Wisconsinan diamict (mostly till) and paleosols at three localities in southwestern Alberta and northern Montana was determined in an attempt to resolve conflicting ideas of their age. Sediments and paleosols at the Mokowan Butte locality carried a normal polarity-reversed polarity-normal polarity magnetization sequence, whereas the other localities sampled (Saint Mary Ridge and Two Medicine Ridge) carried only a normal-reversed sequence. It is suggested that the upper normal polarity sediments were probably deposited during the Brunhes Normal Chron, the reversed polarity sediments during the Matuyama Reversed Chron, and the lower normal polarity sediments deposited during the Gauss Normal Polarity Chron. The most likely correlation of the three localities indicates that paleosol 4 at Saint Mary Ridge, paleosol 4 at Mokowan Butte and paleosol 4 at Two Medicine Ridge are the same unit. The paleomagnetic record implies that glaciation of North America could have occurred at least 2.6 Ma ago.
A paleomagnetic determination of the Early Proterozoic (2250 - 1800 Ma) plate motion of the Archean structural provinces of western Laurentia (Slave-Rae-Hearne and Superior) results in information about the formation of the Trans-Hudson Orogen. The use of minimum reliability criteria and the development of a quality index culled that portion of the data set which could not be considered as representative of the geomagnetic field for the time interval under consideration. After relative rotations within a structural province were determined and corrected, paleolatitude curves and apparent polar wander paths were used to estimate motion between the structural provinces. The final amalgamation of the structural provinces seems to have occurred at 1840 Ma, and is characterized by similar paleolatitudes and overlapping APWPs. Certain discrepancies in the paleomagnetic data are resolved by an hypothesis of relative plate motion.
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UN SDG 14: Life Below Water