Investigation of Kiaman Magnetic Divison in Colorado Redbeds

Palaeomagnetic examination of Middle and Upper Pennsylvanian, Permian and Triassic redbeds from the western and eastern slopes of the Colorado Front Range suggests that a late Pennsylvanian—Permian reversed interval equivalent to the Kiaman magnetic interval has been located on the North American continent. Collections made from a stratigraphic interval of 2000 ft on the eastern slope and 4000 ft on the western slope showed reversed directions only. Available stratigraphic data indicate that the zone extends from the beginning of Late Pennsylvanian to Late Permian or into Early Triassic. This time span is in good agreement with the age assignment, based on radioisotope dating and stratigraphic position, of the Australian igneous rocks on which the magnetic interval was defined. Thus it appears that the redbeds of this study acquired their magnetic direction at the time of deposition or very soon thereafter. Palaeomagnetic poles calculated on the basis of these data are: Middle Pennsylvanian, 39°N, 105°E; Upper Pennsylvanian and Permian, 33°N, 126°E, for the western slope and 48°N, 119°E, for the eastern slope; Lower Triassic, 56°N, 100°E.