A review of paleomagnetic results from the Carboniferous of North America; The concept of Carboniferous geomagnetic field horizon markers

Results from the East Coast Carboniferous Basin contain an important time-stratigraphic horizon of possible global significance. Late Carboniferous units are found to have mostly reversed magnetizations while older Carboniferous units may have normal, reverse or (most frequently) dual-polarity magnetizations. This feature records the change in geomagnetic field from a period of common polarity changes, to a period of mainly reversed polarity—the Kiaman Magnetic Interval. Recognition of the stratigraphic position of this polarity feature provides a time-line for correlation of units within and among Carboniferous basins. In the East Coast Carboniferous Basin of Atlantic Canada, this horizon has now been located at the Riversdale Group level (Early Pennsylvanian; Namurian-Westphalian boundary). Since remanence acquisition of red sediments is often a lengthy process, possibly spanning field reversal time scales, red bed units pre-dating and post-dating this time-line can, in most instances, be readily distinguished, the former generally recording both polarities and the latter, just one (reverse) polarity.A polar displacement of at least 16° is recorded in the results from the East Coast Carboniferous Basin. Paleolatitude maps show that the area was located near the equator and was displaced northwards by about 8° during the Pennsylvanian. It cannot be ascertained if those observations are representative of the whole of North America, or merely the Atlantic seaboard.Poles derived from other areas of North America do not all fit the regular pattern observed on the Atlantic Coast. Using the horizon marker as a tool, it is suggested that those poles are post time-line in age so that none of them is representative of the position of North America prior to the time-line.