Paleomagnetism of some carboniferous rocks from New South Wales and its relation to geological events

Earlier results have indicated that the geomagnetic field in Australia had low or moderate inclination in Upper Silurian and Devonian time and high inclination from Permian to mid-Cretaceous time. Results reported in this paper show that moderate inclination persists to near the end of the Lower Carboniferous and that steep inclination extends down well into the Upper Carboniferous, so that most of the direction change (aside from reversals and secular variation) occurring between the Upper Silurian and mid-Cretaceous was concentrated in a comparatively short time in the Carboniferous. The inclination change corresponds to a latitude change of southeastern Australia from about 30°S to about 75°S over a period of probably not more than 20 m.y. This change coincides at its beginning with the Kanimblan orogeny (the largest tectonic event in eastern Australia) and associated marine regression, and is marked at its end by the onset of positive (reversed) polarity which persist to near the end of the Paleozoic in the Australian sections. Direction changes also occurred in Europe at this time, but they were smaller, suggesting that an episode of relative land movement (called the mid-Carboniferous continental drift episode) occurred before the episode invoked by Wegener and others for the late Mesozoic and Cenozoic. These results indicate that there was a correlation in the Upper Carboniferous of a change of latitude and orogeny (and possible drift episode) with a change in reversal frequency, implying a connection between events in the core and at the earth's surface. It is suggested that field reversals and these surface events have a common cause being governed by the redistribution of mass in the mantle. Other paleomagnetic evidence for `pre-Wegenerian' drift episodes is reviewed, and it is suggested that drift might have been a recurrent process involving the repeated redistribution of continental shields and was not confined to a comparatively late stage in the earth's history.