During the late Triassic and early Jurassic, the location of the earth's magnetic pole changed rapidly. As a result of these changes the inclination of the magnetic field in North America increased considerably in a relatively short time. The igneous rocks emplaced during the late Triassic and early Jurassic, show thermo-remanent directions (T.R.M.) of magnetization with progressively higher positive inclinations.
In Connecticut four periods of late Triassic-early Jurassic volcanic activity have been distinguished geologically. They are from old to young: the Talcott, Holyoke, Hampden, and Higganum volcanic events. The mean inclination of the T.R.M. is + 12° for the Talcott, + 25° for the Holyoke, + 42° for the Hampden, and + 35° for the Higganum volcanic units.
This paleomagnetic stratigraphy enables one to differentiate between the volcanic units and to correlate the units of one basin, with contemporaneous outflows or intrusions in other basins.
By means of their distinctive paleomagnetic data it is possible to correlate the volcanics of the Newark and Gettysburg basins (Pennsylvania) with the Holyoke volcanic event, and the volcanics of the Bay of Fundy (Nova Scotia) with the Hampden volcanic event of Connecticut. Such correlations suggest the possibility of a northeastward displacement of the volcanic activity in late Triassic time. This would indicate a progressive northeastward expansion of the broad geanticlinal arching of the Appalachians in the early Mesozoic time.
The origin of the rapid shift is unknown. It appears, however, that the shift is related to a high order reversal of the magnetic field. The shift occurred in an interval of relatively low field strength separating the Permian positive magnetic era from the Cretaceous negative magnetic era. The same interval was characterized by an increase in the frequency of lower order reversals (magnetic epochs and events).