Paleomagnetism of Carboniferous strata from the Stellarton Gap

Abstract

Deposition of Carboniferous sediments within the Stellarton Graben of Nova Scotia was controlled by displacements on the bounding Hollow and Cobequid fault systems. Periods of both normal and transcurrent faulting have occurred on both faults. As a result, models for the development of the Stellarton Basin have included a pull-apart basin and a thermal subsidence basin. Paleomagnetic study of stratigraphic sequences from within the graben showed evidence for three separate periods of remanence acquisition (ST3 – ST2 – ST1). Ordering the acquisition sequence for these three magnetizations is mainly circumstantial, being based on the distribution of each remanence phase relative to stratigraphic position and deformation of the strata. The oldest magnetization ST3 is grossly divergent from previously reported Carboniferous results suggesting an early period of large-scale clockwise rotation. Magnetization ST2 has a similar pole position to many others from Maritime Carboniferous basins located within the Appalachian orogenic belt. The divergence of these poles from the cratonic poles is interpreted as indicating that these magnetizations were acquired at a time when the reference horizontal was different to the present horizontal. The third magnetization ST3 is identical to a large number of late-stage Carboniferous regional overprint magnetizations. In summary, the paleomagnetic evidence suggests that the Stellarton Basin was formed in an early (Westphalian B to C) pull-apart phase that was followed by a later thermal subsidence phase.