Rock magnetic evidence for inclination shallowing in the Passaic Formation red beds from the Newark basin and a systematic bias of the Late Triassic apparent polar wander path for North America

Abstract

The latest Triassic and earliest Jurassic red beds from the Newark basin possess paleomagnetic inclinations that are ∼ 10° shallower than the inclinations carried by coeval volcanic rocks. It has been suggested that the difference might be due either to inclination shallowing of the sediments or to remagnetization of the volcanic rocks during a Middle Jurassic hydrothermal event. Either explanation would in turn yield significantly different apparent polar wander paths (APWPs) for the Late Triassic and Early Jurassic of North America. Here we present paleomagnetic and magnetic anisotropy data for the latest Triassic Passaic Formation red beds, which reveal deposition and/or compaction fabrics with 10% anisotropy of the high unblocking temperature, reversed polarity remanent magnetization. Inclination correction for the red beds yields similar directions to that carried by the earliest Jurassic volcanic rocks, indicating that inclination shallowing is the major cause for the difference in paleomagnetic pole position between the red beds and the volcanic rocks. Comparison of the inclination corrected data with the Late Triassic North American APWP shows a systematic error in the APWP, likely due to inclination shallowing. In turn, this error may be even more significant for much of the Paleozoic part of the North American APWP.