Tracking Rodinia Into the Neoproterozoic: New Paleomagnetic Constraints From the Jacobsville Formation

The paleogeography of Laurentia throughout the Neoproterozoic is critical for reconstructing global paleogeography due to its central position in the supercontinent Rodinia. We develop a new paleomagnetic pole from red siltstones and fine‐grained sandstones of the early Neoproterozoic Jacobsville Formation which is now constrained to be ca. 990 Ma in age. High‐resolution thermal demagnetization experiments resolve detrital remanent magnetizations held by hematite. These directions were reoriented within siltstone intraclasts and pass intraformational conglomerate tests—giving confidence that the magnetization is detrital and primary. An inclination‐corrected mean paleomagnetic pole position for the Jacobsville Formation indicates that Laurentia's motion slowed down significantly following the onset of the Grenvillian orogeny. Prior rapid plate motion associated with closure of the Unimos Ocean between 1,110 and 1,090 Ma transitioned to slow drift of Laurentia across the equator in the late Mesoproterozoic to early Neoproterozoic. We interpret the distinct position of this well‐dated pole from those in the Grenville orogen that have been assigned a similar age to indicate that the ages of the poles associated with the Grenville Loop likely need to be revised to be younger due to prolonged exhumation. Plain Language Summary There have been times in Earth history when many of the continents are joined together into a big continent that is called a supercontinent. The most recent supercontinent is Pangea which had Africa at its center. An older supercontinent called Rodinia formed about 1 billion years ago and had North America at its center. The old parts of North America that were in the supercontinent are called Laurentia. The position of Laurentia is key to understanding where Rodinia was and how different continents were connected in the supercontinent. We now know the age of sedimentary rocks called the Jacobsville Formation that were deposited in ancient rivers and can use these rocks to determine the past position of Laurentia (and therefore Rodinia) 990 million years ago using paleomagnetism. This position is quite different in current interpretations which rely on data from rocks that cooled slowly within an ancient mountain belt that formed when the supercontinent assembled—they likely show where the supercontinent was after 990 Ma. As a result, we have a new understanding of where the supercontinent was that can enable further progress in putting a