Determination of Basinwide Paleocurrent Patterns in a Shale Sequence via Anisotropy of Magnetic Susceptibility (ams): a Case Study of the Mid- Proterozoic Newland Formation, Montana

It has been demonstrated that in shales of the MidProterozoic Newland Formation the long axis of the AMS ellipsoid A) coincides with the flow azimuth indicated by macroscopic paleoflow indicators and B) is inclined in an upcurrent direction. Following this finding, oriented samples were collected from the Newland Formation and its lateral equivalents over the entire extent of the southeastern Belt basin, the so-called Helena embayment. Two successive stratigraphic units were sampled to determine possible changes in paleocurrent patterns with changing basin configuration. The study resulted in the recognition of coherent paleocurrent patterns that are consistent with earlier stratigraphic and sedimentologic studies. The described investigation is the first of its kind to apply the AMS method to shales on a basinwide scale, and its success suggests that this method could also be successfully applied to paleocurrent investigations of other basins that contain extensive shale sequences.