Paleomagnetic and cyclostratigraphic constraints on the synchroneity and duration of the Shuram carbon isotope excursion, Johnnie Formation, Death Valley Region, CA

• A magnetic reversal stratigraphy is tied to the Shuram Excursion.
• Astrochronology of the Shuram Excursion estimates a duration of 8.2 ± 1.2 Myr.
• The chronostratigraphy can be used to inform the origin of the Shuram Excursion.

Paleomagnetism and rock magnetic cyclostratigraphy of the Rainstorm Member of the Johnnie Formation near Death Valley, CA provide chronostratigraphic constraints on the duration and synchroneity of the Shuram carbon isotope excursion. Magnetic reversal stratigraphies at three localities, the Desert Range of western Nevada, and the Nopah Range and Winters Pass Hills of southeastern California, show consistent polarity zonations with paleomagnetic poles that correspond to Neoproterozoic (Ediacaran) reference poles for cratonic North America. The magnetostratigraphy demonstrates that the nadir of the Shuram Excursion (SE) occurred just after a transition from reversed to normal polarity, and is synchronous at the two localities within Death Valley. Time series analysis of magnetic susceptibility from the Nopah Range and Winters Pass Hills localities shows statistically significant spectral power in frequency bands with orbital-scale ratios (short eccentricity, obliquity, and precession). An astrochronologic interpretation of the cyclostratigraphy yields an estimated duration of 818 ± 122 kyr for the SE between values of δ13C −3.9‰ before the nadir to a recovered value of −9.3‰ after the nadir. Extrapolation of this estimate yields a duration of 8.2 ± 1.2 Myr for the entire excursion, which is in agreement with an independent estimate based on chemostratigraphic correlation of sections containing radiometric dates of ash beds.