UTILIZATION OF SEDIMENT GRAIN SIZE ANALYSIS TO EVALUATE THE ORIGIN OF EDIACARAN PALEOCANYONS IN SOUTH AUSTRALIA AND EASTERN CALIFORNIA

Mid-Ediacaran (~580 Ma) paleocanyons in South Australia and eastern California are associated stratigraphically with the largest carbon-13 isotope excursion in Earth history, the Shuram excursion. The origin of these mid-Ediacaran paleovalleys remains debated between submarine and subaerial, and has implications for the origin of the associated Shuram excursion. Recent high-resolution physical stratigraphic mapping has led to a new interpretation for the origin of the paleocanyons: that they were incised subaerially due to sea level drawdown triggered by the ~580 Ma Gaskiers glaciation. This study will independently test that interpretation using laser-diffraction granulometry on valley fill sedimentary rock samples from both paleocanyons.

Utilizing known process-curve relationships, this study will analyze grain size distributions (GSD) from ancient samples and compare these to modern analogues of subaerial and submarine systems to determine where the distributions most significantly overlap. GSD studies on ancient environments are rare due to challenges in sample preparation, but recent advances in chemical disaggregation and serial digestion allow us to use laser-diffraction granulometry to produce more accurate distribution curves. The results of the laser-diffraction approach will also be compared to a petrographic analysis, and an ImageJ based workflow for GSD on ancient sediments to determine the ideal method approach.

We hypothesize that (1) laser-diffraction granulometry is the most effective sediment grain size analysis approach; and (2) that the grain size distributions from the paleocanyon samples are most similar to the modern fluvial channel distributions, suggesting that a large sea level drawdown potentially triggered by the Gaskiers glaciation led to their origin.