“…Equations representing threshold of motion stresses typically replicate flow conditions occurring during incipient movement of spherical or near‐spherical particles of quartz density (Miller et al ., 1977; Li & Amos, 1995; Soulsby & Whitehouse, 1997; Soulsby, 1997; Paphitis, 2001; Porter‐Smith et al ., 2004; Griffin et al ., 2008; Wiberg & Sherwood, 2008; Li et al ., 2009; Dalyander et al ., 2013; Oberle et al ., 2014). However, natural marine sediments commonly have varied amounts of biogenic particles of non‐uniform size and shape, leading to thresholds of motion strongly differing from those of uniform quartz particles (Paphitis et al ., 2002; Weill et al ., 2010; Rieux et al ., 2019; de Kruijf et al ., 2021). Experiments show that stresses at the threshold of motion can also differ greatly with grain shape (Komar & Reimers, 1978; Komar & Li, 1986; Prager et al ., 1996).…”