Carbonate mudstones are key geochemical archives for past seawater chemistry, yet the origin of carbonate mud remains a subject of continued debate and uncertainty. Prevailing hypotheses have settled on two mechanisms: (1) direct precipitation in the water column and (2) postmortem dispersal of mud-sized algal skeletal components. However, both mechanisms conflict with geochemical observations in modern systems and are problematic in deep time. We tested the hypothesis that abrasion of carbonate sand during sediment transport might produce carbonate mud using laboratory experiments and a sediment transport model. We documented experimental mud production rates up to two orders f magnitude faster than rates estimated for other mechanisms. Combined with model calculations, these results illustrated that transport and abrasion of carbonate sand is a major source of carbonate mud.