Indications of paucity of aragonite needles in Recent lime mud from southern British Honduras led to study of origin of lime mud in this area. Strontium content of carbonate mud fraction of lagoon samples increases toward carbonate shoals. The carbonate mud fraction averages 25 percent high-strontium aragonite, 24 percent low-strontium aragonite, 44 percent high-magnesium calcite, and 7 percent low magnesium calcite. High-strontium aragonite is primarily coral debris. Low-strontium aragonite is primarily mollusc debris. This suggests shelf mud consists of shoal-derived debris. Abrasion in agitated environments is dominant process of lime mud production.