Recent dredgings on Key Largo have exposed previously undescribed deposits within and possibly above the Key Largo Limestone. Associated with the frequently discussed Montastrea-Diploria coral-patch-reef facies are a Chione cancellata shell-mold facies and a black mangrove root-mold facies.
The Chione cancellata shell-mold facies is characterized by a molluscan fauna, typical of modern Florida Bay, consisting predominantly of molds of Chione cancellata. It occurs as a well-lithified quartzose biocalcirudite containing fragments of subaerial crust that it overlies. The Chione cancellata deposit represents a storm accumulation either (1) deposited on a lower subaerial crust within the Key Largo Limestone during a lower stand of sea level or (2) one of the most recent deposits on Key Largo postdating the latest subaerial crust. The nature of preservation indicates subaerial leaching after deposition.