Thrombolites are organosedimentary structures with a clotted organization formed through the activity of microbial communities interacting with their environment. Detailed knowledge of the spatial organization of these communities is lacking. In this study, 16S rRNA sequencing of bacteria and archaea was completed for thrombolite-forming microbial mat communities by vertical depth - zone 1 (0-3 mm), zone 2 (3-5 mm), and zone 3 (5-9 mm) - correlating with changes in oxygen activity. Delineating the composition of the thrombolites is the first step to understanding who is in the community and their functional roles can then be assessed.