Calcretes from humid and semiarid regions of Puerto Rico

Calcretes are most associated with arid and semiarid environments and are frequently used as a proxy for such environments in the geologic record; however, they are also known to form under humid conditions and even environments with substantial rainfall. Correct interpretation of the rock record relies on understanding the effects of environment of deposition on the resulting calcrete, which is lacking for humid environments. Microbes are known to play a role in calcrete formation, as in other carbonate deposits, although the particular organisms involved likely depend on environmental conditions. Calcretes were collected for comparison from the humid northern and semiarid southern coasts of Puerto Rico. DNA was extracted from the samples and 16S amplicons were generated and sequenced to characterize the microbial communities of the samples. Geological analysis of the samples was performed separately.