Very high magnesium calcite formation and microbial communities found in porosity of the Seroe Domi Formation of Curacao, Netherland Antilles

Pores in the Seroe Domi Formation on Curacao contain large quantities of clay minerals, organic material, and protodolomite or very high-magnesium calcite (VHMC) crystals. Transmission electron microscopy (TEM) applied to bio-sectioned rock samples showed the in situ relationship between the organic material, clay minerals, and VHMC. Dumbbells, consisting of two globular bodies connected by a narrow waist, ~20 mm in length and 5–8 mm wide, characterize the organic masses. The dumbbells are coated by clay minerals. VHMC crystals grew from nucleation points within microbial films and sheaths that surround the dumbbells. DNA extraction for 16 s rRNA gene analysis revealed the presence of sulfate- and sulfur-reducing bacteria, a variety of marine cyanophytes, bacteridetes, and proteobacteria, plus freshwater cyanophytes within the rock samples. This study provides evidence from a new field locality for the microbial nucleation and growth of VHMC associated with clay minerals, and the in situ appearance of microbial dumbbells associated with dolomite. Additionally, this study is the first to reveal the internal structure of these dumbbell features indicating that they are organic in origin with crystalline material in the surrounding sheath.