PETROGRAPHIC OBSERVATION OF MOLAR-TOOTH MICROSPAR SUGGESTS FLUID-MIXING AS A DRIVER FOR PRECIPITATION

Molar-tooth structure, an enigmatic Precambrian carbonate fabric, consists of a variety of substrate cracks filled with microcrystalline calcite. Current hypothesis suggest that molar-tooth calcite originated by precipitation of micro-spheres that filled cracks in carbonate sediments in an impressive well-ordered pattern. Here we explore the full range of relationships between crack-filling microspar and the surrounding matrix to better understand the potential origin of microsparitic carbonate.

Some general differences are observed: 1) Cracks are typically filled exclusively with carbonate micro-spheres. These cracks are typically well defined with very sharp edges, showing a large contrast between the filling and the surrounding material. These can be further subdivided into two types, where spheres of roughly equal in size, and spheres showing variable size from edges to the centers of cracks. 2) Some cracks show the presence of detrital grains, such as feldspar and quartz, that may represent spontaneous precipitation in a fluid. 3) Some cracks show diffuse edges, with highly-ordered packing of carbonate micro-spheres within the crack, and scattered outside. 4) A few cracks show oriented crystals at the edges, and micro-spheres in the crack centers. These characteristics, together with the cross-cutting relationships between different cracks, and between cracks and surrounding carbonate suggest interaction of two (or more) different compositional fluids at the moment of formation.

Future work will seek to enhance our understanding of the origin and composition of these fluids by interacting different analytical methods to provide a more comprehensive understanding of fabric genesis, diagenesis, and preservation.