Porosity in bacterially induced carbonates: Focus on micropores

Bacteria are responsible for the precipitation and accumulation of some significant carbonate deposits; prime examples are hot spring travertine accumulations. Bacteria induce precipitation of carbonate minerals immediately surrounding their cell wails and, in doing so, entomb themselves within the crystals. Subsequently, a generation of abiotically precipitated clear spar commonly cements cell colonies as well as the initial bacterially induced carbonate. The relatively rapid decay of the bacterial fossils, consequently, results in localized abundances of unconnected microporosity. This submicron-to micron-size porosity is not normally detected by standardized porosity evaluations. These pore systems, which are especially abundant in hot spring travertine deposits, can influence density measurements and, therefore, any calculations in which density is a factor. The pores have been found to be abundant within different bacterially induced features, such as shrubs, peloids, and oncoids. Other forms of porosity common in hot spring travertines include shelter porosity, foam rock, and some highly irregular early dissolution of the carbonate caused by the abundance of nonmarine waters coursing through these rocks.