Role of Organic Matter in Precipitation of Cement: Examples from Three Different Environments

Brenda L. Kirkland¹, F. Leo Lynch¹, Robert L. Folk², Athena M. Owen¹, John E. Mylroie¹, Jonathan D. Culpepper¹, and William K. Funderburk^1
1Geosciences, Mississippi State University, Mississippi State, MS
²Geological Sciences, University of Texas, Austin, TX

Travertine from hot springs near Viterbo, Italy contains clusters of minute (50-100 nm) spherical structures in the center of aragonite botryoids, fuzzy dumbbells, and aragonite spheres. The distal parts of the aragonite botryoids are composed of smooth needles. A sample embedded in paraffin, thin sectioned, and stained with fast green, shows the aragonite initiated on organic matter. TEM samples fixed with osmium, embedded in resin, sectioned, stained with uranyl acetate and lead citrate, reveal organic matter in the interior of fuzzy dumbbells and aragonite spheres.

Well indurated, iron-rich horizons from the Cretaceous Eutaw and Paleocene Wilcox formations of east-central Mississippi contain hematite cements with botryoidal morphology. The gross morphology of these cements suggests that they coat bacteria. In thin section, organic matter is visible in the center of botryoids. In SEM, tiny spheres (100nm) are present in the interior of botryoids, and like the hot-spring aragonite, the distal portions of the botyroid crystals are smooth.

Meteoric cement in Quaternary carbonate eolianites in the Bahamas initiates on organic-rich allochems. Some of these equant crystals have a smooth face, but where crystal growth is incomplete small spheres (100 nm) are visible under SEM. Bacteria are present at the base of crystals, but small spheres are present throughout the crystals. SEM also reveals meteoric meniscus cement morphology identical to the meniscus formed by biofilms cultured in sandstone in the laboratory. In thin sections cut with oil, relict organic matter is visible in the equant spar.

The very small (100 nm) spherical structures are interpreted as nannobacteria and associated organic matter. Their presence in these three disparate settings suggests that organic matter plays a role in cementation.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas