IMAGING THE INTERFACE BETWEEN ORGANIC MOLECULES AND CARBONATE MINERAL GROWTH

Microbial activity is commonly associated with carbonate mineral development. The overall mechanisms of their association are poorly understood; however, clues are left behind. Authigenic carbonate minerals are present in possible relation to organic structures. This project is designed to promote better understanding of the organic to carbonate mineral interface by imaging their relative association. The goal is to better explain carbonate minerals found in nature by documenting the relationship between organic compounds and carbonate precipitates.

Carbonate mineral growth appears to be induced by organic molecules, which act as nucleation sites for mineral growth. To demonstrate this process, precipitation experiments were conducted growing carbonate minerals along with the organic molecules palmitic and systolic acid, which were chosen because they are abundant in biofilms. In SEM these organic molecules show spheroidal structures that are visibly different from smooth crystal faces. EDX and XRD analysis of the spheroidal structures in the precipitation experiments prove the structures are primarily organic. TEM analysis of these precipitates shows evidence of the carbonate minerals using the organic structures as substrates for nucleation. Though the mechanism is still poorly understood, the association between organic material and carbonate minerals is better established by visual documentation.

A visually similar association between carbonate minerals and spheroidal structures is a pattern found repeatedly in nature. SEM and TEM analysis of Icehouse sea authigenic carbonate rocks in the Permian Capitan Formation in Texas and Lighthouse Reef bluehole in Belize have demonstrated a similar pattern of spheroidal features at the core of aragonite botryoids.