PLANT BIOMINERALS AS GEOLOGIC, CLIMATIC, AND BIOLOGICAL INDICATORS

Biomineralization in plants can serve several functions, such as mechanical and structural roles, storage of chemicals, and sequestration of undesirable or toxic compounds. Plant biominerals generally consist of amorphous silica (phytoliths) or calcium salts of carbonate (cystoliths), phosphate, and oxalate. Because of their high silica content, phytoliths are frequently preserved in the fossil record as distinct and identifiable microfossils, whereas preservation of calcic biominerals is less common. Biominerals may carry morphological characteristics that enable the identification of the original organ parts and are thus useful paleontological indicators of plant types and environmental conditions. Likewise they have been used to determine human diet, climate and environmental conditions in archeological studies.

Very limited plant biomineral research has been done in the southwestern United States, mainly by the archeological community, and concerned primarily with phytoliths of food plants. We are producing a library of plant biominerals focused on the southwest, particularly the Chihuahuan desert, but also extending into the Sonoran and Mojave deserts. Our goal is identification of plant biominerals that may provide climatological and environmental data at paleontological, archeological, and geomorphological study sites. We have collected representative plants from around the region and used methods of ashing and digestion to liberate the biominerals. Coupled with optical and scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction, we are compiling a catalog of biomineral morphologies and chemistry that can be used in comparison studies.

Plant biominerals entombed in cave speleothems and sediments are being studied from Ft. Stanton Cave, NM. Samples of fine-grained sediment are sorted by particle size, and biominerals were separated using heavy liquid floatation. Identifying biominerals from cave flood deposits can reveal the hydrogeological history and other geomorphological processes of significance that have been preserved in the cave.