Travertine Study

Travertine Study

Rebecca Gardner and Laura Crossey

	*Results presented here are taken from an abstract presented at the GSA Annual Meeting, 1996 (Abstracts with Programs, v. 28).*
	Warm, saline CO₂-charged springs and their associated travertine deposits are located at the junction of three geologic provinces in northeastern New Mexico. Stratigraphic evidence indicates that several different episodes of travertine deposition have occurred in this region. Each episode appears to have been influenced by changes in basin hydrodynamics, tectonics, Quaternary geomorphology, and/or climate change. Travertine deposits in this region may provide a useful record of the interplay between these influences. In particular, the laminated deposits may contain a geochemical record of changes in basin-margin paleohydrology.	Swimming Pool Springs flows out of the Pajarito-Naciemento fault, seen behind in the center; the Triassic Chinle Formation on the left is against the Permian Abo Formation on the right.

Big Mama Spring; cistern is 20m deep, and 20m in diameter.

In order to interpret the potential record contained within the travertine deposits, we have undertaken a hydrochemical study of two series of springs and travertine deposits. This study focuses on three areas: 1) regional spring chemistry and potential end-member sources, 2) calcium carbonate mineralogy and geochemistry of the deposits, and 3) aqueous geochemistry of the springs. Monthly and diurnal sampling of both water and calcium carbonate deposits sampled down one spring's flowpath (Big Mama) allow us to couple the geochemistry of the travertine to the geofluid from which it precipitated.

Flow Path Study:
Monthly samples were collected from the deepest parts of a flowing channel. Temperature, pH, and dissolved oxygen were found to increase down the flow path due to exposure in the sun and subsequent degassing/equilibrium with the atmosphere. Na, K, Cl and SO₄ also increased down the flow path, while Ca correspondingly decreased. The decrease in Ca coincided with a 2-fold increase in calcite saturation. At the spring outflow point, water was at or just below calcite saturation; calcite (and aragonite) oversatuation is reached down flow. Calcite growth rates were determined to be approximately 1 mm per month.

Active flow path during summer of 1996. Precipitation of calcite in areas surrounding the flow path form the channels (as opposed to calcite dissolution within the channels). White areas are precipitated salts, while the red areas are an iron precipitate which formed over the summer months.

A core from the travertine mound at Big Mama Spring. The rhythmic laminations are at a cm-scale.

Rimstone dam and pool structures within the travertine that surrounds the flow path channels. The green tinge is bacteria.


	Petromicrograph of some of the precipitated calcite (Field of View = 3.25 mm). The close-up is shown to the right.	Field of View in this photomicrograph is 0.65 mm. Two calcite crystal fabrics can be seen: radiating crystals and "shrub" crystals. The small rhythmic laminations are approximately 20 microns wide.

Cation analyses of the calcite (?? or water?) which precipitated over a 24 hour period at Big Mama Spring.

Diurnal Study:
Water and calcite samples were collected at one location along a flow path at the Big Mama Spring over a 24 hour period. Water was collected every 1/5 hours, while calcite was allowed to precipitate during the entire 24 hour period. Temperature and composition of the waters and calcite were measured. Results indicate that temperature plays a signficant role in the geochemistry of the flow path. We hypothesize that CO₂ degassed at a slower rate at lower temperatures.

Temperature and alkalinity variations during the 24 hour sampling period.

Created: 10/7/98 Updated: 4/9/99