This view shows the extensive deposits of travertine exposed on the walls of the Inner Gorge of the Canyon near Mile 126.  The plethora of travertine observed across the spectrum of both carbonate and non-carbonate units caused me to ponder its source.

This view shows travertine cemented colluvial detritus armoring slopes underlain by the softer Bright Angle Shale along the river channel near its confluence with the Little Colorado.

Field sketch of the scene depicted above.  I hadn’t previously observed travertine deposited on dense micaceous shales.  It likely precipitated from other sources, discussed below.

The classic model for travertine formation is that it emanates from dissolved carbon dioxide (CO2) in percolating groundwater, creating a weak carbonic acid (H2CO3).  This weak acid then reacts with limestone to form soluble calcium acid carbonate, CaH2(CO3), which is precipitated when the water evaporates at some exposed surface (usually springs).

Observations of travertine formation at nearby Lake Powell have generated alternative models for travertine formation in semi-arid climates, such as the mechanisms sketched here.  In this scheme diatoms and phytoplankton breeding in the warmer surface waters of a eutrophic lake cause a seasonal rise in pH, which enhances carbonate precipitation.

In this model carbon is fixated by algae in the warmer surface waters of a lake.  A summertime rise in the pH of the surface waters can trigger calcite precipitation in the lake and along its shores.  This mechanism would enable travertine to be precipitated in the warm water zone.

Longitudinal profile segments of the present day river channel, showing vertical extent of travertine and river gravel deposits preserved on the Canyon walls between Miles 56-73 and 150-157.  The travertine seems to crest around elevation 3440, irrespective of the underlying stratigraphy.  The highest lava dam extended up to about elevation 4125.

Similar longitudinal profile comparisons, between Miles 115 and 157, across the Kaibab Uplift.  The lacustrine sediments appear to peak around elevation 3120 while the travertine extends to around elevation 3480.  In 1979 I suggested that these were remnants of the lakes that must have been impounded behind the lava dams in the western Canyon, downstream of Mile 178.

Histogram illustrating elevation correlations between travertine deposits taken over the entire Grand Canyon, based on the 1976 geologic map.  The absolute level correlations make a convincing case for the travertine being deposited in Pleistocene lakes formed behind lava dams in the western Canyon..

During my forst pass through Marble Canyon I noticed what appeared to be two ancient carbonate bleach lines high on the cliffs above the gorge, downstream of Tanner Wash, Mile 15 (see above image).

Cross section of Marble Canyon near Mile 15, where above photo was imaged.  I’ve sketched in the maximum lake level of the Toroweap lava dam, around elevation 4125.  This appears to correspond with the "bleach lines" shown in the preceding photo, which appear on the Toroweap formation.

Aerial oblique view of the Navajo Bridge area of the Vermillion Cliffs near Lee’s Ferry, at Mile 4.  The Moenkopi shales at the base of the escarpment are unusually rounded and subdued, suggesting that they were inundated beneath lake waters in the relatively recent geologic past.  These cliffs would have been inundated by lakes impounded behind the highest lava dams, up to elevation 4125 feet.

Questions or comments on this page?
E-mail Dr. J David Rogers at rogersda@umr.edu.