The Arizona Geological Survey just released a new geologic map (65Mb) and 18-page report (9Mb) on Petrified Forest National Park in Arizona (located 25 miles east of Holbrook). Both can be downloaded for free here. Printed copies can be purchased from the Arizona Experience Store, 416 W. Congress, Tucson, AZ 85701; e-mail – store.azgs.az.gov, ph. 520.770.3500.

The Upper-Triassic age (ca. 225 million years old) Chinle formation on the Colorado Plateau hosts the petrified wood and represents deposits of river systems originating in what is now western Texas and fed by tributary streams from highlands to the south and north of National Park. The Chinle Formation preserves a suite of lowland terrestrial environments that includes river channels, floodplains, swamps, and small lakes operating in a strongly seasonal subtropical climate. The rocks show that with time, the climate became arid.

Within the National Park, the Chinle formation contains fossils of petrified wood, boney fish, sharks, locally abundant bivalves, gastropods, freshwater crustaceans and trace fossils of a wide variety of insects and other small arthropods.

The well-illustrated report shows the geologic history of the area through a series of cross-sections. That history includes the existence of an extensive lake which persisted for about 12 million years. The report also contains many photographs.

One thing the report does not do is explain how petrified wood forms but the Spring 1989 issue of Arizona Geology has a good description:

After the trees were transported downstream and became trapped in shallow waters, fluvial deposits of silt, mud, and volcanic ash from volcanoes to the south or west buried the logs and cut off the supply of oxygen; decay was thus retarded. Ground water percolating through the sediments dissolved silica from the volcanic ash. As the silica filtered through the logs, it precipitated from solution as microscopic quartz crystals in the woody tissues where air, water, and sap were originally present in the living tree. In some logs, cell structure remained intact, albeit entombed. Where the logs were hollow, woody tissue did not limit crystal growth; large crystals of rose quartz, smoky quartz, amethyst, and other gemstones or large masses of amorphous (noncrystalline) chalcedony and chert lined the cavity walls. Originally, researchers believed that minerals replaced the wood fibers. In recent experiments, however, after acid was used to dissolve the minerals, the original woody tissue was visible under a microscope.

As the silica petrified the wood, other elements in the water, such as iron, copper, manganese, and carbon, added tints of red, yellow, orange, brown, blue, green, purple, and black to the fossilized tissues. In some logs, tunnels and galleries are visible, the remains of ancient excavations dug by Triassic insects. The high degree of preservation of the logs and other fossils in the Chinle Formation is due to favorable conditions, such as warm temperatures, high moisture, and little or no oxygen, during and after deposition of the sediments.

This geologic map was a long time in coming. See notes by Bill Parker one of the authors here.

Citation

Martz, J.W., Parker, W.G., Skinner, L. and Raucci, J.J., Umhoefer,P. and Blakey, R.C., 2012, Geologic Map of Petrified Forest National Park, Arizona. Arizona Geological Survey Contributed Map CR-12-A, 1 map sheet, 1:50,000 map scale, 18 p.

Here is a photo I took in the Park many years ago:

The age of the Grand Canyon of Arizona has always been controversial and more fuel has been added to the controversy with the publication in Science on November 29 of a new study by researchers Rebecca Flowers and Kenneth Farley who say they have evidence that the Grand Canyon “was largely carved out by about 70 million years ago.” Their full paper is behind a pay wall but you can read the press release here. The contentious problem with that age is that the current Colorado River has been flowing along its present course and direction for only about 6 million years. For that story, see my post, written in 2011: “Origin of the Grand Canyon.”

The Arizona Geological Survey has weighed in on this controversy in their new Fall-Winter 2012 issue of Arizona Geology magazine with an article by Wayne Ranney, a geologist who has long studied the canyon and has written a book about it. What follows are excerpts from Ranney’s article.

“The new theory involves two very complex and complicated laboratory techniques that can reveal when the canyon’s rocks were brought close to the surface. Using tiny apatite crystals collected from the basement rocks in the canyon (Vishnu Schist or Zoroaster Granite), the information yielded two different stories, one for the history of the western Grand Canyon and the other for the eastern canyon, where most tourists see the gorge. The results said that western Grand Canyon (downstream from Lava Falls) was cut to within a few hundred meters (about 1,000 feet) of its present depth by 70 Ma [million years ago]. The second story reported that the eastern area was the site of a canyon of similar proportions to the modern canyon by 55 Ma, and cut in Mesozoic rocks now completely eroded away. Incredibly, the western canyon was cut by a river that flowed exactly opposite to the modern Colorado River and the researchers call this the California River.”

Reread the paragraph above. It says that in the eastern canyon area, a canyon equal to the current one was formed, then disappeared.

Ranney continues:

 ”When the Cal Tech group began their study they assumed that the apatite samples would reveal that Grand Canyon’s rocks were buried in unequal amounts of overlying rock – unequal because the canyon today has 5,000 feet of relief and the lower samples should have been buried under more material than those collected from near the top.”

That concept is shown in figure 1. The red dots show the relative position where Flowers and Farley collected their samples.

“After running the laboratory technique the samples produced surprising results to the researchers. They showed that no matter from what depth the samples were collected, they all appeared to have been buried under equal amounts of overlying rock [figure 2]. When the tops of the blue arrows are connected here, they reveal a canyon-like topography in eastern Grand Canyon about 70 Ma. Below is a diagram [figure 3] that shows their interpretation of the data – a gorge of similar proportions was cut into the Mesozoic rocks that are now stripped back to the modern Echo and Vermilion Cliffs.”

 

Ranney opines that the laboratory technique used by Flowers and Farley “is not as evolved as one might hope for. Some assumptions are made that could result in different outcomes.”

Ranney also notes: “The evolutionary history of the Colorado River shows that its exact course through the canyon to the Gulf of California was accomplished in only the last 6 million years.” He emphasizes, however, that the age of the Colorado River is not necessarily the same as the canyon, “the age of its [the river’s] ancestors or some early incarnation of the canyon need not be so strictly confined.”

Read Ranney’s entire article here.

Check out other stories in Arizona Geology Magazine here.

For more geology stories, see my Article Index page.

One way to deal with carbon dioxide emissions from fossil-fuel-burning power plants is to bury the carbon dioxide underground. Deep sedimentary basins such as the Tucson Basin have been proposed as possible depositories.

The Arizona Geological Survey has a new report “Geologic Evaluation of the Tucson Basin for Carbon Dioxide Sequestration Potential.” The citation for the report is:

Gootee, B.F., 2012, Geologic Evaluation of the Tucson Basin for Carbon Dioxide Sequestration Potential. Arizona Geological Survey Open File Report, OFR-12-40, v 1.0, 11 p., 3 plates

Besides the text, the report includes a geologic map and cross-sections, all freely downloadable.

The press release from AZGS says in part:

“A viable geologic repository for sequestering carbon dioxide must meet three conditions. First, it must host a substantial volume of porous and permeable rock or sediment at a depth of more than 800 meters (2,625 feet); a depth sufficient to maintain carbon dioxide in a supercritical state where it behaves more like a liquid than a gas. Second, the repository must host saline groundwater – to prevent contamination of fresh water aquifers. Third, it must be capped by a continuous impermeable layer of clay, salt or some other coherent and impermeable material, to prevent carbon dioxide from migrating surface-ward.”

The report itself concludes:

“A preliminary evaluation of the storage potential for CO2 in saline-permeable strata below an impermeable caprock in the Tucson basin is inconclusive. This is primarily due to the dearth of deep well data in the basin. Permeable strata below 800 m (2,625 ft) depth is sufficiently thick and potentially favorable for CO2 sequestration; however, the lack of salinity data for deep aquifers precludes an adequate assessment of storage volumes in saline formations below 800 m. Based on available data, the presence of an extensive seal or capping unit near or below 800 m (2,625 ft) depth could not be identified.”

Funding for the investigation is supported by the Department of Energy and by WESTCARB, a consortium of seven western U.S. States (including Arizona) and one Canadian Province.

Comment:

As I have written in a previous post: Clean Coal: Boon or Boondoggle?, “While carbon capture and storage (CCS) may be technologically possible, it makes no sense either economically or scientifically. It is a solution seeking a problem; it is utter wastefulness.” The whole idea results from the still unproven contention that carbon dioxide makes a major contribution to global warming. CCS schemes also provide no proof that they would make a measurable difference. Furthermore, carbon dioxide is a salable commodity; it is used by the oil industry to flush oil out of the rocks. Why bury it first?

Having voiced my opinion on the folly of CCS, please note that the Arizona Geological Survey does not judge the merit of the program, they only assess the geologic capacity of certain basins to provide the proper geologic conditions to make it work.

For more information on the Tucson Basin see: What Lies Beneath the Tucson Valley.

The Arizona Geological Survey has also been involved in assessing the geothermal potential of the region, see: New Source of Geothermal Energy in Western US and Arizona Geological Survey Leads Geothermal Energy Study.