Ancient, Gigantic Drainage Basin Become Aquifer On Mars

2.2 MB Quicktime Movie

From Lori Stiles, UA News Services, 520-621-1877

An enormous ancient drainage basin and aquifer system lies hidden and
deformed in one of the most geologically dynamic landscapes on Mars,
scientists conclude from a comprehensive, more than 10-year study.

They estimate that a basin almost the size of the United States or Europe
for billions of years covered part of Tharsis, a magmatically active bulge
in the western hemisphere. Tharsis landforms are a complex of towering
volcanoes, lava flow fields, igneous plateaus, fault and rift systems, flood
channels, vast canyon systems, and tectonic features. Most scientists
believe that periodic release of internal planetary heat at Tharsis has for
more than three billion years had a major impact on Mars’ geology, hydrology
and climate.

Parts of the aquifer may harbor near-surface water and possibly life, they
add.

University of Arizona hydrologist James M. Dohm and his colleagues are
reporting their basin/aquifer system hypothesis both in an article in the
Journal of Geophysical Research – Planets and in a 3-dimensional animation
on the Internet.

A 2.2 megabyte QuickTime version can be downloaded from the UA website,
http://uanews.opi.arizona.edu/movies/tharbasin.mov (QuickTime software can
be downloaded at http://www.apple.com/quicktime/download ). The JGR Planets
paper can be downloaded as a pdf file at
http://www.agu.org/pubs/pip/2000JE001468.pdf.

Collaborating in the research are Justin C. Ferris, Victor R. Baker and
Robert G. Strom of the University of Arizona, Robert C. Anderson of the Jet
Propulsion Laboratory in Pasadena, Calif., Trent M. Hare and Kenneth L.
Tanaka of the U.S. G.S.-Flagstaff, Nadine G. Barlow of the University of
Central Florida, and James E. Klemaszewski of Arizona State University.

They estimate that the 45 million cubic kilometer (11 million cubic mile)
Tharsis basin ranged between 2 kilometers to 7 kilometers in depth (1.2
miles to 4.4 miles) and, if filled to an average depth of 5 kilometers (3.1
miles), would have a capacity of 12 billion billion gallons.

As lavas, sediments and volatiles (primarily water) partly infilled the
basin early in Mars’ history, the basin was transformed into a vast regional
aquifer. This aquifer would serve as a potential source for water that
carved what are believed to be the largest flood channels in the solar
system, and helped fill lakes and oceans on ancient northern Mars.

If the terrestrial materials that filled the Tharsis basin are as porous as
sediments and lavas on Earth, “then the potential volume of water contained
in the aquifer would be more than equivalent to the volume of water required
to create the putative ocean in the northern plains,” the scientists wrote.

Baker, Strom, and others have long theorized that Mars’ northern plains
featured an ocean about a third as large as Earth’s Indian Ocean and a
smaller ocean the size of Earth’s Arctic Ocean at least once in the ancient
past. Baker and colleagues have since developed this idea as the
“MEGAOUTFLO” hypothesis. The theory says that Mars’ history is punctuated by
pulses of magmatic activity which trigger catastrophic floods, formation of
oceans or lakes in the northern plains, and brief episodes of climate change
lasting tens of thousands of years.

The scientists’ 3-D visualization portrays how the Tharsis region landscape
evolved over the past more than 3 billion years. The movie summarizes five
geologic stages, with stage one depicting the ancient drainage basin and
stage five depicting the present-day Tharsis landscape.

Dohm and colleagues based the sequentially reconstructed ancient terrains on
geological and hydrological research. They synthesized analyses by many
planetary scientists who began studying Viking data more than a decade ago
and recently obtained high-resolution topographic data from the Mars Orbiter
Laser Altimeter on the Mars Global Surveyor spacecraft.

The movie is “not a quantitatively accurate reconstruction of martian
paleotopography at discrete time steps,” the scientists wrote. “Such a
reconstruction may well be possible at a future date when more data become
available.” It is “an illustrated working hypothesis” that leads to the
identification of an ancient, gigantic drainage basin that persists through
much of the history of the region” and is consistent with diverse
observations of martian geology, they said.

“Large topographic highs, including mountain ranges, an igneous plateau,
topographic rises resulting from tectonism and other magmatic-driven
processes, and large impact craters formed the margin of the gigantic
drainage basin,” Dohm said.

Magmatic and tectonic activity later fractured, deformed and, in places,
exposed the stacked sequences of water-bearing layers in the aquifer, he
added. The researchers interpret the layered canyon walls of Valles
Marineris at the center of the proposed drainage basin, for example, to be
basin fill comprised of layered flood lavas possibly laced with eroded lake
and wind deposits.

Magmatic and tectonic energy also drove sediment-charged flood waters toward
the northern plains and transferred water laterally so it collected at
unmodified parts of the aquifer.

“The unmodified parts of the basin/aquifer system appear still to contain
near-surface water reservoirs that may one day be sampled and analyzed by
astronauts,” Dohm said. He collaborated with Nadine Barlow of the University
of Central Florida in recent research that suggests Mars today has such a
“watering hole.”

More, there may be hydrothermally active sites in the basin/aquifer similar
to hydrothermally active sites on Earth now known to harbor life, Dohm said.
These potential aqueous environments are prime candidates for hydrologic,
mineralogic and “exobiologic” exploration, Dohm and his colleagues
emphasize.

Before he joined the UA in 1999, Dohm worked more than a decade at the U.S.
Geological Survey in Flagstaff as assistant coordinator of NASA-funded Mars
and Venus mapping programs, now called the Planetary Mapping Program.

Contact Information

James M. Dohm

520-626-8454 jmd@hwr.arizona.edu

Justin C. Ferris

520-370-6357 ferris@hwr.arizona.edu

Victor R. Baker

520-621-7875 baker@hwr.arizona.edu