March GEOLOGY and GSA TODAY media highlights

Boulder, CO, USA - Topics include: imaging of impact strata on Mars' Holden Crater; Eocene-Oligocene conditions leading to the freezing of Antarctica; evidence that liquid water is not responsible for recent changes observed in Martian gullies; new insights into Cretaceous early Albian greenhouse conditions and implications for future atmospheric carbon dioxide levels; new estimates of Earth's copper supply; discovery of large nitrate pools under the Mojave's desert pavement; frequency of magnitude 9 earthquakes; and the pre-Grand Canyon Colorado River.

Highlights are provided below. Representatives of the media may obtain complimentary copies of articles by contacting Ann Cairns at . Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOLOGY in articles published. Contact Ann Cairns for additional information or other assistance.

Non-media requests for articles may be directed to GSA Sales and Service, .

HiRISE imaging of impact megabreccia and sub-meter aqueous strata in Holden Crater, Mars

John A. Grant et al., Center for Earth and Planetary Studies, National Air and Space, Museum, Smithsonian Institution, 6th at Independence SW, Washington, DC, 20560, USA. Pages 195-198.

Grant et al. use images of Holden crater from the High Resolution Imaging Science Experiment (HiRISE) on Mars Reconnaissance Orbiter (MRO) to resolve, for the first time, megabreccia deposits in the walls that were created during the formation of the crater. These impact deposits contain enormous blocks that are up to 50 meters across and are unconformably overlain by water-lain sediments deposited during two ancient phases (during the Noachian Era) of aqueous activity. A lighter-toned and typically finely bedded lower unit exhibiting clay minerals was probably deposited in a long-lived lake setting. An overlying darker-toned and often blocky upper unit drapes the lighter-toned deposits. The upper unit was emplaced during later high-magnitude flooding as a lake, impounded outside of Holden and within adjacent Uzboi Vallis, overtopped the crater rim, draining into the crater. The stratigraphy exposed in Holden crater provides the first geologic context for deposition of clays during persistent wet and perhaps habitable conditions on early Mars.

Identifying tsunami deposits using bivalve shell taphonomy

S.V. Donato et al., McMaster University, School of Geography and Earth Science, Hamilton, Ontario L8P 4A9, Canada. Pages 199-202.

On 28 November 1945, off the coast of what is now Pakistan, a large earthquake (8.1 Mw) produced a destructive tsunami. Despite news reports chronicling the tsunami in Pakistan, Iran, and India, no records describing the magnitude of the event exist for Oman. Donato et al.’s study documents the characteristics of a shell bed deposited by the 1945 tsunami in Sur Lagoon, Oman, and describes a new technique for identifying tsunami deposits in the geologic record using shell preservation. This shell bed provides the first physical evidence that the large tsunami impacted this region of Oman.