March GEOLOGY and GSA TODAY media highlights

Rapid warming and salinity changes of Cretaceous surface waters in the subtropical North Atlantic

Thomas Wagner et al., School of Civil Engineering and Geosciences, Devonshire Building, Newcastle University, Newcastle upon Tyne NE1 7RU, UK. Pages 203-206.

Paleo records reveal occasional and rapid releases of greenhouse gases into the atmosphere. The regional consequences on the surface ocean processes and timing between the atmospheric changes and ocean changes, however, are still far from understood. Wagner et al. examined an exceptionally well-preserved section of the early Albian oceanic anoxic event 1b (OAE) (112 million years ago) occurring in the warm Cretaceous greenhouse period. By studying one distinct and relatively short climate perturbation in the geological past, Wagner et al. aimed to better understand the mechanism and feedbacks of short climate perturbations. Atmospheric carbon dioxide concentrations in the Cretaceous early Albian period were reconstructed to have ranged from 500 to 3000 parts per million. The consensus of climate scientists is that a 200 percent increase of modern levels of atmospheric carbon dioxide may occur by 2100 or later, placing future levels of atmospheric carbon dioxide within the range of early Albian greenhouse conditions.

From slow to ultraslow: A previously undetected event at the Southwest Indian Ridge at ca. 24 Ma

Heather Sloan et al., Environmental, Geographic and Geological Sciences, Lehman College, CUNY, 250 Bedford Park Boulevard West, Bronx, New York 10468, USA. Pages 207-210.

Using a newly compiled set of published and unpublished magnetic data, Sloan et al. reconstruct plate motion at the Southwest Indian Ridge. Findings indicate a 50 percent drop in spreading rate at circa 24 million years ago. This shift from slow to ultraslow spreading had remained undetected because it was not accompanied by a change in spreading direction which would have been observed in fracture zone trends. This change in relative motion appears to have been transmitted to two of the four adjoining plate boundaries. Occurring during a period of significant change in relative and absolute plate motion, the rate of change at the Southwest Indian Ridge is interpreted as part of a global event along the plate boundary system.

Recent bright gully deposits on Mars: Wet or dry flow?

Jon D. Pelletier et al., University of Arizona, Department of Geosciences, 1040 E. Fourth Street, Tucson, Arizona 85721, USA. Pages 211-214.

Flow deposits laid down on Mars within the last few years look like they were laid down by flowing water. In this paper, Pelletier et al. test this hypothesis by computer modeling of water-based versus dry landsliding. Dry landslides can "fluidize" under certain conditions and appear as though they were laid down by water. Model results show that the observed deposit on Mars was most consistent with a dry landsliding process. This has important implications in the debate about the presence/absence of liquid water on the surface of Mars today.