March/April Geological Society of America Bulletin media highlights

Protolith ages and exhumation histories of (ultra)high-pressure rocks across the Western Gneiss Region, Norway
Emily O. Walsh, Cornell College, Geology Department, Mt. Vernon, IA 52314, USA; et al. Pages 289-301.

Keywords: ultrahigh pressure, Western Gneiss Region, secondary ion mass spectrometry, 40Ar/39Ar, exhumation, laser ablation inductively coupled plasma mass spectrometry.

The mechanisms by which ultrahigh-pressure rocks are exhumed remains a geological puzzle that can only be solved by considering the behavior of the entire orogeny, including associated lower pressure rocks. This article presents a series of new U/Pb zircon, Th/Pb monazite, and 40Ar/39Ar muscovite ages from a transect spanning the Western Gneiss Region, Norway, from the orogenic core to the foreland. These data reveal older-than-predicted protolith ages; corroborate existing metamorphic ages, and depict slab geometry during exhumation.

Late Quaternary climate change, loess sedimentation, and soil profile development in the central Great Plains: A pedosedimentary model
Peter M. Jacobs, University of Wisconsin–Whitewater, Geography and Geology, Whitewater, WI 53190, USA; and Joseph A. Mason, University of Wisconsin–Madison, Dept. of Geography, Madison, WI 53706, USA. Pages 462-475.

Keywords: Great Plains, soils, stratigraphy, loess, Holocene, paleosols.

The Great Plains region is known for both its sensitivity to drought and its importance to world food production. Jacobs and Mason conclude that the thick, dark, and highly productive topsoil of the central Plains originated through dust deposition during recurring drought conditions over much of the past 9500 years. In contrast, the clay-rich subsoil represents an ancient soil surface, marking a period of unusually slow dust sedimentation under a rapidly warming and wetter-than-present climate at the end of the Pleistocene ice age. Chemical and mineral signatures were used to trace dust dispersal, from near-source sites where dust deposits are thick and well-dated, to soils across the central Great Plains.

Orbital forcing of mid-latitude Southern Hemisphere glaciation since 100 ka inferred from cosmogenic nuclide ages of moraine boulders from the Cascade Plateau, southwest New Zealand
Rupert Sutherland, GNS Science, Wellington 6009, New Zealand; et al. Pages 443-451.