June 2009 Geology and GSA Today media highlights

Boulder, CO, USA - GEOLOGY includes details on the 12 May 2008 Wenchuan earthquake; a natural gas-hydrate system offshore of Korea; findings that abiogenic methane emissions may be more prevalent than originally thought; two studies on the nature of mud; and three fossil studies, one finding evidence for lush forests and rich animal life in the Eocene High Arctic, and two concentrating on bones in Montana, Madagascar, and Sharktooth Hill, California. GSA TODAY examines Greenland's contribution to sea-level change.

Bedload transport of mud by floccule ripples -- Direct observation of ripple migration processes and their implications
Juergen Schieber and John B. Southard, Dept. of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA. Pages 483-486.

It is a widespread assumption among geoscientists that muds accumulate by settling after suspension in quiescent waters. Recent flume work has shown, however, that mud can accumulate from swift-moving suspensions because floccules form that travel in bedload in the form of ripples. Observing the sediment movement in these ripples is hampered by the inherently turbid nature of muddy suspensions. Schieber and Southard have now succeeded in imaging sediment movement associated with these floccule ripples. Floccule ripples, although having a water content near 90% (by volume), have cross sections comparable to sand ripples, and the transport of sediment across these ripples is directly analogous to the processes observed for sandy ripples. Thus, even though the particles that compose floccule ripples are fragile and significantly less dense than sand grains, transport processes and morphologies are the same in both cases. This is the first direct observation of particle movement and migration processes in bedload ripples of flocculated mud.

Truncation and translation of Appalachian promontories: Mid-Paleozoic strike-slip tectonics and basin initiation
James Hibbard and John W.F. Waldron, Dept. of Marine, Earth and Atmospheric Sciences, Jordan Hall, Faucette Drive, North Carolina State University, Raleigh, North Carolina 27695, USA. Pages 487-490.

The wave-like structural trend, or "grain," of the Appalachian mountain belt was inherited from the original shape of the eastern North American margin after the break up of the supercontinent Rodinia. This shape was imprinted on multiple island arcs and microcontinents that accreted to eastern North America between about 500 and 300 million years ago to form the Appalachians. In the Carolinas and in Newfoundland, the wave-like trend of the mountain belt in the more easterly portions of the Appalachians is offset from that inland. Hibbard and Waldron propose that this offset is the result of more than 200 km of displacement along a fault system that was operative along the entire eastern margin of North America approximately 360 million years ago.

Drainage basin response to climate change in the Pisco valley, Peru
Damian Steffen et al., Institute of Geological Sciences, University of Bern, CH-3012 Bern, Switzerland. Pages 491-494.