August 2008 Geology and GSA Today media highlights

Boulder, CO, USA – GEOLOGY topics include confirmation that East Java's "Lusi" mud volcano was most likely triggered by a blowout in the Banjar Panji-1 well; evidence of the oldest human presence yet discovered along Egypt's northern Nile delta; analysis of Yellowstone's hotspot; and GPS measurements that show why no large earthquakes occur in the Snake River Plain. GSA Today's science article studies the impact of Glen Canyon dam in Grand Canyon on sandbar ecosystems along the Colorado River.

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

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Predynastic human presence discovered by core drilling at the northern Nile delta coast, Egypt

Jean-Daniel Stanley et al., Smithsonian Institution, Rm. E-205 NMNH, Paleobiology, 10th St. and Constitution Ave. NW, Washington, DC 20013, USA. Pages 599-602.

A small but significant find made during a geological survey provides evidence of the oldest human presence yet discovered along the northernmost margin of Egypt's Nile delta. A rock fragment carried by humans to the site was discovered in a sediment core section north of Burullus lagoon near the Mediterranean coast. Radiocarbon analysis of plant-rich matter in the mud surrounding the object provides a date of 3350 to 3020 B.C., the late Predynastic period. This long, thin object, formed of dolomite, had not been deposited by the Nile or the sea, but was collected and transported from an outcrop exposure positioned at least 160 kilometers south of the core site. The fragile object lay buried at a depth of 7.5 meters in dark mud deposited in a brackish lagoon setting close to a marsh. Stanley et al.'s fortuitous find documents an early human presence in the mid-Holocene wetlands along the delta's paleocoast, a sector where traditional excavation and augering are normally incapable of reaching zones of ancient human activity now at considerable subsurface depths.

Mantle earthquakes frozen in mylonitized ultramafic pseudotachylytes of spinel-lherzolite facies

T. Ueda and Masaaki Obata et al., Dept. of Geology and Mineralogy, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan. Pages 607-610.

Ueda et al. present a new type of ultramafic pseudotachylyte from Balmuccia peridotite, a "fossil" of mantle earthquakes. They report a case in which a ductile shear localization led to a seismic rapture and frictional melting of spinel peridotite, and the thus-produced pseudotachylyte was subsequently mylonitized and recrystallized in spinel lherzolite facies. Ueda et al. hypothesize that the chemical evolution of fluid phases, from H2O-rich to CO₂-rich, played a critical role for such a rheological transition.