Boulder, Colo., USA: GSA s dynamic online journal,
Geosphere, posts articles online regularly. Locations and topics studied this month include the Central Anatolian Plateau; the Southern Rocky Mountain Volcanic Field; petrogenesis in the Grand Canyon; and the evolution of the Portland and Tualatin forearc basins, Oregon.
A physical and chemical sedimentary record of Laramide tectonic shifts in the Cretaceous-Paleogene San Juan Basin, New Mexico, USA
Kevin M. Hobbs; Peter J. Fawcett
Abstract: Fluvial siliciclastic rocks bracketing the Cretaceous-Paleogene (K-Pg) boundary in the San Juan Basin, New Mexico (USA), provide records of regional fluvial and tectonic evolution during the Laramide orogeny. Petrographic analyses of sandstones from the Upper Cretaceous Fruitland Formation and Kirtland Formation and the Paleocene Ojo Alamo Sandstone and Nacimiento Formation show that the rivers depositing these sediments were sourced in areas where unroofing of crystalline basement rocks