A physical and chemical sedimentary record of Laramide tectonic shifts in the Cretaceous-Paleogene San Juan Basin, New Mexico, USA

Fluvial siliciclastic rocks bracketing the Cretaceous-Paleogene (K-Pg) boundary in San Juan Basin, New Mexico (USA), provide records of regional fluvial and tectonic evolution during Laramide orogeny. Petrographic analyses sandstones from Upper Cretaceous Fruitland Formation Kirtland Paleocene Ojo Alamo Sandstone Nacimiento show that rivers depositing these sediments were sourced areas where unroofing crystalline basement took place, introducing an increasing proportion immature detrital grains into system through time. After boundary, deposited amount microcline orthoclase feldspar relative to plagioclase feldspar, suggesting a growing source unique rocks. Geochemical significant differences between Al- K-poor K-rich lower Basin. The high sand-sized material suggests it was basin with low ratio sediment supply accommodation. However, magnetostratigraphic age constraints suggest had relatively sedimentation and/or subsidence rate as much 0.38 m/k.y. must have been order deposit basin-wide coarse sand-dominated package, rapid creation topographic relief uplift, proposed area system. observed sedimentary architecture Sandstone, including kilometers-wide sand bodies limited overbank mudstones throughout most outcrop area, are difficult reconcile accepted models aggradation avulsion large systems, but available lithologic data make complete understanding Basin systems evolution. Here, we present new lithologic, petrographic, thickness K-Pg units interpretations their origins.