Evolution of a Plio-Pleistocene volcanogenic-alluvial fan: The Puye Formation, Jemez Mountains, New Mexico

Abstract

The Plio-Pleistocene Puye Formation, north-central New Mexico, contains >15 km 3 of volcaniclastic alluvial sediments deposited in response to rift-margin volcanism associated with the later evolution of the Tschicoma volcanic center, northeastern Jemez Mountains. Stratigraphic and sedimentologic evidence indicates that aggradation of Puye deposits was nearly continuous and contemporaneous with graben development and establishment of the Rio Grande as the through-flowing axial drainage system in this region. Much of the Puye sediments debouched into an adjacent subsiding depocenter, resulting in near-complete preservation of this wedge-shaped volcanogenic fan. Primary-pyroclastic and reworked facies in the Puye Formation exhibit distinctive 5- to 30-m scale cyclicity directly related to volcanic activity in the northeastern Jemez highlands. Reworked-pyroclastic and conglomeratic sequences deposited by high-energy braided streams, sediment-charged sheet-floods, sediment-gravity flows, and in shallow lakes reflect markedly increased sediment loads during and following explosive eruptions. Individual sequences change markedly in character with increased distance from the source area. Analysis of these abrupt lateral and vertical variations reveals that Puye sedimentation was controlled by the influences of semiarid climate and syndepositional tectonism, although the associations that most characterize the fan resulted largely from explosive volcanism. Cessation of fan growth is attributed to waning sediment supply as a result of volcanic quiescence and to the onset of basinwide pedimentation associated with downcutting of the ancestral Rio Grande. The Puye fan therefore provides a detailed record of rift-basin alluvial sedimentation, complete with closely spaced tephrostratigraphic control, and it records the growth and partial denudation of high-standing, northeastern Jemez Mountains volcanoes.