Plio-Pleistocene pumice floods in the ancestral Rio Grande, southern Rio Grande rift, USA

TitlePlio-Pleistocene pumice floods in the ancestral Rio Grande, southern Rio Grande rift, USA
Publication TypeBook Chapter
Year of Publication1996
AuthorsMack GH, McIntosh WC, Leeder MR, H. Monger C
EditorCrook K.A.W., Miall A.D., Sellwood B.W.
Book TitleSedimentary Geology
PublisherElsevier Science B.V.
CityAmsterdam, the Netherlands
Accession NumberJRN00215
Call Number00670
Keywordsbook, books, chapter, chapters, geomorphology, processes, geomorphology, pumice flood, pumice flood, report, reports, volcano, pumice flood

At least four times during the late Pliocene and early Pleistocene pyroclastic eruptions in the Jemez volcanic field, northern Rio Grande rift, flooded the ancestral Rio Grande with gravel-size pumice. Following as much as 400 km of fluvial transport, the pumice was deposited in beds 0.2 to 2.0 m thick in the Camp Rice Formation of the southern Rio Grande rift. A combination of reversal magnetostratigraphy and single-crystal sanidine 40Ar/39Ar dating constrains the ages of pumice-clast conglomerates at 3.1, ~ 2.0, 1.6, and 1.6 Ma. The coarsest pumice beds (cobbles, boulders) were deposited as antidune-like bedforms in a fluvial channel and as a crevasse-play sheet. Granule and pebble-sized pumice was deposited as dune bedforms in a fluvial channels and as ripple bedforms on the floodplain. The abundance of pumice clasts in the gravel fraction (60-100%) suggest very rapid transport downriver, probably in a few days or weeks. The two older pumice-clast conglomerates correlate with the Puye Formation in the Jemez volcanic field, whereas the younger two are coeval to the Lower Bandelier Tuff and Cerro Toledo Rhyolite.