T102 The Virtue of Fieldwork in Volcanology, Sedimentology, Structural Geology, and Tectonics (Posters): A Session to Honor Cathy Busby, MGPV Distinguished Geological Career Award Recipient of 2020

Monday, 10 October 2022
9:00 AM - 1:00 PM
Exhibit Hall F

SEDIMENTOLOGY AND STRATIGRAPHY OF V185, AN OPEN-PIT GRAVEL MINE, AZ

Paper number: T102-6
Program: Technical Sessions
Time: 9:00 AM – 1:00 PM

Authors

Abstract

Recent field studies by the GeoSPACE Field Course (NSF Award 2023124) of a northern Arizona cinder pit (V185) located within the San Francisco Volcanic Field uncovered evidence for successive, small-scale explosive events influenced by the presence of water. Analysis of a well-preserved outcrop at the rim of the pit (35.180833, -111.339444) reveals the eruption sequence yielded six primary stratigraphic units, presented here from oldest to youngest: (1) poorly-consolidated volcanic breccia with Toroweap and Kaibab Formation bombs, (2) unconsolidated tephra fallout unit, (3) reverse-graded welded unit with vesicular basalt and Coconino Formation lithics, (4) bedded surge deposits, (5) matrix-supported volcanic breccia with vesicular basalt and Coconino Formation lithics, and (6) grain-supported oxidized scoria with caliche coating.

We hypothesize that the oldest volcanic breccia unit represents the initial eruption event, incorporating large fragments of country rock, with subsequent layers indicating the occurrence of ash fall, pyroclastic surges, and brief lava flows. Bomb sags, geodes, caliche, and welded surge deposits found throughout the outcrop suggest surface and subsurface water was present over the course the eruptive cycle. Alternating beds of oxidized scoria and volcanic breccia near the top of the outcrop signal the progressive drying out of the site.

This stratigraphic analysis was conducted through traditional field mapping techniques as well as detailed photogrammetry survey to produce a 3D model of the outcrop. To learn more about the GeoSPACE Field Course and our work at V185, search for the keyword “GeoSPACE” in the conference program.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-379023

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