34-9 From Marine Basement to Caldera Fill: Stratigraphic Framework for El Azufre Canyon, Aguajito Caldera (Baja California Sur, Mexico)

Session: Recent Advances in the Gulf of California Oblique Rift: Offshore and Onshore Studies // Avances Recientes en el Rift Oblicuo del Golfo de California: Estudios Marinos y Terrestres (Posters)

Poster Booth No.: 9

Presenting Author:

Antonio Pola

Authors:

Pola, Antonio¹, Pacheco Valdovinos, Pedro Martín², Sereno, Hugo³, Macías Vázquez, José Luis⁴

(1) Geociencias, Escuela Nacional de Estudios Superiores - Unidad Morelia. Universidad Nacional Autónoma de México, Morelia, Michoacán, Mexico, (2) Geociencias, Escuela Nacional de Estudios Superiores - Unidad Morelia. Universidad Nacional Autónoma de México, Morelia, Michoacán, Mexico, (3) Geociencias, Escuela Nacional de Estudios Superiores - Unidad Morelia. Universidad Nacional Autónoma de México, Morelia, Michoacán, Mexico, (4) Instituto de Geofísica - Unidad Michoacán. Universidad Nacional Autónoma de México, Morelia, Michoacán, Mexico,

Abstract:

El Azufre Canyon preserves one of the most complete, laterally traceable stratigraphic transects through the Aguajito caldera succession, capturing the transition from a marine volcano-sedimentary basement to syn-caldera pyroclastic infill and post-caldera volcanic–volcaniclastic cover. The pre-caldera section records shallow-marine deposition dominated by siltstones and fossiliferous sandstones, locally interrupted by a lithic-rich pyroclastic unit and a thin, white pyroclastic-flow marker bed. This sedimentary package is capped by submarine lava flows expressed as slab-structured facies and hyaloclastite, forming the immediate substrate for the caldera-forming ignimbrite, and preserving evidence of paleotopographic and/or structural relief along the basal contact.

The syn-caldera sequence corresponds to the Aguajito Ignimbrite and is subdivided into ten mappable stratigraphic units (U1–U10) recognized by systematic changes in color, internal architecture, and pumice/fiamme and lithic abundance. A basal massive pyroclastic-flow unit (U1) is overlain by a thick package of structured pyroclastic surges (U2) characterized by laminations, crossbedding, dune forms, and clast alignment, providing the most robust correlation interval across the canyon. Above, a pale, non-welded to weakly welded, pseudo-bedded unit (U3) transitions into a massive unit with conspicuous degassing/elutriation pipes (U4). The upper ignimbrite includes a locally preserved, strongly altered white unit (U5), a distinctive very welded violet unit with large fiamme and cross-stratification (U6), and a thin cap (U7–U10) of centimeter- to meter-scale welded to moderately welded units.

Post-caldera deposits record rapid landscape reworking and renewed volcanism, beginning with debris-flow (lahar) deposits, followed by blocky lava flows, thick effusive lavas, and younger channelized debris-flow and reworked deposits. This stratigraphic framework provides a basis for section-to-section correlation, geologic mapping, and reconstruction of caldera evolution in a marine-influenced volcanic setting.

Geological Society of America Abstracts with Program. Vol. 58, No. 3, 2026

doi: 10.1130/abs/2026CD-13459

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.