7-1 Prolonged Occurrences of Menefee Formation Mudstones above the Tsaya Canyon Tongue of the Cliff House Sandstone

Session: The Campanian Crucible: A synthesis of vertebrate paleobiogeography and ecosystem dynamics in Laramidia (Posters)

Poster Booth No.: 14

Presenting Author:

Ronni Chavez

Authors:

Chavez, Ronni¹, O’Callaghan, Ezekiel², Adrian, Brent³, Smith, Heather F⁴, Mohler, Benjamin F.⁵

(1) Southwest Paleontological Society, Mesa, AZ, USA, (2) Garter Snake Research Lab, Northern Arizona University, Flagstaff, AZ, USA, (3) School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, USA; Institute of Human Origins, Arizona State University, Tempe, AZ, USA, (4) Department of Anatomy, Midwestern University, Glendale, AZ, USA; School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, USA, (5) Department of Geosciences, University of Arizona, Tucson, AZ, USA,

Abstract:

The relationship between the Campanian Menefee Formation and overlying Cliff House Sandstone has not been examined in 40 years. Finds of fossil teeth in the lower Tsaya Canyon Tongue of the Cliff House Sandstone has renewed interest in the interaction of the two formations. Stratigraphic surveys revealed new outcrops of the Menefee Formation Tongue, and small intervals of associated mudstone and siltstone lenses throughout a portion of the plateau topologically above Tsaya Canyon. Recent surveys have revealed new fossils of mosasaurs, fish, invertebrates, and plants below the uppermost Menefee Formation Tongue, interfingering with the lowermost Cliff House Sandstone. Some of these fossils represent completely new occurrences, while others represent taxa known from elsewhere in the formation or indeterminate remains. Despite significant erosion in the canyon since earlier studies, our findings are largely in agreement with previous reports, with the Lower Cliff House Sandstone containing multiple mud to siltstone lenses. Those lenses with more carbonaceous material demonstrate increased Menefee Formation environmental influence due to change in river discharge or localized sea level changes. New outcrops of the Menefee Formation and Cliff House Sandstone were located, potentially facilitated by culverts present underneath the nearby highway directing into confined rills. New mudstone outcrops include many carbonaceous shales, suggesting strong terrestrial influence in lagoonal settings. Variation between these and fine-grained sandstones suggests prolonged influence of Menefee Formation deposition interacting with the Lower Cliff House Sandstone. Additionally, two large beds of disarticulated Inoceramus cf. I. barabini. deposited along the bottom of a bedding plane, were identified at Tsaya Canyon and at the hill near La Vida Mission. These are the only such beds identified within the section and represent a single stratigraphic horizon, therefore a single event. The disarticulation of Inoceramus in this bed, slightly above the lowermost contact between the formations and deep (≈1 m) incised sandstone channels, but otherwise flat sandstone beds (≈1 cm) suggests limited influence of current across the lowermost contact between the Menefee Formation and Cliff House Sandstone units. This interaction may vary spatially or temporally. This work represents the first, non-fossil fuel resource focused study of the uppermost Menefee Formation within the southern San Juan Basin. Future studies seek to identify fossil resources and refine the nature of the upper Menefee Formation Tongue and shape.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4, 2026

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