81-6 Assessing the Geological Evolution of Unaweep Canyon Through Scientific Drilling

Session: Investigating Earth’s History With Continental Scientific Drilling

Presenting Author:

Gerilyn Soreghan

Authors:

Soreghan, Gerilyn¹, Dulin, Shannon Ann², Brunig, Danielle Elyse³, Harris, Branson⁴, Valles, Karen Sophia⁵, Jiménez-Moreno, Gonzalo⁶, Noren, Anders⁷

(1) Geosciences, Univ Oklahoma, Norman, OK, USA, (2) Geosciences, University of Oklahoma, Norman, OK, USA, (3) Geosciences, University of Oklahoma, Norman, OK, USA, (4) Geosciences, University of Oklahoma, Norman, OK, USA, (5) Geosciences, University of Oklahoma, Norman, OK, USA, (6) Estratigrafía y Paleontología, Universidad de Granada, Granada, Spain, (7) Continental Scientific Drilling Facility, University of Minnesota, Minneapolis, MN, USA,

Abstract:

Unaweep Canyon is a large (>850 m relief, up to 6 km wide) canyon that bisects the Uncompaghre Plateau on the northeastern Colorado Plateau. The origin of the canyon remains enigmatic because it is carved deeply into Precambrian basement but hosts two underfit creeks that flow in opposite directions from a divide in the midst of the canyon, and hosts (locally) >350 m of sediment fill. Fluvial gravels of Gunnison River provenance occur near both mouths of the canyon, leading to the hypothesis that the ancestral Gunnison River incised Unaweep Canyon during the drainage integration of the Colorado River system (Miocene-Pleistocene). However, glacial-like attributes of the Precambrian-hosted western canyon have inspired the hypothesis of a glacial origin, potentially dating from the pre-Quaternary, with later exhumation by the ancestral Gunnison River.

A new core drilled into the keel of the western canyon reveals strata that help clarify the geologic history of this geomorphic oddity. Destructive drilling was conducted through the uppermost alluvial strata; continuous coring began at ~200 m depth in previously documented lacustrine strata of Pleistocene (~1.3-1.4 Ma) age, consisting predominantly of a succession of graded beds reflecting mass flows. This lacustrine section is ~140 m thick and comprises two sediment cycles defined in part by variations in color, pollen content, and charcoal occurrences. Intervals exhibiting oxidized colors, abundant Picea and Abies pollen, and low charcoal concentrations alternate with intervals exhibiting reduced colors, abundant Artemisia and Pinus pollen, and high charcoal concentrations. We interpret these to record glacial-interglacial climates of the mid Pleistocene. The lacustrine strata lie atop ~23 m of gravels (pebble to boulder size) composing clasts of Precambrian basement, with subordinate Mesozoic sandstone and andesite, consistent with a Gunnison River provenance. The gravels lie atop a ~5 m lithified interval of heavily fractured (cataclastic) and hematized Proterozoic basement material directly atop intact Proterozoic basement. Samples were taken within this interval to perform a paleomagnetic conglomerate test on discrete boulders, which may shed light on the age of this interval utilizing inclination data from the unoriented core. Preliminary evaluation suggests a remanent magnetization held in hematite, based on unblocking temperatures above 580C. The age and origin of the fractured interval will help determine the age and origin of Unaweep Canyon.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11082

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