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81-7 USGS Hanna Draw coring project for a continuous record of the Paleocene – Eocene Boundary, Hanna Basin, Wyoming.

Session: Investigating Earth’s History With Continental Scientific Drilling

Presenting Author:

Marieke Dechesne

Authors:

Dechesne, Marieke¹, Workman, Jeremiah B.², Currano, Ellen³, Dunn, Regan⁴, Foreman, Brady Zangs⁵, Diefendorf, Aaron⁶

(1) Geosciences and Environmental Change Science Center, U.S. Geological Survey, Denver, CO, USA, (2) Geosciences and Environmental Change Science Center, U.S. Geological Survey, Denver, CO, USA, (3) University of Wyoming, Laramie, WY, USA, (4) Natural History Museum of LA, Los Angeles, CA, USA, (5) Geology Department, Western Washington University, Bellingham, WA, USA, (6) University of Cincinatti, Cincinatti, OH, USA,

Abstract:

The Hanna Basin in Wyoming is one of the most rapidly subsiding basins in the Laramide foreland. The Cretaceous – Eocene basin fill is characterized by a succession from marine to fluvial to paludal and lacustrine deposits. The Hanna Formation that spans from about 58-54 Ma contains abundant coalbeds related to the extensive coal swamps, and fluvial and lacustrine sandstones and shales. After extensive fieldwork in previous years, the Paleocene – Eocene Boundary was first identified by plant macrofossils and palynology along Hanna Draw in the center of the Hanna Basin. The Paleocene – Eocene boundary is marked by a world-wide d13C carbon isotope excursion (CIE) that is also found in this area and is characterized by a rapid global release of carbon into the atmosphere, leading to a thermal event that lasted about 170 kyr. The boundary is 140 meters thick, which is significantly thicker than in nearby Laramide basins. The section is considered continuous with minimal erosional scouring by fluvial channels and contains abundant coals and carbonaceous shales which gives a unique opportunity to sample and characterize changes in vegetation cover, ecology, hydrology and fluvial character across this important time interval, however outcrops do not fully expose the shales in this interval. The USGS drilled a first core of two planned cores in 2023, which reached a depth of 828 ft. This drilling operation encountered significant problems and led to not reaching our target depth. Therefore, in the summer of 2025, we are planning to drill a second hole, starting at a depth of 800 ft to a proposed total depth at 1300 ft which should capture the onset of the CIE and targets an earlier Paleocene pre-onset excursion as identified by studies in other regions. Although not all results will be in yet, we are planning to present an overview of our drilling project.

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

doi: 10.1130/abs/2025AM-10118

USGS Hanna Draw coring project for a continuous record of the Paleocene – Eocene Boundary, Hanna Basin, Wyoming.

Description

Session Format: Oral

Presentation Date: 10/20/2025

Presentation Start Time: 09:45 AM

Presentation Room: HBGCC, 214C

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