Geological Society of America

T138 Lacustrine Systems around the World I: In Honor of Michael Rosen

Tuesday, 12 October 2021
8:00 AM - 12:00 PM
Portland Ballroom 252 (Hybrid Room)

TRIPLE OXYGEN ISOTOPE PALEOHYDROLOGY OF EARLY EOCENE PALEOLAKE GOSIUTE (WYOMING, USA)

Paper number: T138-14
Program: Technical Sessions
Time: 11:10 AM – 11:25 AM

Authors

Benjamin Passey Presenting Author
University of Michigan, Ann Arbor, MI
Natalie R. Packard
University of Michigan, Ann Arbor, MI
Julia R. Kelson
University of Michigan, Ann Arbor, MI
Nathan Sheldon
University of Michigan, Ann Arbor, MI
Nathan Niemi
University of Michigan, Ann Arbor, MI
Rebekah Rhodes
North Carolina State University, Raleigh, NC
Ethan G. Hyland
North Carolina State University, Raleigh, NC
Alan Carroll
University of Wisconsin-Madison, Madison, WI

Abstract

The Green River Formation in southwestern Wyoming records the existence of paleolake Gosiute, a massive early Eocene lake that reached areal extents up to ~40,000 km². During its several million-year history, Lake Gosiute shifted from a largely freshwater lake (overfilled to balance-filled) to a largely saline lake (underfilled), and then back to a balance-filled and overfilled lake. The δ¹⁸O values of lacustrine carbonates show pronounced, step-like shifts, with the saline stage ~ 6 to 8 ‰ higher in δ¹⁸O than the preceding and ensuing freshwater stages. However, the significance of these shifts is unclear: what was the importance of changes in evaporation versus changes in the isotopic composition of catchment precipitation? What was the δ¹⁸O of ‘pristine’ (unevaporated) catchment precipitation during different stages of the lake’s history, and what can this tell us about catchment paleogeography?

The triple oxygen isotope composition (Δ′¹⁷O, δ¹⁸O) of lake water and lacustrine minerals is sensitive to evaporation, and can be used to estimate the δ¹⁸O values of catchment waters prior to evaporation. We report triple oxygen isotope compositions of >30 lacustrine carbonates spanning the Green River formation and stratigraphically adjacent units. Our results show that (1) lake waters were strongly modified by evaporation (ca. + 10‰ in δ¹⁸O) during all major stages (overfilled, balance-filled, under-filled); (2) The previously observed 6 to 8 ‰ shift in δ¹⁸O largely represents a shift in the δ¹⁸O of catchment precipitation and not in the degree of evaporative enrichment; and (3) the δ¹⁸O of unevaporated catchment precipitation was ~ –19‰ prior to and following the saline stage, and ~ –12‰ during the freshwater stage. Following previous interpretations, we hypothesize that the saline stage was bracketed by the abandonment and then recapture of a large paloeriver. Using the isotopic mass balance model of Doebbert et al. (2010), a captured river with δ¹⁸O ~ –19‰ would shift lake water δ¹⁸O by the observed ~ –7‰ if it had an annual discharge of ~ 25 x 10⁹ m³/year, comparable to the modern Missouri River at Bismarck, ND. By analogy with modern δ¹⁸O–elevation relationships, a value of –19‰ suggests high elevations (~ ≥ 2500 m) in this region during the early Eocene.

Reference: Doebbert A.C., et al. (2010), GSA Bulletin 122, 236-252.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-369541

© Copyright 2021 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.