Linking Core to Outcrop: High-resolution Isotopic Records of the Wilkins Peak Member (Green River Formation) at White Mountain (Wyoming, USA)

Abstract:

The Early Eocene Climatic Optimum (EECO), the warmest greenhouse period of the Cenozoic, is a proposed analogue for a future warm anthropogenic climate. While the majority of research has studied the marine climate record, the terrestrial response to EECO warmth is not completely understood. We use lacustrine carbonates from the Wilkins Peak Member (WPM) of the Green River Formation (GRF) in southwestern Wyoming to reconstruct a high-resolution terrestrial climate record of the EECO using stable (δ¹³C and δ¹⁸O) isotopes, clumped (Δ₄₇) isotopes, strontium (Sr⁸⁷/Sr⁸⁶) isotopes, and triple oxygen (Δ¹⁷O) isotope analyses. The Wilkins Peak Member was deposited in Eocene paleolake Gosiute during the EECO (51.6 – 49.9 Ma) in a highly evaporative, underfilled phase of the lake. Although the majority of WPM deposits are lacustrine carbonates, there are multiple alluvial pulses found within the WPM that can be located throughout the Green River Basin and occur in phase with 100 kyr eccentricity cyclicity. Samples of carbonates were taken from the White Mountain #1 Core and the White Mountain outcrop near Rock Springs, Wyoming (USA). Carbonate samples consist of sparry calcite and mudstone both with and without kerogenous organic material. Stratigraphic correlation was accomplished using siliciclastic marker beds, tuff beds, and gamma ray logs between White Mountain #1 Core and the White Mountain outcrop. Initial isotope analyses from core samples give a range of 1.66 – 5.38‰ (VPDB) with an average of 3.16‰ (VPDB) for δ¹³C, 5.17 – 8.16‰ (VPDB) with an average of 6.63‰ (VPDB) for δ¹⁸O, and clumped isotope analyses (Δ₄₇) give a range of 0.557 to 0.7‰ (CDES) with a calibrated temperature range of 21 – 85°C (average of 44°C). Further analyses of these carbonate samples using established and novel proxy methods (e.g., clumped, triple oxygen, and strontium isotopes) has the potential to yield important information regarding water sourcing, high-resolution terrestrial climatic variability, and regional expression of potential orbital cyclicity (e.g., eccentricity) during the EECO in southwestern Wyoming.