Reconstructing past elevations from triple oxygen isotopes of lacustrine chert: application to the Eocene Nevadaplano, Elko Basin, Nevada, United States

  • Triple oxygen isotope measurements are an emerging tool in paleoclimate reconstructions. In this contribution we develop the application of triple oxygen isotope measurements to lacustrine sediments to reconstruct past elevations. We focus on a well-constrained sample set from the Eocene North American Cordillera (Cherty Limestone Formation, Elko Basin, NV, United States, 42–43.5 Ma) on the east side of the elevated Nevadaplano. We present triple oxygen isotope measurements on freshwater lacustrine chert samples from the Cherty Limestone Formation. Across an evaporation trend spanning 6.5‰ in δ18O values we observe a negative correlation with Δ′17O ranging from −0.066 to −0.111‰ (λRL = 0.528), with an empirical slope (λchert, δ′17O vs. δ′18O) of 0.5236. Additionally, we present new carbonate clumped isotope (Δ47) temperature results on the overlying fluvial-lacustrine Elko Formation, which indicate an error-weighted mean temperature of 32.5 ± 3.8°C (1σ), and evaporatively enriched lake water spanning δ18O values of −3.7 to +3.5‰ (VSMOW). Paired chert and carbonate δ18O values demonstrate that co-equilbrium among the carbonate and chert phases is unlikely. Thus, as also previously suggested, it is most likely that Elko Basin chert formed during early diagenesis in equilbirium with pore waters that reflect evaporatively 18O-enriched lake water. Using this scenario we apply a model for back-calculating unevaporated water composition to derive a source water of δ′18O = −16.1‰ (VSMOW), similar to modern local meteoric waters but lower than previous work on paired δ18O- δD measurements from the same chert samples. Further, this back-calculated unevaporated source water is higher than those derived using δD measurements of Late Eocene hydrated volcanic glass from the Elko Basin (average δ′18O equivalent of approximately −18.4‰, VSMOW). This suggests, assuming Eocene meteoric water Δ′17O values similar to today (∼0.032‰), either that: (1) the hypsometric mean elevation recorded by the lacustrine Cherty Limestone was lower than that derived from the average of the volcanic glass δD measurements alone; or (2) there was hydrogen exchange in volcanic glass with later low δD meteoric fluids. Nonetheless, our new findings support a relatively high (∼2.5–3 km) plateau recorded in the Elko Basin during the mid-Eocene.
Author:Daniel E. Ibarra, Tyler Kukla, Katharina Methner, Andreas MulchORCiD, C. Page Chamberlain
Parent Title (English):Frontiers in Earth Science
Publisher:Frontiers Media
Place of publication:Lausanne
Document Type:Article
Date of Publication (online):2021/03/25
Date of first Publication:2021/03/25
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2021/11/02
Tag:Eocene; carbonate; clumped isotopes; lacustrine chert; lakes; paleoaltimetry; triple oxygen isotopes
Issue:art. 628868
Page Number:19
First Page:1
Last Page:19
This research was funded by NSF EAR-1322084 and Heising Simons grants to CC. KM and AM acknowledge support through the LOEWE funding program of the Hessen State Ministry of Higher Education, Research, and the Arts as part of the LOEWE VeWa project. DI was supported by the UC Berkeley Miller Institute for Basic Research and UC President’s Postdoctoral Fellowships, and KM was supported by the Feodor-Lynen-Fellowship of the Alexander von Humboldt Foundation.
Institutes:Geowissenschaften / Geographie
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften
Licence (German):License LogoCreative Commons - Namensnennung 4.0