Strontium and uranium isotopic compositions (87Sr/86Sr and 234U/238U) of mid- to late-Holocene lacustrine sediments from Lower Pahranagat Lake, Pahranagat National Wildlife Refuge, Lincoln County, Nevada

Publication Date

2022-10-27

Start Date

2014

End Date

2020

Paces, and J.B., and Theissen, K.M., 2022, Strontium and uranium isotopic compositions (87Sr/86Sr and 234U/238U) of mid- to late-Holocene lacustrine sediments from Lower Pahranagat Lake, Pahranagat National Wildlife Refuge, Lincoln County, Nevada: U.S. Geological Survey data release, https://doi.org/10.5066/P96B7ABG.

Type: Related Primary Publication

Samples of carbonate-rich materials from a 12.4-m-long core driven into Lower Pahranagat Lake (LPAH) sediments have radiogenic isotopes of Sr and U (87Sr/86Sr and 234U/238U) that preserve evidence of past variations in water sources and evolving hydrologic conditions. Isotopic compositions of Sr and U dissolved in groundwater are derived from water-rock interactions in recharge areas and along aquifer flowpaths. Because surface water in LPAH is derived almost entirely from springs discharging into Pahranagat Valley, and because lacustrine carbonate incorporates Sr and U dissolved in lake water without substantial fractionation, those compositions faithfully record the composition of LPAH water at the time they precipitated. Compositions of 87Sr/86Sr and 234U/238U reported here fall within the range previously defined by three primary sources of modern groundwater discharge that supply surface water to Pahranagat Valley (Paces and Wurster, 2014; https://doi.org/10.1016/j.jhydrol.2014.05.011). Those include regionally sourced carbonate-aquifers recharged in northern Nevada and discharge from more locally sourced aquifers recharged in nearby uplands consisting mostly of volcanic rock. Consequently, Sr and U isotopic compositions in sediments reflect systematic shifts in the proportions of those groundwater sources contributing to LPAH hydrology over the last 5.78 ka. A companion interpretive paper compares radiogenic-isotope data included here with a previously published record of oxygen-isotopes from the same core (Theissen et al., 2019, https://doi.org/10.1017/qua.2019.11) to evaluate how shifts in Holocene climate affected hydrologic contributions from different sources recharged in different areas. Conclusions from that paper demonstrate that wetter climate conditions favor increased supply from deeper, regional carbonate aquifers compared to drier conditions when contributions from shallower, local volcanic aquifers became more pronounced.

• USGS Data Release Products