2016

Death Valley

Research

Dr Yuri Dublyansky

+43-6508509494

Innsbruck University
Institute of Geology
Innrani 52
Innsbruck, Select... 6020
Austria

 

juri.dublyansky@uibk.ac.at

Refining the long-term history of the water table of the Ash Meadows Groundwater Flow System

DEVA-00411

DEVA-2015-SCI-0006

Jan 01, 2015

Oct 25, 2016

Jan 31, 2015

Dec 28, 2016

Continuing

___ A final report has been provided to the park or will be provided to the park within the next two years

___ Copies of field notes, data files, photos, or other study records, as agreed, have been provided to the park

___ All collected and retained specimens and retained material originating from such specimens have been cataloged into the NPS catalog system and NPS has processed loan agreements as needed.

Research

Atmosphere / Climate / Weather

Cave / Karst

Geochemistry (inc. Minerals / Petrology)

The main objectives of this study are:
• to reconstruct, at unprecedented resolution, water-table elevations in the Devils Hole area for the last 600,000 yr;
• to obtain robust information on the highest water stands in the Devils Hole area (which has implications for the unresolved issue of the time of isolation of the Devils Hole pupfish); and
• to identify and date the lowermost water stands (i.e., below the modern water table position) which could shed light on the issue of the former survival of pupfish at times when the shallow spawning shelf in Devils Hole was dry.
The key hypothesis which will be tested using these samples is the direct relationship between the water-table elevation in the Devils Hole caves and climate (largely precipitation) on a millennial time scale. This hypothesis will be tested by comparing the U-Th dated oxygen and carbon isotope record from the Devils Hole calcite with paleowater table elevations, as well as by comparing the latter with other available regional paleohydrological proxy records (paleowater levels of Owens Lake, Owens River system, Death Valley sediments and shoreline tufas, Searles Lake, etc.; see summary by Sharpe, 2007).

In the reporting period we continued sampling mammillary calcite deposits in Devils Hole 2. In addition to finishing previously drilled cores by extending them to the calcite/bedrock interface, we drilled three more cores: one at the water table, and two underwater (at -0.8 m and at -1.2 m). These cores are presently short (ca. 25 cm) and will be continued to the bedrock interface in the future.
In the reporting period research was focused on three topics: (1) improvement of the existing isotopic paleoclimate record; (2) developing of the history of paleo water-table elevations at Devils Hole; and (3) extending the paleoclimate record back in time.
Topic 1 (paleoclimate). Currently, the database consists of ca. 120 U-Th age determinations and more than 5000 high-resolution stable isotope measurements. This massive effort was summarized in 2016 as a paper in Science(attached). The publication generated vigorous discussion (see three attached files).
In addition, to clarify some of the models proposed in our publication we have collected 4 x 2L water samples at approximately 0.2 m and 1.3 m depths in February 2016. Samples were measured for uranium and thorium concentrations in May 2016. Notably, these measurements confirmed that 238U concentrations in DH2 cave water are 3 ppb. Thorium was nearly non-existent, at ~50 femtogram per gram.
Topic 2 (paleo water-table). In addition to ca. 50 U-Th dated acquired in 2015, some 60 more U-Th dates were acquired in 2016. The data were obtained from ten cores, collected along a vertical transect of ca. 19 m.
Topic 3 (old paleoclimate). In order to date parts of the calcite which could be beyond the U-Th dating limits, we tested Paleomagnetic method. We were able to de-magnetize our discrete (1 cm) samples on the U-channel, which revealed evidence for a magnetic reversal in cores DH2-d12 and DH2-d10. Simultaneously, our U/Th dates revealed that DH2-d12 was much younger than expected, at apprx. 300 ka. Moving forward, we will focus our attention only on DH2-d10. We determined the age of DH2-d10 using U/U technique. The reversal appears to have occurred somewhere between 772-728 ka (with age errors of 10%), during a period of time that appears—from our stable isotope data—to span either Marine Isotope Stage (MIS) 19 or 18. This reversal in DH2-d10 may correspond to Matuyama-Brunhes boundary (770 ka).

Yes

The collected specimens are in the form of 1 inch-diameter cores, taken across the layers of mammillary calcite. While some cores rich the bedrock, others do not. The latter core sites will be drilled further until the complete cross-section of the mammillary calcite is obtained. As of now, the collection of samples consists of 10 cores, ranging in length from 15 to 85 cm. Each core may consist of one or several fragments, as they tend to break in the process of drilling. The cores are cut longitudinally and polished.