Uranium–uranium (

The mid-20th century discovery of

In freshwater settings, constraining the

The Devils Hole (DH) and neighboring Devils Hole 2 (DH2) caves are ideal
settings for the study of groundwater

Ludwig et al. (1992) were the first to calculate

Building upon the pioneering work of Ludwig et al. (1992), we aim to
decrease the uncertainties of DH and DH2

The DH and DH2 caves are located 100 m apart in a detached area of Death Valley
National Park in southwest Nevada (36

DH and DH2 both intersect the water table of the Ash Meadows Groundwater
Flow System (AMGFS), which is a large (

Calcite has been continuously depositing as dense mammillary crusts on the
submerged walls of DH and DH2 over much of the last 1 Myr at a very slow rate
of roughly 1 mm kyr

A 670 mm long core was drilled from the hanging wall of DH2 cave at

The selected core was cut longitudinally and polished. The core was surveyed for growth hiatuses and features indicative of changing deposition mechanisms and rates (such as folia). Folia was identified at 77.7–97.4 mm (as reported in Moseley et al., 2016), 171.4–199.2, 209.4–229.0, and 305.0–323.0 mm (distances are reported from top of the calcite sequence). In addition, a growth hiatus was discovered between 587.4 and 589.0 mm (Fig. S2).

The mammillary calcite portions of the core were

Samples for stable isotope measurements were micromilled continuously at
0.1–0.2 mm intervals along the core axis between 0 and 158 mm and presented
by Moseley et al. (2016). The values of two to three stable isotope
measurements (0.1–0.2 mm in width) were averaged in order to pair with

A statistical model was built to predict

Using this dataset, we calculated 120

The new

In this study, we split the

Statistics of

DH2 oxygen isotope values reveal a negative correlation with

Correlation coefficient (

Note that all the 95 % confidence intervals do not cross zero,
indicating that all the

The linear relationships presented here are consistent with results from
Moseley et al. (2016) and Ludwig et al. (1992) in the DH2 and DH caves,
respectively. The anti-correlation between

From Table 2, we can see that the modulus value

We evaluated the linear and polynomial (quadratic and cubic) regression
methods primarily by calculating the coefficient of determination (COD),
i.e.,

Adjusted

Note that the robustness of the regression model can be evaluated by the
coefficient of determination (COD),

Among the various models, multiple linear regression (MLR) for the time
period 4–309 ka in terms of both

A

Note that (1) the standard error of fitting parameters was calculated based on
the standard deviation of the residual from the model and used only for the

We then applied statistical methods to test the robustness of the chosen
model, starting with the

Second, we performed a

We now estimate the uncertainty of the SD

Histogram

Using Eqs. (1) and (2), we then calculated the

The

Plot of

The consistency between

SD

Due to the high initial

Evolution of

Figure 5 shows an OxCal-derived age model with 95 % confidence intervals
plotted over depth using all

Growth rate of DH2 mammillary calcite based on the OxCal age model (Fig. 5). The dashed lines indicate the average value and 1 standard deviation above and below the average.

Previous investigations revealed that the DH2 cave opened to the surface at
approximately 4 ka (Moseley et al., 2016), likely due to surface collapse
processes (Riggs et al., 1994). The timing at which the main subsurface
fissure opened, however, remains largely unknown. By

The onset of calcite deposition in the DH2 cave is in agreement with the recent geologic history of this region. The orientation of DH and DH2 is in accordance with the principal northwest-southeast stress direction in this part of the Great Basin that has prevailed over the last 5 Myr (Carr, 1974), suggesting that one or both fissures formed after 5 Ma. Abundant calcareous and siliceous spring and marsh deposits in Ash Meadows and the Amargosa Desert of Pliocene age (2.1 to 3.2 Ma; Hay et al., 1986) and groundwater-deposited calcite veins in alluvium and colluvium of Pleistocene age (500 to 900 ka; Winograd and Szabo, 1988) indicate that groundwater in the discharge zone of AMGFS has been continuously supersaturated with respect to calcite for at least the last 3 Myr. Our results, which suggest that the DH2 fissure opened no later than 736 ka, are therefore in agreement with the modern understanding of the AMGFS' geological history.

OxCal-derived age model (black line), 95 % confidence limits
(grey lines), and

We have developed a novel method to determine the

All the data used in this paper are available in the Supplement.

The supplement related to this article is available online at:

RLE conceptualized the project and XL carried it out. KAW, XL, and
RLE prepared the manuscript with contributions from all co-authors. XL
conducted the formal analysis. CS and YD provided the cave samples. KAW and
GEM conducted the

The authors declare that they have no conflict of interest.

This research was conducted under research permit nos. DEVA-2010-SCI-0004 and DEVA-2015-SCI-0006 issued by the Death Valley National Park. We thank K. Wilson for assistance in the field and M. Wimmer for assistance in the laboratory. Finally, we would like to thank two anonymous reviewers for their insightful comments on the manuscript.

This research has been supported by the National Science Foundation (NSF) (project no. 1602940) (to R. Lawrence Edwards) and the Austrian Science Fund (FWF) (project nos. P263050 and P327510) (to Christoph Spoetl).

This paper was edited by Norbert Frank and reviewed by two anonymous referees.