New Mexico Geological Society Annual Spring Meeting — Abstracts

×

Nash Draw is a karst valley located approximately 30 km east of Carlsbad, NM. It developed on Upper Permian evaporite rocks of the Rustler and Salado Formation (Powers et al., 2006; Goodbar et al., 2020). Surface karst features exist in the southeastern arm of Nash Draw on sulfate beds of the Rustler Formation and surficial gypsite. More recent studies of Nash Draw suggest that there is evidence of subsidence and active karst that are associated with dissolution of underlying formations such as the Salado and Rustler (e.g., Powers et al., 2006). However, several features, as well as the timing and formation of the Draw, remain poorly understood.

Due to the complex nature of evaporitic karst features it is difficult to pinpoint the locations of potential recharge and discharge in the draw. Some elements of the hydraulic system in Nash Draw however, can be gleaned from surface features and previous data collected in the region. A major feature is Laguna Grande de la Sal, a natural lake partially recharged by potash mine effluent. Five smaller lakes, including Laguna Cinco, are located at the mouth of the southeastern arm of Nash Draw. Powers et al. (2006) identified seeps and springs in the Laguna Cinco area, with waters differing in specific gravity and temperature from the brine lake. Laguna Cinco itself is a salt-lake with a spring on its north shore and two seeps emerging on the east and south shores. The Culebra aquifer, a dolomite-dominated member of the Rustler formation, may be the source of the spring and seep water. Samples were collected from the spring, seeps, and the lake, and analyzed for major cations, anions, and field measurements.

The spring and seep waters resemble water produced from the dissolution of evaporites, with Na/Cl molar ratios close to 1, and low Br/Cl ratios (between 1.04E-04 and 2.44E-04). When compared with nearby groundwater from wells that are known to be completed in the Culebra, the springs have a higher TDS, but similar elemental ratios (Figure 1). The lake however, shows depleted sodium compared to chloride indicating that some process may be depleting sodium in the lake system, such as the precipitation of sodium bearing salts.

Future work in this area will focus on analyzing trends in geochemical data and continue to compare that data to regional waters with the purpose of understanding spring sources and potential mixing scenarios. Future analyses may be conducted to model evaporation evolution of the various systems and gain a better understanding of source waters.

References:

1. Goodbar, A.K., Powers, D.W., Goodbar, J.R., and Holt, R.M., 2020, Karst and sinkholes at Nash Draw, southeastern New Mexico (USA), in Land, L., Kromhout, C., and Byle, M.J., eds., Proceedings of the Sixteenth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst (first ed.): NCKRI Symposium 8, National Cave and Karst Research Institute, Carlsbad, NM, p. 287-298.https://digitalcommons.usf.edu/sinkhole_2020/ProceedingswithProgram/Geomorphology_Formation_of_karst_and_sinkholes/
2. Powers, D.W., Beauheim, R.L., Holt, R.M., and Hughes, D.L., 2006, Evaporite karst features and processes at Nash Draw, Eddy County, New Mexico, in Caves & Karst of Southeastern New Mexico, in L. Land and others, eds., NM Geological Society Fifty-seventh Annual Field Conference Guidebook, p. 253-266.