Examination of REE signatures in Shoreline "Tufa", Panamint Valley, California: Reconstructing Pleistocene Climate Change

A Natural Science Divison III examination
Micah J. Jessup, Steve Roof, John B. Reid
Hampshire College, Amherst, Ma. 01002
mjjF94@hampshire.edu
sroof@hampshire.edu

Panamint Valley is a desert basin in eastern California nestled between the Argus and Panamint mountain ranges. In Pleistocene time this now dry landscape was filled by a large lake estimated to have reached a depth of 950 ft. covering 300 square miles. During periods of wet climate in the Sierra Nevada Mountains, increased Sierran runoff flowed, via the Owens River, into Lake Panamint creating stable lake levels which eroded shorelines into the existing landscape and deposited tufa. Because lake level was dependent on the balance between inflow from the Owens River and evaporation, its level and chemistry (e.g., alkalinity and salinity) fluctuated drastically with climate change.

Tufa is calcium carbonate (CaCO3) that forms as a precipitate in saline lakes. The most famous examples are found in Mono Lake, California and Pyramid Lake, Nevada where freshwater spring inputs have created fragile tufa towers which can now be seen due to a lowering of their lake levels. As tufa forms it, like other carbonates, reflects the trace element signature of the water from which it is precipitating. The objective of my Division III research is to examine three questions:

(1) Does tufa record the trace element signature of lake waters as lake volume fluctuated due to variation in the relative amounts of inflow and evaporation?
(2) Does the tufa morphology directly reflect the means by which it was formed i.e. Spring fed or Thromoblitic growth?
(3) Can REE signatures from different shorelines be compared in order to recreate a detailed history of lake level fluctuations and thereby provide more insight into the paleoclimate of this area during Pleistocene time?

Data obtained by a newly developed methodology for tufa analysis on the ICP-MS and detailed petrographic studies found two distinct morphologies at all shoreline locations around Panamint Valley. Results show that Type 1 tufa is the result of Ca2+ spring water input and Type 2 is a detrital rich Thrombolite. Type 2 is suggested to be the best indicator of lake water chemistry due to its isolated growth habit. The Type 2 REE signatures of shorelines may also possibly be used to correlate detached shorelines, yet the small samples size examined by this study cannot prove this statistically. The understanding of both geochemical and petrological aspects of tufa, generated by this study, lay a foundation for future research that will enable a detailed recreation of lake level fluctuations.