61st Annual Report on Research 2016

During the first year and a half of the project, Guleed Ali has been the graduate student paid on the project. He has been examining lake carbonates for their datability, mostly focusing on Mono Basin quaternary deposits with U-series in order to inform our sampling strategy in the Green River Formation. Additionally we have been working with Troy Rasbury at Stony Brook University to use laser ICP-MS to survey a bunch of Green River Formation carbonates that were collected by Malka Machlus in past field expeditions to the Green River Formation. Although this method does not yield precise ages, it yields important information about the levels of U, Th and Pb (as well as rare earth elements) in the samples, and combined with the textural observations, this is yielding some promising samples to measure with ID TIMS. We went out to the Green River Basin, in the area of LaBarge in August 2016, and we studied the insect mound buildups and their relationship to the stratigraphy of the Green River Formation, particularly emphasizing the numerous volcanic layers that we found. This discovery of abundant volcanic layers is very exciting because we will be able to make really detailed tests of the accuracy of the U-Pb carbonate dates. However, it also raises the level of uncertainty about the published claim of the Layered Tuff being found at each of the mound localities. Because there are so many volcanic layers, and because they do not look exactly the same at the different localities, we are going to have to spend more time in the field to define a robust correlation of the volcanic layers. We were able to make enough progress in August that we are very optimistic we will be able to do this. Additionally while in the basin in August we reoccupied the sites of Seard as well as of the Loma Linda group, and we were able to collect several examples of carbonate that we are quite optimistic about U-Pb dating based on the parallels with the carbonate data we have from Guleed Ali’s work in the Mono Basin. During the next year, we will return to the field at least twice for further studies (once in winter in the Rock Springs area and once in the summer back in the LaBarge area) of the carbonate mounds and stromatolites and their associations with the strata- particularly with the volcanic layers. The Rocks Springs area is where Malka Machlus has spent a tremendous amount of time, and she is poised to connect the cyclic deep lake stratigraphy with the more marginal carbonate tufa deposits based on our work in Aug 2016 as well as our work in the Mono Basin- Malka Machlus joined me and Guleed Ali in Mono Basin as well as Searles Lake and Owens Lake to see the context of the Quaternary carbonates. She had seen the tufas in the Rock Springs area before but did not fully appreciate the context. We do not yet have papers or abstracts from this work although a high school student did spend the summer at Stony Brook working on the carbonate deposits, and she is participating in some high school science competitions.