LAKE BONNEVILLE, OSTRACODES, AND RICK FORESTER

Rick Forester showed how ostracode faunas changed through time in Lake Bonneville in response to the geochemical evolution of the lake. Rick described ostracode faunal changes (in a sediment core from Great Salt Lake) related to changes in the relative proportions of dissolved cations and anions as the lake progressed through its closed-basin transgressive phase, to its overflowing (Provo) phase, to its closed-basin regressive phase. Pre-Bonneville sediments contain either no fossils, or brine-shrimp fecal pellets plus a few scattered Limnocythere staplini valves; the first species to appear in Lake Bonneville sediments was L. staplini. Early in the transgressive phase L. staplini (alkalinity/calcium <1) was joined by several species of Candona or Fabaeformiscandona (F. caudata and others), and gradually L. staplini was replaced by L. ceriotuberosa (alk/Ca ~1). Higher in the section several species of Candona and Fabaeformiscandona dominate the ostracode faunas. In many sections, a stratigraphic interval dating to the middle and late transgressive phase contains only two ostracode species – L. ceriotuberosa and C. adunca. The ostracode fauna from the overflowing phase is slightly more diverse than lower in the sequence, primarily because of additional species of Candona and Fabaeformiscandona, but the fauna is similar to that of the late transgressive phase. The regressive phase is characterized by the continued presence of the same species as in the late transgressive and overflowing phases, plus the appearance of Cytherissa lacustris in mountain-front settings, then later a species of Candona that Rick thought resembled C. eriensis. L. sappaensis (alk/Ca >1) appears at the top of the sequence directly below brine-shrimp cysts, and is characteristic of the brackish water at low levels in the lake basin after Lake Bonneville evaporated, including the Gilbert episode. Ostracode changes show that TDS first decreased, then increased, and carbonate alkalinity increased continuously in Lake Bonneville. Rick assimilated new information from sections throughout the basin into the faunal sequence he initially deciphered from one core, to build a valuable and scientifically accurate biostratigraphy. He gladly and very effectively shared his knowledge.