The 87Sr/86Sr ratios of lacustrine carbonates and lake-level history of the Bonneville paleolake system

Abstract

Lakes in the Bonneville basin have fl uctuated dramatically in response to changes in rainfall, temperature, and drainage diversion during the Quaternary. We analyzed tufas and shells from shorelines of known ages in order to develop a relation between 87 Sr/ 86 Sr ratio of carbonates and lake level, which then can be used as a basis for constraining lake level from similar analyses on carbonates in cores. Carbonates from the late Quaternary shorelines yield the following average 87 Sr/ 86 Sr ratios: 0.71173 for the Stansbury shoreline (22-20 14 C ka; 1350 m), 0.71153 for the Bonneville shoreline (15.5-14.5 14 C ka; 1550 m), 0.71175 for the Provo shoreline (14.4-14.0 14 C ka; 1450 m), 0.71244 for the Gilbert shoreline (~10.3-10.9 14 C ka; 1300 m), and 0.71469 for the modern Great Salt Lake (1280 m). These analyses show that the 87 Sr/ 86Sr ratio of lacustrine carbonates changes substantially at low-to mid-lake levels but is invariant at mid-to high-lake levels.Sr-isotope mixing models of Great Salt Lake and the Bonneville paleolake system were constructed to explain these variations in 87 Sr/ 86 Sr ratios with change in lake level. Our model of the Bonneville system produced a 87 Sr/ 86 Sr ratio of 0.71193, very close to the observed ratios from high-shoreline tufa and shell. The model verifi es that the integration of the southern Sevier and Beaver rivers with the Bear and others rivers in the north is responsible for the lower 87 Sr/ 86 Sr ratios in Lake Bonneville compared to the modern Great Salt Lake. We also modeled the 87 Sr/ 86 Sr ratio of Lake Bonneville with the upper Bear River diverted into the Snake River basin and obtained an 87 Sr/ 86 Sr ratio of 0.71414. Coincidentally, this ratio is close to the observed ratio for Great Salt Lake of 0.71469. This means that 87 Sr/ 86 Sr ratios of >0.714 for carbonate can be produced by climatically induced low-lake conditions or by diversion of the upper Bear River out of the Bonneville basin. This model result also demonstrates that the upper Bear River had to be fl owing into the Bonneville basin during highstands of other late Quaternary lake cycles: carbonates from the Little Valley (130-160 ka) and Cutler Dam (59 ± 5 ka) lake cycles returned 87 Sr/ 86 Sr ratios of 0.71166 and 0.71207, respectively, and are too low to be produced by a lake without the upper Bear River input.

Lateglacial and Holocene climatic changes in south-eastern Patagonia inferred from carbonate isotope records of Laguna Potrok Aike (Argentina)

“…Changes in strontium isotope ratios reflect alterations in the Sr sources induced by environmental and climatic changes (e.g. Åberg, 1995;Hart et al, 2004;Kober et al, 2007). Sr isotope ratios of Laguna Potrok Aike range between values of Pali Aike volcanics (D'Orazio et al, 2000) on the one side and Patagonian top soils and eolian dust on the other side (Gaiero et al, 2007;Fig.…”

Influence of the diversion of Bear River into Bear Lake (Utah and Idaho) on the environment of deposition of carbonate minerals

“…The isotopic values of the 20th-century surface sediments do not represent the full range of change because of mixing of high-Mg calcite with older aragonite that is more enriched in 18 O, 13 C, and 87 Sr. The Sr-isotopic ratio of any carbonate (precipitate or shell) will have the same Sr-isotopic composition as the water from which it formed (e.g., Capo and DePaolo 1990;Hart et al 2004). Therefore, the Sr isotopic composition of carbonate that formed in the epilimnion of Bear Lake will be the same as that of the lake water, and we can use the 87 Sr : 86 Sr ratio to infer sources of prediversion Bear Lake water and the origin of the mixtures of minerals in bulk carbonate in the trap sediments.…”

Intracontinental Miocene: Climate and paleolake volumes in the Forez Basin, France (Part I)

“…4). Sr contents and isotopic ratios of carbonate provide a useful proxy to determine the relative contribution of strontium from soil, rainfall and surrounding in paleolakes (cf., Behrens and Land, 1972;Kretz, 1982;Hart et al, 2004). This model requires knowledge of the Sr flux into the system from every major source, which includes surface runoff, groundwater, and rainfall (Table 3).…”

“…This hypothesis suggests that groundwater Sr contributions in carbonate layers were provided by leaching and dissolution of surrounding siliciclastic sediments, salts or carbonates. The mass balance equation is (Hart et al, 2004; …”