| Changes in vegetation, ultimately driven by climate, have influenced the abundance of resources available to humans, thus allowing us to examine how humans adapted to the dramatic environmental changes in the Bonneville basin. Several shifts in the environment (e.g. small mammal die-offs, pinyon pine migration) as well as human adaptive strategies (e.g. cave abandonment, upland vs. lowland strategies) have been inferred from archaeological sites, packrat middens, and faunal deposits in the Bonneville basin. The Blue Lake record provides a well-dated, fine-grained record of paleoenvironmental change that serves as a context to examine these major shifts. The overall goal is to better understand environmental conditions that may have influenced human adaptive strategies during the late Pleistocene and Holocene occupations of the Great Basin.;The marshes at Blue Lake, Utah, contain a long and well-dated series of sediments that cover the last 40,000 years, the entire history of the last rise-and-fall cycle of Pleistocene Lake Bonneville, and the last 10,000 years of the Holocene. This site is located about 40 km south of Wendover, Utah, on the margin of the Great Salt Lake Desert. Pollen analysis was conducted for the terminal Pleistocene and Holocene sections of the core, from approximately 16,000 cal B.P. to 1,500 cal B.P.;Prior to 13,750 cal B.P. (11,750 14C B.P.), climatic conditions were cool and dry, evident by the presence of limber pine and sagebrush pollen. Aquatic vegetation and sedimentology suggest relatively deep water conditions prevailed at Blue Lake, providing further support for Blue Lake submerged by pluvial Lake Bonneville. After about 13,750 cal B.P., pine pollen persists at Blue Lake, but the appearance of grass and Cheno-Am, as well as sedge pollen is indicative of a brief warming and drying trend (i.e.,"Clovis drought") that lasted until approximately 13,000 cal B.P. (11,000 14C B.P.).;Shortly after the drying episode, a return to cooler and wetter conditions occurred during the Younger Dryas climatic event. Accumulation of narrow leaf cattail (Typha angustifolia) pollen, organic matter, and water content all increase sharply at about 11,800 cal B.P., implying rise of Great Salt Lake to the Gilbert shoreline.;The climate during the early Holocene 11,570--9,530 cal B.P. (10,040--8,520 14C B.P.) warmed relative to the late Pleistocene (Younger Dryas) conditions. Grass and Cheno-Am pollen dominate the terrestrial pollen record, suggesting plants from these families were abundant in the lowlands around Blue Lake. Sedges continue to dominate the aquatic pollen record, indicating bulrush-dominated wetlands and shallow-water margins. The timing and expansion of wetlands in several parts of the Bonneville basin coincide with the establishment of the Blue Lake wetlands, around 10,850 cal B.P. (9,590 14C B.P.).;Sometime between 9,500 and 9,000 cal B.P. (8,500 and 8,000 14 C B.P.), a major shift to warmer and drier conditions occurred in the region. Pine and sagebrush pollen decline in the Blue Lake record, and were replaced by pollen of grass and xerophytic shrubs, such as shadscale and pickleweed. Sedge pollen sharply declines in abundance as well. The Blue Lake record shows very low pollen concentration and accumulation rates at this time period, possibly as a result of desiccation.;During the middle Holocene 7,470--3,980 cal B.P. (6,690--3,600 14C B.P.), grass and Cheno-Ams dominate, but pine pollen also increases. The latter probably signals the arrival of pinyon pine in the region. A 'neopluvial' fluctuation toward cooler and wetter conditions in the Blue Lake occurred from about 3,980--3,030 cal B. P. (3,600--2,910 14C years B.P.). After about 3,030 cal B.P. (2,910 14C B.P.), warmer and drier conditions return in the region marked by an increase in Cheno-am and grass pollen and a decrease in sagebrush pollen. At the same time, increased pine and juniper pollen suggest the development of thick pinyon-juniper woodlands in the uplands. |
