Late Quaternary Paleoenvironments of an Ephemeral Wetland in North Dakota, USA: Relative Interactions of Ground-Water Hydrology and Climate Change

This study of fossils (pollen, plant macrofossils, stomata and fish) and sediments (lithostratigraphy and geochemistry) from the Wendel site in North Dakota, USA, emphasizes the importance of considering ground-water hydrology when deciphering paleoclimate signals from lakes in postglacial landscapes. The Wendel site was a paleolake from about 11,500 14C yr BP to 11,100 14C yr BP. Afterwards, the lake-level lowered until it became a prairie marsh by 9,300 14C yr BP and finally, at 8,500 14C yr BP, an ephemeral wetland as it is today. Meanwhile, the vegetation changed from a white spruce parkland (11,500 to 10,500 14C yr BP) to deciduous parkland, followed by grassland at 9,300 14C yr BP. The pattern and timing of these aquatic and terrestrial changes are similar to coeval kettle lake records from adjacent uplands, providing a regional aridity signal. However, two local sources of ground water were identified from the fossil and geochemical data, which mediated atmospheric inputs to the Wendel basin. First, the paleolake received water from the melting of stagnant ice buried under local till for about 900 years after glacier recession. Later, Holocene droughts probably caused the lower-elevation Wendel site to capture the ground water of upgradient lakes

Interpreting basal sediments and plant fossils in kettle lakes: insights from Silver Lake, Michigan, USA

We report on pollen, plant macrofossils, and associated lithostratigraphy of a sediment core extracted from the base of Silver Lake, a kettle in northern Lower Michigan, USA, which reveal a complex deglacial scenario for ice block melting and lake formation, and subsequent plant colonization. Complementary multivariate statistical and squared-chord distance analyses of the pollen data support these interpretations. The basal radiocarbon age from the core (17,540 cal yr BP) is rejected as being anomalously old, based on biostratigraphic anomalies in the core and the dateâ s incongruity with respect to the accepted regional deglaciation chronology. We reason that this erroneous age estimate resulted from the redeposition of Middle Wisconsin- age fossils by the ice sheet, mixed with the remains of plants that existed as the kettle lake formed at ca. 10,940 cal yr BP by ice block ablation. Thereafter, the kettle lake became a reliable repository of Holocene- age fossils, documenting a mature boreal forest that existed until 10,640 cal yr BP, followed by a pine-dominated mixed forest, an early variant of the mixed conifer- hardwood forest that persists to the present day. Our study demonstrates that researchers investigating kettle lakes, a common depositional archive for plant fossils in deglaciated landscapes, should exercise caution in interpreting the basal (late Pleistocene/early Holocene- age) part of lake sediment cores.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author