Browsing by Subject "Pleistocene"
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Item Bulletin No. 26. The History of the Upper Mississippi River in Late Wisconsin and Postglacial Time(Minnesota Geological Survey, 1935) Cooper, William S.This study in glacial geology is the work of a botanist who is a firm believer in what has been aptly termed "cross-fertilization of the sciences." It developed gradually from a beginning that was purely botanical. An area of ancient dunes close to Minneapolis supports a flora that is distinctive and of unusual interest. An ecological investigation begun here necessitated consideration of the dunes themselves. Steadily the field broadened in the manner familiar to every scientific worker. The dunes led back to their source in the outwash. A great glacial lake disclosed itself. Finally the various elements resolved themselves into a history. in which the Mississippi River plays the leading role. Concurrently the botanical field expanded until it covered the vegetation of both dunes and outwash. with particular emphasis upon its development during post-glacial time. The foundational geologic study is here presented: the botanical part is still unwritten.Item Bulletin No. 40. Pleistocene Geology of the Randall Region, Central Minnesota(Minnesota Geological Survey, 1961) Schneider, Allan F.The systematic investigation of the glacial history of Minnesota goes back sixty to eighty years, to the days of N. H. Winchell and Warren Upham, who were as competent in the interpretation of the terrain and surface deposits as they were in working out the relations of the bedrock. A resurvey of the glacial history of the State was completed just before World War I by Frank Leverett of the U.S. Geological Survey, whose comprehensive report, however, was not published until 1932. Leverett had already mapped most of the other states in the Great Lakes region, so the picture for Minnesota fitted consistently with the others. Each successive generation of geologists, however, has different approaches, based on new techniques and on increased understanding of geological processes. After World War II the Minnesota Geological Survey initiated a program of re-examination of the glacial deposits of the State, which has an exceptionally fine record of the complex interactions of ice lobes that invaded the area from different directions. The recent Bulletin 39 on the Geology of Cook County incorporated a modern study of the glacial history of the northeastern corner of the State by Robert P. Sharp, and the present Bulletin by Allan F. Schneider describes a detailed study of an area in central Minnesota northwest of Little Falls. To this problem Dr. Schneider brought the necessary energy and enthusiasm to do the detailed field work required to unravel the complex relationships. In work on a problem of this sort a broad background on the region as a whole is necessary. This was furnished by H. E. Wright, Jr., who has supervised the work on the Pleistocene geology of Minnesota since 1947. Although the field work was supported by the Minnesota Geological Survey, it should be emphasized that untold hours were spent by Dr. Schneider on laboratory work and on drafting and writing the report while he was otherwise employed. The Minnesota Geological Survey is indebted to both Dr. Schneider and Professor Wright for their devoted service.Item Changes in seasonal precipitation of East Central North America with connections to global climate.(2010-10) Hardt, Benjamin FulperResearch on oxygen isotopes in stalagmites collected in West Virginia caves has yielded several new insights into regional climate. Oxygen isotopes most likely represent changes in the mean annual isotopic composition of precipitation, a parameter determined locally by the seasonal distribution of precipitation (Hardt et al., 2010). Holocene samples indicate that summer precipitation represented a greater proportion of annual totals, consistent with lake level results (Shuman and Donnelly, 2006) and climate models (Braconnot et al., 2007; Diffenbaugh et al., 2006). During the Pleistocene, seasonal precipitation varies on precessional timescales, although the phasing appears unusual in that it is in-phase with September insolation rather than June. This offset could be due to several processes, most likely in conjunction with each other. These processes include: changes in Gulf of Mexico sea surface temperatures, partially modulated by glacial meltwater routed through the Mississippi (Oglesby et al., 1989; H Wang et al., 2010); changes in the mean state of the tropical Pacific ocean between to El Nino- and La Nina-like conditions (Timmermann et al., 2007); and a seasonally-lagged sea surface temperature response in the subtropical North Atlantic, which would enhance the anticyclonic circulation of the Bermuda High. These same processes also appear to influence isotopic behavior over the last glacial Termination. During the last glacial maximum, oxygen isotopic composition is enriched, consistent with model results indicating wetter summers near the southern margin of the ice sheet (Bromwich et al., 2005), but inconsistent with a temperature control. Antiphasing in summer precipitation between West Virginia and Florida support a control on seasonal precipitation by changes in the position or size of the Bermuda High (Donders and de Boer et al., 2009). Comparison with speleothems from Northeast Brazil (Cruz et al, 2009) indicates a role for the El Nino Southern Oscillation due to its effect on the position of the Bermuda High (Seager et al., 2005).Item Ecology And Chemistry Of Small Mammals And The Implications For Understanding Their Paleoecology And Environments(2015-07) Haveles, AndrewFundamental goals of paleoecologists and modern ecologists is to understand the evolutionary and ecological patterns in modern and ancient biodiversity. Diet is one ecological trait species may evolve or vary to exploit food resources and increase their fitness. Stable isotope analysis is one method used to infer diet and is transferable between modern and fossil populations. Stable isotope analysis has not been commonly applied to small mammals, mostly because of sampling limitations. Here, three studies focus on furthering our understanding of small mammal ecology and serve as a baseline comparison for interpreting similar data from the fossil record. Chapter 1 illustrates that small mammals varied their diets independently and indicate granivores focused on C4 derived resources, generalists consumed resources readily available, and an invertivore focused on invertebrates. Results indicate that intermediate ?13C values between C3 and C4 resources are likely from integrating multiple resources through direct consumption and invertivory. Therefore, interpreting ?13C values from consumers in the fossil record must be interpreted with caution. Chapters 2 and 3 include a ?13C dataset that expands to the regional scale and assess how rodent partition C3 and C4 resources as C4 biomass on the landscape varies. Small mammals mostly rely on C3 derived resources, but there are some spatial and ecological tendencies with granivores incorporating the most C4 derived resources and varied with C4 biomass. Climate variables explained some variance in C4 consumption for some species, while other species' diets were not explained by climate. Seasonality metrics were the best predictors of C4 consumption and ?13C values in rodent hairs were more positive during peak C4 growing seasons. Chapter 4 estimates temperature and precipitation using the area extant species' geographic ranges overlap today and then applied to ancient faunas where the same species co-occur. Temperature and precipitation estimates for Pleistocene-Holocene localities reflect the general warming during this transition and interpolated temperature and precipitation for climate intervals illustrate deviating spatial gradients through time. The culmination of work presented here greatly improves our understanding of small mammal ecology and sets s baseline for testing modes of evolution and ecology in the fossil record.Item Guidebook 16. Field Trip Guidebook for Quaternary and Cretaceous Geology of West-Central Minnesota and Adjoining South Dakota(Minnesota Geological Survey, 1987) Balaban, N.H., EditorCONTENTS GEOMORPHOLOGY AND PLEISTOCENE GLACIAL GEOLOGY OF CENTRAL MINNESOTA, Barry Goldstein CRETACEOUS ROCKS ON THE EASTERN MARGIN OF THE WESTERN INTERIOR SEAWAY: A FIELD GUIDE FOR WESTERN MINNESOTA AND EASTERN SOUTH DAKOTA, George W. Shurr, Jay P. Gilbertson, Richard H. Hammond, Dale R. Setterholm, and Peter M. WhelanItem High-resolution speleothem record of climate variability during the late Pleistocene from Spring Valley Caverns, Minnesota(2018-02) Nissen, JuliaUnderstanding how the Earth's oceanic and atmospheric systems responded to abrupt climatic forcings in the past is crucial in determining potential effects of anthropogenic climate change. This is of particular importance in the mid-continental United States, an agricultural hub that produces much of the world's corn and soybeans. High resolution paleorecords in the region remain sparse, restricting the predictability of global climate models and limiting our knowledge of atmospheric teleconnections across North America. This study analyses the growth and stable isotopic concentration of late Pleistocene speleothem samples from Spring Valley Caverns, located in SE Minnesota. Timing of growth for six samples was determined using 230Th dating and confocal microscopy, recording ages between 114 - 29 ky BP. This places all sample growth within the last glacial period. Sample growth largely correlates with warm conditions in the North Atlantic, indicating elevated temperature and moisture availability. Growth during MIS4 may be due to enhanced anti-cyclonic activity over the Laurentide Ice Sheet, resulting in anomalous southerly moisture transport. High resolution stable isotope analysis was completed for two samples, showing both long term trends and short term variability. Samples show a steady decrease in d13C values from 104 - 29 ky BP, suggesting a transition from C4 to C3 dominated ecosystems consistent with global cooling. However, d18O values climb steadily throughout this period. This is indicative of drier conditions and an increase in Gulf of Mexico sourced moisture in the region. Short term variability from 64 - 44 ky BP shows impressive correlation to global paleorecords. North Atlantic cold events are shown as an increase in d18O values, and North Atlantic warm events as a decrease d18O values. As d18O and d13C generally covary during this period, elevated d18O values suggest regional aridity. The transport of Gulf of Mexico summer moisture into the region appears significantly susceptible to changes in North Atlantic climate, most likely through large scale atmospheric systems such as the North Atlantic Oscillation and Pacific-North America teleconnection. The results of these records agree with a previous study of Spring Valley Caverns from the Holocene (Dasgupta, 2008). This signifies that large scale dynamics present during the last glacial period continue to affect regional climate, and thus these results may prove useful not only in improving our understanding of abrupt climate events during the late Pleistocene but in predicting impacts on the region from anthropogenic warming.Item The Influence of Bedrock Topography on the Origin of a Mid-Pleistocene Epoch Glacial Lake in Rock County, Southwest Minnesota(Minnesota Geological Survey, 2017) Southwick, David LA circular, closed depression 1.9 miles (3 kilometers) in diameter that was formerly occupied by a shallow lake is located in the glaciated landscape of northern Rock County, southwest Minnesota. The depression is partly framed by Sioux Quartzite and is situated above a bedrock swale on a broad, quartzite-supported upland that is thinly mantled by pre-Wisconsinan glacial deposits. The quartzite-supported upland has been a positive topographic feature since at least the Late Cretaceous Epoch; near the depression, its discontinuous cover of unconsolidated sediment consists of glacial till, outwash deposits, and loess that aggregate to a total preserved thickness between 1 and 82 feet (less than 1 to 25 meters). The depression originated from the melting out of a buried, tabular ice mass that was isolated near the stagnating margin of a mid-Pleistocene Epoch continental glacier. The ice mass was buried in outwash and then further buried by a thin till deposited when the glacier readvanced. The ice mass became isolated and was slow to melt because of its position in a bedrock swale on a topographic high that was near a dynamically fluctuating glacier margin; its relative thickness and protected location in the swale were key factors in its transient preservation. The closed depression that formed upon final melting of the ice mass has survived in the post-glacial landscape because of its location on a geomorphically persistent bedrock upland where the erosive energy of post-glacial and modern streams has been minimal. It has been speculated that this bedrock-framed, geographically unique circular depression may be a deeply eroded meteorite impact structure. No supporting evidence for this speculation has been discovered in the field or laboratory.Item Information Circular 45. Utility of Elemental Geochemical Data in Correlation and provenance Studies of Pleistocene Materials: A Case Study in Stearns county, Central Minnesota(Minnesota Geological Survey, 2000) Morey, G.B.; Lively, R.S.; Meyer, Gary N.Geochemical attributes, especially minor, trace, and rare-earth elements, are commonly used to characterize various kinds of sedimentary rocks and to elucidate their provenance. Similar techniques have been applied to glacial materials with varying degrees of success. In Minnesota, for example, Martin and others (1989, 1991) concluded that few if any geochemical elements were useful for correlating tills across large areas. In contrast, Gowan (1998), in a study of six till units from central Minnesota, concluded that geochemical attributes were useful in delineating stratigraphic units and their provenance. Results of a similar study in southwestern Minnesota (Patterson and others, 1995) were inconclusive. The geochemical studies undertaken to date in Minnesota have utilized the silt and clay-size fraction as a sample medium and Atomic Adsorption spectrometry or Inductively Coupled Plasma emission spectrometry as the principal analytical technique. Unfortunately, both techniques require that the sample medium be dissolved prior to analysis, which can limit the value of the resulting data. For example, relative to the composition of the sample matrix and the particulates, certain minerals and elements may be selectively leached or incompletely dissolved, or spectral signals from some concentrated elements may interfere with weaker signals from less abundant elements. Such problems are best addressed by the use of replicates and standards developed from materials similar to those being analyzed. To our knowledge, sets of material standards that could be used to calibrate the various analytical methods have not been developed for Pleistocene sediments in Minnesota. In this study we avoided problems associated with partial dissolution and interference by using Instrumental Neutron Activation Analysis (INAA) techniques (XRAL Activation Services Inc., Ann Arbor, Michigan). We analyzed 123 subsurface samples from five drill sites in Stearns County, east-central Minnesota, for 32 elements. The results in this report are not directly comparable with those of Martin and others (1988), Gowan (1998), and Patterson and others (1995), because they were obtained on whole-rock samples from which only clasts of pebble or larger size had been removed. Nonetheless, the data provide insight into the utility of geochemical techniques to investigate provenance and transport patterns of glacial materials. The complete file of analytical data is summarized in the Appendix.