Browsing by Subject "glacical geology"
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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 Geologic Map Series 2. Surficial Geology of the New Brighton Quadrangle, Minnesota(Minnesota Geological Survey, 1966) Stone, John E.The New Brighton quadrangle is underlain by as much as 500 feet of glacial drift, which lies directly on Paleozoic sedimentary rocks. The bedrock, which is part of the northern flank of the Twin Cities artesian basin, is traversed by a complex network of buried valleys as much as 400 feet deep that were cut during several cycles of erosion. Most of the surface morphology and the related deposits were formed about 12,500 years ago, during the advance and retreat of the Grantsburg Sublobe, which produced the following formations in the approximate order of their deposition: (1) the Hillside Sand, a proglacial outwash deposit; (2) the Twin Cities Formation, a complex mixture of gray and red till; (3) the Falcon Heights Sand, a retreatal outwash deposit; (4) the Turtle Lake Sand, a lake deposit; (5) the Arsenal Sand, a kame deposit; (6) the New Brighton Formation, a lake deposit; and (7) the Fridley Formation, another lake deposit. The units have been mapped at the surface and traced in the subsurface. After the active ice retreated from the immediate area, the West Campus Sand, a valley-train deposit, was deposited. Later, ice in the drift melted to produce many hundreds of kettle holes, some of which are now occupied by lake or swamp deposits; the valley train was dissected, leaving a terrace along the Mississippi River; and a poorly integrated drainage system was produced. In late-glacial and postglacial time, thin deposits of eolian sand, loess, and colluvium were laid down. The most significant changes in the landscape in postglacial time have been made by man, who settled the area in the 1830's and 1840's. Preliminary data are given on the engineering properties of the surficial deposits. These data in conjunction with the geology are useful for engineering and hydrologic studies, land-use planning, and resource evaluation.Item Geologic Map Series 3. Geology of the Cloquet Quadrangle Carlton County, Minnesota(Minnesota Geological Survey, 1970) Wright, H.E. Jr; Mattson, L.A.; Thomas, J.A.The Cloquet quadrangle is bisected by the St. Louis River, a major stream that flows into the western end of Lake Superior. Precambrian rocks are extensively exposed in the river valley where overlying Pleistocene glacial deposits have been eroded. The Precambrian rocks are dominated by the Thomson Formation, which consists of interbedded slates, slaty graywackes, and graywackes. Small-scale cross-bedding, graded bedding, flute casts, load casts, clastic dikes, and other primary and penecontemporaneous structures are common, as are calcareous and siliceous concretions. The formation probably was deposited in a relatively deep-water basin, in part by turbidity currents. It has only one conspicuous marker bed, the Otter Creek unit, so the stratigraphic thickness across the intricate folds of the region is difficult to determine, but it probably is about 20,000 feet. Normal and reverse faults with displacements of a few tens of feet are common, as are steeply dipping conjugate joints of northwest and northeast trends. Cleavage is well developed in slaty units. The Thomson Formation is correlated with the Animikie Group. Abundant microgabbro dikes were intruded during subsidence of the Lake Superior syncline. The Pleistocene glacial history was marked by three phases of advance and retreat of the Superior Lobe, preceded by a phase of the Rainy Lobe. Drumlins, moraines, outwash plains, eskers, lake plains, and diversion channels constitute distinctive landforms. During final withdrawal of the Superior Lobe from the area, the St. Louis River, which carried the outflow from Glacial Lake Upham, was diverted to form prominent erosional channels leading to the St. Croix River at progressively lower elevations, until it finally flowed into the proglacial Lake Nemadji, whose outlet formed a final channel in the sequence.Item Guidebook 22. Field Trip Guidebook Landforms, Stratigraphy, and Lithologic Characteristics of Glacial Deposits in Central Minnesota(Minnesota Geological Survey, 2006) Knaeble, A.R.This guidebook was prepared for the 50th Midwest Friends of the Pleistocene Field Conference, sponsored by the Minnesota Geological Survey and held at St. John's University on June 4-6, 2004. The purpose of this guidebook is to provide conference participants with an up-to-date general summary of the glacial geology of central Minnesota and a comprehensive reference list of previous research completed in the area. There are a number of reasons why we were motivated to host the Friends of the Pleistocene in central Minnesota. First, over the last 10 years the Minnesota Geological Survey has completed numerous mapping projects in the central Minnesota area (Steams, Pope, and Crow Wing County atlases; the Otter Tail regional hydrogeological assessment; and the USGS Statemap St. Cloud, Baxter, Brainerd, and Gull Lake quadrangle maps), and is in the process of completing mapping projects in Todd, Traverse, and Grant Counties. The large volume of data (samples and descriptions from outcrops and drill holes) collected from these projects has allowed us to evaluate the work done by previous researchers and contribute new insights and interpretations. Second, in 1954 Herb Wright, AI Schneider, and Harold Ameman led the 5th Midwest Friends of the Pleistocene field trip in central Minnesota. We will revisit the area, on this 50th anniversary of that trip, to examine how interpretations have changed and evolved. The guidebook will use a simple, direct approach to summarize the region's glacial geology, similar to that used in 1954. It is our intention to pay tribute to the accomplishments of Herb and AI during the field trip and banquet. We will also acknowledge other researchers who, over the last 50 years, have made contributions to the glacial geology of central Minnesota. Third, we would like to discuss how mapping techniques and technology have changed in the last 50 years. We will examine which techniques have been most effective in understanding the complex stratigraphy of central Minnesota. Finally, field exposures were selected to stimulate interest and discussion about the following glacial topics: erosion, transport, and deposition of source-area materials; processes involved in drumlin formation; the relationship between ice dynamics and glacial landforms; processes important in the formation of the St. Croix moraine; and the challenges of interpreting thick, complex drift stratigraphy. These stops highlight geomorphic features, stratigraphic relationships, and specific unit characteristics (lithology, color, etc.) in an attempt to provide an overview of the glacial geology of this region.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.