Minnesota Geological Survey

Although sediment is a natural constituent of rivers, excess loading to rivers and streams is a leading cause of impairment and biodiversity loss. Remedial actions require identification of the sources and mechanisms of sediment supply. This task is complicated by the scale and complexity of large watersheds as well as changes in climate and land use that alter the drivers of sediment supply. Previous studies in Lake Pepin, a natural lake on the Mississippi River, indicate that sediment supply to the lake has increased 10-fold over the past 150 years. Herein we combine geochemical fingerprinting and a suite of geomorphic change detection techniques with a sediment mass balance for a tributary watershed to demonstrate that, although the sediment loading remains very large, the dominant source of sediment has shifted from agricultural soil erosion to accelerated erosion of stream banks and bluffs, driven by increased river discharge. Such hydrologic amplification of natural erosion processes calls for a new approach to watershed sediment modeling that explicitly accounts for channel and floodplain dynamics that amplify or dampen landscape processes. Further, this finding illustrates a new challenge in remediating nonpoint sediment pollution and indicates that management efforts must expand from soil erosion to factors contributing to increased water runoff.

Research Article| August 01, 1963 Precambrian Ancestry of the Colorado Mineral Belt OGDEN TWETO; OGDEN TWETO U. S. Geological Survey, Denver, Colo Search for other works by this author on: GSW Google Scholar P. K SIMS P. K SIMS Minnesota Geological Survey, Minneapolis, Minn Search for other works by this author on: GSW Google Scholar Author and Article Information OGDEN TWETO U. S. Geological Survey, Denver, Colo P. K SIMS Minnesota Geological Survey, Minneapolis, Minn Publisher: Geological Society of America Received: 14 Nov 1960 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1963, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1963) 74 (8): 991–1014. https://doi.org/10.1130/0016-7606(1963)74[991:PAOTCM]2.0.CO;2 Article history Received: 14 Nov 1960 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation OGDEN TWETO, P. K SIMS; Precambrian Ancestry of the Colorado Mineral Belt. GSA Bulletin 1963;; 74 (8): 991–1014. doi: https://doi.org/10.1130/0016-7606(1963)74[991:PAOTCM]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The narrow northeast-trending Colorado mineral belt, the site of most of the major mining districts of Colorado, is characterized by intrusive porphyries and associated ore deposits of Laramide age and, in some places, by fissures and faults of northeasterly trend. The belt, about 250 miles long, extends diagonally across the generally north-trending mountain ranges of Colorado, occupies several different geologic environments, and seems to be independent of the present mountain structure.The mineral belt follows an ancient zone of weakness defined by northeast-trending shear zones of Precambrian age in a belt 10–35 miles wide. Individual shear zones or clusters of zones are spaced from a mile or less to many miles apart. In most parts of the belt, a major northeast-trending shear zone is flanked by lesser shear zones in an echelon arrangement.Movement occurred along the belt of shear zones through most of the Precambrian time recorded in the region. During this time, deformation progressed from a deep-seated environment characterized by folding and plastic flow to a more shallow environment characterized by fracture and retrograde metamorphism. The earliest movement occurred during regional folding, when folds were oriented parallel to the shear zones or were bent where they impinged upon the shear zones. Cataclastic deformation began after the folds had formed, but the earliest products of cataclasis re-crystallized as new gneisses, indicating that relatively intense metamorphic conditions either still prevailed or recurred. Later, when pressure and temperature were lower, cataclastic gneisses, pseudotachylyte, mylonite, and broad granulated zones formed, and in some places small crossfolds formed in layers of incompetent gneiss between cataclastically deformed competent layers. Still later in the Precambrian, gouge and breccia formed, partly by the degradation of earlier shear products of higher rank.During Paleozoic and Mesozoic time, minor differential movements occurred repeatedly in the regional zone of shearing, as recorded by thinning, wedgeouts, and changes in facies of several sedimentary formations along the zone.With the onset of the Laramide orogeny, magma invaded the regional zone of shearing and imparted to it the conspicuous features that characterize the mineral belt—intrusive igneous bodies and ore deposits. Fault movement occurred along the zone at this stage also but was on a smaller scale than it had been previously. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| December 01, 1980 The Great Lakes tectonic zone — A major crustal structure in central North America P. K. SIMS; P. K. SIMS 1U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar K. D. CARD; K. D. CARD 2Geological Survey of Canada, Ottawa KlA 0E4, Canada Search for other works by this author on: GSW Google Scholar G. B. MOREY; G. B. MOREY 3Minnesota Geological Survey, St. Paul, Minnesota 55108 Search for other works by this author on: GSW Google Scholar Z. E. PETERMAN Z. E. PETERMAN 4U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1980) 91 (12): 690–698. https://doi.org/10.1130/0016-7606(1980)91<690:TGLTZA>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation P. K. SIMS, K. D. CARD, G. B. MOREY, Z. E. PETERMAN; The Great Lakes tectonic zone — A major crustal structure in central North America. GSA Bulletin 1980;; 91 (12): 690–698. doi: https://doi.org/10.1130/0016-7606(1980)91<690:TGLTZA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Great Lakes tectonic zone is a major Precambrian crustal feature more than 1,200 km long extending eastward from Minnesota into Ontario, Canada. It is a zone of distinctive tectonism, affecting both Archean and early Proterozoic rocks, along the northern margin of the early Proterozoic Penokean fold belt adjacent to the Archean Superior province. The zone coincides with the boundary between two Archean crustal segments recognized in the region: a greenstone-granite terrane (∼2,700 m.y. old) to the north (Superior province) and an older (in part 3,500 m.y. old) gneiss terrane to the south. Tectonism along the zone began in the late Archean, during the joining together of the two terranes into a single continental mass, and culminated in the early Proterozoic, when steep or northward-facing overturned folds were formed in the supracrustal rocks, and intense cataclasis and a penetrative cleavage developed in subjacent basement rocks of the greenstone-granite terrane. The Proterozoic deformation took place under low to intermediate pressures.Movement occurred along the Great Lakes tectonic zone through much of the Precambrian time recorded in the region. In the early Proterozoic, crustal foundering, which was parallel to the zone and was diachronous, initiated the structural basins in which the early Proterozoic sequences of the Lake Superior and Lake Huron regions were deposited. Later, during the Penokean orogeny (∼1,850 to 1,900 m.y. ago), compression deformed the sequences in both regions. Still later, intermittent (∼1,850 to 1,100 m.y. ago) crustal extension provided sites for emplacement of abundant mafic igneous rocks. There is no definite evidence that any of the extensional events progressed to the stage of development of oceanic crust; probably the zone has been wholly intracratonal since its inception in late Archean time.During the Phanerozoic, minor differential movements occurred locally in the Great Lakes tectonic zone, as recorded by the thinning of Cretaceous strata and their subsequent tilting and by historic earthquakes in Minnesota. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Ground moraine inside of Beroun moraine_ 48 Mille Lacs morainic system_____________________ 48 Location__________________________________ 48 Topography_______________________________ 49 Character of the drift______________________ 49 Rock outcrops and striae___________________ 49 Outwash__________________________________ 49

Well-known difficulties in applying sequence stratigraphic concepts to deposits that accumulated across slowly subsiding cratonic interior regions have limited our ability to interpret the history of continental-scale tectonism, oceanographic dynamics of epeiric seas, and eustasy. We used a multi-disciplinary approach to construct a high-resolution stratigraphic framework for lower Paleozoic strata in the cratonic interior of North America. Within this framework, these strata proved readily amenable to modern sequence stratigraphic techniques that were formulated based on successions along passive margins and in foreland basins, settings markedly different from the cratonic interior. Parasequences, parasequence stacking patterns, systems tracts, maximum flooding intervals, and sequence-bounding unconformities can be confidently recognized in the cratonic interior using mostly standard criteria for identification. The similarity of cratonic interior and foreland basin successions in size, geometry, constituent facies, and local stacking patterns of nearshore parasequences is especially striking. This similarity indicates that the fundamental processes that establish shoreface morphology and determine the stratal expression of retreat and progradation were likewise generally the same, despite marked differences in tectonism, physiography, and bathymetry between the two settings. Our results do not support the widespread perception that Paleozoic cratonic interior successions are so anomalous in stratal geometries, and constitute such a poor record of time, that they are poorly suited for modern sequence stratigraphic analyses. The particular arrangement of stratal elements in the cratonic interior succession we studied is no more anomalous or enigmatic than the variability in architecture that sets all sedimentary successions apart from one another. Thus, Paleozoic strata of the cratonic interior are most appropriately considered as a package that belongs in a continuum of variable stratigraphic packages reflecting variable controls such as subsidence and shelf physiography. Special conditions of exceptionally slow subsidence rate, shallow bathymetry, and nearly flat regional shelf gradient are manifest mostly by the presence of individual systems tracts of relatively long duration that extend for much greater distances across depositional strike than those that characterize successions deposited in more dynamic tectonic and physiographic settings. These results suggest that if other cratonic interior successions are as anomalous as reported, a low sediment supply may have played a primary role in development of their apparently condensed stratal architecture. The results also lead us to suggest that a nonvegetated lower Paleozoic landscape played a relatively insignificant role in the development of what are commonly perceived to be enigmatic stratigraphic features of sheet sandstones, particularly their widespread yet thin geometry, and a scarcity of shale and siltstone.

Sadler's (1981) analysis of how measured sedimentation rate decreases with timescale of measurement quantified the vanishingly small fractional time preservation—completeness—of the stratigraphic record. Generalized numerical models have shown that the Sadler effect can be recovered, through the action of erosional clipping and time removal (the “stratigraphic filter”), from even fairly simple topographic sequences. However, several lines of evidence suggest that most of the missing time has not been eroded out but rather represents periods of inactivity or stasis. Low temporal completeness could also imply that the stratigraphic record is dominated by rare, extreme events, but paleotransport estimates suggest that this is not generally the case: The stratigraphic record is strangely ordinary. It appears that the organization of the topography into a hierarchy of forms also organizes the deposition into concentrated events that tend to preserve relatively ordinary conditions, albeit for very short intervals. Our understanding of time preservation would benefit from insight about how inactivity is recorded in strata; better ways to constrain localized, short-term rates of deposition; and a new focus on integrated time–space dynamics of deposition and preservation.

Research Article| July 01, 1998 Laurentide glacial landscapes: The role of ice streams Carrie J. Patterson Carrie J. Patterson 1Minnesota Geological Survey, 2642 University Ave., St. Paul, Minnesota 55114 Search for other works by this author on: GSW Google Scholar Author and Article Information Carrie J. Patterson 1Minnesota Geological Survey, 2642 University Ave., St. Paul, Minnesota 55114 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1998) 26 (7): 643–646. https://doi.org/10.1130/0091-7613(1998)026<0643:LGLTRO>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Carrie J. Patterson; Laurentide glacial landscapes: The role of ice streams. Geology 1998;; 26 (7): 643–646. doi: https://doi.org/10.1130/0091-7613(1998)026<0643:LGLTRO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Glacial landforms of the North American prairie can be divided into two suites that result from different styles of ice flow: (1) a lowland suite of level-to-streamlined till consistent with formation beneath ice streams, and (2) an upland and lobe-margin suite of thick, hummocky till and glacial thrust blocks consistent with formation at ice-stream and ice-lobe margins. Southern Laurentide ice lobes hypothetically functioned as outlets of ice streams. Broad branching lowlands bounded by escarpments mark the stable positions of the ice streams that fed the lobes. If the lobes and ice streams were similar to modern ice streams, their fast flow was facilitated by high subglacial water pressure. Favorable geology and topography in the midcontinent encouraged nonuniform ice flow and controlled the location of ice streams and outlet lobes. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| February 01, 1998 Origin of a classic cratonic sheet sandstone: Stratigraphy across the Sauk II–Sauk III boundary in the Upper Mississippi Valley Anthony C. Runkel; Anthony C. Runkel 1Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114-1057 Search for other works by this author on: GSW Google Scholar Robert M. McKay; Robert M. McKay 2Iowa Department of Natural Resources, Geological Survey Bureau, 109 Trowbridge Hall, Iowa City, Iowa 52242-1319 Search for other works by this author on: GSW Google Scholar Allison R. Palmer Allison R. Palmer 3Institute for Cambrian Studies, 445 North Cedarbrook Road, Boulder, Colorado 80304-0417 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1998) 110 (2): 188–210. https://doi.org/10.1130/0016-7606(1998)110<0188:OOACCS>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Anthony C. Runkel, Robert M. McKay, Allison R. Palmer; Origin of a classic cratonic sheet sandstone: Stratigraphy across the Sauk II–Sauk III boundary in the Upper Mississippi Valley. GSA Bulletin 1998;; 110 (2): 188–210. doi: https://doi.org/10.1130/0016-7606(1998)110<0188:OOACCS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The origin of cratonic sheet sandstones of Proterozoic and early Paleozoic age has been a long-standing problem for sedimentologists. Lower Paleozoic strata in the Upper Mississippi Valley are best known for several such sandstone bodies, the regional depositional histories of which are poorly understood. We have combined outcrop and subsurface data from six states to place the Upper Cambrian Wonewoc (Ironton and Galesville) Sandstone in a well-constrained stratigraphic framework across thousands of square kilometers. This framework makes it possible for the first time to construct a regional-scale depositional model that explains the origin of this and other cratonic sheet sandstones.The Wonewoc Sandstone, although mapped as a single contiguous sheet, is a stratigraphically complex unit that was deposited during three distinct conditions of relative sea level that span parts of four trilobite zones. During a relative highstand of sea level in Crepicephalus Zone time, quartzose sandstone lithofacies aggraded more or less vertically in nearshore-marine and terrestrial environments across much of the present-day outcrop belt around the Wisconsin arch. At the same time, finer grained, feldspathic sandstone, siltstone, and shale aggraded in deeper water immediately seaward of the quartzose sand, and shale and carbonate sediment accumulated in the most distal areas. During Aphelaspis and Dunderbergia Zones time a relative fall in sea level led to the dispersal of quartzose sand into a basinward-tapering, sheet-like body across much of the Upper Mississippi Valley. During early Elvinia Zone time a major transgression led to deposition of a second sheet sandstone that is generally similar to the underlying regressive sheet.The results of this investigation also demonstrate how subtle sequence-bounding unconformities may be recognized in mature, cratonic siliciclastics. We place the Sauk II-Sauk III subsequence boundary at the base of the coarsest bed in the Wonewoc Sandstone, a lag developed through erosion that occurred during the regional regressive-transgressive event that spanned Aphelaspis to early Elvinia Zones time. Such sequence-bounding unconformities are difficult to recognize where they are contained within coarse siliciclastics of the Upper Mississippi Valley, because they separate strata that are texturally and mineralogically similar, and because erosion occurred on a loose, sandy substrate along a low, uniform gradient, and in a nonvegetated terrestrial environment. Furthermore, the ultramature mineral composition of the exposed substrate is resistant to the development of a recognizable weathering profile.The well-known sheet geometry of the Wonewoc and other units of lower Paleozoic sandstone of this area is not dependent on atypical terrestrial depositional conditions conducive to the widespread distribution of sand, as commonly believed. Sand was spread into a sheet dominantly within the marine realm in a manner similar to that inferred for many better-known sandstone bodies deposited in the North American Cretaceous Western Interior seaway and Tertiary Gulf of Mexico. The laterally extensive, thin character of the Upper Mississippi Valley sandstone bodies compared to these other sandstone bodies simply reflects deposition of a continuously abundant supply of sand on a relatively stable, nearly flat basin of slow, uniform subsidence during changes in sea level. The dearth of shale in this and other cratonic sandstones can be indirectly attributed to the same controls, which led to an uncommonly low preservation potential for fairweather deposits on the shoreface. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

We propose that the late Paleoproterozoic igneous and deformational history preserved in the northern midcontinent United States can be explained by a change in subduction-polarity from geon 18 south-dipping subduction during Penokean accretion to geon 17 north-dipping subduction as convergence continued after Penokean orogenesis. New U-Pb zircon ages indicate that late to post-Penokean magmatism occurred at ca. 1800, 1775, and 1750 Ma and generally migrated southeastward across the newly accreted Penokean terrane. We suggest that geon 17 Yavapai slab rollback caused continental arc magmatism to step southeastward between 1800 and 1750 Ma. As the slab steepened, reduced compressional stresses and magma-induced thermal weakening allowed for collapse of the overthickened portions of the Penokean crust. Postcollapse crustal stabilization (the 1750-1650 Ma Baraboo interval) was followed by geon 16 Mazatzal arc accretion further south. The 1900-1600 Ma tectonic history of the north-central United States, not surprisingly, records events related to the southward growth and tectonic development of the southern Laurentian margin. New and published 4 0 Ar/ 3 9 Ar mineral ages delineate the northern and western extent of geon 16 Mazatzal deformation. Interestingly, only little exhumed crust intruded by a small volume of shallow-level ca. 1750 Ma plutons (and associated rhyolites) was deformed significantly during geon 16. In contrast, more deeply exhumed crust and crust pervasively invaded by a large volume of post-Penokean magma (i.e., East-Central Minnesota Batholith) were largely unaffected by Mazatzal deformation and reheating. We suggest that posttectonic intrusions and crustal thinning were an important step in strengthening and stabilizing the crust in the southern Lake Superior region.

The most common methods of estimating the relative abundance of species in a fossil assemblage are all maximum likelihood estimates. They differ from one another in their inherent assumptions made about the effects of fragmentation and differential preservation in the assemblage. For many fossil assemblages, relative abundance is best estimated by the relative frequency of specimens or relative frequency of elements. Monte Carlo simulations suggest, however, that in most other circumstances estimates based on frequency of elements divided by the number of elements in a complete individual provide greater accuracy than estimates based on minimum number of individuals. This relation results from an interaction between random sampling error and a variety of biases inherent in the two estimates.

We use the cosmic-ray-produced radionuclides ^26^Al and ^10^Be to date Plio-Pleistocene glacial sediment sequences. These two nuclides are produced in quartz at a fixed ratio, but have different decay constants. If a sample is exposed at the surface for a time and then buried by overburden and thus removed from the cosmic-ray flux, the ^26^Al/^10^Be ratio is related to the duration of burial. We first attempted to date pre-Wisconsinan tills by measuring ^26^Al and ^10^Be in fluvial sediments beneath them and applying the method of "burial dating," which previous authors have used to date river sediment carried into caves. This method, however, requires simplifying assumptions about the ^26^Al and ^10^Be concentrations in the sediment at the time of burial. We show that these assumptions are not valid for river sediment in glaciated regions. ^26^Al and ^10^Be analyses of such sediment do not provide accurate ages for these tills, although they do yield limiting ages in some cases. We overcome this difficulty by instead measuring ^26^Al and ^10^Be in quartz from paleosols that are buried by tills. We use a more general mathematical approach to determine the initial nuclide concentrations in the paleosol at the time it was buried, as well as the duration of burial. This technique provides a widely applicable improvement on other means of dating Plio-Pleistocene terrestrial glacial sediments, as well as a framework for applying cosmogenic-nuclide dating techniques in complicated stratigraphic settings. We apply it to pre-Wisconsinan glacial sediment sequences in southwest Minnesota and eastern South Dakota. Pre-Wisconsinan tills underlying the Minnesota River Valley were deposited 0.5 to 1.5 Ma, and tills beneath the Prairie Coteau in eastern South Dakota and adjacent Minnesota were deposited 1 to 2 Ma.

Abstract A study of Wisconsinan loess in part of southeastern Minnesota confirms earlier suggestions that much of the loess in this region was not derived flora the floodplain of the Mississippi River. Two Wisconsinan loess units, the Peoria Loess and Roxana Silt, occur in the study area. Peoria Loess, 1-8 m thick, fines systematically eastward from an abrupt western border toward the Mississippi. There are no apparent grain-size trends away from other adjacent rivers. Peoria Loess thickness generally decreases eastward, but is highly variable, probably because of differential erosion. Potential sources for this unit are pre-Wisconsinan sediments on the Iowan Erosion Surface immediately west of the border of thick loess and Wisconsinan glacial sources tens or hundreds of kilometers to the west. The underlying Roxana Silt, up to 1 m thick, occurs only near the Mississippi and fines away from that river. The Roxana Silt deposit could reflect aggradation of the Mississippi floodplain because of glacial activity upstream and does not have clear implications for upland vegetation near the study area. By contrast, transport of the Peoria Loess from distant glacial sources or wind erosion of upland surfaces closer to the loess deposit both imply extensive, very sparsely vegetated surfaces west of the study area when the Peoria Loess accumulated.

Research Article| April 01, 1994 Deposition of the uppermost Cambrian (Croixan) Jordan Sandstone, and the nature of the Cambrian-Ordovician boundary in the Upper Mississippi Valley ANTHONY C. RUNKEL ANTHONY C. RUNKEL 1Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114-1057 Search for other works by this author on: GSW Google Scholar Author and Article Information ANTHONY C. RUNKEL 1Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114-1057 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1994) 106 (4): 492–506. https://doi.org/10.1130/0016-7606(1994)106<0492:DOTUCC>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation ANTHONY C. RUNKEL; Deposition of the uppermost Cambrian (Croixan) Jordan Sandstone, and the nature of the Cambrian-Ordovician boundary in the Upper Mississippi Valley. GSA Bulletin 1994;; 106 (4): 492–506. doi: https://doi.org/10.1130/0016-7606(1994)106<0492:DOTUCC>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Jordan Sandstone, of Late Cambrian (Croixan) age, is well known as one of several cratonic sheet sandstones in the Upper Mississippi Valley that are part of the classic Paleozoic "orthoquartzite-carbonate suite". Evidence that the Jordan is an entirely marine, regressive sequence, rather than transgressive as commonly assumed, provides new insight into the origin of cratonic sheet sandstones.The lower half of the Jordan Sandstone is composed of two intercalated lithofacies: (1) extensively burrowed, very fine grained sand-stone interbedded with hummocky cross-stratified beds deposited on the offshore shelf and (2) fine-grained, burrowed, cross-stratified sandstone deposited on the lower shoreface during storms. The upper half of the Jordan consists of medium- to coarse-grained sand-stone deposited on the upper shoreface by tidal and storm-generated currents. This lithofacies is characterized by abundant scour surfaces, tidal inlet fills, and very large angular intra-clasts of sandstone derived from incised beach-rock on the foreshore.Lithofacies associations demonstrate that the Jordan Sandstone is a regressive sequence deposited as part of a shoreline system that prograded across the Hollandale embayment, a shallow depression on the cratonic shelf in the Upper Mississippi Valley region. Progradation was interrupted by transgressive episodes recorded as local tongues of offshore deposits that disconformably overlie shoreface deposits. This sedimentologic model contributes to the evaluation of depositional controls in Late Cambrian time, and to solving some long-standing enigmas associated with cratonic sheet sandstones.Contrary to the long-held view that the Cambrian-Ordovician boundary is conformable in this region, sedimentologic evidence indicates that a regional unconformity separates the Jordan Sandstone from the Early Ordovician Oneota Dolomite. Deep incision into the lowest Jordan lithofacies occurred near the Transcontinental Arch on the western margin of the embayment, and near the Wisconsin Arch on the eastern margin. This differential erosion marks the earliest known tectonic up-lift of the basin's margins relative to the center. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Lusardi, B. A., Jennings, C. E. & Harris, K. L. 2011: Provenance of Des Moines lobe till records ice-stream catchment evolution during Laurentide deglaciation. Boreas, 10.1111/j.1502-3885.2011.00208.x. ISSN 0300-9483. Mapping and analysis of deposits of the Des Moines lobe of the Laurentide Ice Sheet, active after the Last Glacial Maximum (LGM), reveal several texturally and lithologically distinct tills within what had been considered to be a homogeneous deposit. Although the differences between tills are subtle, minor distinctions are predictable and mappable, and till sheets within the area covered by the lobe can be correlated for hundreds of kilometres parallel to ice flow. Lateral till-sheet contacts are abrupt or overlap in a narrow zone, coincident with a geomorphic discontinuity interpreted to be a shear margin. Till sheets 10 to 20 m thick show mixing in their lower 2 to 3 m. We suggest that: (i) lithologically distinct till sheets correspond to unique ice-stream source areas; (ii) the sequence of tills deposited by the Des Moines lobe was the result of the evolution and varying dominance of nearby and competing ice streams and their tributaries; and (iii) in at least one instance, more than one ice stream simultaneously contributed to the lobe. Therefore the complex sequence of tills of subtly different provenances, and the unconformities between them record the evolution of an ice-catchment area during Laurentide Ice Sheet drawdown. Till provenance data suggest that, after till is created in the ice-stream source area, the subglacial conditions required for transporting till decline and incorporation of new material is limited.

The Sonju Lake intrusion, part of the 1.1 Ga Midcontinent rift-related Beaver Bay Complex, is a 1,200-m-thick, strongly differentiated, layered sequence of mafic cumulates located in northeastern Minnesota. Basal melatroctolite and dunite layers are overlain by troctolite, gabbro, Fe-Ti oxide-rich gabbro, apatite diorite, and monzodiorite. Stratigraphic intervals rich in Pt + Pd, Cu, and S occur over ~500 m in the Fe-Ti oxide-rich gabbro and apatite diorite units. Peak concentrations show offsets that are similar to those found in other tholeiitic layered intrusions. Concentrations of Pd in excess of 100 ppb are confined to the lowermost 25 m of the interval. Copper shows a sharp increase to 630 ppm above the Pd-rich interval. Sulfur contents are low (<375 ppm) in the Cu-rich interval, but they increase to values as high as 3,150 ppm above in the apatite diorite. Disseminated sulfides in the intrusion have δ 34S values that range from –2.2 to 3 per mil Vienna-Canyon Diablo Troilite (V-CDT) and suggest that contamination by country rock sulfur was not an important process in the formation of the metal-rich interval. δ 18O values of plagioclase from the intrusion range from 5.6 to 12.0 per mil (V-SMOW) and indicate that a relatively low-18O fluid ( δ 18O ~3–5 ‰) interacted with the rocks of the intrusion at temperatures less than ~275°C. Clinopyroxene and Fe-Ti oxides (ilmenite with minor amounts of titanomagnetite) show much more restricted ranges in δ 18O values (4.6–5.7 and 5.5–6.7 per mil, respectively) and attest to the kinetic control of the oxygen isotope exchange process. The externally derived fluid that interacted with rocks now enriched in platinum group elements (PGE) + Cu- and Fe-sulfide minerals locally liberated sulfur and replaced chalcopyrite and pyrite with goethite. In the Cu-rich zone, goethite that replaces chalcopyrite may contain up to 8.5 weight percent Cu. It is evident that hydrothermal alteration resulted in a decoupling of copper and sulfur, with sulfur being transferred out of the Cu-rich interval. Interaction between rocks in the PGE-Cu-S interval of the Sonju Lake intrusion and an externally derived fluid at low temperatures modified what appears to have been a primary stratigraphic metal-sulfur zonation. The effects of hydrothermal alteration on PGE and base-metal sulfide mobility and redistribution must be understood before models of primary zonation processes can be meaningfully applied.

1970 BRANDT ,1972 )

Research Article| December 01, 1986 Fluvial origin of the lower Proterozoic Sioux Quartzite, southwestern Minnesota D. L. SOUTHWICK; D. L. SOUTHWICK 1Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114 Search for other works by this author on: GSW Google Scholar G. B. MOREY; G. B. MOREY 1Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114 Search for other works by this author on: GSW Google Scholar J. H. MOSSLER J. H. MOSSLER 1Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114 Search for other works by this author on: GSW Google Scholar Author and Article Information D. L. SOUTHWICK 1Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114 G. B. MOREY 1Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114 J. H. MOSSLER 1Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1986) 97 (12): 1432–1441. https://doi.org/10.1130/0016-7606(1986)97<1432:FOOTLP>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation D. L. SOUTHWICK, G. B. MOREY, J. H. MOSSLER; Fluvial origin of the lower Proterozoic Sioux Quartzite, southwestern Minnesota. GSA Bulletin 1986;; 97 (12): 1432–1441. doi: https://doi.org/10.1130/0016-7606(1986)97<1432:FOOTLP>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Sioux (Quartzite of inferred Early Proterozoic age (1,760−1,630 m.y.) occurs in southwestern Minnesota, eastern South Dakota, and adjoining parts of Iowa and Nebraska where it overlies a regolith developed on an older Precambrian crystalline basement. The rocks constitute a red-bed sequence that was deposited by braided streams flowing over a deeply weathered land surface of moderate relief. Deposition was confined largely to fault-bounded basins in a cratonic setting; the basins subsided slowly and were rarely, if ever, areas of steep relief. The Sioux Quartzite is a texturally and mineralogically mature quartz arenite. Sand grains are mainly monocrystalline quartz with rare grains of chert, granular iron-formation, and quartzite. Scattered conglomeratic layers contain lithic clasts that include red quartzite, chert, iron-formation, vein quartz, and rhyolite, together with rare welded rhyolite tuff and granitoid gneiss. Stratigraphic intervals of conglomeratic orthoquartzite are interspersed throughout the basal two-thirds of the formation, whereas thin units of sericitic mudstone are most abundant in the upper third. Overall, the upward fining of size grades in the Sioux may indicate diminishing stream gradients and reduction of relief in source areas during deposition.The diagenetic minerals diaspore, kaolinite, and quartz cement indicate an environment of intense leaching, probably under warm, humid climatic conditions, during or closely following deposition. Detrital feldspar, present in trace amounts in deeper parts of the stratigraphic section, may have been more abundant originally but was destroyed by intrastratal reactions. The sub-Sioux regolith is characterized by (1) fine-grained kaolinite and sericite formed from intensively altered coarse-grained metamorphic feldspar and (2) the presence of abundant secondary hematite and silica.By virtue of its Early Proterozoic age, its alluvial origin, and its unconformable position above older Proterozoic and Archean rocks, the Sioux is inferred to have some potential for unconformity-related, Athabasca-type uranium deposits. Its provenance, which includes older Proterozoic iron-formation and volcanic rocks (greenstone), enhances its potential for paleoplacer gold deposits. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Mesabi Range along the north edge of the Paleoproterozoic Penokean orogen in northern Minnesota has produced 3.6 billion metric tons of ore since its discovery in 1890. Of that amount, 2.3 billion metric tons were extracted from hematite-or goethite-rich deposits generally referred to as ores. The high-grade ores formed as the Biwabik Iron-Formation was oxidized, hydrated, and leached by solutions flowing along open faults and fractures. The source of the ore-forming solutions has been debated since it was first proposed that the ores were weathering products formed by descending meteoritic ground-water flowing in late Mesozoic time. Subsequently others believed that the ores were better explained by ascending solutions, possibly hydrothermal solutions of pre-Phanerzoic age. Neither Wolff nor Gruner could reconcile their observations with a reasonable source for the solutions. In this paper, I build on modern mapping of the Mesabi Range and mine-specific geologic observations summarized in the literature to propose a conceptual model in which the high-grade ores formed from ascending solutions that were part of a continent-scale topographic or gravity-driven ground-water system. I propose that the ground-water system was active during the later stages of the development of a coupled fold and thrust belt and foreland basin that formed during the Penokean orogen.

Abstract The morphometry of 85 gnammas (weathering pits) from Big Stone County in western Minnesota allows the assessment of the relative ages of the gnamma population. The ratio between maximum and minimum depths is independent of the initial size of the cavity and only depends on the weathering evolution. Therefore, the distribution of depth ratios can be used to assess the gnamma population age and the history of weathering. The asymmetrical distribution of depth ratios measured in Big Stone County forms three distinct populations. When these sets are analyzed independently, the correlation ( r 2 ) between maximum and minimum depths is greater than 0·95. Each single population has a normal distribution of depth ratios and the average depth ratios ( δ ‐value) for each population are δ 1 = 1·60 ± 0·05, δ 2 = 2·09 ± 0·04 and δ 3 = 2·42 ± 0·08. The initiation of gnamma formation followed the exhumation of the granite in the region. This granite was till and saprolite covered upon retreat of the ice from the Last Glacial Maximum. Nearby outcrops are striated, but the study site remained buried until it was exhumed by paleofloods issuing from a proglacial lake. These Holocene‐aged gnammas in western Minnesota were compared with gnammas of other ages from around the world. Our new results are in accordance with the hypothesis that δ ‐values represent the evolution of gnammas with time under temperate‐ to cold‐climate dynamics. Phases of the formation of new gnammas may result from changes in weathering processes related to climate changes. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Early Proterozoic sequences in the Lake Superior region, which are sedimentologically related and contain major units of iron-formation, are divisible into allostratigraphic sequences--packages of rock bounded by unconformities. Analysis that emphasizes the hounding unconformities therefore emphasizes processes external to the depositional system, which initiate and terminate deposition of the sedimentologically related successions of rock types. An analysis of this type shows that the region9s iron-bearing strata were deposited throughout the progressive growth and ultimate destruction of a rifted continental margin. The extensional phase of this continuum is marked by sedimentary units having an Archean provenance to the north and iron-formation having many descriptive attributes associated with Algoma-type iron-formation. Unconformities developed during extension resemble the rift-onset and the breakup unconformities recognized in younger continental margin assemblages. The compressional phase deposited in a northward-migrating foredeep basin is marked by sedimentary units having an Early Proterozoic provenance to the south and iron-formation having Lake Superior-type attributes. The boundary between the two is time-transgressive, migrating to the north as the basin migrated in that direction. This stratigraphic reconstruction departs significantly from those of the last 50 years which were based on the assumption of a single correlatable Early Proterozoic iron-formation in all the Lake Superior iron ranges. Sedimentation, although episodic, started around 2200 Ma and was essentially over by 1850 Ma. Thus units of iron-formation were deposited over some 350 m.y. of geologic time, an interval approximately 60 percent as long as that attributed to all of the Phanerozoic eon. Thus precipitation of iron-formation in the Lake Superior region is not a unique product of a single set of factors restricted to a short interval of geologic time. Our challenge will involve identifying underlying factors on a range-by-range basis.