Transport Direction of Wisconsinan Loess in Southeastern Minnesota

1994 ◽  
Vol 41 (1) ◽  
pp. 44-51 ◽  
Author(s):  
Joseph A. Mason ◽  
Edward A. Nater ◽  
Howard C. Hobbs
Keyword(s):  
Grain Size ◽  
Mississippi River ◽  
Wind Erosion ◽  
The West ◽  
Loess Deposit ◽  
Transport Direction ◽  
Potential Sources ◽  
Western Border ◽  
Erosion Surface

AbstractA 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.

Wilkinson

2019 ◽  
pp. 136-149
Author(s):  
Gwynne Tuell Potts
Keyword(s):  
United States ◽  
Federal Government ◽  
Mississippi River ◽  
American History ◽  
The United States ◽  
War Of 1812 ◽  
The West ◽  
Independent Entity ◽  
Do So ◽  
The Revolution

Casual readers of American history may assume the United States enjoyed relative peace between the end of the Revolution and the War of 1812, but in fact, the West remained in turmoil and Kentucky lay at the center of British, French, and Spanish intrigue. Kentuckians struggled with significant decisions leading to statehood: should they remain part of Virginia, join the United States, or become an independent entity aligned with another nation? Navigation rights on the Mississippi River were at the heart of Kentuckians’ concerns, and as long as the federal government refused to negotiate the matter with Spain, most farmers initially were reluctant to commit themselves and their children to land-locked futures. George Rogers Clark, with the encouragement of his former soldiers, agreed to lead a contingent of settlers to form a colony on the Mississippi. Going so far as to ask Spain for permission to do so (as did Sevier, Steuben, and others), Clark unnerved the federal government.

scholarly journals Frontal structures in the West Spitsbergen Current margins

Ocean Science ◽  
2013 ◽  
Vol 9 (6) ◽  
pp. 957-975 ◽  
Author(s):  
W. Walczowski
Keyword(s):  
Thermohaline Circulation ◽  
Baroclinic Instability ◽  
Atlantic Water ◽  
Transport Processes ◽  
The Arctic ◽  
The West ◽  
Jet Streams ◽  
Nordic Seas ◽  
Western Border ◽  
West Spitsbergen

Abstract. The structures of the hydrographic fronts separating the Atlantic-origin waters from ambient waters in the northern Nordic Seas are discussed. Flows of the western and eastern branches of the West Spitsbergen Current create the Atlantic domain borders and maintain these fronts. This work is based on previous research and on investigations carried out in the project DAMOCLES (Developing Arctic Modelling and Observational Capabilities for Long-term Environmental Studies). Most of the observational data were collected during the R/V Oceania cruises. The main focus of the paper is the western border of the Atlantic domain – the Arctic Front, alongfrontal and transfrontal transports, and the front instability and variability. The alongfrontal baroclinic jet streams were described as a significant source of the Atlantic Water and heat in the Nordic Seas. The baroclinic instability and advection of baroclinic eddies which occurs due to this instability were found to be the main transfrontal transport processes. Most of the Atlantic Water transported by the western branch recirculates west and southward. The eastern branch of the West Spitsbergen Current provides most of the Atlantic Water entering the Arctic Ocean. Both processes are very important for the Arctic and global thermohaline circulation.

A Significant middle Pleistocene tephra deposit preserved in the caves of Mulu, Borneo

2012 ◽  
Vol 77 (3) ◽  
pp. 335-343 ◽  
Author(s):  
Joyce Lundberg ◽  
Donald A. McFarlane
Keyword(s):  
Grain Size ◽  
Isotopic Ratio ◽  
The Philippines ◽  
Plinian Eruption ◽  
Middle Pleistocene ◽  
Fall Deposit ◽  
Potential Source ◽  
Tephra Deposit ◽  
Potential Sources ◽  
Ratio Limit

A distinctive white sediment in the caves of Mulu, Sarawak, Borneo is a well-preserved tephra, representing a fluvially transported surface air-fall deposit, re-deposited inside the caves. We show that the tephra is not the Younger Toba Tephra, formerly considered as most likely. The shards are rod-shaped with elongate tubular vesicles; the largest grains ~ 170 μm in length; of rhyolitic composition; and 87Sr/86Sr ratio of 0.70426 ± 0.00001. U–Th dating of associated calcites suggest that the tephra was deposited before 125 ± 4 ka, and probably before 156 ± 2 ka. Grain size and distance from closest potential source suggests an eruption of VEI 7. Prevailing winds, grain size, thickness of deposit, location of potential sources, and Sr isotopic ratio limit the source to the Philippines. Comparisons with the literature give the best match geochemically with layer 1822 from Ku et al. (2009a), dated by ocean core stratigraphy to 189 ka. This tephra represents a rare terrestrial repository indicating a very substantial Plinian/Ultra-Plinian eruption that covered the Mulu region of Borneo with ash, a region that rarely receives tephra from even the largest known eruptions in the vicinity. It likely will be a valuable chronostratigraphic marker for sedimentary, palaeontological and archaeological studies.

Environmental and rock magnetic investigations into provenance and processes of west Iberian margin sediments

2020 ◽  
Author(s):  
Matthew Nichols ◽  
Chuang Xuan ◽  
David A. Hodell ◽  
Carl Richter ◽  
Gary D. Acton ◽  
...  
Keyword(s):  
Magnetic Material ◽  
Grain Size ◽  
Rock Magnetism ◽  
Sediment Cores ◽  
Hysteresis Loops ◽  
Ice Cores ◽  
Sediment Provenance ◽  
The West ◽  
Significant Difference ◽  
Iberian Margin

<p>Ocean sediment records from the West Iberian margin can be correlated to both Antarctic and Greenland ice cores as well as to European terrestrial pollen data. Previous studies have focussed on comparatively short sediment cores collected from relatively deep-water sites (i.e. >~2500mbsl). Here we present magnetic mineralogy and grain size from Integrated Ocean Drilling Programme Sites U1385 (2585mbsl) and U1391 (1085mbsl) to further understand magnetic sediment provenance and palaeocurrent evolution on the west Iberian margin dating back to ~416 ka. The gradient of IRM acquisition curves, shape of hysteresis loops, and marked decrease in magnetic susceptibility at ~580°C indicate that magnetite is the dominant magnetic phase at Site U1391. At depth, increased contributions of a higher coercivity component are seen at intervals where the concentration of magnetic material is low. FORC diagrams indicate the presence of a narrow ridge elongated along the Bc axis consistent with a higher coercivity component observed in IRM acquisition data. Magnetic grain size proxy (k<sub>ARM</sub>/k) records from Site U1391 also show a significant difference in pattern of variability at depth. After ~130 ka k<sub>ARM</sub>/k closely follows relative sea level, however prior to ~130 ka there is higher frequency variability with apparent coarser magnetic grain size, suggesting the higher coercivity component could have resulted from diagenetic processes. This is particularly apparent during warm intervals where magnetic material concentration is low (MIS 7, 9 and 11). This behaviour differs from that observed at either Site U1385, or in the younger portion of the record at Site U1391. We infer that the intervals of diagenetically effected sediments at U1391 could have resulted from increased productivity, vertical migration of the Mediterranean outflow water and associated changes in bottom water ventilation. Further understanding of sediment composition, redox conditions, transport and provenance through the last few glacial cycles underpins much of the other palaeoclimatic investigation at these sites. Results from our analysis of rock magnetism will be used to guide the reconstruction of reliable relative palaeointensity records from the Iberian Margin sediments to assess past geomagnetic changes in the region.</p>

Tarkasnawa King of Mira ‘Tarkondemos’, Boǧazköy sealings and Karabel

1998 ◽  
Vol 48 ◽  
pp. 1-32 ◽  
Author(s):  
J. D. Hawkins
Keyword(s):  
Bronze Age ◽  
Historical Geography ◽  
Western Anatolia ◽  
Late Bronze Age ◽  
Major Advance ◽  
The South ◽  
The West ◽  
South West ◽  
Historical Figure ◽  
Western Border

The historical geography of Anatolia in the period sourced by the Boǧazköy texts (Middle-Late Bronze Age) has proved an on-going problem since they first became available, and nowhere was this more acutely felt than in southern and western Anatolia, generally acknowledged as the site of the Arzawa lands, also probably the Lukka lands. A major advance has been registered since the mid-1980s, with the publication and interpretation of the Hieroglyphic inscription of Tudhaliya IV from Yalburt, and the Cuneiform treaty on the Bronze Tablet of the same king. These two documents have established that the later territory of Rough Cilicia constituted the Late Bronze Age kingdom of Tarhuntassa with its western border at Perge in Pamphylia, and that the Lukka lands did indeed occupy all of (or more than) classical Lycia in the south-west. These recognitions, by establishing the geography of the south and south-west, correspondingly reduced the areas of uncertainty in the west.In 1997 I was fortunately able to establish the reading of the Hieroglyphic inscription attached to the long-known Karabel relief, which lies inland from Izmir in a pass across the Tmolos range between Ephesos and Sardis. This can be shown to give the name of Tarkasnawa, King of Mira, and those of his father and grandfather, also kings of Mira but with names of uncertain reading. This is the same king known from his silver seal (referred to as ‘Tarkondemos' from an early and incorrect identification), and impressions of other seals of his have more recently been found at Boǧazköy. Clearly he was an important historical figure.

scholarly journals Magnetic Properties of a Holocene Sediment Core from the Yeongsan Estuary, Southwest Korea: Implications for Diagenetic Effects and Availability as Paleoenvironmental Proxies

2021 ◽  
Vol 9 ◽  
Author(s):  
Hyeon–Seon Ahn ◽  
Jaesoo Lim ◽  
Sung Won Kim
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Magnetic Susceptibility ◽  
South Korea ◽  
Size Distribution ◽  
Sea Level ◽  
West Coast ◽  
Magnetic Minerals ◽  
The West ◽  
Saturation Moment

The sensitivity of magnetic properties, which characterize the mineralogy, concentration, and grain size distribution of magnetic minerals, to environmental processes may provide useful information on paleoenvironmental changes in estuarine environments. Magnetic property studies of estuaries are less common than other environments and, due to the west coast of South Korea having an abundance of estuaries, it provides a good place to study these processes. In this study, we analyzed a variety of magnetic properties based on magnetic susceptibility, hysteresis parameters, progressive acquisition of isothermal remanent magnetization and first-order reversal curve data from a Holocene muddy sediment core recovered from the Yeongsan Estuary on the west coast of South Korea. We examined diagenetic effects on magnetic properties and tested their availability as proxies of paleoenvironmental change. The presence of generally low magnetic susceptibility, ubiquitous greigite-like authigenic magnetic component, and very fine magnetic particle occurrence suggested that the analyzed sediments had undergone considerable early diagenetic alteration. Electron microscopic observations of magnetic minerals support this suggestion. Our results confirm that the use of initial bulk susceptibility as a stand-alone environmental change proxy is not recommended unless it is supported by additional magnetic analyses. We recognized the existence of ferromagnetic-based variabilities related to something besides the adverse diagenetic effects, and have examined possible relationships with sea-level and major climate changes during the Holocene. The most remarkable finding of this study is the two distinct intervals with high values in magnetic coercivity (Bc), coercivity of remanence (Bcr), and ratio of remanent saturation moment to saturation moment (Mrs/Ms) that were well coincident with the respective abrupt decelerations in the rate of sea-level rise occurred at around 8.2 and 7 thousand years ago. It is then inferred that such condition with abrupt drop in sea-level rise rate would be favorable for the abrupt modification of grain size distribution toward more single-domain-like content. We modestly propose consideration of the Bc, Bcr, and Mrs/Ms variability as a potential indicator for the initiation/occurrence of sea-level stillstand/slowstand or highstand during the Holocence, at least at estuarine environments in and around the studied area.

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