Stratification models for vegetated coastal dunes in Atlantic Canada

1989 ◽  
Vol 96 ◽  
pp. 203-215
Author(s):  
S. B. McCann ◽  
M.-L. Byrne
Keyword(s):  
Internal Structure ◽  
Coastal Dunes ◽  
Atlantic Canada ◽  
Sedimentary Sequences ◽  
Plant Associations ◽  
Depositional Settings ◽  
Aeolian Activity ◽  
Depositional Models

SynopsisThe principal types of stratification and some characteristic sedimentary sequences found in vegetated coastal dunes in Atlantic Canada are described. Four examples are selected to show a range of dune types and depositional settings. In each case the documentation and interpretation of the internal structure and stratification has made an important contribution to understanding the evolution of the dunes. Stratification and depositional models are presented for:(1) a single, continuous, transgressive foredune ridge which maintains its form during transgression;(2) a discontinuous transgressive foredune ridge, interrupted by washover passages;(3) a “precipitation” dune, which buries an existing stable dune; and(4) complex dunes produced by two or more phases of aeolian activity characterised by different plant associations.

Records of climate changes and anthropogenic actions over dune fields in historical times

2020 ◽  
Author(s):  
Mihaela Tudor ◽  
Ana Ramos-Pereira ◽  
Joana Gaspar de Freitas
Keyword(s):  
Climatic Variability ◽  
Coastal Dunes ◽  
Coastal Dune ◽  
Environmental Data ◽  
Dune System ◽  
Climatic Fluctuations ◽  
Dune Systems ◽  
Sand Drift ◽  
Aeolian Activity ◽  
Historical Times

<p>Coastal dunes are very complex systems and very sensitive to climatic variability and human actions. In Portugal, coastal dune fields have undergone major changes over historical times. The aim of the paper is focused on the coastal dune systems evolution over the last five centuries, natural and man induced (namely by deforestation and afforestation) and their transformation under the present global changes (sea level rise and coastal storms). The analysis of historical records and environmental data using a set of proxies recorded over the last 1,000 yrs, show intense aeolian activity and sand drift episodes during Little Age Period, causing serious problems for human settlements and agriculture. Coastal society have responded to the wind-blown sands fixing the dunes through afforestation. The process is well documented in the historical sources and many management measures, including abundant legislation, projects and reports were carried out by Portuguese authorities to avoid sand incursion inland.  According to the main report of the General Forest Administration, in the final of 18th century, was estimated an area of about 72 000 ha of free aeolian sands in need of afforestation. Thus, along Portuguese coastline, the dunes experienced a period of stability during the 20th century, due to planting of grasses and pine forest. This paper examines the pathways of the transgressive dune fields of the Central Western Portuguese coast, over various stages of coastal evolution. Mapping the morphological features between Mondego river mouth and Nazaré, using a combination of satellite images, aerial photographs and Lidar data we identified distinct phases of aeolian activity and landforms modification that were associated to climatic fluctuations. This coastal dune system is composed by a succession of different aeolian phases, including a littoral foredune, which lies inland with a complexity of morphologies with transverse and crescentic ridges, and also parabolic dunes. The results show that the dunes building and sand migration inland appears to be linked to the conditions of predominantly negative winter North Atlantic Oscillation index (NAOi), driven by climatic variability during Holocene/Antrhopocene. The consistency of intense sand drift episodes with abrupt cold events during Little Age Period, drastically reduced the area occupied by vegetation, causing changes in aeolian sedimentary processes. Thus, it seems that coastal dunes evolution over the past centuries have been controlled by the two-way interactions between natural conditions and human activities, shaping the Portuguese coastline. Placing historical evidence in a geographical perspective, we hope to fill the gaps in coastal zone dynamics, providing new insights of the human-landscape relationships to predict the future response of the coastal dune systems to human pressure and climate change.<br>Key-words: coastal dunes evolution, geomorphological features, sand drift, anthropogenic impacts, climatic fluctuation, Western Portugal.</p>

scholarly journals Glacio-lacustrine sedimentation in newly discovered paleo-lakes, Westland, New Zealand

2021 ◽  
Author(s):  
◽  
Adam Michael Thomas
Keyword(s):  
New Zealand ◽  
Glacial Lake ◽  
Glacial Retreat ◽  
Sedimentary Sequences ◽  
Quaternary Glaciation ◽  
Lake Formation ◽  
Landscape Response ◽  
Facies Succession ◽  
Lacustrine Facies ◽  
Depositional Models

<p>The remnant effects of Quaternary glaciation dominate the geomorphology of South Westland, New Zealand. Well-constrained glaciogenic records for the Last Glacial Maximum (LGM) (~MIS 2) show ice to have extended significant distances across the Westland piedmont, becoming tidewater calving in places. Despite clear evidence for glacial advance, landscape response to glacial retreat remains relatively poorly understood, with few described sedimentary sequences clearly recording deglaciation processes. A 240-metre thick glacio-lacustrine sedimentary sequence intercepted by drilling in the Whataroa Valley (DFDP-2) provides the first compelling evidence of pro-glacial lake formation in response to glacial retreat in Westland. To understand the vertical facies succession observed in this sequence, two glacio-lacustrine facies schemes and depositional models were developed. To do this, previously unmapped glacio-lacustrine sedimentary sequences in the Westland region underwent detailed sedimentological analysis to identify key glacio-lacustrine facies. In the Waitangitaona and Arahura river valleys, the presence of glacio-lacustrine sequences is also used to mark paleo-lake formation in the respective catchments.   Using the facies scheme and depositional models, together with 14C chronology and sedimentological analysis, a series of conclusions are developed from the DFDP-2 sequence: 1) Deposition occurred in an over-deepened glacial trough, with the sequence consisting of a basal diamictite, overlain by a ~ 140-metre interval of lacustrine  siltstones and sandstones. 2) The lower ~ 180-metres of sediment accumulated in 659 ± 151 yrs between 16609 ± 151 and 15994 ± 94 cal. yr BP, as the depositional environment at the drill-site evolved from an ice contact to an ice distal lacustrine setting. 3) Extremely rapid sedimentation rates, as well as high lake levels allowed the preservation of glacially over-steepened bedrock slopes beneath the Whataroa Valley.   The formation of a previously unknown, ~190 km2 pro-glacial lake on the Whataroa piedmont is inferred from the DFDP-2 sequence, with lake formation causing accelerated glacial retreat from the late LGM maxima. The presence of several catchments with comparable piedmont geometry suggests pro-glacial lake formation may have been a common response to glacial retreat in Westland. For a period, pro-glacial lakes may have been a significant transitory feature on the Westland landscape.</p>

scholarly journals Glacio-lacustrine sedimentation in newly discovered paleo-lakes, Westland, New Zealand

2021 ◽  
Author(s):  
◽  
Adam Michael Thomas
Keyword(s):  
New Zealand ◽  
Glacial Lake ◽  
Glacial Retreat ◽  
Sedimentary Sequences ◽  
Quaternary Glaciation ◽  
Lake Formation ◽  
Landscape Response ◽  
Facies Succession ◽  
Lacustrine Facies ◽  
Depositional Models

<p>The remnant effects of Quaternary glaciation dominate the geomorphology of South Westland, New Zealand. Well-constrained glaciogenic records for the Last Glacial Maximum (LGM) (~MIS 2) show ice to have extended significant distances across the Westland piedmont, becoming tidewater calving in places. Despite clear evidence for glacial advance, landscape response to glacial retreat remains relatively poorly understood, with few described sedimentary sequences clearly recording deglaciation processes. A 240-metre thick glacio-lacustrine sedimentary sequence intercepted by drilling in the Whataroa Valley (DFDP-2) provides the first compelling evidence of pro-glacial lake formation in response to glacial retreat in Westland. To understand the vertical facies succession observed in this sequence, two glacio-lacustrine facies schemes and depositional models were developed. To do this, previously unmapped glacio-lacustrine sedimentary sequences in the Westland region underwent detailed sedimentological analysis to identify key glacio-lacustrine facies. In the Waitangitaona and Arahura river valleys, the presence of glacio-lacustrine sequences is also used to mark paleo-lake formation in the respective catchments.   Using the facies scheme and depositional models, together with 14C chronology and sedimentological analysis, a series of conclusions are developed from the DFDP-2 sequence: 1) Deposition occurred in an over-deepened glacial trough, with the sequence consisting of a basal diamictite, overlain by a ~ 140-metre interval of lacustrine  siltstones and sandstones. 2) The lower ~ 180-metres of sediment accumulated in 659 ± 151 yrs between 16609 ± 151 and 15994 ± 94 cal. yr BP, as the depositional environment at the drill-site evolved from an ice contact to an ice distal lacustrine setting. 3) Extremely rapid sedimentation rates, as well as high lake levels allowed the preservation of glacially over-steepened bedrock slopes beneath the Whataroa Valley.   The formation of a previously unknown, ~190 km2 pro-glacial lake on the Whataroa piedmont is inferred from the DFDP-2 sequence, with lake formation causing accelerated glacial retreat from the late LGM maxima. The presence of several catchments with comparable piedmont geometry suggests pro-glacial lake formation may have been a common response to glacial retreat in Westland. For a period, pro-glacial lakes may have been a significant transitory feature on the Westland landscape.</p>

scholarly journals The Sedimentary Record of Paleogene Sequences in Sarawak, Malaysia

2021 ◽  
Vol 47 (1) ◽  
pp. 33-56
Author(s):  
Franz L. Kessler ◽  
John Jong ◽  
Mazlan Madon
Keyword(s):  
South China Sea ◽  
South China ◽  
Late Eocene ◽  
Peninsular Malaysia ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Sedimentary Sequences ◽  
Depositional Settings ◽  
Well Data

In this paper, we compare the oldest Tertiary sedimentary sequences in the south ern margin of the South China Sea based on outcrop and well data along the Sarawak margin, northern Borneo. Paleogene rocks in Sarawak are present in three tectono stratigraphic zones and represent three depositional settings. Outcrops and deep exploration wells in the Miri Zone indicate shelfal clastics, carbonates, and clay dominated neritic sediments. In the Sibu Zone (Rajang Fold Thrust Belt), Late Cretaceous to Late Eocene deep marine clastic sediments indicate a shallowing upward of the depositional basin, which was later buried to great depths (?) and metamorphosed. In the Kuching Zone, the Kayan and Plat eau sandstones represent a fluvial dominated non marine depositional setting. There are two major unconformities within the Paleogene of Sarawak: the Rajang Unconformity, dated as approximatively 37 Ma, and the younger near Top Eocene (a.k.a. Base Oligocen e) unconformity of 33.7 Ma. The likely presence of Eocene strata in the margins of Sundaland is associated with an early phase of regional extensional tectonism, which was also observed in the Penyu and Malay basins, offshore Peninsular Malaysia, and is probably related to the onset of rifting of the South China Sea continental crust.

scholarly journals A 7000-year record of coastal evolution, Vejers, SW Jutland, Denmark

2006 ◽  
Vol 53 ◽  
pp. 1-22 ◽  
Author(s):  
Lars B. Clemmensen ◽  
Karsten Pedersen ◽  
Andrew Murray ◽  
Jan Heinemeier
Keyword(s):  
Large Scale ◽  
Coastal Dunes ◽  
Aeolian Sand ◽  
Coastal System ◽  
Dune Field ◽  
The Holocene ◽  
The North ◽  
Sedimentary Evolution ◽  
Sand Drift ◽  
Aeolian Activity

The Holocene coastal lowland at Vejers in western Jutland has formed during the last 7000 years. The lowland is composed of a large, NNE-SSW trending spit system associated with minor and only locally developed strandplain or beach ridge systems. The main spit and back-barrier system is bounded to the north and east (inland) by old moraine landscapes (Varde Bakkeø). Most of the coastal system and also large parts of the adjacent moraine landscape is covered by aeolian sand. In this study one of the minor strandplain systems is investigated. This system is developed at the south-western margin of the old moraine landscape at Grovsø, a lake near Vejers. The Holocene sedimentary evolution of this latter system is evaluated on the basis of data from two closely situated cores and Ground-Penetrating Radar (GPR) mapping. Both cores consist of a lowermost unit with marine sediment, a middle unit with lake-aeolian sand and an uppermost unit with aeolian sandplain deposits. Peat layers and peat-rich paleosols are common. These peat-rich horizons are dated by the Accelerator Mass Spectrometry (AMS) radiocarbon technique, while the intervening sand layers are dated by Optically Stimulated Luminescence (OSL). Combined evidence from the sedimentological and chronological studies of the cores and the GPR survey, indicate that the area was first transgressed at about 5100 BC. During the subsequent period (5100–2700 BC) relative sea level rose about 5 meters, the strandplain prograded, and small coastal dunes formed. During this progradational event a large strandplain lake formed behind the frontal dune ridge and this lake was filled primarily by aeolian sand. Aeolian sand drift may have been most intense around 3000 BC. This first period of large-scale aeolian activity ended some time before 2300 BC with formation of a peat-rich paleosol. Aeolian activity, however, was soon re-established and resulted in the formation of a large sandplain with small dunes. Aeolian sand movement and accumulation, however, was punctuated by periods of landscape stabilisation and peat-rich paleosol formation. Changes from landscape stabilisation to dune field activity took place at about 2300 BC, 1450 BC, 800 BC, and 650 BC. Aeolian accumulation at the study site terminated at about AD 0, but other evidence indicates renewed aeolian activity in the dune field after AD 300 and between AD 1100 and 1900. The chronology of some of these aeolian activity phases are synchronous with cooling events in the North Atlantic region suggesting that climatic change strongly influenced dune field dynamics.

X-ray microtomography

1988 ◽  
Vol 46 ◽  
pp. 998-999
Author(s):  
H.W. Deckman ◽  
B.F. Flannery ◽  
J.H. Dunsmuir ◽  
K.D' Amico
Keyword(s):  
Computed Tomography ◽  
Internal Structure ◽  
Imaging Technique ◽  
Three Dimensional ◽  
Tissue Structure ◽  
Individual Element ◽  
X Ray ◽  
Non Invasive ◽  
Panoramic Imaging ◽  
Three Dimensional Images

We have developed a new X-ray microscope which produces complete three dimensional images of samples. The microscope operates by performing X-ray tomography with unprecedented resolution. Tomography is a non-invasive imaging technique that creates maps of the internal structure of samples from measurement of the attenuation of penetrating radiation. As conventionally practiced in medical Computed Tomography (CT), radiologists produce maps of bone and tissue structure in several planar sections that reveal features with 1mm resolution and 1% contrast. Microtomography extends the capability of CT in several ways. First, the resolution which approaches one micron, is one thousand times higher than that of the medical CT. Second, our approach acquires and analyses the data in a panoramic imaging format that directly produces three-dimensional maps in a series of contiguous stacked planes. Typical maps available today consist of three hundred planar sections each containing 512x512 pixels. Finally, and perhaps of most import scientifically, microtomography using a synchrotron X-ray source, allows us to generate maps of individual element.

The internal structure of medullated wool

1984 ◽  
Vol 42 ◽  
pp. 388-389
Author(s):  
Leo Barish
Keyword(s):  
Light Microscopy ◽  
Internal Structure ◽  
Wool Fiber ◽  
Guard Hair ◽  
Bright Field ◽  
Wool Fibers ◽  
Thin Skin ◽  
Air Pockets

Although most of the wool used today consists of fine, unmedullated down-type fibers, a great deal of coarse wool is used for carpets, tweeds, industrial fabrics, etc. Besides the obvious diameter difference, coarse wool fibers are often medullated.Medullation may be easily observed using bright field light microscopy. Fig. 1A shows a typical fine diameter nonmedullated wool fiber, Fig. IB illustrates a coarse fiber with a large medulla. The opacity of the medulla is due to the inability of the mounting media to penetrate to the center of the fiber leaving air pockets. Fig. 1C shows an even thicker fiber with a very large medulla and with very thin skin. This type of wool is called “Kemp”, is shed annually or more often, and corresponds to guard hair in fur-bearing animals.

The German Post-Critical Belief Scale: Internal and External Validity

2003 ◽  
Vol 34 (4) ◽  
pp. 219-226 ◽  
Author(s):  
Bart Duriez ◽  
Claudia Appel ◽  
Dirk Hutsebaut
Keyword(s):  
Internal Structure ◽  
Present Article ◽  
External Validity ◽  
German Version ◽  
Dutch Version ◽  
German Sample ◽  
Belief Scale ◽  
Internal And External Validity

Abstract: Recently, Duriez, Fontaine and Hutsebaut (2000) and Fontaine, Duriez, Luyten and Hutsebaut (2003) constructed the Post-Critical Belief Scale in order to measure the two religiosity dimensions along which Wulff (1991 , 1997 ) summarized the various possible approaches to religion: Exclusion vs. Inclusion of Transcendence and Literal vs. Symbolic. In the present article, the German version of this scale is presented. Results obtained in a heterogeneous German sample (N = 216) suggest that the internal structure of the German version fits the internal structure of the original Dutch version. Moreover, the observed relation between the Literal vs. Symbolic dimension and racism, which was in line with previous studies ( Duriez, in press ), supports the external validity of the German version.

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