scholarly journals Etude de l'impact des barrages sur la réduction des transports sédimentaires jusqu'à la mer par approche paléohydrologique dans la basse vallée de la Medjerda

2018 ◽  
Vol 377 ◽  
pp. 67-76 ◽  
Author(s):  
Fatma Kotti ◽  
Laurent Dezileau ◽  
Gil Mahé ◽  
Hamadi Habaieb ◽  
Malik Bentkaya ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Global Climate ◽  
Sediment Cores ◽  
Sediment Supply ◽  
Water Storage Capacity ◽  
Sedimentary Deposits ◽  
The Core ◽  
River Bed ◽  
History Of ◽  
Marine Influence

Abstract. The sedimentary contributions of the Medjerda to the coastal zone are poorly measured, and there is no chronicle of observations. In this context, the sediment monitoring appears indispensable for the quantification of sediment transport at the outlet. This study focuses on the largest watershed in Tunisia, the Wadi Medjerda (23 600 km2). The main objective of this work is to assess the reduction of sediment transport following anthropogenic intensification on the basin, especially since the construction of many large dams. In order to collect information on actual deposits over several years, the paleo-hydrological approach was applied through the study of sediment cores sampled in the low valley meanders on alluvial terraces, after the last dam (Sidi Salem, the largest water storage capacity over the basin), but before the estuary to avoid marine influence and near a hydrological station (Jdaida). The sedimentary deposits of the river provide key information on the past sedimentary inputs. A visible succession of sedimentary layers corresponding to the deposits of successive floods on the study site has been determined and the history of the sedimentary contributions of the Medjerda is reconstructed by this approach. The thickest layers of sedimentary deposits are related to exceptional events. They are mainly concentrated on the lower part of the core and are mainly composed of sands. The first 1.2 m of the core from the bottom upward relates to 10 years of river discharges, as can be determined from the 137Cs datation. The next upward 1.05 m of core relates to the following 20 years of discharges, up to 1981, date of the construction of the Sidi Salem dam, and is composed of a mix of sand, silts and clays. The last 75 cm of core near the surface is only composed of clays with thin silt bands, and relates to a period of 32 years. We thus observe that there is no more sand deposits in the river bed since the construction of the Sidi Salem dam. The deficit of sediment supply to the sea is viewed as a major factor to be taken into account for better understanding of the dynamics of coastal areas in the context of global climate change.

Late Quaternary sedimentation on the southwestern Scotian Slope, eastern Canada: relationship to glaciationGeological Survey of Canada Contribution 20070176.

2008 ◽  
Vol 45 (3) ◽  
pp. 267-285 ◽  
Author(s):  
Thian Hundert ◽  
David J.W. Piper
Keyword(s):  
Late Quaternary ◽  
Sediment Cores ◽  
Sediment Supply ◽  
Scotian Shelf ◽  
Eastern Canada ◽  
Glacial Retreat ◽  
Air Gun ◽  
Continental Slopes ◽  
History Of ◽  
Seismic Reflection Profiles

The sedimentary record on continental slopes has the potential to preserve a record of glacial retreat on the adjacent continental shelf. The glacial history of the southwestern part of the Scotian Shelf is poorly known. Air-gun and high-resolution sparker profiles and numerous sediment cores up to 10 m long have been used to determine the character of sedimentation on the southwestern Scotian Slope since the last glacial maximum (LGM). Seismic-reflection profiles show that glacial till was deposited at shallow depths on the upper continental slope, and correlation to dated piston cores farther downslope show that this till dates from the LGM. Slope sedimentation at this time was dominated by local ice and deposited as plume fallout and turbidites. Progressively increasing importance of red-brown sediment derived from glacial supply to Laurentian Channel indicates retreat of ice from the shelf edge and diminishing supply of proglacial sediment from the calving embayment in the mid-Scotian Shelf. With the termination of distal proglacial sediment supply, the sedimentation rate diminished rapidly and hemipelagic sedimentation prevailed through the Holocene.

scholarly journals Three novel species of Bacillariophyta (Diatoms) belonging to Aulacoseira and Lindavia from the Pliocene Hadar Formation, Afar Depression of Ethiopia

Phytotaxa ◽  
2016 ◽  
Vol 272 (4) ◽  
pp. 235
Author(s):  
JOSEPH MOHAN ◽  
JEFFERY R. STONE ◽  
CHRISTOPHER J CAMPISANO
Keyword(s):  
Evolutionary History ◽  
Novel Species ◽  
Sediment Cores ◽  
Core Material ◽  
Afar Depression ◽  
Sedimentary Deposits ◽  
Extant Species ◽  
History Of ◽  
Drilling Project ◽  
Hadar Formation

Paleolake Hadar was an expansive lake in the lower Awash Valley of Ethiopia’s Afar Depression that existed periodically through the Late Pliocene. The sedimentary deposits from this ancient lake (Hadar Formation) have broad importance because a significant number of hominin fossils have been recovered from the formation. Samples of the Hadar Formation lacustrine sequence were collected from sediment cores extracted as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP). A paleoecological study of the HSPDP Northern Awash (Hadar Formation) material has unearthed three novel species of Bacillariophyta (diatoms) from diatomites that appear periodically in the cores. The Hadar Formation assemblage represents a newly revealed excerpt from the evolutionary history of freshwater diatoms in East Africa during the Piacenᴢian age (2.59–3.60 Ma). The HSPDP Northern Awash diatom species are compared to previously reported diatoms from Pliocene outcrops, modern and fossil core material from Lake Malawi, and extant species. Here we describe two new species of Aulacoseira and one of Lindavia. Taxonomic treatment of two diatom varieties reported by previous researchers as Melosira are transferred into Aulacoseira herein.

scholarly journals Glacial-Marine Sedimentation, Canadian Polar Margin, North of Axel Heiberg Island

2007 ◽  
Vol 45 (2) ◽  
pp. 213-227 ◽  
Author(s):  
Frances J. Hein ◽  
Peta J. Mudie
Keyword(s):  
Sediment Cores ◽  
Open Water ◽  
Silty Clay ◽  
Sedimentation Rates ◽  
The Core ◽  
Marine Sedimentation ◽  
Northwestern Shelf ◽  
History Of ◽  
Axel Heiberg Island ◽  
High Sediment

ABSTRACT Sediment cores, taken at depths of 140 to 300 m across the northwestern shelf of Axel Heiberg Island (82° N), record the deposition of sediments under perennial sea ice. Five sedimentary fades are recognized: (A) soft pebbly-sandy-mud with dropstone structures; (B) bioturbated silty muds; (C) wispy-laminated silty clay/clay; (D) laminated sands/silts and mud; (E) firm pebbly-sandy-mud with chaotic pebble fabrics. Other sediments include terrestrial bedrock of Paleogene Eureka Sound Group, and a younger Tertiary deposit, possibly the Beaufort Formation. Ages range from 1530 ± 60 BP (Fades A) to 9950 ± 80 BP (Fades D). Sedimentation rates vary as follows: - 0.8 cm ka-1, Fades B; 4 cm ka"\ Fades A; 90 cm ka-1, Fades C; 134 cm ka~', Fades D. The sedimentation history, as interpreted from the sedimentology, palynology and foraminiferal results, suggests intervals of more continuous ice cover, with a reduced influx of coarse ice-rafted detritus, alternating with more open water conditions, and high sediment input from meltwater and/or floating icebergs. Only marine sediments overlie Neogene bedrock in the cores. The absence of diamictons at the core sites suggests that grounded ice perhaps never occupied this part of the Axel Heiberg Island shelf. The interpreted history of sedimentation generally corresponds to the land-based record from Ellesmere Island, but differs significantly from marine-based studies in more southern latitudes.

scholarly journals Morphological development of river widenings with variable sediment supply

2018 ◽  
Vol 40 ◽  
pp. 02007 ◽  
Author(s):  
Cristina Rachelly ◽  
Volker Weitbrecht ◽  
David F. Vetsch ◽  
Robert M. Boes
Keyword(s):  
Sediment Transport ◽  
Adverse Effects ◽  
Habitat Heterogeneity ◽  
Field Studies ◽  
Sediment Supply ◽  
Morphological Development ◽  
Regime Theory ◽  
Channel Response ◽  
River Bed ◽  
Experimental Flume

River widening is a common restoration approach to mitigate the adverse effects of past stream alterations on infrastructure and the riparian ecosystem by stabilizing the river bed and enhancing habitat heterogeneity. In this study, two river widening approaches, excavated and dynamic, are described for the case of moderately steep gravel-bed rivers in the Alpine foothills, with a focus on dynamic river widening. As most channelized rivers exhibit ongoing degradation due to the lack of sediment supply and efforts to restore sediment transport are increasing, the consideration of the response of river widenings to variable sediment supply is important. For this purpose, insights from regime theory are applied to river widening and several experimental flume and field studies on channel response to variable sediment supply are reviewed. Dynamic river widenings are expected to be morphologically active in weakly degraded rivers with sufficient sediment supply, while they may not be an appropriate restoration approach for highly degraded rivers due to persistent impairment of morphological activity.

Organic carbon isotope ratios and paleoenvironmental implications for Holocene sediments in Lake Melville, southeastern Labrador

1987 ◽  
Vol 24 (10) ◽  
pp. 1994-2003 ◽  
Author(s):  
F. C. Tan ◽  
G. Vilks
Keyword(s):  
Organic Carbon ◽  
Carbon Isotope ◽  
Sediment Cores ◽  
Isotope Ratios ◽  
Carbon Isotope Ratios ◽  
Organic Carbon Isotope ◽  
Glacial Runoff ◽  
Bottom Waters ◽  
History Of ◽  
Marine Influence

Stable isotope 13C/12C ratios of organic carbon in sediments and in particulate organic carbon (POC) change from typically marine values in Groswater Bay to those of terrestrial soils in Goose Bay along an offshore–onshore transect in Hamilton Inlet, southeastern Labrator. The δ13C values in POC collected from close to the water surface change relatively little in Lake Melville, indicating that the integrity of the runoff plume is maintained as it spreads in Lake Melville. The organic carbon isotope ratios in POC collected from the near-bottom waters are similar to those of surficial sediments.Downcore δ13C values reflect paleo-oceanographic changes in Hamilton Inlet during and since deglaciation. In two sediment cores that reached sufficiently old sediments (10 000 years BP), the δ13C values change toward the bottom of the cores to values similar to those of the terrestrial organic carbon in soils, signifying greater terrestrial influence during deglaciation and during the early Holocene.According to the history of postglacial isostatic readjustment of the area, Lake Melville basin was more open to the marine waters during the early postglacial marine incursion because of deeper channels leading into Lake Melville. As a consequence, evidence for greater marine influence during that time should be found in sediment cores. The lack of evidence for the deposition of marine organic carbon brought in by the marine counterflow waters suggests a proximal glaciomarine environment in the Lake Melville basin. Glacial runoff diluted the basin waters, and it is possible that the whole inner Labrador Shelf was relatively fresh during that time.

scholarly journals Preliminary Report on Unique Laminated Holocene Sediments from the Qarun Lake in Egypt

2016 ◽  
Vol 33 (1) ◽  
pp. 35-46 ◽  
Author(s):  
Leszek Marks ◽  
Alaa Salem ◽  
Fabian Welc ◽  
Jerzy Nitychoruk ◽  
Zhongyuan Chen ◽  
...  
Keyword(s):  
Environmental History ◽  
Sediment Cores ◽  
Coarse Grained ◽  
Archaeological Sites ◽  
Varved Sediments ◽  
The Core ◽  
Basal Section ◽  
History Of ◽  
Southwestern Margin ◽  
The One

Abstract The Lake Qarun (Faiyum Oasis, northern Egypt) is a relic of the much larger Holocene lake. Past lake levels and extensions were reconstructed, based on setting of archaeological sites scattered along northern paleoshores of the ancient lake. However, geoarcheological works did not yield enough data to establish continuous environmental history of the lake. A deep drilling FA-1 on the southeastern shore of the lake, performed in 2014, supplied with a core, 26 m long that is the one of the longest lake sediment cores in northeastern Africa. The basal section of the core consisted of thin-laminated diatom marly deposits, underlain at the Late Pleistocene/Holocene boundary by coarse-grained sands. The sediment lamine were quite well developed, especially in the lower part of the core. Preliminary results indicated annually deposited sediment sequence with seasonality signals provided by microlamine of diatoms, calcite, organic matter and clastic material. Early Holocene varved sediments from the Faiyum Oasis supplied with exceptional paleoenvironmental data for northeastern Africa, which enriched a record from previous logs drilled at the southwestern margin of the Qarun Lake.

THE CORE AND PERIPHERY OF THE CURRENT CULTURE OF ARTISTIC CREATION ABOUT THE GREAT PATRIOTIC WAR IN THE STUDENTS’ VIEWS

2020 ◽  
Vol 6 (3) ◽  
pp. 130-149
Author(s):  
Elena N. NARKHOVA ◽  
Dmitry Yu. NARKHOV
Keyword(s):  
Historical Memory ◽  
Soviet Period ◽  
Russian Society ◽  
Student Culture ◽  
The Core ◽  
Musical Works ◽  
Great Patriotic War ◽  
History Of ◽  
Current Student ◽  
Historical Periods

This article analyzes the degree of demand for works of art (films and television films and series, literary and musical works, works of monumental art) associated with the history of the Great Patriotic War among contemporary students. This research is based on the combination of two theories, which study the dynamics and statics of culture in the society — the theory of the nucleus and periphery by Yu. M. Lotman and the theory of actual culture by L. N. Kogan. The four waves of research (2005, 2010, 2015, 2020) by the Russian Society of Socio¬logists (ROS) have revealed a series of works in various genres on this topic in the core structure and on the periphery of the current student culture; this has also allowed tracing the dynamics of demand and the “movement” of these works in the sociocultural space. The authors introduce the concept of the archetype of the echo of war. The high student recognition of works of all historical periods (from wartime to the present day) is shown. A significant complex of works has been identified, forming two contours of the periphery. Attention is drawn to the artistic work of contemporary students as a way to preserve the historical memory of the Great Patriotic War. This article explains the necessity of preserving the layer of national culture in order to reproduce the national identity in the conditions of informational and ideological pluralism of the post-Soviet period. The authors note the differentiation of youth due to the conditions and specifics of socialization in the polysemantic sociocultural space.

Indexicality of Grammar: The Case of Japanese Transgender Speakers

2019 ◽  
Author(s):  
Hideko Abe
Keyword(s):  
Gender Identity ◽  
Gender Identity Disorder ◽  
Grammatical Gender ◽  
Core Structure ◽  
Subject Positions ◽  
Transgender Identity ◽  
The Core ◽  
History Of ◽  
History Of Scholarship ◽  
Grammatical Structures

This article discusses how the intersection of grammatical gender and social gender, entwined in the core structure of language, can be analyzed to understand the dynamic status of selfhood. After reviewing a history of scholarship that demonstrates this claim, the discussion analyzes the language practices of transgender individuals in Japan, where transgender identity is currently understood in terms of sei-dōitsusei-shōgai (gender identity disorder). Based on fieldwork conducted between 2011 and 2017, the analysis reveals how individuals identifying with sei-dōitsusei-shōgai negotiate subject positions by manipulating the specific indexical meanings attached to grammatical structures.

Antarctic Climate History and Global Climate Changes

2017 ◽  
Author(s):  
Pontus Lurcock ◽  
Fabio Florindo
Keyword(s):  
Ocean Circulation ◽  
Climate Changes ◽  
Numerical Models ◽  
Global Climate ◽  
Sediment Cores ◽  
Ice Sheets ◽  
Global Ocean ◽  
Climate History ◽  
Global Climate Changes ◽  
Planetary Albedo

Antarctic climate changes have been reconstructed from ice and sediment cores and numerical models (which also predict future changes). Major ice sheets first appeared 34 million years ago (Ma) and fluctuated throughout the Oligocene, with an overall cooling trend. Ice volume more than doubled at the Oligocene-Miocene boundary. Fluctuating Miocene temperatures peaked at 17–14 Ma, followed by dramatic cooling. Cooling continued through the Pliocene and Pleistocene, with another major glacial expansion at 3–2 Ma. Several interacting drivers control Antarctic climate. On timescales of 10,000–100,000 years, insolation varies with orbital cycles, causing periodic climate variations. Opening of Southern Ocean gateways produced a circumpolar current that thermally isolated Antarctica. Declining atmospheric CO2 triggered Cenozoic glaciation. Antarctic glaciations affect global climate by lowering sea level, intensifying atmospheric circulation, and increasing planetary albedo. Ice sheets interact with ocean water, forming water masses that play a key role in global ocean circulation.

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