Preservation and distribution of detrital clay coats in a modern estuarine heterolithic point bar in the Gironde estuary (Bordeaux, France)

2021 ◽  
Vol 91 (8) ◽  
pp. 812-832
Author(s):  
Maxime Virolle ◽  
Benjamin Brigaud ◽  
Hugues Féniès ◽  
Raphaël Bourillot ◽  
Eric Portier ◽  
...  
Keyword(s):  
Thin Section ◽  
Sedimentation Rate ◽  
Sand Dunes ◽  
Age Dating ◽  
Structure Stability ◽  
Lateral Migration ◽  
Reservoir Properties ◽  
Point Bar ◽  
Sandy Gravel ◽  
Modern Analogue

ABSTRACT Estuaries provide an excellent depositional environment to study the interaction between minerals (clays, quartz sands…) and biofilms. The estuary bottom is largely covered by biofilms that impact sediment stability, the mud and clay-coat content in sands, and sedimentary-structure stability, thus influencing sandstone properties during burial. Although numerous oil, gas, and geothermal reservoirs are exploited in estuarine heterolithic point bars, many questions remain about the origin of reservoir properties and heterogeneities in these sedimentary bodies. In order to better understand the sedimentary and microbiologic processes in estuarine systems and to better predict the reservoir quality of estuarine sandstones, this study characterizes a modern heterolithic point bar located in the Garonne estuarine channel at various scales, ranging from the microscopic (thin section) to the macroscopic (core) scale. Three piston cores 4.5 to 6.8 m long were drilled in the Bordeaux North Point Bar. Three main facies were identified in these cores: 1) sandy gravel, 2) heterolithic, medium-grained sand dunes, and 3) thin heterolithic, fine-grained sand beds with mud drapes. The sands are classified as lithic arkoses to feldspathic litharenites. Detrital clay grain coats, which at deep burial depths are transformed to permeability preserving authigenic chlorite coatings, are observed from the base to the top of the point bar. These detrital clay grain coats are mainly composed of smectite, illite, kaolinite, and chlorite, intermixed with other components, such as diatoms or pyrite. Biofilms of exopolymeric substances (EPSs), mostly produced by diatoms, are believed to control the adhesion of the clay coats to the surface of sand grains. Quantification by thin section shows that on average about 30% of the sands are coated in the point bar. The proportion of clay-coated grains appears to be independent of facies. Radiocarbon age dating measured on organic matter points to significant vertical mixing, highlighting the significance of erosion and redeposition. The activities of 137Cs and 210Pb indicate a vertical sedimentation rate of ca. 0.02 m.yr–1 in the muddy chute channel. These ages, coupled to historical maps, suggest that the present-day point bar has developed over the last 300 years with a vertical sedimentation rate ranging from 0.015 to 0.036 m.y–1 and a lateral migration rate of about 1 m.y–1. The combination of sedimentary geology, thin-section petrography, and mineralogy at high spatial and temporal resolutions highlights the potential of this study area as a modern analogue for ancient tidally influenced point-bar deposits associated with clay coatings.

scholarly journals Autogenic translation and counter point bar deposition in meandering rivers

2021 ◽  
Author(s):  
Z. Sylvester ◽  
P.R. Durkin ◽  
S.M. Hubbard ◽  
D. Mohrig
Keyword(s):  
Satellite Imagery ◽  
Riparian Vegetation ◽  
Kinematic Model ◽  
Time Lapse ◽  
Sediment Deposition ◽  
Lateral Migration ◽  
Meandering Rivers ◽  
Point Bar ◽  
Point Bars ◽  
Meander Bends

Although it has long been recognized that deposition along meandering rivers is not restricted to convex banks (i.e., point bars), the consensus is that sediment deposition on concave banks of channel bends mostly occurs when meander bends translate downstream because erosion-resistant barriers inhibit their lateral migration. Using a kinematic model of channel meandering and time lapse satellite imagery from the Mamoré River in Bolivia, we show that downstream translation and associated concave bank deposition are essential, autogenic parts of the meandering process, and resulting counter point bars are expected to be present whenever perturbations such as bend cutoffs and channel reoccupations create short bends with high curvatures. The implication is that zones of concave bank deposition with lower topography, finer-grained sediment, slack water, and riparian vegetation that differs from point bars are more common than previously considered.

scholarly journals Sedimentation and sediment geochemistry in a tropical mangrove channel meander, Sungai Kerteh, Peninsular Malaysia

2020 ◽  
Author(s):  
Hasrizal Bin Shaari ◽  
Qatrunnada Mohd Nasir ◽  
Che Abd Rahim Mohamed ◽  
Abdul Hafidz Yusoff ◽  
Wan Mohd Afiq Wan Mohd Khalid ◽  
...  
Keyword(s):  
Grain Size ◽  
Sedimentation Rate ◽  
Sediment Cores ◽  
Peninsular Malaysia ◽  
Sediment Supply ◽  
Sediment Geochemistry ◽  
Spatial And Temporal Variability ◽  
Tidal Channels ◽  
Point Bar ◽  
Meander Bends

Abstract Tropical mangrove swamps are commonly characterized by dense networks of tidal channels that may show pronounced meandering and dendritic patterns. Channel meanders are sometimes accompanied by cut offs, and, like classical fluvial meanders, record changes in hydrology and sedimentation over time. Channel meandering can, thus, be an important process that contributes to spatial and temporal variability in the preserved record of the sedimentology and geochemistry of mangrove sediments. The aim of this study is to highlight changes in channel meander sedimentation in response to a meander cut-off in a tropical mangrove swamp. Two short sediment cores were sampled, respectively from a point bar (core KR1, 122 cm) at the junction with the neck cut-off and inside the cut-off (core KR2, 98 cm) in the Sungai Kerteh mangroves of Peninsular Malaysia. The profile comparison was based on sediment characteristics, total organic carbon (TOC) and selected elements (Fe, Na, Mg, Mn, Ba and Sr). Sedimentation rates at both sites were determined from 210Pb. A smaller standard deviation of mean grain size (MGS) was found at the point bar (4.37±0.51 ϕ) than in the cut-off (4.43 ±1.76 ϕ), indicating a difference in flow velocity between the two settings. A small difference in sedimentation rate between the upper (0.41 cm.yr-1) and bottom (0.50 cm.yr-1) parts of core KR1 suggests that water velocity at the point bar area has been rather uniform over the timescale of sedimentation. On the other hand, a higher sedimentation rate in the bottom (0.60 cm.yr-1), compared to the upper (0.39 cm.yr-1) part of core KR2 may reflect a reduction in sediment supply following cut-off. This change also resulted in increased accumulation of selected elements and TOC at the cut-off site from a depth of ~ 60 cm to the core-top segment probably associated with a slowing down of sediment settling. A higher TOC recorded in the cut-off (2.74±1.42%) compared to the point bar (1.14±0.46%) suggests a propensity for prolonged in-situ accumulation of organic matter in the abandoned meander bend. This study provides grain-size and sediment geochemical information that is consistent with patterns of long-term active and inactive sedimentation in the meander bends of mangrove channels.

Thermal regime around the Chile Triple Junction based on JAMSTEC MR18-06 cruise 'EPIC'

2020 ◽  
Author(s):  
Masataka Kinoshita ◽  
Ryo Anma ◽  
Yuka Yokoyama ◽  
Kosuke Ohta ◽  
Yusuke Yokoyama ◽  
...  
Keyword(s):  
Heat Flow ◽  
Sedimentation Rate ◽  
Thermal Regime ◽  
Triple Junction ◽  
Accretionary Prism ◽  
Age Dating ◽  
Spreading Center ◽  
Ridge Axis ◽  
Ridge Subduction ◽  
Chile Triple Junction

<p><span>The Chile triple junction (CTJ) is a unique place where a spreading center of mid-ocean ridge is subducting near the Taitao peninsula. Around CTJ, presence of high heat flow on the continental slope and near-trench young granitic rocks on the Taitao peninsula suggests the thermal and petrological impact of subducting ridge on the continental side. The tectonic history of the southeast Pacific since early Cenozoic to the present suggests that ridge subduction continuously occurred along the Chile trench, which migrated northward.</span></p><p><span>In January 2019, the MR18-06 cruise Leg 2 was conducted at CTJ, as a part of 'EPIC' expedition by using R.V Mirai of JAMSTEC. During the leg, we completed 4 SCS lines, 6 piston coring with heat flow measurements, 2 dredges, and underway geophysics observations, as well as deployment of 13 OBSs. Coring/heatflow sites were located across the ridge axis, HP5 on the seaward plateau of axial graben, HP1/HP2/HP6 on the axis, and HP3/HP7 on the forearc slope near the trench axis. The primary object of heat flow measurement at CTJ is to better constrain the thermal regime around CTJ by adding new data right above CTJ. The key question is whether CTJ is thermally dominated by ridge activity (magmatic, tectonic, and/or hydrothermal) or by subduction initiation (tectonic thickening, accretion, and/or erosion). The ultimate goal is to model the temperature at the plate interface from the heat flow and other data, and to infer how the thermal regime at CTJ contributes the seismogenic behavior at the M~9 megathrust zone. </span></p><p><span>Onboard and post-cruise measurements include; bulk density, porosity, Vp, resistivity, CT imags, iTracks element scan, age dating, etc. Core saples seaward of ridge axis (HP5) has few turbidites with higher density (~2 g/cc) and low sedimentation rate (SR; 0.2 m/ky), whereas cores on the axis the density are turbidite dominant with lower (1.6~1.8 g/cc) and very high SR (1~3 m/ky). The accretionary prism (landward of trench) cores have the density of 1.6~1.7 g/cc and SR=0.5~1 m/ky. They suggest that the turbidite covers only the axial graben. </span></p><p><span>Heat flow in the axial graben range 140-210 mW/m^2, which is lower than on the seaward plateau (370 mW/m^2). This apparent controversy may be due to lower magmatic activity and/or high sedimentation rate on the axis. The lower spreading rate (2.6 cm/yr one side) and the rapid convergent rate at the trench (7.2 cm/yr) may suppress sufficient magma supply or hydrothermal circulation. Heat flow on the accretionary prism (230 mW/m^2) is higher than borehole or BSR-derived heat flow (~<100 mW/m^2). It is suggestive of fluid upwelling along the decollement as proposed in the previous study. Some numerical thermal models will be presented to show the effect of ridge subduction. </span></p>

Aggradation and lateral migration shaping geometry of a tidal point bar: An example from salt marshes of the Northern Venice Lagoon (Italy)

2016 ◽  
Vol 343 ◽  
pp. 141-155 ◽  
Author(s):  
Lara Brivio ◽  
Massimiliano Ghinassi ◽  
Andrea D'Alpaos ◽  
Alvise Finotello ◽  
Alessandro Fontana ◽  
...  
Keyword(s):  
Salt Marshes ◽  
Venice Lagoon ◽  
Lateral Migration ◽  
Point Bar

scholarly journals Uniqueness Deposit of Sediment on Floodplain Resulting From Lateral Accretion on Tropical Area

2017 ◽  
Vol 2 (1) ◽  
pp. 14 ◽  
Author(s):  
Yuniarti Yuskar ◽  
Tiggi Choanji
Keyword(s):  
Low Energy ◽  
Lateral Migration ◽  
Point Bar ◽  
Fine Grained ◽  
Tropical Area ◽  
Almost All ◽  
Fluvial Environments ◽  
Channel Deposits ◽  
Floodplain Sediments ◽  
Mixed Load

Kampar rivers has a length of 413 km with average depth of 7.7 m and width of 143 m. Sixty percent of  this rivers are meandering fluvial system which transport and deposit a mixture of suspended and bed-load (mixed load) along low energy. River channel that moving sideways by erosion is undergoing lateral migration and the top of the point bar becomes the edge of the floodplain and the fining-upward succession of the point bar will be capped by overbank deposits of Kampar River. Along the Kampar Rivers, there are more than 60% of floodplain sediments and almost all of the floodplain formed by bend migration on the suspended-load channels of Kampar watershed. This formation consist of succession of fine to medium sand and silt/mud, with root traces, that form as drapes on the prograding bank. These beds dip mostly channel wards and quickly wedge out as they grade up and onto the floodplain. The depositional model is presented showing how lateral accretion can make a significant contribution to the preservation of fine-grained within channel deposits in contemporary floodplains. The examples presented here demonstrate that analogues to ancient point-bar deposits containing alternating sandstone and shale sequences are common in the low-energy fluvial environments of Riau rivers especially Kampar rivers.

scholarly journals Analisa stabilitas struktur revetmen di Pantai Kedungu, Tabanan Bali

2017 ◽  
Vol 13 (1) ◽  
pp. 11-22
Author(s):  
Vivi Yovita Indriasari ◽  
Johan Risandi ◽  
Rudhi Akhwadhy
Keyword(s):  
Bearing Capacity ◽  
Local Community ◽  
Sand Dunes ◽  
Structure Design ◽  
Structure Stability ◽  
Coastal Protection ◽  
Incoming Wave ◽  
Local Residents ◽  
The Stability ◽  
Proper Condition

Study in Kedungu Beach which has a wide sand dunes and dense vegetation. This place is usually used for tourism by local residents. Causes of erosion is awave come in the form an angle, create longshore current, and litoral drif sediments. The condition is very alarming, because it erodes the amount of land owned by residents. Until now there is no goverment handling yet, only the efforts of the local community by building sea walls and currently also not in a proper condition. Based on the analysis of the data captured in the field and numerical modeling methods, resulting the methode to overcome the erotion problem, i.e. build coastal protection structures such as revetment, where the structure serves as an incoming wave damper and defend the coastline. The purpose of this paper is to provide an overview of the structure stability of revetment against coastal erosion.Stability analysis takes into account the stability of the rolling, sliding, and soil bearing capacity decrease. The dimension and design ofrevetment is secure from overturning (SF = 7.669 > 2); sliding (SF = 4.082>1,5) and bearing capacity support (17.498>3). From this analysis concluded that in the revetment structure design safe and can be applied in the study area. Analysis of the stability of the revetment structure is expected to reduce the level of damage to the building structure coast and surrounding buildings.

Life cycle and age structure of ramets in an expanding population of Salix exigua (sandbar willow)

1992 ◽  
Vol 70 (6) ◽  
pp. 1141-1146 ◽  
Author(s):  
Kimberley A. Ottenbreit ◽  
Richard J. Staniforth
Keyword(s):  
Life Cycle ◽  
Sex Ratio ◽  
Age Structure ◽  
Sand Dunes ◽  
Large Population ◽  
Point Bar ◽  
Salix Exigua ◽  
Expanding Population ◽  
Stem Mortality ◽  
Linear Correlations

The sandbar willow (Salix exigua Nuttall, ssp. interior (Rowlee) Cronquist) is a dominant woody pioneer and stabilizer of riverbanks and sand dunes over much of North America. The growth rates, life-history phases, sex ratio, longevity, and age structure of a large population growing on a point bar in the Assiniboine River, Manitoba were assessed. Average annual height increments were 29.7 cm, and average annual girth increments were 2.6 mm/year. There were no significant differences between sexes. Significant linear correlations existed between basal stem diameter and age and between stem height and age. Flowering occurred in a few 2- and 3-year-old stems, regardless of sex. Flowering frequency increased to 93% at the age of 9 years. Stem mortality was highest in 3-, 4-, and 6-year-old ramets, and senescence was first observed at about 12 years. Though few stems at this site were older than 12 years, the oldest stem encountered was 31 years old and had sprouted soon after the point bar had started to form. The sex ratio of 1.7:1.0 significantly favoured males. Key words: willow, Salix, population dynamics, age structure, life cycle, sex ratio, clonal, ramets.

scholarly journals Sedimentation and sediment geochemistry in a tropical mangrove channel meander, Sungai Kerteh, Peninsular Malaysia

2020 ◽  
Author(s):  
Hasrizal Bin Shaari ◽  
Qatrunnada Mohd Nasir ◽  
Che Abd Rahim Mohamed ◽  
Abdul Hafidz Yusoff ◽  
Wan Mohd Afiq Wan Mohd Khalid ◽  
...  
Keyword(s):  
Grain Size ◽  
Sedimentation Rate ◽  
Sediment Cores ◽  
Peninsular Malaysia ◽  
Sediment Supply ◽  
Sediment Geochemistry ◽  
Spatial And Temporal Variability ◽  
Tidal Channels ◽  
Point Bar ◽  
Meander Bends

Abstract Tropical mangrove swamps are commonly characterized by dense networks of tidal channels that may show pronounced meandering and dendritic patterns. Channel meanders are sometimes accompanied by cut offs, and, like classical fluvial meanders, record changes in hydrology and sedimentation over time. Channel meandering can, thus, be an important process that contributes to spatial and temporal variability in the preserved record of the sedimentology and geochemistry of mangrove sediments. The aim of this study is to highlight changes in channel meander sedimentation in response to a meander cut-off in a tropical mangrove swamp. Two short sediment cores were sampled, respectively from a point bar (core KR1, 122 cm) at the junction with the neck cut-off and inside the cut-off (core KR2, 98 cm) in the Sungai Kerteh mangroves of Peninsular Malaysia. The profile comparison was based on sediment characteristics, total organic carbon (TOC) and selected elements (Fe, Na, Mg, Mn, Ba and Sr). Sedimentation rates at both sites were determined from 210 Pb. A smaller standard deviation of mean grain size (MGS) was found at the point bar (4.37±0.51 ϕ) than in the cut-off (4.43 ±1.76 ϕ), indicating a difference in flow velocity between the two settings. A small difference in sedimentation rate between the upper (0.41 cm.yr -1 ) and bottom (0.50 cm.yr -1 ) parts of core KR1 suggests that water velocity at the point bar area has been rather uniform over the timescale of sedimentation. On the other hand, a higher sedimentation rate in the bottom (0.60 cm.yr -1 ), compared to the upper (0.39 cm.yr -1 ) part of core KR2 may reflect a reduction in sediment supply following cut-off. This change also resulted in increased accumulation of selected elements and TOC at the cut-off site from a depth of ~ 60 cm to the core-top segment probably associated with a slowing down of sediment settling. A higher TOC recorded in the cut-off (2.74±1.42%) compared to the point bar (1.14±0.46%) suggests a propensity for prolonged in-situ accumulation of organic matter in the abandoned meander bend. This study provides grain-size and sediment geochemical information that is consistent with patterns of long-term active and inactive sedimentation in the meander bends of mangrove channels.

The Infection of Cells by Bullet-Shaped Viruses

1969 ◽  
Vol 27 ◽  
pp. 372-373
Author(s):  
Frederick A. Murphy ◽  
Alyne K. Harrison ◽  
Sylvia G. Whitfield
Keyword(s):  
Electron Microscopy ◽  
Physical Properties ◽  
Host Cell ◽  
Thin Section ◽  
Cultured Cells ◽  
Cell Infection ◽  
Thin Section Electron Microscopy ◽  
Section Electron ◽  
Section Electron Microscopy

The bullet-shaped viruses are currently classified together on the basis of similarities in virion morphology and physical properties. Biologically and ecologically the member viruses are extremely diverse. In searching for further bases for making comparisons of these agents, the nature of host cell infection, both in vivo and in cultured cells, has been explored by thin-section electron microscopy.

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