Yr Of Sediment Research Articles

Microfossil evidence for salinity events in the Holocene Coorong Lagoon, South Australia

Nearly 6 m of uncompacted muddy sediment was recovered from the floor of the northern Coorong Lagoon in the core Coorong #5. Radiocarbon analyses of molluscan shells indicate that sedimentation at the core site commenced before 6830 ± 90 yr cal BP, and the presence of Pinus pollen confirms a modern age for the uppermost 0.5 m. Microfossils extracted from the core sediment samples, 2 cm slices at 10 cm intervals, included the foraminifera Ammonia sp., Elphidium excavatum and Elphidium gunteri; the ostracods Osticythere baragwanathi and Leptocythere lacustris; and charophyte oogonia. Shell fragments of the estuarine bivalve Spisula (Notospisula) trigonella in the lowermost 0.7 m of the core are evidence that these sediments were subject to some marine influence, but the absence of foraminifera and ostracods from this same interval indicates that at the core site salinity was not sufficient to support populations of these organisms. Thus, prior to 6830 ± 90 yr cal BP the Younghusband Peninsula was in place, in part isolating the northern lagoon from the Southern Ocean. The initial recorded salinity event is signified by abundant Ammonia sp. at a core depth of 5.2 m. The duration of this event was relatively brief; foraminifera were mostly absent in the immediately overlying 2 m, representing ca 700 yr of sedimentation. This observation is attributed to substantial inflow of freshwater from the River Murray. In the upper 3.0 m, Ammonia sp. was present in most core samples indicating that for most of the past 6000 years the Coorong Lagoon has been sufficiently saline to support a continuing population of this species. At a core depth of 1.3 m, the sediment sample yielded >2000 tests of Ammonia sp., and they were accompanied by maximum pre-modern numbers of E. excavatum, O. baragwanathi and oogonia. Taken together, these data signify the maximum pre-modern salinity event recorded in the core sediments, probably correlating in time with regional drought conditions at ca 3500 yr BP. Elphidium gunteri is confined to the modern sediments where it is abundant and accompanied by equally large numbers of Ammonia sp., E. excavatum, O. baragwanathi and L. lacustris. These data collectively indicate water conditions that are significantly changed from those that prevailed in the Coorong Lagoon for most of the Holocene.

Isotopes Trace Biogeochemistry and Sources of Cu and Zn in an intertidal soil

River floodplain soils are sinks and potential sources for toxic trace metals like Cu and Zn. We hypothesize that stable Cu and Zn isotope ratios reflect both the mobilization and the sources of metals. We determined the soil properties, the concentrations and partitioning of Cu and Zn, and variations in δ65Cu and δ66Zn values in a core obtained from an Aquic Udifluvent developed on a freshwater intertidal mudflat of the River Elbe, Germany. The core was sampled at 2 cm intervals to a depth of 34 cm, which corresponds to approximately 9 yr of sedimentation. Elevated concentrations of Cu (up to 320 μg g−1) and Zn (up to 2080 μg g−1) indicated anthropogenic pollution. At the time of sampling the redox conditions changed from oxic (Eh 200 to 400 mV, above 22 cm deep) to strongly anoxic conditions (-100 to -200 mV, below 22 cm deep). The δ65Cu values varied systematically with depth (from -0.02 to 0.16‰) and were correlated with the Fe, C, and N concentrations. Although pre-depositional variations cannot be ruled out, the systematic variation with depth suggests post-sedimentation fractionation of δ65Cu in response to seasonally variable organic matter deposition and redox conditions. In contrast, the δ66ZnIRMM values were uniform (from -0.07 to 0.01‰) throughout the core, indicating that the Zn isotopes did not significantly fractionate after deposition and that the Zn sources were homogeneous throughout the sedimentation.

Chemistry and mineralogy of ochreous sediments in a constructed mine drainage wetland

The objective of this study was to examine the mineralogy and geochemical stability of ochreous sediments accumulated in a compost wetland constructed in 1990 for acid mine drainage treatment. Intact sediment cores were collected in 1996 and 2000 from an area that had accumulated 33 cm of ochre. Solids and pore waters were subsequently separated by centrifugation and analyzed using conventional methods, including X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and wet chemical techniques. The solid phase had an average Fe content of 585 g/kg and was predominantly schwertmannite [Fe 8O 8(OH) 4.8(SO 4) 1.6] in the upper portion of the sediment column, but transformed to goethite (α-FeOOH) with depth. The rate of transformation was calculated to be 30 mol/m 3/yr in the initial 6 yr of sedimentation as compared to 10 mol/m 3/yr for the 4-yr period from 1996 to 2000. Pore water composition was affected by this mineral transformation through production of acidity and the release of Fe and SO 4. These results demonstrate that the sediment column was not a static environment. In addition, the transformation of schwertmannite to goethite, which has been observed under laboratory conditions, also occurs in natural systems.

Accumulation in East Greenland Fjords and on the Continental Shelves Adjacent to the Denmark Strait over the Last Century Based on 210Pb Geochronology

Sediment (SAR) and mass (MAR) accumulation rates for the last 100 years are derived from 210Pb profiles of box cores collected in three fjords and on the continental shelf in the Kangerlussuaq region, East Greenland, and on the SW Iceland continental shelf. The MAR is lower on East Greenland (0.09 g/cm²·yr) than on SW Iceland (0.14 g/cm²·yr) because of differences in the biogenic component of the sediments, although SAR is similar. The differences in accumulation rates of the three East Greenland fjords are due to their dominant sediment sources and basin areas. Kangerlussuaq Fjord, the largest fjord, is dominated by iceberg sediment input and has a MAR of 0.43 g/cm²·yr at 50 km from the fjord head. Miki Fjord, the smallest fjord, is dominated by glaciofluvial sediment input with a MAR of 0.29 g/cm²·yr of sediment at 10 km from the fjord head. Nansen Fjord is intermediate in size, with an iceberg-dominated sediment supply; MAR is 1.01 g/cm²·yr near the fjord head and 0.17 g/cm²·yr at 20 km from the fjord head. 137Cs is used as a secondary indicator of sediment source, and the high activity level of 137Cs in Miki Fjord indicates glaciofluvial sediment sources. Zones of constant activity in some of the box cores are attributed to either bioturbation in the surface mixed layer or turbidites. We would be hesitant to extend the recent 210Pb-based accumulation rates to estimate the Holocene accumulation rates.

Importance of flood-plain sedimentation for river sediment budgets and terrigenous input to the oceans: Insights from the Brahmaputra-Jamuna River

Research Article| February 01, 1998 Importance of flood-plain sedimentation for river sediment budgets and terrigenous input to the oceans: Insights from the Brahmaputra-Jamuna River M. A. Allison; M. A. Allison 1Department of Oceanography, Texas A&M University, 5007 Avenue U., Galveston, Texas 77551 Search for other works by this author on: GSW Google Scholar S. A. Kuehl; S. A. Kuehl 1Department of Oceanography, Texas A&M University, 5007 Avenue U., Galveston, Texas 77551 Search for other works by this author on: GSW Google Scholar T. C. Martin; T. C. Martin 2Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062 Search for other works by this author on: GSW Google Scholar A. Hassan A. Hassan 3Environment and Geographic Information Support Project for Water Sector Planning (EGIS), House 49, Road 27, Dhaka, Bangladesh Search for other works by this author on: GSW Google Scholar Geology (1998) 26 (2): 175–178. https://doi.org/10.1130/0091-7613(1998)026<0175:IOFPSF>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 MailTo Tools Icon Tools Get Permissions Search Site Citation M. A. Allison, S. A. Kuehl, T. C. Martin, A. Hassan; Importance of flood-plain sedimentation for river sediment budgets and terrigenous input to the oceans: Insights from the Brahmaputra-Jamuna River. Geology 1998;; 26 (2): 175–178. doi: https://doi.org/10.1130/0091-7613(1998)026<0175:IOFPSF>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 Recent authors have suggested that a significant proportion of the worldwide terrigenous sediment budget is trapped landward of the river-ocean boundary in high-load, tectonically active basins. To test this idea, modern flood-plain sediment accumulation rates were determined along a 110 km reach of the Brahmaputra (locally Jamuna) River using 137Cs geochronology of sediment cores and geographic information system (GIS) extrapolation to adjacent areas. 137Cs accumulation rates decrease exponentially away from the channel, from >4 cm/yr on the natural levees to <1 cm/yr within a few tens of kilometers basinward. Important controls on sedimentation in this area include proximity to distributary channels, local topography, and interannual variability of the flood pulse. Model results indicate that an average of 23 m.t./yr of sediment are sequestered in this section of the flood plain. Extrapolated basinwide, as much as 39%–71% of the river sediment budget may be trapped landward of the Ganges-Brahmaputra mouth. 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.

MODELING OF THE LONGITUDINAL RIVER PROFILE AND A NUMERICAL SIMULATION OF TERRACE DEVELOPMENT OF THE TAMA RIVER

The purpose of this paper is to test theoretically one of mathematical models for longitudinal river profiles and to evaluate it by a numerical simulation of terrace development of the Tama River. Significance of mathematical model describing the change of height with time in landform profiles developed by Hirano (1976), Ut=aUxx+bUx was tested with the view of clarifying flow rate of sediment, J=(aUx+bU) where Uxx is curvature, Ux gradient and U height of river bed. The first term of the equation expresses deposition and the second does erosion in the concave river profile. This second order differential equation is the same one that describes the diffusion process having drift. The analogy of river profile development to diffusion process is basically justified either by the existence of Brownian motion of particles in the river system or by a presumption apriori that the flow rate of sediment is proportional to the gradient of river bed. But it is difficult to identify what is the drift under constraint in the river system, because the flow by the forced drift is opposite in direction of the gradient of river bed and the diffusion flow. Although this model has these weak points in physical basis, it has a big advantage that its steady solution; U=Clexp(-rx)+C2 (r=b/a) shows an exponential curve which is accepted empirically to be the most suitable one for the longitudinal river profile. This dynamic model was applied to simulate the terrace development of the Tama River. The Tama River is originated from Kanto Mountains, enters the depositional hanto Plain and ends at Tokyo Bay. Its ca. 1000km2 drainage basin is roughly estimated to discharge ca. 1.5×10-4km3/yr of sediment. And well developed terraces has been studied so in detail that the area has been a type area of Japanese late Pleistocene and Holocene. The values of coefficient a and b in the equation are estimated from the flow rate of sediment of present River in grade. A shape index r=b/a determines the shape of graded profile, and the flow rate gives a rate of asymptotic convergence to the graded form. The profile (Juen, 1965b) of the Musashino Terrace (60×103 yr PP) was given as an initial value of simulation. The gradient at the upper boundary was given as a function of time. Another boundary condition was given by the sea level as a function of time. But it is assumed that the river mouth (the lower boundary) has been so conservative there in gradient that the position of the river mouth was floating horizontally in response both to the change of sea level and the profile itself (as a free boundary problem). The results of simulation well represent the actual development of river profile, which is stated by the early Wi rm fill-strathing in the upper-most reach of the River, the latest Pleistocene over-flowing on the older surfaces in the upper-middle reach, the forming of valley-topography in the lower reach due to the maximum sea level lowering and of drowned valley-topography due to the postglacial sea level rising, and then river mouth advancing toward sea caused by fluvial accretion during the last seven thousand years.