Changes In Depositional Conditions Research Articles

On the nature of the calcareous substrate of a ferromanganese crust from the Vityaz Fracture Zone, Central Indian Ridge: inferences on paleoceanography

A 15-cm-thick carbonate substrate encrusted with ferromanganese oxides from the Vityaz Fracture Zone, Central Indian Ridge was analyzed to reconstruct the paleoceanography of the region. Based on the calcareous nannoplankton assemblage, an early Pliocene age has been assigned to the calcareous substrate. Among the nannoplankton, discoasters outnumber coccoliths and show signs of dissolution. The presence of certain species of benthic Foraminifera such as Uvigerina, Lenticulina, Bulimina and Bolivina, indicates the infringement of the oxygen minimum zone during the deposition of the carbonates. The occurrence of a Reticulofenestra pseudoumbilica zone of early Pliocene age suggests a change in depositional conditions coinciding with the time of formation of the large depositional hiatuses documented in sediment cores from adjacent basins of the western Indian Ocean. These hiatuses resulted from the prevalence of intermediate subsurface currents such as the Somali Current or the Western Boundary Current.

Effects of sea level rise on growth of Spartina anglica and oxygen dynamics in rhizosphere and salt marsh sediments

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 225:197-204 (2002) - doi:10.3354/meps225197 Effects of sea level rise on growth of Spartina anglica and oxygen dynamics in rhizosphere and salt marsh sediments Marianne Holmer*, Britta Gribsholt, Erik Kristensen Institute of Biology, SDU-Odense University, Campusvej 55, 5230 Odense M, Denmark *E-mail: holmer@biology.sdu.dk ABSTRACT: The effect of sea level rise on the growth of Spartina anglica seedlings and on key sediment biogeochemical variables (oxygen concentrations and sulfur cycling) was studied for 4 mo in a laboratory experiment. S. anglica, grown under drained and waterlogged conditions, showed no significant differences in leaf elongation and above-ground biomass between treatments. Sulfate reduction rates were not significantly different between treatments (4.1 and 5.3 mmol m-2 d-1, respectively), and although pools of reduced sulfides were high (12.1 to 14.9 mol S m-2), no dissolved sulfides were detected in the sediments. Measurements of oxygen concentrations in rhizosphere sediment done with microelectrodes revealed a distinct oxic microzone of up to 2.5 mm around the roots of S. anglica. The oxic microzone comprised 30 to 60% of the S. anglica rhizosphere sediment, suggesting that the root-mediated oxygen supply to the rhizosphere has profound effects on the microbial processes in the sediments. The sulfate reduction was probably hampered due to the root-mediated loss of oxygen from the plants. There was no difference in oxygen dynamics in the rhizosphere between treatments, indicating that S. anglica is efficient in oxidizing the sediments also under waterlogged conditions. The root-mediated loss of oxygen from S. anglica counteracts the expected changes in sediment conditions as a consequence of sea level rise, e.g. accumulation of phytotoxic compounds such as sulfides. The results suggest that possible negative impacts of sea level rise are more likely to be found for plants with less developed root systems. KEY WORDS: Spartina anglica · Salt marsh sediment · Sulfur cycling · Oxygen dynamics · Plant-sediment interactions Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 225. Online publication date: January 11, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

A new method for visualizing sediment particle size distributions

Conventional uses of sediment grain size data as a proxy for paleoenvironmental processes are usually restricted to simple statistical descriptions of the particle size distribution (PSD) (e.g., mean, median and mode). These descriptions provide a generalized indication of down-core changes in depositional conditions and processes, but are not sensitive to non-normal or polymodal distributions. In contrast, surface plots of grain size data allow qualitative interpretation of the characteristics of the entire PSD and thus can provide important insights into depositional processes and changing environmental conditions. This method is especially useful for distinguishing multiple sedimentary processes, which can appear as additional modes within the PSD. In general, this approach can be used on sediments from most depositional environments and at any spatial or temporal resolution. In combination with conventional summary statistics, PSD surface plots increase the potential utility of grain size as a paleoenvironmental proxy for identifying changes in clastic and organic depositional processes in lake sequences.

Role of deposition parameters on thephotovoltaic quality of amorphous silicon germanium alloys:correlation of microstructure with defect density and electronictransport

Commonly, the germane fraction (f = flowrateofGeH4/flowrateofSiH4 + GeH4) is changed to vary the opticalgap (Eopt) of amorphous silicon germanium alloy (a-SiGe:H) films. Wereport that for a particular f, the change of deposition conditions, theflow rate of diluent gas (H2) and the radiofrequency (rf) power density canvary the optical gap (1.67-1.40 eV), the germanium content (41.3-22.5 at%)and the microstructural defect density (0.92-0.42), the mobilitylifetime product (ηµτ; 6.81×10-6-1.46×10-8cm2 V-1) in a wide range. Initially, with the increase of theH2 flow rate up to 20 SCCM for the rf power density of 60 mW cm-2 andup to 30 SCCM for the rf power density of 30 mW cm-2, the microstructuraldefects decreases, although, the Ge content of a-SiGe:H films increases. Themicrostructural defects of a-SiGe:H films becomes a direct function of themidgap defect density and a indirect function of ηµτ. Moreover, thenature of diluent gas is also important. We present that in a wide range ofoptical gap (1.74-1.36 eV) the defect density is lower, and ηµτis higher for the optimized He diluted film compared to those of the optimizedH2 diluted films.

Geochemistry of the Mississippian Delle Phosphatic Event, Eastern Great Basin, U.S.A.

ABSTRACT The Middle Mississippian Delle phosphatic event marks a significant change in depositional conditions in the Devonian-Mississippian Antler foreland basin of North America. Stratigraphic and petrographic studies show that deposition of Delle-event rocks ended a long period of open-marine carbonate sedimentation when facies shifted to phosphorites, cherts, fine-grained siliciclastics, and lime mudstones from highly productive waters that may have been episodically anoxic. This drastic change in lithology is reflected in the chemistry of the two suites of rocks. 18O values of the Delle-event lime mudstones and phosphatized wackestones-packstones affected by the Delle event are 3-5o/oo lighter than underlying and overlying open marine wackestones-packstones. Sr concentrations of Delle-event lime mudstones and open marine wackestone-packstone facies are low, suggesting that both of these lithologies have undergone similar postdiagenetic alteration. The uniform Sr concentrations and variable 18O data suggest that either the younger Delle-event rocks were exposed to meteoric water during diagenesis or that the relatively light 18O values represent a primary brackish-water depositional signal. Either interpretation is consistent with sedimentological evidence of the Delle event occurring in a predominantly shallow-water setting. 13C values of Delle-event lime mudstones are also anomalously light, indicating a high input of organic carbon during their formation. Mn concentrations of the Delle-event lime mudstones and stratigraphic equivalents are highly variable, suggesting fluctuating oxygen concentrations during their deposition and diagenesis. Rare-earth-element data from phosphorites and cherts of the Delle event indicate oxic to suboxic depositional conditions.

Signatures of natural catastrophic events and anthropogenic impact in an estuarine environment, New Zealand

The sedimentary record of known natural catastrophic events and anthropogenic activity in an estuarine environment is assessed using sedimentological, chemical and geochronological techniques. Shallow cores collected from intertidal and salt marsh sediments in Ahuriri Estuary, Hawke's Bay, reveal a variety of signatures of natural and human disturbance. Evidence for the 1931 Hawke's Bay earthquake, which resulted in an uplift of one to two metres in the Napier area, is given by a change from silt- to sand-dominated sediment in the lower estuary, which is consistent with a shift toward higher energy depositional conditions following uplift. However, based on physical properties of sediments, the 1931 uplift event does not appear to have caused major changes in depositional conditions in the upper estuary. Similarly, no changes were recorded at one site in the lower estuary, which seems to represent an area of low energy depositional environment. Although the 1960 Chilean tsunami resulted in structural damage in Napier, it did not produce any recognisable sedimentological and geochemical signature in the sedimentary record, suggesting that the study sites were possibly beyond the limit of sedimentation of the tsunami. Post-European settlement impact is mainly restricted to the lower estuary, where increased concentrations of Zn, Cr, Pb and Cu are attributed to industrial discharges. Evidence of agricultural runoff is shown by an increase in Cu concentrations within a fine-grained depositional environment that is distal from industrial sources in the town of Napier. Chemical data (Cl and S) suggest a change in the depositional environment in the upper estuary due to increased freshwater influx and/or decrease in seawater influence. Dating by 210Pb suggests that this occurred around the middle part of the 19th century, and might be attributed to river flooding in the region at that time.

Evolution morphologique des profils de dépôts dans le Sinémurien de la marge cévenole (région de Lodève)

Two types of carbonate facies have been identified in the Sinemurian series of the western margin of the Southeast Basin, and attributed to successive depositional settings of carbonate sedimentation. The first setting is a low-angle and low-energy shallow marine carbonate platform. The second setting indicates a high-energy carbonate ramp. This dramatic change in depositional conditions occurs in a regional context of extension, and can be attributed to localised fault activity resulting in differential subsidence. The combined effect of these two processes gradually modified the platform topography and initiated the changes observed in the depositional profiles.

Changes in hydrocarbon maturity indices with coal rank and type, Buller Coalfield, New Zealand

The Buller Coalfield (South Island, New Zealand) is an inverted late Paleogene Basin that contains middle Eocene bituminous coals which exhibit considerable variation in both coal rank (across-basin), and coal type (in-seam). Twenty-two fractionated bitumen extracts of Brunner Coal Measures coal samples from 12 drillholes were analyzed by GC and GC–MS to characterize the effect of coal rank and type on conventional hydrocarbon maturity indices at the beginning and end of the oil window (0.56–1.26% Ro max). The Carbon Preference Index, pristane/phytane and isoprenoid/ n-alkane ratios evolve throughout the high volatile bituminous B rank stage, while other biomarker ratios [18α( H)-22,29,30-trisnorneohopane/17α( H)-22,29,30-trisnorhopane (Ts/Tm), 18α( H),21β( H)-30-norneohopane (C 29 Ts)/17α( H),21β( H)-30-norhopane and C 30 diahopane/hopane] do not show appreciable change in value until medium volatile bituminous rank. Various aromatic based ratios appear to be more effective in delineating rank throughout the entire oil window; in particular the Methylphenanthrene Index and vitrinite reflectance are positively correlated over the entire bituminous rank range. However, subtle changes in depositional conditions (variable coal type) complicate these rank estimates. Within a given coal seam, variation in CPI, isoprenoid/ n-alkane and hopane/sterane ratios appear to be related to the hydrogen content of the coal, while the homohopane index and the oleanane/hopane ratio covary with sulfur content. As with depressed vitrinite reflectance values, MPI is similarly lowered in the perhydrous samples. The mechanisms that control these hydrocarbon parameters during deposition and diagenesis are complex and convoluted, however, changes in bacterial activity and community (with marine incursion) appear to play an important role. Due to these anomalies, none of the hydrocarbon maturity indices calculated can be singularly used to constrain coal rank.

Species composition and plant performance of mixed seagrass beds along a siltation gradient at Cape Bolinao, The Philippines

The response of mixed Southeast Asian seagrass beds to siltation was analyzed based on field data, a transplantation experiment and experimental manipulation of light availability in seagrass populations along a silt gradient at Cape Bolinao, The Philippines. Seagrass species diversity, shoot density and depth penetration declined with increasing amounts of suspended material and increasing water column light attenuation along the silt gradient. The seagrass species could be ranked according to decreasing tolerance to siltation as: Enhalus acoroides > Cymodocea serrulata > Halodule uninervis > Thalassia hernprichii > Halophila ovalis > Cymodocea rotundata > Syringodium isoetifoliurn. A gradual decline in shoot density and depth penetration of the different species along the silt gradient suggested that changes in the vertical light attenuation coefficient in the water column, primarily caused by differences in suspended inorganic solids, was the most important factor affecting seagrass performance. However, inconsistency among the species in response to Increasing water depth, artificial shading and transplantation indicated that other factors, such as siltat~on-derived changes in sediment conditions, contribute to the sequential loss of seagrass species along the silt gradient.

Early Diagenesis of Organic Matter from Higher Plants in a Malagasy Peaty Marsh. Application to Environmental Reconstruction During the Sub-Atlantic

The purposes of the present work were to examinate the morphological features and chemical composition of organic matter (OM) from a peaty marsh, in order to derive information on biological sources and on the changes in depositional conditions that occurred during the last 2300 years. The studied site, Tritrivakely, is a maar (a former volcanic crater lake) about 600 m wide and 50 m deep, located on Ankaratra Plateau. The maar is presently occupied by a peaty marsh with abundant Cyperaceae. The waterbody is shallow, fluctuating from 0 to 2 m. The study was concerned with the uppermost meter of peat which has accumulated for 2300 years B.P. in the maar. The Cyperaceae living in the marsh were also studied for comparison.

Changes in palaeoenvironmental conditions during deposition of the Permian Kupferschiefer (Lower Rhine Basin, northwest Germany) inferred from molecular and isotopic compositions of biomarker components

Biomarker distributions based on GC and GC-MS data supplemented by stable carbon isotopic compositions based on irm (isotope ratio monitoring) GC-MS data have been used to investigate changes in depositional conditions in a number of samples from a 2 m core (Rheinberger Heide) covering the entire deposition of the Permian Kupferschiefer (Lower Rhine Basin, northwest Germany). Compound classes investigated are aliphatic and aromatic hydrocarbons and maleimides (1 H-pyrrole-2,5-diones). The core has been previously divided into four sections: TI, TIIA, TIIB and TIII based on lithology. The biomarker distributions and the δ 13C values of components indicate contributions from cyanobacteria, algae, green sulphur bacteria and higher plants (minor) throughout Kupferschiefer deposition. All of the phytoplanktonic components show 13C enrichment in the lowest section, suggesting a greater productivity. The occurrence of components derived from green sulphur bacteria (Chlorobiaceae) indicates that the entire deposition was characterised by periods of photic zone anoxia. Such conditions were rapidly established after the initial transgression of the Zechstein Sea and may have been productivity-driven, but were less prevalent during deposition of the upper core sections.

Mineral magnetic properties of Late Weichselian‐Holocene sediments from the northwestern Baltic Proper

Mineral magnetic measurements were carried out on twelve sediment cores from the northwestern part of the Baltic Proper. The purpose was to use magnetic properties to correlate sediment sequences and to investigate changes in depositional conditions (e.g. rate of sedimentation and redox conditions). A general lithostratigraphy consisting of five units was established based mainly on mineral magnetic properties. Sediment has been deposited from the time of the Baltic Ice Lake (before 10 300 14C years BP) to the present, i.e. since the Late Weichselian deglaciation. Five of the cores were also investigated by means of biostratigraphical methods and three by 14C dates. Based on the general stratigraphy and hiatuses, variations in sedimentation rate were identified. The occurrence of authigenically formed ferrimagnetic greigite (Fe3S4), mainly in sediments deposited during the brackish Yoldia Sea and Litorina Sea stages, is implied. These sequences are characterized by low S‐ratios and high SIRM/z ratios. Glacial clay, deposited in freshwater during the Baltic Ice Lake stage and the early freshwater phase of the Yoldia Sea stage, seems to be unaffected by diagenetic processes. Gyttja clay, deposited in the Litorina Sea, has significantly lower susceptibility and SIRM than in the underlying clay. Dissolution of magnetic iron oxides (e.g. magnetite and hematite) in an anoxic environment was suggested as an explanation.

Fluorine‐Doped Tin Dioxide Thin Films Prepared by Radio‐Frequency Magnetron Sputtering

Tin dioxide thin films doped with fluorine were prepared by using a radio‐frequency (RF) magnetron sputtering method. The target was powder mixed with either or powder. The deposition conditions for obtaining films of low resistivity and their physical characteristics were systematically studied. The crystallinity, which was inferior to that of the CVD prepared film, was not improved by increasing substrate temperature, decreasing total pressure, and decreasing RF power. These changes in deposition conditions decreased the fluorine content of the film and consequently decreased carrier concentration.

Comparison of Upper Cretaceous and Paleogene Depositional Sequences in the Eastern Gulf Coastal Plain: ABSTRACT

ABSTRACT Genetic depositional sequences representing durations of 0.5 to 11 million years, their component systems tracts and associated physical surfaces have been identified and mapped in Upper Cretaceous and Paleogene strata of the eastern Gulf Coastal Plain. The time duration in which these sequences were deposited appears to have little impact on sequence development in that the component systems tracts can be recognized in all of the sequences. However, the Upper Cretaceous sequences represent longer periods of time, resulted from slower sedimentation rates, experienced lower subsidence rates, and, generally, reflect more marine paleoenvironmental conditions. In the eastern Gulf Coastal Plain, the Late Cretaceous was characterized by warm climates, relatively high sea levels, and stable depositional conditions. Conversely, Paleogene sequences represent shorter durations of time and were greatly affected by differential rates of sedimentation and subsidence. In Paleogene sequences, usually only the transgressive systems tracts were characterized by marine depositional conditions. In the eastern Gulf Coastal Plain, the Paleogene was typified by widely fluctuating climates and dynamic changes in depositional conditions. Generally, Upper Cretaceous sequences span more than one biozone, whereas Paleogene sequences usually are restricted to a single biozone. The sedimentation rates and patterns, the stable depositional conditions, and high biologic productivity during the Late Cretaceous results in a stratigraphic section that is useful for high resolution sequence analysis. Thus, the diachroneity of sequence boundaries and first transgressive surfaces and the synchroneity of maximum flooding surfaces are more easily discerned by mapping Upper Cretaceous system tracts and associated physical surfaces in the eastern Gulf Coastal Plain. The study of Upper Cretaceous depositional sequences, therefore, is potentially more helpful in identifying the factors affecting global sea level change.

Environment and diagenesis of an Upper Cretaceous bioclastic oyster limestone bed, Red Sea Coast, Egypt

An Upper Cretaceous bioclastic oyster limestone bed, exposed at the Red Sea coastal strip, has been investigated for its depositional environment and the early diagenetic modifications affecting its components. The deposition of this stratum body marks the end of prevailed euxinic conditions and the setting up of an oxic milieu. This dramatic change in depositional conditions is related primarily to the change in the position of oxygen minimum zone during sedimentation. The noticeable negative shift in the δ18O-values of the studied skeletal parts (−2.7 to −6.4‰ PDB) are attributed to some habitat-related controls and the dilution of marine water with a great fresh water influx. In addition, mild diagenetic alterations that have affected some of these skeletals, as indicated by their enriched manganese values and orange-colored luminescence, are also- in part-responsible for the δ18O negative shift. Meanwhile, the negative δ13C signatures (−2.2 to −5.6‰ PDB) are probably related to an upward flux of isotopically-light and reduced pore waters to the bottom water where the oysters are thought to have lived and/or to the reducing conditions during which the alteration of these skeletals occurred. Moldic porosity is quite common although partly or completely occluded by clear equant low-Mg calcite of marine origin. These submarine mosaics are probably formed under oxidizing conditions in the phreatic zone as indicated from their non-luminescence character and stable isotopic values. The wide overlap range between the oxygen and carbon stable isotopic signatures of these mosaics and the skeletal particles may indicate they both are formed under the same conditions provided little effect exerted by the latters. A promising possibility of hydrocarbon accumulations in the area east of Qusier (off shore) is expected.

Stratigraphic evidence of changes in Amazon shelf sedimentation during the late Holocene

Late Holocene sedimentation on the Amazon shelf was investigated using a combination of seismic, sedimentological, and geochronological methods. Piston cores collected in the subaqueous delta region during A Multidisciplinary Amazon Shelf Sediment Study ( AmasSeds) penetrated a regionally traceable (1.25 × 10 4km 2) seismic discontinuity, which corresponds to a dense relict-mud reflector overlain by acoustically transparent sediment. Distinct offsets in profiles of wet-bulk density, P-wave velocity, and 210Pb activity are noted in cores at the reflector horizon (unconformity), signifying a past change in sedimentation conditions on the shelf. Bulk-sediment 14C dating indicates net depositional conditions for the subaqueous delta from > 1800 yr B.P. to 700 yr B.P. and a net erosional phase from about 700 yr B.P. to 100 yr ago. Sedimentological evidence of the erosional phase includes lag deposits and burrows present at the unconformity surface in piston cores. The deposits above and below the unconformity are similar with respect to grain-size parameters and sedimentary structures, suggesting that environmental conditions during the two depositional periods were similar. According to 14C dates of coastal deposits, the shoreline of Amapa State, Brazil served as a major depocenter of Amazon mud during the erosional phase on the shelf. 210Pb geochronology indicates that the most recent phase of sediment accumulation in the study area commenced about 100 yr ago, resulting in rapid progradation of topset deposits and burial of relict strata. In the present environment, oceanographic and meteorologic processes cause along-shelf variations in sediment dispersal and depositional patterns, and about 1400 km 2 of the erosional relict deposits are still exposed at the seabed. The short time scales over which Amazon shelf strata respond to changes in the physical environment preclude the influence of relative sea-level cyclicity on recent sedimentation patterns. During the late Holocene, sedimentation and strata formation on the Amazon shelf are linked to fluvial, oceanographic and meteorologic processes that affect sediment supply, deposition and erosion.

The organic geochemistry of Peru margin surface sediments: II. Paleoenvironmental implications of hydrocarbon and alcohol profiles

We assess the utility of sedimentary hydrocarbons and alcohols as indicators of short-term changes in depositional conditions in the coastal Peruvian upwelling regime at 15°S. The distribution of 35 lipids ( n-alkanes, n-alkanols, hopanols, keto-ols, lycopane, phytol, stenols, stanols, sterenes, and tetrahymanol) in a l m dated core from 253 m water depth are interpreted by (1) a principal components analysis and (2) a consideration of individual source-specific biomarkers. Profiles of odd-carbon-number n-alkanes (C 25-C 33) and even-carbon-number n-alkanols (C 24-C 28) reflect changes in the contribution of terrigenous sediment relative to marine sediment during deposition, as indicated by the correlations between these lipids and inorganic indicators of terrigenous clastic debris. The n-alkane carbon preference index (CPI) provides a less-sensitive record of fluctuations in the terrestrial input than the concentration profiles of the individual n-alkanes and n-alkanols, and these lipids are not well-correlated with the historical El Niño record. The similarity of all the stenol profiles measured and the lack of concordance between these profiles and inorganic indicators of terrigenous input suggest that any fluctuations in the abundance of higher-plant stenols are obscured by the larger marine contribution of these compounds. Similarities between the profiles of total organic carbon (TOC) and cholestanol/cholesterol are consistent with stenol hydrogenation being influenced by the sediment redox conditions.

Heavy metal accumulation and transport through detention ponds receiving highway runoff

Sediment accumulations and associated heavy metal concentration into retention/detention ponds receiving highway runoff from several ponds and metal concentrations in various sediment layers were analyzed to determine the extent of vertical migration. Extraction of heavy metals had been evaluated using various solutions including the United States Environmental Protection Agency Toxicity Characteristics Leaching Procedures (TCLP). Also, sediments were incubated under various conditions of redox potential and pH to investigate the effects of changes in sediment conditions on the stability of metal-sediment associations.

Deposition of Dielectric Optical Coatings: A Microstructural Study of the Deposited Layers and Interfaces

ABSTRACTThin dielectric films for optical applications are deposited on substrates using a variety of techniques including reactive sputtering, solgel reaction, and ion assisted plasma deposition. This transmission electron microscopy study characterizes optical coatings produced by the above deposition techniques and shows how changes in deposition conditions change microstructure and as a result the optical properties.

Measurement and Interpretation of stress in aluminum-based metallization as a function of thermal history

Mechanical stress in interconnections is a problem of growing importance in VLSI devices. The origins of this stress are discussed, and a measurement technique based on the determination of wafer curvature with a laser scanning device is described. The changes in stress observed during thermal cycles are interpreted quantitatively in terms of a simple model of elastic and plastic strain in the metal. The effects of changes in deposition conditions, film composition, and film structure are discussed.