Upper Part Of Core Research Articles

Depositional Cycles of Muara Wahau Coals, Kutai Basin, East Kalimantan

http://dx.doi.org/10.17014/ijog.v1i2.183Fifteen samples were taken ply by ply from a 33 m thick drill core of Muara Wahau coal seams for interpretation of depositional environments. Generally, lithotype variation in the bottom part of the coal seams has a lower frequency than in the upper part. Petrographical analysis was performed to determine the maceral composition, groundwater index (GWI), and gelification index (GI). The samples from lower sections show much higher GWI-GI values and lower variation frequency than from the upper section. This characteristic is interpreted as the result of development of mesotrophic to ombrotrophic peats during the deposition of lower to upper parts of the section, respectively. During the development of the mesotrophic peat, water was more abundant and relatively stable in budget. However, during the development of ombrotrophic peat, water was less abundant and relatively not stable in budget. The latter is related to the water supply depending only on rain, resulted in the more sensitive water table in the om- brotrophic peat. The unstable water table is thought as the reason of higher variation frequency of lithotype, GWI, GI, as well as maceral composition in the upper part of the core. Unstable water table would lead to moist condition in the uppermost layer of the ombrotrophic peat, favoring fungi to grow. This is confirmed by the higher abundance of sclerotinite maceral in samples from the upper part of the coal core.

Provenance of glacial–marine sediments under the McMurdo/Ross Ice Shelf (Windless Bight, Antarctica): Heavy minerals and geochemical data

Sea floor sediments beneath the McMurdo/Ross Ice Shelf in a 900-m-deep depression behind Ross Island have been cored through access holes at two sites. At Site 1, 31 cm of mud and lesser sand, deposited over the last 22 ka, overlies a 30-cm-thick diamictite of the Last Glacial Maximum. At Site 2, the entire core is mud deposited over the last 12 ka. Analyses of very fine sand-sized, heavy minerals and geochemical analyses of the sand and silt fractions have been carried out on samples from both sites to track variations in sediment provenance through the Late Quaternary. The heavy minerals were identified by optical and electron scanning microscope (SEM-EDAX) analysis. Major and trace elements were determined on fused glass discs by X-ray fluorescence (XRF) spectrometry. Heavy mineral assemblages have high concentrations of pyroxenes (titanoaugite, augite, pigeonite, low-Ca augite and enstatite), olivines and glass grains. Amphiboles (Mg-hornblende, actinolite and kearsutite), oxides (titanite and titanomagnetite) and stable minerals (epidote, garnet, and apatite) are present in minor amounts. Olivine, titanoaugite and glass dominate the heavy mineral assemblages both in upper part of core 1 and in all of core 2. In the diamictite, an increase of augite, pigeonite, low-Ca augite, hornblende and stable minerals are observed. The sediment geochemistry is linked to their mineralogical composition both in the sand and in the silt fractions. K and Rb trends probably represent variations in alkali feldspar and/or mica content. The variation of Si/Al ratio is due to sialic minerals and/or to quartz content variation. Mg, Ca, Ti, Sr are probably comprised in femic minerals. The sets of analyses show that the sediments are a mix of local McMurdo Volcanic Group (MVG) rocks and Transantarctic Mountains (TAM) source rocks to the south and west. The diamicton was a strong TAM provenance, suggesting that the main ice streams drained into the Ross Sea from the West at least prior to 18 ky and later than 25 ky. The overlying mud is dominated by a MVG signal, sediments in the two sampled sites derive from basal melting of the ice sheet which entrapped debris from MVG cropping out to the South of the Ross Embayment. Small quantities of minerals from the TAM can be supplied by marine currents inflowing under the shelf from NW.

Variation of heavy metals in recent sediments from Piratininga Lagoon (Brazil): interpretation of geochemical data with the aid of multivariate analysis

In the last decade, the Atlantic coast of south-eastern Brazil has been affected by increasing deforestation and anthropogenic effluents. Sediments in the coastal lagoons have recorded the process of such environmental change. Thirty-seven sediment samples from three cores in Piratininga Lagoon, Rio de Janeiro, were analyzed for their major components and minor element concentrations in order to examine geochemical characteristics and the depositional environment and to investigate the variation of heavy metals of environmental concern. Two multivariate analysis methods, principal component analysis and cluster analysis, were performed on the analytical data set to help visualize the sample clusters and the element associations. On the whole, the sediment samples from each core are similar and the sample clusters corresponding to the three cores are clearly separated, as a result of the different conditions of sedimentation. Some changes in the depositional environment are recognized using the results of multivariate analysis. The enrichment of Pb, Cu, and Zn in the upper parts of cores is in agreement with increasing anthropogenic influx (pollution).

Sedimentary facies and processes of deposition: Ice Island cores, Axel Heiberg Shelf, Canadian Polar Continental Margin

The sedimentological features are described of 24 piston and gravity cores recovered at depths from 140 to 283 m beneath the perennial ice cover of the Arctic Ocean, north of Axel Heiberg Island. Sample sites are located between Nansen and Sverdrup channels, along the drift path of the Canadian Ice Island. Eight facies are characterized and interpreted, as follows: (A) Soft, yellow-brown structureless pebbly sandy mud/silty mud interpreted as strongly bioturbated hemipelagic muds with ice-rafted meltout and fallout deposits; (B) burrowed sandy silty/clayey mud interpreted to be the result of slow continuous suspension fallout concommitant with bioturbation; (C) wispy, laminated sandy silty mud due to slow continuous suspension fallout with bioturbation punctuated by sudden deposition from nepheloid flows or fine-grained turbidity currents; (D) laminated sandy silty mud formed by underflow, turbidity current and suspension fallout; (E) firm, dark grey/olive grey-brown pebbly sandy/silty mud comprising ice-rafted debris or debris flow deposits; (F and G) indurated, reddish brown/ochre and black pebbly sandy mud/silty mud comprising exposed bedrock; and (H) firm, grey and brown structureless silty mud interpreted as suspension deposits with rare ice rafting. The indurated facies F and G occur on a topographic high on the inner shelf. This topographic high is interpreted as an offshore bank which may have provided a sedimentary source during deposition. Facies H is restricted to deeper cores within Nansen and Sverdrup channels, representing a possibly older relict deposit. Other facies show broad correlations throughout the study area. Facies A, B and C are more common in the upper parts of cores, Facies D and E in the lower parts of cores. Deposition by gravity flows in a realm of normal hemipelagic sedimentation is a more important process than fallout and wasting of ice shelves and icebergs. Reworking by waves and bottom currents is minimal. The present facies model compares well with those for other high arctic areas, including Baffin Island fjords and the continental rise of Canada Basin in the western Arctic Ocean. No till facies were cored on the Axel Heiberg Shelf, indicating that this part of the shelf was probably not inundated by grounded ice during the last glaciation. The most abundant mineral in the coarse fraction (> 63 μm) of the samples selected is common quartz. The mafic minerals are far less common than quartz and feldspar, reflecting the instability of these grains; however, igneous augite, typically clinopyroxene, occurs in all samples. Rock fragments include fresh and altered basalt and gabbro, metamorphic and granitic rock fragments and a wide variety of sedimentary rock fragments, including mudstone, sandstone, chert and limestone. The variation of shape and composition of rock and mineral fragments within and between facies suggests a mixed source area dominated by a plutonic terrain. The plutonic and metamorphic rock fragments were probably derived from Pearya, whereas the sedimentary rock fragments were eroded from the Franklinian Mobile Belt and Sverdrup Basin. The occurrence of augite suggests a nearby volcanic source, probably Ellesmere Island. The present data indicate that the source terrains did not vary significantly during the time of the facies distribution of the Axel Heiberg Shelf.

Effect of Asymmetric Upper Plenum Injection on Reflood Behavior

Reflood phenomena of 2-loop PWR with upper-plenum-injection (UPI) type ECCS was studied by examining CCTF experimental data. The major conclusions about the effects of asymmetric UPI and single low-pressure-coolant-injection (LPCI) pump failure on reflood phenomena are as follows: 1. Single failure assumption of LPCI pump is more conservative (worse core cooling) than no failure assumption of LPCI pump under UPI condition. This is consistent with current guide line for reactor safety evaluation.2. The asymmetric UPI promoted a radial ununiformity of the core cooling, although even symmetric UPI lead to the radial ununiformity of the core cooling.3. The asymmetric UPI did not give a local degradation of core cooling in comparison with symmetric UPI but gave an enhancement of core cooling in the upper part of core after the initiation of water fall back.4. The enhancement of core cooling is considered to be caused by increased upward fluid flow due to water fall back and water fall back itself, which are promoted by asymmetric UPI.5. Initiation of water fall back can be predicted with Bankaff's correlation under UPI condition when the fluid temperature is saturated.

Frequency response of the neutron field to localized perturbations in a 3-D heterogeneous lattice and applications

By using the frequency-dependent source-sink formalism of Feinberg and Galanin in one-group diffusion theory with a two-group slowing-down kernel, a model is developed for the investigation of the frequency response of the neutron field to a localized frequency-dependent perturbation in a 3-D heterogeneous lattice of a finite number of fuel and control rods embedded in an infinite moderator with no upper or lower reflectors. A numerical method for solving the equations of the semi-analytical model is indicated and it is shown that the well-known local component of the neutron-noise field is due to attenuation effects in the pure moderator. Finally, with some simplifications, the formalism is applied to the problem of the ‘field of view’ of an incore neutron detector in a BWR with moderator data typical of the lower and the upper part of a BWR core. Within the framework of the present model, it is shown that in the upper part of the core, although with different weighting for different distances from the detector, the detector ‘sees’ at least the whole cross section of the surrounding bundles.

Variability of Sedimentary Textures and Processes on Continental Margin North of Wilmington Canyon: ABSTRACT

Sedimentary properties and processes of a 7,500-km2 corridor seaward of the Baltimore Canyon Trough off New Jersey were studied in detail using over 100 bottom samples consisting of grab samples and box, hydroplastic, and piston cores. The sediments in both canyon and intercanyon areas are primarily bioturbated, olive-gray, sandy silts with local features indicative of gravity-induced mass sediment movements (i.e., graded sequences and load structures). C14-based sediment accumulation rates vary by a factor of three in cores separated by as little as 6 km. These variations seem to be a function of shelf-edge spillover rates. Detailed analyses of the sand grain-size distribution throughout the corridor reveal that the sand component of the slope and rise sediments contains a high percentage of material currently present on the adjacent shelf. The relatively large percentage of sandy sediment in the upper parts of cores from Spencer Canyon suggests its recent role in transporting shelf sediments seaward. Sandy intervals in other slope cores are commonly obscured by intense bioturbation. Cores from the continental rise show an upward decrease in the number of sand layers and lenses. Active transport of sediment to the slope and rise occurred during the late Pleistocene and, although the intensity has declined, the slope is presently the site of deposition for both fine and coarse sediment. End_of_Article - Last_Page 1662------------