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821.
A single Upper Carboniferous fluvio-deltaic cycle (Namurian, R2b5) in the south part of the Pennine Basin of northern England has been reinterpreted using a sequence stratigraphic approach. In upward succession the deposits comprise basinal mudstones, localized thick density current deposits, delta slope deposits and delta-top sandstones, followed abruptly by basinal mudstones. Earlier interpretations linked these elements with a single, mainly regressive, cycle, referred to as a turbidite-fronted delta. Recent evidence for strong glacio-eustatic sea-level fluctuations in the Namurian suggests that it is unlikely that the previous simple model can explain the spatial arrangement of all the lithological units. This paper attempts to identify elements of the Exxon sequence stratigraphic model, in which changes of sea level are an essential part. The basinal mudstones represent deep-water deposition and imply a highstand of sea level. Thick density current deposits are now known to be localized close to the basinward limit of delta progradation, so cannot be seen as a ubiquitous component of the depositional system. They may form a detached fan, or a fan located at the foot of the delta slope. Slope siltstones include turbidite-like sandstones, but these are interbedded with tractional sandstones and Pelecypodichnus trace fossils, giving no clear indication of water depth. The delta-top sandstones, some coarse and pebbly, can in places be shown to consist of two parts separated by a significant erosion surface now regarded as a type 1 sequence boundary. The erosion surface is locally incised about 80 m into the delta deposits, forming a major palaeovalley. Giant cross-beds (foresets 20 m thick) forming part of the palaeovalley fill are restricted to the basinward end of this feature. A curve of relative sea level inferred for the R2b5 interval suggests a fourth-order cycle in which two sharp rises are separated by a gradual fall. Possible minor (fifth-order) rises and falls may be superimposed. © 1997 John Wiley & Sons, Ltd. 相似文献
822.
The impact of realistic representation of sea surface temperature (SST) on the numerical simulation of track and intensity
of tropical cyclones formed over the north Indian Ocean is studied using the Weather Research and Forecast (WRF) model. We
have selected two intense tropical cyclones formed over the Bay of Bengal for studying the SST impact. Two different sets
of SSTs were used in this study: one from TRMM Microwave Imager (TMI) satellite and other is the weekly averaged Reynold’s
SST analysis from National Center for Environmental Prediction (NCEP). WRF simulations were conducted using the Reynold’s
and TMI SST as model boundary condition for the two cyclone cases selected. The TMI SST which has a better temporal and spatial
resolution showed sharper gradient when compared to the Reynold’s SST. The use of TMI SST improved the WRF cyclone intensity
prediction when compared to that using Reynold’s SST for both the cases studied. The improvements in intensity were mainly
due to the improved prediction of surface latent and sensible heat fluxes. The use of TMI SST in place of Reynold’s SST improved
cyclone track prediction for Orissa super cyclone but slightly degraded track prediction for cyclone Mala. The present modeling
study supports the well established notion that the horizontal SST gradient is one of the major driving forces for the intensification
and movement of tropical cyclones over the Indian Ocean. 相似文献
823.
A new specimen of basal neoceratopsian dinosaur Liaoceratops yanzigouensis is described. The specimen comes from the Lujiatun Bed of the Lower Cretaceous Yixian Formation in Beipiao City of western Liaoning Province, and is represented by a very well preserved three-dimensional partial skull and mandible. It is also the smallest among the three specimens of L. yanzigouensis, and several features in the new specimen, such as the short preorbital length and the round rostroventral orbital rim, can be ontogenetically-related. The superb exposure of the palatal complex may be caused by the removing of its brain by a small predator in the contemporary Jehol Biota. 相似文献
824.
D. Elaine Evers Charles E. Sasser James G. Gosselink Deborah A. Fuller Jenneke M. Visser 《Estuaries and Coasts》1998,21(1):1-13
Delta islands in the Atchafalaya and Wax Lake deltas in Atchafalaya Bay, Louisiana, are in an extremely dynamic successional phase. These islands initially supported large marshes dominated by the pioneering plant species Sagittaria latifolia and Sagittaria platyphylla. A general decrease in vegetated areas has occurred in the delta island marshes in the Atchafalaya Delta since about 1980, while in the Wax Lake Delta portion of the complex the vegetation still flourished. The Atchafalaya Delta provides an interesting setting for the study of herbivory because of the complex interaction of biotic and physical factors operating in this delta. We hypothesized that grazing by herbivores has a marked effect on vegetation in these developing marshes. To test this hypothesis, exclosures were erected on islands in both deltas in September 1985 and January 1986. Each set of exclosure treatments included an openly-grazed control area, an ungrazed area, an area allowing nutria grazing, and one allowing waterfowl grazing in each site. Results of the experiment, based on field sampling of vegetation, indicated decreases in plant biomass and changes in plant species composition in grazed treatments. Waterfowl and nutria reduced biomass aboul equally, but there was a more marked effect in the openly grazed areas. These findings may be extrapolated to sediment diversion areas along the Mississippi River. 相似文献
825.
826.
In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, ‘Riftlink’. The group's focus is the Albertine Rift, the northern part of the western branch of the East African Rift System, and in particular the rising Rwenzori Mountains that stretch along the border of the D.R. Congo and Uganda. Major questions relate to the timing of the formation of the Rwenzori Mountains, and whether the height of these mountains (> 5000 m) relates to rift movements in Neogene times, or represents an old basement block that formed a topographic high long before. Though, at first, research concentrated on the eastern (Ugandan) part of the Albertine Rift and Rwenzori Mountains, it has now moved further to the west to the D.R. Congo. A first field‐campaign, covering the area from northern Lake Edward along the rift shoulder up to the Blue Mountains at Lake Albert, was conducted in summer 2009, in cooperation with the Ruwenzori State University of Butembo. Here, we present a brief overview of the field‐campaign, with impressions gathered on the morphology and geology of the study area. 相似文献
827.
828.
P. K. Pal W. J. Prakash P. K. Thapliyal C. M. Kishtawal 《Meteorology and Atmospheric Physics》1999,71(3-4):157-168
Summary ?A methodology has been developed to assimilate satellite-measured rainfall during the initial phase of model integration
for extended range monsoon prediction. The vertical profiles of latent heating corresponding to different rain rates have
been derived from the model statistics. These heating rates have been assimilated through nudging in the thermodynamics equation
of the model. This procedure of assimilating observed heating has corrected the simulation of heating location in the model
and consequently removed the anomalous sinking motion over Indian landmass. With the correction of vertical circulation, both
mean July rainfall over India and the distribution have improved. Interannual variability has been brought out for the years
1987 and 1988. In view of the availability of rainfall profile from Tropical Rain Measuring Mission (TRMM) there is a scope
of adopting this method of assimilating observed rainfall, for extended range monsoon prediction.
Received February 12, 1999/Revised May 4, 1999 相似文献
829.
830.