Sediment dispersal and quantitative stratigraphic architecture across an ancient shelf

Two large (200 to 300 km), near‐continuous outcrop transects and extensive well‐log data (ca 2800 wells) allow analysis of sedimentological characteristics and stratigraphic architecture across a large area (ca 60 000 km²) of the latest Santonian to middle Campanian shelf along the western margin of the Western Interior Seaway in eastern Utah and western Colorado, USA. Genetically linked depositional systems are mapped at high chronostratigraphic resolution (ca 0·1 to 0·5 Ma) within their sequence stratigraphic context. In the lower part of the studied interval, sediment was dispersed via wave‐dominated deltaic systems with a ‘compound clinoform’ geomorphology in which an inner, wave‐dominated shoreface clinoform was separated by a muddy subaqueous topset from an outer clinoform containing sand‐poor, gravity‐flow deposits. These strata are characterized by relatively steep, net‐regressive shoreline trajectories (>0·1°) with concave‐landward geometries, narrow nearshore belts of storm‐reworked sandstones (2 to 22 km), wide offshore mudstone belts (>250 km) and relatively high sediment accumulation rates (ca 0·27 mm year^?1). The middle and upper parts of the studied interval also contain wave‐dominated shorefaces, but coeval offshore mudstones enclose abundant ‘isolated’ tide‐influenced sandstones that were transported sub‐parallel to the regional palaeoshoreline by basinal hydrodynamic (tidal?) circulation. These strata are characterized by relatively shallow, net‐regressive shoreline trajectories (<0·1°) with straight to concave‐seaward geometries, wide nearshore belts of storm‐reworked sandstones (19 to 70 km), offshore mudstone belts of variable width (130 to >190 km) and relatively low sediment accumulation rates (ca ≤0·11 mm year^?1). The change in shelfal sediment dispersal and stratigraphic architecture, from: (i) ‘compound clinoform’ deltas characterized by across‐shelf sediment transport; to (ii) wave‐dominated shorelines with ‘isolated’ tide‐influenced sandbodies characterized by along‐shelf sediment transport, is interpreted as reflecting increased interaction with the hydrodynamic regime in the seaway as successive shelfal depositional systems advanced out of a sheltered embayment (‘Utah Bight’). This advance was driven by a decreasing tectonic subsidence rate, which also suppressed autogenic controls on stratigraphic architecture.     

Mixed layer modelling with respect to ocean-atmosphere interactions in the eastern Indian Ocean

Summary As a precursor to the embedding of a thermal stratification model of the ocean into an Ocean General Circulation Model (OGCM) we have compared the performance of an integral (or bulk) (Kraus-Turner) and a differential (Eddy Diffusion Dimension 1) thermal stratification model for the eastern Indian Ocean. Forced with the Comprehensive Ocean-Atmosphere Data Set (COADS) and Subjectively Estimated Cloudiness in the Australian Region (SECAR) data sets, both models successfully stimulated the annual cycle in sea surface temperature. On the other hand, their predictions of the mixed layer depth differed substantially. Whereas the differential model slightly underestimated the winter mixed layer depth, the winter mixed layer depths calculated by the bulk model were substantially larger than the observed values. An additional analysis of the simulated heat storage cycle of the eastern Indian Ocean with respect to the activity of tropical-extratropical cloudbands in the Australian region has reveaved a strong relationship between these two parameters. The results have shown that a stronger activity of the tropical-extratropical cloudbands coincides with periods of heat transfer oriented from the ocean to the atmosphere.With 11 Figures     

COMPARISON BETWEEN RESULTS OF MODEL TESTS AND OBSERVED DATA FOR THE FLUCTUATING BACKWATER REGION OF THE GEZHOUBA RESERVOIR

The fluctuationg backwater region of a reservoir has a twofold property of a river as well as a reservoir and undergoes scouring and deposition alternately. Phys- ical model simulating the fluvial processes in a fluctuating backwater region has to ensure the similarities of both scouring and deposition. This causes some difficulties in model design and the selection of model sediment. This paper describes the model study of the fluctuating backwater region of the Gezhouba Project on the Yangtze River. Plastic particles with specific gravity of 1 .056 are used. The physical. model covers a reach of mountainous river 130 km in length. The experimental results show that the total amount of deposit, its distribution along the reach, the size distribution of the deposit, and lengths of the backwater region for various discharges all agree very well with the measured data in reservoir after 5 years of operation. This fact indicates that the model design, including the selection of model sediment, is quite acceptable.     

SUSPENDED SEDIMENT TRANSPORT CAPACITY OF OPEN CHANNEL FLOW

I.~ODUCTIONSuspendedsedimenttransportcapacity(SSTC)ofopenchannelflowisoneofthebasicsubjectsinsedimenttransportmechanicsandsedimentationengineeringpractice.Mostexistingformulationsareempiricalandsemiempiricalorrestheavilyonassumptionswhicharenotyetjustified.Thisarisesmostlybecauseofthecomplexityoftheproblem.Forafullydeveloped,in-equilibriumflowinawiderectangularchannel,theSSTCcanbbdeterminedasfollowsor=n:,ty)cab)-dy=Ca'I(l)1I=J4(D)'exp[--V,(n)]'da(2)unwhereCTIsSSTC,uistheaveragedflo…     

MECHANISM OF ARMORING PHENOMENA

I. INTRODUCTIONArmor coats, which are comPOSed of particles coarser than those of the under layers, are usually foundon the bed surfaces of mountain streams or gravel bed rivers. A large number of P8pers have been publishedon armor coats. Most of them emphasize that the selective entrainment or transportation plays an imPOrtantrole on the armoring processes.Some recent studies indicate that the difficulty arises in describing the propagation of armor coats interms of selective entrainm…     

A comparison of three methods for regional flood frequency analysis in Saudi Arabia

The objective of the study was to compare the relative accuracy of three methodologies of regional flood frequency analysis in areas of limited flood records. Thirty two drainage basins of different characteristics, located mainly in the southwest region of Saudi Arabia, were selected for the study. In the first methodology, region curves were developed and used together with the mean annual flood, estimated from the characteristics of drainage basin, to estimate flood flows at a location in the basin. The second methodology was to fit probability distribution functions to annual maximum rainfall intensity in a drainage basin. The best fitted probability function was used together with common peak flow models to estimate the annual maximum flood flows in the basin. In the third methodology, duration reduction curves were developed and used together with the average flood flow in a basin to estimate the peak flood flows in the basin. The results obtained from each methodology were compared to the flood records of the selected stations using three statistical measures of goodness-of-fit. The first methodology was found best in a case of having short length of record at a drainage basin. The second methodology produced satisfactory results. Thus, it is recommended in areas where data are not sufficient and/or reliable to utilise the first methodology.     

Dynamic Buckling of Laminated Composite Bars Subjected to Axial Impact

The impact buckling of a laminated composite bar is investigated in case of one of its endsmoving due to axial impact compression.The governing equations considering the first-order sheardeformation effect are derived by the Hamilton principle and solved by the finite difference method.Thecritical axial shortness is determined by the B-R cirterion.The given example is used to highlight the in-fluences of initial imperfection,impact velocity,stress wave and coupled stiffness.It is found that theunsymmetrically laminated bar has a quite different dynamic buckling behaviour from that of thesymmetrically laminated bar.     

Modification of Wirsching’s Model for Fatigue Reliability Analysis

First,Wirsching＇s model,which is widely employed in fatigue reliability anlysis of marine andoffshore structures,is analysed systematically.It is found that the very important random variable △ inWirsching＇s model can not be directly determined from fatigue experiment because of the irreversibility offatigue test,and in fact,what Wirsching studied from testing results is not △ but α of the statistical Miner＇srule.Second,by use of the statistical Miner＇s rule,a modified Wirsching＇s model is proposed.Thirdly andmore importantly,based on the two-dimensional probabilistic Miner＇s rule,a new model is established forfatigue reliability analysis of structural components subjected to specified cyclic loading of variableamplitude or stochastic time history.In the end,an example is presented,from which it will be seen thatthis new model is very convenient to use and feasible to engineering practice.     

An Expression of Apparent Energy Distribution of Sea Waves by Wave Characteristics

Based on observed wind waves,the relationships between wave spectrum products and wavecharacteristics are established successfully,and the apparent energy distribution of sea waves is expressed as afunction of wave characteristics.     

Three-Dimensional Boundary Element Method Applied to Nonlinear Wave Transformation

For higher accuracy in simulating the transformation of three dimensional waves,in consid-eration of the advantages of constant panels and linear elements,a combined boundary elements is appliedin this research.The method can be used to remove the transverse vibration due to the accumulation ofcomputational errors.A combined boundary condition of sponge layer and Sommerfeld radiation condi-tion is used to remove the reflected waves from the computing domain.By following the water particle onthe water surface,the third order Stokes wave transform is simulated by the numerical wave flume tech-nique.The computed results are in good agreement with theoretical ones.