Multi‐scale analysis of a migrating submarine channel system in a tectonically‐confined basin: The Miocene Gorgoglione Flysch Formation,southern Italy     

Claudio I. Casciano  Marco Patacci  Sergio G. Longhitano  Marcello Tropeano  William D. McCaffrey  Claudio Di Celma 《Sedimentology》2019,66(1):205-240

The Miocene Gorgoglione Flysch Formation records the stratigraphic product of protracted sediment transfer and deposition through a long‐lived submarine channel system developed in a narrow and elongate thrust‐top basin of the Southern Apennines (Italy). Channel‐fill deposits are exposed in an outcrop belt approximately 500 m thick and 15 km long, oriented oblique to the palaeoflow, which was roughly south‐eastward. These exceptional exposures of channel‐fill strata allow the stacking architectures and the evolution of the channel system to be analyzed at multiple scales, enabling the effects of syn‐sedimentary thrust tectonics and basin confinement on the depositional system development to be deciphered. Two end‐member types of elementary channel architecture have been identified: high‐aspect‐ratio, weakly‐confined channels, and low‐aspect‐ratio, incisional channels. Their systematic stacking results in a complex pattern of seismic‐scale depositional architectures that determines the stratigraphic framework of the deep‐water system. From the base of the succession, two prominent channel complex sets have been recognized, namely CS1 and CS2, consisting of amalgamated incisional channel elements and weakly‐confined channel elements. These channelized units are overlain by isolated incisional channels, erosional into mud‐prone slope deposits. The juxtaposition of different channel architectures is interpreted to have been governed by regional thrust‐tectonics, in combination with a high subsidence rate that promoted significant aggradation. In this scenario, the alternating ‘in sequence’ and ‘out of sequence’ tectonic pulses of the basin‐bounding thrusts controlled the activation of coarse‐clastic inputs in the basin and the resulting stacking architectures of channelized units. The tectonically‐driven confinement of the depositional system limited the lateral offset in channel stacking, preventing large‐scale avulsions. This study represents an excellent opportunity to analyze the stratigraphic evolution of a submarine channel system in tectonically‐active settings from an outcrop perspective. It should find wide applicability in analogous depositional systems, whose stratigraphic architecture has been influenced by tectonically‐controlled lateral confinement and associated lateral tilting.  相似文献   

伶仃洋茅洲河口滩槽演变水沙模拟及治导线优化          下载免费PDF全文

陆永军  莫思平  王志力  季荣耀  顾继一 《水科学进展》2019,30(6):770-780

为适应伶仃洋茅洲河口治理开发条件,以保证行洪顺畅为泄洪纳潮的首要原则,同时顺应水沙运动和河势发展规律,对河口进行治导线比选和优化。该河口治导线方案分单、双通道,两类通道不同扩宽率下设计有围填、围填加开挖2种方案,开展水动力泥沙数学模拟计算和物理模型试验。结果表明:河口治导线各方案对伶仃洋涨、落潮流速的影响范围主要集中在交椅湾及其附近海域;方案实施后,周边海区冲淤变化较小,未对河势造成不利影响;根据对水动力、河口泄洪、河势稳定影响的综合分析,单双通道相比较而言,对洪水位、纳潮量、高低潮位、流速、河床冲淤的影响规律具有较好的一致性,相同扩宽率下各方案的影响程度均在同量级。  相似文献   

腹板开槽冷弯薄壁卷边槽钢抗火性能有限元分析模型     

马奇杰  王培军  郑英杰 《地震学刊》2012,(2):205-209

位于冷弯薄壁型钢构件腹板的槽孔,可延长构件两边的热量传递路线,减弱冷弯薄壁钢构件作为墙板龙骨引起的冷桥效应。常温下冷弯薄壁构件的屈曲破坏模态已非常复杂,包括整体屈曲、局部屈曲和畸变屈曲等,且不同的屈曲破坏模态可能会相互影响。火灾下冷弯薄壁构件的破坏机理将更为复杂,根据常规的稳定理论难以求解其火灾下的临界荷载。本文利用有限元方法对火灾下腹板开槽冷弯薄壁卷边槽钢的受力性能进行了模拟,研究了单元类型、材料模型、初始几何缺陷以及求解方法等因素对分析结果的影响,为同类构件抗火性能的有限元模拟分析提供了建模依据。  相似文献   

The stratigraphic record and processes of turbidity current transformation across deep‐marine lobes          下载免费PDF全文

Ian A. Kane  Anna S. M. Pontén  Brita Vangdal  Joris T. Eggenhuisen  David M. Hodgson  Yvonne T. Spychala 《Sedimentology》2017,64(5):1236-1273

Sedimentary facies in the distal parts of deep‐marine lobes can diverge significantly from those predicted by classical turbidite models, and sedimentological processes in these environments are poorly understood. This gap may be bridged using outcrop studies and theoretical models. In the Skoorsteenberg Formation (South Africa), a downstream transition from thickly bedded turbidite sandstones to argillaceous, internally layered hybrid beds, is observed. The hybrid beds have a characteristic stratigraphic and spatial distribution, being associated with bed successions which generally coarsen and thicken‐upward reflecting deposition on the fringes of lobes in a dominantly progradational system. Using a detailed characterization of bed types, including grain size, grain‐fabric and mineralogical analyses, a process‐model for flow evolution is developed. This is explored using a numerical suspension capacity model for radially spreading and decelerating turbidity currents. The new model shows how decelerating sediment suspensions can reach a critical suspension capacity threshold beyond which grains are not supported by fluid turbulence. Sand and silt particles, settling together with flocculated clay, may form low yield strength cohesive flows; development of these higher concentration lower boundary layer flows inhibits transfer of turbulent kinetic energy into the upper parts of the flow ultimately resulting in catastrophic loss of turbulence and collapse of the upper part of the flow. Advection distances of the now transitional to laminar flow are relatively long (several kilometres) suggesting relatively slow dewatering (several hours) of the low yield strength flows. The catastrophic loss of turbulence accounts for the presence of such beds in other fine‐grained systems without invoking external controls or large‐scale flow partitioning and also explains the abrupt pinch‐out of all divisions of these sandstones. Estimation of the point of flow transformation is a useful tool in the prediction of heterogeneity distribution in subsurface systems.  相似文献   

Sequence architecture and depositional evolution of the Late Miocene to quaternary northeastern shelf margin of the South China Sea     

《Marine and Petroleum Geology》2017

Based on an integrated analysis of seismic, well logging and paleontological data, the sequence architecture and depositional evolution of the northeastern shelf margin of the South China Sea since Late Miocene are documented. The slope deposits of the Late Miocene to Quaternary can be divided into two composite sequences (CS1 and CS2) bounded by regional unconformities with time spans of 3–7 Ma, and eight sequences defined by local unconformities or discontinuities with time spans of 0.8–2.3 Ma. Unconformities within CS1 feature shelf-edge channel erosion, while in CS2 they form truncations at the top of the shelf margin as prograding complexes and onlap contacts against the slope.Depositional systems recognized in the slope section include unidirectionally migrating slope channels, slope fans or aprons, shelf-edge deltas and large-scale slope clinoforms. CS1 (Late Miocene to Pliocene) is characterized by development of a series of shelf-margin channels and associated slope fan aprons. The shelf-margin channels, oriented mostly NW-SE, migrate unidirectionally northeastwards and intensively eroded almost the entire shelf-slope zone. Two types of channels have been identified: (1) broad, shallow and unconfined or partly confined outer-shelf to shelf-break channels; and (2) deeply incised and confined unidirectionally migrating slope channels. They might be formed by gravity flow erosion as bypassing channels and filled mostly with along-slope current deposits. Along the base of the shelf slope, a series of small-scale slope fans or fan aprons are identified, including three depositional paleo-geomorphological elements: (1) broad or U-shaped, unconfined erosional-depositional channels; (2) frontal splays-lobes; and (3) non-channelized sheets. CS2 (Quaternary) consists mainly of a set of high-angle clinoforms, shelf-margin deltas and lower slope unidirectionally migrating channels.The relative sea level changes reflected in the sequence architecture of the study area are basically consistent with Haq's global sea level curve, but the development of regional unconformities were apparently enhanced by tectonic uplift. The development of high-angle (thick) clinoforms in the Quaternary may be attributed to a high sediment supply rate and rapid tectonic subsidence. The formation of the unidirectionally migrating channels appears to have resulted from the combined effects of the northeastward South China Sea Warm Current (SCSWC) and downslope gravity flow. The formation of the slope channels in the outer-shelf to shelf-break zone may be predominately controlled by bottom current, whereas those developed along the middle to lower slope zone may be dominated by gravity flow.  相似文献   

Simulations of measures to control lava flows     

Eisuke Fujita  Masataka Hidaka  Akio Goto  Susumu Umino 《Bulletin of Volcanology》2009,71(4):401-408

We evaluated the quantitative effects of artificial barriers, water-cooling and guiding channels on lava flow using the lava simulation program LavaSIM. Lava flow is basically subject to the topography around the path, effusive rate and viscosity. To prevent damage due to lava flow, we conducted experiments in controlling the flow direction, velocity and temperature. The simulation demonstrated that artificial barriers can successfully change the direction of a lava flow and is more effective when placed nearly parallel to the flow direction at a point where the topography is not very steep, while a barrier placed perpendicular to the flow direction can only stop the flux temporarily, ultimately allowing the solidified crust to accumulate and causing the following mass to go over the barrier. The water-cooling trial was also effective in controlling the direction and temperature, although the amount of water was as much order as 10⁵ m³. The guiding channels successfully control the direction and inundated area but only in local areas.  相似文献   

Morphodynamics and seismostratigraphy of a deep hole at tidal channel confluence     

Silvia Susana Ginsberg  Salvador Aliotta  Guillermo O. Lizasoain   《Geomorphology》2009,104(3-4):253-261

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Analytical solution of specific energy and specific force equations: Trapezoidal and triangular channels     

Ali R. Vatankhah 《Advances in water resources》2010

The specific energy and specific force equations have many applications in open-channel flow problems. At present, these equations have analytical solution only for rectangular channels. Trial and error procedure also graphical solutions are the existing methods of solving these equations. No analytical solutions are available in the technical literature for these equations in trapezoidal and triangular channels because it is presumed that these equations are quintic equations. The inversion of such equations consists of finding the roots of quintic equations. In the current study for a given channel geometry and discharge, the subcritical (supercritical) depth is analytically found in terms of the other supercritical (subcritical) depth. For this purpose, by considering physically meaningful domains, a quintic equation has been reduced to a quartic equation. In the next step, this quartic equation has been converted to a resolvent cubic equation and two quadratic equations. This research shows these steps clearly to reach an acceptable physical analytic solution for water depth in trapezoidal and triangular channels.  相似文献   

曲流点坝沉积模式、三维构形及其非均质模型   总被引：47，自引：3，他引：44  

马世忠  杨清彦 《沉积学报》2000,18(2):241-247

通过对曲流点坝形成过程、洪水事件的水动力条件及冲淤机制分析,结合大庆长垣曲流点坝垂向层序、侧积体类型与组成、岩石相、粒度、储油物性,建立了单一侧积体横向与垂向沉积模式和点坝侧积体沉积迭式,由此建立了点坝三维构形,进而对点坝砂体内部非均质控制格架、层次性、各级实体规律性、空间形态进行研究,建立三维非均质模型。  相似文献   

A field comparison of three pressure-difference bedload samplers     

S. E. Ryan  L. S. Porth   《Geomorphology》1999,30(4):420

The movement of bedload over a cross-section is often sampled using a “pressure-difference bedload sampler”, such as the Helley–Smith. Whereas several types are in use, no one device has gained universal acceptance as the standard for use in all types of streams. Moreover, evidence suggests that similar devices may collect substantially different amounts of bedload because of only slight modifications in design. In this study, sample weights collected by three types of pressure-difference samplers are compared to determine whether differences are statistically significant or whether sampler performance is so irregular and overlapping that one might regard them as being the same. The results confirm that the weights of samples collected by the devices are significantly different. Generally, the US BLH 84 collected less material, the Sheetmetal Helley–Smith collected more material, and the Original Helley–Smith was intermediate; these tendencies were consistent at two sites where bedload was measured. The implication of these results is that measured transport rates will vary depending on the sampler used and, therefore, they are not directly comparable without some mode of calibration. To place this finding in a larger context, sediment rating curves, determined from weights of samples and measurements of flow, were integrated over available flow records and used to estimate annual yield. Three estimates of annual yield, one for each device, were then compared with measures of annual accumulation from a weir pond below one of the collection sites. The results indicate that despite differences between the devices, data obtained with pressure-difference samplers estimated annual accumulations of sediment reasonably well. Predicted accumulations were within 40–50% of the measured yield for two samplers whereas the third sampler predicted within 80%.  相似文献