Early Jurassic palaeoenvironments in the Surat Basin,Australia – marine incursion into eastern Gondwana     

Andrew D. La Croix  Jianhua He  Valeria Bianchi  Jiahao Wang  Sebastian Gonzalez  Jim R. Undershultz 《Sedimentology》2020,67(1):457-485

Interpretations of palaeodepositional environments are important for reconstructing Earth history. Only a few maps showing the Jurassic depositional environments in eastern Australia currently exist. Consequently, a detailed understanding of the setting of Australia in Gondwana is lacking. Core, wireline logs, two-dimensional and three-dimensional seismic from the Precipice Sandstone and Evergreen Formation in the Surat Basin have been used to construct maps showing the evolution of depositional environments through the Early Jurassic. The results indicate the succession consists of three third-order sequences (Sequence 1 to Sequence 3) that were controlled by eustatic sea level. The lowstand systems tract in Sequence 1 comprises braidplain deposits, confined to a fairway that parallels the basin centre. The strata were initially deposited in two sub-basins, with rivers flowing in different orientations in each sub-basin. The transgressive systems tract of Sequence 1 to lowstand systems tract of Sequence 3 is dominated by fluvio–deltaic systems infilling a single merged basin centre. Finally, the transgressive and highstand systems tracts of Sequence 3 show nearshore environments depositing sediment into a shallow marine basin. In the youngest part of this interval, ironstone shoals are the most conspicuous facies, the thickness and number of which increase towards the north and east. This study interprets a corridor to the open ocean through the Clarence–Moreton Basin, or the Carpentaria and Papuan basins, evidence of which has been eroded. These results challenge a commonly held view that eastern Australia was not influenced by eustasy, and propose a more dynamic palaeogeographic setting comprising a mixture of fluvial, deltaic and shallow marine sedimentary environments. This work can be used to unravel the stratigraphic relationships between Mesozoic eastern Australian basins, or in other basins globally as an analogue for understanding the complex interplay of paralic depositional systems in data poor areas.  相似文献   

A densification mechanism to model the mechanical effect of methane hydrates in sandy sediments     

Maria De La Fuente  Jean Vaunat  Héctor Marín-Moreno 《国际地质力学数值与分析法杂志》2020,44(6):782-802

Recent pore-scale observations and geomechanical investigations suggest the lack of true cohesion in methane hydrate-bearing sediments (MHBSs) and propose that their mechanical behavior is governed by kinematic constrictions at pore-scale. This paper presents a constitutive model for MHBS, which does not rely on physical bonding between hydrate crystals and sediment grains but on the densification effect that pore invasion with hydrate has on the sediment mechanical properties. The Hydrate-CASM extends the critical state model Clay and Sand Model (CASM) by implementing the subloading surface model and introducing the densification mechanism. The model suggests that the decrease of the sediment available void volume during hydrate formation stiffens its structure and has a similar mechanical effect as the increase of sediment density. In particular, the model attributes stress-strain changes observed in MHBS to the variations in sediment available void volume with hydrate saturation and its consequent effect on isotropic yield stress and swelling line slope. The model performance is examined against published experimental data from drained triaxial tests performed at different confining stress and with distinct hydrate saturation and morphology. Overall, the simulations capture the influence of hydrate saturation in both the magnitude and trend of the stiffness, shear strength, and volumetric response of synthetic MHBS. The results are validated against those obtained from previous mechanical models for MHBS that examine the same experimental data. The Hydrate-CASM performs similarly to previous models, but its formulation only requires one hydrate-related empirical parameter to express changes in the sediment elastic stiffness with hydrate saturation.  相似文献   

The Cathedral of S. Giorgio in Ragusa Ibla (Italy): characterization of construction materials and their chromatic alteration     

Germana Barone  Mauro Francesco La Russa  Antonino Lo Giudice  Paolo Mazzoleni  Antonino Pezzino 《Environmental Geology》2008,55(3):499-504

The Cathedral of St. Giorgio in Ragusa Ibla (Sicily) is one of the most important Baroque monuments of eastern Sicily. The restoration of the monument underway has put forward notable questions regarding the stone materials used and their state of degradation. The façade appears to be made mainly of a creamy white calcarenite, and of mortars and plasters. However, detailed analysis has highlighted a more complex use of the raw material. The mortar and plaster have a different composition in regards to their architectural use while the natural stone material is distinguished not only by a creamy-white calcarenite but also by a dark coloured bituminous calcarenite (pitch rock), which now appears whiter because of superficial chromatic alterations. This process was reproduced in the laboratory using an accelerated aging technique on samples of bituminous calcarenite, which allowed the cause of the alternation to be identified as photo-oxidation of the asphaltenes. Following this process of photo-oxidation, other forms of chromatic alterations affected the façade (brown–orange-coloured patinas). FTIR, Scanning Electron Microscope and thin section microscopic observation allowed the characterization of also the products of this process to be carried out, highlighting the complex mechanism which the processes underwent.  相似文献   

非均匀下垫面局地气候效应的数值模拟   总被引：18，自引：24，他引：18  

高艳红  吕世华 《高原气象》2001,20(4):354-361

使用美国NCAR非静力平衡模式MM 5V3,模拟了黑河地区非均匀下垫面局地小气候效应 ,再现了山谷风环流及夏季“绿洲效应”、沙漠上的“逆湿”和由于地表热力分布不均匀引起的绿洲—沙漠垂直环流等绿洲—沙漠相互作用的典型特征 ,较全面地揭示了非均匀地表大气边界层内的风、温、湿度场与陆面相互作用的物理机理 ,验证了野外实验的结果  相似文献   

西藏高原夏季降水对ENSO的响应   总被引：3，自引：0，他引：3  

周顺武  假拉等 《南京气象学院学报》2001,24(4):570-575

通过合成分析指出包括雅藏布江中西段在内的西藏高原中西部地区夏季（6－8月）降水在ENSO的不同位相期间存在着显著的差异。利用交叉谱和奇异值分解等方法，分析了高原夏季降水场与太平洋海温场在时间和空间上的联系，结果表明，ENSO的暖（冷）位相期，高原大部分地区夏季降水以偏少（多）为主。  相似文献   

The geomagenetic storm effect in the middle atmosphere — First results     

Jan Laštovička 《Studia Geophysica et Geodaetica》1991,35(2):100-108

Summary Geomagnetic storms belong to the most important phenomena of solar origin which affect the ionosphere and atmosphere. We study the responses of the lower ionosphere, middle stratospheric ozone, total ozone and the troposphere (vorticity area index at 500 hPa) to isolated and major geomagnetic storms. The expected positive effect is observed in the lower ionosphere. No observable effect is detected in the middle stratospheric ozone. An effect (not very significant) can be found in the total ozone and the troposphere.Contribution No, 109/90, Geophysical Institute, Czechosl. Acad. Sci., Prague.  相似文献   

Nitric oxide density measurements at middle latitudes     

G. A. Tuchkov  A. M. Zadorozhny  Jan Laštovička 《Studia Geophysica et Geodaetica》1990,34(3):261-268

Summary The measurements of nitric oxide density were made by the photoionization method at 30–90km in several rocket flights near Volgograd. TheseNO densities are well within the range of other measurements below 60km, but become rather high above 70km. The upper mesosphericNO densities estimated by two different methods from ionospheric data in Central Europe (50 °N) are rather high, as well. The appropriateNO densities in the upper mesosphere still seem to be an open question.  相似文献   

Complementary Investigative Techniques for Site Assessment with Low-Level Contaminants     

Mark E. Byrnes  R. Wayne Nelson  Robert G. La  Poe  Dennis E. Lundquist  William McNeill 《Ground Water Monitoring & Remediation》1990,10(4):90-95

A remedial investigation (RI) was performed in an area downgradient from an abandoned missile silo at Vandenberg Air Force Base, California, as part of the United States Air Force Installation Restoration Program (IRP). A number of complementary investigative techniques were used to assure a reliable assessment of site contamination. These included the review of aerial photographs, the use of an organic vapor analyzer (OVA) and carbon adsorption/mass spectrometer (MS) method to conduct a soil-gas survey; magnetic and electromagnetic geophysical surveys; bedrock permeability testing; and the chemical analysis of soil, sediment, surface water, and ground water samples. The results from this investigation revealed the presence of an undocumented landfill and a small trichloroethylene plume in ground water at concentrations ranging from 6.7 ppb to 31 ppb. The investigation also identified local ground water flow direction, provided strong evidence of the location of potential sources of contamination, and defined the downgradient extent of ground water contamination. Because the identified contaminants have not as yet reached the environmentally sensitive wetland at the base of the slope below this facility, there is still time to propose remedial alternatives that would serve to protect this environmentally sensitive area.  相似文献   

Tithonian age of dinosaur fossils in central Patagonian,Chile: U–Pb SHRIMP geochronology     

Manuel Suárez  Rita De La Cruz  Mark Fanning  Fernando Novas  Leonardo Salgado 《International Journal of Earth Sciences》2016,105(8):2273-2284

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Diel feeding of the transparent goby Aphia minuta (Pisces,Gobiidae) in the Northwestern Adriatic Sea in spring time          下载免费PDF全文

Valentina Tirelli  Sara Legovini  Diego Borme  Elena Di Poi  Mario La Mesa 《Marine Ecology》2016,37(4):920-926

The present study provides the first estimate of the daily ration for a goby species in the Mediterranean Sea, using a new approach to determine the mass of fish stomach contents through the sum of individual prey dry mass derived indirectly from prey size. Diel feeding activity and daily ration of the pelagic goby Aphia minuta were studied under natural conditions in the coastal waters off Comacchio (Northwestern Adriatic Sea) during the spring season. A total of 318 individuals of A. minuta, collected by 14 trawls carried out on 4 consecutive days, was examined for gut contents. The diel pattern of the vacuity index and the stomach fullness index indicated that A. minuta has nocturnal feeding behaviour. The daily ration, computed over a period of 16 h, was equivalent to 2.23% wet body mass.  相似文献