Horizontal crustal movements in the United States     

Buford K. Meade 《Journal of Geodesy》1965,39(3):215-236

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Terrace aggradation during the 1978 flood on Powder River, Montana, USA     

J.A. Moody  R.H. Meade 《Geomorphology》2008,99(1-4):387-403

Flood processes no longer actively increase the planform area of terraces. Instead, lateral erosion decreases the area. However, infrequent extreme floods continue episodic aggradation of terraces surfaces. We quantify this type of evolution of terraces by an extreme flood in May 1978 on Powder River in southeastern Montana. Within an 89-km study reach of the river, we (1) determine a sediment budget for each geomorphic feature, (2) interpret the stratigraphy of the newly deposited sediment, and (3) discuss the essential role of vegetation in the depositional processes.Peak flood discharge was about 930 m³ s^− 1, which lasted about eight days. During this time, the flood transported 8.2 million tons of sediment into and 4.5 million tons out of the study reach. The masses of sediment transferred between features or eroded from one feature and redeposited on the same feature exceeded the mass transported out of the reach. The flood inundated the floodplain and some of the remnants of two terraces along the river. Lateral erosion decreased the planform area of the lower of the two terraces (~ 2.7 m above the riverbed) by 3.2% and that of the higher terrace (~ 3.5 m above the riverbed) by 4.1%. However, overbank aggradation, on average, raised the lower terrace by 0.16 m and the higher terrace by 0.063 m.Vegetation controlled the type, thickness, and stratigraphy of the aggradation on terrace surfaces. Two characteristic overbank deposits were common: coarsening-upward sequences and lee dunes. Grass caused the deposition of the coarsening-upward sequences, which had 0.02 to 0.07 m of mud at the base, and in some cases, the deposits coarsened upwards to coarse sand on the top. Lee dunes, composed of fine and very fine sand, were deposited in the wake zone downstream from the trees. The characteristic morphology of the dunes can be used to estimate some flood variables such as suspended-sediment particle size, minimum depth, and critical shear velocity. Information about depositional processes during extreme floods is rare, and therefore, the results from this study aid in interpreting the record of terrace stratigraphy along other rivers.  相似文献   

Terrestrial sensitivity to abrupt cooling recorded by aeolian activity in northwest Ohio, USA     

Melinda C. Campbell  Timothy G. Fisher  Ronald J. Goble 《Quaternary Research》2011,75(3):411-416

Lower slopes of the Sandia Mountains are characterized by granitic corestone topography and weathering-limited slopes with thin grusy colluvium and weakly developed soils. In contrast, thick soils with illuvial clay and pedogenic carbonate have developed below aplite outcrops. Aplite is resistant to chemical decomposition, but physically weathers to blocky clasts that enhance surface roughness and erosional resistance of colluvium, promoting accumulation of eolian fines. Thick B horizons on aplite slopes indicate limited erosion and prolonged periods of stability and soil development. Accretion of eolian material limits runoff and prevents attainment of a steady-state balance between soil production and downslope transport.  相似文献   

Suspended-sediment and fresh-water discharges in the Ob and Yenisey rivers, 1960–1988     

R. H. Meade  N. N. Bobrovitskaya  V. I. Babkin 《International Journal of Earth Sciences》2000,89(3):461-469

Of the world's great rivers, the Ob and Yenisey rank among the largest suppliers of fresh water and among the smallest suppliers of suspended sediment to the coastal ocean. Sediment in the middle reaches of the rivers is mobilized from bordering terraces and exchanged between channels and flood plains. Sediment in the lower reaches of these great rivers is deposited and stored (permanently, on a millennial time scale) in flood plains. Sediment discharges, already small under natural conditions, are diminished further by large manmade reservoirs that trap significant proportions of the moving solids. The long winter freeze and sudden spring breakup impose a peakedness in seasonal water runoff and sediment discharge that contrasts markedly with that in rivers of the tropics and more temperate climates. Very little sediment from the Ob and Yenisey rivers is being transported to the open waters of the Arctic Ocean under present conditions.  相似文献   

Sensitivity Analysis of the Super Heavy Rainfall Event in Henan on 20 July (2021) Using ECMWF Ensemble Forecasts     

黄绮君  葛旭阳  彭顺台  邓中仁 《热带气象学报(英文版)》2022,28(3):308-325

An unprecedented heavy rainfall event occurred in Henan Province, China, during the period of 1200 UTC 19-1200 UTC 20 July 2021 with a record of 522 mm accumulated rainfall. Zhengzhou, the capital city of Henan, received 201.9 mm of rainfall in just one hour on the day. In the present study, the sensitivity of this event to atmospheric variables is investigated using the ECMWF ensemble forecasts. The sensitivity analysis first indicates that a local YellowHuai River low vortex(YHV) in the southe...  相似文献   

Climate‐modulated sequence development in a tropical rift basin during the Late Palaeocene to Early Eocene super greenhouse Earth          下载免费PDF全文

Arpita Samanta  Melinda K. Bera  Anindya Sarkar 《Sedimentology》2016,63(4):917-939

Sequence developments in rift basins are considered to be influenced largely by tectonics and to a lesser extent by eustatic sea‐level and climate. Studies indicate that in passive margin basins, climate can mask the effects of tectonics and eustasy by modulating the sediment supply. It is, however, less understood how the sedimentary sequence in rift basins might respond to strong climatic fluctuations where tectonic pulses generate rapid accommodation space. Here a case study has been provided to assess the effect of climate vis à vis sea‐level and tectonics on sequence development in the Cambay rift basin, western India, during the Early Palaeogene (Late Palaeocene to Early Eocene) super greenhouse globe. Facies analysis of this shale–lignite sequence suggests deposition in a lagoon/bay, developed over the Deccan Trap basement. Detailed sequence stratigraphic analysis using basin‐wide representative composite sections, marker lignite seam, event bed and high‐resolution carbon isotope (δ¹³C) chemostratigraphy suggest an overall transgressive motif. Among the three prominent Early Eocene eustatic highstands, only the one at ca 53·7 Ma is expressed by the thickest coal accumulation throughout the basin. Expression of the other sequence stratigraphic surfaces is subdued and can be due to the overall finer grain size of the sediment or local variation in the subsidence rate at different fault‐controlled mini‐basins. Enigmatic presence of a maximum flooding surface coinciding with the 53·7 Ma climate event (Eocene Thermal Maximum 2), manifested by negative carbon isotope excursion, indicates possible influence of climate over and above tectonics in developing the rift sequence. Qualitative rainfall variation assessed using the magnitude of the carbon isotope excursion and pollen abundance show that a relatively dry/low precipitation climatic phase during the Eocene Thermal Maximum 2 hindered the siliclastic supply to the basin. Thus, it has been inferred that climate‐induced high siliciclastic supply possibly enhanced the autocyclic reorganization and hindered the development of the key sequence stratigraphic surfaces across the basin during climate extremes.  相似文献   

Revisiting the orogenic energy balance in the western Taiwan orogen with weak faults     

Brendan J. Meade 《地学学报》2013,25(2):160-164

Orogens at convergent margins must meet the energetic requirements necessary to lift rocks against gravity, allow for frictional sliding along basal detachments and accommodate internal deformation processes. The combination of critical taper and kinematic wedge theories predicts the partitioning between these energy sinks as a function of both fault and crustal strengths. Integrating contemporary estimates of both crustal pore fluid pressures and the coefficient of friction on major faults, we find that work associated with internal deformation processes is the dominant energy sink in the western Taiwan orogenic wedge. These processes consume 54% of the total work budget, while the dissipation rates associated with frictional sliding on the basal detachment and lifting rocks against gravity are lower, requiring only 11% and 35% respectively. These results suggest a mechanical dichotomy in orogenic wedges where the faulting dominates the kinematic deformation budget, but internal distributed deformation processes dominate the energy budget.  相似文献   

Absolute diffuse calibration of IRAC through mid-infrared and radio study of H ii regions     

Martin Cohen  Anne J. Green  Marilyn R. Meade  Brian Babler  Rémy Indebetouw  Barbara A. Whitney  Christer Watson  Mark Wolfire  Mike J. Wolff  John S. Mathis  Edward B. Churchwell 《Monthly notices of the Royal Astronomical Society》2007,374(3):979-998

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Biomimetic phosphoryl transfer catalysed by iron(II)-mineral precipitates     

Icenius I. de Zwart  Susie J. Meade  Andrew J. Pratt 《Geochimica et cosmochimica acta》2004,68(20):4093-4098

Iron(II) minerals have been found to catalyse the formation of pyrophosphate from activated phosphate compounds and inorganic phosphate at near neutral pH in water. Iron(II) phosphate catalyses the formation of pyrophosphate, from either acetyl phosphate or phosphoenolpyruvate as the activated phosphoryl donor, in yields of up to 25% and 14% respectively. Under similar conditions, these minerals also retard the hydrolysis of pyrophosphate. The catalysis of pyrophosphate formation is tolerant of sulfide ions: pyrophosphate being produced from acetyl phosphate in 12% yield in the presence of equimolar amounts of sulfide. These reactions mimic the extant biosynthesis of ATP from acetyl phosphate or phosphoenolpyruvate; they counter the concern that hydrolysis of polyphosphates would out-compete their accumulation under prebiotic conditions; and hence suggest a possible prebiotic route to polyphosphates under conditions that may have occurred on the early earth.  相似文献   

RBCA Closure at DNAPL Sites     

Joseph W. Sheahan  CPG    Roy O. Ball  P.E.  Melinda W. Hahn 《Ground Water Monitoring & Remediation》1998,18(3):78-81

The closure of sites with identified or suspected DNAPL (dense nonaqueous phase liquids) under the requirements of the Resources Conservation and Recovery Act of 1976 (RCRA), or the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) has not been well defined. With respect to RCRA, the U.S. Environmental Protection Agency (EPA) has required that all contamination must be removed at closure such that no residual risk to human health or the environment remains. Therefore, even though many states administering the RCRA program have adopted or are considering Risk-Based Corrective Action (RBCA) procedures (including the statistical methods described in SW-846) for RCRA closure, the treatment of DNAPL is, at best, challenging.
The methodology for closure in CERCLA is described in "Risk Assessment Guidelines for Super-fund (RAGS)," which requires that risks above the National Contingency Plan criteria must be remediated, preferably by on-site or in situ destruction. Most risk-based Brownfield or voluntary cleanup programs do not provide any explicit allowance for DNAPL. However, while the ASTM methodology for RBCA in E1739-95 (ASTM 1995) does not explicitly treat the problem of DNAPL, a basic framework for DNAPL assessment is implicitly provided.
A uniform methodology for RBCA closure of VOC (volatile organic compounds) DNAPL sites can be used to achieve the program objectives of RCRA, CERCLA, and Brownfield or voluntary cleanup programs. The regulatory acceptance of the application of RBCA methods to DNAPL sites will require education and discussion, but the use of a uniform methodology should facilitate acceptance.  相似文献