An Ipswichian fluvial deposit at Fulbeck,Lincolnshire and the chronology of the Trent terraces     

Allan Brandon  Michael G. Sumbler 《第四纪科学杂志》1988,3(2):127-133

Mammalian fossils recently discovered near Fulbeck in Lincolnshire, include abundant hippopotamus, suggesting an Ipswichian date for the Fulbeck Sand and Gravel (new name). These deposits mark a former course of the River Witham; clasts indicate derivation from outcrops of Jurassic rocks and chalky till to the south and south-east. The relationship of the Fulbeck Sand and Gravel to the terrace deposits of the River Trent necessitates a revised chronology. The Balderton Sand and Gravel (new name), laid down by the Trent along its former course to the Lincoln Gap, is shown to be older than the Ipswichian Fulbeck Sand and Gravel, and was probably deposited during the Wolstonian Stage. The Eagle Moor Sand and Gravel (new name), probably glaciofluvial outwash from the chalky tills of the region, is considerably older than the Balderton Sand and Gravel and, together with the tills, is assigned to the early part of the Wolstonian, or the Anglian glacial Stage. It is suggested that the Balderton and Eagle Moor terraces equate with the lower and upper facets of the composite Hilton Terrace of the Middle Trent.  相似文献   

The Digital National Framework and Digital Photogrammetry at Ordnance Survey   总被引：1，自引：0，他引：1  

David A. Holland  & Lynne E. Allan 《The Photogrammetric Record》2001,17(98):291-301

Over recent months the Ordnance Survey, Britain's national mapping agency, has changed the way in which it uses photogrammetry to update its large scales topographic database. The nature of the database itself has also changed during the same period, as the concept of a "Digital National Framework" has developed. This paper describes the Digital National Framework, the topographic data captured by Ordnance Survey within this framework and the capture methods currently used. The paper concentrates on the use of photogrammetry in the update process, describing the methods of the past, the methods currently in production, and the outlook for photogrammetry within the Ordnance Survey in future.  相似文献   

Hydrogeological Decision Analysis: 2. Applications to Ground-Water Contamination   总被引：3，自引：0，他引：3  

Joel Massmann  R. Allan Freeze  Leslie Smith  Tony Sperling  Bruce James 《Ground water》1991,29(4):536-548

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Hydrogeological Decision Analysis: 3. Application to Design of a Ground-Water Control System at an Open Pit Mine   总被引：1，自引：0，他引：1  

Tony Sperling  R. Allan Freeze  Joel Massmann  Leslie Smith  Bruce James 《Ground water》1992,30(3):376-389

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Hydrogeological Decision Analysis: 1. A Framework   总被引：6，自引：0，他引：6  

R. Allan Freeze  Joel Massmann  Leslie Smith  Tony Sperling  Bruce James 《Ground water》1990,28(5):738-766

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Mixing of magmas from enriched and depleted mantle sources in the northeast Pacific: West Valley segment,Juan de Fuca Ridge   总被引：1，自引：0，他引：1  

Brian L. Cousens  James F. Allan  Matthew I. Leybourne  R. L. Chase  Nancy Van Wagoner 《Contributions to Mineralogy and Petrology》1995,120(3-4):337-357

The 50 km-long West Valley segment of the northern Juan de Fuca Ridge is a young, extension-dominated spreading centre, with volcanic activity concentrated in its southern half. A suite of basalts dredged from the West Valley floor, the adjacent Heck Seamount chain, and a small near-axis cone here named Southwest Seamount, includes a spectrum of geochemical compositions ranging from highly depleted normal (N-) MORB to enriched (E-) MORB. Heck Seamount lavas have chondrite-normalized La/Sm_cn0.3, ⁸⁷Sr/⁸⁶Sr=0.70235–0.70242, and ²⁰⁶Pb/²⁰⁴Pb=18.22–18.44, requiring a source which is highly depleted in trace elements both at the time of melt generation and over geologic time. The E-MORB from Southwest Seamount have La/Sm_cn1.8, ⁸⁷Sr/⁸⁶Sr=0.70245–0.70260, and ²⁰⁶Pb/²⁰⁴Pb=18.73–19.15, indicating a more enriched source. Basalts from the West Valley floor have chemical compositions intermediate between these two end-members. As a group, West Valley basalts from a two-component mixing array in element-element and element-isotope plots which is best explained by magma mixing. Evidence for crustal-level magma mixing in some basalts includes mineral-melt chemical and isotopic disequilibrium, but mixing of melts at depth (within the mantle) may also occur. The mantle beneath the northern Juan de Fuca Ridge is modelled as a plum-pudding, with plums of enriched, amphibole-bearing peridotite floating in a depleted matrix (DM). Low degrees of melting preferentially melt the plums, initially removing only the amphibole component and producing alkaline to transitional E-MORB. Higher degrees of melting tap both the plums and the depleted matrix to yield N-MORB. The subtly different isotopic compositions of the E-MORBs compared to the N-MORBs require that any enriched component in the upper mantle was derived from a depleted source. If the enriched component crystallized from fluids with a DM source, the plums could evolve to their more evolved isotopic composition after a period of 1.5–2.0 Ga. Alternatively, the enriched component could have formed recently from fluids with a less-depleted source than DM, such as subducted oceanic crust. A third possibility is that enriched material might be dispersed as plums throughout the upper mantle, transported from depth by mantle plumes.  相似文献   

Production of lunar fragmental material by meteoroid impact     

Allan H. Marcus 《Icarus》1973,18(4):621-633

The rate of production of new fragmental lunar surface material is derived theoretically on the hypothesis that such material is excavated from a bedrock layer by meteoroid impacts. An overlaying regolith effectively shields the bedrock layer from small impacts, reducing the production rate of centimeter-sized and smaller blocks by a large factor. Logarithmic production rate curves for centimeter to meter-sized blocks are nonlinear for any regolith from centimeters to tens of meters in thickness, with small blocks relatively much less frequent for thicker (older) regoliths, suggesting the possibility of a statistical reverse bedding. Modest variations in the exponents of scaling laws for crater depth-diameter ratio and maximum block-diameter to crater diameter ratio are shown to have significant effects on the production rates. The production rate increases slowly with increasing size of the largest crater affecting the region.  相似文献   

Introduction     

Paola Malanotte-Rizzoli  Allan R. Robinson 《Deep Sea Research Part II: Topical Studies in Oceanography》1993,40(6)

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Modelling trace metal concentration distributions in estuarine waters   总被引：2，自引：1，他引：2  

Yan Wu  Roger Falconer  Binliang Lin 《Estuarine, Coastal and Shelf Science》2005,64(4):699-709

The concentration of dissolved organic carbon (DOC) was measured every few months from September 2000 through October 2001 at a coastal location in the center of Suruga Bay, Japan (34°51′N, 138°38′E). Water samples were collected three times per day (midday, night and predawn). DOC concentrations ranged from 91.3 to 45.2 μM C on the surface to 100 m depth. Diel variation in DOC concentrations, among the three sampling times, was greater in the upper 20 m, with a maximum difference of 21.7 μM C in July 2001, and reflected in diel DOC inventory variations from the surface to 50 m. Diel variations were controlled by both physical and biological factors. DOC concentrations were significantly correlated with potential density in the deeper layers (100–1000 m), indicating that the distribution of DOC concentrations in the deeper layer was mainly due to mixing. Most DOC concentrations in the upper layer (0–50 m) did not display the same relationship as in the deeper layer. Using the relationship with potential density at 100–1000 m, the DOC concentration in the upper layer, due simply to mixing, was calculated. The difference between the calculated and observed DOC was used to estimate biological contribution. The biological contributions to the DOC inventory in the upper layer (0–50 m) were found greatly in November 2000 and April 2001. This indicates that excess DOC accumulated, by biological processes, in the upper layer during these periods. In November 2000, the excess DOC in the inventory was constant throughout the sampling days (0.36–0.37 mol C m⁻²), whereas diel variations of DOC in the vertical profile were large and contrary to the variation between 10 and 20 m. This suggests that the excess DOC was contributed biologically during daytime in the uppermost layer and reached to the 50 m depth by deeper mixing. As a result, the inventory appeared to be stable over a day because of the compensating effects of DOC production and consumption throughout 50 m. In contrast, in spring and summer, there was a distinct diel inventory decrease in the nighttime, with apparent rates ranging from −0.61 to −0.35 μM C h⁻¹. It is probable that the DOC, which accumulated during the daytime, was mostly labile, with a turnover time of a few hours. The results indicate that the dynamics of diel DOC variations varied seasonally, and suggest that these variations need to be considered when estimating seasonal DOC pools in the coastal ocean.  相似文献   

Multidimensional GPR array processing using Kirchhoff migration   总被引：1，自引：0，他引：1  

Mark L. Moran  Roy J. Greenfield  Steven A. Arcone  Allan J. Delaney 《Journal of Applied Geophysics》2000,43(2-4)

We compare the ability of several practical ground-penetrating radar (GPR) array processing methods to improve signal-to-noise ratio (SNR), increase depth of signal penetration, and suppress out-of-plane arrivals for data with SNR of roughly 1. The methods include two-dimensional (2-D) monostatic, three-dimensional (3-D) monostatic, and 3-D bistatic Kirchhoff migration. The migration algorithm is modified to include the radiation pattern for interfacial dipoles. Results are discussed for synthetic and field data. The synthetic data model includes spatially coherent noise sources that yield nonstationary signal statistics like those observed in high noise GPR settings. Array results from the model data clearly indicate that resolution and noise suppression performance increases as array dimensionality increases. Using 50-MHz array data collected on a temperate glacier (Gulkana Glacier, AK), we compare 2-D and 3-D monostatic migration results. The data have low SNR and contain reflections from a complex, steeply dipping bed. We demonstrate that the glacier bed can only be accurately localized with the 3-D array. In addition, we show that the 3-D array increases SNR (relative to a 2-D array) by a factor of three.  相似文献