Quaternary stratigraphy of the fladen area,central North Sea: A multidisciplinary study     

H. P. Sejrup  I. Aarseth  K. L. Ellingsen  E. Reither  E. Jansen  R. Lvlie  A. Bent  J. Brigham-Grette  E. Larsen  M. Stoker 《第四纪科学杂志》1987,2(1):35-58

Based on detailed stratigraphic investigations on a 200.6m long core (BGS borehole No. 81/26) from the Fladen Ground area (British sector), core material from the Sleipner field (Norwegian sector) and shallow seismic profiles between the core-sites, the following conclusions are drawn: (1) The North Sea was glaciated sometime during th elaterpart of Matuyama reversed period. A complete glacial-interglacial-glacial cycle is recorded in these sediments. (2) In a period of marine sedimentation in the Middle Pleistocene, a transgression-regression cycle under boreal-arctic regime is recorded. (3) The Fladen area has subsided between 0.9 and 0.6 m/ka through the later parts of the Quaternary (4) A major glacial event dated at between 130 and 200 ka is recorded as a thick till unit in 81/26. This till, which was deposited by ice moving from the southwest (Scotland), probably represents a period when the Scandinavian and British ice sheets coalesced in the North Sea. (5) Based on the seismic data and the stratigraphy of the Sleipner core, an ice-free, open embayment/dry land is favoured for the central North Sea during the Late Weichselian. (6) From the amino-acid data, it is shown that there has been an episodic style of sedimentation through the Quaternary. (7) of the investigated sediments (which span the last 1 mill. year) ca 98% have been deposited under arctic to boreal-arctic conditions.  相似文献   

Improving Groundwater Model Calibration with Repeat Microgravity Measurements     

Jeffrey R. Kennedy  Libby Wildermuth  Jacob E. Knight  Joshua Larsen 《Ground water》2022,60(3):393-403

Groundwater-flow models depend on hydraulic head and flux observations for evaluation and calibration. A different type of observation—change in storage measured using repeat microgravity—can also be used for parameter estimation by simulating the expected change in gravity from a groundwater model and including the observation misfit in the objective function. The method is demonstrated using new software linked to MODFLOW input and output files and field data from the vicinity of the All American Canal in southeast California, USA. Over a 10-year period following lining of the previously highly permeable canal with concrete, gravity decreased by over 100 μGal (equivalent to about 2.5 m of free-standing water) at some locations as seepage decreased and the remnant groundwater mound dissipated into the aquifer or was removed by groundwater pumping. Simulated gravity from a MODFLOW model closely matched observations, and repeat microgravity data proved useful for constraining both hydraulic conductivity and specific yield estimates. Specific yield estimated using the infinite-horizontal slab approximation agreed well with model-derived values, and the departure from the linear, flat-water-table approximation was small, less than 2%, despite relatively large and dynamic water-table slope. First-order second-moment parameter uncertainty analysis shows reduction in uncertainty for all hydraulic conductivity and specific yield parameter estimates with the addition of repeat microgravity data, as compared to drawdown data alone.  相似文献   

Correction: Geochemical and isotopic evidence for upward flow of saline fluid to the Mississippi River Valley alluvial aquifer,southeastern Arkansas,USA     

Larsen  Daniel  Paul  Justin  Cox  Randy 《Hydrogeology Journal》2021,29(4):1691-1691

Hydrogeology Journal - A Correction to this paper has been published: https://doi.org/10.1007/s10040-021-02350-y  相似文献   

Geosciences of the Himalaya–Karakoram–Tibet orogen     

Soumyajit Mukherjee  Barun Kumar Mukherjee  Rasmus C. Thiede 《International Journal of Earth Sciences》2013,102(7):1757-1758

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A Review of “Collaborative Land Use Management: The Quieter Revolution in Place-Based Planning”     

Soren Larsen 《The Professional geographer》2013,65(1):128-129

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Resolving the source and mixing proportions of modern leakage to the Memphis aquifer in a municipal well field using geochemical and ³H/³He data, Memphis, Tennessee, USA     

John Koban  Daniel Larsen  Stephanie Ivey 《Environmental Earth Sciences》2012,66(1):295-310

The Memphis aquifer in southwestern Tennessee is a confined to semi-confined unconsolidated sand aquifer and is the primary municipal water source for the Memphis metropolitan area. Leakage of modern water from shallow unconfined aquifers through the upper Claiborne confining unit locally degrades water quality in the Memphis aquifer and makes the aquifer more vulnerable to contamination. Major solute chemistry, tritium, and ³H/³He data were used to investigate the source and mixing proportions of modern water in the Memphis aquifer in the Davis well field, Memphis, Tennessee. Water quality in several production wells in the Davis well field has declined over the past 30 years, mainly through increased total dissolved solids, iron, alkalinity, and hardness. Trends in chemical data, tritium, and other hydrogeologic data support a source for the leakage from the Mississippi River Valley Alluvial aquifer. Mixing proportions of alluvial water in production well water obtained by inverse chemical modeling with PHREEQCi range from 7 to 45%. For two of the production wells, MLGW 414 and 432, ³H/³He data yield mixing ratios similar to those obtained from PHREEQCi in three of four cases; the dissimilar ratio is likely due to a poor solution from the PHREEQCi inverse modeling. Modeling of the age distribution obtained from MLGW 414 and 432 using an exponential-piston flow model (EPM) with an inverse solution computer code yielded mixed results. The EPM solution obtained for MLGW 414 converged with difficulty only for a 5-year transit time in the shallow aquifer and is consistent with a source from the Mississippi River Valley Alluvial aquifer; however, the modeled age of the water is greater than that observed. In comparison, the EPM solution for MLGW 432 converged for the 5- and 7-year transit periods in the shallow aquifer and yielded model ages consistent with observed ³H/³He ages; however, the extent of the maximum radii for infiltration source is not consistent with a Mississippi River Valley Alluvial aquifer source. Other potential sources for leakage to MLGW 432 include water from the Fluvial-terrace aquifer migrating along a fault east of the well field or infiltration of water from a lake south of the well field.  相似文献   

Conducting sensitive research in the present and past tense: Recounting the stories of current and former child domestic workers     

Natascha Klocker 《Geoforum》2012,43(5):894-904

In recent years, scholarship on children’s work has increasingly incorporated the perspectives of working children. Although laudable, this shift toward children’s inclusion in research has concentrated on those employed at the time of data collection. Former child workers have largely been overlooked as a source of information. This paper reflects on research conducted with current and former child domestic workers in Tanzania. The child domestic working experiences reported by those two groups diverged markedly: those who had already ceased employment reported far higher rates of dissatisfaction with child domestic work, and far more experiences of exploitation and abuse, than those who were still employed in the sector. This paper explores issues of memory, identity, representation and performance to propose explanations for such dissonance. It concludes that the (near) exclusive focus of the literature on children who are currently employed is of some considerable concern, as scholars often make practical and policy-oriented recommendations about children’s work on the basis of their findings. This paper makes a case that all ‘versions’ of a phenomenon offer (at best) partial insights into lived experiences and that researchers investigating sensitive issues, whether with adults or children, may benefit from conducting research in both the past and present tense.  相似文献   

Assessing auroral electric field variance with coherent and incoherent scatter radar     

D.L. Hysell  G. Michhue  M.J. Nicolls  C.J. Heinselman  M.F. Larsen 《Journal of Atmospheric and Solar》2009,71(6-7):697-707

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Shoreline trajectories on a glacially influenced stable margin – insight from the Barents Sea Shelf, NW Russia     

Maria A. Jensen  Eiliv Larsen 《Basin Research》2009,21(5):759-779

This study describes shoreline migration paths for late Quaternary sediments on the inner Barents Sea shelf between Kola and the Pechora Sea. The depositional geometries provide an example of stratigraphical architecture in a glacially influenced basin prone to isostatic movements as well as rapid and high-amplitude changes in eustatic sea level. The depositional geometries reflect asymmetrical relative sea level changes characterised by marine inundation upon deglaciation and prolonged forced regressions. Thus, all deposition occurs during the falling stage and lowstand systems tracts. The transgressive and highstand systems tracts are lacking and the maximum landward position of the shoreline is coinciding with the basal surface of forced regression. Shoreline migration is dominated by downward and seaward trajectories, but aggradation occurs on the falling limb of the relative sea level curve due to superimposed eustatic cycles of lower hierarchical order. Fluvial aggradation behind the shoreline takes place during the lowstand systems tract, but is also linked to high sediment supply and may also respond to superimposed lower order sea level fluctuations. Lateral variations in isostatic load due to asynchronous ice advances lead to regional variations in shoreline trajectories. Significant differences in sea level history exist across former ice margins leading to time-transgressive and laterally discontinuous stratigraphical surfaces. Sequence boundaries are not only diachronous along the depositional profile, but also laterally, and basal surfaces of forced regression are strongly diachronous across former ice margins. Absolute age control allows for estimates of the time differences along significant stratigraphical surfaces.  相似文献   

Distribution and transport of sedimentary trace metals in the tidal portions of the Kennebec/Androscoggin River system, Maine, USA     

Peter Foster Larsen  Henri E. Gaudette 《Marine pollution bulletin》2010,60(8):1325-1335

Previous investigations suggest that contaminant transport from the large Kennebec/Androscoggin watershed is an important large-scale process in mid-coast Maine. To investigate this phenomenon, we determined the concentrations of Cd, Cr, Cu, Ni, Pb, Sn and Zn in the surface sediments of 47 stations in the tidal Kennebec/Androscoggin system. Most stations exhibited elevated metal concentrations. Highest levels were found in the main stem of the system. Distribution patterns lead to the conclusion that metals enter the system from the watershed and are transported to the nearshore Gulf of Maine. The coarse-grained, ebb tide dominated flow prevents the accumulation of contaminants in the estuary. This supports the hypothesis of Larsen and Gaudette (1995) that the Kennebec and Androscoggin watersheds are sources for contaminants observed in the nearshore Gulf of Maine.  相似文献