COMPUTER TECHNIQUES FOR THE ZONING AND CORRELATION OF WELL-LOGS*

This paper reviews computer techniques used in the automatic zoning and correlation of well-logs. Prior to correlating, well-logs are to be segmented–or ‘zoned’–so as to delineate sections that have similar properties. Techniques discussed include statistical methods such as variance tests and Student's t-test, linguistic analysis, the use of Walsh functions and spectral analysis. Well-log correlation, which may be between traces from different wells or between traces from the same hole (as in dip logs), is used in basin studies and the determination of structural dip. A variety of methods are reviewed including conventional time and frequency correlation, sequence slotting, pattern recognition and frequency analysis. Future directions for investigation are proposed.     

SUSPENDED SEDIMENT AND PARTICULATE PHOSPHORUS TRANSPORT AND DELIVERY PATHWAYS IN AN ARABLE CATCHMENT,GELBÆK STREAM,DENMARK

Reliable quantification of suspended sediment (SS) and particulate phosphorus (PP) transport, and identification of the various delivery pathways at the catchment level, is an important and necessary aid to appropriate catchment management. In this study we measured storm event, seasonal and annual losses of SS and PP from a Danish arable catchment, Gelbæk Stream, using a multisampling strategy. SS losses for the study years May 1993–April 1994 and May 1994–April 1995 ranged from 71 to 88 kg ha⁻¹, while PP losses ranged from 0·32 to 0·36 kg P ha⁻¹. In both cases losses mainly occurred during infrequent storm events. In comparison with intensive storm sampling, infrequent (fortnightly) sampling underestimated annual transport during the two study years by −24 and −331%, respectively, for SS, and by −8·6 and −151%, respectively, for PP. Reliable estimation of the transport of sediment and sediment-associated nutrients and other substances thus necessitates the use of an intensive monitoring approach. Turbidimeters proved to be a good substitute for direct measurement of SS, especially during storm events, although careful calibration is needed at the seasonal and storm event levels. Experience shows that in artificially drained and geologically complex catchments such as Gelbæk, simultaneous comparative monitoring of different sources (e.g. subsurface drainage water) is an important means of reliably discriminating between the various diffuse sources of sediment and phosphorus. Subsurface drainage water was found to account for 11–15% of the annual SS export from the catchment; the corresponding figure for PP being 11–18%. Surface runoff was only a source of SS and PP during the first study year, when it accounted for 19% of SS and 7% of PP catchment export. Stream bank/bed erosion must therefore have been the major diffuse source of SS and PP in both study years. The study also revealed that analysis of the trace element content (e.g. ¹³⁷Cs, ²¹⁰Pb) of the SS transported in subsurface drainage water and stream water during storm events is a useful means of discriminating between diffuse losses of SS delivered from topsoil and subsoil compartments. © 1997 by John Wiley & Sons, Ltd.     

The vegetation and climate of northwest Iberia over the last 14,000 years

A new pollen record from an upland lake in north-west Spain, Laguna de la Roya, spans the last ca 14,500 yrs and includes clear evidence of a Weichselian Lateglacial event correlative with the Younger Dryas. Pollen-climate response surfaces have been used to make quantitative reconstructions of palaeoclimate conditions at this and two other sites in the region. These reconstructions indicate that the climate was dry and cool during both the Late Weichselian and the Younger Dryas; in contrast, conditions during the Lateglacial Interstadial were relatively moist. During the early Holocene the climate was more continental in character than it has been for the last three millenia. Human activity has had a substantial impact upon the upland vegetation around Laguna de la Roya only during the last two millennia.     

Career Migration as Personal Biography: New Zealand Case Studies

The paper is based on autobiographical details of residential mobility for a small sample of New Zealand male career professionals collected in 1981. Classified by cohort and employment sector, the information is used to examine migration in the context of personal career development. Aspects explored include age of entry to the workforce, frequency of movement, migration and career promotion, and the spatial structure of migration. Also discussed, in conclusion, is the impact on career-related migration of the surge of national economic restructuring initiated in 1984.     

Observation bias correction with an ensemble Kalman filter

This paper considers the use of an ensemble Kalman filter to correct satellite radiance observations for state dependent biases. Our approach is to use state-space augmentation to estimate satellite biases as part of the ensemble data assimilation procedure. We illustrate our approach by applying it to a particular ensemble scheme—the local ensemble transform Kalman filter (LETKF)—to assimilate simulated biased atmospheric infrared sounder brightness temperature observations from 15 channels on the simplified parameterizations, primitive-equation dynamics (SPEEDY) model. The scheme we present successfully reduces both the observation bias and analysis error in perfect-model simulations.     

Late Wisconsinan glacial landsystems on Atlantic Canadian shelves: New evidence from multibeam and single-beam sonar data

Multibeam sonar surveys in the past decade, augmented by single-beam data from the OLEX charting system, reveal landsystems on Atlantic Canadian shelves that are diagnostic of Late Wisconsinan ice-sheet dynamics. Four landsystems are described. (1) The Bay of Fundy landsystem comprises two contrasting sets of bedforms, and is interpreted as evidence of topographically controlled fast-flowing ice adjacent to slower-moving ice. (2) The German Bank landsystem off southwest Nova Scotia is comprised of glacially fluted terrain overprinted by De Geer moraines and arcuate recessional moraines. We infer that a flow of grounded glacial ice out of the Bay of Fundy was followed by steady retreat, punctuated by at least one major re-advance. (3) The Placentia Bay landsystem consists of a convergent field of streamlined landforms with superimposed De Geer moraines, overprinted in one area by flutings. We infer that this landsystem was formed in the onset zone of fast-flowing ice, and that overprinting was due to a re-advance of ice from offshore. (4) The south coast of Newfoundland landsystem, which includes arcuate, fjord-mouth moraines and a coast-parallel, fluted moraine, indicates strong topographic control on a retreating marine ice margin as it reached a fjord coastline. These submarine glacial landsystems are not inconsistent with a conceptual model showing Late Wisconsinan ice advance to shelf edges, rapid calving retreat along deepwater channels and slower retreat of ice margins grounded in shallow water. The re-advances documented two of the study areas have parallels in the Last British Ice Sheet, confirming that the reorganization of marine-based ice sheets, caused by calving in embayments, led to internally forced re-advances.     

The Late-Devensian proglacial Lake Humber: new evidence from littoral deposits at Ferrybridge, Yorkshire, England

Proglacial Lake Humber is of UK national significance in terms of landscape drainage and development of the British Ice Sheet (BIS) during Marine Isotope Stage 2 (MIS 2), yet it is poorly understood in terms of its dynamics and timing. Sands and gravels exposed at Ferrybridge, West Yorkshire, UK, are interpreted as part of the Upper Littoral sands and gravels related to a high-level Lake Humber, which inundated the Humber Basin to ∼30 m OD during MIS 2. Excavations exposed well-rounded gravels of local origin extending downslope from the 27.5 m OD contour and interbedded sands and fine gravels, which are interpreted as the coarse littoral deposits and nearshore associated deposits. A sample from the distal sands returned an Optically Stimulated Luminescence age of 16.6±1.2 kyr, providing the first direct age for the high-level lake and for when North Sea Basin ice must have blocked the Humber Gap. An underlying sequence included a diamicton dated to after 23.3 ±1.5 kyr and before 20.5±1.2 kyr, indicating that the Late Devensian ice reached at least 15 km south of the Escrick Moraine prior to the high-level lake. Previous to both the high-level lake and this ice advance, loess found at the two sites investigated indicates a long period of loess deposition earlier in MIS 2. These new data for the history of Lake Humber are discussed in the context of ice-marginal oscillations in both the Vale of York and the North Sea Basin.