J.J.M. van der Meer

Till and moraine emplacement in a deforming bed surge — an example from a marine environment

The glacier Sefstrombreen in Spitsbergen surged across an arm of the sea between QSR 1882 and 1886 and rode up onto the island Coraholmen. Marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location, transported, and smeared over the sea bed and ~ Coraholmen as a deformation till. The glacier emplaced about 210Sm ~ (0.2 km 3) of drift in the terminal 2 km of its advance in a maximum of 14 years, leaving a thickness of up to 20 m on Coraholmen, which was doubled in size as a result. ~ During the surge, subglacial muds were characterised by high water pressures, low effective pressures and low frictional resistance to glacier movement. Original sedimentary inhomogenities permit fold structures to be identified, but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills. The surge was probably shortlived, and as the heavily crevassed glacier stagnated, underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface. Reticulate crevasse-intrusion ridges on Coraholmen and the sea floor reflect the orientation of surge generated crevasses. Water and sediment was also extruded beyond the glacier at its maximum extent, to form extensive flows producing till tongues both on Coraholmen and the sea floor extending over 1.3 km from the glacier. It is argued that subglacial deformation of pre-existing sediment will almost invariably be associated with glaciation of marine areas and that this process will not only produce deformation tills through remoulding of pre-existing sediments, but will also play a fundamental role in glacier dynamics. Criteria which perrait glacial tills produced by such events from marine and glaciomarine muds are discussed. Copyright

THE SEDIMENTARY AND STRUCTURAL EVOLUTION OF A RECENT PUSH MORAINE COMPLEX : HOLMSTROMBREEN, SPITSBERGEN

Abstract The glacier Holmstrombreen, in Spitsbergen, surged into the ice contact scarp of a proglacial outwash sequence at some time during its Neoglacial maximum. The outwash sediments were pushed along a decollement to produce a moraine in which deformation extended for 1.5xa0km beyond the furthest extent of the glacier front. The style of folding and faulting and the nature of the pre-, syn- and post-tectonic sedimentary sequence across the whole push moraine is described from a continuously exposed section of the push moraine which extends from its proximal to distal extremities. The precise extent of incremental compressive shortening of the pushed sediments, of some 900xa0m, is established. The depth to the underlying decollement is inferred to be an average of about 30xa0m, indicating that stresses and movement were transmitted through a thin nappe with an aspect ratio of about 1 in 30. It is suggested that this nappe was frozen and that an artesian water pressure head of 60xa0m immediately beneath it reduced friction along its base to a very low value. It is calculated that a glacially generated force of about 1.5×10 7 xa0kN was responsible for pushing the sediment nappe. The nature of the glacially controlled groundwater flow system rather than the magnitude of longitudinal forces generated by the glacier is the principle determinant of large-scale push moraine characteristics. The changing ice topography produced by the pushing event during the surge and in the post-surge decay had a major influence on the evolution of the meltwater drainage system and the style of fluvial sedimentation. The structure, sedimentary architecture and evolution of the whole glacitectonic/fluvial complex can best be understood by considering the impact of the surge on a complete outwash system. It is suggested that the setting and processes which produced the Holmstrombreen push moraine could account for many broad, multi-ridge and fold push moraines which formed proglacially, and that the thickness of original sediments above the decollement can be a guide to the thickness of contemporary permafrost.

CLASTIC DYKES IN OVER-CONSOLIDATED TILLS : EVIDENCE FOR SUBGLACIAL HYDROFRACTURING AT KILLINEY BAY, EASTERN IRELAND

Abstract A swarm of vertical gravel-filled dykes up to 6 m high and several decimetres wide, cut through an over-consolidated till at Killiney Bay. The dykes are rooted in a gravel layer and many display plumes of clastic debris ejected into the overlying sediments — `burst-out structures. Such features have not previously been described. These clastic dykes are interpreted as the infillings of hydrofractures which formed when water pressures in the basal gravel layer exceeded the overburden pressure and tensile shear strength of the capping till. The burst-out structures extend up to 7 m from the tops of the dykes and provide strong evidence for forceful upward flow. Evidence suggests that the hydrofractures formed subglacially, probably during a minor re-advance. Their presence in Late Devensian (26–13 ka BP) tills with an Irish Sea provenance (`Irish Sea till) may have important implications for the subglacial hydrology of the last Irish Sea ice sheet. These hydrofractures cannot form in unconsolidated glacimarine sediment and their presence precludes a glacimarine origin for these deposits. They greatly affect the geotechnical properties of Irish Sea tills, in particular providing very permeable routes through otherwise impermeable layers, with important consequences in situations elsewhere in the Irish Sea basin, where they have been used as aquicludes in landfill and low-level nuclear waste disposal sites.

A comparison of internal mammary artery and saphenous vein grafts after coronary artery bypass surgery. No difference in 1-year occlusion rates and clinical outcome. CABADAS Research Group of the Interuniversity Cardiology Institute of The Netherlands.

BACKGROUNDnSuperior patency rates for internal mammary artery (IMA) grafts compared with vein coronary bypass grafts have been demonstrated by retrospective studies. This difference may have been affected by selection bias of patients and coronary arteries for IMA grafting.nnnMETHODS AND RESULTSnTo estimate the difference between IMA and vein grafts, we analyzed graft patency data of 912 patients who entered a randomized clinical drug trial. In this trial, 494 patients received both IMA and vein grafts (group 1) and 418 only vein grafts (group 2). Occlusion rates of IMA grafts and IMA plus vein grafts in group 1 were compared with those of vein grafts in group 2. Multivariate analysis was used to compare occlusion rates of IMA and vein grafts while other variables related to graft patency were controlled for. In addition, 1-year clinical outcome was assessed by the incidence of myocardial infarction, thrombosis, major bleeding, and death. Occlusion rates of distal anastomoses in group 1 versus group 2 were 5.4% (IMA grafts) versus 12.7% (vein grafts) (P < .0001) and 10.4% (IMA plus vein grafts) versus 12.7% (vein grafts) (P = .14). There was no difference in adjusted risk of occlusion between IMA grafts and vein grafts (P = .089). Type and location of distal anastomosis and lumen diameter of the grafted coronary artery were shown to be predictors of occlusion. Clinical events occurred in 17.8% (group 1) and 16.0% (group 2) of patients (P = .53).nnnCONCLUSIONSnThe observed difference in 1-year occlusion rates between IMA and vein grafts can be explained by a maldistribution of graft characteristics by selection of coronary arteries for IMA grafting rather than being ascribed to graft material. One-year clinical outcome is not improved by IMA grafting.

Identification of the incubation product of Boucher's renin activity assay, by means of radioimmunoassays for angiotensin I and angiotensin II, and a converting enzyme preparation from lung tissue

Abstract Renin activity can be determined by measuring the quantity of angiotensin generated during incubation of plasma under standard conditions. The angiotensin can be protected from enzymatic breakdown by adsorption onto a cation exchange resin added to the plasma (Boucher method). Till now, it has been assumed that the decapeptide angiotensin I (A I) was converted during this incubation by “converting enzyme” into the octapeptide angiotensin II (A II). With a radioimmunoassay for A II, which does not measure A I, no angiotensin was detectable after the Boucher procedure. The possible explanation that A I rather than A II is the product of the incubation was investigated. From lung, a converting enzyme preparation was made, which converted synthetic A I to a high degree into A II. After treatment with this preparation the product of the Boucher procedure could be measured with the A II immunoassay. Without this enzymatic treatment generation of angiotensin was only detectable with a radioimmunoassay for A I. Obviously, A I rather than A II is the product of the renin activity in the Boucher procedure. Therefore renin activity can be measured adequately with a radioimmunoassay for A I.

Measurement of renin activity in plasma by a radio-immunoassay for angiotensin I

Abstract In plasma, incubated in the presence of a cation exchange resin, the decapeptide angiotensin I is the final product of the enzymatic action of renin. The quantity of the generated peptide can be measured properly with a radioimmunoassay for angiotensin I, provided that factors present in plasma, which do interfere in the immunoassay, are eliminated. After incubation according to the Boucher method, a purification procedure is applied, which removes the disturbing material by alcohol precipitation. With the method described, adequate measurement is possible of the incubation product of renin in plasma by means of a radioimmunoassay. Recovery of angiotensin I added to plasma before incubation is 80–90%.

Solid-state ion-selective electrodes as end-point detectors in ompleximetric titrations: Part I. The titration of mixtures of two metals

Abstract The compleximetric titration of mixtures of copper(II) and other metal ions by means of potentiometric indication with a copper(II)-selectivc electrode has been investigated. The theoretical titration curves have been calculated, the effects or the selectivity of the electrode and the limit of detection of the electrode being taken into account. The experimental curves generally agree very well with the theoretical curves. Determinations in the range 10-3–10-5M are possible

Solid-state ion-selective electrodes as end-point detectors in compleximetric titrations

Abstract The determination of several metal ions in the concentration range 10 -2 –10 -5 M by means of compleximetric back-titrations with a copper(II)-selective indicator electrode is described. The ligand, in most cases EDTA, is added in excess, which is then back-titrated with copper(II). There is good agreement between the theoretical and experimental titration curves.

The micro determination of copper(II) with a solid-state copper-selective electrode

Abstract The standard addition and standard subtraction methods are discussed briefly. Both methods are applied to the determination of copper(II) in very small sample volumes. A microcell (25 μl) and a copper-selective micro-electrode are described for this purpose; a nanoliter burette was constructed for the addition of very small increments. The results are compared with those obtained in a 10-ml cell.

Solid-state ion-selective electrodes as end-point detectors in compleximetric titrations : Part III. Selection of some experimental conditions for back-titrations in alkaline medium

Abstract The applicability of the copper(II) solid-state electrode in alkaline medium for compleximetric back-titrations of the alkaline-earth metals with EDTA and EGTA has been studied. Copper(II) is used as the back-titrant. Special attention is given to the use of ammonia and cyclohexylamine as the buffer substance.