Jack Jarvis

Dispersal of glacially derived sediment over part of the continental shelf of south Iceland and the geometry of the resultant sediment bodies

Abstract The southern continental shelf of Iceland is crossed by a series of troughs 200–300 m below sea level with intervening banks 100–120 m below sea level. The troughs were eroded by the Pleistocene ancestors of the large valley glaciers which descend from the Vatnajokull ice cap. A study of sedimentation and sediment history in one such trough, its flanking banks and the adjacent coastal belt is presented. Coarse sediments discharged from the glaciers have built out as a massive coastal sediment wedge which has filled up the mouth of an earlier fjord, of which the shelf trough is an extension. Strong bottom currents across the flanking banks transport sand to depths of 140 m. The proximal part of the trough is infilled by muddy sediments derived from gravity flows down the face of the coastal sediment wedge and by sediment transported over the bank to the west. The trough infill is strongly asymmetric, being banked up against the western flank of the trough. Deep turbidite channels occur in the middle part of the trough and on its flanks. Strong bottom currents over the shelf edge have denuded the outer part of the trough of sediments. A Pleistocene phase of sedimentation on the shelf is represented by very thick till accumulations on the banks. A major moraine which extends across the inner part of the trough reflects a phase of glacier stillstand during the last retreat of ice across the shelf, and forms a dam behind which debris-flow sediments derived from the coastal sediment wedge have accumulated.

Middle Devensian ice-proximal gravels at Howe of Byth, Grampian Region

Synopsis Ice-proximal glaciofluvial gravels at Howe of Byth, Grampian Region, have given luminescence ages of 45 ± 4 and 37±4 ka BP. The gravels were laid down by meltwater draining from an ice margin in the Moray Firth and provide the first firm evidence of extensive glaciation in NE Scotland during the Mid Devensian.

Devensian organic interstadial deposits and ice sheet extent in Buchan, Scotland

Pre-Late Devensian organic deposits in the Buchan area of northeast Scotland were investigated for their geomorphological and palaeoecological (pollen, plant macrofossils, coleoptera) properties. Close ecological agreement exists between fossil indicators and allows the inference that the environment in the vicinity of the deposits was a dwarf shrub tundra of the type met today in high latitude areas of Scandinavia and arctic Russia. The latest in a series of radiocarbon dates from the site produced determinations beyond the limits of the method, although the geomorphological and fossil evidence appears to point to an interstadial date within Oxygen Isotope Stages 5a or 5c. The site has special significance for arguments concerning the much-debated concept of ‘Moraineless Buchan’; indeed, evidence is presented which supports the concept of extensive ice sheet glaciation during the Late Devensian for this crucial geographical area. If Buchan is to be seen as a further casualty amongst other disputed ice-free enclaves, then a return to earlier models of extensive ice sheet glaciation in the Late Devensian of Scotland would seem to be necessary.

Sediment transport in the mouth of the Eden estuary

Abstract Observations of water movement and sediment transport were made from a fixed platform at an intertidal location in the mouth of the Eden estuary. The effects of wave activity on water movement and suspended sediment fluxes were evaluated, and an empirical relationship between suspended sediment concentrations and near bed water movement is described. The circulation of water in St Andrews Bay indicates a residual movement onshore near to the bed. Onshore movement of sediment in the mouth of the estuary is indicated by suspended sediment fluxes and bedload transport (determined from bedform migration). The relative roles of suspended sediment and bedload transport are discussed. Morphological changes in the estuary mouth over the three-year survey period are relatively small and indicate a stable environment.

A multiple till sequence near Ellon, Grampian Region: T. F. Jamieson’s ‘indigo boulder clay’ re-examined

Synopsis Jamieson in 1906 described an ‘indigo boulder clay’ lying beneath younger glacial deposits in the Ellon area, Grampian Region. A pitting survey has revealed that this unit (the Pitlurg Till) lies beneath Late Devensian glacial and glacifluvial deposits (the Hatton Till and the Kippet Hills Gravels and Sands) and rests on a basal till (the Bellscamphie Till). The Pitlurg Till contains palynomorphs of Kimmeridge Clay age and shows weak northerly fabrics, suggesting ice transport from the Moray Firth. Amino acid ratios for sparse included shells indicate that the Pitlurg Till is younger than Oxygen Isotope Stage 7 and may post-date Stage 5e. The Bellscaphie Till lies beneath weathered gravels at Tillybrex and probably predates Stage 5.

A concealed Lower Cretaceous outlier at Moss of Cruden, Grampian Region

Synopsis Recent excavations at Moss of Cruden, Grampian Region, show that Lower Cretaceous sedimentary rocks pass beneath the margin of the Tertiary Buchan Ridge Gravels and are intensely weathered. These findings indicate that previous interpretations of these rocks as a glacially-transported erratic mass or masses were incorrect and that they are probably in situ. The rocks include fine-grained, glauconitic quartz-arenites with pollen of Late Hauterivian-early Barremian age. Overlying flint gravels demonstrate the presence of a former Cretaceous chalk cover and helped the preservation of this small outlier.

North-east Scotland

North-east Scotland covers the mainly lowland area between lower Strathspey and Aberdeen (Figure 8.1). Geologically, it is underlain by the same Dalradian metamorphic rocks and younger granitic intrusions as the central and south-west Highlands, and hence its lowland character indicates a distinctive geomorphological evolution. Since the early Tertiary, north-east Scotland has been a ‘hinge zone’ between the mountain zone to the west, which has been uplifted and subsequently dissected to produce spectacular mountain scenery, and the North Sea Basin, which has undergone continuing downwarping (Hall , 1987). This relative stability has resulted in the preservation of Tertiary gravel deposits and extensive areas of deeply weathered bedrock.

Morphology, sedimentary bedforms and sand transport across a ridge- and- runnel beach under the action of summer waves

As part of a collaborative study between the 3rd Institute of Oceanography, Xiamen, and the U. K. Universities of East Anglia and St. Andrews, a 4-day experiment was conducted on a ridge- and- runnel beach of north Norfolk on the North Sea coast. Detailed surveys were made of every low water of an area 10m by 30m and electromagnetic current meters were used to measure wave-induced currents over the ridge and in the runnel. The locations of bedform fields were noted, fluorescent sand was used to follow the sand movement and, at the end of the experiment, lacquer peels were taken of the top 0.2m of a vertical section through the ridge- and- runnel.During the 4 days 0.75m3 of sand per metre width of beach accreted in the runnel and a similar volume was eroded from the upper foreshore. The dominant shoreward transport, identified qualitatively by the movement of the fluorescent sand, suggests the ridge- and- runnel system migrated shorewards up the general beach slope of 1o by 2–3m. The wave orbital currents were used to predict the bedforms to be expected over the tidal cycle: an upper phase plane- bed was predicted for most of the period but vortex and rolling- grain ripples were predicted and observed when the water level over the ridge was low. As the tide dropped ripples on the ridge were eliminated by swash action but the ripples in the runnel were protected by the ridge and remained on the beach after the tide dropped.The observed accretion of the beach in the runnel and on the lee slope of the ridge was used to calculate that a net average shoreward transport of 0.11g/cm·s−1 occurred over the ridge crest during the period it was underwater. The current meter measurements of the wave orbital currents and the mean currents over the ridge crest were used with the wave- current interaction model of Grant and Madsen (1982), ripple dimensions defined by Nielsen (1981), and resuspension coefficient of Vincent and Green (1990), to compute bedload sand transport rates from the equations of Madsen and Grant (1976), Sleath (1978), and Vincent et al. (1981), and also the suspended sand transport rates. The results from one of these bedload equations (Madsen and Grant, 1976) compared well with the observed net transport. The calculated suspended load transport rates (due to steady currents alone) were a factor of 5 too great, and were also several orders of magnitude greater than suspended transport rates measured directly under similar or more energetic wave and current conditions.