The deglaciation of Arfon and Southern Anglesey, and the Origin of the Menai Straits

Embleton, Clifford

doi:10.1016/s0016-7878(64)80020-1

Cited by 14 publications

(10 citation statements)

References 7 publications

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“…1). These drainage networks, and the form of the Strait itself, led to interpretations of pre-glacial fluvial erosion of the Dinorwic Fault contributing to the evolution of the Strait, subsequently modified by glacial erosion and deposition (Ramsay, 1876;Edwards, 1904;Greenly, 1919;Embleton, 1964).…”

Section: Regional Context and Previous Workmentioning

confidence: 99%

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Late Devensian and Holocene relative sea‐level change in North Wales, UK

Roberts

Scourse

Bennell

et al. 2011

J Quaternary Science

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Deglacial sea-level index points defining relative sea-level (RSL) change are critical for testing glacial isostatic adjustment (GIA) model output. Only a few observations are available from North Wales and until recently these provided a poor fit to GIA model output for the British-Irish Ice Sheet. We present results of an integrated offshore geophysical (seismic reflection), coring (drilling rig), sedimentological, micropalaeontological (foraminifera), biostratigraphical (palynology) and geochronological (AMS 14 C) investigation into a sequence of multiple peat/organic sediment horizons interbedded within a thick estuarine-marine sequence of minerogenic clay-silts to silty sands from the NE Menai Strait, North Wales. Ten new sea-level index points and nine new limiting dates from the Devensian Late-glacial and early Holocene are integrated with twelve pre-existing Holocene sea-level index points and one limiting point from North Wales to generate a regional RSL record. This record is similar to the most recent GIA predictions for North Wales RSL change, supporting either greater ice load and later deglaciation than in the GIA predictions generated before 2004, or a modified eustatic function. There is no evidence for a mid-Holocene highstand. Tidally corrected RSL data indicate initial breaching of the Menai Strait between 8.8 and 8.4 ka BP to form a tidal causeway, with final submergence between 5.8 and 4.6 ka BP. Final breaching converted the NE Menai Strait from a flood-dominated estuary into a high energy ebb tidal delta with extensive tidal scouring of pre-existing Late-glacial and Holocene sequences. The study confirms the value of utilising offshore drilling/coring technology to recover sea-level records which relate to intervals when rates of both eustatic and isostatic change were at their greatest, and therefore of most value for constraining GIA models.

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Section: Regional Context and Previous Workmentioning

confidence: 99%

“…The evidence presented here is consistent with the notion that the NE Menai Strait was, until breaching, an estuary (cf. Embleton, 1964). Characterised by a meso-to macrotidal regime (Uehara et al, 2006), and by analogy with existing Welsh estuaries (cf.…”

Section: Hydro-and Sedimentary Dynamics In the Menai Straitmentioning

confidence: 99%

Late Devensian and Holocene relative sea‐level change in North Wales, UK

Roberts

Scourse

Bennell

et al. 2011

J Quaternary Science

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“…Glacial depositional landforms record Irish Sea ice recession from the Clwydian Range (e.g. Brown and Cooke, 1977;Embleton, 1957Embleton, , 1961Embleton, , 1964. The glacial features of the Wheeler Valley have received attention from various researchers, early reconstructions indicating the presence of a glacial lake (Embleton, 1957;Peake, 1961).…”

Section: North Walesmentioning

confidence: 99%

The last British Ice Sheet: A review of the evidence utilised in the compilation of the Glacial Map of Britain

Evans

Clark

Mitchell

2005

Earth-Science Reviews

126

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This paper reviews the evidence presently available (as at December 2003) in an effort to stimulate further research on the last British Ice Sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology. The wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions. Landforms interpreted as being of unequivocal ice-marginal origin (moraines, ice-contact glacifluvial landforms and lateral meltwater channels) and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice-sheet margins throughout the last glacial cycle. Subglacial landforms (drumlins, flutings and eskers) have been used to demarcate former flow patterns within the ice sheet. The compilation of evidence in a regional map is crucial to any future reconstructions of palaeo-ice sheet dynamics and will provide a clearer understanding of ice sheet configuration, ice divide migration and ice thickness and coverage for the British Ice Sheet as it evolved through the last glacial cycle.2

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“…1) is a narrow, shallow sea strait separating the Isle of Anglesey from the North Wales mainland. It occupies a composite valley, which was submerged following deglaciation (Embleton, 1964). It is orientated southwest to northeast, has a minimum width of about 300 m, a maximum width of about 2 km, and a length of 20 km.…”

Section: Menai Strait North Walesmentioning

confidence: 99%

Springs–neaps cycles in daily total seabed light: Daylength-induced changes

Roberts

Bowers

Davies

2014

Journal of Marine Systems

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In shallow, tidal seas, daily total seabed light is determined largely by the interaction of the solar elevation cycle, the tidal cycle in water depth, and any temporal variability in turbidity. Since tidal range, times of low water, and often turbidity vary in regular ways over the springs-neaps cycle, daily total seabed light exhibits cycles of the same periodicity. Corresponding cycles are likely to be induced in the daily total primary production of benthic algae and plants, particularly those light-limited specimens occupying the lower reaches of a sub-tidal population. Consequently, this effect is an important control on the growth patterns, depth distribution and survival of, for example, macroalgal forests and seagrass meadows. Seasonal changes in daylength exert an important additional control on these cycles, as they alter the fraction of the tidal and turbidity cycles occurring within daylight hours. Bowers et al. (1997) modelled this phenomenon numerically and predicted that for a site with low water at about midday and midnight at neaps tides, 6 am and 6 pm at springs, daily total seabed light peaks at neaps in winter, but the 'sense' of the cycle 'switches' so that it peaks at springs in summer -the longer daylength permits the morning and evening low water springs to contribute substantially to the daily total. Observations for such a site in North Wales (UK), presented in this paper, show that no such 'switch' occurs, and neaps tides host the largest daily totals throughout the year. The predicted 'switch' is not observed because turbidity increases generally at spring tides, and specifically at low water springs, both of which were not accounted for in the model. Observations at a second site in Brittany (France), diametrically opposite in terms of the times of low water at neaps and at springs, indicate a peak at springs throughout the year. Analytical tools are developed to calculate the percentage of daily total sea surface irradiance reaching the bed at a site of interest on any given day, and to determine the sense of any springs-neaps cycle thereof for a given season. The conditions required for a 'switch' are explored graphically, resulting in the identification of criteria (and a useful parameter) for predicting their occurrence. Consequences for the growth patterns, depth limits and longterm survival of benthic algae and plants are discussed.

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The deglaciation of Arfon and Southern Anglesey, and the Origin of the Menai Straits

Cited by 14 publications

References 7 publications

Late Devensian and Holocene relative sea‐level change in North Wales, UK

Late Devensian and Holocene relative sea‐level change in North Wales, UK

The last British Ice Sheet: A review of the evidence utilised in the compilation of the Glacial Map of Britain

Springs–neaps cycles in daily total seabed light: Daylength-induced changes

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