Abstract
The lower reaches of the River Ure, on the flanks of the Pennine Hills in northern England, contain sedimentary and erosional landforms that are a record of fluvial activity during deglaciation and valley-glacier retreat at the end of the last (Devensian) glacial period, and in the subsequent post-glacial Holocene. Terraces and channels, most of which are now relict features well above the altitude of the present river, attest to the impacts of massive meltwater discharge and deposition of sand and gravel outwash, and dynamic river regimes with rapid incision. Through field survey, we have created a detailed geomorphological map of these landforms and glacial and fluvioglacial surface deposits, as well as the terraces and palaeochannels that were abandoned by the river due to avulsion and incision-driven course changes. We have recorded the nature of the outwash gravels, now effectively terrace features, from exposed sections in working quarries, one of which we discuss here. The palaeochannels have accumulated sediment fills and we have examined several which lie within the range of 100 and 16 m above present sea level. The results of lithostratigraphic, palynological, and radiocarbon analyses at two main and three subsidiary sites indicate that palaeochannel ages range from almost 14,000 to approximately 4000 calibrated years ago in a clear altitudinal sequence. The oldest are probably caused by rapid incision due to deglaciation-driven isostatic uplift. The similarity in date of the three downstream sites suggests that a late Holocene combination of climatic deterioration and increased human activity in the catchment caused instability and entrenchment. Pollen data from the channel fills provide relative dating, and agree well with pollen records from other regional Lateglacial and Holocene sites. Non-pollen palynomorph (NPP) analysis at one of the sites allows reconstruction of the hydrological history of channel infill. This research shows that the application of an integrated suite of research techniques can yield a highly detailed understanding of fluvial evolution and landscape history.
Highlights
The sedimentary and palaeoenvironmental records from deglaciated landscapes form an important archive that provides information regarding the timing and rate of deglaciation, and allows reconstruction of fluvial history, including the re-establishment of drainage systems and their influence on the development of the wider landscape [1,2]
The area of study lies in the Yorkshire Dales, which form the northern part of the Central Pennine hills in northern England
This paper reviews the findings of research into the fluvial and environmental history of the washland reaches of the River Ure valley from north of Masham to south of Ripon (Figure 1), work undertaken in advance of quarrying in areas scheduled for aggregate extraction, at sites which quarrying would destroy, and at sites where an exceptionally important research archive was likely to be preserved [14,15]
Summary
The sedimentary and palaeoenvironmental records from deglaciated landscapes form an important archive that provides information regarding the timing and rate of deglaciation, and allows reconstruction of fluvial history, including the re-establishment of drainage systems and their influence on the development of the wider landscape [1,2]. These rivers were initially gravel-bed, high-energy braided river systems with active floodplains and frequently avulsing channels [8] They cut deep valleys in the glaciofluvial outwash sediments, creating terraces and redistributing large amounts of sand and gravel downstream. In their middle ‘piedmont’ reaches, locally termed ‘washlands’, where lower gradients and wider valleys reduced flow rates, there was aggradation, with rivers reoccupying established channels and depositing the sands and gravels as stacked valley fills [9,10,11,12,13]. These clastic valley-fill sequences can be Quaternary 2021, 4, x FOR PEER REeVxItEreWmely thick and have provided a valuable resource of aggregates, leading to the ex3coafv28ation of numerous sand and gravel quarries in the Ure valley
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