Editing Mill of Dyce - locality, Cainozoic of north-east Scotland

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== Sedimentological interpretation of the Mill of Dyce sequence ==
 
== Sedimentological interpretation of the Mill of Dyce sequence ==
[[File:P915320.png|thumbnail|Quaternary deposits and landforms of the Kippet Hills area. P915320.]]
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All of the laminated silty deposits in the vicinity of the Mill of Dyce have been interpreted as glaciolacustrine deposits (Auton and Crofts, 1986; Aitken, 1995) and their presence has important implications for interpretation of the lithofacies that were seen in the pit. This interpretation agrees in most aspects with the model presented by Aitken (1995), which differs from that of Murdoch (1977), who suggested that much of the sequence in the Mill of Dyce pit was deposited as a subglacial delta. Subsequent investigations (Auton and Crofts, 1986; Aitken, 1995) indicate that much of the pit sequence represents an ice-marginal delta which prograded into a lake ponded by ice downstream (Figure A1.21). The lake level, which at its maximum probably stood at about 50 m above OD, varied as a result of periodic outflow, either subglacially or englacially, through the ice dam.
All of the laminated silty deposits in the vicinity of the Mill of Dyce have been interpreted as glaciolacustrine deposits (Auton and Crofts, 1986; Aitken, 1995) and their presence has important implications for interpretation of the lithofacies that were seen in the pit. This interpretation agrees in most aspects with the model presented by Aitken (1995), which differs from that of Murdoch (1977), who suggested that much of the sequence in the Mill of Dyce pit was deposited as a subglacial delta. Subsequent investigations (Auton and Crofts, 1986; Aitken, 1995) indicate that much of the pit sequence represents an ice-marginal delta which prograded into a lake ponded by ice downstream [[Media:P915320.png|(P915320)]]. The lake level, which at its maximum probably stood at about 50 m above OD, varied as a result of periodic outflow, either subglacially or englacially, through the ice dam.
 
  
 
Deposition at Mill of Dyce commenced by the laying down of coarse ice-proximal gravels by high-discharge, sediment-laden streams and debris flows near the mouths of meltwater conduits at an ice margin. It occured during a stillstand in the active retreat of a glacier in the Don valley. The debris flow deposits, which have been extensively deformed, pass down dip into less deformed gravels that were deposited by sediment-laden meltwater streams. Deformation of the proximal gravels resulted from a combination of collapse, owing to the melting both of buried and buttressing ice, and ice push resulting from minor fluctuations of the ice margin. Both gravel deposits directly overlie sandy foresets in parts of the pit. The foresets represent progradation of the delta into the lake during periods of stable lake level. In places, foresets pass gradationally into bottomsets that were deposited by a combination of small-scale turbidity flows and sedimentation from suspension. The absence of dropstones in the bottomset beds may indicate that the ice margin had little direct contact with the ponded water body while the bottomsets were being deposited.
 
Deposition at Mill of Dyce commenced by the laying down of coarse ice-proximal gravels by high-discharge, sediment-laden streams and debris flows near the mouths of meltwater conduits at an ice margin. It occured during a stillstand in the active retreat of a glacier in the Don valley. The debris flow deposits, which have been extensively deformed, pass down dip into less deformed gravels that were deposited by sediment-laden meltwater streams. Deformation of the proximal gravels resulted from a combination of collapse, owing to the melting both of buried and buttressing ice, and ice push resulting from minor fluctuations of the ice margin. Both gravel deposits directly overlie sandy foresets in parts of the pit. The foresets represent progradation of the delta into the lake during periods of stable lake level. In places, foresets pass gradationally into bottomsets that were deposited by a combination of small-scale turbidity flows and sedimentation from suspension. The absence of dropstones in the bottomset beds may indicate that the ice margin had little direct contact with the ponded water body while the bottomsets were being deposited.

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