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Attical Complex - Attical Valley OutwashDown
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Summary Full report
Site Type: Inland exposure
Site Status:
District:
Grid Reference: J269193
Rocks
Rock Age: Quaternary (Late Midlandian)
Interest
Other interest: No data, No Data, outwash

Summary of site:

Lake sediments at Brown Hill Pit in the lower Windy Gap (Pigeon Rock) valley and in Deers Meadow suggest that they were washed into temporary meltwater lakes. Most of the deposits show active flow of sands and gravels into shallow water, forming cross-bedding, imbricate structures and cobble beds, some in channels swept clear by forceful currents. They lie in horizontal beds, some ripple marked, but less commonly with undulating surfaces. Some deposits are a chaotic mix of different grain sizes and materials.

These kinds of sediments are all typical of loose glacial debris swept into expanses of standing water, probably small lakes, judging by the evidence available. Perhaps the largest, with an area of 2.5 kmē, was at Deers Meadow. These lakes were features of the final stage of melting of the mountain glaciers when meltwater gathered behind the moraines which acted as temporary dams. Eventually the lake level would top the rim of the damming moraine and once a breach was achieved the uncemented wall would collapse, the lake would drain and the lake bed was then exposed to the open air. These events were the last phase of deglacial activity, perhaps 12,000 to 13,000 years ago.


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