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Murnies Delta, Dungiven BasinLondonderry
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Summary Full report
Site Type: Inland exposure, Pit
Site Status:
District:
Grid Reference: X00
Rocks
Rock Age: Quaternary (Late Glacial)
Rock Type: Diamict, Gravel, Sand
Interest
Other interest: No data, Glaciolacustrine deposit, Gilbert-type delta, proglacial lake

Summary of site:

At this site there is a simple delta type termed Gilbertian following the classic description of G K Gilbert. Such deltas build into lakes where debrisūladen, fast flowing water enters a lake, in his case created by an ice-dam. The sediment spills down slope, banking against the submerged lake margin, until it reaches lake surface level at the point of entry. The sediment then builds out further into the lake creating a terrace at the level of the lake surface that the meltwater then has to cross to reach the top of the front slope of the delta. In the process it cuts a channel or several braided channels into the terrace surface which constantly shift as they silt-up.

The horizontal beds on the terrace are called the topsets, those on the inclined delta front the foresets, and where the foresets flatten out onto the lake bed in front of the delta slopes are the bottomsets. Structures falling into these categories are commonly encountered in glacial lake environments. There is a more detailed account of this locality under Faughan and Dungiven Basins ū The Murnies, site 499.


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