Publication Date:
2017-01-12
Description:
Deep erosional gullies dissect landscapes around the world. Existing erosion models focus on predicting where gullies might begin to erode, but identifying where existing gullies were initiated and under what conditions is difficult, especially when historical records are unavailable. Here, we outline a new approach for fingerprinting alluvium and tracing it back to its source by combining bulk sediment optically stimulated luminescence (bulk OSL) and meteoric 10 Be ( 10 Be m ) measurements made on gully-derived alluvium samples. In doing so, we identify where gully erosion was initiated and infer the conditions under which such erosion occurred. As both 10 Be m and bulk OSL data have distinctive depth-profiles in different uneroded and depositional settings, we are able to identify the likely depths in potential source areas of alluvium. We demonstrate our technique at Birchams Creek in the southeastern Australian Tablelands – a well-studied and recent example of gully incision that exemplifies a regional landscape transition from unchannelled swampy meadow wetlands to gully incision and subsequent wetland burial by post-European settlement alluvium. We find that such historic alluvium was derived from shallow erosion of valley fill upstream of former swampy meadows and was deposited down the center of the valley. Incision likely followed catchment deforestation and the introduction of livestock, which overgrazed and congregated in valley bottoms in the early 20 th century during a period of drought. As a result, severe gully erosion was likely initiated in localized, compacted, and oversteepened reaches of the valley bottom.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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