This suggests that the predominantly bedrock hillslopes erode very slowly and sediment is transferred very gradually in most regions within Death Valley.Comparisons of Be TCN ages within sample sets on individual surfaces most closely approximate to the age of landforms that are younger than ~ 70 ka.The rate of this production is dependent on cosmic-ray flux, which increases with latitude and elevation.Because quartz does not absorb radionuclides from precipitation, the "exposure age," or the length of time present at the surface of the earth may be effectively determined by Be produced in the upper atmosphere from that produced in situ through interaction with rocks and soils.These cosmic rays do not penetrate deep into the earth’s surface.This is important for glacial geologists, as it means that surfaces that have had repeated glaciations with repeated periods of exposure to cosmic rays can still be dated, as long as they have had sufficient glacial erosion to remove any inherited signal.When particular isotopes in rock crystals are bombarded by these energetic cosmic rays neutrons, a reaction results.
This long period of applicability is an added advantage of cosmogenic nuclide dating.
Alluvial fan surfaces older than ~ 70 ka have begun to undergo sufficient erosion such that the majority of Be TCN ages for beach bars near Beatty Junction and shorelines ~ 8 km south of Furnace Creek is large, ranging from ~ 119 ka to ~ 385 ka and ~ 109 ka to ~ 465 ka, respectively.
New and previously published luminescence ages and soil development suggest that these landforms may have formed during marine isotope stage (MIS) 2 (~ 22–18 ka), but these younger ages may reflect elluviation of material into the bar deposit long after deposition, and hence the younger ages do not record the true antiquity of the landforms.
Cartoon illustrating cosmogenic nuclide exposure ages. A glacier transports an erratic boulder, and then recedes, exposing it to cosmic rays.
Spallation reactions occur in minerals in the rocks upon bombardment by cosmic rays.