Also at CEREGE, BP 80, Europole Méditerranéen de l'Arbois, F-13545 Aix en Provence CEDEX 4, France [1] We present a user-friendly and versatile Monte Carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides (TCNs). Our program (available online at http://geochronology.earthsciences.dal. ca/downloads-models.html) permits the incorporation of site-specific geologic knowledge to calculate most probable values for exposure age, erosion rate, and inherited nuclide concentration while providing a rigorous treatment of their uncertainties. The simulator is demonstrated with 10 Be data from a fluvial terrace at Lees Ferry, Arizona. Interpreted constraints on erosion, based on local soil properties and terrace morphology, yield a most probable exposure age and inheritance of 83.9 −14.1 +19.1 ka, and 9.49 −2.52 +1.21 × 10 4 atoms g −1 , respectively (2s). Without the ability to apply some constraint to either erosion rate or age, shallow depth profiles of any cosmogenic nuclide (except for nuclides produced via thermal and epithermal neutron capture, e.g., 36 Cl) cannot be optimized to resolve either parameter. Contrasting simulations of 10 Be data from both sand-and pebble-sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with TCN depth profiles and, when possible, sand-not pebbles-should be used for depth profile exposure dating.Components: 9500 words, 7 figures, 4 tables.
The mid-Pliocene was a global warm period, preceding the onset of Quaternary glaciations. Here we use cosmogenic nuclide dating to show that a fossiliferous terrestrial deposit that includes subfossil trees and the northern-most evidence of Pliocene ice wedge casts in Canada’s High Arctic (Ellesmere Island, Nunavut) was deposited during the mid-Pliocene warm period. The age estimates correspond to a general maximum in high latitude mean winter season insolation, consistent with the presence of a rich, boreal-type forest. Moreover, we report that these deposits have yielded the first evidence of a High Arctic camel, identified using collagen fingerprinting of a fragmentary fossil limb bone. Camels originated in North America and dispersed to Eurasia via the Bering Isthmus, an ephemeral land bridge linking Alaska and Russia. The results suggest that the evolutionary history of modern camels can be traced back to a lineage of giant camels that was well established in a forested Arctic.
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