Chronometric Analysis of Abstraction and Recognition

2017 ◽  
Vol 82 (3) ◽  
pp. 593-608 ◽  
Author(s):  
James C. Chatters ◽  
James W. Brown ◽  
Steven Hackenberger ◽  
Patrick McCutcheon ◽  
Jonathan Adler

Radiocarbon dating using charcoal and bone collagen, two standards of archaeological chronology, can be difficult to impossible in environments where natural burning is common and bone does not preserve well. In such settings, charcoal ages cannot always be trusted and collagen is unavailable. Calcined bone can be a viable alternative medium in these situations but it has rarely been exploited in the Americas. One area that could benefit from its use is the forested Pacific Northwest. We compare calcined bone ages with charcoal and/or collagen dates from individual features or discrete cultural strata in 10 Washington, Oregon, Idaho, and British Columbia sites dating between 9000 and 100 B.P. Resulting radiocarbon age estimates based on calcined bone closely match those based on charcoal and/or collagen in nearly all cases. We obtained calcined bone dates from three additional Holocene-aged sites that had not previously produced accurate results, obtaining findings consistent with estimates based on cross dating. Preserving well where all other organic media of cultural origin are lost or unreliable, calcined bone holds promise for dating sites in conifer forests and other acidic soil settings, and can allow researchers to refine archaeological sequences that have long defied accurate chronometric analysis.


1986 ◽  
Vol 14 (6) ◽  
pp. 488-500 ◽  
Author(s):  
Peter Dixon ◽  
Marcel Adam Just

1986 ◽  
Vol 2 (4) ◽  
pp. 345-362 ◽  
Author(s):  
Roderick K. Mahurin ◽  
Francis J. Pirozzolo

2020 ◽  
Author(s):  
Matthijs Smit ◽  
Philip Pogge von Strandmann

<p>Slabs in subduction zones with geotherms of 7 K km<sup>-1</sup> or higher are expected to dehydrate effectively in the forearc. Nevertheless, large amounts of water are released from these slabs at and beyond subarc depth, indicating that H<sub>2</sub>O remains slab-bound to much greater depth than expected. It is possible that this reflects a transient sealing effect exerted by the subducting lower crust—a section of the lithosphere that typically undergoes delayed recation and is effectively impermeable until then. To test this concept, we investigated gabbros that were partially transformed to hydrous eclogite along shear zones during subduction. The rocks were subjected to a textural, petrological and Li-chronometric analysis. The observations characterize the progressive stages of transformation, and provide detailed insight into the governing feedbacks among fluid flow, deformation, and reaction. Lithium chronometry indicates that it took only a few weeks for the shear zone network to develop and for the externally derived fluids to traverse this network and drive eclogitization; the switch in these rocks—going from strong to weak and from impermeable to sustaining long-range fluid flow—thus was essentially instanteneous on subduction time scales. The re-equilibration of the rocks occurred well beyond equilibrium at c. 90 km depth, which is where large fluid-filled channel system typically emanate from warm slabs. Our data suggest that the fluids that are produced in the slab mantle throughout the forearc accumulate beneath the Moho until the lower crust is breached by dynamic fluid vents and commences its delayed transformation. The subducting lower crust may thus be a exert a strong control on H<sub>2</sub>O and element budgets, and the rheology of slabs in warm subduction zones.</p>


1999 ◽  
Author(s):  
Claudia Mello-Thoms ◽  
Calvin F. Nodine ◽  
Harold L. Kundel

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