Paul Glombick^1,†, Douglas R. Schmitt², Wei Xie², Todd Bown^2,3, Ben Hathway¹ and Christopher Banks^1,4

¹Alberta Geological Survey, Alberta Energy Regulator, Edmonton, Alberta, Canada
²Department of Physics, Institute for Geophysical Research, CCIS 4-183, University of Alberta, Edmonton, Alberta, Canada
³OptaSense Canada, Calgary, Alberta, Canada
⁴Schlumberger Information Solutions, Dyce, Aberdeen, AB21 0LQ, UK
^†Alberta, Canada

Geological and geophysical evidence is presented for a newly discovered, probable remnant complex impact structure. The structure, located near Bow City, southern Alberta, has no obvious morphological expression at surface. The geometry of the structure in the shallow subsurface, mapped using downhole geophysical well logs, is a semicircular structural depression approximately 8 km in diameter with a semicircular uplifted central region. Detailed subsurface mapping revealed evidence of localized duplication of stratigraphic section in the central uplift area and omission of strata within the surrounding annular region. Field mapping of outcrop confirmed an inlier of older rocks present within the center of the structure. Evidence of deformation along the eastern margin of the central uplift includes thrust faulting, folding, and steeply dipping bedding. Normal faults were mapped along the northern margin of the annular region. Isopach maps reveal that structural thickening and thinning were accommodated primarily within the Belly River Group. Evidence from legacy 2-D seismic data is consistent with the subsurface mapping and reveals additional insight into the geometry of the structure, including a series of listric normal faults in the annular region and complex faulting within the central uplift. The absence of any ejecta blanket, breccia, suevite, or melt sheet (based on available data) is consistent with the Bow City structure being the remnant of a deeply eroded, complex impact structure. Accordingly, the Bow City structure may provide rare access and insight into zones of deformation remaining beneath an excavated transient crater in stratified siliciclastic target rocks.

Reference
Glombick P, Schmitt DR, Xie W, Bown T, Hathway B and Banks C (in press) The Bow City structure, southern Alberta, Canada: The deep roots of a complex impact structure? Meteoritics & Planetary Science
[doi:10.1111/maps.12296]
Published by arrangement with John Wiley & Sons

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O. Trippella^1,2, M. Busso^1,2, E. Maiorca^2,3, F. Käppeler⁴ and S. Palmerini⁵

¹Department of Physics, University of Perugia, via A. Pascoli, I-06123 Perugia, Italy
²INFN, Section of Perugia, via A. Pascoli, I-06123 Perugia, Italy
³INAF, Observatory of Arcetri, viale E. Fermi 5, I-50125 Florence, Italy
⁴Karlsruhe Institute of Technology, Campus North, Institute of Nuclear Physics, P.O. Box 3640, D-76021 Karlsruhe, Germany
⁵INFN, Laboratori Nazionali del Sud, via Santa Sofia 62, I-95125 Catania, Italy

Slow neutron captures at A  85 are mainly guaranteed by the reaction ¹³C(α,n)¹⁶O in asymptotic giant branch (AGB) stars, requiring proton injections from the envelope. These were so far assumed to involve a small mass ( 10^-3 M☉), but models with rotation suggest that in such tiny layers excessive ¹⁴N hampers s-processing. Furthermore, s-element abundances in galaxies require ¹³C-rich layers substantially extended in mass ( 4 × 10^-3 M_☉). We therefore present new calculations aimed at clarifying those issues and at understanding whether the solar composition helps to constrain the ¹³C “pocket” extension. We show that: (1) mixing “from bottom to top” (as in magnetic buoyancy or other forced mechanisms) can form a ¹³C reservoir substantially larger than assumed so far, covering most of the He-rich layers; (2) on the basis of this idea, stellar models at a fixed metallicity reproduce the main s-component as accurately as before; and (3) they make nuclear contributions from unknown nucleosynthesis processes (LEPP) unnecessary, against common assumptions. These models also avoid problems of mixing at the envelope border and fulfil requirements from C-star luminosities. They yield a large production of nuclei below A = 100, so that ^86,87Sr may be fully synthesized by AGB stars, while ⁸⁸Sr, ⁸⁹Y, and ⁹⁴Zr are contributed more efficiently than before. Finally, we suggest tests suitable for providing a final answer regarding the extension of the ¹³C pocket.

Reference
Trippella O, Busso M, Maiorca E, Käppeler F and Palmerini S (2014) s-Processing in AGB Stars Revisited. I. Does the Main Component Constrain the Neutron Source in the 13C Pocket?. The Astrophysical Journal 787:41.
[doi:10.1088/0004-637X/787/1/41]

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