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Lookup NU author(s): Carol Mahoney,
Professor Thomas Wagner
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© 2017 by Walter de Gruyter Berlin/Boston 2017. Visual inspection (optical microscope point counting) and silica abundance show that laminated shale from the Late Cretaceous of Colombia contains high levels of detrital quartz silt and sand particles. Closer examination using the charge contrast imaging (CCI) technique, however, illustrates that much of the quartz is authigenic micro-quartz, and thus not exclusively of detrital origin. In addition, many "sand" grains that otherwise appear to represent simple detrital quartz particles are actually of biogenic origin, representing the tests of agglutinated foraminifera, formed from cemented silt-sized quartz particles. Finally, CCI shows that original detrital grains have undergone authigenic modification, with both syntaxial overgrowths and micro-quartz. Without recognition of these features, the relative proportion of detrital quartz (sand) would otherwise be greatly overestimated, with important implications for environmental interpretation. Furthermore, the recognition of biogenic structures, including agglutinated foraminifera, provides additional environmental information that otherwise could be easily overlooked.
Author(s): Buckman J, Mahoney C, Marz C, Wagner T, Blanco V
Publication type: Article
Publication status: Published
Journal: American Mineralogist
Online publication date: 03/04/2017
Acceptance date: 26/10/2016
ISSN (print): 0003-004X
ISSN (electronic): 1945-3027
Publisher: Mineralogical Society of America
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