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Identifying biogenic silica; mudrock micro-fabric explored through charge contrast imaging

Jim Buckman, Carol Mahoney, Christian Maerz, Thomas Wagner and Vladimir Blanco
Identifying biogenic silica; mudrock micro-fabric explored through charge contrast imaging
American Mineralogist (April 2017) 102 (4): 833-844

Abstract

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.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 102
Serial Issue: 4
Title: Identifying biogenic silica; mudrock micro-fabric explored through charge contrast imaging
Affiliation: Heriot-Watt University, Institute of Petroleum Engineering, Edinburgh, United Kingdom
Pages: 833-844
Published: 201704
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 49
Accession Number: 2017-041515
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, sketch map
N04°00'00" - N07°00'00", W74°00'00" - W72°45'00"
Secondary Affiliation: Newcastle University, GBR, United KingdomUniversity of Leeds, GBR, United KingdomInstituto Colombiano del Petroleo, COL, Colombia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201723
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