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Conversion of diatoms to clays during early diagenesis in tropical, continental shelf muds

Panagiotis Michalopoulos, Robert C. Aller and Richard J. Reeder
Conversion of diatoms to clays during early diagenesis in tropical, continental shelf muds
Geology (Boulder) (December 2000) 28 (12): 1095-1098


In coastal muds downdrift from the Amazon River mouth, marine diatom frustules are rapidly converted to various forms of authigenic aluminosilicate phases during burial. The dominant neoformed crystalline phases have a composition similar to K-smectite, yield electron diffraction patterns characteristic of clay minerals, and exhibit a range of crystal sizes and morphologies, including euhedral pseudohexagonal crystals and anhedral flakes replacing biogenic silica. A poorly crystalline or microcrystalline K-rich and Fe-rich aluminosilicate material also replaces the siliceous frustules. The conversion process is not always complete, leaving relics of the original frustule in the resulting authigenic aluminosilicate phases. Laboratory incubation experiments with cultured diatoms demonstrate that the conversion process occurs in 20-23 months. The conversion of biogenic silica to authigenic clays occurs throughout the Amazon deltaic deposits and presumably takes place in other comparable depositional settings. Biogenic silica alteration provides proof for a direct link between the biogeochemical cycle of silica in nearshore environments and the neoformation of cation-rich aluminosilicate phases, and it may prove to be important for oceanic geochemical cycles as a sink for Si, K, and other elements incorporated in the authigenic aluminosilicates. Rapid formation of authigenic K-smectite may also represent a reaction stage leading to eventual formation of illitic clays during later diagenesis.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 28
Serial Issue: 12
Title: Conversion of diatoms to clays during early diagenesis in tropical, continental shelf muds
Affiliation: State University of New York at Stony Brook, Marine Sciences Research Center, Stony Brook, NY, United States
Pages: 1095-1098
Published: 200012
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Accession Number: 2000-075431
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
S04°30'00" - N01°00'00", W73°30'00" - W49°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200024
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