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Significance and Distribution of Apatite in the Triassic Doig Phosphate Zone, Western Canada Sedimentary Basin Lacerda Silva, Pablo; Bustin, R. Marc

Abstract

The Doig Phosphate Zone (DPZ) is a phosphate-bearing marine unit located at the base of the Doig Formation, in the Triassic section of the Western Canada Sedimentary Basin. The DPZ has a maximum thickness of 90 m and extends across northeastern British Columbia and west-central Alberta. In this study, we characterize the significance and interpret the origin of apatite in the DPZ through mineralogical and geochemical analyses, thin section study, and field emission scanning electron microscopy. The occurrence of apatite in the DPZ is not evenly distributed but restricted to discrete 10 to 20 cm thick beds, located near the base of the DPZ. Phosphorites are of two types: grainstones composed primarily of unconformity-bounded coated grains, and intraclastic phosphorites composed of detrital silt-sized grains and apatite coated grains in a cryptocrystalline phosphatic matrix. The phosphorite beds are records of stratigraphic condensation due to low detrital input during transgression. The erosionally truncated phosphatic coated grains and intraclasts are interpreted to be a result of various phases of phosphatization, exhumation, erosion, reworking, winnowing, and redeposition in alternating quiescence and storms or bottom currents. The abundance of pyrite and chalcophile trace elements, as well as the low concentration of proxy elements for organic matter productivity and preservation, are further evidence of stratigraphic condensation, with sulfidic pore water development and extensive organic recycling promoted by biological activity during the long exposure times. The phosphorites were formed under oxygenated water conditions, as suggested by the depletion in Ce and the presence of a diverse benthic fauna.

Item Metadata

Title
Significance and Distribution of Apatite in the Triassic Doig Phosphate Zone, Western Canada Sedimentary Basin
Creator
Lacerda Silva, Pablo; Bustin, R. Marc
Publisher
Multidisciplinary Digital Publishing Institute
Date Issued
2020-10-12
Description
The Doig Phosphate Zone (DPZ) is a phosphate-bearing marine unit located at the base of the Doig Formation, in the Triassic section of the Western Canada Sedimentary Basin. The DPZ has a maximum thickness of 90 m and extends across northeastern British Columbia and west-central Alberta. In this study, we characterize the significance and interpret the origin of apatite in the DPZ through mineralogical and geochemical analyses, thin section study, and field emission scanning electron microscopy. The occurrence of apatite in the DPZ is not evenly distributed but restricted to discrete 10 to 20 cm thick beds, located near the base of the DPZ. Phosphorites are of two types: grainstones composed primarily of unconformity-bounded coated grains, and intraclastic phosphorites composed of detrital silt-sized grains and apatite coated grains in a cryptocrystalline phosphatic matrix. The phosphorite beds are records of stratigraphic condensation due to low detrital input during transgression. The erosionally truncated phosphatic coated grains and intraclasts are interpreted to be a result of various phases of phosphatization, exhumation, erosion, reworking, winnowing, and redeposition in alternating quiescence and storms or bottom currents. The abundance of pyrite and chalcophile trace elements, as well as the low concentration of proxy elements for organic matter productivity and preservation, are further evidence of stratigraphic condensation, with sulfidic pore water development and extensive organic recycling promoted by biological activity during the long exposure times. The phosphorites were formed under oxygenated water conditions, as suggested by the depletion in Ce and the presence of a diverse benthic fauna.
Subject
Doig Phosphate Zone; phosphorite; apatite; coated grains
Genre
Article
Type
Text
Language
eng
Date Available
2020-11-05
Provider
Vancouver : University of British Columbia Library
Rights
CC BY 4.0
DOI
10.14288/1.0394905
URI
http://hdl.handle.net/2429/76456
Affiliation
Science, Faculty of; Alumni; Earth, Ocean and Atmospheric Sciences, Department of
Citation
Minerals 10 (10): 904 (2020)
Publisher DOI
10.3390/min10100904
Peer Review Status
Reviewed
Scholarly Level
Faculty
Rights URI
https://creativecommons.org/licenses/by/4.0/
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CC BY 4.0