Paleoenvironments and origin of the sedimentary phosphorites of the Napo Formation (Late Cretaceous, Oriente Basin, Ecuador)

The Napo phosphorites were deposited at the edge of a stable marine shelf during the Upper Cretaceous (Coniacian) oceanic anoxic event (OAE 3) at the transition from bioclastic limestone to organic-rich shale facies. Phosphogenesis was triggered in the shelf margin environment by a number of factors...

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Bibliographic Details
Published inJournal of South American earth sciences Vol. 28; no. 2; pp. 180 - 192
Main Authors Brookfield, M.E., Hemmings, D.P., Van Straaten, P.
Format Journal Article
LanguageEnglish
Published Elsevier Ltd 01.08.2009
Subjects
Ecuador
Late Cretaceous
Napo
Origin
Paleoenvironments
Phosphorites
Origin
Ecuador
Paleoenvironments
Napo
Late Cretaceous
Phosphorites
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Summary:The Napo phosphorites were deposited at the edge of a stable marine shelf during the Upper Cretaceous (Coniacian) oceanic anoxic event (OAE 3) at the transition from bioclastic limestone to organic-rich shale facies. Phosphogenesis was triggered in the shelf margin environment by a number of factors including strong upwelling currents, high biological activity, plankton blooms, and large amounts of organic matter production and subsequent accumulation. Dissolved phosphate levels increased in the sediment from a combination of anoxic conditions and microbial activity. Once dissolved phosphate concentrations were high enough, apatite began to form around nucleic sites including mineral grains, shells, wood fragments, and foraminifera tests forming peloidal fluorine rich carbonate fluoroapatite (francolite). As the peloids formed, sedimentation continued and dissolved phosphate concentrations diminished. A period of minor winnowing ensued, and as dissolved phosphate concentrations remained low, shale layers were deposited separating the various phosphate layers.
ISSN:0895-9811
1873-0647
DOI:10.1016/j.jsames.2009.02.004