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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


The Mesozoic of Middle North America: A Selection of Papers from the Symposium on the Mesozoic of Middle North America, Calgary, Alberta, Canada — Memoir 9, 1984
Pages 361-372
Sedimentology

The Rapid Creek Formation: An Albian Flysch-Related Phosphatic Iron Formation in Northern Yukon Territory

F. G. Young, B. T. Robertson

Abstract

An unusual sedimentary phosphatic iron formation in the Richardson Mountains of northern Yukon and Northwest Territories is here named the Rapid Creek Formation. It comprises the upper and youngest portion of an Aptian-Albian flyschoid sequence which reaches a maximum thickness of four kilometres in the Blow Trough. The Rapid Creek Formation constitutes proportionately more of the sequence as it thins eastward over the Cache Creek High, where it is only 60 metres thick. Farther east, in the subsurface of the Mackenzie Delta, the iron formation changes facies to carbonaceous dark grey shale of the Arctic Red Formation.

The Rapid Creek Formation is easily distinguished from adjacent units by its hard and brittle nature and characteristic white, powdery dypingite (hydrated magnesium carbonate) coatings. Unusual lithologies in this deposit have been described using a three end-member classification based on phosphate grains, siderite or clay mud matrix, and detrital quartz grains. Phosphate grains are composed primarily of rare minerals such as satterlyite, arrojadite and gormanite, which reflect an original calcium-deficient composition. The deposition of iron and magnsium phosphates as well as apatite is strongly indicated, and this condition is unique for marine phosphorites.

In the type section the Rapid Creek Formation is divided into nine units. The lower five units each consist of a coarsening-upward sequence from mudstone to packstone and grainstone. All are phosphate-rich and are capped by a non-phosphatic conglomerate. The upper four units here, and in other outcrops, commonly consist mainly of phosphatic sideritic mudstone and pelletal wackestone.

This most northerly known phosphorite (75 degrees North paleolatitude) probably resulted from cold, northeast-flowing currents upwelling on the western flank of the Cache Creek High.


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