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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 52 (1968)

Issue: 3. (March)

First Page: 538

Last Page: 539

Title: Flint Kaolins in Non-Coal-Bearing Triassic of Sydney Basin, Australia: ABSTRACT

Author(s): F. C. Loughnan

Article Type: Meeting abstract

Abstract:

Claystones, similar in composition, texture, and structure to the flint kaolins of the Pennsylvanian of North America, the Westphalian of Europe, and the Permian coal measures of South Africa and Australia, form a persistent marker bed in the non-coal-bearing Triassic Narrabeen Group of the Sydney basin.

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The claystones are indurated and characteristically possess oolitic textures, although vermicular crystals and brecciated fragments are present in most samples. Well-crystallized kaolinite is the only clay mineral present and is associated invariably with anatase and locally with abundant (> 50 percent) boehmite or siderite. Quartz, either as discrete grains or as chalcedony, is rare or absent.

The unit ranges in thickness from 1 to 6 ft and can be traced for more than 50 mi along the southeastern margin of the basin. However, extensive boring downdip has shown that it thins out abruptly in that direction.

The underlying sediments consist of red claystones, known locally as the "chocolate shales." Apart from well-crystallized kaolinite and anatase, these claystones contain appreciable quantities of hematite (15-25 percent), but quartz and clay minerals, other than kaolinite, are sparse or absent. The overlying sediments, however, are composed of quartz, illite, and degraded illite as well as kaolinite.

The "chocolate shales" are believed to represent a transported laterite or lateritic bauxite and the flint kaolins are considered to be the reduced equivalent, formed by the advent of swampy conditions at the close of deposition of the sedimentary sequence.

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