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Book Chapter

Depositional controls on Cretaceous coals and coal measures in New Zealand

By
A. M. Sherwood
A. M. Sherwood
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J. K. Lindqvist
J. K. Lindqvist
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J. Newman
J. Newman
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R. Sykes
R. Sykes
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Published:
January 01, 1992

Cretaceous coals and coal measures onshore and offshore New Zealand record a period of great tectonic change in the region. Coal measures accumulated mainly within fault-controlled depressions resulting from a complex early rifting history during the breakup of eastern Gondwanaland. Lithofacies relationships and coal properties reflect a complex interplay between paleoenvironmental and contemporaneous tectonic influences.

Mid-Cretaceous terrestrial sediments up to 4,500 m thick accumulated in narrow fault-angle depressions interpreted as failed rifts. Fan breccias and conglomerates predominate, with minor fine-grained sediments and thin, uneconomic coal seams. Latest Cretaceous coal measures in the order of 1,000 m thick accumulated mainly as floodplain deposits in generally more extensive basins, some probably exceeding 60 km along their axes. The coal measures are lithologically variable, with sandstone and conglomerate dominant in most basins, many of which contain economically important coalfields. Seams are characterized by marked lenticularity and maximum thicknesses of 20 to 30 m. Some latest Cretaceous coal measures were deposited in near-shore environments as a consequence of marine transgression, which also influenced coal measure deposition in some tectonically controlled basins. Coal properties vary, although ash and sulphur contents are commonly low. A range of coal rank from lignite to low-volatile bituminous results from different burial histories.

The most extensive mid- to Late Cretaceous coal measures are in offshore basins. Up to 2,000 m of lithologically variable coal measures with numerous seams accumulated in rapidly subsiding basins up to a few hundred kilometers in extent.

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Contents

GSA Special Papers

Controls on the Distribution and Quality of Cretaceous Coals

Peter J. McCabe
Peter J. McCabe
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Judith Totman Parrish
Judith Totman Parrish
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Geological Society of America
Volume
267
ISBN print:
9780813722672
Publication date:
January 01, 1992

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