--> Abstract: Reef Development and Extinction in Response to Sealevel Change in the Devonian of the Canning Basin, by P. E. Playford; #91004 (1991)

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Reef Development and Extinction in Response to Sealevel Change in the Devonian of the Canning Basin

PLAYFORD, PHILLIP E., Geological Survey of Western Australia, East Perth, Western Australia

Relative change in sealevel, due to eustatism, basin subsidence, and local tectonism, strongly influenced the development and extinction of Devonian reefs in the Canning basin of Western Australia. Several eustatic events of platform emergence, backstepping, and drowning are recognized, and well-developed Milankovitch cyclicity is apparent in backreef and forereef deposits. Basin subsidence proceeded at rates of about 120 micro m/yr, to accommodate some 2000 m of reefal deposits.

A type 1 sequence boundary separates the two major reef cycles, the Givetian-Frasnian Pillara cycle and Famennian Nullara cycle. The boundary unconformity in the reefal platforms has erosional relief of several meters, with associated minor karstification, and is believed to have resulted from an abrupt, small, and short-lived eustatic fall in sealevel. Although this was apparently only a small-scale event, it coincided with the world-wide mass extinction of many metazoans, marked in the Canning basin by the elimination of the Frasnian stromatoporoid-coral reefbuilders, and their replacement in the Famennian by cyanobacteria alone. An iridium anomaly close to the Frasnian-Famennian boundary is of biogenic origin; it is not thought to have resulted from bolide impact.

Preliminary correlations can be made with the development and extinction of equivalent reefs in China, Canada, and Europe. Detailed dating of the Canning basin complexes is proceeding, using conodonts and ammonoids, and this will facilitate more precise global correlation of the eustatic events.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)