--> Abstract: Tectonism and Eustacy in Devonian Reef Complexes of the Canning Basin, Western Australia; #90063 (2007)

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Tectonism and Eustacy in Devonian Reef Complexes of the Canning Basin, Western Australia

 

Hocking, Roger M.1, Phillip E. Playford2 (1) Geological Survey of Western Australia, East Perth, Australia (2) Geological Survey of Western Australia, Perth, W.A, Australia

 

Platform limestones in Frasnian and Famennian reef complexes of the Canning Basin show well-developed cyclicity on two scales. Metre-scale cycles, averaging 3.5 to 4 m thickness, show gradual upward shallowing, local progradation at the top, and abrupt deepening to the next cycle. Cycle duration is generally hard to quantify, but in one late Frasnian platform an estimate of about 20 000 years per cycle is possible. Sets of about 5 consecutively shallower cycles followed by abrupt deepening are apparent locally, and indicate a second cyclic frequency, of about 100 000 years. Cycles and cycle sets have comparable thicknesses and facies successions across the outcrop belt, allowing for faunal changes through the Late Devonian, suggesting a persistent, shelf-wide control. This was probably orbital forcing, with obliquity and short precession signals. Very regular tectonic movement (“jerky subsidence”) is also possible.

 

Siliciclastic conglomerates interfinger with and cut through reefal carbonates at platform and basin levels, and less commonly on marginal slopes. They span many metre-scale cycles, from both point and line sources. Two major conglomerate outpourings are apparent, each during periods of marginally greater platform accommodation, one Frasnian and one Famennian. Deposition extended well into basinal areas on the southeast and northwest Lennard Shelf in the Frasnian and Famennian respectively, indicating variability in timing and provenance. Shallowing-upward conglomerate cyclicity is present in one area, with cycles averaging 12 m thick. The conglomerates are attributed to major tectonic pulses, and the cycles to orbital forcing

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California