--> Abstract: Late Devonian Carbonate-Conglomerate Association in the Canning Basin, Western Australia, by A. E. Holmes; #91004 (1991)

Datapages, Inc.Print this page

Late Devonian Carbonate-Conglomerate Association in the Canning Basin, Western Australia

HOLMES, ANN E., Lamont-Doherty Geological Observatory, Palisades, NY

Siliciclastic conglomerates of Late Devonian to Carboniferous age crop out discontinuously along the northern margin of the Canning basin in Western Australia, where they are associated with a classic example of reefal carbonate rocks. An understanding of these deposits is relevant to the timing of extension in the basin, uplift of the adjacent Kimberley block, and to the interpretation of the sequence stratigraphy of the carbonates. The conglomerates indicate that the Kimberley block was high-standing, even though most normal faulting appears to have ceased by Late Devonian time, and provided a continuous source of siliciclastic material.

The carbonate-conglomerate relationships were studied in detail at two localities, with brief visits to several other sections to provide a regional context. Although coarse detritus was probably transported preferentially across the platforms at times of lowered sea level, conglomerate is present also in the transgressive systems tracts of several sequences, and highstand carbonates are locally sandy. Lowstand conglomerates (e.g. Van Emmerick Range) are preserved as incised-valley fill deposits (gravity flow-type deposits grading up to laminar and cross-bedded burrowed sandstones). Cobble (b-axis imbrication) and arkosic sandstone beds are interbedded with carbonate bafflestones and floatstones at Stony Creek. These represent transgressive marine sediments with episodic terrigenous i flux related to floods rather than base-level changes. At all localities, highstand sediments are characterized by rounded to subangular carbonate blocks and whole or fragmented fossils in a fine-grained carbonate and terrigenous sand-silt material. In contrast to transgressive sediments, the highstands lack siliciclastic gravel.

A sequence boundary of late Frasnian age is exposed at several localities. Incised valleys with 10 m relief (e.g. Van Emmerick and Mt. Elma) and onlapping relationships (e.g. Stony Creek, Van Emmerick) provide strong evidence for a type 1 boundary that likely formed during a eustatic base-level drop (cf., Devonian carbonates of Canada). The recognition of several intervals of siliciclastic conglomerate influx in the Canning basin is important because it suggests the presence of distal lowstand sandstone reservoirs that may represent potential petroleum targets.

 

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