About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 495

Last Page: 495

Title: Scheck Breccias from Devonian Reef Complexes of Canning Basin, Western Australia: ABSTRACT

Author(s): Charles Kerans, Phillip E. Playford


Late Frasnian and early Famennian marginal-slope deposits of the Canning basin reef complexes include distinctive red open-framework breccias, characterized by red micritic clasts cemented by white calcite spar. They closely resemble the Adneter Scheck breccias in the Jurassic Adnet Limestone of the Austrian Alps.

Scheck breccias from the Canning basin are largely confined to red stromatolitic and terrigenous marginal-slope sediments having depositional slopes of 10-14°, which were deposited in water depths of some tens to hundreds of meters. Individual breccias beds are strongly lensoid, with concave, locally scoured bases. They are between 10 and 100 cm (4 and 39 in.) thick, and are composed predominantly of irregular red micritic clasts reworked from associated nodular limestones.

Breccias are clast-supported and may be inverse-to-normally graded, normally graded, or massive.

The proposed depositional mechanism began with slumping of muddy sediment containing abundant early-cemented nodules. This initiated bimodal density-modified grain flows. Nodules were supported by dispersive forces, and deposited by frictional freezing as the depositional slope decreased, producing clast-supported graded sequences. The finer sand and mud fractions continued downslope as turbidity currents, leaving behind minor perched mud trapped in the open-framework breccias. Early cementation by radiaxial calcite prevented further sediment infilling.

These Devonian scheck breccias are characteristic components of condensed sequences, as shown by conodont dating. They represent infrequent events; only about one bed of breccia was deposited for every 10 m (33 ft) of section (in about 300,000 years) over a vertical section of about 200 m (660 ft).

End_of_Article - Last_Page 495------------

Copyright 1997 American Association of Petroleum Geologists