About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 56 (1972)

Issue: 3. (March)

First Page: 605

Last Page: 605

Title: Sedimentology of a Middle Devonian Shale, Erie County, New York: ABSTRACT

Author(s): R. G. Bray, J. R. Beerbower

Article Type: Meeting abstract


The predominance of clay minerals, pelleted texture, burrow traces, and pyritized material in the Wanakah Shale member of the Ludlowville Formation suggests a soft, granular sediment. An analysis of the fossil assemblages reveals a relation between the distribution, growth, and persistence of animals and the character of the substrate. Several brachiopod species are aggregated on bedding surfaces and some microcommunities are present, largely composed of suspension feeding epifauna. A detailed study of taxonomic composition, functional adaptations, and taphonomy of 3 microcommunities leads to the conclusion that the depositional site received continuous rather than episodic addition of sediment.

The high brachiopod mortality in early growth was the consequence of smothering in the soft, "floc" zone covering the sediment. The sizes of brachiopods involved (2.0 mm) suggest a minimum thickness of approximately 1-2 mm for this zone. Survival to maturity of 2.0-mm brachiopods was high, setting a maximum floc thickness and annual sedimentation increment of approximately 2 mm/yr. The preservation of large, articulated brachiopods in positions normal to substrate requires a minimum annual sedimentation rate of approximately 1 mm/yr. The sea bottom was sufficiently oxygenated for benthic life, but the presence of penecontemporaneous sulfide suggests that the interface between oxidizing and reducing environments was very near the sediment-water interface. Turbulence was very low.

End_of_Article - Last_Page 605------------

Copyright 1997 American Association of Petroleum Geologists