--> Abstract: Disrupted Conodont Assemblages, Upper Bakken Formation (Lower Mississippian), from the Subsurface of Western Canada, by D. I. Johnston and C. M. Henderson; #90039 (2005)

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Disrupted Conodont Assemblages, Upper Bakken Formation (Lower Mississippian), from the Subsurface of Western Canada

D. I. Johnston1 and C. M. Henderson2
1 103 - 3017 Blakiston Dr. NW, Calgary, AB
2 Department of Geology and Geophysics, University of Calgary, Calgary, AB

Discrete conodonts processed from shales often appear less well preserved than those from limestones due to post-mortem compaction of mudstones and processing methods. Elements preserved intact on bedding plane surfaces provide valuable supplementary information about conodonts from these lithologies. Disrupted conodont bedding plane assemblages are described from two mudstone core samples from the Lower Mississippian upper shale member of the Bakken Formation in the subsurface of southeastern Alberta and southwestern Saskatchewan. Element clusters are dominated by Bispathodus and Polygnathus communis on the bedding plane surfaces of the core sample from southeastern Alberta. Bispathodus, Mehlina and Siphonodella dominate conodont bedding plane assemblages on the core samples from southwestern Saskatchewan. Several of the Siphonodella Pa elements are paired. This genus is dominant compared with Bispathodus and Mehlina in collections of discrete elements.

The conodont core bedding plane assemblage from southeastern Alberta shows little evidence of winnowing. Thus, this assemblage, along with collections of discrete conodont elements from these strata, is a reliable source of data for reconstructing paleoecology and taphonomy and for testing apparatus reconstructions. The assemblages from the southwestern Saskatchewan core, however, show a greater degree of breakage and winnowing of elements, making it less suitable as a source of interpretive data.

The bispathodid biofacies appears to be represented by the conodont core bedding plane assemblage from southeastern Alberta whereas the siphonodellid biofacies is represented in the assemblage from southwestern Saskatchewan.

An apparatus reconstruction is proposed for a species of Prioniodina.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005