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The AAPG/Datapages Combined Publications Database

CSPG Bulletin

Abstract


Bulletin of Canadian Petroleum Geology
Vol. 39 (1991), No. 2. (June), Pages 217-217

"Shales of the Cretaceous Colorado Group in Western Canada - 1: What is the Fish Scale Marker Bed and Can it Produce Hydrocarbons? [Abstract]"

Leckie, D.A.1, Bloch, J.1, Singh, C.2, Wall, J.3, Wilson, M.4

ABSTRACT

The Fish Scale Marker Bed (FSMB; Albian-Cenomanian boundary) and contiguous strata from Smoky River, Alberta indicate two shale facies. Shale below the FSMB has high foraminiferal and dinoflagellate species diversity, low Total Organic Carbon (TOC) content (1-2%), low HI (11-101 mgHC/gOC) and a predominance of Type III OM indicating a stable, well oxygenated, well circulated environment. The FSMB basal contact is knife-sharp and overlain by interbedded sandstone, siltstone, and shale with no bioturbation. This unit is overlain by 8 cm of phosphatic, fish-hash conglomerate. These last two units suggest shallowing followed by deepening and the formation of a ravinement surface and lag. Above the conglomerate is 1.2 m of shale with no benthonic foraminifers, low dinoflagellate diversity, no bioturbation, high TOC values (2-7%), high HI (70-254 mgHC/gOC) and Type II OM. This shale represents a condensed section during the peak of marine transgression with anoxic bottom water and well oxygenated surface water. The anoxic event may have been caused by mixing of water of different salinity and temperature from the Arctic Ocean and the Gulf of Mexico. The upper shale is similar to the FSMB but has increased Type III OM and decreased TOC, characteristics of progradational clinoforms above a condensed section.

A basin-wide unconformity occurs at the base of the FSMB, characterized by coarse fish debris or well sorted, medium to coarse grained, crossbedded sandstone and conglomerate with some mud drapes (?tidal). Hydrocarbon reservoirs such as the Barons Sandstone in southwestern Alberta are related to the unconformity and are typically thin, discontinuous, and in direct contact with potential source beds; they are an ideal target for horizontal drilling. Hydrocarbon reservoirs associated with the FSMB produce from nonfractured siliciclastic sediment, in contrast to reservoirs in the Second White Speckled Shales, which produce from fractured calcareous pelloids.

End_of_Record - Last_Page 217-------

ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES

1 Geological Survey of Canada, Calgary, Alberta T2L 2A7

2 Alberta Geological Survey, Edmonton, Alberta T6H 5X2

3 Geological Survey of Canada, Calgary, Alberta T2L 2A7

4 University of Alberta, Edmonton, Alberta T6G 2E9

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