“Pipe Rock” Ichnofabrics and Microbial Mats From Lower Cambrian Shallow Marine Sandstones of Western Newfoundland, Canada

The Hawke Bay Formation of western Newfoundland has been identified as a possible hydrocarbon reservoir, although detailed analysis of potential reservoir facies and quality have, until now, been lacking. Quartzites of the Hawke Bay Formation were deposited during the Lower Cambrian on the Laurentian margin during rifting of the Iapetus Ocean. This marginal marine, wave and tide influenced unit has abundant arthropod grazing and resting traces (Cruziana and Rusophycus), and, in vertical section, the rocks contain complex and diverse ichnofabrics. The dominant ichnofabric-forming ichnotaxa are the vertical pipes, and U-shaped burrows of Skolithos, Arenicolites and Diplocraterion. Ichnofabrics are comparable with those of the Lower Cambrian "Pipe Rock" of NW Scotland. Bioturbation intensities are highest at the base of the 2-8m thick parasequences, in association with authigenic phosphate and glauconite at flooding surfaces. Intense bioturbation is recorded from ripple cross-laminated, wave and tidally influenced lower shoreface sandstones. Bioturbation is almost absent in the upper parts of parasequences which are dominated by thick (2-4m) intervals of planar and crinkly-laminated sandstones, with associated microbially induced sedimentary structures on bedding planes. The depositional environment of this unusual facies is interpreted to have been deposited in a (non-uniformitarian) microbially bound upper shoreface to foreshore palaeoenvironment.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California