Stratigraphy of the Blow Me Down Brook formation, Humber Arm Allochthon, western Newfoundland, Canada

Gillis, Erin S. (2006) Stratigraphy of the Blow Me Down Brook formation, Humber Arm Allochthon, western Newfoundland, Canada. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Cambrian age Blow Me Down Brook formation of the Humber Arm Allochthon has been poorly understood since geological study began in the area more than 140 years ago. A detailed study has never been carried out exclusively on the formation, nor a complete stratigraphy designated. The aim of this thesis is to compose a stratigraphy for the Blow Me Down Brook formation based upon sedimentology, petrography and ichnology. -- Regional mapping of coastal sedimentary strata from the community of Fox Island River, north to Rope Cove is used to show extensive and continuous sections of Blow Me Down Brook formation. These exposures, paired with a recently documented basal contact between Blow Me Down Brook red shale beds and underlying Fox Island River volcanics, have allowed development of a composite stratigraphy for the Blow Me Down Brook formation. The formation, herein estimated to be about 400 m thick, is formed of six informal, but distinct stratigraphic units: A, B, C, D, E and F. Unit A, massive red shale interbedded with volcanics; Unit B, thick bedded red (hematitic) and greenish coloured micaceous sublithrenite and lithic subarkose; Unit C, quartz and feldspar pebble conglomerate with calcarenite boulders; Unit D, coarse grained greenish coloured quartzarenite and sublitharenite with minor subarkose interbedded with red, green and grey shale; Unit E, massive siliceous red and black shale, and Unit F; a quartzose greenish sandstone interbedded with black shales. -- The sandstones of Unit F are commonly petroliferous, and tend to be associated with the calcareous Northern Head Group. One area (near Sluice Brook) shows evidence for a petroleum system in the Blow Me Down Brook formation. Here, petroliferous Blow Me Down Brook formation overlies the Northern Head Group in an antiformal structure. The shales of the Northern Head Group have a 'greasy' texture and may have acted as a source rock; overlying beds of red shales form a seal. -- The Blow Me Down Brook formation is derived from offshore turbidity flows, with little understanding of how the formation relates to the Summerside and Irishtown formations of the same age. With knowledge of the stratigraphy and petrography stronger arguments may be made for correlating the Summerside formation with lower units A and B of the Blow Me Down Brook formation. The more quartzose upper units C, D, E, and F of the Blow Me Down Brook formation may be correlated to the Irishtown formation. -- By careful recognition of strata and successions, it may be feasible to effectively map these rocks across the region.

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