Petrology of the Signal Hill and Blackhead formations, Avalon Peninsula, Newfoundland

Singh, Chatra Ket (1969) Petrology of the Signal Hill and Blackhead formations, Avalon Peninsula, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Detailed studies on the Precambrian Signal Hill Formation and the overlying Blackhead Formation exposed between Flatrock and Ferryland reveal minor lithological variations. Lithofeldspathic Sandstone is predominant and forms most of the lower and middle members of the Signal Hill Formation and most of the Blackhead Formation. Conglomerate forms most of the upper member of the Signal Hill Formation. It is composed mainly of pebbles of tuff and rhyolite, sedimentary rocks, granitoid rocks, quartzite, and basic volcanic rocks, in order of decreasing abundance. -- The mineralogy of the Signal Hill and Blackhead Formations is similar and indicates common source rocks. Sediments were derived from Harbour Main, Conception and Holyrood - type rocks, exposed at that time somewhere to the north of the site of deposition. Ripple marks and cross-bedding displayed in the sandstone and siltstone of the lower and middle members of the Signal Hill Formations suggest deposition in an environment similar to the undathem environment of Rich (1951). Progressive upward fining of the Signal Hill conglomerate and concomitant change from planar bedding to cross bedding suggest a change in the depositing streams from conditions of predominantly rapid flow of the upper flow regime to those of tranquil flow of the lower flow regime. The rocks of the Blackhead Formation show features, characteristic of fluvial braided river deposits. These are mainly planar and trough cross-bedding, channels and mud cracks.

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