Stratigraphy, petrography, structural geology, and geochemistry of the Humber Arm allochthon, North Arm, Bay of Islands - South Arm, Bonne Bay, Newfoundland

Kelly, Michael (2017) Stratigraphy, petrography, structural geology, and geochemistry of the Humber Arm allochthon, North Arm, Bay of Islands - South Arm, Bonne Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Humber Arm Allochthon in Western Newfoundland has long been recognized as a region where an ancient hydrocarbon system is thought to have developed. Nevertheless, and in spite of the many oil seeps along the western Newfoundland coast, no significant commercial discoveries have been made in this fold and thrust belt. The complex structural geology and stratigraphy may hinder any development of successful exploration plays. Recent mapping in other parts of the allochthon may be pointing towards other interpretations of the strata as possible targets for unconventional source rock reservoirs. To address at least part of this hypothesis, higher resolution mapping of parts of the Humber Arm Allochthon on and north of Bay of Islands is used as an indicator for another direction in exploring the petroleum system that developed across this area. In exploring the rocks north of the Bay of Islands new data will offer a better pattern for the distribution of the muddy, deep marine (source rock) strata in western Newfoundland. The Blow Me Down Brook formation is the most expansive sedimentary unit in the map area. Regionally, this tightly cemented low grade metamorphic rock structurally overlies organic rich and petroliferous strata of the Cooks Brook, Middle Arm Point, and Lower Head formations. The overlying ophiolitic rocks are separated from the Blow Me Down Brook formation by a dismembered unit of Lower Head formation containing exotic clasts and herein considered mélange. Petrographic and geochemical analyses of the sandstone blocks in the mélange indicate both the Blow Me Down Brook and Lower Head formation lithologies dominate the mélange sandstones. Significant differences in geochemistry indicate a more complicated pattern for origins and transport for volcanic strata that lies adjacent to and sometimes interbedded with. Mapping indicates identifiable deep marine outer shelf and slope strata are significantly folded before or during emplacement of the ophiolite suites. In this setting, tightly cemented Blow Me Down Brook formation sandstones may become the seal laying upon folded and fractured, muddy source rock reservoirs.

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