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St. John's 2001
Technical Programme

SS16:  The Architecture, Origin and Evolution of the Paleozoic Continental Margin of Laurentia 
Organizers / Organisateurs:  Dennis Lavoie
Room / Salle:  A1046

Date:  30/05/2001
Time:  10:40 AM
Presenter:  Tom Calon

Stratigraphy and structure of sedimentary rocks in the Humber Arm Allochthon, southwestern Bay of Islands, Newfoundland

CALON, T., tcalon@esd.mun.ca, BURDEN, E.T., STROWBRIDGE, S. and NORMORE, L., Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NF, A1B 3X5

The allochthon comprises westerly transported thrust slices of lower Paleozoic rocks representing remnants of Iapetus Ocean and its flanking Laurentian margin emplaced during the Taconic orogeny. Upper slices contain oceanic crust-mantle (Bay of Islands Ophiolite) and an island arc suite ( Little Port Complex). Melanges and broken formations surrounding and underlying these suites in southwestern Bay of Islands can be stratigraphically resolved into four distinctive rock assemblages. The Blow-me-down Brook Assemblage is an arkosic sandstone with local shale intervals containing the trace fossil Oldhamia and acritarchs indicating an early Cambrian age. The Little Port Assemblage contains volcanic boulder conglomerate, sandstone, limestone and red chert unconformably overlying volcanic rocks.  The Bear Cove Assemblage has calcareous shale, oolitic grainstone, ribbon limestone, and limestone breccia, with turbiditic structures.  Palynomorphs recovered from these rocks indicate and early Ordovician (Tremadoc) age.  Riley's Brook Assemblage is a succession of varicoloured shales with several intervals of coarse grained sandstone; acritarchs indicate an Arenig age for these beds  Each assemblage is tentatively correlated over the map area using lithostratigraphy, tectonostratigraphic characteristics, and palynomorph biostratigraphy, and provisionally assigned to existing Cambrian and Ordovician formations of the Curling and Northern Head groups.

The Blow-me-down Brook Assemblage is the most coherent structural unit and shows a westerly verging fold-thrust pattern on the islands in the bay, but a broken and overturned cleavage fold system with northerly vergence underneath the Blow-me-down Massif.  Little Port and Bear Cove assemblages are typically broken formation with thin imbricate panels characterized by mesoscopic polyphase fold patterns.  The Riley's Brook Assemblage at Bear Cove is contained in relatively thick thrust panels with simple imbricate structure.

Significantly, two of the younger (Tremadoc and Arenig) biostratigraphic assemblages examined and mapped in this structurally complex region remain in the oil window.