Provenance and paleodrainage of Late Jurassic and Early Cretaceous reservoir sandstones in the Flemish Pass and Orphan Basins

Lowe, D. G. (David George) (2009) Provenance and paleodrainage of Late Jurassic and Early Cretaceous reservoir sandstones in the Flemish Pass and Orphan Basins. Masters thesis, Memorial University of Newfoundland.

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Abstract

Late Jurassic to Early Cretaceous potential reservoir sandstones from three industry exploratory wells in the Flemish Pass and Orphan Basins were studied for provenance analysis. The sandstones from this study formed during intracratonic rifting that preceded the breakup between North America and its European conjugate margins and seafloor spreading in the North Atlantic. Most were deposited during the Tithonian and Neocomian North Atlantic Rifting stage, during which rifting intensified between Iberia and the Grand Banks and the deposition of important reservoir sandstones occurred regionally. -- Heavy mineral fractions were isolated from cuttings samples from six syn-rift sandstone units. The studied sandstones range in age from Tithonian to Albian. Three heavy mineral approaches were used to determine provenance and make correlations: (1) U-Pb geochronology and petrography of detrital zircons, (2) detrital heavy mineral grain counts and ratios, and (3) geochemistry of detrital tourmalines. -- Based mainly on detrital zircon ages and petrography and detrital tourmaline geochemistry, the predominant first-cycle sediment sources included the Neoproterozoic arc-phase igneous rocks of the Avalon Zone as well as the Ordovician to Devonian magmatic rocks and metasedimentary rocks present in the Central Mobile Belt. There is abundant petrographic and heavy mineral evidence to support significant recycling of material from cover sequences in these tectonic zones as well, likely including Early and Late Paleozoic sedimentary rocks which are ubiquitous in both zones. -- Such a source signature requires uplifted source areas to be present in the west, including parts of the Bonavista Platform, Interior Newfoundland, Northeastern Newfoundland Shelf, and potentially parts of the Irish conjugate margin, including the Porcupine Bank. Thus, paleodrainage orientations and delivery of coarse clastic detritus into the Flemish Pass and Orphan Basins was predominantly from the west during the Late Jurassic to Early Cretaceous, as seafloor spreading began between the Grand Banks and Iberia. Based on this information, one would expect to find reservoir facies sandstone units of this age concentrated along the western margins of the Flemish Pass and Orphan Basins, with deteriorating reservoir grade towards the east. -- A number of the studied sandstones in the Flemish Pass Basin show evidence for partial sourcing from the south, including proximal sources and distal sources as far south as the Avalon Uplift; verifying previous ideas that the Avalon Uplift existed as a significant positive regional tectonic element as incipient seafloor spreading began between Iberia and the Grand Banks. There is no evidence to support sourcing from the east, off of the Iberian margin or the Flemish Cap-Galicia Bank continental fragment, and material from these areas is instead interpreted to have been shed into the incipient Atlantic Ocean or Bay of Biscay. -- Mesozoic aged detrital zircons were present in two samples, and proved useful for constraining the depositional age of these sandstones. The most likely known sources of these grains include the Budgell Harbour Stock, in Central Newfoundland, or an Early Cretaceous granite basement intercepted by the Bonavista C-99 well in the West Orphan Basin. Both of these potential sources are located to the west of the studied units.

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