Stratigraphy, mud buildups, and carbonate platform development of the Upper Ordovician to Lower Devonian sequence, Ellesmere, Hans, and Devon Islands, Arctic Canada.
Creators: name: De Freitas, Tim A.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1991
Subjects: subject: Geology.

description: The Upper Ordovician to Lower Devonian platform in the Canadian Arctic twice evolved from a ramp to a rimmed shelf profile. Platform backstepping occurred in the fastigatus, acuminatus, cyphus?, sakmaricus (in North Greenland only) and linearis graptolite zones. Two major phases of pinnacle reef development followed platform backstepping, the first beginning in the lower Llandovery (cyphus Zone) and the second in the Ludlow (linearis Zone). Pinnacles of the first phase are uncommon, occur in the vicinity of Baumann Fiord, and show a vertical succession of lime mudstone, poorly exposed microbial carbonate, and coralgal biolithite, representing upward shallowing. The last named lithofacies is newly interpreted as representing a high-energy, wave-stressed environment that excluded stromatoporoid growth but favoured a sparse skeletal metazoan fauna, thickly encrusted by microbes. Paleo-surface area of these structures was apparently important for the accumulation of extensive ooids, which are associated with the upper parts of some pinnacle reefs. Three large mud buildups on central Ellesmere Island were established on the shelf margin subsequent to Upper Ordovician (fastigatus Zone) platform drowning. These structures show a vertical lithofacies succession: bioturbated lime mudstone is overlain by microbial carbonate then by mudstone-rich stromatoporoid floatstone and bindstone. The succession records overall upward shallowing. The olive green shale unit, well exposed in the vicinity of Trold Fiord, is an areally extensive and mappable middle Ludlow unit of the Cape Phillips Formation that postdates diachronous, middle Ludlow platform backstepping in the vicinity of Baumann Fiord. After backstepping, condensed sequences occurred over paleotopographic highs and expanded sections over lows, and a subsequent second major phase of platform rimming occurred. Stratigraphy known in the southern Arctic Islands is generally applicable to northeastern Ellesmere Island, but local lithological variations occur. The upper part of the Allen Bay Formation at Darling Peninsula, in particular, is unusually thick, and subtidal, perhaps resulting from greater subsidence, related to lithospheric flexure and deep marine clastic sedimentation that drowned the contiguous platform on North Greenland. Other formations recognized in this area include the Cape Storm, Douro, and Goose Fiord formations, although these, too, show minor lithological differences from type sequences. A thick grey siltstone unit in the vicinity of Bay and Vesle fiords is suggested to be a distal facies of the Red Canyon River Formation. This sequence is a progradational clastic wedge that likely represents the first, largest phase of the tripartite Caledonian Inglefield Uplift which profoundly affected carbonate deposition in the areas of southern and central Ellesmere Island during the late Silurian and early Devonian time. The base of this unit is diachronous and likely late Silurian in age. (Abstract shortened by UMI.)