Paleoenvironments and Correlation of Cretaceous-Paleogene Strata, Bylot Island, Nunavut
James W. Haggart1, Arthur R. Sweet2, Graham L. Williams3, Lisel Currie2, Vicki McNicoll4, Elliott T. Burden5, Philip H. Benham6, and Jennifer Galloway2
1Geological Survey of Canada, Vancouver, BC, Canada.
2Geological Survey of Canada, Calgary, AB, Canada.
3Geological Survey of Canada, Dartmouth, NS, Canada.
4Geological Survey of Canada, Ottawa, ON, Canada.
5Earth Sciences, Memorial University Newfoundland, St John's, NF, Canada.
6Shell Canada Ltd., Calgary, AB, Canada.
Cretaceous-Paleogene (K-P) rift-related basins are distributed widely around the Baffin Bay region, with significant onshore successions found on West Greenland and Bylot Island, Nunavut. Bylot Island strata are correlative with Albian-Paleocene rocks of the Nuussuaq Group of West Greenland, which have known petroleum indicators. A detailed biostratigraphic, paleoenvironmental, and provenance study of K-P strata of Bylot Island is thus being undertaken to help assess petroleum potential of offshore regions of Lancaster Sound and the continental shelf of northern Baffin Island.
K-P sedimentary rocks on Bylot Island total > 1 km in thickness. A continuous stratigraphic section is nowhere exposed and coarser units grade laterally into finer facies. Lowermost strata are typically in fault contact with Proterozoic basement rocks and consist of well-sorted quartz arenite with lesser siltstone and coal, locally to ca. 120 m thick. Overlying mudstone ca. 400 m thick was deposited in marine environments and includes interstratified sandstone to considerable thickness. On SW Bylot Island, a successive ca. 500 m-thick coarse-grained sandstone unit is widespread, grades laterally into deep-marine mudstone, and reflects progradation of shallow- to non-marine environments; local boulder conglomerate may reflect proximity to active fault scarps. Youngest strata on SW Bylot Island include geographically-restricted dark-grey to black mudstone while on N Bylot Island the succession is capped by sandstone and boulder conglomerate reflecting basin infilling.
Invertebrate fossils are rare and correlation relies on pollen and spores, with associated dinoflagellate cysts (dinocysts). Six pollen and spore assemblages are recognized, most associated with co-occurring dinocysts. Oldest strata lack dinocysts and indicate an age within the range of middle Albian to possible Turonian, suggesting correlation with the Hassel Formation, widespread in the western Canada Arctic. Successively younger strata contain assemblages suggestive of Coniacian, Santonian, early late Maastrichtian, late early or early late Paleocene, and late Paleocene ages. Biostratigraphic data suggest that disconformities may be present in the section, but further data are needed to qualify this. Quantitative analysis of floral assemblages, based on relative counts of dinocysts and spores and pollen, as well as dinocyst groups, has provided new paleoenvironmental data which, with outcrop sedimentology, indicate deposition in a variety of alluvial-fan, delta-plain, and submarine-fan environments.
U-Pb SHRIMP ages for detrital zircons from K-P sandstones of Bylot Island indicate a change in the provenance of sandy sediments deposited on SW Bylot Island between the Coniacian and Paleocene, but no apparent change in the N Bylot area, where the sediment source is interpreted to be local throughout K-P time.
AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.�����������������������������������������������������������������