Updated Lithological, Biostratigraphic, and Thermal Alteration Data for the Lower Paleozoic, Offshore Labrador, Canada

Abstract

Paleozoic strata is encountered in 7 wells located offshore Labrador, Canada (Hopedale E-33, South Hopedale L-39, Tyrk P-100, Gudrid H-55, Roberval K-92, Indian Harbour M-52, and Freydis B-87) where it represents erosional remnants now restricted primarily to the floors of select Cretaceous syn-rift half grabens in the Hopedale Basin. The Paleozoic section ranges from 4 m at Tyrk P-100 to over 400 m in thickness at Indian Harbour M-52 and is predominantly composed of carbonates (limestone and/or dolomite) with siliciclastics (siltstones and sandstones) accounting for over 300 m of strata in the Freydis B-87 well. Previous biostratigraphic analyses of this interval have been hindered by varying degrees of diagenetic alteration and associated limited palynological recovery, resulting in an assortment of ages including: undifferentiated Paleozoic, Ordovician, Devonian, and Carboniferous. Inconsistent age data and a lack of lateral continuity has prevented the correlation of Paleozoic strata along the Labrador margin at both a regional and global-scale. New biostratigraphic analyses of the Labrador margin Paleozoic strata was conducted on cuttings (7 wells) and core (4 wells) resulting in the observance of Upper Ordovician palynomorphs in 6 of the 7 wells, with no palynomorphs older than the Sandbian identified. The seventh well, Gudrid H-55, contained poorly preserved, undifferentiated lower Paleozoic palynomorphs; however, based on lithological resemblance and a similar degree of thermal maturation to other wells, specifically Roberval K-92, this interval is also interpreted as Upper Ordovician. Thermal maturity was determined from palynomorphs observed in Gudrid H-55, Roberval K-92, Indian Harbour M-52, and Freydis B-87 with thermal alteration indices (TAI) ranging from 5+ to 6 (dry gas). A significant amount of Carboniferous contamination is also noted in cuttings from these four wells with spores exhibiting TAIs of 3+ to 4 (immature to mature). This new biostratigraphic data demonstrates that the entire Paleozoic interval in the Hopedale Basin is Upper Ordovician in age, and correlations between wells are now possible. Additionally, the Paleozoic of the Labrador margin can now be correlated on a global-scale to other time-equivalent deposits in an attempt to further the understanding of Upper Ordovician paleoenvironments and the changes that occurred during this tectonically active period preceding the Ordovician-Silurian mass extinction.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019