Palynostratigraphy of the lower Paleogene Margaret Formation at Stenkul Fiord, Ellesmere Island, Nunavut, Canada

Abstract

The upper Paleocene to lower Eocene Margaret Formation exposed at Stenkul Fiord on southern Ellesmere Island, Nunavut, Canada, represents a nearly continuous terrestrial succession of microfossilrich clastic sediments and coal. These strata were deposited at a time of extensive tectonic activity associated with Eurekan deformation. The precise chronology of the Eurekan deformation is poorly known. Prior studies at Stenkul Fiord provided a stratigraphic overview and relative age estimates for exposed strata but lack the absolute age control required to investigate the timing of deformation events. Strata at Stenkul Fiord preserve evidence of Arctic forests that may have grown during hyperthermal events that characterized the Paleogene, namely, the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2). A quantitative palynological approach is herein used to define a new higher-resolution biostratigraphic framework for the Margaret Formation strata at Stenkul Fiord. This resulting improved biostratigraphic framework is integrated with new absolute age control of 53.7 ± 0.06 Ma provided by U-Pb ID-TIMS of zircon preserved in an ash bed within the studied succession. Nine pollen zones are defined based on cluster analysis, NMDS ordination, firstand last occurrences of taxa, and angiosperm pollen taxa diversity (H 0 ). The presence of thermophilic pollen taxa at Stenkul Fiord provides evidence of climates related to the globally warm climates during the early Paleogene.

Geochemical indications for the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM-2) hyperthermals in terrestrial sediments of the Canadian Arctic

“…The degree of coalification was measured as 0.34 HRm/VRm% (lignite and/or subbituminous coal), confirming the results of Kalkreuth et al (1996). Thermal Alteration Indices (after Pearson, 1984) ranged between 1 and 1+ for terrestrial palynomorphs preserved in the section (Sudermann et al, 2021).…”

“…The slightly higher range of 1.2‰ for the interval 10-20 cm above volcanic ash layer MA-1 compared to 1.1‰ found as a lateral range value over 1.2 km is within the expected range of local environmental effects. This finding further confirms the interpretation that the early Eocene forest ecosystems of Stenkul Fiord experienced lengthy periods of ecological stability, as recorded in the carbon isotope signature and palynology (Sudermann et al, 2021) of individual coal seams. Thus, vertical changes of δ 13 C values toward lower or higher values, in a range exceeding ~1.1‰ to 1.2‰, likely represent changes to the global carbon isotope composition through time.…”

“…The range of 1.1‰ indicates that overall similar and relatively stable environmental conditions prevailed in the coal swamp ecosystem. This finding is also shown by results of the palynological investigation of Sudermann et al (2021), who identified similar palynoflora in stratigraphically correlated segments of different sections at Stenkul Fiord. Accordingly, taphonomic and early diagenetic processes, which were active during coalification, apparently did not significantly affect the carbon isotope results.…”

“…The majority of the samples measured for bulk δ 13 C values of the stratigraphic section are from fully developed coal seams, lacustrine deposits (Sudermann et al, 2021), and other floodplain deposits with a subordinate degree of clastic influence. Only ~15% of the samples were determined on coal particles and plant remains sampled from fluvial clastics in Units 3 and 4, which could have been transported prior to sedimentation, but do not necessarily represent a priori old carbon.…”

“…Coal seams and accompanying organic-rich sediments were additionally sampled for palynological analyses. The results of the palynological studies are reported in Sudermann et al (2021).…”