Late Cretaceous terrestrial ecosystems reconstructed from aromatic biomarkers, Smoking Hills, Canadian Arctic

The Smoking Hills and Mason River formations in Arctic Canada were investigated to evaluate changes in high latitude terrestrial ecosystems during the middle Coniacian-early Paleocene (?). Deposition of the Smoking Hills Formation occurred during Oceanic Anoxic Event 3, reflected by a marine transgression in the Anderson Basin and surrounding areas. The Anderson Basin was characterized by highly oxygenated and productive marine surface waters, anoxic to suboxic conditions at the sediment–water interface and low input of terrigenous organic matter. Despite the low concentration of terrestrially derived organic matter, the relatively high concentration of aromatic sesqui- and diterpenoids in samples from the Smoking Hills Formation indicates that gymnosperm vegetation dominated local terrestrial ecosystems. Aromatic biomarkers in samples from the overlying lower Mason River Formation show an increase in terrigenous organic matter with a slight increase in pentacyclic triterpenoids with oleanane, ursane and lupane carbon skeletons, which are common in all angiosperm families. These aromatic compounds increase considerably in the upper part of the lower Mason River Formation, suggesting diversification of angiosperms during the latest Campanian-early Maastrichtian. This increase in abundance and diversity of angiosperm indicators is associated with a broadly contemporaneous increase in wildfires as evidenced by the high total concentrations of pyrogenic polycyclic aromatic hydrocarbons in this stratigraphic interval. Wildfires may have increased erosion in the hinterland, increasing the flux of soil-derived organic matter into the marine basin. The findings reported here align with palynological and geochemical evidence shown in previous studies that indicate a global increase in angiosperm diversity in the Late Cretaceous. Wildfires likely played a crucial role in the diversification of angiosperms and the increase in soil erosion and river runoff in the Cretaceous Arctic.