THE ALBIAN/CENOMANIAN BOUNDARY CARBON-ISOTOPE EXCURSION RECORDED IN A COAL/LIGNITE DEPOSIT, MOOSE RIVER BASIN, ONTARIO

The application of carbon-isotope stratigraphy in terrestrial sequences as a tool for correlation is well developed. Recently, Gröcke et al. (2006; Geology) produced a terrestrial δ¹³C across the Albian/Cenomanian boundary in a near-shore setting, but noted that the positive segment of the overall excursion was not recorded due to the global D₂ sequence boundary. It was suggested by Gröcke et al. (2006) that positive δ¹³C excursions, if associated with regressions, might be absent in terrestrial records. In order to clarify this, a continuous coal-lignite sequence from Moose River Basin, Ontario has been investigated for δ¹³C and palynology. While several cores have been investigated, the Onakawana B core (~40 m) has provided the most complete record of the Albian/Cenomanian boundary δ¹³C excursion in bulk terrestrial sediments (claystone, coal, lignite). The δ¹³C record shows a rapid negative excursion of ~3.6‰ followed by a broad positive excursion of ~2‰ beyond background values. Since the complete isotopic excursion was shown in the Onakawana B core, it is plausible to suggest that the terrestrial record is not biased by regressive sequence boundaries. The core is located within a deep basin, unaffected by moderate sea-level changes, which is likely the primary factor as to why the record was preserved. Palynology assemblages suggest that the base of the succession is latestest Albian, and is comparable to sections in Wyoming and the mid-continent. Palynofloral ranges for the Albian–Cenomanian interval are long-ranging common forms thus the constraint of the boundary based on palynology is difficult. Thus, highlighting the fact that terrestrial isotope stratigraphy, coupled with palynology, could prove to be a method in which to constrain palynofloral assemblages to confined time intervals.