Meandering River Floodplain Processes and Sources of Organic Matter in the Late Cretaceous, Dinosaur Provincial Park, Alberta, Canada

Paleoenvironmental studies of the Late Cretaceous at Dinosaur Provincial Park (Alberta, Canada) have refined reconstructions of terrestrial fluvial environments and dinosaur habitat. However, most studies were confined to channel deposits while associated floodplain deposits have generally been overlooked. To address this knowledge gap, sedimentological and geochemical techniques were applied to a floodplain-dominated exposure to investigate meandering river floodplain dynamics during the Late Cretaceous.

A detailed stratigraphic section, including lithology, grain size, bed thickness and pedogenic features, was recorded of the 47.5-m-high outcrop. Samples were collected every 0.5 m for Total Organic Carbon and δ13C of organic matter analysis, palynofacies analysis, and X-ray diffraction. Field-based grain-size measurements were corroborated by laser particle size analysis.

Trough-cross stratified sandstones, mudstone-clast breccia, and siltstone with organic interbeds comprise meandering channel-belt deposits. Intervals between channel belts are dominated by silty-mudstone facies with pedogenic features such as dispersed organic matter, mottling, root traces, and slickensides consistent with accumulation in adjacent floodplains environments. A continuous section of floodplain deposits (~22 m), capped by a volcanic ash, record floodplain dynamics over ~0.5 million years. Physical structures indicate extensive paleosol development that indicate wet-dry climate fluctuations. Palynofacies assemblages suggests exposure to fresh-water conditions. The record of δ13C in terrestrial organic matter shows a negative trend, which agrees with the global composite δ13C curve. This suggests that the terrestrial organic matter assemblages preserved in the Dinosaur Park Formation record contemporary changes in the global carbon, not entirely overprinted by local and regional carbon cycling processes.