Anomalous, Temporary Terrestrial Sedimentary Environments Following Cretaceous-Tertiary Ecosystem Disruptions: North America, Asia, and Europe

In the Western Interior of the United States, the local Cretaceous (K/T) extinction produced an abrupt paleoenvironmental change, from forested gleyed floodplain paleosols to laminated siltstones and coals, representing short-term, ubiquitous flooding. We attribute this to the loss of vegetation in the aftermath of the K-T impact, which likely caused an increase in upstream erosion, producing sediment-choked streams and wide-spread downstream flooding. Loss of all large vertebrate herbivores and many herbivorous insects increased the amount of vegetation reaching the ground, reflected in the onset of coal deposition at the start of the Tertiary. This explains why initiation or large-scale increase of coal deposition commonly signals earliest Tertiary terrestrial sediments in K/T deposits stretching from Alberta to New Mexico, including Raton Basin, CO and NM, Denver Basin, CO, Powder River Basin, WY, Williston Basin, western ND, eastern MT, and Alberta, Canada.

A preliminary global survey suggests that these dramatic earliest Tertiary changes aren't limited to North America. The Nanxiong Basin of China shows thicker mudflow deposits directly above boundary. Depositional style eventually returned to emphemeral stream and vertic paleosols development, such as was observed in antecendent Upper Cretaceous deposits.

The K/T boundary in the Vallcebre Basin of the southeastern Pyrenees (Spain) is imprecisely located; nonetheless, K/T deposits preserve a regression maximum that is marked by input of coarse-grained alluvial sediments which record a dramatic change from quiet muddy floodplains to sandy deposition by high-energy currents. This was followed by a period of quiescence and then Cenozoic flooding. These data suggest an interval of higher energy sedimentation and flooding, consistent with increased erosion and downstream flooding arising from ecosystem disruption.