Bedload Transport of Mud Across A Wide, Storm-Influenced Ramp: Cenomanian-Turonian Kaskapau Formation, Western Canada Foreland Basin--Discussion

Abstract

We would like to comment on a recent paper by Plint et al. (2012) that discusses mud transport across a Cretaceous shelf. The authors have taken to heart recent research that advocates looking for evidence of bedload transport of aggregated clays, and we are comfortable that much of the clay component in the Kaskapau Formation did indeed arrive via bedload transport rather than simply settling out of the water column. However, whereas we are perfectly comfortable with the proposed mode of transport, we do have several concerns and suggestions concerning one type of mud aggregate discussed by Plint et al. (2012). In the depositional model that the authors present (their fig. 16), they envision that cohesive mud is reworked by storms into intraclasts and that these then are carried across the seabed in bedload. That in itself is no problem, because it can be shown in experiments that surficial muds with as much as 85% water content can be transported as millimeter-size aggregates for considerable distances (Schieber et al. 2010). One class of aggregates, however, described as intraclastic aggregates (IAs for the remainder of this manuscript) by the authors, did capture our attention. The authors state that “ Storm wave reworking of the seafloor produced intraclastic aggregates…because the mud had been rendered cohesive by the chemical compaction and biostabilization processes that operated shortly after deposition .” We are aware that surficial sediments can gain enhanced cohesion and improved erosion resistance due to mucus from benthic worms and endo-sedimentary microbes, but we are not quite sure what the authors mean by chemical compaction. If they mean that cementation renders the muds firmer and more cohesive, it would have been rather appropriate to document this critical factor in the aggregates in question. By definition, …