Highlights—Muddy Coastal Systems

Mud-dominated coastal systems play by their own rules. Many of the generalizations derived from years of study of sandy shoreline systems appear to not apply to shaley successions, or at least apply in unique ways. To better understand spatial changes and proximal-to-distal facies relationships of muddy systems, Harazim and McIlroy describe sedimentological, ichnological, and geochemical characteristics of the Lower Ordovician (Tremadocian) Beach Formation, Bell Island Group, Newfoundland. The results demonstrate that ancient fine-grained coastal systems are incompletely incorporated into sequence stratigraphic models owing to their atypical proximal-to-distal facies relationships, unique physical sedimentologic properties, and burial efficiency. The interpretations highlight the importance of 1) frequency of sediment supply events, 2) direction of mud transport, 3) diagenetic reactivity of minerals and bioavailable organic carbon, and (4) residence time of mineral grains and organic matter close to the sediment–water interface on facies architecture of this non-uniformitarian paleoenvironment, deposited prior to the evolution of soils. Face it, mud is complicated.

Mud-rich density-driven flows along an Early Ordovician storm-dominated shoreline: implications for shallow-marine facies models by Dario Harazim and Duncan McIlroy