Phanerozoic shallow marine sole marks and substrate evolution

The presence of erosive sole structures such as tool and flute marks in the sedimentary record can be used to interpret flow dynamics of ancient storm-dominated settings, as well as seafloor sediment properties. The formation and preservation of these structures require a hydroplastic and cohesive substrate. Therefore, the temporal distribution of these structures can be employed to track secular changes in seafloor rheology, which can significantly alter early diagenetic processes and thus shape global biogeochemical cycling. Herein I present a global compilation of Phanerozoic shallow marine successions bearing erosive sole structures, derived from assessment of the sedimentological, tectonic, and paleontological literature. The frequency of sole mark preservation in shallow marine environments has dramatically declined through the Phanerozoic. This first-order trend suggests that the rheological nature of the seafloor has experienced major secular transformations over the past 541 m.y. This record provides evidence for a marked decrease in sediment cohesion and increase in sediment porosity of the uppermost seafloor sediment column through time. I attribute this change in seafloor sedimentary properties to increases in the extent of bioturbation through the Phanerozoic, because the activity of sediment-mixing infauna dramatically increases the fluid content of the shallow sediment pile, decreasing the hydroplasticity necessary for sole mark formation and preservation. The gradual decline in the frequency of abiogenic sole marks in shallow marine successions through the Phanerozoic indicates that the development of bioturbation has been a similarly protracted process.