Squishy in the sloshy: paleoecology as a proxy for tides?

The ocean tides are a key driver of a range of Earth system processes. Tidal energy drives vertical mixing with consequences for ocean circulation, climate, and biological production, and the tidal stream transport sediments, pollutants, and other matter through the ocean. Tides have also been proposed to be one component influencing key evolution and extinction events, including initiating the radiation of terrestrial vertebrates. Over the past decade it has become clear that the key controller of tidal energetics on long time scales is tectonics because the size of the ocean basins controls the resonant properties of the tides. Consequently, having accurate reconstructions and paleoDEMs (Digital Elevation Models, i.e., topography) would lead to accurate deep-time tides.  Here, we propose that paleoecology can be used to constrain the paleoDEMs, and thereby improve deep-time tidal models results: if a fossil is from a coastal setting, we know where the coastline should be in the reconstructions. We use extensive literature reviews of fossil cnidarian medusae (“jellyfish”) and ichnites (footprints), with focus on those from dinosaurs, to constrain Cambrian and Jurassic paleoDEMs. The early results are encouraging, and in many cases estimates of tidal current speeds can be obtained as well from grainsize estimates of the sediments in the rocks.