Tidal Modeling of an Ancient Tide-Dominated Seaway, Part 2: The Aptian Lower Greensand Seaway of Northwest Europe

Abstract

Abstract The Cretaceous Lower Greensand deposits of southeastern England and northern France contain abundant evidence of diurnal (once-daily) paleotides, with tidal influence increasing into the late Aptian. The Imperial College Ocean Model (ICOM) is used herein to determine the amplitude, origin (astronomical or co-oscillating), and characteristics (diurnal or semidiurnal) of the tides in the shallow marine “Lower Greensand Seaway” where these sediments were deposited. A global ocean paleotidal model of the Aptian predicts very low tidal ranges (microtidal) in the proto–Central Atlantic Ocean and Boreal Ocean, with higher tidal amplitudes, especially of the diurnal constituents, predicted in the northwestern Neotethys Ocean. This suggests that the Neotethys Ocean was the only significant source of oceanic tides to the Lower Greensand Seaway. Herein, the results of the global ocean paleotidal model are used to supply boundary conditions to a higher-resolution regional paleotidal model of the Lower Greensand Seaway. The regional paleotidal model shows that the tidal range of the Lower Greensand Seaway is largely controlled by the width of the connections to the open ocean. As sea levels rose during the Aptian, the oceanic connections widened, resulting in reduced frictional damping of the oceanic tidal wave. Coupled with funneling, shoaling, and Coriolis effects, this led to tidal amplification. Sensitivity tests using a variety of paleogeography and paleobathymetry scenarios suggest that the model predictions are robust. The global- to regional-scale paleotidal modeling presented here strongly suggests that there was a connection through France (in the Aube region of the Paris Basin) from the Neotethys Ocean to southeastern England. However, there are no time-equivalent deposits in this region to validate this suggestion. It is herein argued that that this is due either to postdepositional erosion or to low sediment supply coupled with strong tidal currents sweeping the seafloor to exposed bedrock.