Tidal modeling of an ancient tide-dominated seaway, part 1: Model validation and application to global early cretaceous (aptian) tides

摘要

The utility of deep-time global paleotidal modeling is evaluated with a series of modeling experiments focused on the Early Cretaceous (Aptian). The results from a series of paleobathymetry sensitivity experiments indicate that, despite paleogeographic and paleobathymetric uncertainty, appropriate use of global paleotidal models complements and enhances stratigraphic and sedimentological methods. Before being applied to global paleotidal modeling, the Imperial College Ocean Model (ICOM) is validated for the computation of modern global tides. The ICOM results only deviate slightly from a "state-of-the-art" published model and were achieved with considerably less computational expense and without data assimilation. The results from global paleotidal modeling of the Early Cretaceous (Aptian) were assessed by comparison with the published geological record. ICOM predicts high mesotidal to macrotidal ranges on the Arabian Platform, around India (especially to the north and west), along the Pacific coast between North and South America, northeast of Australia, and around Southeast Asia. The model predicts low microtidal ranges in the proto-South Atlantic Ocean and Weddell Sea. A further validation test assessed the ability of the model to predict the dominant tidal constituents (diurnal or semidiurnal) in the Aptian "Lower Greensand Seaway" of southeastern England and Northern France. During the Aptian this region was connected to the Boreal, Proto-Atlantic, and Neotethys oceans and now preserves superbly documented tidal deposits. The model predicts low microtidal ranges in the proto-Central Atlantic Ocean and Boreal Ocean, suggesting that they had little impact on tides in the Lower Greensand Seaway. Higher tidal amplitudes, especially of diurnal (once-daily) tides, are predicted in the northwestern Neotethys Ocean, suggesting that this ocean was an important source of tidal energy to the Lower Greensand Seaway. Sensitivity tests to paleogeographic and paleobathymetric uncertainty indicate that the model predictions are robust. The prediction of predominantly diurnal tides is supported by published analyses of large dune-scale deposits in the Lower Greensand of southeast England.