Constraining Palaeogeography and Palaeotides for the Cambrian using cnidarian medusae
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The ocean tides influence key Earth system processes at a range of spatial and temporal scales. It is known that the geometry of ocean basins is the leading controller of tidal energetics, so well-constrained palaeogeographic reconstructions and tidal properties for Earth’s past are imperative when investigating other Earth system processes. Here, we present a novel way to constrain both deep-time tidal model results and reconstructions, by combining palaeoecology with sedimentology. We compare new palaeo-tidal model simulations for the Cambrian period, significant for the early origin and radiation of major animal fauna, to tidal proxies. One of the most abundant soft-bodied organisms preserved during this time are cnidarian medusae (“jellyfish”). A total of 17 cnidarian medusae localities were obtained through the literature, which had an adequate global distribution and occurred at regular intervals throughout the period of study. In some locations there were also estimates of palaeo-tidal range. Our results show a good agreement between the simulations and proxy data. In the few locations where there is disagreement, it is proposed that the palaeogeographic reconstructions are missing details, e.g., island chains, and our results allow for the palaeogeographic reconstructions to be improved. The proxy method presented is promising and can be applied to other time-periods with different marine fossils, particularly at evolutionary and extinction periods where the marginal marine environment is of importance.
Key Points
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First use of palaeoecology combined with sedimentology to constrain both reconstructions and tidal simulation outputs, trialled in this study on the Cambrian period.
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Good agreement between proxy and simulation data for tidal ranges.
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Proxy method holds potential for use with different marine fossils to examine other time periods.
Plain Language Summary
Ocean tides are crucial for shaping Earth’s environment on short and long timescales. The shape and layout of ocean basins are the main factors that influence how tides behave. To understand how tides affected Earth’s history, we need accurate models of ancient ocean conditions and how they interacted with the environment. Here, we use a new approach to improve tidal models by combining fossil evidence with sediment analysis. We focused on the Cambrian period, a time when many major animal groups first evolved. One of the most common fossils from this time are jellyfish. We investigated 17 locations where jellyfish fossils have been found by looking at the surrounding sediments for signs of tidal influences, including tidal range. Our tidal models generally matched the data from the fossil sites, but where they didn’t, we believe it’s because the ancient maps are missing features, like small islands. This can be used for other time periods, especially those tied to important evolutionary or extinction events in shallow marine environments. We believe there is poetry in this type of research and provide an example in the supplementary material.
