Comparative sedimentology between greenhouse and icehouse stratigraphic successions

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Hummocky cross-stratification is believed to be one of diagnostic sedimentary structures in a storm-dominated shallow marine environment. In general, the wavelength of hummocky cross-stratification increases with the increase in bed thickness of tempesties. Within a tempestie bed, the wavelength of hummocky cross-stratification decreases upsection and this relationship may correspond to the decrease in the orbital diameters during the waning stage of storm waves. Furthermore, paleoflow directions of tempesties, which were investigated on the basis of sole marks, tend to more orthogonal relative to the paleo-shorelines with the increase in bed thickness of tepmestites and this relationship may reflect higher degree of coastal setup in response to the increase in storm intensities. Therefore, the wavelength of hummocky cross-stratification is interpreted to be a function of the orbital diameters of storm-induced oscillatory currents near sea floors and many reflect the intensity of storm … More waves. Here I investigated temporal variation in the hummocky cross-stratification wavelength as a proxy for the storm intensity through the Phanerozoic. The hummocky cross-stratification wavelength shows secular changes though the Phanerozoic with two major peaks at middle Cretaceous and late Devonian, together with two other secondary peaks at early Jurassic and late Ordovician. These secular changes largely correspond to major greenhouse-and-icehouse cycles of global environmental changes. The peaks of the hummocky cross-stratification wavelength, however, are earlier or later than major warmer periods of independently estimated long-term fluctuation in the global temperatures. These time lags are interpreted to indicate that the threshold conditions for the intensification of storms occurred at some times before and after the extreme warmth of global temperatures. The outcome of this study suggests that the storm intensity would be the highest before and/or after the maximum stage of the global warming with an ongoing greenhouse phase in future. Less