Paper No. 25
Presentation Time: 9:00 AM-6:30 PM

STRATIFICATION, VERTICAL MIXING AND TIDAL FRONT BEHAVIOUR IN EPICONTINENTAL SEAS


ABSTRACT WITHDRAWN

, P.A.Allison@imperial.ac.uk

At times in the geological past the continents were covered by vast (up to 106 km2), typically shallow (100’s m) epicontinental seas that lack suitably scaled modern analogues. Almost everything that we know about pre-Jurassic (200 million years ago) marine life and environmental change originates from such settings as most of the truly oceanic sediments deposited before this time have either been subsequently subducted or metamorphosed.

A proper understanding of the flow processes that controlled circulation in epicontinental seas is clearly important as it would have impacted upon biological evolution, stratigraphy, and the global carbon cycle. Herein, we evaluate the formation and impact of tidal fronts in geologically ancient epicontinental seas. Tidal fronts are common occurrences in the summer months in modern coastal seas and separate thermally stratified water from well mixed water. Stratification occurs in deeper water as a result of solar heating. As the tidal wave propagates into shallower water it reaches a point where it interacts with the bathymetry and produces sufficient turbulence to vertically mix the water. In modern seas the fronts are associated with variations in productivity, biological diversity and the accumulation of fine grained carbon rich sediments (e.g. see Uehara et al., 2006).

In the absence of suitably scaled modern analogues we use a modeling approach applied to a highly idealized but suitably scaled domain to determine the impact and reach of fronts into epicontinental seas during an idealized transgression. We use Fluidity-ICOM (Imperial College Ocean Model), an unstructured mesh finite-element ocean model. This model has previously been validated for modeling modern and paleotides and tidal bed shear stresses (Mitchell et al, 2010).

References

Mitchell AJ, et al. (2010) Modelling tidal current-induced bed shear stress and palaeocirculation in an epicontinental seaway: the Bohemian Cretaceous Basin, Central Europe, Sedimentology, 2010, Vol:57, Pages:359-388,

Uehara, K et al., (2006) Tidal evolution of the northwest European shelf seas from the Last Glacial Maximum to the present. Journal of Geophysical Research, 111, C09025-40.