Circulation in large ancient epicontinental seas: what was different and why?

At times in the geological past, vast epicontinental seas flooded the continents. Almost everything we know about pre-Jurassic (200 million years ago) marine life and environmental change originates from such settings. Most of the truly oceanic sediments deposited before this time have either been subsequently subducted or metamorphosed (Allison and Briggs, 1993). An understanding of ancient epicontinental seas is clearly essential to our interpretation of past ecological and environmental change. Epicontinental seas, however, really have no suitably scaled modern counterparts. They were typically shallow, on the order of 10 to 200 m deep, but of vast extent, covering areas of up to ∼106 km2 (Wells et al., 2005a, 2005b). Such modern seas as the Baltic are of similar depths but are considerably smaller. Without suitably scaled modern analogues our understanding of these important water bodies is handicapped.