Coon Creek Formation - The Geology of The Mississippi Embayment and Coon Creek

The Geology of The Mississippi Embayment and Coon Creek

This thumb print-shaped bay extends roughly north-south from central Mississippi to southern Illinois. It was formed when rocks, weakened by gradual spreading of the North American continent, sagged into a wide, shallow trough. The Gulf of Mexico filled the trough on several occasions between 80 and 50 million years ago. The Mississippi Embayment stretched West from the Tennessee Valley to the area of Little Rock, Arkansas. It may have been 1,000 feet deep where Memphis is now. The embayment gradually filled with sand, clay, and gravel brought in by rivers on uplands to the north, east, and west (Wade 1926).

The margins of the bay teemed with marine life. Crabs, snails, lobsters, clams, scallops, whelks, nautilus, sharks, and other familiar animals lived in the warm, shallow sea, eating, reproducing, and being eaten (Sohl 1960 and 1964). Giant reptilian mosasaurs, highly ornamented cephalopods, and other less familiar sea creatures lived in the water. Their shells, bones, carapaces, teeth, and other hard parts were constantly being buried in the sandy mud of the sea floor. The lack of distinct layering indicates that clams, shrimps, and other burrowing organisms mixed the bottom sediments. Periodic hurricanes may have brought in heavy loads of river sediment to bury the plants and animals living there. Conditions for life were ideal; the water was warm and of normal salinity (Wade 1926). Wave action ensured sufficient oxygenation for animal life.