Copyright  MegMawL.com © 1997-2005.  All rights reserved.

In the river bed of the Wando River in South Carolina we find fossil bones from the great Wooly Mammoth that lived about 14 thousand years ago alongside teeth from the Carcharocles auriculatus shark that were lost about 40 million years ago.  How is it possible that a land mammal lived in the same place as an ocean fish during geologically different times?

For the purpose of this discussion we will consider the interface between ocean and land - coast lines - at certain points in time.  Coastlines change over time due to many forces like sinking of the land mass or the increased volume of the ocean water due to Global Warming.  The rise and fall of land masses contribute to a coast line's movement but the changes in the volume of liquid water in the world's oceans cause the most change.

During the long history of the earth there have been many coast line changes.  The most recent Ice Age started about 5 million years ago.  Many scientists believe that we are still in this Ice Age, although in one of its "warm cycles". 

This time was characterized by intense cold periods, moderately cold periods, relatively warm periods and periods that are warmer than today's temperatures.

Today about 10% of the earth's surface is covered by ice.  The ocean borders of the East and Southeast Coast of the United States are shown in Figure 1.

It has been estimated that if all the ice currently locked up in glaciers and polar caps were to melt today, the ocean waters would rise about 210 feet (63.5 m).  Parts of North and South Carolina as far west as Rocky Mount and Columbia would be underwater.  During the last 750,000 years, major ocean transgressions occurred 6 times.  During the last 2 million years, major ocean transgressions occurred over 20 times.
 

During periods of ocean inundation most of the Coastal Plains of the Carolinas were part of the Atlantic Ocean.  Peninsulas were formed by the Great Carolina Ridge and the Norfolk Arch.  (See Note 4 below.)  Vast coastal areas were part of "embayments" - shallow, warm water bays where marine mammals migrated to birth their babies.  This also brought the sharks that found these mammals easy prey.

Example:
Beginning about 4.5 million years ago during a warming period, the ocean waters returned to inland areas of North Carolina and began forming the Yorktown Formation.

The graph below was generated from spreadsheet data provided by the University of Bristol, UK.  A direct correlation is shown between Earth's temperature and sea level.  Looking "between the lines" one can see the Miocene Period, Pungo Formation and the Pliocene Period, Yorktown Formation deposition at Lee Creek, NC.  For an in-depth discussion see:

Lee Creek Mine Stratigraphy

FIGURE 4

*****************

NOTES:

1.)  Notice that there are no Great Lakes, Long Island, NY, or Cape Cod, MA. in Figure 3.  These features were formed millions of years later during the last Ice Age.  Long Island is largely the product of the Terminal Moraine and Recessional Moraines of the Wisconsinan Glacier.  Cape Cod is mostly the Terminal Moraine of the Cape Cod Bay Lobe of the glacier.

2.)  Weird things happen during a Glacial Retreat.  The land under the glacier had been pushed down by the massive weight of the ice, and it was rebounding upward because it no longer was covered by millions of tons of ice.  The upward rebound of the land was accompanied by a rise in sea level as water from the melting glacier returned to the sea.  For a brief period in geological time, there was a complex interplay between the rising sea and the rising land.

3.)  "Sea Level" is a term that is probably best measured from some "absolute" like the center of the earth, but that is not how it is done.  If we state that the top of our home's front steps is 253.5' above sea level, we actually should use the term "Mean Sea Level" to average out the effects of waves, wind and tides.  For our purposes, in the discussion above, a more "absolute" way of considering this issue is to talk about it in terms of where the coast line lies at certain points in time. This basically neglects the effects of the vertical movements of land masses and ocean volumes. 

4.)  All formations in the area around Wilmington, NC, overlay a geological oddity known as "The Great Carolina Ridge".  Some scientists believe that this localized section uplifted during the Late Eocene Epoch causing a "high spot" that could have aided in the erosion or Reformulation of the 10 possible formations that overlay the Peedee formation at that time.  The "high spot" that remained could have prevented ocean inundations and subsequent marine fossil depositions during periods of mild oceanic transgressions along this ridgeline.                    

Figure 5. - Great Carolina Ridge.              
 

During certain periods, the Ridge stood as a peninsula when the surrounding Coastal Plain was submerged and the geologic strata exposed on it represent older beds that elsewhere within the region are buried by younger sediments.  During the Ice Ages and a period of intense ocean transgression, a Pleistocene Formation like the Waccamaw could have been deposited on top of a Cretaceous Formation like the Peedee.  (Although widely considered to be a cold period in the earth's history, there were often times during the Pleistocene when the earth's temperatures were higher than those of today and coastlines far inland of those of present time.)

5.)  Another complication in this simplistic view of local geology is the idea of "Reformulated Formations".  In the Miocene Epoch after the second Great Appalachian Uplift and during a time of earth warming and intense ocean transgressions, some fossils were washed out of their original formations and conglomerated together in a "new" formation.  After the ocean regressed, sedimentation covered this "reformulated" formation and later "pure" formations formed on top of it.  For more information on these topics see:

MegMawL - Definitions - Ocean Regression

MegMawL - Definitions - Ocean Transgression

MegMawL - REFORMULATED FOSSIL FORMATIONS

MegMawl - Stratigraphy of The Lee Creek Mine

This information is copyrighted and can not be reproduced in any manner without our written permission.   Copyright  MegMawL.com  ©  1997 - 2005.  All rights reserved.  If you would like to use any of this information - verbatim - for your website or school paper, please email us first.