Figure 1. -- Coastal Plain of the Carolinas.                               

Figure 2. -- Key to features found in Figures 3 - 6.

Figure 3 shows what the Atlantic Ocean off the South Carolina coast might have looked like 22 million years ago (MA).  There were fossil layers sequentially deposited on top of older layers.

About 12 million years ago the Appalachian Mountains went through their second rebuilding.  These mountains were formed early after the breakup of the continents and almost completely eroded during the Cretaceous Period.  (This is one of the main reasons that we have very few dinosaur fossils in the Carolinas.)  Plate Tectonic forces pushed them up again during the Miocene Epoch.  The fossil and sediment layers many miles on either side were folded and uplifted along with the much older, igneous or metamorphic bedrock.  The folding in Figures 3, 4, 5 and 6 have been exaggerated for emphasis.

Figure 4. - South Carolina Coast 12 million years ago.                 

One of the major tenants in the study of geology is that high places get eroded and low places get filled in - EROSION and DEPOSITION.  Nature sometimes exhibits a "split personality" - one side working to fold the flat land into ridges and mountains and another side working to level it out again.  For millions of years after the re-birth of these mountains, the forces that cause erosion systematically worked to tear down this mountain range and redistribute its constituents, in some places like river deltas, far out to sea.

This process is at work on a macro and micro level.  In North America the mountains are being eroded to form the rich farmland of the plains.  The Triassic Rift Valley of Chatham County, NC, is being filled in by eroded material from the Appalachian Mountains.  Steep creek banks are being turned into gentle slopes.  The high places in your yard fill in the low places.

      Figure 5. - South Carolina Coast 6 million years ago,
            an intermediate stage in the erosion process.

Now here is the important part:  In some places inland from the coast, this process brought to the surface fossils and destroyed them.  Some of the upper, younger fossil layers were eroded away completely.    For a more intensive discussion of how this occurs see:    ENVIRONMENTAL DAMAGE TO SHARK TEETH

Figure 6 is a representation of the present day layers at the surface and underneath the South Carolina Coastal Plains.  The yellow layer underneath present day Charleston is what geologists call Quaternary Continental - present period deposition of material that long ago eroded from the Appalachian Mountains.  The fossil layer underneath Columbia originated in the Cretaceous Period while the layer under Charleston contains recent Pleistocene material.

Figure 6. - South Carolina Coast Present Time.                   

Seemingly complicated, the scenario outlined above is a very simplistic view of the actual geologic forces at work in this region over the last 100 million years.  Not discussed are intermediate stages where land erosion forces and ocean transgressions completely obliterated some sections of fossil formations.  Also complicating the picture - localized uplifting left some sections high and dry while nearby areas were inundated by a transgressing sea.  This dry land area would not be available for deposition of a marine fossil layer.

As an example, in the chart (see "Fossil Formations of the Carolina Coastal Plains") in Horry County, SC, there are areas where the 2 million year old, Pliocene-Pleistocene, Waccamaw Formation directly overlies the 68 million year old, Cretaceous, Peedee Formation.  The fossil record in Table 1 on that same page shows about 21 distinct layers that could have separated these 2 formations.  Another example in Northampton County, NC, shows the 5 MYO Yorktown Formation directly overlying the 88 MYO Cape Fear Formation.  Scientists would say that the younger formations UNCONFORMALLY overlie the older ones.  There are several possible explanations for this.

All formations in this area overlies 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.

                        Figure 7. - 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.  Any combination of these events could have allowed the Waccamaw to be deposited on top of the Peedee during a period of intense ocean transgression during the Ice Ages.  (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.)

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 formations 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 - Ice Ages

MegMawL - Definitions - Ocean Regression

MegMawL - Definitions - Ocean Transgression

MegMawL - REFORMULATED FOSSIL FORMATIONS