If one depended on the strata exposed by the strip mining operation at the PCS Mine to provide a complete record of the events that occurred over the past 40 million years, he would find that there are gaps in the geographic record.  Of particular interest are the discontinuities that exist in the serial deposition of sediments from the ocean, sediments from rivers and wind blown deposits.  These unconforming boundaries between horizons of different times indicate that there were periods when environmental forces stripped off soil, rock and fossils that were laid down in earlier times.  There were many of these events in the history of the present day mine, some not pictured in the following figures.  The first one of interest occurred at roughly the beginning of the Miocene Epoch.  See Figure 1 below.  Others occurred about 800 thousand years after the beginning of the Pliocene Epoch, during the Pliocene about 4 MYA and the last toward the end of the Pliocene.    (MYA = million years ago and MYO = million years old.)

Figure 1 above represents the stratigraphic column at the Lee Creek Mine as it is today.  From looking at the figure it is evident that there are sections of deposited material missing in at least 4 places.  These gaps in the geological record have been caused by environment forces that have removed this "dirt".  Many factors can be blamed for these events, but none have happened on a grander scale than the high energy Transgression (sea over-runs the land) and Regression (sea retreats from the land) caused by Ice Age warming and cooling cycles.  Click on Blue Underline words for formal definitions.

Figure 2 shows a cross section of the land that would one day become the Lee Creek Mine as it might have appeared about 21 million years ago.  We show the section as if there had been no erosional changes for the time period 41 MYA to 21 MYA.  In fact there were many ocean incursions during this period so the strata could have been composed of either land or oceanic sediments.  In other parts of the East Coast there have been several stable geological formations laid down during this 20 million year time period.  About 20.5 million years ago, a period of ocean transgressions and recessions effectively stripped off 20 million years of accumulated deposits.

Figure 3 shows the stratigraphic column shortly after this massive erosional episode ended.  The 20 million years (41 million year old to 21 million year old) accumulated sediments were scoured off by ocean changes and redeposited further inland and out to sea.  The Sandhills of North Carolina were formed in this manner as the incoming ocean moved sand deep inland.  The Continental Shelf was added to by the action of the outgoing ocean.  The fossils that were deposited during this period were either moved or Reformulated into the bottom of the future formation.

A far more interesting event occurred during the next period of deposition. During the period 20.5 MYA to 4.5 MYA more sediments and fossils were deposited.  Figure 4 shows what Lee Creek might have looked like at this point in time.

During most of this time period, the area was dry land.  For example, 6 MYA TO 4.8 MYA the earth went through one of the most intense cold periods of the Tertiary Period.  During this time, because of the growth of the ice caps and several other reasons, the Mediterranean Sea dried up completely.

Another ocean incursion happened about 4.5 million MYA which was right after the beginning of what we now call the Pliocene Epoch.  This was a high energy, relatively rapid event in geo-time.  During this overrun sediments were removed and carried away. This is the unconformable, discontinuous contact between the Yorktown and Pungo River Formations.  It provides one of the best examples of Oceanic Reformulation.  10 million years of Late Pungo River Formation and the Eastover Formation in this part of North Carolina were scowered out and largely removed.  The "dirt" that was deposited between 14.8 to 4.5 million years ago was relocated inland and seaward.  Many fossils uncovered from their former layers found a new home on the new ocean floor and were reworked into the lowest part of the Yorktown Formation.  Here may be found Great White teeth, usually black in color, that were initially deposited in the Late Miocene and Early Pliocene and now found in the Earliest Yorktown, Pliocene sediments.  See Figure 5 above.

The next half million years are the most interesting paleontologically.  During this time the ice caps had undergone extensive melting to the point that this area was deep underwater and the shoreline far inland.  The offshore currents were such that the water temperature was cold.  During this time the famed Sunken Meadow Member of the Yorktown Formation, Unit 1 - the Placopectin clintonius Zone was formed.  As stated before, the Horizon Wide, Oceanic Reformulation at the bottom of this strata formed the boundary between the Pungo River and Yorktown Formations.  At the top of this zone at its contact with Unit 2 another Ocean Regression occurred. During the time this area was "dry land" unconformities within the horizon show up.  What this implies is that there was Reformulation going on but in limited sections of the strata caused by rivers and streams.

During the 4.5 MYA to 3 MYA time period that the Yorktown Formation was formed, there were several periods of both Oceanic and River Reformulation which altered the color of the teeth.  (See Note 1 below.)  One such incident when River Reformulation occurred was at the boundary of the Yorktown Formation, Unit 1 and Unit 2.  This was a period where the ocean had briefly retreated and rivers flowed through Beaufort County, NC.  See Figure 6 below.

At the end of this "dry land period" another mild ocean incursion occurred with a corresponding sediment and fossil deposition.  During this period the largest C. megalodon were deposited.  A later transgression and regression conglomerated these fossils in a reformulated layer at the bottom of Unit 2 - the Rushmere Member of the Yorktown Formation.

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