Unconformities often puzzle geologists. An unconformity is a geological term in the study of stratigraphy for a region where sediment from one age overlays sediment from an older age, but fill from the age in between is missing. For example at the Peace River fossil site located in southwest Florida, late Pleistocene-age fossils are found in sediment over fossiliferous Miocene-age sediment, but rocks and fossils from the Pliocene and early Pleistocene are completely absent. Geologists are some times at a loss to explain exactly why unconformities occur in certain areas, and of course, creationists jump all over the lack of a definitive answer as proof against an old age earth. However, they are wrong. Though scientists don’t know for sure why an unconformity occurs, there are plausible reasons.
Most likely, the Pliocene and early Pleistocene were particularly arid. The rivers in the region dried up and floods were rare. Floods wash sediment over bones, thus creating fossils, so without fluvial sedimentation, fossil evidence never was preserved from this intervening age. This dry climate phase may explain why Georgia’s piedmont is almost barren of Pliocene and Pleistocene fossils, though I’m convinced a concerted search of Georgia’s river basins would discover some of the latter age here.
The fossiliferous strata off the coast of Edisto Beach, South Carolina parallels that of the Peace River fossil site and may be due to the same climate phase. This site too yields both late Pleistocene fossils mixed with Miocene shark’s teeth, so this unlocated Pleistocene strata must overlay Miocene strata, and the ocean currents are eroding both. At the Ashley River site, also in South Carolina, the Pleistocene fossils overlay even older Oligocene strata.
In the Peace River the fossils are located in an area of only about 84 square feet in sediment about 6-12 feet underwater. Scuba divers uncovered the fossils. Miocene fossils are not only found underneath the Pleistocene ones, but they’re intermixed with them and river currents even work them to modern surfaces. As river currents wash away ancient sediment, they expose these fossils. Nevertheless, scientists can use knowledge of chemistry to discern the difference in age between Miocene and Pleistocene fossils.
Scientists analyze the ratio of rare earth elements within the fossils. Rare earth elements are a family that aren’t particularly rare but consist of few a layman would know. They include 14 in the lanthanide series and 14 in the actinide series. All actinides, such as uranium, are radioactive. Lanthanum, cerium, and erbium are some examples of lanthanides. Rare earth elements exist in small quantities in ground water, and they occur in consistent ratios with each other. However, these ratios change over time. When animals drink water they ingest these elements and absorb them into their bones in the same consistent ratios. Naturally, Pleistocene fossils have ratios of rare earth elements that occured in Pleistocene ground water, while Miocene fossils have ratios of rare earth elements from Miocene-age water.
The list of Pleistocene fossils found at the Peace River is impressive and includes large, warm climate species.
red bellied turtle
undetermined duck or goose
pampathere (giant armadillo)
eremotherium (giant ground sloth)
Harlan’s ground sloth
Florida spectacled bear
white tail deer
Miocene fossils from this site are largely marine–shark’s teeth, ray plate teeth, fish bones, dugong bones, and whale bones. Notably though, 20 specimens from 5 species of three-toed gazelle horses have been recovered here. Here’s the list:
Three-toed gazelle horses were a common herbivore of the Miocene. They had a slender build resembling modern day deer. During the later Pliocene deer likely began to replace them in the ecological niche they occupied, while surviving horses evolved into the one-toed horses of today.
Hulbert, Richard; Gary Morgan, and Ardreas Kerner
“Collared Peccary (Mammalia, Artiodactyla, Tayassuidae, Pecari) from the late Pleistocene of Florida.”
Museum of Northern Arizona bulletin 65
Whitten, Kenneth; and Kenneth Gailey
General Chemistry with Quantitative Analysis
Saunders College Publishing 1984
Bob Perkins has shipped me an atlatl. Future blog entries will include an erratic series entitled “Adventures with an Atlatl.” I’m also planning on entries about Georgia’s Pleistocene Horses, Pleistocene deer, a study of passenger pigeons, and another erratic series detailing my time travel fantasy of living in Georgia’s Pleistocene before people colonized the region. This includes what technology I would bring back with me, what kind of house I would build, and what foods would I procure.