On November 5th, Dinosaur Park hosted a group of scientists visiting from the Geological Society of America's annual conference. We were the first stop on a day-long field trip led by Pete McLaughlin of the University of Delaware and Heather Quinn of the Maryland Geological Survey, which aimed to explore the stratigraphy and palynology of the Maryland coastal plain.
What is palynology? Glad you asked. Palynology is the study of microscopic fossils like plant pollen and spores. These fossils are both abundant and temporally specific, which makes them very useful for correlating different rock strata in different parts of the world. Palynology has been essential for determining the absolute ages of the Potomac Group rocks in Maryland, including the Arundel Clays of Dinosaur Park.
When paleontologist O.C. Marsh was studying fossils from the Dinosaur Park quarry in 1888, he assumed that the deposit was Jurassic in age because of the presence of sauropod (long-necked) dinosaurs. Today, we know that sauropods survived well past the Jurassic Period, thriving until the very end of the age of dinosaurs. Fortunately, fossilized pollen gives us a much more precise age for Dinosaur Park. In 1963, Gilbert Brenner divided the layers of the Potomac Group into four palynological zones, designated Pollen Zones I-IV. The Arundel Clay occupies Pollen Zone I, which includes abundant spores from plant species like Exesipollenites
, as well as low percentages of pollen from flowering plants. Later, James Doyle and Leo Hickey determined that the same kinds of pollen are present in English and North African rocks, where absolute dates have been determined through radiometric dating methods.
All this means that we can confidently place our dinosaur fossils in the late Aptian or early Albian ages of the Cretaceous Period, between 115 and 100 million years ago. For many, palynology is not as inherently interesting as the study of giant dinosaurs, but this work is arguably more important, as it gives us a much more definite idea of the time intervals between the ecosystems we study.