Written In Stone
One of the most important geological sites in the world is found in the cliffs of Fortune Head. Located near the town of Fortune, on the southwest tip of the Burin Peninsula, in southeastern Newfoundland. It is the “global stratotype”, or international reference point, for the Precambrian-Cambrian boundary. Of vital importance in the history of the earth, this boundary marks a most significant stage in the evolution of life, thought to have occurred almost exactly 543 million years ago.
Before the Cambrian period, this area is believed to have been part of a small ancient continent called Avalonia. Precambrian land masses were split and reformed by powerful forces of uncertain origin on the eve of the Cambrian. That was when the cliffs of Fortune Head came into being.
A 1977 geological survey recorded “hyolithid fragments” and “worm burrows” in the Fortune Head section. The next year, geologists from around the world visited the site, which is thought to contain more trace fossils than anywhere else in the world.
Later field trips determined that the Fortune Head site dated from the Late Precambrian to the Early Cambrian period. The older rock layer, dating from the Precambrian era, contains the trace fossils of soft-bodied creatures, some of which could be as much as two billion years old. The more recent layer shows, for the first time, the fossils of creatures that had shells.
Clarification of the Precambrian-Cambrian boundary, marking a definitive location of the so-called “Big Bang” of evolution, has long been a puzzle in the scientific world. This boundary is agreed to be the point at which the hard bodied animals of the Cambrian period first appear in the rock record. The International Union of Geologists (IUGS) had been searching for such a benchmark site since at least 1972. What the scientists wanted was a site that illustrated an unmistakable change in the kind of fossils occurring from one rock layer to the other.
The Fortune Head site is a prime example because it is fairly large and contains well-defined layers of rock with fossils which show this change. The sequence is almost complete, with very few breaks. Geologists believe that the Fortune Head site best represents the boundary between the Precambrian and Cambrian periods.
What makes the Cambrian explosion so important is more than just worldwide upheaval, and rearrangement of global features. It literally gave birth to more new and varied species than any other single geological time period. Soft-bodied organisms and life forms began to develop hard, protective shells, jaws, and claws. It is also when they evolved from asexual to sexual reproduction. As one palaeontologist jokingly put it, “You could say that sex began in Fortune!” The cliffs of Fortune Head are a visual record of those changes.
In 1992, after more than twenty years of discussion, the IUGS declared a portion of the rock section at Fortune Head as a global stratotype. Fortune Head Ecological Reserve is one of eleven reserves in the province, and one of three ecological sites protecting valuable fossil deposits. It was the first unique boundary point marking the base of any system which the IUGS had approved in the whole of North America. There is a truly remarkable amount of trace fossils in this sequence and that preceded the appearance of the small shelly fossils. The wide distribution of the trace fossils and being able to recognize the same sequence of trace fossils on a worldwide basis, made it possible for the boundary to be located at Fortune Head.
Public awareness and education, as well as protection of the Reserve, are of vital importance, as is the tourism potential. The historic cliffs of Fortune Head, with their age-old tales carved in stone, have earned the area an important place in the history of the Earth.
From a scientific viewpoint, the definition of the Precambrian-Cambrian boundary provides opportunities for research and study which will extend decades into the future, with both academic and scientific benefits.
© F. Herridge
Published in Canadian Stories, Oct/Nov 2013
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