Gladstone Gladiators on Neoproterozoic Roads and Cambrian Terranes

As we began our journey from central Virginia back to Williamsburg, our team immediately began to reminisce on the last four days spent in the field. The van was smelly and weighed down with rock samples to be analyzed, elements that could only mean one thing: the “Gladstone Gladiators” (derived of course from our mapping of the Gladstone Quadrangle) had quite the time exploring enigmatic geologic terranes and setting the stage for our next 7 weeks of research. Each day began more or less the same with an early wake-up time, hot water for breakfast or coffee, and piling into the van as we headed towards the starting point of our traverse. To get to each starting point we drove along gravel roads that stretched over probable Cambrian terranes (geologic units that were deposited during the Cambrian) and kicked up dust that most likely contained zircons that originate from the Grenville orogeny in the Neoproterozoic era. These traverses often consisted of hikes through woods, up ridges, and along streams to find outcrops of exposed bedrock. At these outcrops we recorded our observations and marked our location on the map before heading out in search of our next specimen. Much of the quadrangle has been clear cut by timber companies, making hiking difficult but the science very rewarding.

But what exactly did we find?

Well that’s the golden question, isn’t it? So far, things are probably a bit too early to extrapolate an overarching hypothesis about what we saw in the field. A lot of the rock outcrops we saw were of phyllite (a low grade metamorphic rock), but there were plenty of other rocks that got us excited, even if they only seemed to muddy the waters. In the northwest corner of the quadrangle we found a beautiful phyllite, featuring preserved crossbedding, interlaid with a pebbly quartzite hosting Blue Ridge originating blue quartz. If you consult the research, there are very different interpretations as to what groups these rocks are associated with. Are they Blue Ridge cover sequence a la the Lynchburg Group, or are they part of their own group known as the Evington Group? The answer to this question will come with time and sample analyzation.

We also found that the map our group believed to be the most accurate (a map produced by Espenshade in 1954) was missing key geologic units we found in the field. These discoveries allow us to make a more accurate map and answer some of our burning research questions. And what of my own research? Our last trek today found higher grade metamorphic rocks, garnet-biotite schists, in the area mapped as the Smith River Allochthon in the 1993 VA state map. This is consistent with the hypothesis that the SRA is present in the southeastern corner of the Gladstone Quadrangle, but more sample analyses and traverses are needed before a full assessment can be made.

And there it is! One week of research wrapped up nicely with many more to go. As one would expect, this week begged more questions than provided answers, but that’s what research is all about.