“In the Field” - Hunting for Bedrock
by Karin R. Tilberg, Deputy Commissioner
Department of Conservation
We were blessed with a classic October day – beech leaves set aglow with fall sunshine and perfect temperatures for tromping through the woods and fields of central Maine. I was spending a day in the field with Henry “Spike” Berry, bedrock geologist for the Maine Geological Survey, Department of Conservation. Spike was on the prowl for outcroppings of bedrock; that is, glimpses of bedrock that are above the surface of the ground. These sightings are used to create maps of the underlying bedrock of our state.
There is a real clamor for these bedrock maps now that computer-based map analysis (GIS) is coming of age. Bedrock maps have a multiplicity of uses. They are incorporated in site work proposals or comprehensive plans. Private consultants and government regulators rely on regional bedrock maps to put specific sites in context. The chemical makeup of underlying bedrock, including things like sulfur, manganese, or lime, influences the soil chemistry. This in turn can influence natural plant communities and productivity for agriculture or sustainable tree growth. Water quality in drilled wells is also related to the rock type. Ground water flow is controlled by the bedrock structure, knowledge critical to effective clean up of environmental contamination. Landowners may be interested in the potential for mineral deposits (copper, zinc, tin, gold, silver, etc.) or stone quarries.
I learned that obtaining this information is time consuming and costly. There are 707 map quadrangles in Maine and each takes about 2 to 3 years of a person-time to complete (amounting to some 1500 years of field work). Some regions of the state have been more intensely mapped than others but much remains to be done. The United States Geological Survey has virtually stopped systematic bedrock mapping east of the Rockies and so it is largely up to the states to conduct this important work. Maine is fortunate to have a vibrant bedrock mapping advisory committee that can help provide a sense of priority and support to the MGS’s efforts, and some strong federal and university partnerships to assist with the cost of mapping.
Spike and I drove to the quadrangle that he is currently mapping. We parked the vehicle and began our search for bedrock. Our first stop struck “gold” – actually Bucksport formation, a type of metamorphic sandstone. There it was, showing through a homeowner’s lawn in a number of places and this particular resident was pleased to have us take a long look at these outcroppings. Spike explained that the rock we were looking at was created from sands deposited in the Iapetus ocean some 430 million years ago that was then compressed and heated with the buckling and pressure of the movement of the earth’s crust, a transforming process known as metamorphism. As I thought about the eons that had passed since these events, I felt my life shrink to a mere speck – both a humbling and strangely comforting sensation.
Given the ease of our initial finding, I imagined that finding evidence of bedrock was not such a difficult task after all. I was wrong. We traipsed for some time through wood and dale following land contours with potential for bedrock outcroppings but with no success. During our wanderings, I observed how important the Global Positioning System (GPS) has become to field science. Spike emphasized that GPS has enabled the mapping to have a much finer level of detail than even a few years ago because the geologists can pin-point the location of a bedrock outcropping faster and with greater precision. There is enormous discipline involved in this type of work. In addition to the unexpected rigors associated with weather, unknown territory and periods of no data, one must be absolutely certain an outcropping of rock is truly bedrock and not just a large “free” boulder embedded in the soil.
I asked Spike how he came to be a bedrock geologist. He explained that while he was a junior at Wesleyan University and was taking a geology class, “kind of a requirement,” he found he was fascinated by the subject. “The physical processes that resulted in what we saw on the earth stirred something in me.” Also, the excitement and wonder of the natural world was a strong motivating factor for him. He felt that his math background and analytical mind helped him see the pattern and the reason for the pattern in the stories told by bedrock. Our last stop revealed his strong talents. On the shores of a lake in coastal Maine there were a number of granite bedrock outcroppings that were helpful in defining the boundary of an important fault that runs through this part of Maine. He was testing a theory about how the land masses had shifted over millions of years and this new puzzle piece was shedding light on the answer.
Spike’s work is extremely important basic scientific research. Perhaps it is not a glitzy as bedrock geology research in far-away places, but it is of “rock-solid” importance to Maine people, communities and businesses. By the end of the day, we had filled in some gaps on the quadrangle map and, as a result, may help someone in the future with an important decision that could affect their life.
