Patterns

In gravel pit after gravel pit, we’re seeing a similar pattern in sediments and depositional environments. Dr. Erikson has pointed out that almost every good exposure over about 10 m tall has a base of sand and cobble beds that gradually become finer grained upward in the section. This is typically overlain by more than a meter of bluish-grey marine clay, and then by the rapid return of sandy beds. As he explained, this is evidence of a history of dropping energy levels as sea level rose (yielding finer grain sizes), until only the finest particles (clay) accumulated in an offshore location, and then finally increasing energy levels as sea level fell (producing the return of sand above the clay). Occasionally, we’ve found large boulders dropped in the middle of the clay or sandy layers (as seen in the picture); the boulders are far too large to have been transported by ocean currents, so we can tell that glaciers were floating around in the ocean above the gravel pits dropping boulders and other debris as they melted.

We’ve made a number of observations this week and a half that have nothing to do with science. Our live animal sightings have extended to include another moose, a mouse, deer, groundhog, porcupine, blue herons, three fox kits, and dozens of alewives and herring in a fish lift. Other interesting sightings include two large windmill blades (allegedly 150-ft) pulled by semis. There has been a dramatic change in lifestyle in this upper region of Maine. We have found that people have been universally friendly and they have allowed us unrestrained access to their land, the traffic among the towns is nearly nonexistent, and everywhere we have eaten the portions have been plentiful. Our campground for the week located in Madison was much bigger than the last, but just as quiet. Our tent site includes an Adirondack structure which is a 3-walled shelter, which came in handy this week as we saw a drastic change from sunny and high temps, to rainy and low temps.

First-day Clay

First field day! After packing up on campus, we drove to Farmington and found this week’s base camp at the Troll Valley Campground. Intrepid scientists that we are, we were not intimidated by the prospect of the trolls being offended by our modern, albeit rustic, pursuits in their valley.

The major discovery of the day was on our first foray, northward from Farmington along the Sandy River. In a black fly-infested tributary valley, we found an outcrop with the most impressively plastic grey clay. Saint Joseph's student Jeff Boudreau holds up a sample of this Quaternary marine clay that a potter would covet. The presence of the clay overlain, first by silt then by sand and pebbles, indicates environmental conditions that changed from tranquil, relatively deep water (clay) to an increasingly energetic nearshore setting (sand and pebbles). This sequence is consistent with sediments accumulating as relative sea level was falling and the shoreline was moving southward through the area (termed a regressive sequence).