Blueberry barren or glaciomarine delta? EarthCache
Blueberry barren or glaciomarine delta?
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Many of Maines blueberries are grown on top of marine glacial deltas that were formed during the last ice age. This roadside pull off will give you to better understanding of the surface of the land that you are traveling through along the coast.
Many of Maines blueberries are grown on top of marine glacial deltas that were formed during the last ice age. This roadside pull off will give you to better understanding of the surface of the land that you are traveling through along the coast.
The most recent glacial episode in Maine began about 25,000 years ago, when the Laurentide ice sheet overspread New England and Eastern Canada. During its peak development evidence of the direction of the glacier movement is preserved in the northwest-southeast striations and grooves visible in the bedrock in surrounding areas. Approximately 17,000 years ago, the ice reached its maximum extent, which extended beyond the current coastline onto the continental shelf. The slowly flowing ice was thick enough to cover Maine's highest mountains. It swept away much of the evidence of earlier glaciations, even removing the bedrock in many places. The weight of this glacier was so great that it depressed the underlying land mass. The ice began to retreat from the shelf between 17,000 and 15,000 years ago. As the ice withdrew, the land remained depressed due to the previous weight of the glacier, allowing marine waters to flood the coastal lowland. The land remained below sea level as it began to rebound until approximately 12,000 years ago when the present coastline was exposed above sea level.
Even as the ice margin withdrew, internal flow within the glacier continued to transport its sediment load southward toward the edge of the vast ice sheet. Large quantities of sediment were dumped into the ocean at the edge of the melting ice sheet, and these deposits are now exposed to view because the land rose above sea level. The coarser sediments and large boulders were dropped right at or near the edge of the glacier. The water-laid sediments were often deposited as layered accumulations. The clearest markers of glacial retreat are ridges of sediment called moraines. These ridges were heaped up along the edge of the glacier during brief periods (as short as a single year) when the ice margin remained in a stationary position or readvanced slightly. Scientists find moraines interesting because they good indicator of both the position and orientation of the glacial margin at a particular point in time.
But there is another feature that was formed at this glacial edge. Sand and gravel was also discharged in large quantities from glacial eskers, building submarine fans. Wherever the sediment supply was adequate and the glacier margin remained in one place long enough, these sediments built up to the ocean surface, eventually becoming flat-topped deposits known as glaciomarine deltas.
The interior of these deltas typically has three stratigraphic components. From top to bottom, these are the topset, foreset, and bottomset beds. The topset beds is mostly gravel forming a horizontal layer extending across the top of the delta that were deposited down by streams flowing across the delta surface and are usually coarser than the rest of the delta. This is generally what you see at the surface of the blueberry barren. The foreset a bed was formed when sediments were carried all the way to the front of the delta cascaded down into deeper waters, forming the sloping delta front. The bottomset bed is composed of the finest delta sediment deposited as horizontal or gently sloping layers on the bottom of the water body in front of the delta. These layers can be seen in a road side gravel pit just the west heading toward Ellsworth on the north side of the road.
The glacial feature that you are looking at was actually left behind during the final northward retreat of the ice sheet, when the pulverized rock debris was released from the melting ice. This delta can be identified by its shape and general design. You can also see several of the layers in the road cut not far from the coordinates. These deltas are economically important to this area as agricultural lands. In this case they are being used for the cultivation of blueberries. Cultivation is the key word here so please do not enter the fields or pick the blueberries as they are an important agricultural crop to Maine.
To log this Earthcache: Send an email to me through my profile with the following information: At the coordinates listed above you are looking directly up at the face of a delta. Describe the direction the water must have been flowing to form this delta. If you need addition help making a decision go to Waypoint #1 for a different view of this glacial feature. Please begin your email with the name of the earthcache and make sure your log includes the number of people in your group. It also would be nice if you would post a photo so others would know what they have to look forward to at this earth cache.
If you enjoy this earthcache you may want to check the Maine Geological Survey located at (visit link)
They have developed a number of information sheets or field localities giving a great deal of information about geologic features. They also have a number of books and maps about Maine’s natural history/ geology that you might find interesting.
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