Monday, July 1, 2013

A Tale of Two Conglomerates: Chapter 2

This is Chapter 2 of a 3 part blog post.  Click here to read part 1.

Chapter 2: The Matrix
Conglomerates share there stories in several ways.  The pebbles that fall together to make the rock tell a story of what came before.  The stuff that holds the rock together - the matrix - speaks about what was happening when the rock came together.

Four hundred and fifty million years ago, Mars Hill would have been pretty close to the Equator.  This time period also happened to be when coral were distributed widely around the world.  These facts were unknown to me at the time I first visited Mars Hill.  What I did know, however, was that Mars Hill was not far from a town called Limestone.  I looked at those clasts, and I looked at the stuff that held them together (called the matrix in the geology world), and I wondered.  I have since broken my piece of conglomerate and, logically, dropped it in vinegar.  The neat thing about limestone is that you don't have to wonder for long.  Dropping limestone in vinegar causes a reaction between the acetic acid of vinegar and the limestone base, causing carbon dioxide to fizz off.  Soon after the rock hit the bottom of the mug, bubbles started rising to the surface of the vinegar.  Four hundred and fifty million years ago, about the same time that ocean bottom rock was being torn apart, a coral reef, not far from Mars Hill was breaking down as well.  While the majority of this calcium carbonate piled up on flat ocean bottom, creating the substrate for Aroostook County's potatoes, some followed the flow of water over some sort of cliff into some kind of deep water canyon allowing shale pebbles and limestone mud to mix together.

The pebbles that make up the Mount Battie conglomerate are held together by something else.  500 million years ago, Mount Battie was in a part of the world not very likely to host coral.  The Avalonian microcontinent, perhaps similar in form to today's Japan, was on the bottom part of the world, below the 60th parallel.  The matrix here, insoluble in acid, is quartzite, indicating a sandy environment.  Layering at the site indicates the sand gathered in an ocean basin, where wave action swept away most of the smaller sediments, leaving behind sandstone pebbles in a matrix of sand.  This shore line would have been a bit cold for developing coral reefs, excluding the development of limestone in the area.  This gravelly beach the stage for our future coastal mountain.      
Modern World Coral Reef Locations - Credit: NASA

Berry, Henry N., IV. "The Bedrock Geology of Mount Battie, Camden." Maine Geological Survey: , Maine. Maine Geological Survey, 19 Apr. 2012. Web. 01 July 2013. <>.

Scotese, C. R. "Earth History." Plate Tectonic Maps and Continental Drift Animations. PALEOMAP Project. Web. 01 July 2013. <>.

Wang, Chunzeng, Gary Boone, and Bill Forbes. "Geology of Mars Hill Mountain and Vicinity." Http:// Web. 1 July 2013. <>.

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