Tuesday, July 27, 2010

Upper Peninsula rocks and friends

It was a fabulous weekend, full of friends, beer, and really old rocks. Not necessarily in that order. Don and I saw amazing nickel sulfide cores at the Kennecott mine on Friday and heard a rather self-serving lecture on why operating this particular mine would be the best thing since sliced bread. It is true, there is lots of nickel in the rock, but it is only a 10 year operation to extract the nickel and then the company would be gone after making a projected 12 billion dollar profit.  They insist that the locals will get their share, but...   Yeah EPA, at least make them move the entrance away from Eagle Rock... This is a photo taken at Jasper Knob in Ishpeming, west of Marquette, made up of Negaunee banded iron formation (BIF). The red layers are Jaspilite and the gray is Specularite, a cherty hematite iron ore. These rocks are 1.5 billion or so years old.  The photo doesn't do it justice, the black Specularite is shiny and this formation just glows in the sun. This type of formation is found world-wide, and is a sedimentary rock formed formed in shallow seas. It was then heavily metamorphosed to give it the complex folding. There is a lot of speculation that since this rock contained lots of oxygen and the atmosphere at the time was oxygen poor, that a substantial amount of atmospheric oxygen was formed when these formations were "squished". This is one incredibly tough rock. For the most part, you can't touch it with a rock hammer, you have to pick up pieces that have frost heaved at the base of the hill. I already have quite a bit at home so I saved my strength (and D's of course). The next photo is of pillow basalts in the Mona Schists. These circular structures were formed when basalt flowed from a volcano under water and the rock was quickly quenched. This rock is about 2.6 to 2.7Ga or billion years old. Absolutely massive bedrock, no hammers at this stop either.

This is a photo of the Marquette harbor taken from a hill of quartzite a couple miles from Lake Superior. That is Presque Isle in the background.  It was a beautiful day.

This is one of my favorite stops and has been since field camp, over 30 years ago.  This rock is Kona dolomite, only found in the Marquette area and the swirly things in the rock are stromatolites. Stromatolites are mats of bacteria formed in shallow seas about 2 billion years ago.  The layers were covered up with silt and sand, reformed, covered up again, until you have columns of rock at least 30' tall with these circular structures with differential weathering.  Though you can't see it here, the fresh face of the Kona is a pink dolomite with lines of darker pink and red stromatolite layers in it.  It is a beautiful polished rock and everybody takes home a piece.  But nobody pounds on the columns, this is one of the very few stromatolite structures in the world that has this weathering.  Geologists have been admiring this structure since Douglas Houghton described it in the early 1800s, and it was probably enjoyed much earlier than that.  We also saw Mesnard quartzite and Jacobsville Sandstone in Marquette and then went to Pictured Rocks National Lakeshore to look at where the Jacobsville and the Munising sandstone come together at Sable Falls.  We drank beer both evenings, told stories, caught up with each others lives, families and work, and planned the next trip before we are all too old to do this.  We had fabulous cajun food on Friday night in a new restaurant in Marquette and ate pasties until they came out our ears.  All in all, a good weekend.  Don, thanks for sharing it with me.         

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