In my Field Geology class at the University of Colorado, we are learning to create geologic maps. We have been using our Brunton compasses (not just your everyday compass) to make measurements about the rocks. We look at things like how thick the section of rock is, what kind it is, where it is pointed, and which way it "dips", which is the direction that a rock unit is sloping downward. Making both quantitative and qualitative observations, and gathering LOTS of observations, we should be able to produce a geologic map of the region that describes the history and rock types of that area.
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| The class listens as our professor, Lon Abbot, describes a brief history of the stramatolite |
Today, we were just practicing making these measurements, because the details of these procedures raise lots of questions in their application and accuracy, so that we can be prepared when we head into the field. The weather forecast had given a high of 45 degrees, and it may have reached that in the morning, but by noon when we head into the field it was getting nasty and cold. A storm coming into the region promised 7" of new snow and a high of 11 the next day, so the mother nature was feeling tempermental.
There was plenty of snow on the ground as we took notes on outcrops of varying rock types and ages. We followed a hiking trail that took us through the depositional history of the front range of Colorado, getting younger and younger from the Pennsylvanian aged Fountain formation (a notable red rock characteristic of places like Red Rocks Ampitheatre and Garden of the Gods) to rocks that had been recently moved within the last few million years.
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A pattern characteristic only of
stromatolites. |
The particular rock that we are looking at in the picture is a stramatolite. It has close, thin wavy bands on its side, and these differ from ripple patterns in the fact that they are not symmetrical or of a constant amplitude. The rocks at first did not appear overly interesting. We had examined several rocks from this formation when we came upon one which was different. One person within our group correctly identified it as a stramatolite. Our professor Lon was explaining to us that these stramatolites are the oldest organism that we have on fossil record, and they consist of bacterial mats that grow in humps
together. This first organism was quickly outdated by other organisms, and later became a food source for some creatures. The theory is that stramatolites are only preserved in fossil record in areas that were of high salinity or otherwise unfavorable for creatures to eat them. They grow only in areas of calm water movement, but could grow in either freshwater or saltwater environments. The other rocks (which did not have stramatolites) we had been looking at surrounding it further indicated that these organisms flourished in one particular spot.
For what at face value had appeared to be a quite dull rock, its history is actually quite remarkable, and it turns out that these characteristics are specific to only stramatolites, and even more can be interpreted about the environment that those rocks were deposited in. In creating our geologic maps, we are being taught to rely on our ability to piece together clues that lead to the complete history of those rocks. Our next project is to begin mapping a decent sized chunk of land, Mt. Sanitas in close proximity to Boulder.
