VI. Cambrian When the Cambrian started, there was an epicontinental sea that covered the Southeastern portion of what is today Minnesota (Ojakangas and Matsch 1982). Streams were flowing into the sea off the land in western and northern Minnesota carrying sand to the seashore. This is why there was a lot of sandstone deposited during the Cambrian. Figure 11 shows a strat column for the Cambrian rocks found in Minnesota. The sand that was deposited came from the erosion of the igneous and metamorphic rocks that were formed during the volcanism and orogenies from earlier in history. Ojakangas and Matsch state that the weathering and erosion has been occurring since the end of the Algoman mountain building event 2.8 billion years ago. The reason why mainly sand was …show more content…
Lawrence Formation is 20 meters thick, and is unique in that it is the first major carbonate unit in the Paleozoic strat column of Minnesota. A limestone unit would signify the dominance of chemical and biochemical precipitation of calcium carbonate out of the seawater, a lack of sand and mud reaching that part of the basin of deposition, and probably a depositional site far from shore. Most of the Paleozoic carbonates were originally composed of calcite but were altered by the replacement of calcium ions by magnesium to form the mineral dolomite. The St. Lawrence Formation is not clean but contains clay, silt, sand, and glauconite, indicating fluctuating conditions. The Jordan Sandstone is 25 to 35 meters thick, and variable in sandstone type. The Jordan Sandstone is either a white or yellow, fine to coarse grained quartz sandstone with well-rounded and well sorted grains. There are burrows present at the middle and bottom of the Jordan Sandstone and the coarser grain size is at the top. There is some hummocky cross stratification inter mixed with the burrows at the bottom of the sandstone, and there is trough cross bedding present in the middle of the sandstone (Runkel
Marshak, S. (2009) Essentials of Geology, 3rd ed. New York: W.W. Norton & Company, ch. 11, p. 298-320.
The St. Peter sandstone lies in an unconformity. It is 250 feet thick, it can be up to 500 feet thick and it fills erosional channels in the underlying strata. Buffalo Rock is an erosional remnant of Ordovician St. Peter Sandstone and overlying Pennsylvanian clastics. Sign for swift, turbulent, and deep water includes gravel bars and erosional features that are 180 feet above the current level of the river and massive cross bedded sand and gravel deposits along the river course.
Glacial Lake Peterborough had many attributing spillways attached to it, feeding meltwater and sediment from the ice margin and or other glacial lakes. Much of the sediment that was deposited in Glacial Lake Peterborough came from either from the stagnant ice blocks located on the Oak Ridges moraine or from the Lake Algonquin drainage system. Much of the deposition in this lake was dominated by sediment stratification, which may have been largely influenced by thermal stratification. As a result of thermal stratification occurring in this glacial lake sediment inputs were greatly influenced depending on the different sediment densities between the lake bottom water to that of the incoming meltwater and if the inflow density was less/more than the bottom water than the lake water bottom, than new transport and depositional paths were created
This is a report based on three days of observations and testing in the region known as the Peterborough drumlin field. It will address a variety of regional elements, such as climate, soil, vegetation, hydrology, geomorphology, and geology. A variety of sites located on the Canadian Shield, the zone of thick glacial deposits to the south, and the transition between them will be the focus of the report. It is supplemented with previous research on the region. September 8, 1999, day one of the field study involved an area of largely granite bedrock that is part of the Canadian Shield and is the most northern point of study (see Map 2). September 9, 1999, day two, involved three main areas of study: the Bridgenorth esker (Map 3), Mark S. Burnham Park (Map 4), and the Rice Lake drumlin (Map 6). These sites are in areas of thick glacial deposits. September 10, 1999, day three, involved studying the Warsaw Caves (see Map 5) as a transition zone between Precambrian Shield rock to the north and Paleozoic rock to the south. A general map of the entire study region is provided by Map 1.
Sedimentary rock from the older Silurian Period is further from the river banks (Geological map of Victoria, 1973). Mudstone, inter-bedded shale and greywacke depositions indicate the Maribyrnong River may have previously taken a different shape, and younger sediments have replaced the older sediments in more recent geological periods.
...e morphed it into the quartzite that is seen surrounding the butte (4). Rocks that undergo this process are called metamorphic rock, which is the same as the rock seen years ago by dinosaurs and other extinct creatures. The quartzite rocks were formerly seafloor sediment that was forced upwards, and then surrounded by lava basalt flows. Once erupted through fissures and floods through out most of the area, lava flow eventually created enough basalt to form a thickness of about 1.8 kilometers (1). All of this basalt flow eventually led to the covering of most mountains, leaving the buttes uncovered. The igneous lava flows and loess is reasons that the Palouse consists of such sprawling hills, and rich soil for farming (2). In result of the lava flows, the Precambrian rock Quartzite was formed. And lastly covered by the glacial loess, which were carried by the wind.
More specifically, Trois-Rivieres is located in an area with flat and rolling hills, and fertile soils that play a huge part of Trois-Rivieres’s economy. The formation of the Great Lakes-St Lawrence Lowlands happened during the Paleozoic era. “The Great Lakes-St Lowlands were formed by the effects of glaciation. This is caused the city’s rolling landscape where flat plains are interrupted with glacial hills and deep river valleys. After the glacial period, when a large volume of water melted out from the glaciers, the lakes were large, even larger than they are today. However, the lakes shrank to their present size, and flat plains of sediments remained. These sediments formed excellent soil for farming” (Pandya, n.d). This process left behind a large amount of sediment rock, which was beneficial for the manufacturing industry.
Shown in the picture above is volcanic extrusive igneous rock known as andesite. They were imported here to Laguna Beach to help minimize erosion (Merton Hill, p. 10-11). Extrusive Igneous rocks are formed on Earths surface due to lava quickly cooling or mixing with different materials such as ash or cinders from an eruption. There are two different types of extrusive igneous rocks; Plutonic and Volcanic. Andesite is known for being gray in color and being made up of very coarse grainy textures, which make it much harder to break down than sedimentary rocks. Unlike loose gravel and other sediments igneous rocks are known for being able to slow down seismic waves from earthquakes which cause less damage to surface structures.
Plummer, C.C., McGeary, D., and Carlson, D.H., 2003, Physical geology (10th Ed.): McGraw-Hill, Boston, 580 p.
"Sedimentary Rocks." Backyard Nature with Jim Conrad. N.p., 18 May 2015. Web. 25 Oct. 2015.
Morton, J. W. (n.d.). Metamorphosed melange terrane in the eastern piedmont of north carolina. Retrieved from http://geology.geoscienceworld.org/content/14/7/551.abstract
Soon after the sea reached longer distance westward and the sandy tidal deposits were converted to deep water deposits. Mancos Shale is the name given to represent these deposits, which are comprised of organic material and small particulates. Another interesting fact to note is that this type of sediment consists of fossils. These remains can include prehistoric shell fish, shark teeth, and many other types of organisms. The hills seen at the foundation of the mesa in the Montezuma Valley are comprised of gray
Han, J., Zhang, Z. F., & Liu, J. N. (2008). A preliminary note on the dispersal of the Cambrian Burgess Shale-type faunas. Gondwana Research, (1), 269-276. doi:10.1016/j.gr.2007.09.001
There are several theories about how the Cambrian Explosion started. There were major changes in marine environments and chemistry from the late Precambrian into the Cambrian, and these also may have impacted the rise of mineralized skeletons among previously soft-bodied organisms. One theory as to what happened is that oxygen in the atmosphere, with the contribution of photosy...
...nt. Due to this observation we can conclude that there were no catalysts or enzymes present in the sand.