Before we get started, I guess we should actually distinguish, ‘What IS the Burgess Shale?’ Well, it is said to be a “shrouded legend” deep in the Canadian Rockies discovered in the early 1900s by Charles D. Walcott, notorious Smithsonian Secretary (Adler 2013). According to Haug, Caron, and Haug in their research article ‘Demecology in the Cambrian: Synchronized Molting in Arthropods from the Burgess Shale’ the Burgess is “arguably the best-known Konservat-Lagerstätte”. While the Burgess Shale is primarily known for the intricate preservation of soft-bodied creatures dating from the early Cambrian Period (Haug, Caron, Haug 2013); furthermore, what seems to make this specific site so special is the fact that not only the soft parts of …show more content…
Even though anoxia is in general reflected on as an essential pre-requisite, “anoxia alone is not sufficient enough to account for Burgess shale-type preservation,” (Garson 2012). Furthermore, the necessity of anoxia is not universally agreed upon (Garson 2012). Yet, while rare and commonly absent from today’s fossil record, this type of preservation is very common throughout most Burgess shale-type deposits of these ancient fossils (Gaines 2012). Localities of these types are somewhat confined to Series 2 and 3 of the Cambrian (Garson 2012). The type of preservation, as stated above, that are a shared style within these various deposits, referred to by Garson in the Academic Journal ‘Dynamic palaeoredox and exceptional preservation in the Cambrian Spence Shale of Utah’, the “BST (Burgess Shale-type) preservation”. She, along with the other authors of the journal, claim, “Insight into the preservation of BST assemblages may be just as important as the exceptional fossils themselves as it speaks directly to the unique environmental conditions that were widespread in the marine realm at the time” (Palaeoredox 2012). I was almost positive this type of preservation was pretty basic until Gaines and his associates told me differently; here we jump back to ‘Mechanisms for Burgess Shale-type Preservation’, get into the nitty gritty and further discuss the different ways BST preservation actually goes down. In the article is provided
The black Pierre Shale is the bottom layer of the Badlands and was deposited between 69 and 75 million years ago when a shallow sea stretched across what is now the Great Plains. Sediment filtered through the seawater, forming a black mud on the sea floor that has since hardened into shale. Fossil clams, ammonites, and sea reptiles are
Approximately 17 meters thick, Unit A defines the lowest third of the Juniata Formation. Fragments of marine fossils, including bryozoans, brachiopods, and gastropods, are commonly found in the bottom-most portion of this unit of structureless mudstone and quartz arenite. Quartz grains in the sandstone beds of Unit A are typically immature and fine-grained, though the sandstone packages tend to coarsen upwards. Though typically structureless, intermittent bedding of the sandstone and shale packages is observed in this unit, and some areas display
The reason for this is because a sedimentary rock is mainly because it is the only rock that would be able to keep the fossils form. If a fossil was to be in a metamorphic rock in would be deformed because i metamorphic rock needs pressure which would then flatten the fossil. If it was to be in an igneous rock the fossil would melt because an igneous rock is created from hot lava from
Starved Rock State covers about 200 miles and some 470 million years, from Ordovician sandstones to Pleistocene glacial till. The Ordovician St. Peter Formation sandstone was deposited across the midcontinent during the second major marine transgression of the Paleozoic Era. The first transgression deposited Upper Cambrian to Lower Ordovician clastics and carbonates. The clastic to carbonate rock transition is consistent with gradual sea level rise over the North American craton. Sea level dropped late in the early Ordovician, exposing the carbonate strata to processes of cave development.
The author and his colleagues specifically chose to focus on 375 million year old rocks in their search for fossils because this was the time frame that provided fish that would be useful to study from. The 385 million year old rocks provided fish that look too similar to the ones we have now and the 365 million year old rocks have fossils that don’t resemble fish. The 375 million year old rocks, however, provide fossils that show the transition between fish and land living animals.
One of the major things noticeable from the cross section is that quite a few of the rock layers are over turned, where the older rock layers are above the newer rock layers. This is seen in the contact between the Quartz Monzonite of Papoose Flat and the Campito Formation which is also a disconformity. Next there is some fault zones separating the Camptio, Poleta, and Harkless formations. We then see some more overturned layers with the contacts between Saline Spring Valley Formation (lower and upper members) above the Mule Spring Formation along with some inferred folding. With a normal fault separating the inferred folding event, we see where the overturning occurs. In between the Cambrian layers we see Tertiary Basalt nonconformities also being folded, thus with that we know that the folding event was more recent than the formation of the Basalt. Next there is a large Basalt field with a spot of the Harkless formation. Again we see over tuning as the Basalt field ends there are the Devonian and Mississippian rock Layers on top of the basalt. Separating these overturned layers from the Harkless Formation and the Saline valley Formation (upper member), which are not overturned, is a thrust fault. From this information, there was a major stress event sometime after the Tertiary period causing the rock layers to fold and overturn. And from this stress event and from the folding, normal and thrust faults are formed. Finally we see that there were alluvial and landslide deposits from the Quaternary after the folding, faulting, and over
Below these Carboniferous rocks, Devonian rocks are also exposed. These rocks can be found along the northern edge and southeastern margin of the plateau, where strata is nearly vertical. These two geologic systems have also been subdivided into numerous formations categorized according to their lithologic aspect and the fossil fauna and flora which they
In order to find evidence of the transition from fish to land animals, the author and his colleagues chose to focus on 375 million year old rocks. In 2004, they studied sedimentary rock on Ellesmere Island in Canada’s Arctic as they thought that the rocks there would be exposed and untouched by humans, which would be ideal for fossil excavations. They studied sedimentary rocks (limestone, sandstone, siltstone and shales) because these
In addition, per my knowledge none of the western US geologists have documented passive margin deposits as young as of upper Paleozoic age or younger. Therefore, Hildebrand (2009, 2013) hypothesis faces deficiency to explain the thrusting of Roberts Mountain and the emplacement of the Proterozoic rocks over the rocks of Lower Paleozoic age.
Evidence for life on early Earth (e.g. in the Pre Cambrian) has proved difficult to find because: SELECT ALL THAT APPLY Select one or more: A. rocks from these early times are rare due to the recycling of the Earth's crust through plate tectonics B. there was no oxygen in the Earth's atmosphere at this time C. life at this time lacked hard parts (such as shells or bones) that fossilise easily D. life had not yet emerged onto land E. life at this time was mostly microbial
The author and his colleagues chose to focus on 375 million year old rocks in their search for fossils because amphibians that look dissimilar to fish were discovered in 365 million year old rocks, while fish without amphibian characteristics were discovered in 385 million year old rocks. Thus, it is possible that the evolutionary intermediary, or the “missing link” between fish and amphibians, would be discovered in 375 million year old rocks, between the two time periods. The rocks examined were sedimentary in composition, as the gradual and relatively gentle formation of sedimentary rock under conditions of mild pressure and low heat are conducive to the fossilization of animal remains. Sedimentary rock is also often formed in rivers and seas, where animals are likely to live. This site provides a resource that describes means by which fossils are formed and how the fossil record may be interpreted, and shows some examples of fossils demonstrating evolution through geological periods: http://www.fossilmuseum.net/fossilrecord.htm. In 2004, Shubin and his colleagues were looking for fossils on Ellesmere Island, in northern Canada. This location was chosen because of its lack of human development, as well as of obstructing natural formations and life forms such as trees, which
These techniques led to the discovery of the boundary between the two eras. A single thin layer of clay found within predominantly limestone rocks established this. By comparing the marine life found in, above, and below the clay, the marine life, like the dinosaurs, had been terribly affected by the extinction event. The percentage of life in the upper layers was dramatically lower than that in the lower. This was far more compelling than what was suggested by dinosaur’s fossils.