In the cross section of the land mass Vicunia there are sixteen identifiable layers. As we reconstruct the history of Vicunia we can also recognise distinct geological events that have occurred, which allow the layers of Vicunia to lie as we now observe them. Many of the layers contain fossils that have been dated to certain prehistoric periods; this allows us to apply a time scale to the deposition and construction of these layers. We can use the principles of geology and the principles of stratigraphy to explain the geological reasoning behind each episode that lead to the formation of the rock units in the strata. Using these elements we can construct a comprehensive geological outline of the layers of Vicunia.
By the reasoning of Steno’s …show more content…
Granite is an igneous rock formed when large amounts of magma lowly solidify deep in the earth. The granite layer is not a straight edged layer like most in Vicunia, this represents the way magma has crept up into the landmass as opposed to being deposited, creating a nonconformity between the next layer. The next identifiable layer that lies directly on top, and partially in the middle of the granite, is a contact metamorphic rock layer. Contact metamorphic rock masses are formed with the aid of pressure and particularly heat (Crampton et al. 2014), which in this case will have been provided from the magma that formed the granite as it was extruded into, and cooled, in the surrounding area. The next two layers are a sandstone layer spanning from west to east and a limestone layer sitting on top of it. Both layers contain Devonian trilobite fossils. The Devonian period lasted from 416ma- 358ma (Bagley 2014), which gives us a clue into how old this strata is. Sandstone is a detrial sedimentary rock composed of particles of weathered or eroded rocks and minerals ranging in size from 1/16-2mm while limestone is composed mostly of calcium …show more content…
In situations like this we lose a lot of data regarding the environment of Vicunia that could represent millions of years. On top of the erosion is a small deposit of breccia in the east of Vicunia. The angular fragments and the cement like calcareous material that make up breccia have an overlapping relationship with the sandstone layer above it, this suggests that the breccia deposit wasn 't able to completely form a rock unit before the sandstone layer began to form (Crampton et al. 2014). As breccia is often found near an outcrop we could presume this unit was deposited by an alluvial fan connected to the water source that formed the sandstone (Geology.com 2005). Cretaceous clam fossils are found in the next layer of mudstone. The Cretaceous period spanned from 145.5ma – 65.5ma (Bagley 2016), this information alone tells us that between the first sandstone layer, containing Devonian, fossils and this mudstone layer is a time gap of at least 212.5 million years. More strata may have formed between the two time periods however the erosion above the Devonian limestone layer has stripped Vicunia of some material. The detrial mudstone containing Cretaceous fossils lies under a layer of limestone; this limestone will have formed with the presence of skeletal animals, as it did during the Devonian period. Tectonic movement
By the reasoning of Steno’s …show more content…
Granite is an igneous rock formed when large amounts of magma lowly solidify deep in the earth. The granite layer is not a straight edged layer like most in Vicunia, this represents the way magma has crept up into the landmass as opposed to being deposited, creating a nonconformity between the next layer. The next identifiable layer that lies directly on top, and partially in the middle of the granite, is a contact metamorphic rock layer. Contact metamorphic rock masses are formed with the aid of pressure and particularly heat (Crampton et al. 2014), which in this case will have been provided from the magma that formed the granite as it was extruded into, and cooled, in the surrounding area. The next two layers are a sandstone layer spanning from west to east and a limestone layer sitting on top of it. Both layers contain Devonian trilobite fossils. The Devonian period lasted from 416ma- 358ma (Bagley 2014), which gives us a clue into how old this strata is. Sandstone is a detrial sedimentary rock composed of particles of weathered or eroded rocks and minerals ranging in size from 1/16-2mm while limestone is composed mostly of calcium …show more content…
In situations like this we lose a lot of data regarding the environment of Vicunia that could represent millions of years. On top of the erosion is a small deposit of breccia in the east of Vicunia. The angular fragments and the cement like calcareous material that make up breccia have an overlapping relationship with the sandstone layer above it, this suggests that the breccia deposit wasn 't able to completely form a rock unit before the sandstone layer began to form (Crampton et al. 2014). As breccia is often found near an outcrop we could presume this unit was deposited by an alluvial fan connected to the water source that formed the sandstone (Geology.com 2005). Cretaceous clam fossils are found in the next layer of mudstone. The Cretaceous period spanned from 145.5ma – 65.5ma (Bagley 2016), this information alone tells us that between the first sandstone layer, containing Devonian, fossils and this mudstone layer is a time gap of at least 212.5 million years. More strata may have formed between the two time periods however the erosion above the Devonian limestone layer has stripped Vicunia of some material. The detrial mudstone containing Cretaceous fossils lies under a layer of limestone; this limestone will have formed with the presence of skeletal animals, as it did during the Devonian period. Tectonic movement