Cross sections of folded and dipping beds - ppt download
Base your answers to questions 1 and 2 on the cross sections of three rock outcrops, A, B, and C. . The large cone-shaped mountain on Earth's Which statement correctly describes the relative ages of rocks A and C and gives the best supporting evidence from the .. accurately dating the age of a rock is the isotope's. On the cone surface, we can recognize areas of varying degrees of stability. increase in relative age from the centre of the channel toward the margins of the cones mostly in 3 Schematic cross-section through the natural vegetation belts of. Folded and dipping cross sections This presentation is to be completed in conjunction with exercise worksheet 4. Dating Rocks Ways to tell the age of a rock.
Then using a protractor, measure a dip of 22o and draw on the dipping beds. School of Earth and Environment 10 Folded and dipping cross sections: Now fill in the beds lithological patterns. School of Earth and Environment 11 Folded and dipping cross sections: School of Earth and Environment 12 Folded and dipping cross sections: Problems Using exercise worksheet 4, complete problem 2 before continuing onto the next slide.
Questions for problem 2: On the map draw structure contours for each boundary i. Siltstone-Shale boundary; Shale-Grit boundary. Calculate the true thickness of the shale bed.
- Cross sections of folded and dipping beds
Using the topographic and structure contours, construct a cross section through A to B. Indicate on the map the position of an anticlinal axis with the symbol: School of Earth and Environment 13 Folded and dipping cross sections: Problems Answers for problem 2: Remember to calculate true thickness: The distance between these is: The difference in height is: School of Earth and Environment 16 Folded and dipping cross sections: Then mark on the lithological interfaces.
School of Earth and Environment 17 Folded and dipping cross sections: Then assuming constant dip, structure contour points from other areas of the map can be added to this.
School of Earth and Environment 18 Folded and dipping cross sections: Now the beds can be drawn on. Remember to use solid lines where the actual boundaries are and dotted lines for where the boundaries are unknown as well as where they would of extended to above ground level prior to erosion. How does the measured thickness of the cross section compare with your calculated actual thickness? School of Earth and Environment 19 Folded and dipping cross sections: Now you have drawn the cross section you can place the axis on the folds.
School of Earth and Environment 20 Summary We have now worked through how to: Construct cross sections of dipping beds. Preserved in these rocks is the complex record of the many transgressions and regressions of the sea, as well as the fossil remains or other indications of now extinct organisms and the petrified sands and gravels of ancient beaches, sand dunes, and rivers. Statue of seated man said to be Herodotus; in the Louvre, Paris. Xenophanes of Colophon ?
These early observations and interpretations represent the unstated origins of what was later to become a basic principle of uniformitarianismthe root of any attempt at linking the past as preserved in the rock record to the present. Loosely stated, the principle says that the various natural phenomena observed today must also have existed in the past see below The emergence of modern geologic thought: Although quite varied opinions about the history and origins of life and of the Earth itself existed in the pre-Christian eraa divergence between Western and Eastern thought on the subject of natural history became more pronounced as a result of the extension of Christian dogma to the explanation of natural phenomena.
Increasing constraints were placed upon the interpretation of nature in view of the teachings of the Bible. This required that the Earth be conceived of as a static, unchanging body, with a history that began in the not too distant past, perhaps as little as 6, years earlier, and an end, according to the scriptures, that was in the not too distant future.
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This biblical history of the Earth left little room for interpreting the Earth as a dynamicchanging system. As such, they were considered unlikely to recur on what was thought to be an unchanging world.
With the exception of a few prescient individuals such as Roger Bacon c. He recognized that the marine organisms now found as fossils in rocks exposed in the Tuscan Hills were simply ancient animals that lived in the region when it had been covered by the sea and were eventually buried by muds along the seafloor.
He also recognized that the rivers of northern Italy, flowing south from the Alps and emptying into the sea, had done so for a very long time. In spite of this deductive approach to interpreting natural events and the possibility that they might be preserved and later observed as part of a rock outcropping, little or no attention was given to the history—namely, the sequence of events in their natural progression—that might be preserved in these same rocks.
Following from this observation, Steno concluded that the Tuscan rocks demonstrated superpositional relationships: This is the crux of what is now known as the principle of superposition. Steno put forth still another idea—that layered rocks were likely to be deposited horizontally. Steno, NicolausNicolaus Steno, engraving, Steno's four laws of stratigraphy.
The early English geologist John Stracheyfor example, produced in what may well have been the first modern geologic maps of rock strata.
He also described the succession of strata associated with coal-bearing sedimentary rocks in Somersetshire, the same region of England where he had mapped the rock exposures. Classification of stratified rocks In Johann Gottlob Lehmann of Germany reported on the succession of rocks in the southern part of his country and the Alps, measuring and describing their compositional and spatial variation. In Italy, again in the Tuscan Hills in the vicinity of Florence, Giovanni Arduinoregarded by many as the father of Italian geology, proposed a four-component rock succession.
In addition, Arduino proposed another category, the Tertiary division, to account for poorly consolidated though stratified fossil-bearing rocks that were superpositionally older than the overlying alluvium but distinct and separate from the hard underlying stratified rocks of the Secondary.
These rock bodies would constitute formations in modern terminology. Nearly 1, kilometres miles to the east, the German naturalist Peter Simon Pallas was studying rock sequences exposed in the southern Urals of eastern Russia. Thus, by the latter part of the 18th century, the superpositional concept of rock strata had been firmly established through a number of independent investigations throughout Europe. Were the various layers at each site similar to those of other sites? In short, was correlation among these various sites now possible?
The emergence of modern geologic thought Inherent in many of the assumptions underlying the early attempts at interpreting natural phenomena in the latter part of the 18th century was the ongoing controversy between the biblical view of Earth processes and history and a more direct approach based on what could be observed and understood from various physical relationships demonstrable in nature.
A substantial amount of information about the compositional character of many rock sequences was beginning to accumulate at this time. Thus arose an increasingly vocal challenge to the Neptunist theory. Perhaps the quintessential spokesman for the application of the scientific method in solving problems presented in the complex world of natural history, Hutton took issue with the catastrophist and Neptunist approach to interpreting rock histories and instead used deductive reasoning to explain what he saw.
Relative Dating Notes. - ppt video online download
The rocks of the Scottish coast and the area around Edinburgh proved the catalyst for his argument that the Earth is indeed a dynamic, ever-changing system, subject to a sequence of recurrent cycles of erosion and deposition and of subsidence and uplift.
Courtesy of Lord Bruntisfield; photograph, J. It was not easy for Hutton to popularize his ideas, however. Nonetheless, another 30 years were to pass before Neptunist and catastrophist views of Earth history were finally replaced by those grounded in a uniformitarian approach.Relative Dating - Example 1
Also, it was becoming increasingly difficult to accept certain assertions of Werner that some rock types e. It was this latter observation that finally rendered the Neptunist theory unsustainable. Hutton observed that basaltic rocks exposed in the Salisbury Craigsjust on the outskirts of Edinburgh, seemed to have baked adjacent enclosing sediments lying both below and above the basalt.
This simple observation indicated that the basalt was emplaced within the sedimentary succession while it was still sufficiently hot to have altered the sedimentary material.
Relative Dating Notes.
Clearly, basalt could not form in this way as a precipitate from the primordial ocean as Werner had claimed. While explaining that basalt may be intrusive, the Salisbury Craigs observations did not fully satisfy the argument that some basalts are not intrusive.
Perhaps the Neptunist approach had some validity? The resolution of this latter problem occurred at an area of recent volcanism in the Auvergne area of central France. Lyell, however, imposed some conditions on uniformitarianism that perhaps had not been intended by Hutton: No accommodation was made for past conditions that do not have modern counterparts. In short, volcanic eruptions, earthquakes, and other violent geologic events may indeed have occurred earlier in Earth history but no more frequently nor with greater intensity than today; accordingly, the surface features of the Earth are altered very gradually by a series of small changes rather than by occasional cataclysmic phenomena.
This, along with the increased recognition of the utility of fossils in interpreting rock successions, made it possible to begin addressing the question of the meaning of time in Earth history. Determining the relationships of fossils with rock strata The hypothesis of fossil succession in the work of Georges Cuvier During this period of confrontation between the proponents of Neptunism and uniformitarianism, there emerged evidence resulting from a lengthy and detailed study of the fossiliferous strata of the Paris Basin that rock successions were not necessarily complete records of past geologic events.