112lect4 - GY 112 Lecture Notes D Haywick(2006 1 GY 112...

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GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Stratigraphy and Geological Time Lecture Goals : A) Stratigraphic terms B) Geological Time C) Geological Systems Textbook reference: Levin 7 th edition (2003), Chapters 1,3; Levin 8 th edition (2006), Chapters 2, 5 A) Stratigraphy By now you should realize that a lot of people had a lot to do with getting geology organized into a proper science. One of those people was Fossil Bill ( William Smith ; the English hydrologist/surveyor). He was one of the first people to trace out rock units across the countryside. In order to do this, he had to develop a nomenclature specific to the area. He identified specific clay units, limestones and other rock types and gave them proper names (e.g., Church Clay, Cornbrash Limestone). The reason for doing this was simple. If you are going to map out a succession of sedimentary rocks containing multiple limestones or sandstones or shales etc, you better have a means by which to distinguish them. The fundamental unit in stratigraphy is the formation which Smith defined as: “a lithologically distinct rock unit that possesses recognizable upper and lower contacts with other units and which can be traced across the countryside from place to place” . Today, naming formations must follow acceptable guidelines. You cannot simply name a rock unit after a girlfriend. It must be named according to a place name or a geographical feature near the most outstanding exposure of the formation in question. Allow me to give you some personal insight to how this is done. When I was doing my Ph.D. in New Zealand, I identified several distinct rock units that satisfied the definition of formations. I determined the best locations for these formations (I had to label them on topographic maps etc) and then looked at the topographic maps to find an appropriate nearby place name. I named one sandstone formation the Darkys Spur Formation after a road (Darkys Spur) which cut right through a 2 km long section of the unit. I named a shale unit Esk Formation after a river that flowed at its lower contact. I even named one rock unit after a farm house (The Wairoa Formation). Not all names are acceptable and some suggestions have been refused by the governing body of stratigraphers (this varies from country to country. In North America, it’s the North American Commission on Stratigraphic Nomenclature). I was partial to a little pub known as the Hairy Armpit but knew that it
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GY 112 Lecture Notes D. Haywick (2006) 2 would be a hard name to get accepted by anyone without a sense of humor. Still, you have to admit that the Hairy Armpit Formation would have been a memorable name. Formations do not have minimum or maximum thickness requirements. They can be thin (5 metres thick) or thick (200 metres thick). They just have to be laterally continuous.
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