Geological Maps 1 Horizontal and Inclined Strata A well rounded geologist must be familiar with the processes that shape the Earth as well as the rocks and minerals that comprise it These processes cover the entire spectrum of geology from sedimentation through rock deformation to mountain building This is all very different from the material that you covered in the first portion of GY 111 e g rocks and minerals but don t panic Many students find rock deformation and mountain building to be the most fascinating areas of geology Rock deformation is defined as all changes that occur to the volume and or shape of a rock body As you will learn in the lecture portion of GY 111 rock deformation is a component of structural geology The lectures will mostly be dedicated to the theoretical aspects of rock deformation structural geology and mountain building The labs will be dedicated to teaching you how to recognize and interpret the consequences of rock deformation and structural geology They include tilted and overturned strata folds and faults At this point a warning is called for In the first portion of GY 111 you were responsible for learning the properties that characterize rocks and minerals This was largely a self regulating process You worked at your own pace and were in the lab at times that best suited your schedule Clever students did most of their learning during the lab sessions Others you know who you are did it the night before exams 0 Geological Maps Horizontal and Inclined Strata 1 Cramming for the rocks and minerals section of this course might have actually worked for you but if you try the same for the geological map component of GY 111 you will surely fail Structural geology and ultimately the interpretation of geological maps requires a significant amount of background knowledge It is our job to teach this to you and we do it a little bit at a time to ensure that your brains do not explode However if you do not keep up with the work you will be in over your head in no time The lab exercises at the end of each chapter will help you to learn the concepts necessary to survive structural geology and each subsequent series of exercises builds upon the previous ones Make sure that you do each set of lab exercises when instructed to and be prepared to turn them in for assessment at the beginning of the next lab period As already implied it is a good idea to get as much of the lab done as possible in your assigned lab period In this way you will be able to ask questions in the lab when there are one or more instructors available for help Geological maps are not all that difficult but they do commonly cause problems for students because they involve three dimensional configurations of rock layers or strata and a whole lot of geological information This chapter of the lab manual contains useful information about rock types geological time map symbols and other related information that you will need to interpret geological structures e g folds and faults and geological maps e g map symbols strike and dip vertical exaggeration map scales etc If you can understand the material as it is presented here you should have few problems with the lab exercises and exams in GY 111 But if you do have difficulties consult the lab instructors for assistance We will do our best to help you understand this material 1 1 Geological Time Rock units are labeled on geological maps in both a predictable and a sensible fashion The age of the rocks in terms of geological periods are usually indicated by a capital letter For example Ordovician rocks are labeled with an O Silurian rocks with an S Tertiary rocks with a T etc see Table 1 below for the complete series Age alone is insufficient to label rock units on a map If you are going to map out a succession of sedimentary rocks containing multiple limestones or sandstones or shales etc you really need to have a means by which to distinguish them Geologists use a Individual lab instructors may vary this policy e g you may have more than a week or less than a week to complete the labs Your instructor will advise you of his or her policy before the first lab is assigned If not ask Geological Maps Horizontal and Inclined Strata 2 system of nomenclature consisting of Groups Formations and Members The fundamental unit in stratigraphy is the formation which was 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 Most formations and many other rock units are given specific names For example the upper most sedimentary rocks that underlie Mobile are called the Citronelle Formation after Citronelle AL where these rocks are best exposed The Citronelle Formation is Quaternary to Tertiary in age hence its age label on geological maps is usually QT In order to distinguish the Citronelle Formation from other Quaternary Tertiary rock units it is conventional to use a lower case c in conjunction with the age label Hence QTc or more rarely QTci is used to label the Citronelle Formation The Ordovician Prairie Dog would be designated Opd the Devonian Boardwalk Formation would be designated Db and the Jurassic Boring Rock Formation would be designated Jbr Occasionally a rock unit or units without a name will be identified on a geological map For example K1 might refer to the first rock unit within the Cretaceous Period 1 2 Maps and Map Symbols The most useful and informative maps are those that convey vital information but in a manner that does not entirely confuse the reader A city map of Mobile that shows streets parks schools large buildings bus routes railroads fire hydrants and the location of every known pizza restaurant would be so confusing that you could never use it to navigate from one point to another Most maps are therefore selective in what they show Scale the relative size of the map is another issue that needs to be taken into account when examining maps Small scale maps like those that cover whole counties or states are good when travelling between cities but they would not be very useful if you were trying to locate a specific building on the main campus of USA1 Large scale maps which cover smaller areas like cities or university campuses but which show much more detail are what you need Scale and clarity are two of the most important factors to consider when you are producing maps Table 5 1 The Geological time scale 1 Hey