Name: Date: Class: Tell the Story of Rock Sequences Earth Science Exercise Parts 1 and 2: Look at the illustrations below which show several horizontally layered sedimentary rock layers, unconsolidated (loose) sediments, igneous intrusions and a faults. They have been numbered and lettered for ease of reference. For these illustrations you will tell the "story" of the rock sequences by observing certain characteristics: 1- The order in which the rock layers appear. 2- Erosional Surfaces 3- Unconformities 4- Intrusions and Faults The Key: Be sure to look at the key before observing the series of illustrations. Assume that an Igneous Intrusion will cause Contact Metamorphism of the surrounding layers that it intruded. For Rock Sequences 1 and 2, in the text boxes provided, list the order in which rock layers formed and events occurred, such as igneous intrusions, faulting, contact metamorphism or displacement of rock layers. Be sure to include the following terms in your answers, should they apply to an illustration: submergence, emergence, deposition, formation, unconformity and contact metamorphism. Also answer all questions pertaining to the Rock Sequences in the spaces provided. For Part 3: Look at the illustrations and answer all questions. If you need help with the submergence, emergence and unconformity issues, go to Submergence and Emergence of Rock Layers With Respect to Sea Level, look at the illustrations and read the captions. This is a printable assignment. Part 1: Tell the "story" for Rock Sequence 1 in the box below (page 2). Be sure to number your events in the order in which they occurred. Number "1" should be the first thing that happened in the rock sequence. 1
Questions for Rock Sequence 1: 1- In your sequence did you put Fault B before or after the Igneous Intrusion? Give a reason for your answer: 2- How many unconformities appear in this illustration? 3- Between what layers do any unconformities exist? 4- Give the numbers of all layers that would have been contact metamorphosed close to the igneous intrusion. Part 2: Tell the "story" for Rock Sequence 2 in the box below. Be sure to number your events in the order in which they occurred. Number "1" should be the first thing that happened in the rock sequence. 2
Questions for Rock Sequence 2: 1- How many unconformities appear in this illustration? 2- How many times was the land submerged? 3- How many times did the land emerge? 4- What do you think caused the folding of rock layers 1, 2 and 3? 5- Did you place the Igneous Intrusive Batholith before or after the deposition and formation of layers 4 and 5? Give a reason for your choosing this order: 6- Why are rock layers 4-7 not folded? Part 3: Look at the 2 illustrations below and answer the questions that pertain to each one. 1- Look at the first illustration called "Inclusions in an Igneous Intrusion". Next to each number below, place the name of the rocks (see Key) in the order in which they were formed. Number "1" is the oldest rock. Rock #1: (Oldest) Rock #2: Rock #3: Rock #4: Rock #5: (Youngest) 3
Look at inclusions #1 and #2. 2- Compare the age of inclusion #1 with that of the actual horizontal sedimentary rock layers. 3- Compare the age of inclusion #2 with that of the actual horizontal sedimentary rock layers. 4- State the Law (see the end of this assignment) that applies to relatively dating these inclusions. 5- How do you think the country rock inclusions became embedded into the igneous intrusion? 6- Look at the second illustration called "A Conglomerate Sedimentary Rock". The rock fragments, which compose the rock as a whole, were compacted and cemented to form the conglomerate. Each rock fragment had its own original origin prior to becoming an inclusion in the conglomerate. Without using sophisticated laboratory analysis, is it possible to know the relative ages (which is older and which is younger) by just looking at each individual fragment in the conglomerate? Check one: Yes No 7- Compare the age of all the inclusions to the age of the conglomerate rock itself. 8- State the Law (see the end of this assignment) that applies to relatively dating these inclusions. Take Note! A few rules apply when considering the relative ages of rock layers, i.e., which layer is oldest and which is youngest. To fully understand the history of the illustrations, one must keep the following laws and principles in mind: Concerning Rocks: Principle of Original Horizontality: Nicholas Steno (1638-1686) stated that sedimentary rock layers form in the horizontal position. Any deviation from this horizontality indicates that the rocks were later disturbed, (for example, by crustal movement). Law of Superposition: The principle that the oldest rock layers are at the bottom of a rock sequence with younger rock layers deposited on top of them. This can be considered a rule that applies in all situations, except where overturning of rock layers and/or extreme deformation has occurred. Law of Inclusions: Fragments of rock inside a larger rock are older than the matrix surrounding them. This includes country rock that was ripped apart by the force of intruding 4
magma and which ended up inside the cooling and crystallizing igneous material. It also includes rock fragments that compose a larger sedimentary rock. Example: conglomerate. Intrusions: Igneous Intrusions are younger than the rocks into which they have intruded. Law of Faunal Succession: Maintains that different rock strata of different ages, contain individualized fossils of flora (plant) and fauna (animal life), and that worldwide these fossils succeed each other in a predictable order. For example, a dinosaur fossil will not be found in the same rock layer as an early hominid (human) fossil. Therefore, fossils are of great importance and assistance in placing rock layers in proper order, even those layers that have been disturbed and severely overturned. Concerning Events: Faults: Faults are younger than the rocks they have faulted and/or displaced. Tilting: The event of tilting is younger than the rocks that are tilted and displaced. Folding: The event of folding is younger than the rocks that are folded. Metamorphism with resulting Contact Metamorphism of preexisting rocks: The metamorphic event came after the rocks that have been metamorphosed. Any rocks changed by contact metamorphism had to be their before they were changed. Erosion: Erosional Events are younger than the rocks that are eroded. This lesson and all graphic images are L. Immoor Geoteach.Com, Geolor 2006 Inspiration for Rock Sequence 1 was an image in a NY Earth Science Regents Exam however, the image as it appears here was created from scratch. 5