ES1083F_Tutorial Assignment 4 GeoTime_Worksheet_2023

Page 2 of 4 Exercise 1: Filling in Some Gaps Before determining geological time, let’s first identify the rock types used in Figure 2. Based on the hand specimens of rocks set out by the TAs in your tutorial session, using your notes from class and/or from your last tutorial assignment on rocks (your textbook might be useful too ), identify the rock types for the lettered rock units as listed below. To help you keep track of everything, write the rock type identified below in the blank space next to each of the corresponding lettered units in Figure 2. Rock Unit in Figure 2 Number of Hand Specimen Provided in Tutorial Session Name of Rock Type C I-9 E S-7 F S-11 G S-9 H M-5 I I-6 (/6 marks) Exercise 2: Unconformities and Missing Time The three main types of unconformities described in one of your lectures are represented by prominent erosion surfaces (shown as wavy lines between rock units) in the rock sequence in Figure 1. Identify which erosion surface (Surface 1, Surface 2, Surface 3 or Surface 4) matches each type of unconformity listed below. 1. Surface ___ is an angular unconformity. 2. Surface ___ is a non-conformity. 3. Surfaces __ and ___ are disconformities. (/4 marks) Exercise 3: Putting Radiometric Dates into the Picture There are three rock units in Worksheet Figure 1 that could be dated using the potassium-argon (K-Ar) method (C, I and J). Their numerical ages in millions of years (m.y.) are indicated directly on the diagram in Worksheet Figure 1. If you can’t remember the principles behind K -Ar dating, refer back to your lecture notes to brush up on the concept. You will be using principles of superposition, cross-cutting relationships and unconformities, in conjunction with radiometric dates to answer the questions below. 1. What is the maximum possible amount of time (in millions of years) represented in surface 3 (i.e., how much time is missing due to the erosion and/or interval of non-deposition that produced surface 3)? Answer;______ million years . ( /1 mark) 2. Complete the following sentence: The numerical age of rock unit B (limestone) is somewhere between ______ million years (oldest possible age) and ______ million years (youngest possible age). ( /2 marks) Exercise 4: Dealing with Faults In terms of their role in relative dating, faults (large fractures along which displacement occurs) can be treated like igneous intrusions- they are necessarily younger than the rocks they cut through. With this in mind, is the fault: Older or Younger than Rock unit C? Answer: ____________ Older or younger than rock unit J? Answer: ____________ ( /2 marks)