Geology 302 – Lab #4 – Fall 2008

Local Surficial Deposits – Field Trip Interpretation of Texture and Compositional Data

Introduction: The purpose of this lab is to examine textural characteristics and composition of local late Pleistocene surficial sediments. Your goal will be to develop an integrated understanding of the relationship between texture, composition and depositional setting. The second week of this lab will engage us in use of GIS (Geographic Information Systems) analysis of the compositional data, and comparison of the data with existing surficial geology coverage of the area. This week, we will take a field trip to a number of the sample sites, and then return to lab to complete lithological counts of pebble samples for a number of recently sampled localities. We will also complete development of a database to be used in our GIS work next week.

Grain Size and Compositional Data: Sieve data for previously analysed samples is included in the Excel file ‘Textural Data’. Statistical parameters derived from this data are included in the “Textural and Compositional Parameters’ file. The lithologic data is based on counts of the pebble+cobble fraction (grains > 16mm). We will discuss the various rock types and their provenance during the field trip. During the last part of the lab this week, we will add to this database with information from new samples

Map image files included in the lab folder illustrate the location of the samples. Note that we will visit some of the sample sites on our field trip, but not all. While in the field, be sure to take careful notes because these will be helpful in interpreting the data.

Analysis of Data:

While the write-up for this lab is not due until week after next (October 7), you should use the data to plot graphs which illustrate the variation in texture and composition. Differences in the depositional setting of these materials may result in result in significant differences in texture. Why does the pebble composition vary?