Unit 3.1: Geology and Geomorphology

Introduction

The basic concepts of geology will be considered to address the concept that rocks and sediments have widely ranging textures and compositions formed in a wide range of environments. These variations in turn can affect soil formation and many related Critical Zone processes.

This unit requires substantial reading to cover basic concepts of geology: the rock cycle, plate tectonics, geologic time, erosion, weathering and deposition, so that you have a firm grasp on how geology relates to and controls Critical Zone processes. In this unit, you will:

• recognize the three rock types and the processes by which they form
• describe the rock cycle and plate tectonics
• distinguish between weathering and erosion and their relationship to soils
• recognize the Critical Zone as a feed-through reactor
• recognize the differences between bedrock and surficial geologic maps and what each illustrates, and analyze site-specific information to evaluate the Critical Zone at a study site

Unit 3.1: Geomorphology and Pedogenesis

Part 1 - Basic Geological Concepts

Pre-class (this is a major component of this unit and will take you 4-6 hours of time).

Review all the web sites listed directly below and be prepared to discuss them. You will be responsible for understanding these terms and concepts for unit assessments. As you read these broad introductory materials make sure you: 1) read the introductions to the wikipedia articles and outline the major terminology and concepts introduced throughout the full article, 2) think about how each of these processes operates in areas you are familiar with, and 3) determine how does each of these processes affect erosion or deposition of soils?

• General geology, plate tectonics and the rock cycle
  • Wikipedia article on Geology
  • Wikipedia article on Plate Tectonics
• Geologic time:
  • Geologic Time from USGS
  • Geologic Time article from Indiana University Bloomington
• Weathering, erosion and deposition:
  • Wikipedia article on Weathering
  • Wikipedia article on Erosion
  • Wikipedia article on Deposition

Pre-class reading groups (Read the following journal articles and be prepared to discuss in class).

• The class will be divided into 4 different reading groups
• Each group will be assigned an article(s) to read.
• Each group will make a brief (
  • Articles should be reviewed prior to class to capture the main themes and topics discussed and how these relate to this class, module and entire course. As the course proceeds, students will begin to tie concepts learned in earlier lessons to the ongoing lessons and in the process will make the links that are at the heart of this very interdisciplinary science.
  • Research articles should also be reviewed prior to class using the following generic scientific analysis framework and any specific questions provided.
    • Reading Reports: Scientific Analysis Framework: Paper Review Questions (Microsoft Word 17kB Dec23 16)
• Each group will pre-read and meet outside of class to prepare their brief presentation on one of the 4 scientific papers listed below.
  • focus on concepts of general and broad importance, as well as topical questions specific to each article.

Pre-class reading articles:

1. The Critical Zone can be thought of as a "feed-through reactor" in which physical denudation and erosion are closely tied to chemical weathering.

• Anderson, S., von Blanckenburg, F., and White, A., 2007, Physical and chemical controls on the Critical Zone, Elements, v. 3, n. 5, p. 315-319. (Google citation for un-official web version)
• Consider the following questions as your read the article:
  • Do you think all soil parent materials were subject to erosion and deposition?
  • Are some soils the result of weathering of bedrock in place, that is not subjected to erosion and deposition?
  • If so, how do soils developed directly from bedrock differ from soils developed on unconsolidated material, if at all?
• Critical Zone (and soil) formation can be greatly affected by landscape position, particularly in actively uplifting systems.
  • Goodfellow, B., Hilley, G., Webb, S., Sklar, L., Moon, S., and Olson, C., 2016, The chemical, mechanical, and hydrological evolution of weathering granitoid, J. Geophys. Res. Earth Surf., 121, 1410-1435, doi:10.1002/2016JF003822.
  • Consider the following questions as your read the article:
    • What is the progression of chemical weathering in an uplifting system?
    • What links exist between rock chemistry and physical properties as a function of weathering?
    • How do changes in rock physical properties feedback on chemical weathering?
• Biota exert a fundamental role on landscape evolution and development of Critical Zone architecture.
  • Dietrich, W., and Perron, T., 2006, The search for a topographic signature of life, Nature, 439/26, 411-418, doi:10.1038/nature04452.
  • Consider the following questions as your read the article:
    • How does life impact CZ architecture on long and short time scales?
    • What biotic mechanisms can be linked to various processes of erosion?
    • Do slope-dependent versus water-flow processes produce different landscapes?
• Bedrock disintegration into erodable soil declines with increasing soil mantle thickness.
  • Heimsath, A., Dietrich, W., Nishiizumi, K., and Finkel, R., 1997, The soil production function and landscape equilibrium, Nature, 388, 358-361.
  • Consider the following questions as your read the article:
    • What is the relationship between soil depth and hillslope curvature?
    • What is a cosmogenic nuclide and how might one be used to study soil production rates?
    • Why might the thinnest soils and highest soil production rates be found on ridge tops?

In-class

Class Discussion

• Think-pair-share small sub-groups to discuss the readings and questions done prior to class and then a class discussion on important factors of soil formation and erosion/deposition. Consider the aforementioned questions specific to each article and: If all state factors of soil formation except parent material (e.g., rock or sediment type) were held constant in a select locale, do you think similar or different soils would be developed on the different parent material types? Why?

Part 2 - Bedrock Mapping

In-class

National Geologic Map Database Activity

• Introduction and class demonstration of the bedrock mapping activity that will follow. You will select a region of interest and produce a list of available resources and if possible, an example of a bedrock and surficial geologic map.
  • Activity Worksheet

Additional Resources

• Hilton et al, 2012, Climatic and geomorphic controls on the erosion of terrestrial biomass from subtropical mountain forest, Global BGC Cycles.
• Anderson, R.S and S.P, Geomorphology: The Mechanics and Chemistry of Landscapes, Cambridge University Press,
• Anderson, The Little Book of Geomorphology, in http://instaar.colorado.edu/people/robert-s-anderson/publications-detail/