Overview

Photograph of hoodoos and Bryce Canyon National Park.

Destructive geologic processes break down bedrock. Mechanical weathering physically breaks down bedrock into smaller pieces, called sediment or grains, while chemical weathering dissolves and alters minerals. Weathered materials are transported from their provenance (place of origin) by mass wasting and agents of erosion, streams, glacial ice, waves, or wind to a place of deposition, when the erosional agent slows or melts, causing it to lose the energy needed to transport the load of sediment further. This place of deposition is the depositional environment and represents the origin of a sediment rock. Clastic (detrital) sedimentary rocks form when grains are compacted and cemented together through the process of lithification. In contrast, chemical sedimentary rocks form when dissolved minerals precipitate from water to form a rock through chemical reactions or living organisms. In this way, rock material moves through the Rock Cycle.

An illustration of part of the rock cycle.
Part of the Rock Cycle. Highlighting the processes needed to make sedimentary rocks.

Sedimentary rocks are rocks that form at the Earth's surface via the processes of weathering, erosion, and lithification. They are unique because they record past environmental conditions on Earth's surface and preserve evidence of past life as fossils. Sedimentary rocks are the pages in which Earth's history is written and can inform us about a wealth of subjects, from the occurrence of ancient catastrophes to the productivity of life. In a sense, sedimentary rocks are the pages of the book of Earth's history that earth scientists read to tell us the story of Earth, such as the evolution of life as depicted by fossils.

Steps in making a sedimentary rock.
Making sedimentary rocks flowchart.

Sedimentary rocks always form on or near Earth's surface and therefore provide a record of paleogeography - ancient environmental conditions where the sedimentary rock formed. This makes sedimentary rocks especially useful to geologists, who know how to read the clues provided by the texture, composition, sedimentary structure, and fossils contained within the rock. By completing this module, you will gain some of the skills needed to read rocks so you, too, can make interpretations about paleography.

Learning Objectives

Course SLOs
- Students can explain the rock cycle, differentiate among the three types of rocks, and use texture and composition to identify common rocks and their origin
- Students can describe the role weathering, mass wasting, and erosion play in shaping Earth’s surface and can provide and/or identify examples of each of these processes
- Students can differentiate between constructive and destructive geologic processes, can explain the energy driving these processes, and can identify examples of each
Module SLOs
- Describe the processes that form different types of sedimentary rocks
- Use texture, fossils, and structures to interpret environmental conditions.

Directions

Like previous modules, work your way through this module one assignment at a time. Please email or attend study hall or tutoring Zoom sessions with any questions.