To recognize the various types of sedimentary (i.e., primary) bedding structures.
To connect sedimentary structures with the processes that created them.
To use computer and physical models to understand sedimentary processes (i.e., how sediment is transported and deposited), and how sedimentary structures are created.
In preparing for your new job at EcoEarth Inc., you realize that describing sedimentary particles is only part of the process you will need to complete in the field. You must also be able to describe and identify the types of primary structures that are found in layers of sediment (that is, how sediment particles are organized to form cross bedding, plane bedding, and other features). So you get your friends together again to find examples of sedimentary structures and to figure out what they mean.
Before you can interpret various types of sedimentary structures, you need to identify the processes that can transport and deposit sediment. Looking at your textbook (Chapter 3), you see that the author divides the processes that move sediments into three types: (1) dry (non-fluid-assisted) gravity-driven mass wasting processes; (2) wet (fluid-assisted) gravity-driven processes; and (3) processes that involve direct fluid flows of air, water, and ice. Consider the following questions while you read about the three processes.
Now that you have explored types of processes that transport and deposit sediment, you are ready to examine different types of sedimentary structures and to figure out which processes are responsible for forming each of the structure types. You and your friends have a few samples of sedimentary structures but, based on the list in your sedimentology book, you know that you do not have a very complete set. You decide to search for sedimentary structures on the web and come up with some good sites that have photographic catalogs and movies of bedform simulation.
A variety of sedimentary structures are listed below. These are structures you should be able to recognize by the end of the semester. Over the next several weeks,.describe each structure and the process that forms it. Also include the types of environments within which they are likely to be found.
A. Bedding plane structures on the base of beds (i.e., sole marks) formed by fluid flow
2. Tool marks
B. Bedding plane structures on the tops of beds
1. Mud (dessication) cracks
2. Raindrop impressions
C. Internal structures that produce cross bedding/lamination and associated terminology
1. Ripples, dunes, megaripples, sand waves
3. Climbing ripples
4. Herringbone cross bedding
5. Hummocky cross stratification (HCS)
6. Interference effects / superimposed ripples or dunes
7. Stoss side and lee side, crest and trough, foresets
8. Tabular versus trough bounding surfaces
9. Planar versus tangential foresets
10. Linear, sinuous, or linguoid crests
11. Flaser bedding, wavy bedding, lenticular bedding
D. Other internal structures associated with fluid/sediment flows
1. Planar or flat bedding/lamination
2. Normally graded beds
3. Reversely graded beds
4. Massive beds (no structures!)
5. Imbricated clasts
E. Sedimentary structures formed soon after deposition by sediment loading or fluid escape
1. Load casts (also ball-and-pillow structure)
3. Dish and pillar structures
4. Convoluted bedding (soft-sediment deformation)
5. Sand dikes (may form long after deposition)
F. Biogenic sedimentary structures (called trace fossils or ichofossils)
1. Skolithos ichnofacies
2. Cruziana ichnofacies
3. Zoophycos ichnofacies
4. Nereites ichnofacies
G. Also consider bedding contacts
1. Sharp or gradational
2. Planar, wavy, etc.