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Geology 109L Lab 3: Modern Sedimentary Environments --Field Trip to Bodega Bay--

Goal: The purpose of this lab is to recognize characteristics of modern sedimentary environments, which will aid you in your interpretation of ancient sedimentary environments as they are preserved in the rock record. This is your opportunity to apply everything that you have learned about sedimentary particles and sedimentary structures (Labs 1 and 2) and how they reflect depositional processes. At the end of the lab you will have a collection of sediment samples and a photo journal that documents geologic features and processes that you observed.

You will need: Field notebook, grain size card, hand lens, camera (1 for each group of two or three), trowel for digging (1 for each group of two or three). Depending on the weather, bring warm, water-proof clothing or sunscreen. Rubber boots are nice to keep your feet dry.

In the field:

While we are in the field, your job will be to collect multiple sediment samples (3-5) from three localities that we will visit, and describe the context in which you found them. The suite of samples that you collect should capture the diversity of local depositional environments. To put the sediment sample in context and determine how the environment changes through time, dig a small hole and look at the deeper sediment layers. A sketch in your field notebook of where each sample was collected relative to the others may be useful. Start thinking about the differences in texture and composition between samples at each locality.

Each sample description should include:1) A sample ID (such as BH-1 for the first sample collected from Bodega Head).2) Where it was collected (in the breaker zone, in a tidal channel, in a sand dune, etc.).3) Any sedimentary structures that you observed, including a cross-section sketch if relevant, and how the sediment texture and composition changes with depth. 4) An interpretation of the flow conditions (energy, variability in flow, current direction, etc.) that deposited the sediment you will keep thinking about this back in the lab5) A log of photos that you take of the environment, sedimentary structures, changes in grain size with depth and laterally **At localities where we are not collecting sediment samples, e.g. Horseshoe Cove, note general characteristics of the depositional environment, and photo document and describe different geologic processes and features for your photo journal.

More on the photo journal:

Throughout the day take photos of different geologic features and processes. At the end of the day you should have at least 20 photos. Dont forget to record in your field notebook what you took a picture of, and make sure to have something in your photo for scale! You will identify

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and describe the photos, and use drawing features in MS Word to label features on your photos, such as ripples, current direction, variable sorting of sediment, etc. Make sure that you are not just taking photos of scenery and trying to identify things. Take each picture with a purpose, and think about whether or not you are documenting the feature in its geologic context.

Keeping a Field Notebook

The field notebook is the original scientific record of your observations and is one of the most important items for any geologist. Organizing your notes systematically as you take them will help you when you refer back to your notes. Each entry in your field notebook should include first the date, time and locality. Table 2.1 (page 16) in Sedimentary Rocks in the Field provides a good summary of information to include as part of your sedimentological observations. Field sketches can be very useful, and should focus on the features of interest, rather than things like vegetation. Make sure to include a scale for any sketches.

In the lab:

Describe the texture and composition of each sediment sample you collected, as you did in Lab 1. Give the relative abundances of each grain composition, overall grain size, shape, sorting, and textural maturity.

Field Trip Stops:

Stop 1 Salmon Creek Beach Collect sediment samples along a transect perpendicular to the shoreline from the waters edge to the inland margin of the beach and describe the environment where they are deposited. Take pictures for your photo journal.

Lunch at Bodega Marine Lab

Stop 2 Horseshoe CoveCompare the texture and composition of the sediment here with the sediment at Salmon Creek Beach, and describe your observations in your field notebook. Take pictures for your photo journal.

Stop 3 Bayside Park Collect a sample of sediments from the Bay. Observe and describe how these sediments are different from the beach sands at Salmon Creek and Horseshoe Cove. Pictures!

Stop 4 Bodega HeadCompare the sediments deposited at Bodega Head with sediments from Salmon Creek and Horseshoe Cove. Collect a sample of the weathered bedrock and of the beach sediment. Pictures!

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What you will hand in:

1. Your field notebook.

2. A mini-report that summarizes your observations and interpretations and includes as appendices:

a. A sediment description (texture and composition) for each sediment sample.

b. Your photo journal 1 per group of 2 or 3 is fine since you are sharing cameras.

Mini-report: Put together all of the information that you have collected and write a well organized mini-report that summarizes the depositional environment and processes at each locality based on data and observations. Include your description of each sediment sample, and a summary the processes that contributed to its development and deposition. Include a discussion of variability in grain size, sorting, sedimentary structures, and maturity between samples. Also compare the beach sediment from Bodega Beach with the sediment at Bodega Head, and discuss what may be responsible for the observed differences. Refer to your photos and your sediment descriptions in your report, and include these as data appendices.

Questions to consider:

How does the grain size change along a transect across Salmon Creek beach? How do grain size changes reflect the depositional processes and flow energy? (Hint: explain WHY the energy changes as it does.)

How does grain size correlate with sedimentary structures observed where each sample was collected?

How does sediment texture vary with depth in each location and between locations?

Do certain sedimentary structures occur more commonly in different deposition settings? Under different energy conditions?

How does the sorting vary at the different localities? Interpret sediment sorting based on depositional processes.

Based on the composition of grains from Salmon Creek Beach, Horseshoe Cove, and Bodega Head, what is a likely source of grains at each beach? Why does it vary.

1/24/08 4:43 PMDriving Directions from Davis, CA to Bodega Bay, CA

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Start: Davis, CA US

End: Bodega Bay, CA US

Notes:

Directions Distance

Total Est. Time: 1 hour, 56 minutes Total Est. Distance: 101.30 miles

1: Start out going WEST on 3RD ST toward F ST. 0.1 miles

2: Turn LEFT onto E ST. 0.1 miles

3: E ST becomes RICHARDS BLVD. 0.1 miles

4: Merge onto I-80 W toward SAN FRANCISCO. 38.8 miles

5: Merge onto CA-37 W toward SAN RAFAEL. 21.3 miles

6: Merge onto US-101 N toward SANTA ROSA / EUREKA. 12.1 miles

7: Take the CA-116 E exit toward SONOMA / NAPA. 0.2 miles

8: Turn RIGHT onto LAKEVILLE HWY / CA-116. Continue to follow CA-116. 0.2 miles

9: CA-116 becomes LAKEVILLE ST. 0.9 miles

10: Turn LEFT onto E WASHINGTON ST. 0.6 miles

11: E WASHINGTON ST becomes BODEGA AVE. 7.9 miles

12: BODEGA AVE becomes VALLEY FORD RD. 10.5 miles

13: Turn SLIGHT LEFT onto CA-1 / VALLEY FORD CUTOFF. Continue to

follow CA-1.

7.7 miles

14: Turn SLIGHT RIGHT onto WINDY LN. 0.1 miles

15: End at Bodega Bay, CA US

Only text visible within note field will print.

1/24/08 4:43 PMDriving Directions from Davis, CA to Bodega Bay, CA

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Start:

Davis, CA US

End:

Bodega Bay, CA US

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