Workshop on Sedimentary Rocks,

Environments of Deposition,

And

Interpretation of Sediment and Soils

3-31-2011

Part One: Sediment Particles

Origin: Where do the particles come from?

- rounding, sorting look at sample 1 (sand)

Composition: What are the particles made of?

- mineral composition, rock compositions look at sample 2 (sand)

Classification of Particles:

- boulders, cobbles, pebbles, sand, silt clay

Lithification:

- process that turns loose material into solid rock

- two steps: compaction, cementation

Part Two: Sedimentary Rocks (Example of Sedimentary Rocks Classification)

Classification of Sedimentary Rocks:

Clastic or Detrital Sedimentary Rocks: contain grains that traveled some distance as solid particles

- very large and rounded grains: Conglomerate

- very large and angular grains: Breccia

- small grains (feels rough): Sandstone

- very small grains (feels smooth): Shale

(Bio-) Chemical Sedimentary Rocks: contain grains that precipitated from a solution (usually water)

- made of calcite: Limestone

- made of quartz: Chert

- made of salt: Rock Salt

- made of gypsum: Rock Gypsum

- made of plant material: Coal

Part Three: Environments of Deposition

What can be used to determine environments of deposition?

- Composition:

o Evaporates (salt and gypsum) form in desert-like areas

o Certain limestones form in tropical seas (e.g. Coquina, Chalk)

o Tillites (glacial deposits) form in cold environments

- grain size and shape

o rounding is best in water

o sorting is best in wind

o frosting of grain surface occurs in wind, not water

- sedimentary structures

o mud cracks indicate wet and dry cycles

o ripple marks indicate water and wind currents

o cross-bedding indicate migrating sand dunes

o fossils tell about past living organisms and the environment in which they lived

Part Four: Soils (Global Map of Soils)

What is soil?

- soil is dynamic

- soil is alive

- soil forms layers over time (soil horizons)

Factors affecting soil formation

- original parent material (rock)

- time

- climate

- organic components

- slope and direction of slope

What does soil tell us about the environment?

- certain soils only develop in certain climatic conditions

- the amount of organic material tells about diversity of life

- well developed soils tell about time that must have passed to form these soils

Part Five: Sediment Interpretation (on the microscopic scale)

This is your opportunity to apply some of the information you just learned. Enjoy!

- Look at samples 1 through 8.

- Work according to the following outline:

- Make sure you take good notes of what you see!

- Make sketches of what you observe!

1. What to look for?

a. grain size

b. grain shape

c. rounding of grains

d. sorting of grains

e. presence of organic material

f. color of grains

g. mineral composition

2. How to look at fine grains?

a. Chose the right magnification. You may need to play with the instrument to find the right magnification.

b. Chose the right amount of light to illuminate the samples (on-light vs. through-light).

3. What do you see?

a. make a list of what you see.

b. sketch the particles, fossils, grains, etc.

4. How to interpret small objects?

a. What kind of environment is represented in this sample?

i. Beach (tropical, cold, volcanic)

ii. Dune field (on continent, desert)

iii. River deposit

iv. Glacial deposit