Earth History: Investigation 4 Sandstone & Shale

Review of Sand Types  Mountain Stream –subangular to subrounded –poorly to moderately well sorted –medium to coarse grain sand size –Variety of colors & minerals

Review of Sand Types  Beach –Rounded to well-rounded shape –Well sorted to very well sorted –Fine to medium sand grain size –Clear quartz, pink to brown feldspar, other varieties of colors & minerals

Review of Sand Types  Dune Sand –Sub-rounded to rounded, some subangular shapes –Well sorted to very well sorted – fine to medium sand grain size –Mostly clear/white quartz, other clear minerals –Appears frosted and scratched from the wind

Sedimentary Processes  Sediments- particles of earth material that settled out of the water, wind, ice  Erosion- the removal and transportation of loose earth material  Deposition- the settling out of eroded earth material  Sediments form through the processes of chemical and physical weathering. Weathering is the breaking down of rocks and other materials.

Sedimentary Rock Formation  Matrix- the material that glues the sand together in sandstone.  Basins- low areas that collect water and sediments  Compaction- pressure is applied to a material, can be by other materials above of sand, silt  Sediments turn into rock through the process of lithification, which involves cementation, compaction and crystallization.

Sandstone Formation  Sandstone Formation:  1. Sand is loosely packed soon after deposition.  2. Sand is compacted long after deposition.  3. Sand gets surrounded by a cementing mixture (matrix)  4. Sandstone is created over time.

Shale Formation  1. Shale is made from silt & clay particles  2. Deposits of clay and silt harden into rock when the water is removed and cementation occurs.  3. The water can be removed by drying or from pressure squeezing the particles together.  4. No matrix is needed to form shale.

Sandstone & Shale – Past Environments  Sandstone –Made of different sized sand particles. Can be from a mountain stream, beach, or desert dune  Shale –Shale commonly has plant/fern fossils. –Small particles of silt & clay –Indicates a swampy past environment

Sediment Deposition & Rock Layers  Sediments are naturally deposited in flat, horizontal layers.  Principle of Original Horizontality – each new deposit of sediment forms a new horizontal layer on top of the layers below.

How can we use rock layers to describe Earth’s history?  Uniformitarianism – the present is the key to the past.  Geologists use the observations they make about processes happening today, such as erosion, deposition, & formation of sediments, to infer events that happened in the past.