EEES 1010, Spring 2004,  Dr. James Martin-Hayden

 

Sedimentary Rocks

 

A.        Types of Sedimentary Rocks

1.    Clastic

2.    Biochemical (e.g., Limestone)

3.    Organic (e.g., Coal)

4.    Chemical (e.g., Evaporites)

B.        Sediment Size Classification

            -                            Boulders

Bowling Ball, 256mm

-                            Cobbles

Pool Ball, 64

-                            Pebbles

Buck Shot, 2

-                            Sand

Powder, 1/16

-                            Silt

Very fine powder, 1/256

-                            Clay

C.        Following the Life of Sediment

a) Size

b) Sorting

c) Shape

d) Composition

1.    Talus Slopes

a)    Gravel (boulders, cobbles etc.)

b)    Poorly sorted

c)     Angular

d)    Fragments of rocks and minerals Fig. 5.6 and 9.15

2.    Mountain Stream (Upstream)

a)     Gravel (Cobbles, Pebbles etc.)

b)     Poorly sorted

c)      Sub-angular (Somewhat rounded)

d)     Fragments of Rocks and minerals Fig. 6.3

3.    Alluvial Fans

a)    Sand

b)    Poorly Sorted

c)     Sub-angular

d)    Many minerals Fig. 6.11

4.    Mountain Stream (Downstream)

a)    Gravel (Cobbles, Pebbles etc.)

b)     Poorly sorted

c)      Rounded

d)     Fragments of Rocks and minerals Fig. 10.15

5.    River in the Plains

a)    Sand

b)    Somewhat Sorted

c)     Sub-angular

d)    Many minerals

6.     Beach Sand

a)    Sand

b)    Well Sorted

c)     Rounded

d)    Quartz (other minerals have been chemically weathered to clay and winnowed out) Fig. 14.7

7.    Delta

a)    Silt and Clay i.e., Mud

8.    Deep Sea (Lakes, Oceans)

a)    Clay

D.        Recipe for Clastic Sedimentary Rocks

1.    Sediment (collections of clasts)

a)    Source rock

b)    History of weathering and transport

c)     Environment of deposition

2.    Accumulation and Preservation

3.    Lithification Fig 6.6

a)    Compaction

b)    Cementation by precipitation of dissolved ions (e.g., quartz or calcite)

E.        Classification of Clastic Sedimentary Rocks

a) Size

b) Sorting

c) Rounding

d) Composition

e) Environment of deposition

1.    Breccia Fig. 6.8

a)    Size: Gravel

b)    Sorting: Poorly sorted

c)     Rounding: Angular

d)    Composition: Rock Fragments

e)    Environment of deposition: Mountains, bases of cliffs, I.e., Talus slopes

2.    Conglomerate 

a)    Size: Gravel

b)    Sorting: Poorly sorted

c)     Rounding: Well Rounded

d)    Composition: Rock Fragments

e)    Environment of deposition: Mountain streams

Sandstones

3.    Quartz Sandstone

a)    Size: Sand

b)    Sorting: Well sorted

c)     Rounding: Well Rounded

d)    Composition: Quartz clasts

e)    Environment of deposition: Beach and/or dunes

4.    Arkose

a)    Size: Sand

b)    Sorting: Moderately sorted

c)     Rounding: Sub-angular

d)    Composition: Feldspar, Quartz, and other minerals that have not been chemically weathered

e)    Environment of deposition: Alluvial fans, rivers near mountains

5.    Graywacke

a)    Size: Sand

b)    Sorting: Poorly sorted

c)     Rounding: Angular

d)    Composition: Many minerals of parent rocks (possibly mixed with marine clay)

e)    Environment of deposition: Turbitity currents, submarine fans

6.    Silt stone and mudstone (clay stone)

a)    Size: Silt and clay size

b)    Sorting: Poorly sorted

c)     Rounding: gritty quartz (rounded?) and flat clay minerals

d)    Composition: Quartz and clay

e)    Environment of deposition: Deltas (lakes and marine platforms)

7.    Shale

a)    Size: Clay size

b)    Sorting: (Not part of classification)

c)     Rounding: Flat clay minerals

d)    Composition: Clay (perhaps some quartz)

e)    Environment of deposition: Deep sea and lake

 8.    History of Weathering, Erosion, Transportation, and Deposition determines Sediment Type and ultimately, if lithified, Rock Type

Increasing Duration of Weathering and

Winnowing out of silt and Clay sized particles (predominantly clay minerals)

                                 

 

Immature

 

 

Mature

Clast Comp.

Rock Fragments

Unstable Minerals

More Stable Min.

 

 

Quartz

Clast Shape

Angular

Rounded

Rounded,

 

Rounded,

All Sand

Clast Size and Sorting

Coarse

i.e., Gravel and Sand, Poorly Sorted

Sand and Silt Poorly Sorted

Well Sorted

Depositional Environment

Mountains

Cliffs, Glaciers

Mountain Streams

Rivers,

(Flood Plains)

Beaches

Rock Type

Breccia

Conglomerate

Arkose

Quartz Sandstone