SEDIMENT AND SEDIMENTARY ROCKS Chapter 7
A.
Introduction
1.
Sedimentary Rocks form from sediment in the
surface (or near-surface) environment
2.
Source of sediment: Weathering and Chemical Precipitation
3.
Two Types of Sediment
a.
Clastic Sediment----derived
directly from the weathering process (solid weathering products)
b.
Chemical Sediment----chemical precipitation from
solution
Table 7.2 on page 150 is helpful, but there are several important
differences from the notes (and remember the test comes from the notes, NOT the
text). Differences include: 1) learn that silt makes siltstones; clay
makes SHALE—ignore mudstone, claystone, mudrock and arkose that appear in the text; 2) the textbook uses “Detrital”
not “Clastic” (both are acceptable terms, I prefer “clastic”. 3) I consider
“Biochemical Sed. Rocks” as part of “Chemical Sed. Rocks” so I have 2 categories, not the 3 that the
textbook considers.
1.
Clastic Sediment & Rocks--- p150-151
a.
Sediment (and corresponding sedimentary rocks)
is classified on the basis of particle size see Table
7.1, p. 146
b.
Know relative particle size in order---from
largest to smallest:
Boulder,
Cobble, Pebble (collective called “Gravel”---usually rock fragments)
Sand,
Silt, Clay (most
sand is quartz, almost all clay size particles are clay minerals)
c.
Know which particles form which clastic sedimentary rocks using the names given below.
Gravel forms either breccia (angular particles) or conglomerate (rounded
particles)
Sand forms sandstones
Silt forms siltstone
Clay forms shale (ignore mudstone or
claystone)
2.
Chemical Sediment and Rocks (includes
Biochemical) pp. 151-152
a.
Sediment is precipitated from solution—rocks
classified on basis chemical composition
b.
Chemical Sedimentary Rocks usually consist of
essentially one mineral
c.
Know the following rock names: (also know
constituent mineral)
Calcite
(mineral) makes up Limestone (rock)
Dolomite
(mineral) makes up Dolostone (also called Dolomite)
Gypsum
(mineral) makes up Rock Gypsum
Halite
(mineral) makes up Rock Salt
d. Others: Coal & Chert
1.
Transportation:
consider only transportation by streams at this time p. 129-130
During transportation:
a.
Particles become smaller (particularly true for
larger particle, less so for smaller particles)
b.
Particles (especially gravel and sand) become
rounded (as opposed to being “angular”)
c.
Sediment is sorted according to particle size
(particles of the same size are placed together)
2.
Deposition:
p. 120-131
a.
There are numerous clastic
sediment deposits on the land surface, but almost all are “temporary”
b.
In order to be preserved as sedimentary rock
(with a few exceptions), the sediment need to be deposited:
i.
on a
continental shelf
ii.
in a large inland sea (rare at moment, but
plentiful for most of the earth’s history)
1.
Terms:
solvent, solute, solution, solubility, saturation, precipitation
2.
“Normal” Marine precipitation—evaporation is not
a significant factor
a.
composition of ocean water—remarkably constant
b.
calcite precipitation---factors p. 137-139
c.
dolomite formation (secondary)
d.
others: chert, Mn, phosphates
3.
Evaporite
Deposits (only covered in one paragraph, p. 152, in the textbook)
a.
Sequence
of precipitation during evaporation (least soluble first)
b.
Typical mineral sequence: Calcite (first---“least soluble”, gypsum,
halite (last---“most soluble”)
Steps:
1. Burial (many texts do not consider this as a first step, but I do in this course)
2. Compaction—compresses sediment and squeezed out much of the water
3. Diagenesis—minor mineralogical/chemical changes---may or may not occur
4. Cementation—especially sandstones: mineral cement is commonly quartz or calcite
1. About 80% of the land surfaces are comprised of sed rock; but sed. rk make up only 5% of the crust.
2. The approximate relative abundances of the different sed rk types are:
a.
Shale---------60%
b.
Sandstone---20%
c.
Carbonate---15%
d.
All others----5%
IGNORE: Sedimentary
Facies (p. 152-153)
1.
Stratification in water-deposited sediment
a. “Original
horizontality”---initial horizontal deposition of sediment see Fig 7.16
b. “Superposition”---oldest
layer on bottom; youngest on top
2. Stratification
in sand dunes (wind blown sand deposits)
a.
Cross-bedding---see Fig 7.10-b, p.156; Fig. 7.15, p. 160
3.
Other features---see
pp. 145-146
a.
Fossils
(important---found only in sedimentary rocks) see
p.159
b.
Ripple marks see Fig. 7.12, p. 157
c.
Mud cracks see Fig 7.13, p. 159