Kelly Mobley
Sedimentary Lab MAKE-UP
Geo 113 – Mr. Quarles
Grade: -2 pts for missed lab, -1 for
details: 7.0 (out of 10).
Al Quarles, 10/27/14
Sedimentary Rocks
1.
Describe how the following processes in the formation of a sedimentary rock:
a.
Chemical and Physical Weathering- Weathering processes continue to alter clasts
throughout the formation processes until the deposition. Physical weathering includes all
processes that crack, abrade, crunch, and break rocks; examples being exfoliation, wedging, and
abrasion. Chemical weathering is the breakdown of rocks due to chemical reactions; examples
being acid/base reactions, oxidation/reduction reactions, hydration and dehydration, and
hydrolysis. Both physical and chemical weathering tend to make clasts smaller and rounder.
b.
Erosion and Transportation- Transportation and erosion is the movement of the clasts
from the source area to a depositional basin. There are four modes of transportation: mass
wasting, wind(Eolian Transportation), ice, and water(Fluvial Systems, Sediment Load).
c.
Weathering as transportation occurs- Both physical and chemical weathering continue
during transportation; they alter the chemical composition of clasts as well as the physical
appearance. [need more discussion here, details of the physical and chemical weathering, even in
a repeat from above, and what the clasts in a sedimentary rock can tell you about the transporting
media.]
d.
Deposition- This is the process in transportation when the medium does not have enough
energy to carry a certain size of clasts, these clasts left behind are deposited. It would take more
energy to transport larger clasts. There are proximal depositional environments, which are near
the source rock and contain poorly rounded and poorly sorted clasts, and there are also distal
depositional environments, which have traveled further and are more well-rounded and wellsorted clasts. [so what can the clasts in a sedimentary rock tell you about the depositional
environment?]
e.
Lithification- Lithification is the transformation of a pile of sediment into sedimentary
rock. There are two types of Lithification: compaction and cementation. Compaction is when the
weight of overlying sediment presses sediment together; important for clay-sized particles.
Cementation is when mineral precipitate in pore spaces between clasts; sort of find their own
spot to fill in.
2.
Describe the differences in formation of the following sedimentary rock types:
a.
Clastic or Detrital- Clastic rocks are sediments derived from fragments of pre-existing
rocks. The major processes in clastic rock formation are the weathering, transportation,
deposition, and lithification of the clasts. Physical and Chemical weathering make clasts smaller
and rounder. Transportation is the movement of clasts from the source area to a depositional
basin. Transportation of clastic sedimentary rocks will sort the clasts from being very poorly
sorted, to very well sorted. Deposition is when the transportation has too little energy to carry a
certain size of clasts. The clasts that are not carried are deposited. Lithification is the
transformation of a pile of sediment into sedimentary rock. Two types of lithification are
Kelly Mobley
Sedimentary Lab MAKE-UP
Geo 113 – Mr. Quarles
compaction and cementation.
b.
Chemical- These rocks are formed by the evaporation of water from lakes or oceans.
Molecules such as calcium, sodium, and chlorine are left behind after evaporation, which means
the remaining water is filled with these molecules and rocks tend to form from the remains.
Chemical limestone, tufa, and evaporates are examples of chemical Sedimentary rocks.
c.
Biochemical/Bioclastic- These types of sedimentary rocks are from sediment that is made
up of biological processes. For the most part, this process takes place in the ocean where atoms
float among water molecules. Many different ions (calcium, magnesium, potassium) and
elements(silicon, fluorine, iron, phosphorous) form hard and soft tissues. When a marine plant or
animal dies, this tissue becomes a biochemical sediment that can become compacted and
cemented together (Lithification) to form a solid rock. Coal, chert, diatomite, and biochemical
limestone are examples of biochemical/bioclastic sedimentary rocks.