Name(s): ________________________________________________
W2105:
Section (please circle one): 1Thurs or
2Mon
Lab 6: Sedimentary Rocks, Processes and Environments
This exercise is based on questions & materials in the 10th edition AGI lab manual.
Read Chapter 6 from your manual covering sediments p 153-170. Use materials as provided and
answer the questions of the same number in the lab manual. Numbered rocks resembling those in the book
will be available on the benches. There are also 12 small samples in the Ward’s kits. On those, use only hand
lenses, no acid.
Sediments are solid deposits of pre-existing minerals, rock fragments, dissolved salts, or organic
matter. They are the residues of weathering processes that require transport mechanisms for the movement of
physical materials. Sediments also require a low-lying depositional environment wherein things can
accumulate. Contained within them are; biological and chemical fossils, sedimentary structures and evidence
for environments of deposition and preservation. As such they are the most important geological
environments and settings because they hold a record of past times and sequences. Additionally, they are
important to the environment because they are the most abundant substrates. The materials nearest to the
surface are the most porous and least compacted. Sediments contain important water resources and can easily
become polluted or contaminated with anything from toxic chemicals to bacteria.
Sediments and sedimentary rocks are classified by their particle size, shape, composition, cement type
and porosity. There are three major sedimentary environments, which are classified as clastic, chemical and
biological. These are based on the type of matter that is collected or deposited.
Clastic means broken bits or detritus of rocks and minerals and implies both a source terrain and a
transport mechanism or medium. When rock is exposed by erosion, it mechanically weathers or breaks down
to detrital sediment. Examples of this include; lithic sands made out of sand sized rock fragments and
transported by water to be deposited in rivers or the sea, or loess made of windblown quartz rich silts, and
mud’s made from clay minerals or clay and silt sized resistant minerals. If there are rock fragments, mineral
grains and organic matter all in the same sediment these obviously require diverse sources. By contrast, silt
sized windblown volcanic ash and glass requires only one special source. Water is the most abundant
transport medium and most sediments are water lain. Ice is the most efficient transport medium, and, has for
particular periods of time made very thick localized deposits. Wind is of lesser importance except for
prevailing peri-glacial or onshore winds or catastrophic circumstances like storms or volcanic eruptions. All
of these sediment are distinguished by their grain sizes, shapes, sorting and compositions. Big pieces require
lots of energy to transport them. Angular pieces have not been transported very far or may have just got
transported once. A deposit with logs, boulders and mud is poorly sorted and requires high energy. A deposit
of uniformly fine-grained quartz silt implies long range transport, generally over hundreds of kilometers,
and/or many cycles of transport.
The most abundant chemical sediments include limestones precipitated from salty or hyper saline
warm tropical shallow waters or travertine from hydrothermal spring waters. Gypsum, halite’s and other
evaporate mineral deposits are formed by evaporation in restricted hot basins both in coastal settings and on
land. Banded Iron formations originally (iron oxides) were deposited in the Precambrian as the atmosphere
and seas came to have free O2 from the appearance of cyanobacteria. Modern oxy-hydroxides of iron and
manganese are deposited in bogs, seeps and as deep sea nodules. Metal sulfide chemical sediments from in
reducing or acidic environments from submarine hot springs and dense metalliferrous brines, in bogs and other
1
oxygen poor sediments. Sometimes chert and barite can be exhalative chemical sediments from the
discharge of warm submarine springs or nearby volcanoes. Tropical and arid environments are the most
favoured for chemical sediments in shallow restricted basins or in playa lakes and salt flats on land.
Biological sediments include any material produced exclusively as a product or byproduct of living
organisms. This includes: chert from diatoms or radiolarians, chalk and carbonate ooze from foraminifera or
other calcareous nanno-fossils, limestone made from marine calcareous animal fragments, phosphate rock
mainly from fish fecal pellets, teeth and bones. On land, plants that generate cellulose can accumulate faster
than bacteria or fungi can decompose them to make deposits like peat. There are endemic in high latitude
marshes and bogs, which are also lacking in oxygen needed for the breakdown. Throughout the Phanerozoic
since trees existed (post Silurian) most accumulation and coalification has taken place in bayous and oxbow
lakes in the terrestrial ends of river deltas. Modern environments, where much organic waste is dumped, also
lead to eutrophic conditions and the accumulation of organic matter (behind large dams, off sewage outfalls,
sewage ponds, landfills). Examples of cellulose rich sediments include: wet fibrous peats, cannel coals (algae
in lakes) and super-hydrous organic slimes such as effluent from abattoirs, pulp mills and sewage outfalls.
Organic rich sediments such as silicate muds and limestone muds (oil shale) contain bacterially degraded
organic matter form living plants on land or in the sea. These form the organic source rocks for major oil and
gas deposits.
Sediments deposited by a species or by an assemblage of fossil and microfossils, record prevailing
evidence of where the organisms grew and indicate what the specific prevailing thermal and chemical
conditions were at the time. Calcium carbonate (CaCO3) in microfossils preserves both the oxygen and
carbon stable-isotopic records of water sources and temperatures. This information can be used to give a
paleo-record of environmental changes with time. Even organic molecules like hormones and porphyrins,
unique to life and biosynthesis make chemical trace fossils of past life and past environments in sediments.
Sediments can be dated by a number of physical means depending on their age and composition. For
materials that have modern carbon as wood or shells dates can be obtained on sediment younger than 60,000
years a by the 14C method. Minerals can make good chemical, temporal and isotopic tracers to their source
areas. An example would be using a particular volcanic glass or feldspar composition as a horizon or event
marker. Meteorite impacts leave widespread aerosols of fine particles (tektites) that can be physically and
chemically recognized in sediments. Beach sands with plastic and Styrofoam are reworked or deposited in
modern time. In Nanaimo Harbour and on Roberts Bank, on the Lower Mainland near the coal port, coal
detritus shows up in the sediments when it was first mined and shipped in the 1800’s. Below that level there is
no coal detritus present as it is too soft to survive ordinary erosion and sedimentary transport. When clastic
rocks contain coal fragments, they are coalified wood that was transformed during burial and lithification.
For polluted sediments, the mere presence of anthropogenic pollution marks the onset of that industrial
activity or source and thus they can be used for correlation. When lead (Pb) was added to gasoline’s as tetraethyl lead anti-knock compounds its’ combustion byproducts ended up in the dust of the world between the
1920’s and 1980’s in North America and Europe and is still present in some places without environmental
legislation like the Philippines. Many industrial metals are of this type; Copper (Cu), Zinc (Zn), Lead (Pb),
Manganese (replacement for lead, and in steels), Cadmium (Cd), Mercury (Hg) from batteries and various
industrial processes appear when the industry or waste appears and persist until the source is discontinued
(throwing batteries away, etc.).
Radioactive fallout of Cesium (137Cs), Strontium (90Sr) etc. from atmospheric weapons testing is a
good horizon marker from 1954 through 1964. Even after the Nuclear Test Ban Treaty this material continues
to work its way through the sedimentary system or accumulates from new sources, for example; accidents like
Three Mile Island’s leak, Chernobyl’s catastrophic meltdown (1987) and the ongoing leakage and loss of
radioisotopes from the destroyed Fukushima reactors since 2011. Radioactive Cesium (137Cs) is particularly
immobile in clayey and peaty sediments up to acidities sufficient to gelatinize and destroy clay mineral
2
structures. Radioactive Strontium (Sr) is immobile in modern lime mud and alkaline lakes. Lead (210 Pb) is a
natural background isotope from Radon and the Uranium decay series. It is present at low levels in all
sediments and rocks. For sediments older than 200 years, there are only the naturally generated background
amounts. For sediments younger than this there is an excess of Lead (210Pb) related to nuclear fallout; radon
(222Rn) converts to lead and falls out on atmospheric dust.
Measuring the changing concentration of these elements over corresponding changes in sediment
depths can be used to infer the modern epoch versus pre-industrial background levels. This is important for
setting environmental loads and backgrounds. Measuring the sequence of dis-equilibrium isotopes in the
Uranium (238,234U ) to Thorium (230Th ) decay series can be used back to 1.6 Ma in appropriate environments
like calcareous sediments, corals and speleothem cave formations. Potassium (40K) is good beyond 1.6 Ma in
feldspars and volcanic ash deposits. The conclusion is that while not all sediments can be dated analytically,
many types and environments can be. Where they occur calibrated radiometric ages and environmental
studies can be made.
Answer questions from Lab 6 in the manual in the spaces provided on this sheet.
Activity 6-1: Sedimentary Rock Inquiry (compare photos in lab book p. 171 to lab
specimens provided).
Questions: Complete the following table. You may examine the specimens under hand lens to note
composition, textures such as layering, grain sizes or fossils and cements. For additional information on these
read the paragraph below the table and refer to tables in chapter 6. ______________________________ (18)
Rock name
Composition: min’s/grains Textures ____ Cements
1. Quartz Pebble Conglomerate
2. Coquina
3. Rock salt
4. Glauconitic sandstone
5. Lacustrine shale
6. Quartz Arenite
3
Composition: lithic versus mineral clasts or crystals and which minerals. These grains or crystals tell where
sediment originated (provenance). Common sedimentary mineral grains are from the low temperature end of
Bowen’s reaction series: Quartz, Muscovite, Feldspars and other hard minerals > 6 (hornblende, epidote,
tourmaline, beryl, corundum, diamond). Lithic fragments may be igneous (granite, basalt), metamorphic
(Gneiss, Schist), sedimentary (chert, sandstone, shale). Crystalline sediments include limestones (calcite,
dolomite), Gypsum rock, travertine, caliche and salts which all precipitated from salty waters. Economically
important sedimentary massive sulphides precipitated from submarine hot springs. Bioclastic sediments
include: shells- (coquina), microfossils (diatom or radiolarian Cherts), (foraminifera or coccolith chalks),
Banded Iron Formation, peat, coals etc. Textures: refers to layering, grain sizes, cements, concretions, fossils
etc. Common sedimentary cements form after sediment is deposited and are found at grain-grain contacts or
infilling pore spaces. They include water soluble or low temperature minerals which can precipitate from
solution: silica, calcite, dolomite, clays, iron oxides (hematite, goethite, limonite), and pyrite. Sandstones,
siltstones and carbonate rocks are cemented while clastic shales tend to be compacted but not cemented. Many
crystalline minerals in sedimentary rocks expecially carbonates or sulphides involved bacteria or other living
organisms to originally form the crystals or cements. Sediments also contain pore spaces which are often filled
with gases, water, brine or petroleum.
Activity 6-2: Sedimentary Analysis from the Slopes of Mt. Rainier, Washington.
(Salish name is Tahoma from which Tacoma gets it name). Tacoma is built on former
lahar deposits shed from Mount Rainier. (Geeze, this volcano catastrophically dumps
rocks, mud and ash down here so why don’t we build a city here?)
Questions 1-2: Complete the following table based on photos on p. 172. Note the order A-B-C-D is
counterclockwise from upper right! Use Google Earth to visit the geographic coordinates of each site and note
how far it is from the summit. A is actually 46.823N, 121.776W, enter locations a decimal degrees Lat.xxxN,
Lon.yyyW. Use the elevation drop and distance to calculate the average slope leading down to each site (B, C,
D) and compare the distances and slopes to the average grain size of sediments transported to and found at
each site. Wentworth size class names and their particle size limits are given on p. 156 and in the table on p.
159. That table also has examples of grain shapes: angular to rounded. Apply correct terms. 20
Site
A. Mt. Rainier
B. Mt. Rainier
C. Nisqually River
D. Alder Lake
Setting
Summit outcrop
Talus slope
Upper channel
Delta
Elevation
metres.
Distance to
km.
Slope angle°
Angularity
Wentworth
size class &
dimensions
4
3. Circle the correct term:
These sediments are: a. detrital
b. biochemical
c. chemical.
Explain or justify your answer: ____________________________________________________________
______________________________________________________________________________________(2)
4. Suppose Mt. Rainier were to erupt again and bury all of these sites (and residential Tacoma) under a
new welded tuff or lahar (http://www.dnr.wa.gov/Publications/ger_psrc01_pringle_scott.pdf) allowing the
sediments at the previous 4 sites to become compacted, dewatered, cemented and thus lithified. Name the
sedimentary rock which would result from each sediment type. Use the tables 6.1-6.4 to find the correct terms
and answer this question.
(4)
Rock A: ______________ ______________ (2 words), Rock B _______________________________
Rock C: ______________ _______________ (2 words), Rock D ___________ _______________ (2 words)
5. Note the coloured: pink, yellow or orange surface coatings on the sedimentary particles at Site B. What is
this material (circle the correct answer): a. Fumarole deposits b. Dried elk urine c. Iron oxy-hydroxides
Explain where this coloured material came from? ______________________________________________
______________________________________________________________________________________
_____________________________________________________________________________________ (2)
6. The sediments in each image are the result of chemical and or mechanical weathering as well as some sort
of sedimentary transport. For each photo on p 172 A-D as above, find and name a weathering product describe
the transport as short or long and high energy or low energy etc. Mechanical weathering includes fracturing,
abrasion and rounding during transport, Chemical weathering includes hydration, hydrolysis, oxidation of iron
bearing minerals to iron oxides, dissolution of any minerals, alteration of glass or feldspar to clays and soluble
salts. High energy of transport includes: rockfalls, landslides, fast streams which may move at many metres
per second. Lower energy of transport can only carry fine grained sands, silts or muds or light or tiny
biological particles and generally has slower flow at a few cm per second or less.
(16)
Environment
A. Mt. Rainier
B. Mt. Rainier
Summit
Talus
Mechanical Weathering
Chemical Weathering
Energy (rate of Transport)
Distance of Transport
5
C. Nisqually River
Upper Channel
D. Alder Lake Delta
B. Reflect and discuss your observations and interpretations of the last 6 steps. What is the net effect for
sedimentary transport as distance increases from the source area. What happens to the original siliciclastic
materials and how do they change? Try and turn this around to use the sediment particle composition,
weathering, sizes, shapes etc. to infer something about the original sedimentary system that moved and finally
deposited them? ______________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________ (4)
Activity 6-3: Clastic and Detrital Sediment
Questions: Obtain 2 pieces of weathered, friable or poorly consolidated rocks. Igneous rocks comprise the
majority of the crust whether on continental shields, continental mountain belts, island arcs and oceanic
islands. You may select plutonic phaneritic rocks (Granite, diorite etc) or volcanic aphanitic or pyroclastic
rocks (tuff, scoria etc). Metamorphic rock like schist, slate or marble also comprise part of continental shields
and uplifted mountain belts. Sedimentary rock like friable sandstone, coquina and shale comprise the cover on
the crust and many continental margins. Each of these rock types has its own diagnostic textures and minerals
which permit even sand grain sized pieces to be identified under a microscope. Particles of these rocks tell us
about provenance (where they came from) and transport distances and directions. For older sedimentary
systems which are eroded or poorly preserved, these clues of origin persist in the derived sedimentary rocks.
A. Obtain a piece of weathered, friable plutonic rock like a granite or diorite, a pyroclastic rock like a volcanic
tuff, a metamorphic rock like a schist or marble and a sedimentary rock like a friable sandstone, coquina or a
shale from the bin of weathered rocks, your hand lens and a piece of coarse sandpaper (quartz, garnet or
corundum glued on hard paper).
1. Hold 2 rocks together and gently abrade them over a piece of clean paper until some fragments or grains fall
off onto the paper. Alternatively do this on sand paper. Save the grains in a plastic tray for Q3 and determine
visually what they are. Circle which one it is: a. rock fragments b. individual minerals c. mixture of both. (1)
Identify the minerals as best you can and list them here ________________________________________. (3)
2. Circle the correct term for the type of sediment you just made: bioclastic , pyroclastic , siliciclastic and
explain why this is the correct choice. ________________________________________________________
_____________________________________________________________________________________ (3)
3.a. Use the grains from Q1 and examine them for angularity-roundedness. Draw the shapes of at least 3 of
them here making sure to select ones that represent the total variation in shapes. Describe the grains with the
best term from the chart on p 174 and on figure 6.3 p. 159. For this an all other drawings put in a scale bar.
Shape Name _____________________________ (1)
Drawing of your grains:
(3)
6
3.b. Particle shape depends on the original mineral shapes or the texture in the parent rock. Quartz and
feldspar tend to break in chunky more equant shapes while micas can only be flat. Homogeneous rock textures
break evenly and foliated or bedded rocks break in flat layers. Transport tends to round things by abrading off
edges. Your rock rubbing or sand papering acted like transport distance. Explain what caused your particles to
have the shapes they did. Was it original mineral shape and rock texture or abrasion? ___________________
_______________________________________________________________________________________
____________________________________________________________________________________ (2)
4. Feel your grains with your fingertips. Coarse sand and gravel feel gritty. Silt is too small to see the grains
but you can feel them rolling over the ridges in your fingerprints. Silt when wetted also rolls into little worms
or micro-doobies! Clay slips and smears leaving a film on your fingertips but has no obvious grains that you
can feel or see. Use the grain size tool in the back of the book and the ruler to describe the grain sizes. Give
the grain size range both in mm ______________________ < your grains < ______________________ (2)
and according to the Wentworth scale. Circle the correct terms: a. Gravel b. Sand c. Silt d. Clay (2)
Comment about the significance of this grain size sorting for sedimentary transport by gravity, water, wind or
ice. ______________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________ (2)
5a. Find one of your weathered rocks with a sharp corner. Draw this corner profile below. Next take a piece
of coarse sandpaper and abrade this same corner. Now draw it again next to your first sketch. Describe in
words what your abrasion did to the sharp corner.
Corner Profile Sketch Before:
Corner Profile Sketch After:
What happened to the corner: __________________________________________________________ (3)
6. On the image of the Mississippi River Delta below, Write a capital ” D” on the region with the greatest
deposition of detrital (clastic) sediments. (1)
7
B. Sediment is transported under the influence of gravity (rockfalls, landslides) and via fluids such as wind, water or ice.
Due to the weight and hardness of sedimentary particles, any transport can erode a channel or abrade the underlying
surface. Of thee three transport agents, Ice can carry the greatest range of sizes but is not very discriminating & when
ice ages end, its glacial-marine deposits are the thickest in the sedimentary record, > 4 km. Water can transport
boulders in debris flows or flash floods, or mud in a lazy river. Wind at its strongest usually moves sand, though in blasts
even rocks can be transported this way as when volcanoes erupt violently or when “someone pulls” The World Trade
Center!
Take a homogeneous fine rained rock with a flat surface (shale, siltstone, limestone) and draw its initial
surface. Next rub it several different directions with the sandpaper (side to side, up and down, circles etc. and
draw the surface again. This is like grain surface abrasion during transport. Wind-blown quartz sand tends to
get frosted like bathroom privacy glass (left). Quartz in glacial meltwater stream transport tends to get hard
knocks and appears faceted as chips come out which appear fresher than the rest of the abraded surface (right).
Even the surface texture of sand grains tells something about its conditions or environment of transport.
Modern Eolian Sand Tunisia
Permian Fountain Fm Colorado
B.1 Rock Face Sketch After 1-D Motion: (2)
B.2 Rock Face Sketch After 2-D Motion: (2)
What happened to the face after 1-D motion B.1: ____________________________________________
___________________________________________________________________________________(2)
What happened to the face after 2-D motion B.2: ____________________________________________
___________________________________________________________________________________(2)
How do either of these compare to the quartz grain surfaces shown above? _____________________
___________________________________________________________________________________ (2)
C. Describe how
you could distinguish sediment grains which have had different transporting fluids (ice,
water, wind) and different flow regimes of transport? ______________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________ (3)
8
Activity 6.5: Sediment Analysis, Classification and Interpretation: Use the photos of
sediment on p 178, earlier tables and the geo-tools card in the back of your manual.
Additionally, obtain a small weighing boat and take a few grains of the ~7700 year old
Mazama ash to examine & describe and return to the jar when you are done with it.
The texture of sediment is used to interpret its provenance (where it came from), what kind of
transport fluid carried it (water, wind, ice), how far it had travelled. Maturity is measured in 2
ways: chemical and mechanical. A high Mechanical maturity is when the majority of grains
are all the same size (well sorted) and also well rounded, indicating either a great distance or
a great number of cycles of transport and deposition, as with sand that rolls up and down the
beach with every wave millions of times. Chemical maturity is judged by the relative
presence of chemically resistant minerals like quartz (both hard and pretty insoluble). Other
minerals whose proportions increase with increasing chemical maturity are clays, iron and
other metal oxides and some tough heavy minerals like: corundum, diamond, garnet , topaz,
tourmaline, zircon. By contrast the presence of easily weathered materials like: rock
fragments, calcite, feldspars and common ferromagnesian minerals means a low chemical
maturity. Questions:
A. Examine the photo of sample A and figures 6.2 p158 & 6.3 p159 and the roundedness images above.
Note the scale bar on Sediment 6.5A on p178 like you should have in each of your own drawings! This is an
oolite (comprised of spherically rounded and radially grown little balls of calcite. Examine this in thin section
at the petrographic scopes on the side of the lab). Make visual estimates of the following using your tables
referred to above and your geo tools card in the back of the manual.
1. The grain size range in mm is:
from _________ mm to ________ mm.
2. The % of each grain size class is:
Clay ____
3. Grain sorting (circle best choice):
a. Poor
4. Grain roundedness (circle best choice):
5. Sediment composition (circle):
a. Angular
Silt ____ Sand ____
b. Moderate
b. Sub-Rounded
(2)
Gravel ____
(4)
c. Well
(1)
c. Well-rounded
(1)
a. Detrital (Siliciclastic) b. Biochemical (or Bioclastic) c. Chemical (1)
6. Describe the process of transport and deposition ____________________________________________ (2)
7. Select the best environment putting an “A-oolite” on Figure 6.10 p.165, (below) for its likely origin.
8. Draw and label an oolite rock hand specimen and a thin section include a scale bar for each. Low power
objective on microscope has a field of view of 7 mm diameter. _________________________________ (6)
9
B. Examine the photo of sample B. This is mostly comprised of faceted to frosted quartz with a few black
chert grains. Make visual estimates of the following as above.
1. The grain size range in mm is:
from _________ mm to _________mm (2)
2. The % of each grain size class is:
Clay ____
Silt ____ Sand ____
3. Grain sorting (circle best choice):
a. Poor
4. Grain roundedness (circle best choice):
a. Angular b. Sub-Rounded c. Well-rounded
5. Sediment composition (circle):
b. Moderate
Gravel ____ (4)
c. Well
(1)
(1)
a. Detrital (Siliciclastic) b. Biochemical (or Bioclastic) c. Chemical (1)
6. Describe the process of transport and deposition. ______ _____________________________________ (2)
7. Select the best environment putting an “B-Quartz Sand” on Figure 6.2 below for its likely origin.
8. Draw and label a quartz rich sandstone with silica (clear overgrowths) and hematite (red rims) as cements.
On low power, the microscope has a field of view of 7 mm diameter. _____________________________ (6)
Examine the photo of sample C. This is mostly comprised of small periwinkle gastropod shells of calcium
carbonate. Make visual estimates of the following as above.
1. The grain size range in mm is:
from _________ mm to ________ mm.
2. The % of each grain size class is:
Clay ____
3. Grain sorting (circle best choice):
a. Poor
4. Grain roundedness (circle best choice):
5. Sediment composition (circle):
a. Angular
Silt ____ Sand ____
b. Moderate
b. Sub-Rounded
(2)
Gravel ____
(4)
c. Well
(1)
c. Well-rounded
(1)
a. Detrital (Siliciclastic) b. Biochemical (or Bioclastic) c. Chemical (1)
6. Describe the process of transport and deposition ____________________________________________ (2)
7. Select the best environment putting a “C-coquina shells” on Figure 6.10 p.165 (below) for its likely origin.
10
Figure 6.10: Plot: A-Oolite, B-Quartz Arenite and C-Coquina on the figure above from the previous
sediments whose photos you analysed. After doing 6.4 add F-Chalk and D-Chert.
(5)
Examine the Scanning Electron Microscope image of Mazama Ash and draw your own image
through a binocular scope beside it. This is mostly comprised of volcanic glass shards with subordinate
mineral crystals. http://nwgeology.wordpress.com/the-fieldtrips/skagit-river-valley-and-highway-20/a-10meter-thick-mazama-ash-deposit-in-a-skagit-river-valley-landslide-dammed-lake/ (near Marblemount)
The eruption cloud came from Central Oregon Cascades in winter about 7700 years ago and was blown by
wind, fell on snow and was re-deposited up the Skagit River Valley south of Bellingham to make finely
laminated sediment about 10 m thick near Marblemount in a landslide dammed lake. For decades Union
Carbide mined it to make “Lava-the hand soap”. What is the size of these grains? Use the classic field
geologist’s test – put a few grains in your mouth. Sand-sized grains (between 1/16 and 2 mm) crunch in your
teeth. Silt (1/256 – 1/16 mm) feels gritty on the tongue, but not so in your teeth. Clay-sized grains are too fine
to feel in your mouth. Go ahead, test the sediment but don’t put your tastings back in the jar! What did your
mouth tell you about the grain size? _______________________________________________________ (2)
Next to the SEM image draw your own grains as seen through a binocular scope.
(3)
11
Make visual estimates of the following.
1. The grain size range in mm is:
from _________ mm to ________ mm.
2. The % of each grain size class is:
Clay ____
3. Grain sorting (circle best choice):
a. Poor
4. Grain roundedness (circle best choice):
5. Sediment composition (circle):
Silt ____ Sand ____
b. Moderate
a. Angular
b. Sub-Rounded
(2)
Gravel ____
(4)
c. Well
(1)
c. Well-rounded
(1)
a. Detrital (Siliciclastic) b. Biochemical (or Bioclastic) c. Chemical (1)
6. Describe the process of transport and deposition ____________________________________________ (2)
Activity 6-4: Biochemical and Chemical Sedimentary Rock
Questions
A. Obtain some seashells, a plastic sandwich bag, 2 boards and a hammer and smash some shells to sediment.
1. What kind of sediment did you just make? Choose one:
a. pyroclastic b. bioclastic c. siliciclastic (1)
2. Describe the roundedness of the grains you made: a. angular b. sub-angular c. sub-rounded d. rounded (1)
3. Describe the roundedness of the grains in the photo: a.angular b.sub-angular c.sub-rounded d.rounded (1)
What environment did the rounding of the shells in the photo? ___________________________________ (2)
4.a. Most Chalk is made of single celled microfossil tests of calcium carbonate (calcite or aragonite)
biologically precipitated by either phytoplankton or zooplankton (foraminifers-left plane polarized light,
coccoliths-right SEM). Chalk feels smooth and the grains are too fine to see with the naked eye. Look at a
chalk thin section under medium power (field of view = 1.4 mm) and not how tiny the grains are. The lower
limit of optical resolution for grains is 2 microns (micrometers). This is literally biologically precipitated lime
mud particles. Note their grain size here. Chalk Grains are < __________________________ mm across. (1)
12
4.b. Obtain a piece of chalk and test is streak, hardness and reaction to hydrochloric acid. Describe your
findings here and explain how you could recognize chalk from these tests. __________________________
_____________________________________________________________________________________ (2)
5. Calcium carbonate mainly precipitates in warm, salty, clear tropical seas. Plankton can bloom in the
uppermost ocean regardless of how deep it is. Too close to shore or in shallow water, small particles tend to
get buried among more abundant larger sand grains. For really deep, cold and high latitude oceans, all calcium
carbonate tends to dissolve (below the carbonate compensation depth). Describe how chalk originates and
explain why it is mainly found or formed in quiet, low energy deep water locations. ___________________
______________________________________________________________________________________
_____________________________________________________________________________________ (2)
6. Examine pieces of chert with some surrounding matrix from our collection and a thin section under medium
power (FOV-1.4 mm). Both the chalk and the chert should feel smooth and even under a hand lens there are
usually no visible grains. This is because they are made with the individual hard, heavy, silica mineral tests of
one celled phytoplankton called diatoms (left) now or dominantly radiolarians (right) for Mesozoic & older.
Diatom
Rad
While these microfossils are present as traces in many sediments, to obtain pure deposits requires deep water
far offshore. Diatoms and radiolarian prefer cooler boreal or subtropical latitudes. Both diatoms and
foraminifera occur in deep sea sediments west of Vancouver Island today. Look at a chert thin section under
the petrographic microscope and estimate its grain size. Grains < ________________________ microns. (1)
Examine a piece of chert with a hand lens and test its hardness agains glass and a streak plate to get a feel for
how hard it is. Describe your tests and explain what mineral it is made of. _________________________
____________________________________________________________________________________ (2)
Go back to Figure 6.10 and add F-Chalk and D-Chert to your sedimentary facies map for where they should
most likely form.
B. Obtain
some charcoal or charred wood from Dallas Road Beach and a piece of coal from our collection.
Take the charcoal, place it in a plastic bag and crush it at the hammering station between 2 wooden blocks.
Bring it back and place your fragments into a plastic weighing boat tray for examination. Compare this to the
piece of coal provided from the Quinsam Mine in the Upper Cretaceous Nanaimo Group west of Campbell
River.
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1. Examine the charcoal fragments for density, shape and internal structures. How is this different from the
wooden block you used at the hammering station. Draw a piece of modern charcoal and label any biological
structures you can see.
(3)
2.a. Peat is a high latitude and high altitude bog deposit of small mosses, heathers and sedges. It does not
accumulate for long enough nor become compacted and buried to turn it into coal. Examine a piece of Peat
and note its plant structures. Describe 3 of them here. _______________________________________ (3)
2.b. Charcoal is made by burying a pile of burning wood so that is smolders slowly with a lack of abundant
oxygen. Under these heated reducing conditions, hydrocarbon molecules outgas and fall apart leaving a carbon
rich residue, which like coal might be 75% carbon by weight. Coal is made by burial of cellulose and other
organic matter under water and sediment so that there is no free oxygen for bacteria to degrade it and use it for
food. In either case, lacking abundant oxygen, the organic matter instead of breaking down to CO2 and H2O,
leaves a carbon rich residue and holds it in sediments for geological amounts of time. Burned or charred wood
is less bioavailable as a ready food source so many coal fragments in the sedimentary record, began their
sedimentary life as particles of charred wood left over from some forest fire. Until plants conquered land in
Late Silurian, and made abundant forests in Late Devonian, there are no coal deposits in the geological record.
It takes 8-10 m of plant material to make 1 m of coal. Canada and the US each have about 700 trillion tones of
reserves. It dwarfs the present biosphere by a factor of 40 or more. Things were obviously much different in
the geological past! Examine your specimen of coal and search for any evidence of compaction or layering.
Sometimes there are clay layers or pyrite that contribute to a coal’s ash content and pollution problems as a
fuel source as they make toxic metal dust and acid rain. The ash is also a pain in the ash as it must be hauled
away and disposed of. It is rich in toxic metals so it cannot just be thrown on the land as a soil remediant as
the coal burning industry promoted through the 1980s. Examine your coal specimen under a hand lens or
binocular microscope and look for any remnant biological structures or fossils. While these may be present in
some coal seams, usually the coal is too recrystallized or organically metamorphosed into other organic
compounds. While these are not minerals, we give them mineral like names: fusain for dusty black matter,
durain for dull appearing hard blocky matter, vitrain for shiny, glassy appearing coal. When coal is mined
underground, powdered limestone dust is wet sprayed on the coal face to cut down on explosive or flammable
coal dust.
Coal thin sections and macerals: Left reflected light: Liptinite, Inertinite. Right transmitted light, Boghead
(Canal Coal) with 2mm flattened spore, Sporinite, Vitrinite and smaller Algal cysts.
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2.b. Draw your coal specimen and label as many structures or components as you can see.
(3)
C. Reflect and discuss what it takes to make a biochemical or bioclastic sedimentary rock and preserve it for
the sedimentary record rather than having it return to the biosphere or carbon cycle. ___________________
______________________________________________________________________________________
______________________________________________________________________________________
_____________________________________________________________________________________ (5)
D. Iron Oxides and Sedimentary Deposits. Most of the colour in rocks, minerals and soils is due to iron as
ferrous Fe+2 or ferric Fe+3 ions due to iron oxides’ abundance ~7% of the crust. Other transition metals also
contribute colours but these are so much less abundant (a few tens of ppm for Co, Cr, Cu, Ni ) that aside from
Manganese (Mn2+ , Mn3+ and Mn4+ ) oxide at about 0.2 %, the others are rare aside from ore deposits of those
particular elements. Iron tends to make yellow and red in oxidized forms and dark green in reduced form.
Manganese oxides are in shades of blacks and browns. These red/brown and black bands are common along
coasts and as desert varnish. As economically important sedimentary deposits: Banded Iron Formation (BIF of
red jasper and black hematite – upper left) is the most important iron ore. In Iron Age times, Bog iron Ore
(Wad – Lower Left) was mined in Europe to make small iron objects using charcoal for reduction. Manganese
crusts (upper right) adorn the upper surface of seamounts and nodules cover the deep sea floor (lower right) in
areas of low sedimentation. Because Fe and Mn are the most common elements to gain or lose an electron
they form oxidation or reduction cements, coatings, soil minerals etc., wherever water and oxygen meet or
wherever bacteria need a sink for electrons garnered by breaking organic molecules.
BIF
Mn Crust
Bog Fe
Mn Nodules
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D.1 What is the chemical formula and streak of Hematite? Formula _________ Streak ______ rub some (2)
D.2 What is the chemical formula of Limonite and streak? Formula _________ Streak ______ rub some (2)
D.3 Examine a specimen of ferruginous sandstone and name the Fe mineral making its cement ? ______ (2)
How can you tell? ____________________________________________________________________ (2)
D.4 Watch the demonstration and examine the final product of heating limonite powder in a flame. ______
Describe what came off the mineral powder? _______________________________________________ (1)
What is the colour and likely compostion (chemical formula) of the final product? Colour ___________ (1)
What is its formula? __________________________________________________________________ (1)
Go to Mindat.org or Webmineral.com for formulae as needed
D.5 The 2 most common Manganese oxide minerals are pyrolusite and birnessite. Write pyrolusite’s formula
here: _______________________ and birnessite’s formula here: _______________________________ (2)
Find some pyrolusite to examine its streak and also look at the pyrolusite dendrites but don’t destroy them.
Give the streak colour _____________________________ and show some of it here _______________ (2)
Gently examine the Mn crust from Hodgekin’s seamount and see what else is present besides the dark oxide
minerals? Describe or tell what that other sedimentary component is here. _________________________ (1)
Activity 6-6: Replacement. Porosity Estimates for a Coarse Sedimentary Rock
A. Examine the photo in the manual on p 171 of coquina 6.1.A.2 and find one from our collection. A coquina
is a “beach rock” comprised almost entirely of coarse shell fragments. A modern name for this type of coarse
limestone is a “biorudite”, meaning shells and angular, coarse gravel size. Check the photos in Fig 6.6 on
p.161. Compare your coquina to both photos B & C and to the photo of loose shell fragments and to your
smashed shells. Describe the kind of sedimentary environment, transporting fluid and possible depositional
setting using one of the depositional facies locations indicated on figure 6.10. ______________________
Rocks like this occur along a:
a. steep mountain front b. river floodplain c. tropical coastline
(1)
The fluid that moved and abraded these particles was: a. glacial ice b. sea water waves c. blowing wind (1)
The sedimentary facies or depositional setting was a/an: a. coral reef b. alluvial fan c. beach
(1)
Estimate the % of porosity = Φ, (void space between the shells). You can do this visually using a geo tool
chart, but check this estimate by first by taking a plastic weighing boat (small square tray) weighing your
coquina dry. The sample weight is mostly shells of calcium carbonate with a density of 2.70 g/mL. Therefore,
the volume of shells in the coquina is: Shells mL = (Dry weight)______ g / 2.70 g/mL This is also called the
grain volume. Calculate this proportion of the total sediment volume here__________________________ (2)
Now immerse your coquina in a beaker of water until the bubbles stop and weigh it again. The weight gained
is all water at a density of ~1.00 g/mL filling the pore spaces, so the space filled by water is:
H20 mL = H20 _(weight gained)_ g / 1.00 g/mL : Calculate this here_____________________________ (2)
Now that you have the volume of your sample which is shells and the volume which is water, or voids which
can hold water, you can calculate the porosity, or volume % voids like any other percentage calculation:
Φ % = 100 x (H20 mL) / (Shells mL + H20 mL) : Calculate this here_____________________________ (2)
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Give 2 reasons why it would be a good aquifer or reservoir rock. It has ____________________________
and it also has __________________________________________________________________________ (2)
Activity 6-7: Outcrop Analyses and Interpretation. Refer to p 183 and replacement
image below along with Figure 6.12 for Sedimentary Structures.
West
East
A. Permian Age (250-230 Ma) De Chelly Sandstone is the cliff former. Note the “White House” Cliff
Dwellings – 2-3 stories tall for scale. This formation is wind blown, hematite cemented quartz arenite
sandstone. It has dark stripes of desert varnish (Mn oxides) running vertically down the eroded cliffs. The
sandstones have not been tilted since they were deposited so this is their original orientation. During Permian,
Pangea has been eroded dwon to the Precambrian basement rocks, here a Proterozoic Granite and an overlying
set of structurally tilted quartzites (meta sandstones). This part of Arizona was located in a supercontinent redbed desert setting and covered by dunes > 100 m tall.
Dunes move by restricting and speeding up flow over their backs and expanding and slowing down flow over
their slip faces. Paradoxically it is not the shape of the dune or ripple which gets deposited and preserved for
the rock record, but the orientation of the slip face. See the diagram on the right. Depending on flow
velocities, water or wind velocity field and particle sizes dunes may be rather 2 dimensional and straight like
ripple marks or complex, curved and branching.
1. Draw in the major bedding boundaries ~50 m or so apart and in lighter ink, sketch in the cross bedding on
the image above left for at least 3 sets of superposed cross beds. ________________________________ (3)
2. Do the cross beds dip only one direction or two: Circle which answer: a. 1 – unimodal b.2 bimodal
(1)
3. Look at the sedimentary Structures in Figure 6,12 and name the type of cross bedding found here. Are they:
____a. Current Ripple Marks ___b. Bimodal (alternate flow directions) ____c. Climbing Wave Ripples (1)
4. Speculate about what the environment, climate, direction and seasons might have been like in Permian to
generate the sedimentary structures in these red sandstones? ______________________________________
______________________________________________________________________________________
____________________________________________________________________________________ (3)
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5. Look in your AGI manual at the Grand Canyon outcrop pictures for the Kaibab Limestone as the 3 photos
depict on p. 183. A. Describe the environmental conditions present at 270 Ma along what was to become the
South Rim such that cross bedded marine fossiliferous calcarenite was being deposited. ________________
______________________________________________________________________________________
____________________________________________________________________________________ (3)
6. At 270 Ma from the evidence discussed above Canyon de Chelly was eroding down to bedrock granite and
metamorphic quartzite. Therefore it was:
a. under the sea b. on land (1)
At the same time, The Grand Canyon near Kaibab was depositing crossbedded calcarenite. ____________
Therefore it was:
a. under the sea b. on land (1)
7. It is about 400 km as the crow flies from the Grand Canyon’s Kaibab trail in the west to Canyon de Chelly
in the east. What important geographic feature must have lain between these 2 sites about 270 Ma in Early
Permian? Choose the most likely feature: a. coastline, sea to the west b. coastline, sea to the east ______ (1)
8. How does this paleogeography differ from this same region in northern Arizona today? Explain what must
have changed or happened to get from the geography and climate of the Permian to that we know today? __
______________________________________________________________________________________
____________________________________________________________________________________ (2)
Activity 6-8: Using the present to visualize the past: Part 1, Triassic of Pennsylvania.
Examine the photos on p 152 and see our sample of a slab of mudcracked
“redbed” rock from a similar setting. Refer to the sedimentary structures Fig. 6.12.
A. How are the modern environment pictured on the left and the Triassic one pictured on the right, the same?
_______________________________________________________________________________________
____________________________________________________________________________________ (2)
B. How are the modern environment pictured on the left and the Triassic one pictured on the right, different?
______________________________________________________________________________________
____________________________________________________________________________________ (2)
C. Describe the sedimentary environment and Triassic ecosystem including: land or water, sediment type,
vegetation, organisms and climate. __________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
____________________________________________________________________________________ (4)
Activity 6-9: Stratigraphy: Reading Earth History and sea Level Changes from a sequence of
sedimentary beds. There are paired photos for each level of strata. One is a sidelong view of the
bedding and weathering character of the sedimentary rocks. The next one is a plan view looking
down onto a bedding plane, showing sedimentary structures or fossils. Each pair of rock photos has
general descriptions of the materials present. Use your tables for sedimentary rock identification,
grain sizes, sedimentary structures and the facies diagram 6.2 to come up with a short (1 to 5 word)
description of the overall environment or setting that the sediments were deposited in. Then simplify
this interpretation even further to place a single x in the best choice for an environment or facies.
See the examples for the lowest 2 strata. Complete the figure provided. Time only moves to the
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future. Use an arrow to show which way sea level shifted (towards sea = transgression or towards
land = regression
Pick a single environment for each bed of rock, describe it in a few words, Give its position or elevation on a
traverse between land and sea. Put unconformities between non-adjacent facies & draw sea level curve at
(right). Transgressive sequences tend to deposit and preserve, regressive sequences tend to erode. (15)
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