Download GEOS240-W17-Lab-01-Review Introduction

Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
LAB 1 – REVIEW & INTRODUCTION TO SEDIMENTS &
SEDIMENTARY GEOLOGY
OBJECTIVE
Review some of the concepts and components of sedimentary geology: Weathering, Sediment
Production, grains, cements, mechanical erosion, Rock Classification, Transport, Deposition, facies,
Hiatus, Geological Time, Maps, Cross Sections, Tectonic settings & Wilson cycles from Introductory
physical geology.
MATERIALS
Materials for this lab will be set out on the benches. Please keep all items with their trays. Return
hand lenses, acid bottles to their carriers and rock test kits to the back SW drawer. Return binocular
microscopes to the cabinets under the scales.
Minerals in labelled trays 1 of each type as per first table below: Augite through Serpentine.
Rocks: in labelled trays, 3 of each type: Volcanic tuff (porous, layered, friable), basalt (1. With
plagioclase phenocrysts, 2. amygdaloidal basalt or andesite with quartz or chalcedony, and
zeolites), Granite (1. weathered pegmatites from Nova Scotia for weathered and 2. Fresh Wards or
small trays in white wire shelves for fresh), schist (fine grained, micaceous), amphibolite (foliated),
gneiss (lineated, layered or foliated), shale (with leaf fossils), siltstone, sandstone (1.brown,
weathered, friable, stained with limonite, 2. White with silica cement), conglomerate (with lithic
pebbles), limestone (fossiliferous), travertine (porous, layered), chert (various colours not all
black), coal. Bin of poorly sorted beach sand pebbles to dust, and one of clean well sorted coarse
“Ottawa quartz sand” for grain size and sorting estimates.
Apparatus: Clean white paper, weighing boats, sandpaper, lunch trays, rock test kits, acid bottles,
hand lenses, binocular microscopes and lamps, beakers, ice, water.
PRODUCTION OF SEDIMENTS AND SEDIMENTARY ROCKS
I. Rocks, Minerals, Provenance and Weathering
Some rocks are monominerallic others contain a few different minerals. Rock fragments eventually
weather or abrade to smaller rock fragments (basalt etc., VRF = volcanic rock fragments; slate,
chert, flint, fish teeth = SRF = sedimentary rock fragments; and mineral grains. Limestone blocks
and rock fragments rarely survive in continental systems as transported particles as they are too
soft and soluble. In marine carbonate facies they are abundant and siliciclastic material is rarer as it
does not reach offshore to banks or reefs where limestone forms. Lithic sands are dark in colour
and composed mainly of tiny sand grain sized rock fragments. Quartz is common to many different
rock types as a primary abundant mineral or as later hydrothermal veins. It and the other Si02
minerals (agate, chalcedony, opal) are mechanically hard and chemically resistant so that they
resist weathering and make gravelly, sandy or silty residues. Mature, second cycle and long
1|Page
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
transported sands are quartz rich. Olivine is as hard as quartz but oxidized and reacts so it is rarely
found in sediments. Softer minerals (micas, ferromagnesian minerals, carbonates, salts) tend to get
dissolved in water, oxidized in air or abraded away during sedimentary transport. This chemical
weathering produces: more or less soluble salts (Halite NaCl, Calcite CaCO3, Gypsum CaSO4-2(H2O)),
oxide and hydroxide (bauxite, limonite, wad) or clay mineral (kaolinite, illite, montmorillonite,
chlorite) residues. Close to eroding rock sources, heavy mineral residues are deposited along with
sands and can indicate provenance = source (garnet, aquamarine, corundum, tourmaline:
metamorphic rocks; epidote, topaz, zircon, diamond, gold, platinum: igneous rocks) and (apatite,
chert, flint, petrified wood) sedimentary rocks. Examine, test and read about the following minerals
to fill out the blank second table below and answer the following questions.
II. Sediment particle shapes
Minerals have definite chemical compositions and regular internal crystal structures. Because of
this some minerals tend to have particular external crystal forms depending on environmental
conditions. Due to crystal face development in hard and well formed minerals and cleavage planes,
many minerals can fall on a flat side and tend to orient. Since sediments are deposited in flat
horizontal layers, mineral particles can enhance this effect. Heavy minerals can collect in the
troughs of ripple marks or on the slip face of dunes if winnowed by slight currents so placers often
form layers with more gold or diamonds in them. Hard minerals with fracture only become
rounded grains while those with cleavages or hard well formed minerals can be somewhat blocky
as sant grains. Quartz can form hexagonal prisms but in igneous rocks is usually irregular and
equant so it usually weathers to rounded grains. Garnet is often dodecahedral similar to a soccer
ball but with flat sides. Corundum forms hexagonal prisms but has conchoidal fracture and basal
parting. Feldspars are usually tabular or blocky. Augite and hornblende from igneous and
metamorphic rocks are often blocky prisms or blades. Zircon makes stubby tetragonal prisms with
pyramidal ends. Magnetite is usually octahedral or cubic in form. Magnetite grains also attract one
another so magnetite ins sediments often joins together in strings along octahedral faces. Minerals
can also break in irregular fractures or along particular planes of weak bonds to make flat cleavage
surfaces. Minerals can have: 0, 1, 2, 3, 4, or 6 cleavage directions depending on the mineral. Quartz,
tourmaline, apatite, zircon and magnetite have conchoidal fracture while garnet fractures hackly or
irregular. Micas (biotite, muscovite, chlorite) and clays (kaolinite, illite, montmorillonite and
serpentine) tend to be flat crystals with one perfect basal cleavage but clay crystals are so tiny that
they often appear as earthy masses. Pyroxenes, amphiboles and all types of feldspars are prismatic
with 2 different cleavage directions. Minerals which occur as microcrystalline masses and those as
fine grained veins in other rocks like chalcedony, opal and epidote, tend to weather as rounded
sediment particles. Calcite is rhombohedral but so soft that it usually abrades to rounded particles
in calcarenites and most carbonate sedimentary rocks with well formed rhomb crystals are
recrystallized rather than deposited as such.
Some rocks, especially sedimentary and regional metamorphic rocks, are inherently layered due to
bedding planes, foliations, compositional differences (sand versus clay, quartzo-feldspathic versus
micas or ferromagnesian minerals), shearing as in fault zones. When these rocks fall apart their
particles tend to be flattened (skippy stones). Other rocks are massive or comprise unoriented
uniform assemblages of mineral grains such as: sandstone, granite, gabbro, basalt, chert, flint,
gneiss, quartzite. These rocks tend to make more equant particles when they weather or abrade to
gravel and sand sized rock fragments.
2|Page
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
1. Read the paragraph and table above (or other tables on mineral physical properties) and
examine or test the minerals to fill out the following table. The figure below that table
relates to particle shapes and will be useful for you to interpret the shapes of mineral sand
grains and whether they might make oriented sediments as in the last column.
3|Page
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
A. Example: If the mineral is harder than Quartz (7 on Moh’s hardness scale or your
testing) put an “x” in the space, if softer, leave it blank. Anything is as hard as itself and can
abrade, polish or frost grains like that.
B. Example: If a mineral forms as a residual weathering product of other rocks or minerals
and is found in soils, put an “x” in its space, otherwise ignore and leave it blank. (32 points)
Mineral
Augite
Biotite
Calcite
Chlorite
Corundum
Epidote
Garnet
Gypsum
Halite
Hornblende
Kaolinite
Magnetite
Muscovite
= Illite
Plagioclase
K-Feldspar
Quartz
Serpentine
Zircon
4|Page
Harder
Than
Quartz
Heavier
Than
Quartz
Residue In
Soils
Precipitate Matrix in
from salty shales
water
Grains
in
sands
Forms
oriented
grains
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
III. Sediment Production, Transport, Particle Shape, Grain Sorting, Grain Size, Sedimentary
Deposition
Introduction to Sediment production, transport and deposition.
Sediments are produced by mechanical and chemical weathering of pre-existing rocks on land as
per Section I above. Residues from this process are smaller lithic fragments, insoluble and
mechanically hard mineral remnants, oxidized and hydrated, insoluble or concretionary
precipitated soil minerals (formed above the water table when soils dry out). For example a
bedrock lithology might be gabbro (coarse grained equivalent of basalt, made of olivine, augite,
plagioclase, glass and magnetite with a few quartz amygdules or veins) or granite (made of Kfeldspar, plagioclase, quartz, micas and magnetite) but a soil developed on either parent rock could
have quartz, clay minerals, calcite, and other and more iron oxides (hematite, goethite, limonite) in
varying proportions because these minerals are stable at earth’s surface environments (cool, low
pressure, moist, oxidized etc’ compared to igneous or metamorphic rocks at depth.
With land elevations above sea level, sediment particles move downhill by transport agents like
glacial ice, rain runoff or flood water, and wind. In fluids like water and air, big particles tend to fall
close to sources and aren’t much transported, abraded or rounded. Smaller flatter particles like clay
minerals or clay sized materials could blow downwind and move across whole ocean basin widths.
Particle shapes, sizes and sorting:
When fluids like air or water move they have mass, momentum, viscosity and the capacity to carry a
sedimentary load. As these fluids slow down due to decreasing topographic or bathymetric gradient
or expand into larger volumes as from a river channel flowing into a lake or ocean, the flows slow,
lose momentum and begin to drop their heaviest particles. There are 2 different modes of transport
for sedimentary particles in fluids like water or air: suspended by high velocity and turbulent
motion relative to the particle size and rolling along near the riverbed, seabed or earth’s surface on
land. The former are called suspended load. The latter are termed bedload. Suspended load can be
transported great distances by laterally flowing winds or currents and they slowly settle out over
5|Page
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
many hours to many days depending on how high they were suspended above the bed. They form
relatively fine grained, gently blanketing uniform deposits such as mudstone, shale and deep sea
ooze rich in microfossils. Granular particles from boulders and cobbles down to fine sand and silt
size ranges are also transported by fluids like air or water. Generally particle size decreases with
progressive transport distance as does rounding and quartz content (because everything else wears
away). Particle size diminishes with increasing transport distance from the sediment source.
Sorting, the uniformity or lack thereof of sediment particle size distributions, also tends to improve
or to become more uniform as distance increases and energy of transport decreases.
2. On the figure below all of the pebbles (1-2 cm across) are made of many tiny quartz grains
and are derived from eroded pieces of metamorphic quartzite. Look at the progressive
change in particle shapes and rounding across the figure. Draw an arrow above this figure
pointing towards the direction of greatest transport from the direction of least transport
using a symbol like this >>-----.
(2 points)
Sediments and sedimentary rocks are classified by their predominant particle sizes. This is useful
because it takes more energy to transport bigger particles. It is also useful because the different
rock textures that result affect everything from how the rocks appear and weather to what their
porosity is like and their potential value as reservoirs or other resources.
As sediment is successively transported and re-deposited by flowing water such as along rivers or
up and down beaches or offshore bars, the fines are progressively washed away to be deposited
further away in deeper water, while the coarser, cleaner, sand and gravel sizes remain as a lag.
Therefore sandy environments like beaches tend to have more “clean” well sorted sands or gravels
with rounded grains. In contrast, debris flows in steep mountain streams or turbidity currents in
submarine canyons can contain poorer sorted sediments or a range of grain sizes and more angular
particles. Thus we can interpret poorly sorted sediments with a serial range of grain sizes as things
that were transported quickly and just deposited once (like landslides or debris flows).
Grain sizes are divided into 4 broad classes: Gravel and larger are particles > 2mm, sand is 2 mm to
1/16 mm ( 200 µ to 62.5 µ), silt is 1/16 mm to 1/256 mm (62.5 µ to 3.95 µ) and clay particle size is
< 1/256 mm (~<4 µ ).
6|Page
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
3. In the 2 examples above the grain size distribution (proportion of particles of successive
sizes) varies. Plot 2 little cartoon bar graphs depicting the % of: clay, silt, sand and gravel.
Assuming the “o” in the label “poorly sorted” is 0.1 mm = 100 microns or medium sized
sand.
(6 points)
4. Examine the cartoon figure above and read the caption. Then go back to the previous
photograph of the 2 sediment samples with different sorting. Explain in a few words why
well sorted sediments make the best reservoirs for fluids like aquifers or oil and gas
reservoirs.
(4 points)
7|Page
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
5. Sediment Production: Provenance & Mechanical Weathering: Make and describe the grains
(rock and mineral fragments) formed by mechanical abrasion of a rock and sandpaper onto
a clean white piece of paper. Do this for 2 of: Tuff, Friable sandstone, Shale, Weathered
granite, fine grained schist. Transfer your “sediment” to a weighing boat for examination by
hand lens and binocular microscope. Also feel your sediment, roll it between your fingers to
determine whether it is angular or rounded, uniform in size or variable, clean mineral
grains or it leaves your fingers dirty with crushed cements or film of clay sized fines.
A. Describe the compositions (lithic fragments: Sedimentary, Volcanic, Plutonic,
Metamorphic, or minerals) of the sediment(s) you made.
(4 points)
B. Draw and describe the sizes of your particles (Gravel, sand, silt, clay) as well as their
shapes. Include a scale bar with 0.1 mm divisions so that 1 mm is about 1 cm in your
drawing.
(6 points)
C. Are there mineral cements present and if so what colour and mineral are these. Are
there clays present? Identify this by wetting your dirty fingers or some of the fines and
see if it makes mud that “slips”. For cements SiO2 is harder than class and even thedust
portion you produced will polish, frost or scratch glass. For Fe oxides and hydroxides
like limonite, goethite and hematite. Rinsing a small portion of your produced
weathered sediment will leach yellow stain into a watch glass and leave a stain if
decanted onto a filter paper. For chalk or limestones, your powder put in a watch glass
with a few drops of acid will fizz. The calcite cements are soft and will not polish glass.
Describe any cements or clays and tell how you identified them. .
(6 points)
6. Sedimentary particles are transported by gravity with or without a fluid such as wind, water
or ice. Most sediments start moving as mass wasting off slopes by rockfalls, landslides or
solifluction off the side of slopes.
A. Take 2 pieces of paper, lay one flat and place the other onto a tray which you can slowly
tilt. Place your sediment on the tilt-able one at the top (far end of the paper). As you tilt
it, note at what angle the sediment starts to move. Do this again this time with gentle
tapping on the tray you are tilting to simulate an earthquake. Note the particle sizes that
8|Page
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
move first and describe the effect on the critical slope angle of transport with the
addition of gentle tapping. Put your sediment back in the plastic weigh boat for later
use. Describe what happens as the result of tilting with and without tapping and draw a
conclusion about the stability of loose sediment and particle size variations on various
landscapes.
.
(6 points)
B. Pretend you are the wind. Take some of your sediment on a piece of paper over another
clean sheet on a lunch tray. Gently blow across your sediment towards the tray until
sediment starts to move. Note which particle sizes moved first and were moved to the
other sheet versus which were left behind. Estimate your wind speed by blowing with
the same force over the garbage can and drop some confetti (paper punch outs). (Get
help from a partner using a ruler and a stop watch to time how far your particles move
at this wind speed. Express this velocity in cm/sec and kilometers per hour. Explain why
the sediments sort and react this way to a single velocity, and relate it to the energy of
your wind and its velocity or momentum versus your range of particle masses. Explain
how this relates to dust storms and sediment transport. .
(10 points)
9|Page
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
7. From the table’s above and below (p.11-13), classify the following sedimentary rock types
as either the result of chemical or mechanical weathering, whether their texture is due
cementation, compaction or crystallization, and note thir composition to classify them as
detrital, chemical or biochemical / bioclastic sediments.
(18 points)
Weathering
Texture & Lithification
Composition/Class.
Rock type
Arkose
Breccia
Calcarenit
e
Diatomite
Gypsum
Shale
10 | P a g e
Mech.
w
Chem.
w
Cemente
d
Compacte
d
Crystallize
d
Detr
.
Chem
.
Bio
.
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
The following 3 part rock classification table will help you examine and understand some common
sediment and sedimentary rock types based on compositional differences and particle size and
formative process in addition to how to fill out the classification chart above.
1.12 a. Siliciclastic rocks made predominantly of silicate rock fragments and silicate minerals.
1.12 b. Geochemical and biochemical sedimentary rocks made predominantly of materials
precipitated from solution. Most limestones are directly produced by calcareous algae, bacteria or
shell forming planktonic or nektonic organism. Diagenetic processes may replace original minerals
by other materials such as rudist corals or siliceous sponges getting transformed to dolomite, wood
getting replaced by silica or calcite (petrified), calcareous foraminifers getting replaced by pyrite.
11 | P a g e
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
1.12 c. Bioclastic and biochemical sedimentary rocks made predominantly of organic or inorganic
materials produced by living organisms. Chalk is made by the tests (mineral hard parts) of
coccoliths (calcareous algae) and sometimes foraminifera (calcareous zooplankton). Diatomite in
temperate to sub tropical lakes and high latitude open oceans is a rock made of microscopic tests of
opaline silica of many species of siliceous phytoplankton. Chert in older rocks is often made of
radiolarians which are microscopic tests of protista that are either zooplankton or zooplankton
with symbiotic algae. Tropical warm, salty waters give rise to many forms of calcium carbonate
particles. Whether large or small most are both bioclastic and biochemical from calcareous bacteria
to coral heads. Coquina is a porous limestone mass of bioclastic shell fragments of one or more
types of calcareous invertebrates, chiefly pelecypods in the Cenozoic. Peat is a cold climate or alpine
deposit of cellulose from terrestrial plants in acidic bogs (bioclastic and biochemical made of roots,
stems and twigs of mosses, sedges, heather, grasses, seeds, twigs, and roots. This is always
unconsolidated and it never remains uneroded or becoms deeply buried enough to ever transform
into a rock. Lignite is a soft brown low rank coal of tree trunks, twigs, leaves from shallow burial
and slight compaction of forest species that fell into swamps or oxbow lakes in meandering river
systems and deltas. Bituminous coal is high rank coal that has separated into various different
classes of organic molecules and makes masses of brittle, black, light weight matter that is now
~75% carbon principally as aromatic compounds: anthracene, phenanthrene, napthalene along
with waxes and other classes of organic molecules. Coals have only been formed since vascular
plants conquered land in the Silurian Period. The thickest and most widespread deposits are
Devonian, Carboniferous, Permian, Jurassic, Cretaceous and Paleocene/Eocene, all hothouse climate
times when the carbon cycle on land was the most vigorous.
12 | P a g e
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
IV. Sedimentary Environments and Sediment Facies
Wet or dry, hot or cold, steep or flat, fast or slow all matter in the making, transport and deposition
of sediments. Biology and ecosystems also matter a great deal especially for bioclastic and
biochemical sediments. These variables, climate, geography, underlying bedrock type, local tectonic
processes and especially sea level or local base level on land matter a great deal as to how
widespread or limited the different sedimentary environments are. Channels in rivers transport all
13 | P a g e
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
types of sediment at some stage but floodplains only receive silt and mud deposits at flood stages.
Glacial facies are limited to high latitude, high altitude or ice age conditions. Deltas only form at
river or stream mouths. Desert dune systems are only found in dry continental settings. Beaches
are narrow transitional environments dependent on geography, tectonics and sea level. If
conditions change, so do environmental boundaries and sedimentary facies. There are 3 classes of
environments: terrestrial or continental, marine and transitional (beaches, estuaries, deltas).
8. Study the map and block diagram above to match a rock type or sediment to a particular
environment for the list below. For “type” put continental, transitional or marine. Use
simple 1 and 2 word facies as labelled for Environment.
(12 points)
Deposit or rock type
Type: Cont./Trans/Mar. Specific Environment
Poorly sorted cobble conglomerate
Coarse sand with marine shells
Muds with tree stumps and leaves
Moraine with boulders in clay
Bedded gypsum and halite
Turbidites with graded beds
Sedimentary facies vary laterally and give way to adjacent environments. The following block
diagram shows how changing conditions such as transgression (sea level rise) or tectonic
subsidence of a coast like that of B.C. could shift environments laterally and create vertical
14 | P a g e
Geoscience 240 – W-2017 Lab 1: Review & Introduction to Sediments and Sedimentary Geology
_____________________________________________________________________________________________________________________________
stratigraphic sequences at a given location. This is a simple statement of Walther’s Law to explain
vertical facies successions. No environment lasts forever nor does any one extend across the whole
planet. Change is the only constant. When we find a stack of sedimentary rock with missing lateral
facies, either the crustal or sea lavel motion was not uniform or some degree of erosion occurred.
When we find sequential beds that are not adjcaent facies, we suspect there is an unconformity or
missing time (hiatus in deposition). To some degree every stratigraphic contact is a hiatus or pause
and change to a different environment. Another consequence of this reasoning is that stratigraphic
contacts between the same pair of lithologies (rock types) are not a single event in time but they
must vary laterally across a broad sedimentary basin.
9. What does the top of the block diagram represent. __________________________________ (1 point)
_______________________________________________________________________________________________
10. Draw a strip log similar to the one above, but have it represent a marine regression or local
crustal uplift. Use the same 3 rock types.
(3 points)
11. Draw another stratigraphic sussession with an unconformity or hiatus using the same
lithofacies and a wavy line to represent the unconformity. _______________________ (3 points)
15 | P a g e