Laboratory Manual - UTEP :: Geological Sciences

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GEOL 1312 (1304)
Laboratory Manual
Earth Sciences 2
1
Text by Anthony D. Feig, Cathy Willermet and Sandra Reece
Cover Photograph by Kate Miller
Cover Photo: Northeast Franklin Mountains, El Paso, Texas
2
Contents
Preface to the student
........................................................................................... 4
Preface to the instructor
........................................................................................... 4
Acknowledgements
........................................................................................... 4
Review of Plate Tectonics, Minerals and Igneous Rocks............................................................... 9
Part 1: Tectonics Review ............................................................................................................ 9
Part 2- Mineral and Igneous Rock Review ............................................................................... 11
Fossils
......................................................................................... 24
Sedimentology, Microscopy and the Campus Field Trip ............................................................. 35
Sedimentary Rocks
......................................................................................... 40
Stratigraphy
......................................................................................... 45
Relative Dating and Absolute Dating ......................................................................................... 51
Interpreting Geologic History
......................................................................................... 56
Impact Craters and Exploring the Solar System ........................................................................... 59
Interpretation of Hellas Planitia Geologic Map ............................................................................ 69
Surface Water and Groundwater
......................................................................................... 80
Introduction to Geophysics
......................................................................................... 86
Arroyo Park Field Trip
......................................................................................... 94
3
Preface to the student
This laboratory manual is designed for use in GEOL 1304 Laboratory, which accompanies the
three-credit GEOL 1304—Principles of Earth Science 2. You receive one grade for both the
lecture and lab classes, and they must be taken at the same time. The minerals, rocks, maps and
other materials needed to complete the exercises are available in the lab. You must bring this
manual to each lab, as well as a pencil, calculator, ruler, and protractor for the labs that require
them.
Preface to the instructor
These exercises are designed to be self-contained within a lab period of one hour and 50 minutes.
The explanations and discussions contained in the lab exercises are not intended to stand alone
without a brief (5-15 minutes) in-class verbal discussion/demonstration session. Please refer to
your Instructor’s manual for more information.
Acknowledgements
Many thanks go to Drs. Kate Miller, Nick Pingitore, Bill Cornell, and Jerry Hoffer of the UTEP
Geological Sciences Department for their guidance in drafting the content of this manual.
Thanks also to the Graduate Instructors who have provided input to the design and content of
these exercises. Finally, thanks also go to the thousands of UTEP students who have been the
real purpose for all of our work.
Anthony D. Feig
June 2007
4
RELEASE AND INDEMNIFICATION AGREEMENT
(Adult Participant)
Participant: (Name and Address)
University:
_____________________________
_____________________________
_____________________________
The University of Texas at El Paso
Department:____________________
______________________________
Description of Activity or Trip:
______________________________________________________________________________
_____________________________________________________________________________________
________________________________________________________________
Location:
________________________
Date(s):
___________________
I, the above named Participant, am eighteen years of age or older and have voluntarily applied to
participate in the above-referenced Activity or Trip. I acknowledge that the nature of the Activity or Trip
may expose me to hazards or risks that may result in my illness, personal injury or death and I understand
and appreciate the nature of such hazards and risks.
In consideration of my participation in the Activity or Trip, I hereby accept all risk to my health and of
my injury or death that may result from such participation and I hereby release the University of Texas at
El Paso, its governing board, officers, employees and representatives from any liability to me, my
personal representatives, estate, heirs, next of kin, and assigns for any and all claims and causes of action
for loss of or damage to my property and for any and all illness or injury to my person, including my
death, that may result from or occur during my participation in the Activity or Trip, whether caused by
negligence of the University, its governing board, officers, employees, or representatives, or otherwise. I
further agree to indemnify and hold harmless the University and its governing board, officers, employees,
and representatives from liability for the injury or death of any person(s) and damage to property that may
result from my negligent or intentional act or omission while participating in the described Activity or
Trip.
I HAVE CAREFULLY READ THIS AGREEMENT AND UNDERSTAND IT TO BE A
RELEASE OF ALL CLAIMS AND CAUSES OF ACTION FOR MY INJURY OR DEATH OR
DAMAGE TO MY PROPERTY THAT OCCURS WHILE PARTICIPATING IN THE
DESCRIBED ACTIVITY OR TRIP AND IT OBLIGATES ME TO INDEMNIFY THE PARTIES
NAMED AND FOR ANY LIABILITY FOR INJURY OR DEATH OF ANY PERSON AND
DAMAGE TO PROPERTY CAUSED BY MY NEGLIGENT OR INTENTIONAL ACT OR
OMISSION.
_____________________________________________ Date:
Signature of Participant
_________________
_____________________________________________ Date:
Witness
_________________
5
RELEASE AND INDEMNIFICATION AGREEMENT
(Minor Student Participant)
Participant: (Name and Address)
University:
_____________________________
_____________________________
_____________________________
The University of Texas at El Paso
Department:____________________
______________________________
Description of Activity or Trip:
______________________________________________________________________________
_____________________________________________________________________________________
________________________________________________________________
Location:
________________________
Date(s):
___________________
I am the Parent/Guardian of the above-named Participant who is under eighteen years of age and am fully
competent to sign this Agreement.
I give permission for Participant to participate in the above-referenced Activity or Trip. I acknowledge
that the nature of the Activity or Trip may expose Participant to hazards or risks that may result in
Participant’s illness, personal injury or death and I understand and appreciate the nature of such hazards
and risks.
In consideration of Participant being permitted to participate in the Activity or Trip, I hereby accept all
risk to Participant’s health and of his/her injury or death that may result from such participation and I
hereby release the University of Texas at El Paso, its governing board, officers, employees and
representatives from any liability to Participant, Participant’s personal representatives, estate, heirs, next
of kin, and assigns for any and all claims and causes of action for loss of or damage to Participant’s
property and for any and all illness or injury to Participant’s person, including Participant’s death, that
may result from or occur during Participant’s participation in the Activity or Trip, whether caused by
negligence of the University, its governing board, officers, employees, or representatives, or otherwise. I
further agree to indemnify and hold harmless the University and its governing board, officers, employees,
and representatives from liability for the injury or death of any person(s) and damage to property that may
result from Participant’s negligent or intentional act or omission while participating in the described
Activity or Trip.
I HAVE CAREFULLY READ THIS AGREEMENT AND UNDERSTAND IT TO BE A
RELEASE OF ALL CLAIMS AND CAUSES OF ACTION FOR PARTICIPANT’S INJURY OR
DEATH OR DAMAGE TO PARTICIPANT’S PROPERTY THAT OCCURS WHILE
PARTICIPATING IN THE DESCRIBED ACTIVITY OR TRIP AND IT OBLIGATES ME TO
INDEMNIFY THE PARTIES NAMED AND FOR ANY LIABILITY FOR INJURY OR DEATH
OF ANY PERSON AND DAMAGE TO PROPERTY
CAUSED BY PARTICIPANT’S
NEGLIGENT OR INTENTIONAL ACT OR OMISSION.
_____________________________________________ Date:
Signature of Parent/Guardian
_____________________________________________
Address, if different than Participant’s
_________________
_____________________________________________ Date:
Witness
_________________
6
ACUERDO DE LIBERACION DE RESPONSABILIDAD E INDEMENIZACION
(Participantes Adultos)
Participante: (Nombre y domicilio)
Universidad:
___________________________________
___________________________________
___________________________________
La Universidad de Texas en El Paso
Departamento: ___________________
________________________________
Descripcion de la Actividad o Viaje:
_____________________________________________________________________________________
_____________________________________________________________________________________
________________________________________________________________
Lugar: _____________________________
Fecha(s): ________________________
Yo soy el/la Participante cuyo nombre aparece arriba, tengo 18 o màs años de edad y he solicitado
voluntariamente participar en la Actividad l Viaje que se especifica arriba. Reconozco que por su
naturaleza, dicha Actividad o Viaje puede acarear ciertos peligros que tal vez me causen enfermedad,
lesiones o la muerte, y estoy consciente de la naturaleza de dichos riesgos.
En consideraciòn de mi participaciòn en la Actividad o Viaje, por la presente acepto todos los riesgos
correspondientes a mi salud y el riesgo de lesiones o muerte que puedan resultar con motivo de mi
participaciòn y asimismo libero y descargo a la Universidad de Texas en El Paso, su consejo directivo,
oficiales, empleados y representantes de toda responsabilidad hacia mi persona, mis representantes
personales, mi patrimonio, mis herederos, parientes o cesionarios con respecto a toda reclamaciòn o
acciòn legal por concepto de pèrdida o daños ocasionados a mi propiedad y toda enfermedad o lesiones a
mi persona, incluso mi muerte, que puedan derivarse de o suceder durante dicha Actividad o Viaje, sin
importar que èstos sean causados por negligencia por parte de la Universidad, su consejo directivo,
oficiales, empleados, representantes u otras entidades. Acepto asimismo indemnizar y liberar de
responsabilidad a la Universidad y su consejo directivo, oficiales, empleados y representantes en caso de
las lesiones o muerte de cualquier persona o personas y de daños a la propiedad que puedan ocurrir como
resultado de un acto intencional o de negligencia mìo o de una omisiòn de mi parte durante mi
participaciòn en la susodicha Actividad o Viaje.
HE LEIDO CON CUIDADO ESTE DOCUMENTO Y ENTIENDO QUE SE TRATA DE UNA
LIBERACION Y DESCARGO DE RESPONSABILIDAD RESPECTO DE TODO RELCAMO Y
CAUSA DE ACCION CON MOTIVO DE MIS LESIONES O MUERTE O DAÑOS
OCASIONADOS A MI PROPIEDAD QUE PUEDAN OCURRIR DURANTE MI
PARTICIPACION EN LA ACTIVIDAD O VIAJE EN CUESTION, Y QUE ME COMPROMETE
ADEMAS A INDEMNIZAR A LAS PARTES NOMBRADAS Y A ASUMIR RESPONSABILIDAD
POR LESIONES A LA MUERTE DE CUALQUIER PERSONA Y POR DAÑOS A LA
PROPIEDAD AJENA OCASIONADOS PRO UN ACTO INTENCIONAL MIO O DE UNA
NEGLIGENCIA DE MI PARTE.
____________________________________
Firma del (de la) Participante
Fecha: _________________________
____________________________________
Testigo
Fecha: _________________________
7
ACUERDO DE LIBERACION DE RESPONSABILIDAD E INDEMENIZACION
(Estudiantes Menores de Edad)
Estudiante: (Nombre y domicilio)
___________________________________
___________________________________
___________________________________
Universidad:
La Universidad de Texas en El Paso
Departamento: ___________________
________________________________
Descripcion de la Actividad o Viaje:
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Lugar:_____________________________
Fecha(s): ________________________
Yo soy el padre/la madre o tutor(a) legal del (de la) Particiante cuyo nombre aparece arriba, y que tiene
menos de 18 años de edad, y soy competente para firmar este Acuerdo.
Doy mi permiso para que el/la Participante participe en la Actividad o Viaje descrito arriba. Reconozco
que por su naturaleza, dicha Actividad o Viaje puede acarear al (a la) Participante ciertos riesgos que tal
vez le causen enfermedad, lesiones a su persona o la muerte, y estoy consciente de la naturaleza de dichos
riesgos.
En consideraciòn de la participaciòn del (de la) Participante en la Actividad o Viaje, por la presente
acepto todos los riesgos correspondientes a su salud y el riesgo de lesiones o muerte que puedan resultar
con motivo de su participaciòn y asimismo libero y descargo a la Universidad de Texas en El Paso, su
consejo directivo, oficiales, empleados y representantes de toda responsabilidad hacia el (la) Participante,
sus representantes personales, su patrimonio, mis herederos, parientes o cesionarios con respecto a toda
reclamaciòn o acciòn legal por concepto de pèrdida o daños ocasionados a la propiedad del (de la)
Participante y toda enfermedad o lesiones a su persona, incluso su muerte, que puedan derivarse de o
suceder durante dicha Actividad o Viaje, sin importar que èstos sean causados por negligencia por parte
de la Universidad, su consejo directivo, oficiales, empleados, representantes u otras entidades. Acepto
asimismo indemnizar y liberar de responsabilidad a la Universidad y su consejo directivo, oficiales,
empleados y representantes en caso de las lesiones o muerte de cualquier persona o personas y de daños a
la propiedad que puedan occurrir como resultado de un acto intencional o de negligencia por parte del (de
la) Participante o de una omisiòn de su parte durante su participaciòn en la susodicha Actividad o Viaje.
HE LEIDO CON CUIDADO ESTE DOCUMENTO Y ENTIENDO QUE SE TRATA DE UNA
LIBERACION Y DESCARGO DE RESPONSABILIDAD RESPECTO DE TODO RELCAMO Y
CAUSA DE ACCION CON MOTIVO DE LESIONES O MUERTE DEL (DE LA)
PARTICIPANTE O DAÑOS OCASIONADOS A SU PROPIEDAD QUE PUEDAN OCURRIR
DURANTE SU PARTICIPACION EN LA ACTIVIDAD O VIAJE EN CUESTION, Y QUE ME
COMPROMETE A MI A INDEMNIZAR A LAS PARTES NOMBRADAS Y A ASUMIR
RESPONSABILIDAD POR LESIONES A LA MUERTE DE CUALQUIER PERSONA Y POR
DAÑOS A LA PROPIEDAD AJENA OCASIONADOS PRO UN ACTO INTENCIONAL MIO O
DE UNA NEGLIGENCIA DE MI PARTE.
____________________________________
Firma del Padre/la Madre o Tutor(s)
____________________________________
Domicilio (Si es diferente del Participante)
____________________________________
Testigo
Fecha: _________________________
Fecha: _________________________
8
Laboratory Exercise: Review of Plate Tectonics, Minerals and
Igneous Rocks
Part 1: Tectonics Review
by B. Drenth
Purpose: This exercise will reacquaint you with tectonic processes you saw in 1311
The theory of plate tectonics is the single most important and unifying notion of the way the
Earth behaves. In this lab you will look at the geometry of the motion of tectonic plates. By
geometry we mean the ways plates move and how they get their shapes.
Part 1: Basic Terminology
Lithosphere: The thin outer shell of the Earth. It behaves as an elastic material, and is divided
up into many pieces, or plates. The thickness of the lithosphere is typically about 100 km in
ocean basins and about 200 km thick beneath continents.
Plate: Portion of the lithosphere that moves on the Earth as a single piece; for simple tectonic
motion studies we normally assume these to be rigid with discrete or easily perceived
boundaries.
Asthenosphere: Layer below the lithosphere. It contains a small amount of melted rock, causing
it to deform plastically and allowing it to accommodate plate motion of the overlying
lithosphere.
Velocity Field: Arrow or set of arrows drawn on a plate to show the direction and speed of the
plate’s motion.
Ridge: Mid-oceanic feature lying along and representing divergent plate boundaries, where new
lithosphere is created.
Trench: Effective location of inception of plate subduction at a convergent boundary (where
converging plates meet).
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Transform: Plate boundary fault in which two plates slide laterally past each other. In the ocean
basins these are only defined as active plate boundaries between ridge segments (see figure
below).
Fracture Zones: Fossil, inactive transform faults that no longer represent plate boundaries (see
figure below).
Discussion Question: How do fracture zones form? Fracture zones connect segments of
oceanic ridges. Draw an example on the board and show the relative motions across the fracture
zones.
Part 2: Rules for Plate Motions
1. Ridges: Two different plates grow in different directions on opposite sides of the
boundary. The direction of plate growth and motion does not need to be perpendicular to
the boundary. Ridges are shown by a pair of parallel lines, with arrows showing the
directions of plate motion, as shown below:
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2. Trenches: Two plates collide, causing one to be subducted. The direction of
convergence does not need to be perpendicular to the trench. In other words, oblique
convergence is allowed. Any symbols used to define this type of boundary (such as tick
marks) are placed on the overriding plate (the plate that is not being subducted):
Discussion Question: What fundamental physical property determines which plate will be
subducted?
3. Transform faults: Plate motion MUST everywhere be PARALLEL to the fault itself.
Arrows show sense of motion across the fault.
Part 2- Mineral and Igneous Rock Review
Purpose: This exercise will re-acquaint you with rock-forming minerals and the igneous rocks
you saw in GEOL 1311.
Goals: Identifying the mineral, and identifying and classifying the igneous rock. You will be
tested on these at the beginning of next lab.
Group Learning
Collaborative work: One set of answers from the group, everyone has to agree, everyone has to
be able to explain the procedure used to identify minerals.
Criteria for success: Everyone must be able to identify the minerals and explain the
procedure used to solve the problem.
Individual accountability: Your instructor will select one person at random to identify a
mineral and explain why the group gave it the name they did—that is, what physical
properties are important?
Expected behaviors: Everyone should participate and encourage each other; HAVE FUN!
Reflection: After you are done list three things you did well as a group, and list one thing you can
do better next time. Do this as a group, and spend 5 minutes with this discussion.
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Activity 1: Getting started. Divide the samples using this flow chart:
Does the sample look like it’s made of one kind of material?
YES
MORE LIKE 2 OR 3
It’s a MINERAL
It’s a ROCK
Activity 2: MINERALS.
Your instructor will guide you through the process of observing these physical properties:
1. Color: we tend to group objects based on their color, but sometimes this
characteristic doesn’t work so well with minerals. Use your observations of color
together with other physical properties when identifying minerals.
2. Luster: for our purposes, it is appropriate to consider two types of luster, metallic
and non-metallic. That is, does the mineral look like it’s made out of metal? Be
careful—shiny specimens don’t necessarily have a metallic luster.
3. Hardness: literally, how hard is the specimen on a scale of 1-10? If you can scratch
it with your fingernail (it doesn’t file your nail, your nail leaves a mark), then it’s a 2
on the hardness scale (called the Moh’s Scale). If it cuts glass, it’s harder than a 5.
The official “Moh’s Hardness Scale” looks like this:
10 = diamond
9 = corundum (the main ingredient in sandpaper and some abrasive cleaners)
8 = topaz
7 = quartz (in your kit)
6 = potassium feldspar (also in your kit)
5.5 = glass, steel
5 = apatite
4 = fluorite
3.5 = penny
3 = calcite (also in your kit)
2.5 = fingernail
2 = gypsum (this is what the wallboard in your house is made of; also called
“sheetrock.”)
1 = talc (which is sometimes ground into baby powder).
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4. Streak: this refers to the color it leaves when you rub it on the white porcelain streak
plate. This color is sometimes different than the color of the specimen itself.
5. Cleavage: this is the tendency of a mineral to break along lines or planes of
weakness. For example, if your sample made of flat sheets that peel away, then your
mineral has one direction of cleavage, which is parallel to the orientation of the
sheets. If your mineral is boxy, then it has cleavage in three directions:
The property of cleavage allows a mineral with cleavage to retain its shape even
when it is broken.
6. Fracture: Minerals that break into irregular shapes are said to have fracture, not
cleavage. You will find that some minerals that have nice crystal shapes, like quartz,
do not in fact break along preferred lines or planes. This is fracture.
7. First impressions: What is the first obvious thing you notice about the specimen? Is
it heavy? Pretty? Somehow strange? Often, your first impression will eliminate
about half the work of identifying a mineral in the future.
Make your observations on the following pages. Then use the handouts your instructor gives
you to compare your observations and to give your specimens their proper names.
Specimen 1
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Streak color ______________
Steel
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
13
Specimen 2
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 3
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 4
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Streak color ______________
Steel
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 5
First impressions: _____________________________________________________
Color __________________
Luster: Metallic
Hardness. It is harder than:
14
glassy
earthy
silky
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 6
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 7
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 8
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Streak color ______________
Steel
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
15
Specimen 9
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 10
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 11
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Streak color ______________
Steel
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 12
First impressions: _____________________________________________________
Color __________________
Luster: Metallic
Hardness. It is harder than:
16
glassy
earthy
silky
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 13
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 14
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Steel
Streak color ______________
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
Specimen 15
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Streak color ______________
Steel
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
17
Specimen `16
First impressions: _____________________________________________________
Luster: Metallic
Color __________________
glassy
earthy
silky
Hardness. It is harder than:
My fingernail
A penny
Streak color ______________
Steel
Glass plate
Hardness number:______
It has __________ directions of cleavage
Mineral Name___________________
18
Activity 3, ROCKS. Divide your rocks using this flow chart:
Can I see grains when I hold the rock at arm’s length?
NO
SORT OF
This rock is FINE-GRAINED
YES
This rock is COARSE-GRAINED
It looks like a bunch of coarse
grains swimming around in a
very fine-grained “matrix”
NO
YES
This rock is PORPHYRITIC
You now have three groups of rocks: fine-grained (Aphanitic), coarse-grained (Phaneritic), and
Porphyritic. You now have to decide if these rocks are extrusive VOLCANIC (crystallized at the
surface) or intrusive PLUTONIC (crystallized deep in the earth’s crust, or if they are some kind
of MIX of the two. Use the diagram on the next page to decide, and your instructor will check
your work.
19
LAVA makes extrusive rocks and is found at the earth’s surface. It cools quickly so large
crystals don’t have time to form.
MAGMA makes intrusive rocks and is found deep in the earth’s crust. It cools slowly, allowing
time for large crystals to form.
Volcano
Pluton
20
Activity 4: Identifying textures and naming the rocks. Both extrusive and intrusive rocks can
be classified by the identification of textures. The six common types are:
Coarse-grained, also called phaneritic. These rocks contain large, easily seen crystals
that fit together. If you can easily see grains or crystals when you hold an igneous rock at
arm’s length, it is a phaneritic rock. Phaneritic rocks are intrusive.
Fine-grained, or aphanitic. These rocks are invisible or hard to see with the naked eye.
Aphanitic rocks are extrusive.
Porphyritic. This texture is a mix of fine and coarse grains. Usually, the larger crystals
are “floating” in a fine grained “matrix,” and they are not touching each other. It is easy
to confuse a porphyritic rock with a phaneritic rock, so look carefully to see if the large
grains are touching or not. Porphyritic rocks are both intrusive and extrusive.
Glassy. This kind of rock looks just like broken glass, and you can’t see any grains no
matter how hard you try. This magma cools so quickly that crystals have no time to form
at all.
Vesicular. Vesicles are holes, so a vesicular rock is a “holey” rock. The holes are
formed when gas and other volatiles escape the lava before it hardens. Vesicular rocks
are extrusive.
Fragmental. This rock can be very confusing, because it often looks like a sedimentary
rock. It is formed when hot ash flowing out of a volcano picks up other rocks and
sediment as it flows, and it all hardens together.
Procedure for identifying igneous rocks.
1. Determine the texture of each rock.
2. For phaneritic rocks, do the following:
a. identify any minerals you can see;
b. determine if the color of your rock is light, intermediate, or dark.
c. record your observations.
3. For aphanitic, porphyritic, vesicular, and fragmental rocks, determine if the color of your
rock is light, intermediate, or dark.
4. Use the chart on the next page to name the rock.
Notes:
21
1_________________
9__________________
2_________________
10 _________________
3_________________
11_________________
4_________________
12. ________________
5_________________
6_________________
7_________________
8_________________
22
Igneous Rock Key
Minerals and/or color
Rock
Texture
Fine-grained
(Aphanitic)
microcline and
plagioclase
quartz, and maybe
and
plagioclase
amphibole
--light color
--intermediate color
plagioclase
and
pyroxene
--dark color
Rhyolite Andesite Basalt
pyroxene
and/or
olivine
Dunite
Rhyolite Andesite Basalt
porphyry porphyry porphyry
--
CoarseGrained
(Phaneritic)
Granite
--
Vesicular
Pumice
Porphyritic
(coarse and
fine)
Glassy
Fragmented
Diorite
Gabbro
Scoria
Obsidian
Tuff
23
---
Lab Exercise—Fossils
Purpose: To introduce you to some common fossils.
Objectives:
1. You will be able to recognize the presence of fossils within rocks;
2. You will learn to distinguish bilateral and five-fold symmetry in fossils;
3. You will practice making sketches of fossil samples;
4. You will learn to speculate on the mode of life of selected fossils.
Activity 1: Identifying fossils.
1. Compare each fossil to the drawings provided by your instructor and identify them. Your
instructor will check your identifications.
2. Make a good, detailed sketch of each fossil specimen and label the features on your
sketches. For each sketch, point out some difference between your specimen and the
drawings of the complete, or “ideal” specimens. That is, what feature was broken off,
missing from, etc. the fossil that you drew?
3. Then, after you have identified and sketched the bivalve and the brachiopod, each group
will show your instructor the orientation of the bilateral symmetry on each one. How do
they differ?
The next pages show detailed drawings of different fossils for you to use in identification.
24
Figure 1. Side view of bivalve shells showing bilateral symmetry. The left shell is the same as
the right shell, but the top is not the same as the bottom.
Figure 2. Bivalve shell form. The left and right side of this one shell are not symmetrical, but
the clam had another shell that was the mirror image of this one.
25
Figure 3. The bryozoan Archimedes.
Figure 4. Some examples of brachiopods. The line shows the symmetry.
Symmetry this way
No symmetry this way
26
Figure 4a. Some more brachiopods.
27
Figure 5. A typical trilobite.
Figure 6. A rolled trilobite.
28
Figure 7. Cephalopods (left and middle) coil in a plane and show bilateral symmetry when
viewed edge-on; gastropods (right) coil upwards and have no symmetry.
Figure 8. Examples of gastropod shells.
29
Figure 9. A straight-coned nautiloid.
Figure 10. Some examples of echinoids, showing the 5-fold symmetry. For example, a star has
5-fold symmetry because it has five points, all at even spacing.
Figure 11. Two views of crinoid stems, showing the stacks of disks.
30
Figure 12. An example of Rugosa, a solitary coral.
Figure 13. Some examples of colonial corals.
31
Figure 14. An Example example of fern leaves.
Source, Proctor Museum of Natural History web Site http://www.proctormuseum.us/Oklahoma/
Figure 15. Some examples of shark teeth.
32
Activity 2: Dating a rock by using its fossils. Geologist can tell the approximate age of a rock
by examining the fossils in it, known as the rock’s fossil assemblage. The age ranges of certain
fossils are well known. For example, we know that the dinosaurs have an age range from the
Triassic to the end of the Cretaceous (240-66 million years ago). Therefore, no rocks of Tertiary
age (65 million years ago) or younger will contain dinosaur fossils. It is also true that if a rock
contains dinosaur fossils, it MUST be between Triassic-Cretaceous age. Here are the age ranges
of some common fossils:
Fossil
Rugose corals
Crinoids
Seedless plants
Ammonoids
Echinoids
Gryphaea
Brachiopods
Fusulinid foraminifera
Mammals
Trilobites
Sharks
Gastropods
Colonial corals
Age Range
Ordovician-Permian
mostly Mississippian, but ranging from Cambrian-present
Devonian-present
Devonian-Cretaceous, but most common from Triassic-Cretaceous
usually Tertiary-present, but as old as Ordovician
Cretaceous
Cambrian-Permian, but some species still present today
Mississippian-Permian
Tertiary-present, but some rare ones of Cretaceous age
Cambrian-Permian
Devonian-present
Cambrian-present
Cambrian-present
In the following questions, you are given the fossil assemblages of various rocks. Use the table
below by filling in the sections of each column to show the age ranges of the fossils in each rock.
Finally, decide on the age or age range of the rock. Use a different color pencil for each rock.
1. What is the age of a rock which contains seedless plants, shark teeth, and mammal
bones?
2. What is the age of a rock which contains crinoids, fusulinids, and trilobites?
3. What is the age of a rock which contains ammonoids, Gryphaea, gastropods, and corals?
4. What is the age of a rock which contains trilobites, corals, brachiopods, and shark teeth?
5. What is the age of a rock which contains fusulinids, trilobites, and brachiopods?
33
Rugosa Crin. Seedless
plants
Amm.
Echin. Gryph. Brach. fusul.
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Pennsylvanian
Mississippian
Devonian
Silurian
Ordovician
Cambrian
34
mamm.
trilos. sharks
gastrop. col.
corals
Lab Exercise—Sedimentology, Microscopy and the Campus Field
Trip
Purpose: This exercise will acquaint you with sedimentary textures and environments of
deposition, and you will learn to observe and scientifically describe the textures of grains
contained in rocks. You will also have the opportunity to explore the world on a microscopic
level.
Goals: Identifying sedimentary textures; making field observations; learning to use a
microscope, learning to visualize objects on a microscopic scale. You will be quizzed on these at
the beginning of the next lab session.
Part 1: Sedimentary Textures
Discussion: Your instructor will hand out Sediment Sizing Charts, like this one:
Examine this card closely. To the right, you see examples of the kinds of grains that you would
find in some sedimentary rocks. Look at the coarsest grains. They are 2 mm in size, although
the card gives you units in microns, which are millionths of a meter (millimeters are thousandths
of a meter), and the abbreviation for micron is this symbol: μ. To convert to microns, move the
decimal three places to the right; 2000 microns = 2 mm.
If you look farther to the right, you will see the letters “vcU.” This stands for “very coarse
upper” sand-sized particles, which have a range of 1.4-2.0 millimeters in size. The letters “cU”
stand for “coarse upper,” “mU” stands for “medium upper,” “mL” stands for “medium lower,”
the “f” stands for “fine,” and the “vf” stands for “very fine.”
Anything bigger than 2.0 millimeters is called “gravel,” and we refer to grains >2mm as “gravelsized.” This chart won’t be very useful for gravel-sized grains.
At the bottom of the chart, you will see a scale for Angular, Subangular, Subrounded, Rounded,
and Well Rounded. Remember that some sedimentary rocks are made from other rocks that
were broken down, transported, deposited and lithified. The more rounded the grains are in a
rock, the farther they were transported.
35
Size in mm
Bigger than 2
2 to 1/16
1/16-1/256
Smaller than 1/256
Sediment Name
Gravel
Sand
Silt
Clay
Sedimentary Rock Name
Conglomerate -- Breccia
Sandstone
Siltstone
Claystone
Activity 1: Look at your card and answer the following questions:
1. Look at the card where the pictures of grains are, and decide what is the smallest size that
you can see with your eye. It’s okay for different people to have different answers.
a. What letters correspond to the finest grains you can see?
b. How many microns is the range? How many millimeters is this?
2. Examine three of the sediment samples provided by your instructor.
a. What are the letter designations and millimeter ranges?
b. How rounded or angular are they? Assign them to a category using your card.
Part 2. The arroyo field trip.
Your instructor will lead you to the arroyo trail on the south side of University Street, at the west
end of the parking lot on the west side of the Liberal Arts Building.
1. As you cross the fence and stand on the side of the hill, look down and identify how
many different types of rock you see. Pick up a piece of each kind and take notes on
them here. Try to identify whether they are igneous, metamorphic, or sedimentary.
36
2. Which type of rock naturally occurs here in an outcrop, and which kind was transported?
How do you know?
3. Follow the trail down into the arroyo. Once you get to the bottom, decide about how
wide across the arroyo is. Find a clast that has been transported a long distance, and
another one that has been transported a short distance. Show them to your instructor.
4. Follow the arroyo until you get to the point it goes under the building. Is the arroyo
wider here or more narrow?
5. Where will water be flowing faster—in a wider channel or in a more narrow one? (Class
discussion. Make drawings as necessary here.)
6. Follow the arroyo through the concrete tunnel and into the wide area. Look at the
sediment piled up on the side and make a sketch of it here. Do you see any patterns or
lines in the sediment?
37
7. Was this sediment deposited by the water in the arroyo, or was it eroded by the arroyo, or
both? How would you know?
8. Each lab group should bring back a small amount of the sediment to the lab for Part 3.
Once you have secured your sample, follow your instructor up the stairs and back to the
lab room.
Part 3. Microscopy.
Your instructor will demonstrate the video and optical microscopes to you as a group. Be sure to
ask questions and explore its function.
Activity 1: Sorting of sediment.
Discussion: Sedimentary rocks are composed of grains that are SORTED. Sorting refers to how
many different sizes there are in a rock. For example, when you look at a rock, do all the grains
look to be about the same size? Or are there many different sizes of grains? The latter would be
an example of a “poorly sorted” sediment, while the former would be an example of a “wellsorted” rock. Other categories include “moderately well sorted,” and “very well sorted.”
1. Look at the samples of sediment you brought back from the arroyo under a microscope
and make sketches of what you see. Describe the sorting and roundness of the grains by
comparing them to the figures on the next page.
38
2. Do you see a “flaky”, shiny mineral, in the samples? Does it looks familiar to you (you
saw it last week)? These are microscopic muscovite flakes. Make sketches of them.
Activity 2: Each group should spend 30 minutes examining the following objects under the
microscopes:
1. glass and streak plates
2. a piece of jewelry
3. the LCD display of a cell phone
4. ID cards
5. paper money, paying particular attention to the microwriting around the president.
6. A piece of fabric
7. Your skin, especially your fingerprint
Make sure that each of you use both the standard microscopes and the video scope.
Now make drawings of each object as they appear in the field of view:
Reflection/wrap-up: After lab, visit this website:
http://micro.magnet.fsu.edu/optics/tutorials/java/powersof10/index.html
This is an excellent Java application of different views of the world from macro to micro
scales. You are encouraged to visit the site and email it to your instructor.
39
Lab Exercise—Sedimentary Rocks
Purpose: This lab will acquaint you with the sedimentary rocks.
Goals: Identifying the sedimentary rock, and determining its environment of deposition. You
will be tested on these at the beginning of the next lab session.
Activity 1: Identifying sedimentary Rocks
Discussion
In general, sedimentary rocks can be divided into two basic types. Clastic rocks are sedimentary
rocks that are made from other, pre-existing rocks that were eroded into sediment, transported,
deposited, and lithified. Chemical sedimentary rocks are different in that they form by
precipitation of ions and minerals out of a solution, most commonly seawater. The clastic rocks
include conglomerate, breccia, sandstone, siltstone, and some shales.
A conglomerate is made from a mix of gravel-sized and smaller-sized grains that are rounded in
shape.
A breccia is also made of gravel-sized and smaller grains, but the grains are angular, instead.
40
A sandstone is made up primarily of sand-sized grains, and often has a matrix between the sand
of a much finer material. It feels sandy or gritty, and grains are easily visible.
A siltstone is similar to a sandstone, but the grains are much smaller (from 1/16 mm to 1/256
mm). Both siltstones and sandstones can be a variety of colors.
A shale is made up of grains that are too small to see with the unaided eye (1/256 mm and
smaller), and are black, green or reddish in color. The main feature of shales is that they usually
have well-formed, thin layers. The word to describe this property is fissile.
Chemical rocks include limestone, dolomite, chert, evaporite, diatomaceous earth and coal.
Limestone is made of CaCO3 and fizzes in acid. Often limestone contains fossils. This rock
forms in a marine setting (ocean). Sometimes limestone is “chalky” and doesn’t contain fossils;
often you can see large crystals of calcite.
Dolomite also contains CaCO3, but also has MgCO3 as well. As a result, it looks and feels
much like limestone, but you have to scratch it (powder it) in order for it to fizz in acid.
Chert is a rock made entirely of SiO2 grains that are so small you can’t see them at all. It looks
glassy and has a conchoidal fracture similar to obsidian, but it is usually not black; chert can be
tan, white, red, brown, or green.
The evaporates that you will see in lab all come from the Castille Formation in the Permian
Basin of west Texas. They are mostly white in color with thin black layers. Each set of one
black and one white layer is called a varve, and each varve represents one year of time; the black
layer was formed in winter and the white layer in summer. The thicknesses of the varves give
you information about the length and intensity of individual seasons in the Permian, more than
250 million years ago!
41
Diatomaceous earth is white and powdery, and leaves individual powder grains on your hands
and everything else it touches. The grains are microscopic oceanic plants that have not shells,
but tests, made of SiO2.
Coal can also be thought of as a metamorphic rock because it is formed by subjecting organic
matter (plants and animals) to heat and pressure as a result of rapid and deep burial. The coal
that you will see today is shiny, black and lightweight. Don’t light it on fire!
Use the chart on the next page to identify the sedimentary rocks in your kit. Your instructor will
check your work when you have finished.
42
43
Activity 2: Documenting the sorting and roundness of clastic rocks.
Separate out the conglomerate/breccia, sandstone, siltstone, and shale. Use the sediment
classification card (provided by your instructor) and the figures in the Sedimentology Lab in this
manual to observe and record the sorting and roundness of these rocks.
Sample
Grain Size (mm)
Sorting
Notes:
44
Roundness
Lab Exercise—Stratigraphy
Purpose: You will be introduced to the concepts of sequence of events, and stratigraphic
correlation. You will be introduced to the concepts of radioactive decay and how it is used to
determine the age of rocks.
Goals: Learning lithologic symbols; identifying transgression and regression events; ordering of
geologic events. Understanding how radioactive decay works; learning what half-life is;
calculating the age of a rock. You will be tested on these at the beginning of the next lab session.
PART 1: RELATIVE DATING AND STRATIGRAPHY
Activity 1: Unconformities.
Discussion: These are breaks in the deposition of sedimentary rocks, due to either nondeposition, non-deposition with erosion, or tectonic activity.
Disconformity: This is a hiatus or break in the deposition of sedimentary rocks, with
erosion. In other words, deposition simply stops for awhile. It looks like this:
Disconformity
Nonconformity: This is a break in deposition accompanied by erosion, which often is
extensive enough to expose deeply buried igneous or metamorphic rocks. When
deposition starts again, horizontal sedimentary rocks are layered on top of the
igneous/metamorphic rocks, and looks like this:
Sedimentary rock
Nonconformity
Granite
45
Angular unconformity: Tectonic activity causes layers of rock to be tilted, folded, or
faulted. A flat surface is then eroded, and deposition begins there. It can look like this:
Flat rocks
Angular unconformity
Tilted rocks
Questions about unconformities:
1. Describe, in words, what you see in the three unconformity diagrams above.
Activity 2: Time-ordering of geologic events.
Questions:
2. If you bake a loaf of bread and then cut a slice, which happened first, the baking or
the cutting?
3. Which “event” is older? The event of baking or the event of cutting?
4. If a set of rocks is faulted (cut), which is older, the set of rocks, or the fault?
5. If you make a stack of rocks, which did you put down first, the layer on the bottom,
or the layer on the top? Which layer is oldest?
46
Activity 3: Visualizing geologic events
Your instructor will guide you through a group activity on the visualizing the time-order of
geologic events. On the following page, complete the ordering on your own.
47
Activity 4: Correlation. If you drill down into the ground below UTEP and examine the rocks
in your drill core, you will see a unique set of rock layers. If you drill down into the ground
below Ciudad Chihuahua you will see a similar, but different set of rock layers. How would you
make comparisons (correlations) between the two? If these cores are from two different areas
now, how can we tell a story about what the environment was like in the past in these two areas?
The comparison of the stratigraphy of two or more areas is called stratigraphic correlation.
Stratigraphic correlations can be done using the rocks, fossils, even the chemical signatures of
the rock layers. You will be using the rocks themselves, and this practice is known as “lithologic
correlation.” The idea is to match the rock types in different locations to see how the
environment varied between the two. Remember, the type of sedimentary rock is dictated by its
environment.
Figure 4a. Key for lithologic symbols used in stratigraphic columns.
Conglomerate
Sandstone
Siltstone
Limestone
Correlate the stratigraphic columns on the next page.
48
A
B
49
C
Questions:
1. Which column was closest to land? How do you know?
2. Was sea level rising? Falling? Both? How do you know?
50
Lab Exercise—Relative Dating and Absolute Dating
Discussion. Half life is the time it takes for one half of a given amount of a radioactive
substance, the “parent,” to decay into its stable product, known as the “daughter.” Here’s a
simplified example. The half life of uranium (U) is 4.5 billion years. If you start with one
kilogram of U, and wait for 4.5 billion years, you will end up with a half-kilogram of U, and a
half-kilogram of its daughter, lead. If you waited around another 4.5 billion years, half of the
leftover parent, (1/2 kg) would decay into the daughter. This would leave you with ¼ kg of U
and ¾ kg of lead, after two half-lives have passed.
Activity 1: Discovering half-life. Each group will get a box of 100 pennies from your
instructor. Start by putting all the pennies on the table face up (heads), and verify that there are
100 pennies. Each face-up penny represents an unstable, radioactive “parent” atom. You are
starting with 100% unstable, radioactive material.
Now place the pennies in the box, shake it, and dump it out on the table. Separate out the heads
and the tails. The heads are still the parent, but the tails represent the stable daughter product.
Count the number of each, and record these data on the chart on the next page. One half-life of
your pennies has passed. How much time (minutes) did it take you to do this? This is how long
your “half life” is.
Now return the HEADS-UP pennies to the box, shake it thoroughly, and dump it out on the table.
Separate the heads from the tails, count the number of each, and record these data on the chart.
This is the second half-life.
Repeat eight more times, for a total of ten. Connect the dots on your graph. What is the shape of
the line?
Notes:
51
Half-life
Start
Radioactive atoms
(heads)
Stable atoms
(tails)
100
0
1
2
3
4
5
6
7
8
9
10
100
75
# of
pennies
w heads
50
25
0
1
2
3
4
5
6
# of half-lives
52
7
8
9
10
Activity 2: Calculating the age of a rock. Since we know the half-lives of the radioactive
elements, we can measure the age of a rock in a laboratory. This is done by collecting a clean
sample of the rock, crushing it, separating out the “heavy” mineral crystals, and measuring the
amount of parent vs. daughter in individual crystals.
An example problem:
The half-live of uranium-238 is 4.5 billion years. In your laboratory, you count 750 atoms of U238 and 250 atoms of lead-206 (Pb-206). How old is the rock?
Set up the math problem like this:
U-238 = Parent =
750 atoms
Pb-206 = Daughter = 250 atoms
Total =
1000 atoms
Now divide the amount of parent by the total to get the percent of the parent remaining:
750 / 1000 = 0.75 = 75%
Now read off the chart and determine how many half-lives have passed. Find 75 and move your
finger straight to the right until it meets the dark curved line. Move your finger STRAIGHT
down and note which mark it meets. It should fall halfway between 0 and 1.
You see that 75% of parent remaining corresponds to half of a half life, or 0.5. Now, multiply
this number times the half-life of U-238, or 4.5 billion years.
0.5 X 4,500,000,000 = 2,250,000,000, or 2.25 billion years
So your rock is 2.25 billion years old. That’s how we do it!
53
Half-lives of common radioactive isotopes.
Parent isotope
Daughter isotope
Half-life
Uranium-238
Lead-206
4.5 billion years
Potassium-40
Argon-40
1.3 billion years
Uranium-235
Lead-207
713 million years
Carbon-14
Nitrogen-14
5730 years
Rubidium-87
Strontium-87
47 billion years
Chart showing exponential decay.
54
1. Your rock contains 250 atoms of U-235 and 750 atoms of Pb-207. How old is your rock?
2. Your rock contains 456 atoms of Rb-87 and 127 atoms of Sr-87. How old is your rock?
3. Your fossil clamshell contains 973 atoms of C-14 and 2713 atoms of N-14. How old is
your shell?
4. Your rock contains 6733 atoms of K (potassium) –40 and 10312 atoms of Ar-40. How
old is your rock?
5. Your piece of wood contains 2512 atoms of C-14 and 143 atoms of N-14. How old is
your wood?
55
Lab Exercise—Interpreting Geologic History
Purpose: To build your skill in making geologic interpretations based on rock observations and
data.
Goals: Interpreting depositional environment, transgression/regression history, using fossils as
tools, and stratigraphic correlation using real rocks.
You will find two sets of rock arranged for your study. Each set represents a stratigraphic
column, and therefore a complex geologic history. Your tasks will be to 1) identify and name
the lithologic (rock) types, 2) identify transgression/regression events, 3) document the fossil
assemblages in each column, and 4) correlate the two columns.
Strategy: Each small group in the class will work independently on tasks 1, 2, and 3. Then each
group will report their results to the whole class. Afterwards. the whole class as a group will
complete task 4.
TASK 1: Identifying the rocks. Your rock descriptions should start out with a general sketch
of the column, noting where lithologic changes are. You should then number the different rocks
you observe, so that your finished sketch looks something like this:
1
2
3
4
Then begin at the bottom of the column with a systematic description of the rock type that
includes the following information:
Texture: this means grain sizes (if visible), sorting, and roundness;
Thickness of the bed—or in this case, the rock;
Colors, both of the fresh and weathered surfaces;
Any features in the rock, like layers, lines, curves, etc;
Are fossils present?
Then based on the information above, name the rock. Complete your descriptions for both
columns.
56
TASK 2: Identifying transgression and regression events. Your group should also be doing
the same kind of sketch as the group completing Task 1. What you should be paying particular
attention to is the general rock type, for example, is the rock a sandstone, siltstone, shale,
limestone, etc.? Then in your sketch, put in symbols to show the relative grain size.
Remembering the relationship between grain size and water depth, give an approximation of the
water depth (shallow, deep marine, beach, river, etc.). Do this for both columns.
TASK 3: Documenting fossil assemblages. For each rock layer that has fossils present, you
will need to sketch and identify the fossils, using the handouts from Lab Exercise 5. Then you
will need to make a sketch of each column, showing (briefly) the lithologic types. Next to this,
you should sketch the appearances of the fossil assemblages in a style that is similar to the chart.
TASK 4: Correlating the columns. Once the presentations of each group have been made, and
the differences in interpretation have been straightened out, each group should independently
correlate the two columns, in the same way that you did in Lab Exercise 4. Your group should
have one representative set of columns that everybody contributes to, containing all the
information obtained by all groups. Your instructor will evaluate your work.
Notes:
Part II – Geologic History – You will be given a handout to review.
There will be a quiz on the Geologic Time Scale next week.
57
58
Laboratory Exercise—Impact Craters and Exploring the Solar
System
Part 1: Impact Structures. Impact structures are created as a result of the collisions between
planetary bodies. We tend to refer to them loosely as “craters,” but the term “crater” has a
specific definition. In general, we can use the word crater to refer to an impact structure that is
smaller than 300 km (~160 miles) in diameter. Small craters, less than 10 km (~6mi) in
diameter, tend to be simple bowl-shaped depressions with raised rims (Figure 11a). Craters
larger than 10 km tend to have slumped walls, and sometimes a central peak in the middle of the
basin (Figure 11b). This peak forms as a result of the rebound (bounce) of material that melts
during the high heat caused during impact. The peak “freezes” into this shape as it cools off
after the impact. Structures larger than 300 km are termed “impact basins”. Very large impact
basins have multiple rings of ridges and depressions around the center, as a result of a huge
impact. These are called multiring basins, and a single one can cover a large part of a planet’s
surface (Figure 11c).
Figure 11a. A small crater on Mars, about 2 km across. Note the perfect bowl shape.
Figure 11b. Copernicus Crater (left), about 77 km across, and Euler Crater (right), about 28 km
across. Both craters are on the Moon. Note the well-formed central peaks in both craters.
59
Figure 11c. Callisto, a moon of Jupiter. The multi-ring structure is called Valhalla and is about
3000 km across.
Activity 1: Identifying craters. Using the following image (Figure 11d), find, circle, and label
the at least two each of small craters and large craters with central peaks (don’t forget to label
the central peaks.
Figure 11d. Lunar impact structures.
Can you see the large rings of craters in this image (Figure 11e) of the planet Mercury? It may
help to trace features out with your pencil.
60
Figure 11e. The southern hemisphere of Mercury, as photographed by the Mariner spacecraft.
61
Activity 2: Learning about craters. You will use the box of sand and round objects provided.
Start by smoothing out the sand. Then measure and record the mass and diameter of each round
object (impactor). Drop each impactor into the sand from a height of 1 m. Use the charts below
to plot the size of your craters vs. a) mass of the impactor, and b) size of the impactor.
Object Mass vs. Crater Size
1
0.8
0.6
0.4
0.2
0
Crater Size (cm)
Object Size vs. Crater Size
1.2
Object Size (cm)
Object Mass (grams)
1.2
1
0.8
0.6
0.4
0.2
0
Crater Size (cm)
62
Now drop the objects from a variety of different heights, up to at least 2 meters, and plot the
results below.
Object Height vs. Crater Size
Object Height (cm)
1.2
1
0.8
0.6
0.4
0.2
0
Crater Size (cm)
Question: Based on your observations, did the size, mass, or height of your impacting body
have more of an effect on crater size? Which had the least effect? Why do you think this is
true?
Activity 2b: How would you calculate the velocity of the impactor when it hits the sand? If the
impactor is dropped from an initial height at which it isn’t moving, its velocity can be calculated
using the following equation:
Velocity at impact =
2* g *h ,
Where g is gravitational acceleration (9.8 m/s2), h is the drop height in meters, and velocity at
impact is in meters per second (m/s).
Calculate the velocity at impact for each of the impactors you used to make the final chart,
and write the answers next to the individual data points on the chart.
63
It turns out that the most important factor that determines the size of a crater is the energy of the
impactor. Kinetic energy (the energy an object in motion carries) can be described by the
following equation:
2
Kinetic Energy = ½ m v = m g h,
Where m is the mass of the object in kilograms, v is the velocity in meters per second, and
Kinetic Energy is in Joules (J).
Which term in this equation (mass or velocity) is more important (i.e. which has a greater
effect)?
Calculate the kinetic energy of each impactor you used to make the final chart above and
plot the results on the chart below.
What did you find?
Object Energy vs. Crater Size
1.2
Energy (J)
1
0.8
0.6
0.4
0.2
0
Crater Size (cm)
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Activity 3:: Understanding Lunar Cycles. The phasing of the Moon is one of the most commonly
misunderstood natural processes, yet it’s one of the things that ALL teachers in the State of Texas must
understand for their certification exams.
Each group will use the foam sphere mounted on a pencil to be the Moon, and either the lamp or overhead
projector provided to serve as the Sun. Your head will be the Earth. Turn off the room lights.
With the overhead in the center of the room, place the ball at arm's length between the bulb and your
eyes. You should hold the pencil in your left hand. The view from your eyes is the same both for this
exercise and for observations of the real sky.
At the start, the "Moon" is blocking the "Sun." (This is actually demonstrating a total solar eclipse which
is very rare for any given location on Earth.) Usually the Moon passes above or below the Sun as viewed
from Earth. Now move your moon up or down a bit so that you are looking into the Sun. As you look up
(or down) at their moon you will see that all of the sunlight is shining on the far side, opposite the side
that you see. This phase is called "new moon" (like "no moon").
Viewed from above the solar system
E
M
What the moon looks like in the sky
Sun
You should now move your hand towards the left, about 45° counter-clockwise. Now observe
the sunlight on the Moon. You should see the right hand edge illuminated as a crescent. The
crescent will start out very thin and fatten up as the you move the Moon farther away from the
Sun. (Note: although the Moon is closer to the Sun during new and crescent phases, it is still 400
times closer to Earth; i.e., the Sun is VERY far away in reality.)
Viewed from above the solar system
What the moon looks like in the sky
M
E
Sun
65
When your Moon is at 90° to the left you will see the right half of the Moon illuminated. This
phase is called "first quarter." Remember that fully one half of the sphere is illuminated at all
times, but the illuminated portion that we observe changes as the Moon changes position.
Viewed from above the solar system
What the moon looks like in the sky
M
Sun
E
As you continue to move the Moon counter-clockwise past first quarter, it goes into its "gibbous"
phase (more than half, but less than fully illuminated). This grows as the Moon moves towards
180°.
Viewed from above the solar system
What the moon looks like in the sky
M
E
Sun
66
When the Moon reaches the position directly opposite the Sun, as viewed from Earth, the half
viewed from Earth is fully illuminated (unless your head is causing a lunar eclipse). Of course
only half of the Moon is illuminated. It has taken the Moon about two weeks to move from new
to full. This growth in illumination is known as "waxing."
Viewed from above the solar system
M
E
What the moon looks like in the sky
Sun
You should now switch the pencil to your right hand and face in the general direction of the
Sun. Starting with the Moon at full, continue the Moon's counterclockwise motion. You will
observe the reverse of the Moon's phases seen so far with the left portion of the Moon
illuminated.
Viewed from above the solar system
E
M
What the moon looks like in the sky
Sun
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As the gibbous phase diminishes, the Moon will reach the 270 degree position, straight out to the
right. This is "third" or "last quarter."
Viewed from above the solar system
E
What the moon looks like in the sky
Sun
M
Finally, the moon returns to a thinning crescent and then back to the new moon. From full to new
the Moon has been "waning" and leading the Sun.
Viewed from above the solar system
What the moon looks like in the sky
Sun
E
M
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Optional The Moon Landing Hoax!
Objectives: To give future teachers and other interested persons the opportunity to refute bogus
claims made by television shows with huge production values. Also, this lab gives you the
opportunity to see that your own eyes and brains are far superior to any “pop-science.”
Reference: http://www.badastronomy.com/bad/tv/foxapollo.html#shadow
Fox TV and the Apollo Moon Hoax (February 13, 2001), by Phil Plaitt
On Thursday, February 15th 2001 (and replayed on March 19), the Fox TV network aired a
program called ``Conspiracy Theory: Did We Land on the Moon?'', hosted by X-Files actor
Mitch Pileggi. The program was an hour long, and featured interviews with a series of people
who believe that NASA faked the Apollo Moon landings in the 1960s and 1970s. The biggest
voice in this is Bill Kaysing, who claims to have all sorts of hoax evidence, including pictures
taken by the astronauts, engineering details, discussions of physics and even some testimony by
astronauts themselves. The program's conclusion was that the whole thing was faked in the
Nevada desert (in Area 51, of course!). According to them, NASA did not have the technical
capability of going to the Moon, but pressure due to the Cold War with the Soviet Union forced
them to fake it.
Sound ridiculous? Of course it does! It is. So let me get this straight right from the start: this
program is an hour long piece of junk.
From the very first moment to the very last, the program is loaded with bad thinking, ridiculous
suppositions and utterly wrong science. I was able to get a copy of the show in advance, and
although I was expecting it to be bad, I was still surprised and how awful it was. I took four
pages of notes. I won't subject you to all of that here; it would take hours to write. I'll only go
over some of the major points of the show, and explain briefly why they are wrong. In the near
future, hopefully by the end of the summer, I will have a much more detailed series of pages
taking on each of the points made by the Hoax Believers (whom I will call HBs).
Instructor: Ask your students if they’ve seen this TV show. Read a hoax aloud to your
students, then do the demonstration, then give a summary of the explanation. Whenever
possible, have your students put it in their own words.
Hoax 1: The first bit of actual evidence brought up is the lack of stars in the pictures taken by the
Apollo astronauts from the surface of the Moon. Without air, the sky is black, so where are the
stars?
DEMONSTRATION: Take your students outside along with the string of decorative lights and
the Polaroid camera. Have one student stand in the bright sun holding the lights, which have
been plugged in. have the rest of your class stand several meters away from the lights. Ask
them if it is difficult to see the lights. Then ask a student to take one Polaroid picture of the
student with the lights, making sure the picture is composed in the sunlight. When the picture
develops, the lights will be hard to see!
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Answer: The stars are there! They're just too faint to be seen.
This is usually the first thing HBs talk about when discussing the Hoax. That amazes me, as it's
the silliest assertion they make. However, it appeals to our common sense: when the sky is black
here on Earth, we see stars. Therefore we should see them from the Moon as well.
I'll say this here now, and return to it many times: the Moon is not the Earth. Conditions there are
weird, and our common sense is likely to fail us. The Moon's surface is airless. On Earth, our
thick atmosphere scatters sunlight, spreading it out over the whole sky. That's why the sky is
bright during the day. Without sunlight, the air is dark at night, allowing us to see stars.
On the Moon, the lack of air means that the sky is dark. Even when the Sun is high off the
horizon during full day, the sky near it will be black. If you were standing on the Moon, you
would indeed see stars, even during the day.
So why aren't they in the Apollo pictures? Pretend for a moment you are an astronaut on the
surface of the Moon. You want to take a picture of your fellow space traveler. The Sun is low off
the horizon, since all the lunar landings were done at local morning. How do you set your
camera? The lunar landscape is brightly lit by the Sun, of course, and your friend is wearing a
white spacesuit also brilliantly lit by the Sun. To take a picture of a bright object with a bright
background, you need to set the exposure time to be fast, and close down the aperture setting too;
that's like the pupil in your eye constricting to let less light in when you walk outside on a sunny
day. So the picture you take is set for bright objects. Stars are faint objects! In the fast exposure,
they simply do not have time to register on the film. It has nothing to do with the sky being black
or the lack of air, it's just a matter of exposure time. If you were to go outside here on Earth on
the darkest night imaginable and take a picture with the exact same camera settings the
astronauts used, you won't see any stars! It's that simple. Remember, this the usually the first
and strongest argument the HBs use, and it was that easy to show wrong. Their arguments get
worse from here.
Hoax 2: In the pictures taken of the lunar lander by the astronauts, the TV show continues, there
is no blast crater. A rocket capable of landing on the Moon should have burned out a huge crater
on the surface, yet there is nothing there.
DEMONSTRATION: Have your students observe the cars moving around on the streets by the
building. Watch the cars as they park. Ask your students how fast they drove on the freeway on
the way to campus—60 MPH? 70 MPH? 150 MPH? Now ask them if they were going that fast
when they parked the car. Did they slow down? Do they think that a spacecraft would slow
down as it landed, or would it slam into the moon at maximum thrust?
Answer: When someone driving a car pulls into a parking spot, do they do it at 100 kilometers
per hour? Of course not. They slow down first, easing off the accelerator. The astronauts did the
same thing. Sure, the rocket on the lander was capable of 10,000 pounds of thrust, but they had a
throttle. They fired the rocket hard to deorbit and slow enough to land on the Moon, but they
didn't need to thrust that hard as they approached the lunar surface; they throttled down to about
3000 pounds of thrust. [Note (added March 31, 2001): I have been told my math below is
incorrect, and that thrust does not convert simply to pressure. I am investigating this, and will
correct this page when I get better info.] Now here comes a little bit of math: the engine nozzle
was about 54 inches across (from the Encyclopaedia Astronautica), which means it had an area
of 2300 square inches. That in turn means that the thrust generated a pressure of only about 1.5
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pounds per square inch! That's not a lot of pressure. Moreover, in a vacuum, the exhaust from a
rocket spreads out very rapidly. On Earth, the air in our atmosphere constrains the thrust of a
rocket into a narrow column, which is why you get long flames and columns of smoke from the
back of a rocket. In a vacuum, no air means the exhaust spreads out even more, lowering the
pressure. That's why there's no blast crater! Three thousand pounds of thrust sounds like a lot,
but it was so spread out it was actually rather gentle. Two last bits: the engines were designed to
cut off a couple of meters above the surface of the Moon to prevent too much dust from kicking
up and obscuring the vision of the astronauts. So they actually fell the last little way; that's yet
another reason there is no blast crater.
Hoax 3: When the astronauts are assembling the American flag, the flag waves. Kaysing says
this must have been from an errant breeze on the set. A flag wouldn't wave in a vacuum.
DEMONSTRATION: Pass around the picture of the astronaut and the flag on the moon,
pointing out the ripple in the flag that makes it look like it’s waving. Have a student hold the
demonstration flag and the supporting metersticks. Then ask the student to extend the flag out as
far as it will go, using gentle pressure. Now ask the student to shove it into the soft ground so it
will stand up. As this is happening, ask the other students if the wind is blowing around the flag,
or if the act of putting into the ground is making it wave. When its in the ground, make sure it
has a dimple in it. If you were to take a picture, would it look like the flag was waving?
Answer: Of course a flag can wave in a vacuum. In the shot of the astronaut and the flag, the
astronaut is rotating the pole on which the flag is mounted, trying to get it to stay up. The flag is
mounted on one side on the pole, and along the top by another pole that sticks out to the side. In
a vacuum or not, when you whip around the vertical pole, the flag will ``wave'', since it is
attached at the top. The top will move first, then the cloth will follow along in a wave that moves
down. This isn't air that is moving the flag, it's the cloth itself. New stuff added March 1, 2001:
Many HBs show a picture of an astronaut standing to one side of the flag, which still has a ripple
in it (for example, see this famous image). The astronaut is not touching the flag, so how can it
wave? The answer is, it isn't waving. It looks like that because of the way the flag was deployed.
The flag hangs from a horizontal rod which telescopes out from the vertical one. In Apollo 11,
they couldn't get the rod to sit horizontally, so the flag didn't get stretched fully. It has a ripple in
it, like a curtain that is not fully closed. In later flights, the astronauts didn't fully deploy it on
purpose because they liked the way it looked. In other words, the flag looks like it is waving
because the astronauts wanted it to look that way. Ironically, they did their job too well. It
appears to have fooled a lot of people into thinking it waved. This explanation comes from
NASA's wonderful spaceflight web page. For those of you who are conspiracy minded, of
course, this doesn't help because it comes from a NASA site. But it does explain why the flag
looks as it does, and you will be hard pressed to find a video of the flag waving. And if it was a
mistake caused by a breeze on the set where they faked this whole thing, don't you think the
director would have tried for a second take? With all the money going to the hoax, they could
afford the film! Note added March 28, 2001: One more thing. Several readers have pointed out
that if the flag is blowing in a breeze, why don't we see dust blowing around too? Somehow, the
HBs' argument gets weaker the more you think about it.
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Hoax 4: The program has two segments dealing with what they call ``identical backgrounds''. In
one, they show the lunar lander with a mountain in the background. They then show another
picture of the same mountain, but no lander in the foreground at all. The astronauts could not
have taken either picture before landing, of course, and after it lifts off the lander leaves the
bottom section behind. Therefore, there would have been something in the second image no
matter what, and the foreground could not be empty. Obviously, the mountain background is a
fake set, and was reused by NASA for another shot.
DEMONSTRATION: Take your students to the grass southeast of the flagpole, and have them
face the ADMIN building. Now have them put their hands up around their eyes like
“binoculars.” Now stand in front of them and ask if they can see you. Now make them take 5
large steps to the side, either right or left, but you stay put. Now ask them if they can see you
(NO). Now ask them if the ADMIN building still looks the same (YES). Tell them that the
building is a painting that you faked just for this experiment. Then tell them this is a
phenomenon called parallax.
Answer: Actually, the pictures are real, of course. As always, repeat after me: the Moon is not
the Earth. On the Earth, distant objects are obscured a bit by haze in the air, and we use that to
mentally gauge distances. However, with no air, an object can be very far away on the Moon and
still be crisp and sharp to the eye. You can't tell if a boulder is a meter across and 100 meters
away, or 100 meters across and 10 kilometers away! That's what's going on here. The lander is
close to the astronaut in the first picture, perhaps a 20 or 30 meters away. The mountain is
kilometers away. For the second picture, the astronaut merely moved a few tens of meters to the
side. The lander was then out of the picture, but the mountain hardly moved at all! If you look at
the scene carefully, you'll see that all the rocks and craters in the foreground changes between the
two pictures, just as you'd expect if the astronaut had moved to the side a ways between the two
shots. It's not fraud, it's parallax! For an outstanding example of this, take a look at video taken
during Apollo 16. There is a boulder in the background that looks to be about 3 or 4 meters (1013 feet) high. About ¾ of the way through the segment the astronauts walk over to it.
Amazingly, that boulder is the size of a large house! Without air, we have no way to judge
distances, and a huge rock looks like a medium sized one until we have some way to directly
judge its size; in this case, by looking at the tiny astronauts next to it.
Hoax 5: The next evidence also involves pictures. In all the pictures taken by the astronauts, the
shadows are not black. Objects in shadow can be seen, sometimes fairly clearly, including a
plaque on the side of the lander that can be read easily. If the Sun is the only source of light on
the Moon, the HBs say, and there is no air to scatter that light, shadows should be utterly black.
DEMONSTRATION: Go back to the lab room and set up the over head to shine on the table.
Have the students stand around the table. Put the large black piece of paper down. Then put
down the toy figure on it, then block the light with the inflatable space shuttle so that the toy is in
shadow. Now put down in the shadow the card with the small writing. Ask your students if they
can read the writing from where they’re standing. Now flip the paper over so that the white
surface is facing up. Then ask if anything’s changed, and if the writing is easier to read. Ask
them to put into words what they are seeing. (The reflected light from the paper makes
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everything brighter.) Ask them what the basic color of the moon is, and what the brightness is
like on the moon’s surface.
Answer: This is one of my favorite HB claims. They give you the answer in the claim itself:
"...if the Sun is the only source of light..." It isn't. There are actually two sources of light besides
direct sunlight. The Earth was in the lunar sky as seen by the astronauts, and was at least half full
(for Apollo 11 and 17 the Earth was nearly full). The Earth is far brighter as seen from the Moon
as the Moon is from the Earth The Earth is larger in the sky than the Moon is from here (about
15 times or so) and it reflects light roughly 5-8 times better, making it about 100 times brighter
than the full Moon. The full Moon is easily bright enough to read by here on Earth, so the Earth
would be a very good source of light, even if it were only half full. Another source of light is the
Moon itself. The brightly lit lunar landscape would also be a source of light that could fill in the
shadows. Between the Earth and the Moon, there is plenty of light besides the Sun! Again, a very
simple answer to a HBs claim of hoax.
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Interpretation of Hellas Planitia Geologic
Map
by B. Drenth
Reference: Leonard, G.J., and Tanaka, K.L., 2001, Geologic Map of the Hellas Region of Mars, U.S.
Geological Survey Geologic Investigations Series I-2694.
In this lab exercise you will examine a geologic map of a portion of Mars and interpret the
geologic history of the region covered by the map. The map covers the spectacular Hellas
Region, home to the largest well-preserved impact crater on the planet (see Figure 1). Numerous
other structures are superimposed on the impact structure, including volcanic features, channels,
and eolian (wind blown) deposits. This map was prepared using images of the surface collected
by the Viking Orbiter during the 1970s. As you work through the following questions, think
about what the different mapped geologic features tell you about what was happening on this
portion of the Martian surface when those features formed. You should work in groups of at
least 2 people.
Figure 1: Shaded relief map of Mars. The location of the Hellas basin is shown by the white
oval. The basin is about 2000 kilometers across and sits as much as 9 kilometers lower than the
surrounding highlands(!).
74
Begin by examining the map and getting yourself oriented. Things to notice:
•
•
•
•
•
•
•
•
•
The large Hellas basin (Hellas Planitia) in the center of the map is the remnant of a large
impact crater
The topography generally slopes inward toward the basin over the mapped area
Rugged mountains lie along the rim of the basin
There are three different general ages of rocks displayed here, that represent the three
major time periods of Martian history: Noachian, Hesperian, and Amazonian (from oldest
to youngest)
Noachian rock units have labels that begin with “N”
Hesperian rock units have labels that begin with “H”
Amazonian rock units have labels that begin with “A”
Where the age of a particular unit cannot be uniquely determined, a combination of
letters is used to display the ambiguity. For example, if it cannot be determined that a
unit is Amazonian or Hesperian, its label will begin with the letters “AH.”
Note the symbols used for faults, craters, depressions, and volcanic flow fronts.
Answer the following questions, using the map, stratigraphic column (labeled “CORRELATION
OF MAP UNITS”), and rock unit descriptions provided:
1. Take a look at the map, noting the distribution of craters in the different age units. Each
time period is shown by the first letter of its name on the map, and each period has a set
of unique colors that correspond to it. Look around and find the areas dominated by rocks
of Noachian, Hesperian and Amazonian time. Also, look at the distribution of craters in
the three main rock packages. What general statements can you make about cratering in
the three different time periods? In other words, how much, how big and where? Don’t
look at the explanation to the right just yet.
2. Now take a look at the chart of crater size distributions on the right side of the
stratigraphic column. Were your guesses about cratering correct? What age of craters
would you expect to be the most downgraded (eroded) today? Why?
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3. What are the two oldest units in the map area, and where do they occur (NW, SE, etc.)?
4. How do you think these oldest units formed? Look at the explanation for clues. Don’t just
repeat the explanations, think about the PROCESSES that go with the actual rocks.
Example: volcanic rocks would have been formed by volcanoes!
5. Notice the profound asymmetry in outcrop pattern (broad extent southeast of the basin,
largely buried to the south) of one of the two units. Think back to the cratering activity
you did. How was basin (crater) shape influenced by the speed, size and path of the
impactor? In that activity, you dropped the impactors straight down. What would have
happened if the impactor came in from an angle? How might this be meaningful when
looking at the shape of the Hellas basin?
6. Examine the outcrop pattern of unit Nts at Tyrrhena Patera in the extreme northeastern
portion of the map. Describe what the unit’s boundaries look like in map view. What do
you think could have made the Nts?
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7. Now compare your answer above to the unit description and interpretation. How are they
different?
8. Compare and contrast the two different rock units in the Tyrrhena Patera. (Nts and Htf).
Talk about composition, extent and shape. Use your textbook or class notes to define
“pyroclastic.” Would you expect Htf to be mafic or felsic in composition?
9. Was the process that made these two rock units operating over short or long periods of
time? How do you know? Why is this important in the geologic history of Mars?
10. Locate Peneus Patera and Amphitrites Patera in the southwestern portion of the map.
Describe the surface features (faults, channels, etc.) of these structures. Hint: What was
the likely source of unit HNad?
11. Now draw a schematic cross section (simple sketch) through either of the Paterae,
showing the internal structure and stratigraphy.
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12. BONUS QUESTION** Name the type of geologic feature that is characterized by
symmetric ring faults, fractures, and scarps. Use your textbook and class notes.
13. What types of rocks are inferred to be represented by unit HNpr?
14. Notice the spatial extent of these units. Why are they concentrated around the western
rim of Hellas Basin? Hint: they post-date the impact itself.
15. What makes up most of the interior of Hellas Planitia? List the units below.
16. What are the dominant mechanisms of rock formation inside the basin?
17. Describe the geologic processes acting on the surface of the map area during Amazonian
time. Are they mostly tectonic, volcanic, erosional or related to cratering?
18. What was the level of tectonic activity (e.g. faulting and volcanism) during this time
period, compared to other time periods?
19. Examine the outcrop patterns of the younger, elongated units such as AHv. Do these
patterns look like anything we observe on Earth? What does this suggest?
78
20. Summarize, in paragraph form, the geologic history (from oldest to youngest) of the
mapped region.
79
Laboratory Exercise— Surface Water and Groundwater
Purpose: This exercise will acquaint you with how water moves across a landscape and how
water alters a landscape. This lab will also acquaint you with rock porosity and water table
maps. You will learn how salinity and temperature affects the circulation of liquid.
Goals: Visualizing water movement, calculating porosity, and making a contour map of a water
table. Predicting the circulation of the oceans, based on temperature and salinity of ocean water.
Activity 1: Surface water.
1. Your instructor will use the stream table to demonstrate delta formation. As you see the
demonstration, answer the following questions.
a. Make a sketch of the delta after the water has run for one minute and again after 3
minutes.
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2. Your instructor will use the stream table to demonstrate the erosion cycle of a stream.
First, you will see a young stream, with a float in it. Observe the float as it makes its way
down the stream.
a. Measure and record the time it takes the float to run the length of the young
stream.
b. Calculate the water velocity in cm/second and in m/sec.
c. Measure the width and depth of the stream at three points, the head, the middle
and the mouth. Divide the depth by the width at each point.
3. 3. Now you will see a mature stream. Observe the float as it makes its way down the
stream.
a. Measure and record the time it takes the float to run the length of the young
stream.
b. Calculate the water velocity in cm/second and in m/sec.
c. Measure the width and depth of the stream at three points, the head, the middle
and the mouth. Divide the depth by the width at each point.
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4. Now you will see a stream in its old age. Observe the float as it makes its way down the
stream.
a. Measure and record the time it takes the float to run the length of the young
stream.
b. Calculate the water velocity in cm/second and in m/sec.
c. Measure the width and depth of the stream at three points, the head, the middle
and the mouth. Divide the depth by the width at each point.
5. Your instructor will use the stream table to demonstrate the formation of an alluvial fan.
After two minutes, measure the angle of the sloping fan surface with respect to the
bottom of the stream table.
Activity 2: Groundwater.
Discussion: Groundwater and the rock it moves through is called an aquifer. Water can move
between the grains of a rock due to porosity, which is defined as the amount of space between
grains in the rock. The aquifer contains a saturated zone, where the water is located, an
unsaturated zone above, and the water table, where these two zones meet. The efficiency with
which rock transmits water is called the rock’s permeability. Permeability is expressed in units
called “darcys.”
Porosity is expressed as a percent. It is calculated by dividing the volume of empty spaces in the
rock by the total volume of the rock.
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Well
Unsaturated zone
Water table
Saturated Zone
Activity 1. Calculate the porosity of these sediments. Remember to divide the volume of pore
space by the total volume of the sample. Your number should be a decimal that you will convert
into a percent. All volumes are in cubic centimeters.
Material
Total Volume
Pore Space Volume
Gravel
500
210
cU Sand
600
270
Sandstone 1
650
163
Sandstone 2
800
40
Clay
825
404
Shale
435
57
Limestone
950
123
Unfractured
Granite
500
5
Fractured
Granite
700
35
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Percent Porosity
Activity 3: Mapping the water table.
If enough wells are drilled, it is possible to locate the depth to the water table in the form of a
contour map. This is useful because the map will reveal any slopes in the water table, and since
water flows down a slope, the general movement of groundwater can be figured. Look at the
map showing elevations of the water table. The dots are individual wells, and the numbers are
the water table elevations.
Use pencil and not pen, since you will need to do a lot of erasing!
Start by connecting equal depths with curved lines. Once you have each well on a line, then
answer the following questions.
1. Assuming north is at the top of the map, which way is the water table sloping?
2. Which way should the groundwater be moving?
3. Do the shallowest and deepest wells show any kind of trend? In other words, are they in
a cluster, or a line, or some other arrangement?
4. Is there a divide in this map where you can see water flowing in two different directions?
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85
Laboratory Exercise— Introduction to Geophysics
Geophysics Lab, by C. Flores, M.S., and B. Drenth, M.S.
Geophysics is simply the application of physics concepts in geological work. It is a quickly
growing field with a wide range of different techniques and applications. We use geophysics to
delineate geological features that we normally cannot observe directly from or on the surface. In
this lab we will explore two of the most commonly used geophysical techniques: seismic
reflection and gravity prospecting.
Section 1: Reflection Seismic Section Interpretation
Seismic reflection is essentially the use of sonic echoes for depth sounding. The technique is
very useful for constructing cross sections of the Earth that in many cases can closely resemble
actual geologic cross sections. The echoes, or waves, are produced by a powerful source, such as
dynamite. Different rock layers in the subsurface cause some of the echoes to be reflected from
different interfaces back to the surface, where they are detected by sensors (called geophones).
This is a simple example of what it looks like in cross section:
As the seismic energy (echoes) reaches different interfaces (contacts between rock units), some
of the energy is reflected back to the surface, where it is detected by the geophones. Doing this
many times with many sources and many geophones allows us to make seismic sections like the
one shown below.
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from 1
This shows a section of seismic energy, with time in milliseconds on the left vertical axis, and
depth on the right vertical axis. This section has been interpreted as follows, with stratigraphic
information and faults shown:
from 1
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What features do you see in this seismic section? Sketch in different things you see, and try to
follow individual rock layers across the section.
from 2
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Using regular or colored pencils, draw in geological features you see here. Discuss your results
as a class. What sort of geological environment is this?
from 1
References:
1. Griffiths, D.H., and King, R.F., Applied Geophysics for Geologists and Engineers: The
Elements of Geophysical Prospecting, 2nd Ed. Pergammon Press Inc. 1981.
2. Mussett, A.E., and Khan, M.A., Looking Into the Earth: An Introduction to Geological
Geophysics. Cambridge University Press. 2000.
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Section 2: Gravity Map Interpretation
The strength of Earth’s gravity can vary from place to place, due to lateral variations in the
density of subsurface materials. The strength of gravity, or field strength, can be measured in
many different places, allowing cross-sectional profiles (such as Figure 1) and maps to be made
of the variations (such as Figure 2). Variations are called anomalies, defined as any deviation
from the uniform. High values of gravitational acceleration indicate that high-density materials
(such as igneous/metamorphic rocks) lie in the subsurface, and low values indicate the presence
of low-density materials (such as sediments and sedimentary rocks). Sharp gradients indicate the
presence of faults that place dense rocks next to low-density rocks.
In the southwestern United States, horst and graben structures and normal faulting are quite
common. Figure 1 below displays a hypothetical gravity profile over such a set of structures.
Cross-Sectional View:
Figure 1: Hypothetical gravity profile (gray line) measured over horst and graben structure
formed by two normal faults. High gravity values lie over the horst blocks since solid rocks that
are more dense than the overlying sediments lie closer to the surface there. Notice that sharp
gravity gradients are measured over the normal faults.
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Figure 2: Gravity anomaly map of the El Paso region, in milligals (one gal is equal to one
centimeter per square second). Warm colors (oranges, reds, pinks) represent high accelerations,
indicating relatively high-density rocks in the subsurface. Cool colors (blues, greens) represent
low-density rocks in the subsurface.
Using the above map, sketch in where you think there may be faults. Also label horst blocks and
graben blocks. Finally, locate the following horst/grabens:
Franklin Mountains
Hueco Mountains
Hueco Bolson (basin)
Mesilla Bolson
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Laboratory Exercise—Arroyo Park Field Trip
Starting point: the intersection of Robinson and Piedmont Streets.
The Franklin Mountains are here because of the extension of the North American continent in
the Rio Grande Rift.
Look at Crazy Cat Mountain behind you. This mountain is actually a landslide block that slid of
the western flank of the Franklins sometime between 3-5 m.y.a. We know this because the
jumbled-up rocks we see here match the dark purplish rocks you see about 2/3 up the side of the
Franklins. Look at the leftmost TV tower and see if you can find these rocks.
Turn your attention away from the mountains to the landscape right around you. What is
happening to the Earth’s surface right here?
The air photos below show Arroyo Park. Can you find where we are on each photo?
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Look out across the arroyo at the surface where the houses are along Rim Rd. This is the same
surface (with the same age) as the surface you’re standing on. The two surfaces were cut and
separated by the arroyo.
Which one of Steno’s Principles applies here, and why?
-Original Horizontality, Lateral Continuity, Superposition, or Cross-Cutting Relationships?
Now imagine a time before the arroyo, when this surface sloped all the way down to the Rio
Grande and met the river. This was a time before the Rio Grande had cut down its channel to
where it is now, so the surface you’re standing on actually met the river about 100m above what
is now the surface!
Look at the vegetation covering Crazy Cat and compare it to what you see in the arroyo. What’s
different?
Follow your instructor out on the spur leading into the arroyo. You are standing on an old
“terrace” surface that the arroyo cut through. Notice the lack of vegetation. This is because of the
buildup of a caliche soil, which plants generally don’t like.
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While you’re standing here, look for and collect as many different rocks as you can find. Use the
following checklist:
- a limestone with fine layers in it;
- a limestone that looks like “elephant skin”
- a fossiliferous limestone;
- chert or chert inside a limestone;
- (bonus) a limestone with a fine gravel layer in it.
Your instructor will tell you about these rocks.
Because the arroyo cut downward over time, the surfaces that are higher and farther away from
the center of the channel are older. Walk down into the arroyo and try to observe at least four
different terrace surfaces and point them out to each other and your instructor.
Walk around and try to find an “active channel.” How do you know when you’ve found one?
Find the mesquite tree with the orange flagging tape on it. You're standing in an active channel at
this point. With the tree at your back, look down at the channel. Note the different grain sizes,
the natural levee formed here and the braids of the channel. the levee was formed by overflow of
the channel, which carried the big clasts to this point and then dumped them.
Follow the channel about 10m downstream to the tree with the green flagging tape. Look at the
outcrop. What happened here to put the coarsest clasts here? Which came first, the big clasts or
the fine-grained material?
Sketch the outcrop and mark the different layers you see in your sketch.
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Look at the big clast. There are two fossils here worth noting. First are the solitary corals, which
were one of the most successful and abundant life forms in the shallow seas that deposited these
rocks ~400 m.y.a. You will also find a straight-cone cephalopod (like a squid). This fossil looks
like an ice cream cone which has been sliced in a funny oblique way. Make a sketch of the
fossils.
Why aren’t there any (or few) plants in the active channels?
Climb up the terrace that you have been sketching. Is it older or younger than the surrounding
terraces. How do you know? Look for at least four different terrace levels around you and
compare heights.
Can you use vegetation cover to differentiate between terrace surfaces? How?
Look around for a limestone breccia (your instructor will help you). These formed shortly after
these limestones were lithified around 400 m.y.a. After these rocks were lithified, the shallow
ocean here retreated, and the pore spaces of these rocks were emptied, allowing rain and
groundwater to percolate in and dissolve large networks of caves. Eventually, the caves
collapsed and the jumbled rocks were lithified into breccia.
These breccia rocks are found at the surface in west Texas, but at depth in the eastern parts of the
state. At depth, these breccias are petroleum reservoir rocks.
Did you find any “oddball” rocks in the arroyo, different from the others and seeming to not
belong here? How do you think they got here?
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