Geosc001LabManual_FA2022 (1)
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1 PHYSICAL GEOLOGY GEOSC 001 LAB MANUAL FALL 2022
modified from original by Prof. Roger Cuffey NW SE
2 Acknowledgments
These laboratory exercises first were developed by Professors Lisa Greer and Peter Heaney in Spring 2002, and they were amended by Professor Eliza Richardson in Spring 2005. Material updates have been provided by graduate students Ellen Herman, Sara Bier, Jamie Fulton, and Jason Sitchler. This laboratory manual was significantly revised in 2009 by graduate students Andy Wall and Tim Fischer with assistance from Jessica Yakob. Revisions in 2010 were made by Jessica Yakob and Melissa Pardi. Revisions and additions were made in 2019 by Professors Peter La Femina and Tanya Furman. The most recent revisions, additions, and subtractions were made in 2021 and 2022 by Drs. Miquela Ingalls and Jesse Reimink, and Julia Carr. The contributions of these students, as well as the constructive suggestions offered by many years of geoscience undergraduates, are gratefully acknowledged by the instructors of GEOSC 001.
3 Lab Manual GEOSC 001 –
Physical Geology Introduction Welcome to the Laboratory section of GEOSC 001
—
Physical Geology. Most of the information required for lab is given to you in this lab manual, but additional handouts may be provided to you at the beginning of your lab meetings. Also, bring a scientific calculator and your lecture textbook to each lab meeting. Your instructor will provide a Lab Schedule as part of your syllabus. In this course, the lectures and laboratories are integrated, and contribute jointly to your final grade, so we may assign readings from your lecture textbook as part of the lab activities. The field trips also have required readings from this lab manual. Readings should be done before
lab to provide you with background information. There may also be quizzes given at the beginning of lab, for which you will need to know this background information. Hopefully you will find these activities helpful in applying the information you learn from lecture in a hands-on manner. Good Luck!
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4 Table of Contents Fall 2022 Lab Week Title Page 1 –
Sept. 12-16 Discovering Plate Boundaries Through Earthquake Maps 5 2 –
Sept. 19-23 Properties of Minerals 7 3 –
Sept. 26-30 Sedimentary Processes and Sedimentary Rocks 16 4 –
Oct. 3-7 5 –
Oct. 10-14 Geologic Maps and Stratigraphy Geologic Time 26 34 6 –
Oct. 17-21 Mapping Geologic Structures 45 7 –
Oct. 24-28 The Salona Formation: Field Trip
50 8 –
Oct. 31-Nov. 4 Streamflow and Flooding of Spring Creek: Field Trip 59 9 –
Nov. 7-11 Igneous Processes 64 10 –
Nov. 14-18 Metamorphic Rocks 71 11 –
Nov. 28-Dec. 2 Porosity, Permeability, and Petroleum 79
5 GEOSCIENCE 001 FALL 2022 Name LAB 1: DISCOVERING PLATE BOUNDARIES
Section Date Plate tectonics is the governing paradigm of modern geology. It is a model, developed from extensive geological data, and is generally very successful at providing a predictive framework for earth processes. Plate tectonic processes play a crucial role in the large-scale cycling of material both on
the earth’s surface and between
the planetary surface and interior. In this lab we explore plate tectonics with the help of an activity developed by Dale Sawyer and colleagues at Rice University (
http://plateboundary.rice.edu/
). Discovering Plate Boundaries is a data rich exercise to help you discover the phenomena that are found at tectonic boundaries. The exercise is built around four global data maps: (1) Earthquake location and depth; (2) Location of recent volcanic activity; (3) Seafloor age; and (4) Topography and bathymetry. The emphasis of the activity is to focus on some of the data from which plate tectonic theory was developed. It is often difficult to separate what we “know” from what we “see”, and most of you have some understanding of plate tectonics already. However, sometimes our prior knowledge turns out to be a house of cards if we don’t understand the scientific underpinnings. By working with a rich dataset, we can construct our knowledge from something approaching first principles. A second goal of this activity is to build positive and collaborative relationships across the class. Please be respectful of one another, allowing and supporting each person to speak openly. The story of plate tectonics is one of how a community began to accept diverse viewpoints, and became much stronger and scientifically more robust as a result. Discovering Plate Boundaries (Four Map Version) You have been (or will be) assigned to one of four Scientific Specialties and to one of five Plates or Plate Groupings. The Scientific Specialties are: A.
Seismology B.
Volcanology C.
Geography D.
Geochronology The Plates or Plate Groupings are: 1.
North American Plate 2.
Pacific Plate 3.
African Plate 4.
South American Plate 5.
Eurasian Plate Each Scientific Specialty group has been provided a world map showing data relevant to locating plate boundaries and understanding plate boundary processes. Each student will be provided two Plate Boundary Maps. You will mark these as described below and turn them in at the end of the exercise.
6 Part 1: Assemble in your Scientific Specialty groups with your group's map Task 1. Look at your group's map and talk about what you see. What you look for will vary with data type. For the point data (volcanoes and earthquakes) you are looking for distribution patterns. For surface data (topography and seafloor age) you are looking for where the surface is high and where it is low, where it is old and where it is young. Work as a group. Let everyone talk about what they see. During this period concentrate on the whole world, not just your assigned plate. Task 2. Now focus your attention on the plate boundaries. Identify the nature of your data near the plate boundaries. Is it high or low, symmetric or asymmetric, missing or not missing, varying along the boundary or constant along the boundary, and etc. As a group, classify the plate boundaries based on your observations of your group's data. Restrict yourselves to about 4-
5 boundary types. At this point, do not try to explain the data; just observe! Task 3. Assign a colored pencil color to each boundary type in your classification scheme. Color your first Plate Boundary Map to locate your group's boundary types. If the data are asymmetric at a particular boundary type, devise a way of indicating that on your plate boundary map. Each person should mark the boundary types identified by the group on their own map. Each person should write down descriptions of the group's plate boundary classifications on the back of their map. These maps and descriptions will be turned in at the end of the exercise.
Part 2: Assemble in your Plate groups Task 1. As a group, discuss each Scientific Specialty data and classification scheme. Task 2. Compare the classifications of boundary type for your plate based on each type of data. Are there commonalities between the different classifications? Can your plate group come up with a new classification scheme that includes data from all four Scientific Specialties? As above, assign a color to each of your plate boundary types. If a boundary is asymmetric, be sure to devise a way to represent the asymmetry. Mark the boundaries of your plate or plate grouping using your color scheme on your second Plate Boundary Map. Make sure that you write a description of the plate boundary classes you used. The map and description should be turned in at the end of the exercise. Part 3: Whole Class Discussion (if time permits) One student from each Plate Group should make a presentation to the class. They should talk about their group's plate boundary classification scheme and how they classify the boundaries of their plate. Deliverables: To be turned in by each student: 1.
Plate Boundary Map with classified using data from your assigned scientific specialty. Descriptions of the plate boundary classifications devised by your specialty group should be on the back of the map (if in person) or on a separate page (if remote). 2.
Map with your assigned plate's boundaries classified using data from all four scientific specialties. Descriptions of the plate boundary classifications devised by your plate group should be on the back of the map.
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7 GEOSCIENCE 001 SPRING 2022
Name
LAB 2: PROPERTIES OF MINERALS
Section Date Atomic Structure and Mineralogy The structure and chemical composition of a mineral control its physical properties. By definition, each mineral has a unique structure and chemical composition. Therefore, we expect that minerals can be distinguished by their physical properties. We would also expect that different samples of the same mineral would display similar physical properties. As rocks are aggregates of minerals, as well as fragments of other rocks, geologists must have a thorough understanding of mineral properties and how they relate to atomic structure in order to accurately analyze everything from earthquakes to volcanoes to soils –
in short, everything you will be learning in the following labs and throughout this course. This lab has two main goals: 1.
Gain an understanding of how mineral properties relate to atomic structure. 2.
Learn how to identify hand samples of common rock-forming minerals. What is a mineral, and why do we care? Minerals are defined by meeting the following five criteria:
Naturally occurring
–
not synthetic/man-made
Inorganic
–
not produced by life (e.g., bones are not minerals)
Solid Crystalline
–
show an orderly arrangement of atoms in a mineral-specific crystalline structure
Set chemical composition, homogeneous
–
a predictable composition
A compound must meet all of these criteria to be considered a mineral. Rocks are not
minerals. They are physical aggregates of minerals. There are many reasons to care about minerals! Minerals are widely utilized for a variety of products. For example, rutile and muscovite are commonly used in cosmetics. Talc is used to produce talcum powder, and Borax soap is made from ulexite. Iron-rich minerals like hematite are used as iron ore and to fortify breakfast cereals. Uraninite, a uranium oxide mineral, is mined to produce nuclear fuel. Plaster is made from gypsum. We eat halite (salt - NaCl) at almost every meal. Glass is made from quartz. We use minerals containing rare earth elements in modern technologies like phones. Naturally occurring water ice is a mineral. The list could go on for a while! Geologists have even more reason to care about minerals: Rocks are aggregates of minerals,
and the specific minerals found in a rock can tell us a lot about the rock's history. We'll learn more about this in
8 later labs, but specific minerals are typically found together in rocks. Mineral assemblages reflect the chemical make-up of a rock as well as the temperature and pressure it experienced. Rocks are identified by their mineral assemblages. For example, granite contains biotite, hornblende, orthoclase, and quartz. These minerals are all unique chemicals with specific crystallization temperatures, so their presence together can tell us how hot the rock was when it was a fully molten magma. Also, since we know the compositions of these minerals, we can estimate the composition of the rock, which is the same as the magma from which it solidified. There are many more ways that minerals can help geologists understand rocks, but first we need to be able to identify the minerals. Today, we focus on different characteristics of minerals that allow geologists to identify them in the field. In subsequent labs, we will use the presence of different mineral assemblages to help us identify rocks. Cleavage Planes and Habit A crystal’s habit
is the term used for the shape of a crystal. Cleavage planes
are planes of weakness along which minerals break. The angle between two faces of a mineral after breaking is known as a cleavage angle
. Q1 Look at the ball-and-stick model of halite
(NaCl) provided. Halite is otherwise known as table salt. Examine the model and make a hypothesis about the habit and cleavage angle of halite. Q2 Now look at a mineral sample of halite. a.
Describe the crystal habit of halite. b.
Does it support or refute your hypothesis? Q3 Using the contact goniometer measure the cleavage angle of halite. a.
What is this angle? b.
Does this support or refute your hypothesis? Q4 Look at a mineral sample of calcite (CaCO
3
) and measure the cleavage angles. a.
What are the angles? b.
What would you predict the angles are at the atomic scale? Q5 Examine the sample of muscovite [KAl
2
(AlSi
3
O
10
)(OH,F,Cl)
2
], a common mineral found in igneous and metamorphic rocks. Muscovite has a special property--it breaks off in flat sheets. Observe the specimen of muscovite.
9 a) What is the cleavage angle of muscovite? Hint - think about the way muscovite breaks. b) Based on the cleavage angle you observe, make a hypothesis about the crystalline structure of muscovite. How might the atoms be arranged to result in flat sheets?
(Please include a drawing in the space below.) Halite, calcite and muscovite are all said to have perfect cleavage
. However, not all minerals have cleavage. Examine the quartz (SiO
2
) sample. Quartz does not have cleavage but displays what is known as conchoidal fracture
–
which means it breaks in smoothly curved surfaces like plate glass. Minerals with good cleavage have planes of atomic weakness. Typically, these planes contain no atoms. Q6 What can you say about the atomic structure of quartz? Mohs hardness scale Cleavage and fracture are properties of minerals used in mineral identification that fall into the class of mechanical cohesion
. The other primary tool in this class is hardness
, the ease with which a mineral is scratched. The hardness of a mineral is another property directly related to its atomic structure and chemical composition. We can determine a mineral's hardness by attempting to scratch the mineral with various objects, using the Mohs hardness scale
to help. This is a qualitative scale that can be easily used in the field. For example, if a mineral can be scratched by a US penny but scratches your fingernail, it would have a hardness between 2 and 3. If a mineral scratches a streak plate, its hardness is greater than 7. When answering these questions, providing a (small) range is acceptable. In this exercise, there are two unnamed minerals (mineral 62 and mineral 64). Keep careful note of any observations you make of these minerals, as you will need to identify them later.
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10 Mohs hardness scale: Hardness
Mineral
10 Diamond (hardest mineral on Earth) 9 Corundum (rubies and sapphires) 8 Topaz 7 Quartz 6 Orthoclase 5 Apatite (this is in your teeth!) 4 Fluorite 3 Calcite 2 Gypsum 1 Talc Hardness of common materials: Hardness
Material
~7 Ceramic streak plate 6.5 Hardened steel file 5.5 Window/bottle glass 5-6 Steel nail ~4 Wire nail ~3 US penny ~2 Fingernail Q7 Using the streak plate, nail, penny and your fingernails, estimate the hardness of your eight mineral samples, this may be a range. Make sure to try and scratch the streak plate with the mineral instead of the other way around. Record the hardness of the minerals below:
11 calcite __________ halite __________ quartz __________ muscovite __________ pyrite __________ hematite __________ orthoclase __________ magnetite __________ Q8 Based on your findings, which mineral likely has the strongest atomic bonds and which has the weakest? Strongest _________________________ Weakest _________________________ Color, luster, streak, and special properties Color and luster
Some light that strikes a mineral surface is reflected, and some is transmitted. A mineral's color is entirely dependent on the absorption of some wavelengths in the visible spectrum. A mineral's luster
is associated with the mineral's ability to transmit and reflect light. The two basic categories of luster are metallic
and non-metallic
. Within the non-metallic category there are several lusters, such as glassy (vitreous)
, earthy (dull)
, pearly
, silky
, or resinous
. When a mineral appears almost metallic but appears duller than the bright, reflective sheen of polished metal, this luster is termed sub-metallic.
Q9 Examine pyrite (FeS
2
). What is its color and luster? Q10 Now examine orthoclase (KAl
3
Si
3
O
8
), a common mineral found in granites. Describe its color and luster. Q11
Some minerals are opaque and some are transparent. Examine quartz and calcite. a.
Are they opaque or transparent? b.
Based solely on color and luster, could you easily tell these minerals apart?
12 Streak For some minerals, streak is a diagnostic property. We can use a ceramic streak plate to grind minerals into a fine powder. The powder interacts differently with light. For most minerals, the streak will be the same color as the hand sample. Fluorite, which can be a variety of bright colors, will always leave a white streak. The same is true for rhodochrosite, even though it is pink. Pyrite, which is a golden metallic color, always leaves a greenish-gray streak. Quartz has the same hardness as the streak plates, and therefore does not leave a streak. An important example of a diagnostic streak is that of the mineral hematite
. Hematite, a form of iron oxide, can have a variety of colors and lusters, ranging from rusty-red and submetallic to black and metallic. It can also take a variety of crystal habits, from botyroidal to massive to even blocky. However, regardless of the color, luster, or habit of a hematite sample, it will always
have a rusty-
brown streak. Q12 Examine the samples of hematite (Fe
2
O
3
) and magnetite (Fe
3
O
4
). What are their colors and lusters? Q13 Now, using the streak plates, describe the streaks of hematite and magnetite. Other Properties: Solubility, Double Refraction, Magnetism, and Taste Only a few minerals, like halite, are highly soluble in pure water. Most minerals do not noticeably dissolve in water, even after weeks or months. But in a weak acid, many minerals dissolve. This happens because the acid breaks the bonds that hold t
he mineral’s atoms together within the mineral’s crystal structure. Acid contains hydrogen ions, which are good at breaking chemical bonds in certain minerals, particularly carbonate minerals. These minerals release carbon dioxide gas (CO2) as they dissolve in the acid. Calcite is calcium carbonate (CaCO3). All carbonate minerals have relatively weaker bonds than minerals containing silica (SiO
-
), so they dissolve in even the weakest acids. This dissolution is commonplace in nature because ordinary rainwater generally is slightly acidic. The natural source of the acidity in rainwater is carbon dioxide gas. Carbon dioxide is a natural part of Earth’s atmosphere, and it dissolves into raindrops to form weak carbonic acid. The reaction of calcite (CaCO
3
) with hydrochloric acid (HCl) is as follows: CaCO
3
+ 2HCl --> CaCl
2
+ CO
2
+ H
2
O
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13 The calcite sample bubbles and fizzes, termed effervescence. The bubbles are CO
2
gas. There are many types of carbonate minerals, and they all effervesce in the presence of acid. Carbonate minerals can be strikingly beautiful (such as azurite, malachite, and rhodochrosite) Q14 Drop a few drops of dilute acid onto quartz. Describe what happens. Q15 Now, drop some dilute acid on calcite. What happens this time? Q16 Just for kicks, try it on three more samples and describe what you find. Q17 Calcite also has the property known as double refraction
. a.
Place the calcite crystal on this page and describe what you see. b.
Why do you think this happens? Hint: light interacts with the crystal lattice (tell us more). Q18
Some minerals are magnetic. Which of the minerals available to you is magnetic? Lastly, geologists often like to taste rocks. Please don’t do this here because somebody in a previous lab may have been dropping hydrochloric acid on all the samples. But what mineral do you think would have a very distinctive taste?
14 Identification Time Eight different samples of the minerals you just investigated have been set out for you to identify. Identify each one, using two diagnostic properties to identify the mineral (do NOT use color).
1.) Property 1: Property 2: 2.) Property 1: Property 2: 3.) Property 1: Property 2: 4.) Property 1: Property 2: 5.) Property 1: Property 2: 6.) Property 1: Property 2: 7.) Property 1: Property 2:
15 8.) Property 1: Property 2:
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16 GEOSCIENCE 001 SPRING 2022 Name LAB 3: SEDIMENTARY ROCKS Section Date AND PROCESSES
During this lab, we will investigate sedimentation processes and the results of those processes, sedimentary rocks. Pick up a handful of sand on the beach and you will find that each of the individual grains that comprise it is unique. Different sizes, shapes, colors, densities, etc. all act as a sedimentary “fingerprint” that can be used to identify where grains came from (
provenance
), how they were transported (
sorting, roundness, sphericity
), and what chemical processes (
mineralogy, cementation
) they experienced during transport and deposition. In general, grain sizes decrease the longer they are subjected to sedimentary processes, making identification of the above characteristics more difficult. However, careful examination using a 10x hand lens (in the field) or a stereo microscope (in the lab) can improve accuracy of mineral identifications of most grains. For more accurate mineralogical studies of sedimentary grains, grain mounts or rock thin sections are studied using a petrographic microscope to identify mineralogy from optical characteristics of light transmitted through the grains. We’ll do this in upcoming labs!
After assessing the variety of minerals comprising a sample, the relative abundance of each is estimated. Qualitatively
, this is done using charts and relative proportions (attached). Quantitatively
, this is done by manually sorting each mineral type in unconsolidated sediments, or by conducting "point counts" across a thin section of lithified samples. Once this information is obtained, it is possible to identify the sedimentary rock. I. Determining Grain Size Distribution in a Sediment Take a close look at the two sediment samples provided. We will look at the sorting of these samples, not to be confused with the grading of a sample. In order to make the best use of everyone’s time, we have sieved the samples and share that data with you here. Q1 Would you characterize these samples as well sorted or poorly sorted? Sample A: Sample B: Estimate
the percentage of each the following grain sizes by mass in samples A and B. Sample A Sample B Pebbles Coarse Sand Medium Sand Fine Sand Silt
17 Calculate each sample’s total mass.
Sample Container and Sample Mass Mass of Container Total Mass of Sample A 963.2 g 130.1 g B 598.1 g 91.9 g We are going to calculate how much of each grain size makes up your sediment sample. Sieves are used to sort grains by size in sediment samples. Sieve sizes are provided below. #5 Five holes per inch Each hole is 0.508 cm captures pebbles #10 Ten holes per inch Each hole is 0.254 cm captures coarse sand #35 Thirty-five holes per inch Each hole is 0.0726 cm captures medium sand #60 Sixty holes per inch Each hole is 0.0423 cm captures fine sand Base captures silt Instructions for sieving: 1.
Nest the sieves by increasing sieve #, the largest # nests in the base. Pour your sample into the top sieve and place the cover on top of the nested set of sieves. 2.
To sieve a sample, gently shake the whole stack of sieves. One person should shake the sieve while the other taps the top of the sieve for approximately 1 to 2 minutes. Once you have shaken the sieves long enough to adequately separate the sediment, separate the sieves and place each on the table. 3.
Measure the mass of the contents in each sieve and the base using the container provided. Remember to subtract the mass of the container from each measurement. When youa r e finished, return sample A to its original container. It’s okay to remix the sample. Repeat the process with sample B. Sample Mass in #5 Sieve (Pebbles) Mass in #10 Sieve (Coarse Sand) Mass in #35 Sieve (Medium Sand) Mass in #60 Sieve (Fine Sand) Mass in Base (Silt) Total Sieved Mass (sum) A B Calculate the mass percent of each fraction of the samples by dividing the mass in the sieve by the Total Sieved Mass. Enter your results below.
18 Sample Weight % in #5 Sieve (Pebbles) Weight % in #10 Sieve (Coarse Sand) Weight % in #35 Sieve (Medium Sand) Weight % in #60 Sieve (Fine Sand) Weight % in Base (Silt) A B Q3 Were you surprised by any of these results? How did they compare with your estimates on the first page of this lab? Q4 Do you still agree with your assessment of the samples in Q1
? If not, explain. Q5 Which sample, A or B, do you think might have been deposited
in the highest energy environment? Explain your thinking. Q6 Why aren’t the sediments completely sorted (all fine sand or all gravel for example)? Why is there usually a mixture of sizes? Q7 You’ve looked at sorting in sediments. The same ideas can be applied to sedimentary rocks. Rank sedimentary rock samples 1 through 4 from well sorted to poorly sorted. well sorted poorly sorted
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19 II. Identifying Sedimentary Rocks and Environments
You’ve now taken a look at sediments before they become rocks. The above exer
cises should help you identify sediments that have become rocks. Use the Sedimentary Rock Identification section below to help. In the final two columns, include any observations you make about the energy of the environment or formation mechanisms, and make an educated guess at the depositional environment. Refer to some of the figures at the end of this lab. Sample Clastic or Chemical Grain Roundness (if clastic and visible) Grain Size (clay, sand, gravel) Other Characteristics Rock Name Observations about energy and structures Depositional environment interpretation 1 2 3 4
20 5 6 7 Q8 Samples 2 and 5 are both sandstones. Sample 2 comes from the Tuscarora Formation and Sample 5 comes from the Bald Eagle Formation. What is the difference between these two samples? Which one is made of sediments that have traveled further from their source?
21 III. Sedimentary Structures and Depositional Environments Three samples have been provided for you to use in this exercise. Please don’t take these samples back to your seat. Q9
This sample shows a sedimentary structure that is quite useful to field geologists. a.
Name the structure (using your textbook if necessary). b.
Hypothesize how field geologists use this structure. Hint: Structures like this only form on the surface of a sedimentary layer. Q10
This sample shows a different sedimentary structure that is quite useful to field geologists. a.
What type of structure does this sample show? b.
Which way (away from or toward the x) did water flow over the sediment that became this sample? c.
Why would this sample be useful to geologists? (There are a few reasons.) Q11
This sample shows yet another sedimentary structure that is quite useful to field geologists. a.
Name this rock. Begin with the sedimentary structures and then the sedimentary rock name. For example: rippled shale __________ b.
Note the sedimentary structures in this rock. Describe an environment in which this rock might have formed.
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22 SEDIMENTARY ROCK IDENTIFICATION Clastic vs. Chemical Clastic sedimentary rocks are rocks formed by deposition of sediment and compaction and lithification (rock forming). Chemical sedimentary rocks are formed by chemical processes, such as evaporation, and precipitation. Clastic Grain Size - the size of the grains in the rocks. Coarse - greater than 2 mm. in diameter. Pebbles, cobbles, boulders. Sand - 2 mm. to 1/16 mm. in diameter. Sand Silt - 1/16 mm. to 1/256 mm. in diameter. Dust, gritty. Clay - less than 1/256 mm. in diameter. Mud or modeling clay. The best way to differentiate between silt and clay clast size is to chew a small piece of the rock. If the rock feels gritty, it is silt, if it feels mushy, it is clay. Cement - the material holding (cementing) the grains together. Usually silicon or carbonate. Can be tested by dropping a small amount of dilute HCl on the rock. Sorting - the rock may be all one grain size (well sorted) or more than one grain size (poorly sorted). Mineral Identification Quartz - hardness 7, usually transmits light, may be grayish, may look glassy. Potassium Feldspar (Orthoclase) - hardness 5.5 –
6.5, pink to light gray, two good cleavages at right angles, opaque, rectangular minerals with good cleavage. Plagioclase - hardness 5.5 –
6.5, gray, two good cleavages at right angles, striations on one cleavage, opaque, rectangular minerals with good cleavage and striations. Clay - aphanitic, soft, usually gray, but can be red or green, looks muddy. Calcite - hardness 3, fizzes in acid. Dolomite –
hardness 3, fizzes in acid when it is powdered. To powder the mineral, scratch it with a knife, steel nail, or other metal object.
SEDIMENTARY ROCK IDENTIFICATION (CONT.)
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23
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24 Clastic Sedimentary Rocks (particles or granular texture) Texture Rock Identifying Characteristic Coarse Conglomerate Contains rock fragments (rounded particles) Coarse Breccia Contains rock fragments (angular particles) Sand Sandstone Mostly quartz Sand Arkose Usually red to pink in color, noticeable amount of feldspar Sand Graywacke Poorly sorted, lots of clay, often dark colored Silt Siltstone Foliated (layered in sheets) or massive Clay Shale Soft, foliated, may be red, black, green, gray, tan, depending on content
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25 Chemical Sedimentary Rocks (interlocking or jigsaw puzzle texture)
Mineralogy Rock Identifying Characteristic Calcite Limestone Hardness 3. Calcite fizzes in acid, frequently has fossils. Dolomite Dolostone Hardness 3. Dolomite fizzes when you powder it by scratching it with a knife. Usually does not have fossils. Halite Rock Salt Hardness 2. Tastes salty. Gypsum Gypsum Hardness 2. Doesn’t taste
salty. Silica Chert, Flint Hardness 7. Luster is glassy to waxy. Shows conchoidal fracture.
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26 GEOSCIENCE 001 SPRING 2022 Name LAB 4: GETTING TO KNOW THE Section Date NITTANY VALLEY
(AND TEXAS) A big part of geoscience is the presentation of information about the characteristics of the Earth’s surface: elevation, surficial and underlying geologic materials, hydrologic features, and geophysical attributes such as the gravity and magnetic fields. Because of this, it is important to develop a few basic map-reading skills —
these will serve you well through the rest of the semester. But first, we need to review a few basic things about the whole Earth, this quasi-spherical planet on which we live. The Shape of the Earth
The Earth is, of course, roughly a sphere. The average radius is 6371 km, but it differs from 6356 km at the poles to 6378 km along the equator. This means that the circumference is roughly 40,000 km and the surface area is 510,000,000 km
2
. Humans have superimposed on this sphere a set of latitude and longitude lines to help describe different places on the surface. Latitude lines run east-west and go from 0° at the equator to 90°N and 90°S at the poles; longitude lines all pass through the two poles and go from 0° (the prime meridian, passing through Greenwich, England) to 180° E and 180°W (alternatively, longitude runs from 0° to 360° in a counterclockwise fashion looking down from the north pole). Both latitude and longitude are subdivided into units of minutes (60’ per degree) and seconds (60” per minute). This spherical surface is depicted best in the form of a globe, but the difficulties of printing onto a sphere have led people to develop a range of different strategies for projecting parts of this sphere onto planar sheets of paper. Some of these projections preserve (i.e., do not distort) area, others preserve angles, but none preserve both at the same time; a full rundown on various map projections can be found at the US Geological survey web page (google - map projections USGS). The highest point is Mt. Everest, at 8850 m and the lowest point is in the Marianas Trench at -10,924 m. This total range of almost 20 km over the circumference (40,000 km) of the Earth, makes the Earth comparatively smoother than an orange, so even though on a local, human scale, the topography can seem impressive, on a global scale it is pretty minor. Topography of the continents is also called hypsography. The reasons why the relief is so minimal have a lot to do with a very active plate tectonic and hydrologic cycle on Earth, with rain and glaciers constantly wearing away at the high spots. Looking more closely at global topography, a rather startling fact appears: topography on our planet is bimodal —
there are two main peaks rather than just one on a histogram (next page).
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27 Why is this distribution of topography bimodal? To most geoscientists, this suggests that there are two fundamentally different types of crust on our planet. This in turn suggests two main processes for forming crust. We have discussed the different types of crust and their formation in lecture. Maps in the Geosciences The traditional tools geoscientists use are topographic maps and geologic maps. Topographic maps depict the form of the earth’s surface via a set of contour l
ines that connect points of equal elevation. Topographic (“topo”) maps also show lakes, rivers, springs, roads, trails, buildings, and many other cultural features; many of them also indicate forested regions. Geologic maps show the different types and ages of rocks that are either exposed at the surface or lie beneath a veneer of soil at the surface; this information usually is drawn over the top of a topographic map, so they depict a tremendous amount of information. Geologic maps also show information about geologic structures; faults, folds, and the orientation of planar features in the rocks. To fully understand geologic maps, one must first understand topographic maps. Geophysical maps overlay information about geophysical characteristics such as the strength of the magnetic or gravity fields. Hazard maps show the potential for earthquakes, volcanic processes, landslides, or flooding damage on top of normal topographic maps. In recent years, observations from a vast range of satellites have become available to help us understand the nature and changes to the Earth’s surface. The satellite sensors can provide information about surface temperature, vegetative activity, and mineralogical content of rocks and soil at the surface, among other observations. The map below shows satellite imagery of the State College area (taken from Google Earth). This image was made during the summer, and dark green colors show trees in areas of higher elevation while light green areas include farm fields and lawns at lower elevation. The shapes of the ridges reflect folding of passive margin sediments (limestone, sandstone and shale) during formation of the Appalachian mountains.
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28 Understanding and Reading Topographic Maps
Now, on to the topographic maps for some analysis. Use the topographic map provided as a separate download to answer the following questions. 1. What are the latitude, longitude and elevation of the Deike Building? Give your answer to the nearest 10”. Latitude , Longitude , Elevation ___________ 2. When I was a kid, someone told me that if you dug straight down, you’d come out in China. Was this right? If you dug a hole straight down from State College, where would you come out on the other side? (This will require consulting a globe or some world maps, or google earth.)
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29 3. What is the highest elevation point in the State College quadrangle? Describe the feature (i.e., the shape, steepness of the contours) and state its distance and azimuth (compass direction) from Deike building. 4. What is the stream gradient of Spring Creek from Oak Hall to just upstream of Houserville? Use a piece of string to measure the path length of the stream between the places where contour lines cross the stream. Express this as an angle (this will require some basic trigonometry —
remember that the tangent of an angle is equal to the length of the opposite side (elevation change) divided by the length of the adjacent side (distance)). 5. What is the stream gradient of Roaring Run from its source to where it crosses the 1200 foot contour south of Shingletown? Express this as an angle.
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30 STRATIGRAPHY OF ROCKS IN TEXAS Now we’ll switch gears and look at a different type of map also
common in geoscience. A geologic map is a map on which is recorded geologic information about the rocks at or near the earth's surface directly beneath the soil cover. (Rocks at the surface without any soil cover are called exposures or outcrops.) Information typically portrayed includes: 1.) Distribution of rocks by age (Periods or Epochs) or distribution of rocks by rock type and other physical features (Formations). Formations and the age of rocks are both generally shown by different colors and symbols on the map. 2.) Occurrence of structural features like folds and faults. A good geologic map (with cross sections) is essential to any additional work, such as petroleum and mineral exploration, groundwater studies, or the interpretation of the geologic history of an area. Answer the following questions using the attached 8 1/2 by 11 Geology of Texas map, the cross section, and the stratigraphic section for South Texas (last two pages). Note that for the chart showing formation names, the terms “system” and “series” are equivalent to the terms “era” and “epoch” respectively. 1.) What Formation (by name) is found around Corpus Christi, and in fact around most of the Texas coastal zone? ____________________________ 2.) What is its age? (Give the geologic epoch) 3.) In the Mathis area the flat, clay-rich Pleistocene coastal plain ends, and older, Tertiary-aged Goliad Formation sandstones can be seen forming hills and in sand quarries. The white sand of the Goliad is very distinctive here and contains fossil horse teeth. What is the age of the Goliad Formation as shown on the geologic map? (Give the Epoch.)
__________________________ 4.) The Catahoula Formation is a tuffaceous sandstone. The abundant tuff fragments were blown in from extensive volcanic eruptions hundreds of miles to the west and northwest, in the Trans-Pecos region. The Catahoula can be seen in outcrops along I-37 (west side of the highway in particular) about 60 miles from Corpus Christi. What is the age of the Catahoula Formation? (Give the Epoch.)
__________________________ 5.) Near Pleasanton, south of San Antonio, snail and clam fossils can be found in the Cook Mountain Formation of the Claiborne Group. What is the age of the Cook Mountain Formation? (Give the Epoch.)
__________________________
6.) What is the age (
Period
)
of the rocks portrayed in green on the geologic map, and with a 'K' symbol? __________________ (Rocks of this age are shown in green on most geologic maps made in the United States. Colors are standardized for rocks of each of the Geologic Periods.) The southeast edge of the area of outcrop of these rocks passes more or less through San Antonio and Austin and marks the
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31 position of both the Late Cretaceous Gulf of Mexico shoreline and the buried, tightly folded Paleozoic rocks of the Ouachita Mountains. The Balcones Fault zone, activated about 10 million years ago, follows this same trend. 7.) Are the Balcones faults (use cross-section) normal or reverse? (Pick one)
_____________________ 8.) If you drilled a well on the border between Guadalupe and Gonzales County, approximately how deep would it have to go to hit rocks of the buried Ouachita Fold Belt? ________________ Feet 9.) All of the dinosaur footprints preserved in Texas rocks are found in the Glen Rose Formation of the Trinity Group. Give the age of the Glen Rose in the space below: (
Give the Period,
and whether the rocks formed in the Early (first half) or Late (second half) part of the Period.)
___________________________ 10.) Precambrian rocks are the oldest in Texas, dating back earlier than the dinosaurs to the formation of Earth’s first continents. What two geologic processes occurred to expose these rocks as they are currently? 11.) _____________________________ 12.) _____________________________ What kind of rocks are they (rock type)
? (Look at the cross section) 13.) __________________ 14.) __________________ 15.) As you drive from Corpus Christi to San Antonio or Austin, the rocks get progressively ____________________ in age. (
older or younger)
16.) How can you explain this age progression?
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32 South Texas Stratigraphic Section NN
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33
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34 GEOSCIENCE 001 SPRING 2022 Name LAB 5: GEOLOGIC TIME Section Date This lab is modified from “Geology from Experience” by E. Kirsten Peters and Larry E. Davis, from “Investigating Earth” by C.
Gil Wiswall and Charles H. Fletcher, and by the geologic history lab developed by Michael Harris of the Department of Geology at James Madison University. Introduction Large sequences of layered sedimentary rocks can represent millions of years of elapsed time. Each distinct layer or bed in a sequence is called STRATUM, and multiple layers are collectively called STRATA. The study of sequences of strata is called STRATIGRAPHY. A sequence of strata may also be referred to as a STRATIGRAPHIC SECTION. Extrusive igneous rocks such as lava flows and ash falls may also form as beds and can occur as discrete layers in a sequence of sedimentary rocks or they may cut across pre-existing layers of rock. All sequences of rock world-wide are sometimes collectively referred to as the ROCK RECORD. Each rock type and geologic structure in a sequence represents a different geologic event. As geologists we want to understand the history of the Earth and the rate of geologic processes. To do this, we must be able to date stratigraphic sections and the rock record. This lab provides exercises to investigate the two types of dating that geologists use, RELATIVE and NUMERICAL or ABSOLUTE DATING. Relative Dating
RELATIVE DATING refers to the placing of events in the order in which they occurred without any understanding of the actual time or absolute time during which any one event occurred. In other words, we can discuss that a certain event happened first, or previous to the next event, or another event couldn’t have occurred until other events had. A set of very simple principles in conjunction with careful observation allows the determination of the relative order of geologic events represented by the rocks in an exposed stratigraphic section. Principles of Geology An understanding of stratigraphy begins by recognizing certain principles. Natural processes such as erosion, deposition, and plate tectonics, and the natural laws of gravity and isostasy that have produced the current features of the Earth, are thought to have operated in the same way in the distant past as they do now. This idea is known as the PRINCIPLE OF UNIFORMITARIANISM and was first stated by James Hutton in the 18
th
century. Given an understanding of uniformitarianism, the relative timing of geologic events can be determined by applying other simple ideas, collectively known as the PRINCIPLES OF GEOLOGY which include: 1)
THE PRINCIPLE OF ORIGINAL HORIZONTALITY –
sediments that are deposited or precipitated on the Earth’s surface are done so in mostly horizontal layers. Thus, if the rocks are noted to be tilted, folded, or metamorphosed, then these events must have followed deposition and lithification;
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35 2)
THE PRINCIPLE OF SUPERPOSITION –
in a series of layered rocks that have accumulated on the Earth’s surface, the oldest rocks are at the bottom of the sequence and the youngest are at the top; 3)
THE PRINCIPLE OF CROSS-CUTTING RELATIONSHIPS –
any geologic feature that is crosscut or modified by another feature must be the older unit, i.e.
, the crosscutting feature is the younger feature, it needed something to already be there for it to cut across. THINGS TO REMEMBER –
each of the rock types, sedimentary, igneous, or metamorphic, represent a unique geologic event, which is referred to using the appropriate terminology that reflects the process(es) that formed it, i.e.;
o
Sedimentary
rocks are deposited, so we refer to the DEPOSITION of a sedimentary rock (
e.g.,
deposition of shale or sandstone) o
Plutonic
rocks are intruded, so we refer to the INTRUSION of a plutonic rock (
e.g.,
intrusion of granite or mafic dike) o
Volcanic
rocks are erupted onto the Earth’s surface, so we refer to the ERUPTION of a volcanic rock (
e.g.,
eruption of basalt or rhyolite) o
Metamorphic
rocks form through the METAMORPHISM of a protolith. The protolith, not the metamorphic rock, was deposited, intruded, or extruded. We report the event that formed the protolith, AND THEN the metamorphic event. The metamorphism itself is considered a separate event.
Deformation
and erosion of rocks are also geologic events. Some but not all of the rock units may be folded or faulted, and the discussion of the relative ages of these deformation events follows the same as if talking about the rock units. Erosion events are also discussed as events relative to other events. Unconformities Unconformities are (usually) irregular contacts between strata in a stratigraphic sequence produced during periods of erosion or non-deposition. These contacts, thin boundaries between layers of rock, represent episodes of missing information, where there are no recorded rock units. Unconformities are labeled according to the nature of the strata above and below the unconformity. There are three types: 1)
DISCONFORMITY –
a boundary between parallel, undeformed layers of rock, usually formed due to erosion or non-deposition; 2)
NONCONFORMITY –
a boundary between layers of sedimentary rock overlying igneous or metamorphic rocks. This relationship usually indicates that the underlying igneous or metamorphic rocks were exposed before being buried and deposited upon; 3)
ANGULAR UNCONFORMITY –
a boundary between layers of sedimentary rock overlying tilted or folded beds. This relationship suggests that the older rocks were deformed, exposed, and then deposited upon.
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36
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37 FIGURE 2
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38 I. RELATIVE DATING
Use the figures to determine the relative order of geologic events. List the events and corresponding evidence for each event. Don’t skip any steps and remember that the oldest event should be listed at the bottom of the table (i.e., start with #1). USE FIGURE 1 FOR THIS PROBLEM Event Description Evidence 9 8 7 6 5 4 3 2 1 USE FIGURE 2 FOR THIS PROBLEM Event Description Evidence 9 8 7 6 5
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39 4 3 2 1 1.
What principle of relative dating did you use to determine whether Sandstone B pre- or postdated Shale Q in Figure 2? 2.
Draw a series of 8 cross sections that represent the history described in the table below (USE A PENCIL). Your 8
th
box should record the complete history described below. (Each box builds on the previous box) Event Description (youngest) 8 The glacier melts, erosion occurs, and trees grow. 7 A glacier deposits glacial till across the whole area. 6 Sea level drops during the Ice Age, exposing the rocks at the surface. 5 Shale is deposited. 4 A shallow sea covers the area. Sandstone is deposited. 3 The granite is uplifted and exposed at the surface by erosion. 2 Magma intrudes the rocks and cools deep underground to form granite. (oldest) 1 A stratigraphic succession of sandstones and shales exists within the crust.
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40 1 2 3
2 4
2 5
2 6
2 7
2 8
2
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41 Absolute Dating: Half-life of 40
K Don’t use the decay equation –
this exercise is to use the graph! Potassium 40 is a naturally radioactive element that decays to 40
Ar with a half-life of just over 100 million years (1.192 x 10
8
years). Potassium is an abundant element in the crust and is found in a wide range of igneous and metamorphic rocks. Consequently, this decay series is important for dating a wide variety of geologic events. 1. Column I in Table 2 indicates the number of half-lives that have passed since the geologic clock started. Calculate the time represented for each half-life interval. Enter your result in column II. 2. Assume that a biotite crystal originally contained 3000 atoms of 40
K (N
o
= 3000). Determine the number of 40
K atoms remaining after each half-life interval. Enter your results in column III. 3. Calculate the number of daughter atoms after each half-life interval. Enter the results in column IV. 4. For each half-life interval, add the number of 40
K atoms in column III to the number of 40
Ar atoms in column IV. Enter your answer (N
o
) in column V. 5. Plot your results in the graph provided below (
plot atoms of 40
K on the y-axis
). 6. The curve you generated is an exponential decay curve, which can be used to estimate the age of a rock or mineral that originally contained 3000 atoms of 40
K. a. If a mineral now contains 500 40
K atoms, how old is it? b. What is its age if it now contains 2750 40
Ar atoms? 7. It is possible to date radiometrically rocks and minerals that contain naturally radioactive elements. They are the basis for quantifying the timing and duration of geologic events and have produced an entire new subdiscipline of geology. a.
What quantities can we measure? b.
What quantity must we assume was initially zero?
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42 Table 2. Calculating radiometric decay Half-lives Time (x 10
8
year) (t) Number 40
K atoms (N) Number 40
Ar atoms (D) D + N (No) I II III IV V 1 2 3 4 5 6 7 8 9 10
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43 III. COMBINING RELATIVE AND ABSOLUTE DATING TECHNIQUES First, determine the ages of the following units in Figure 3: Granodiorite, Granite, and Basalt. ROCK ISOTOPE HALF-LIFE FRACTION OF ELAPSED HALF-
LIVES AGE Granodiorite 238U/206Pb 4,500,000,000 0.09 Granite 235U/207Pb 710,000,000 0.46 Basalt 235U/207Pb 710,000,000 0.36 Use these dates and relative dating to answer the following questions: 1
. a) How old is the unconformity underneath the sandy shale (this should be a range)? b) Approximately how long did this period of erosion and non-deposition last? 2
. Using the radiometric ages of the intrusive rocks in the diagram, how long did it take for conglomerate, shale, and sandstone below the unconformity to be deposited? 3
. What sort of depositional environment existed immediately after the basalt flow?
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44 Figure 3
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45 GEOSCIENCE 001 FALL 2022 Name ________________________ LAB 6: MAPPING GEOLOGIC STRUCTURES In this lab, you will practice creating a geologic map based on “field” observations at discrete points. When you are in the field doing research (or at field camp), you rely on observations of rocks exposed at the Earth’s surface (outcrop exposures), as o
pposed to covered in plants and dirt. You must extrapolate your observations at these discrete outcrops to the surrounding area/region/basin. In this lab, you will make observations of a set of seven rocks and identify in them in the table in the assignment. You will then figure out where these different geologic units outcrop on the map by matching your observations, the lists of localities associated with each sample (1-7), and locations on the map. You will then draw in contacts between formations on your map and color, and follow the rest of the instructions below. You will then interpret the geologic history of the region based on your cross section through your map area. Method: 1.
Complete your rock identifications first using the table on page 3. Hint: There is only one metamorphic rock.
Fill in the Rock Unit
column, Symbol
column, and Color column. Choose simple symbols to identify (a capital letter works well) and assign seven colors that are easily distinguished. 2.
Add rock unit symbols as appropriate to the map based on the field site data provided in the table on page 3 (use pencil). 3.
Read through “things to keep in mind,” “preliminary dating results,” and “preliminary observatio
ns.”
4.
Interpret (draw) contacts (boundaries) between rock units on the map (use pencil). Draw contacts as straight lines (use a ruler) between all rock units EXCEPT sample #4. 5.
Color the rock units on the map as per your Field Site Data table on page 3. Hint: Shade in the units lightly so that you can still see your lines and notations.
6.
Add strikes and dips as indicated in the preliminary observations (use pencil). Write them in ink when you are confident of their orientation and placement. 7.
Draw a cross-sect
ion using the fold over technique. Don’t forget to color and add symbols to units. Identify any fault types and label slip direction with arrows. 8.
Develop a geologic history in the table provided on page 2 including events (for example deposition or deformation) and evidence (for example cross-cutting or superposition). 9.
Complete the stratigraphic key to the left of your geologic history, include rock unit names and symbols. 10.
Complete the interpretation section at the bottom of page 3. Things to keep in mind: •
The field site is eroded flat, there are no noticeable topographic changes. •
Sedimentary rocks generally maintain the same thickness throughout. •
We will assume dip angles remain constant along each contact. Preliminary dating results: •
The mafic igneous rock is the youngest rock and event in the field site. •
The metamorphic rock is older than the sedimentary rocks.
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46 Preliminary observations: •
Sedimentary rocks form a syncline and dip at 45° toward the hinge of the syncline. •
The metamorphic rock lies on top of other rock units at a low angle (<20°). Remnants of the metamorphic rock are even found on top of rock unit #4, although they are not large enough to include on the map. Field Site Data (Rock Identification):
Sample Rock Unit Symbol Color Locality
1 1, 5, 6, 24 2 9, 11, 17, 18, 19, 27, 28 3 2, 13, 25, 4, 22, 31 4 7, 8, 15, 16 5 10, 20, 30 6 3, 14, 26, 12, 21, 29 7 23, 32 Sites Dip/Dip direction 1,5,6,24 20°/NW 2,3,9,14,13,17,25,26,26 45°/SE
4,11,12,18,19,21,22,23,28,29,31,32 45°/NW
7,8,10,15,16,20,30 Not visible
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47 A
A’
1
2
3
6
5
7
9
8
11
10
4
12
14
13
15
16
17
18
19
20
22
21
24
23
26
25
29
28
27
30
31
32
youngest
oldest
Rock N
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48 Geologic History Event Evidence 1 Limestone deposition Principle of superposition 2 3 4 5 6 7 8
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49 Cross Section: Interpretation: Provide a brief interpretation of how the environment was changing during deposition of the sedimentary rock units. A
A’
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50 GEOSCIENCE 001 SPRING 2022 Name Section_________Date_________________
LAB 7: THE ORDOVICIAN SALONA FORMATION TRANSITION FROM SHALLOW-WATER CARBONATES TO SILICICLASTICS Materials
: Rock hammers, compasses, meter sticks, hand lenses, acid bottles, field notebooks. Site
: We’ll be looking at the road cut along the east side of Hwy 322 bypass from two locations (Figure 1a). The first stop is along the bike path on the southwest side of 322. The second stop is at the outcrop. This is a busy road, so please always stay well off the shoulder and keep your wits about you. The exposure itself is very steep and you should avoid climbing up onto the face —
you can see plenty from the ground level. Background
: You should refer to the background material from lecture, the textbook, and the lab “
Sedimentary Processes and Sedimentary Rocks
” that discusses the kinds of things we generally want to know about sedimentary rocks. The Salona Formation represents the lower section (older) of the Upper Ordovician, about 458 to 450 Ma (Figures 1b & 2). The Salona Formation is the last vestige of the Great American Carbonate Bank, a shallow carbonate bank that existed during Ordovician time. A modern analog is the Great Bahama Bank. The lower section of the Salona is comprised of thick, shallow water carbonates with bioturbation. This grades into the middle section comprised of medium thickness carbonate muds with abundant fossils. The upper section is a mix of carbonate muds and siliciclastics (i.e., shales and siltstones) with occasional sedimentary structures (e.g., ripple marks and cross-bedding). This transition from carbonate dominated to a mix of carbonates and siliciclastics represents a change in water depth to deeper water, and a change in the tectonic setting where mountains to the east were weathering, eroding and depositing sediment to the west and on top of the carbonates. An additional piece of background here concerns a few unusual layers within this sequence of strata; layers composed of altered volcanic ash (now in the form of bentonite, a clay mineral). These ashes occur over vast areas (Figure 3a & b) and provide all kinds of useful information; they can be dated using radiometric techniques to tell us the age of the sedimentary rocks, and they allow precise correlations of strata across vast areas. This latter piece of information allows us to put together a precise regional (and larger) view of the paleogeography (the spatial relationships of different surface environments). These ashes also represent colossal eruptions that could potentially have a noticeable impact on the biota of the area where the Salona Formation was being deposited. The Deicke (449.8 ±2.3 Ma) and Millbrig (448.0 ±2.0 Ma) bentonites represent very large explosive eruptions with volumes exceeding 1200 km
3
(Min et al., 2001), as large as eruptions from Yellowstone caldera. These bentonites are separated by several meters of carbonates and have slightly different chemical compositions. A similar in age bentonite found in Sweden, the Kinnekulle bentonite, was once thought to be similar to the Millbrig; however, the Kinnekulle is slightly older (454.8 ±2.0 Ma) and compositionally different from the Millbrig.
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51 The presence of these ashes also suggests a change in the regional tectonics, that is a change in the type of plate boundary along the eastern edge of the North American craton or Laurentia (Figure 4). The ashes in question here are similar in composition to those erupted from subduction-related volcanoes today. The patterns of contour lines of ash thickness (called isopachs) shown in Figures 2a and 2b imply something about the proximity of these two land masses where the ashes are found today. Ash dispersal patterns typically form elongate ellipses, with the volcano located on the long axis, near one end of the ellipse (see the example from New Zealand). The direction of the long axis is a function of the wind direction during the eruption and these two continents need to be positioned so that the thickness patterns make sense —
so that they could “point to” the same volcanic source, with neither too far away from the probable source. Goals
: The goals of this lab are: 1) describe the lithologies that make up the Salona Formation; 2) study their arrangement stratigraphically; and 3) look for (and describe/document) clues that relate to the depositional environment. Be sure to get your eyes "tuned" to seeing the fossils in these rocks. One thing to consider here is what the vertical succession of lithologies might mean —
what might have caused the changes you observe? Are there cycles of lithologies that repeat over time? Are there noticeable changes after (above) the biggest ash layer? How does the orientation of the stratigraphy relate to the tectonic setting? Stop 1:
Overview of the Salona Fm and the Mount Nittany syncline. Looking northeast across 322, one can see the Salona FM outcropping. In the distance is Mount Nittany, which is comprised of the younger Reedsville and Bald Eagle Formations. You are standing within the Mount Nittany syncline (see cover image of your lab book). Listen to your TA describe the outcrop and from this location explore the Salona Fm: What to turn in for Stop 1
: 1)
How does the bedding thickness change from the older units to your left to the units to your right? 2)
Are there cycles of lithologies that repeat over time? 3)
Is there a change in color of the sedimentary rocks? 4)
Are the strata dipping or are they horizontal? 5)
How does the orientation of the lithologies fit with them being within the Mount Nittany syncline?
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52 Draw an annotated sketch of the outcrop. The sketch should include: •
The outcrop of the Salona Formation along the road, including: o
Beds drawn to show orientation and thickness o
Identify the oldest and youngest beds o
Indicate the approximate locations where facies change •
Site orientation compass directions •
Approximate scale •
Mount Nittany
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53 Stop 2: At the outcrop. First, orient yourself with your sketch from Stop 1. Follow your TA instructions on navigating around the outcrop and make observations of the rocks in the outcrop. Look at the outcrop both up close (at a scale where you can see individual grains in the rock) and from a short distance away (where you can put individual beds in context with those above and below). Make sure to move around the outcrop to identify how the units are changing over the sequence. What to turn in for Stop 2
: 1. Describe the different facies in this outcrop. Each facies description should include rock types, composition, typical bedding thicknesses, fossils, bedding structures (e.g., ripple marks, cross-bedding), contact types (e.g., sharp, gradational, flat, undulatory), approximate grain or particle sizes (clay, silt, fine sand, medium sand, coarse sand); please write ~1 paragraph per facies. 2.
Interpret a depositional environment for each facies. What is the water depth? What is the energy level of the environment? 3.
Write a few paragraphs summarizing your observations and interpretations. You will cover the depositional and tectonic history across the entire stratigraphy sequence. Here are some questions to guide you: How was the water depth changing over time? Where is the sediment coming from? How were the tectonic plates moving during this time period? Where did the ash come from? You can also refer to any of the figures in the lab guide. Reference: Min, K., Renne, P.R., Huff, W.D., (2001). 40
Ar/
39
Ar dating of Ordovician K-bentonites in Laurentia and Baltoscandia, Earth & Planetary Science Letters
, 185, 121-134.
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54 Figure 1. a) Topographic map of the field site. b) Regional geology overlain on topography showing the Nittany syncline. Note the field site is located in the Salona formation.
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55 Figure 2. Stratigraphic column of the upper Ordovician of central Pennsylvania. The Nealmont and Salona Formations comprise the outcrop along the 322 Bypass.
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56 Figure 3. A) Isopach map of the Deicke bentonite. B) Isopach map of the Millbrig bentonite. Contour values are in cm.
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57 Figure 4. Paleogeography of the North American craton (Laurentia) during the Ordovician period. Note Laurentia was straddling the equator during this time period and was subducting towards the southeast beneath an active volcanic arc. This volcanic arc was the source of the Deicke, Millbrig and Kinnekulle bentonite layers.
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58 Figure 5.
Interpreted cross section of the tectonic environment during the Ordovician showing the subduction of Laurentia beneath the volcanic arc.
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59 GEOSCIENCE 001 SPRING 2022 Name LAB 8: STREAMFLOW AND Section Date FLOODING OF SPRING CREEK
Materials
: notebooks, calculators, meter sticks, tape measures, stopwatches, a couple of oranges, clothing appropriate for working in a stream on a cold day.
In this lab, we’re going to study the stream flow and the size of boulders in Spring Creek near Houserville, just a couple of miles NE of campus, with the goal of understanding some things about stream behavior and the history of flooding. We will divide ourselves into groups of 4; 2 people will measure the channel cross-section, the others will measure the velocity and measure the largest clast size in your section of the river. For this lab, you need to come prepared to get a bit wet —
there is no other way to study streams! We have some waders, but you should nevertheless bring old shoes or sandals that can get wet and wear some pants that can be rolled up so that you can wade out into the stream. Bring plenty of warm clothing for the parts of you that are not wet. Measuring Discharge Part of this lab will involve using data collected at a US Geological Survey stream monitoring gauge near Houserville; this gauge monitors the stream depth, which can be converted through the use of a rating curve, into the discharge of the stream —
the volume of water moving through the channel over a given time period (usually expressed in cubic feet per second). We will use these data to calculate the 100-year flood, which planners use to dictate where people should and should not build near a stream. In order to gain a better understanding of what discharge means, we’re going to make some measurements of our own. This requires doing two things: 1) measuring the cross-sectional profile of the stream; and 2) measuring the velocity at a few points along the cross-section. The details and steps to do this are provided in the figures below.
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60 Plot your cross-section on the graph below, showing the velocity measurements as well. Area v * 0.7 Discharge Note: you take 70% of the surface velocity in order to approximate the average velocity from the surface to the bed of the stream (where the velocity diminishes). Sum the discharge boxes and write the total discharge here (don’t forget the units):
Estimating Maximum Flood From Clast Sizes The other task while in the field will be to measure the largest clast size in the portion of the stream where you measured your cross-section. You may have to look 5 meters upstream or downstream to get what appears to be the biggest clast. You need to be a bit careful here because large boulders have been brought to the channel to make small dams or to try to prevent bank erosion —
you want to measure something that has definitely been transported by the river. Once you’ve located the biggest clast, measure the intermediate dimension, imagining that it is approximately a rectangular block that would have three mutually perpendicular dimensions. A Triangle
= ½ *b*h A Trapezoid
= ½* h*(a+b)
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61 Write your clast size here in mm: _____________________________________ Below are some data that show the relationship between shear stress and clast size for a range of values. Either graph these data and use a best-fitting line to project the shear stress inferred by your largest clast size, or use the data to make an equation for a line, then apply that equation to the clast size you measured. Clast Name Intermediate Diameter (mm) τ
crit
(Pa) Boulders 256 248.976 Cobbles 64 62.244 Very Coarse Gravel 32 29.686 Coarse Gravel 16 15.322 Medium Gravel 8 7.661 Fine Gravel 4 3.352 Very Fine Gravel 2 1.412 Very Coarse Sand 1 0.589 Coarse Sand 0.5 0.259 Medium Sand 0.25 0.174 Fine Sand 0.125 0.147 Very Fine Sand 0.0625 0.123 Write your shear stress (inferred by the largest clast) here: Then, use the formula relating critical shear stress (the shear stress at the stream bed needed to initiate movement) to water depth to estimate the water depth implied by the clast. τ = r*
g*
h*sin(a) where τ
is shear stress (in units of Pascals, which are Newtons/m
2
), r
is density (for water, 1000 kg/m
3
), g
is the acceleration of gravity (9.8 m/sec
2
), h
is the water depth (in meters) and a
is the slope (in degrees) of the stream, which here has a drop of 20’ over a distance of 5100’.
Write your clast-inferred water depth here: Is this a maximum or minimum water depth? (think about what would happen if you had a stream bed that simply had no large boulders and there was a huge flood that could easily have transported clasts larger than anything present in the stream bed). Next, we move on to consider how this water depth compares with the 100-year flood. This is work to be done outside of the lab period.
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62 Analysis of Historical Streamflow Data from Houserville Estimate the 100-year flood discharge and gauge height
for Spring Creek in Houserville using the data provided. First, calculate the Rank (1 being the flood with the greatest discharge) and Recurrence Time, using the formula RT = (n+1)/m (
n
is the number of yearly peak flood data —
20 in this case, and m
is the rank of the peak discharge), filling in the results for the table below. Year Date Gauge Height (ft) Discharge (cfs) Rank Recurrence Time 1985 Feb. 12, 1985 4.93 318 1986 Mar. 15, 1986 6.79 687 1987 Apr. 04, 1987 5.54 440 1988 Aug. 29, 1988 4.98 351 1989 Jun. 21, 1989 5.62 476 1990 Jun. 09, 1990 5.05 364 1991 Oct. 23, 1990 5.62 476 1992 Dec. 03, 1991 4.55 269 1993 Apr. 01, 1993 7.14 835 1994 Mar. 25, 1994 7.02 800 1995 Jan. 20, 1995 5.55 466 1996 Jan. 19, 1996 10.05 2,370 1997 Oct. 19, 1996 6.79 748 1998 Apr. 09, 1998 6.14 599 1999 Jan. 24, 1999 7.13 832 2000 Jun. 15, 2000 5.09 363 2001 Aug. 19, 2001 5.36 423 2002 Jun. 06, 2002 6.98 795 2003 Aug. 03, 2003 6.89 772 2004 Sep. 18, 2004 9.76 2,110 Next, plot the data on the semi-log graph below, and extrapolate to the 100-year event by using a best-fit straight line. Note that this must be done with logarithmic scale for the x-axis. Then, use the gauge height and discharge data to construct another graph that will enable you to extrapolate to the gauge height of the 100-year flood. 2500 500 2000 0
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63 Write your results here: 100-yr discharge: 100-yr flood height: How does your clast-inferred flood height compare with the 100-year flood? Use the graphs above to estimate the discharge and recurrence time of the clast-moving flow event: Clast-Inferred Discharge: Clast-Inferred Recurrence Time:
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64 GEOSC 001 SPRING 2022
Name LAB 9: IGNEOUS ROCKS & PROCESSES
Section Date In lecture and in your textbook, the processes that form igneous rocks are considered in detail. A quick word of nomenclature: Igneous rocks formed by magma that cools beneath the surface
of the earth are called intrusive. Igneous rocks formed by the cooling of magma after erupting
to the earth’s surface (lava) are called extrusive. The magma itself forms by melting of rocks in the mantle or in the crust. This melting takes place under well-defined conditions and the melting products are readily identified. In this lab, you will be looking at the end products of those processes, i.e., the rocks they leave behind. The exercise today will help you identify different igneous rocks and understand a bit more about the conditions under which they were produced. You may need to refer to your textbook for further information. Part 1: Igneous Texture and Cooling History The size of the minerals (crystals) in igneous rocks reflects the rate of cooling of the magmas. In volcanic eruptions, magma is forcibly ejected from the earth in the form of lava. In this case, magma cools very rapidly, leaving no time for large crystals to form. In the case of magma that cools very slowly beneath the surface (because it failed to erupt, or was left behind), there is ample time for large crystals to grow. This is an important idea: in order to form large crystals in igneous rocks, long cooling times are necessary. Igneous rocks that have large crystals form intrusively, because of the slow cooling of the magma. Igneous rocks that have small crystals form extrusively, leaving little or no time for large crystals to grow. Obsidian Q1. Could you see any individual minerals in the obsidian? Q2. Describe the fractures you see on the obsidian sample. Granite Q3. Granite has large mineral grains (phenocrysts). What might explain the difference between the obsidian and granite?
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65 Basalt If you were to take away all of the water on Earth, it would no longer be known as the blue planet. It would become the black planet, because the crust beneath the oceans, which cover 70% of the Earth’s surface, is basalt, the most common igneous rock. Examine the basalt (the dark rock) you have been given. Q3. Describe the minerals t
hat compose basalt. We don’t expect you to identify any individual minerals and sometimes the individual grains may be difficult to see, but please describe what you observe. Q4. Now look back at the granite. Do you think that any of the minerals are found in both samples? Q5. Which of these rocks (basalt and granite) is intrusive and which is extrusive? Q6. If a rock had large crystals surrounded by very fine crystals, what can you say about its cooling history? This texture is known as porphyritic, and you can see it in some samples in lab. This texture shows us that the molten magma cooled slowly over a small temperature range, allowing large crystals to grow. It then erupted quickly, causing the remaining liquid to cool quickly into a solid, and grow a very fine suite of crystals known as groundmass. Part 2: Composition of Igneous Rocks Igneous rocks are primarily composed of silicate minerals, a class of common minerals including quartz, orthoclase and plagioclase feldspars, mica, amphibole, pyroxene, and olivine –
all of which we will see next week in lab. Igneous rocks are further classified by their composition and overall color. Felsic rocks contain large amounts of fel
dspar and si
lica (quartz). Mafic rocks have minerals with large amounts of ma
gnesium and iron (
fe
rrum). These groups can typically be distinguished based on their color: mafic rocks tend to be dark (basalt, gabbro) and felsic rocks tend to be lighter colored (rhyolite, granite). Mafic and felsic (and intermediate) lavas are often found to have erupted from a single volcano. This observation suggests a genetic relationship between these various rock types. Here we explore a simple
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66 process that can explain this relationship: fractional crystallization. To be fair, the process does not seem simple when you first think about it, but it is a good test of your ability to think in geological terms. We start by considering a large mafic (basalt) magma body newly arrived in a storage chamber beneath a volcano at the earth’s surface. This magma formed by melting the mantle, so it is rich in Mg, Fe, and Ca. It is liquid at a temperature just over 1200° C but it soon begins to cool; crystals form as it starts to solidify. Let’s also assume that the volca
no fed by our new magma erupts periodically and allows us to observe changes within the chamber over tens of thousands to millions of years. Here are some key questions to ask yourself about this magma body. Our goal is to think through the processes associated with both crystallization and eruption. Will this mafic magma body crystallize into solid gabbro (the intrusive equivalent of basalt)? No, because we specified that there will be periodic eruptions from the volcano. During the slow cooling process, the first crystals the form will sink to the bottom of the magma chamber. The remaining liquid has a slightly different composition, and these differences are exacerbated over time. There will be some gabbro at the bottom of the chamber when it is cooled entirely, but there will be other rocks as well. How do we know that melt composition in the magma body can change during crystallization?
We can use the composition of volcanic rocks to track this process. When individual volcanoes erupt a range of lava compositions, we know that the melt composition has changed during crystallization. How does this change occur?
The first minerals to grow at high temperatures (typically olivine and pyroxene) consume large amounts of Mg and Ca. These minerals are denser than the magma and settle to the floor of the chamber. The remaining magma is now cooler and somewhat depleted in Mg and Ca, so (1) it is no longer a basalt, and (2) the minerals that need those conditions can no longer grow. Instead, over time we see a gradual change in the composition of the magma and the formation of minerals that are appropriate to the new thermal and chemical conditions. This process is shown schematically below. It is termed fractional crystallization because during each step (really a continuum) a fraction
of the melt undergoes crystallization
. Notice that the composition of the magma changes as cooling proceeds. Successive volcanic eruptions will tap this evolving liquid, giving us a range of lava types at the earth’s surface.
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67 Rocks are made of minerals, and for igneous rocks we can use the minerals we observe to determine the temperature at which a rock crystallized. We can also infer a great deal about the composition of the lava, and the way in which it erupts. Rock Type Basalt Andesite Rhyolite SiO
2
content 45-55 wt.% 55-65 wt.% 65-75 wt.% Magma temperature 1000-1250
o
C 800-1000
o
C 600-800
o
C Viscosity Low Increasing High Gas escape from magma Easy Increasing Difficult Eruptive style Peaceful Increasing Explosive Q7. Consider our large magma body that was initially basaltic in composition. Assuming that geologic processes operated ideally (which they do not, but today we can pretend), what would be the sequence of lavas erupted from the volcano as it cooled? Q8. How would the dangers associated with eruptions change over the life of this imaginary volcano? Q9. Pumice and obsidian (sample 4) are formed from similar magma types and often during the same eruption. What is different about the rocks? What would cause this difference? Think about what, besides lava, gets ejected in volcanic eruptions.
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68 Q10. Sample 5 has an unusual feature among the other rocks you’ve been provided. It doesn’t have a purely extrusive texture. The splintery dark minerals (the only visible individual crystals) are the amphibole hornblende. Develop a crystallization history for the sample. Describe the scenario below. Part 3: Identifying Igneous Rocks (use the table on the next page) Igneous rocks can be described in terms of their cooling rate (texture) and composition (color and mineralogy). Q11. Fill in the table on the following page. You should identify the 9 samples based on texture and composition.
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69 GEOSCIENCES 001 LAB: IGNEOUS ROCKS SAMPLE MAFIC, INTERMEDIATE OR FELSIC GRAIN SIZE / COOLING RATE TEXTURE ROCK NAME 1 2 3 4 5 6 7 8 9
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70 IDENTIFYING IGNEOUS ROCKS TEXTURE MINERAL COMPOSITION FELSIC (light –
pink/white) INTERMEDIATE (white/gray) MAFIC (dark / black) ULTRAMAFIC (very dark / green) INTRUSIVE Phaneritic (coarse grained) GRANITE DIORITE GABBRO PERIDOTITE EXTRUSIVE Aphanitic (fine grained) RHYOLITE ANDESITE BASALT Porphyritic (larger crystals in fine groundmass) ADD PORHYRITIC TO ROCK NAME Vesicular (vesicles / open holes) PUMICE SCORIA Glassy (vitreous) OBSIDIAN (black) Pyroclastic (contain other fragments) TUFF
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71 GEOSCIENCE 001 FALL 2022 Name ________________________ LAB 10: METAMORPHIC ROCKS Metamorphic rocks (sedimentary or igneous rocks transformed by the effects of high pressures and temperatures) are classified by their mineralogy and texture. Rocks with abundant platy minerals (usually micas or clays) are typically layered on a fine scale; this layering is called foliation
. Three examples of foliated metamorphic rocks are slate, phyllite, and schist. The size of the mica grains increases from slate to phyllite to schist, corresponding with an increase in the temperatures and pressures that the rocks were subjected to during the metamorphism. If the rock is foliated, but has a dull luster (not shiny), the rock is a slate
. If the rock has a shiny luster (caused by microscopic-sized micas grains), the rock is a phyllite
. If micas are clearly visible with a hand lens, the rock is a schist
. A rock with this coarse-grained foliation of platy minerals is considered to have schistocity. Another foliated rock is gneiss
, but it is usually foliated on a coarser scale and appears as bands of minerals. Foliation in gneisses is caused by segregation of minerals into different layers. In most gneisses, equi-dimensional mineral grains of quartz and feldspar are more abundant than the platy micas. Metamorphic rocks are named by prefacing the textural name (e.g., schist or gneiss) with the names of the minerals present (those that you can identify). Some typical rock names are glaucophane-
garnet-muscovite schist, biotite-garnet gneiss, and quartz-biotite-garnet schist. Non-foliated metamorphic rocks include marble (metamorphosed limestone)
, quartzite (metamorphosed sandstone)
, and hornfels (fine-grained, either metamorphosed sedimentary or igneous rock).
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72 Q1.
Complete the table to identify metamorphic rocks. Use the flow chart (next page) as an aid SAMPLE FOLIATED OR GRANULAR? PARENT ROCK ASSOCIATED MINERALS METAMORPHIC ROCK NAME METAMORPHIC GRADE 1 2 3 4 5 6 7
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73
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74 Q2
. Arrange the first three samples in order of least metamorphosed to most metamorphosed: LEAST: __________________ MIDDLE: __________________ MOST: __________________ Q3. Pick three of the samples from Q1 that has foliation. Sketch the rock in an orientation where you can clearly see the foliated planes. Label the directions of maximum compression that formed the foliation. Sample # _______ Sample # _______ Sample # _______
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75 Mylonite is a metamorphic rock, often formed in ductile shear zones with high rates of strain. The image below shows a mylonite with a granite protolith that is made up of feldspar (large grey minerals), quartz (smaller greyscale minerals), and biotite (black minerals). This is an image taken with a petrographic microscope. Figure 1. Feldspar porphyroclasts in a quartz-biotite groundmass, Khumbu (Nepal). Cross polarized image, 2X magnified, Field of view=7mm
. Image Source: Alex Strekeisen
Q4
. Draw a sketch of the mylonite. The sketch should clearly show the different minerals and be labeled with scale. Q4. Some minerals in the mylonite are deforming plastically
and some are deforming brittlely
. Which minerals?
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76 Part 2: Metamorphic processes in the crust
Pressure and temperature change in the crust, and different minerals are stable at different conditions. Geologists classify mineral assemblages into metamorphic facies based on the pressure temperature conditions. Tectonic patterns in the earth influence the patterns of pressure and temperature. Figure 1. Metamorphic facies diagram. Preh-pump is short for prehnite-pumpellyite facies
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77 Q6. a) The typical geothermal gradient of the crust is 25ºC /km. Plot a line on Figure 1. showing this gradient. Helpful values: 1 kbar = 100 MPa; 1 MPa = 1,000,000 Pa; density of the earth =2700 kg/m
3
; gravity =9.81 m/s
2
Pressure (Pa) = density (kg/m
3
) * gravity (m/s
2
) * depth (m) b) Based on your plot, what metamorphic facies would you expect to find in typical crust? Q7. Contact metamorphism is a type of metamorphism when rocks are heated without burial to high temperatures close to high temperature igneous intrusions. A granitic pluton intrudes into the crust, stopping at a depth of 200 meters below the surface. The pluton has a temperature of 900° C. A)
Based on Figure 1, what metamorphic facies would you expect to see right next to the pluton? B)
What metamorphic facies would you expect to see as you move away from the pluton?
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78 Q8.
A) Draw a sketch of a subduction zone in cross section. Clearly label both tectonic plates, and show where there is oceanic and continental crust. B) In your sketch above, label where you would expect to see low, medium, and high-grade metamorphic rocks. C) Oceanic crust loses all of its water at a pressure of approximately 30 kbar, or a depth of approximately 104 km. Label on your sketch above where the oceanic crust loses its water, and where the surface volcanic arc should be.
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79 GEOSCIENCES 001 SPRING 2022 Name LAB 11: INVESTIGATING POROSITY
Section Date & PERMEABILITY THROUGH ENERGY EXPLORATION Introduction
The major source of power for industrial use, the home, and transportation comes from burning fossil fuels including petroleum, natural gas, and coal. To a lesser extent, wood and peat are also burned as a source of power but these two sources are less commonly used and neither accounts for a major fraction of the fuel used worldwide. Renewable energies (wind, solar, hydropower) play an increasing role in the national energy budget, but exploration for hydrocarbons remains a significant area of effort. Fossil fuels evolve at depth in the Earth from organic matter
, both plants and animals. Much of the organic matter produced on the surface of the Earth or within the oceans is oxidized during weathering and decay and not preserved during burial. Preservation of organic matter to produce fossil fuels after burial requires an environment where
oxygen is restricted or not present
. Such anoxic environments
are found in deep basins where sea-water circulation is restricted or in swamps where burial is so rapid that bacteria have no time to break down organic matter. All fossil fuels are generated when preserved organic matter is subjected to the heat and pressure of burial. Chemical reactions can produce fossil fuel in one of three forms: solid (coal), liquid (petroleum), or gas (natural gas). Pennsylvania was blessed with large quantities of all three fossil fuels. Coal was produced in bulk before the Civil Was for home heating and industrial energy for such purposes as making steel. The first oil well was drilled in 1859 in Titusville and, later in the 19
th
century, Pennsylvania became the largest producer of petroleum. More recently, natural gas has become a major source for industrial and home energy. Background One job of the exploration geologist is to locate fossil fuels in the subsurface. The geologist operates under the premise that fossil fuels are produced within a restricted temperature range (80
o
C to 150
o
C). If the in situ
temperature was always less than 80
o
C, any preserved organic matter remains in a state which is difficult to burn. If at any time the in situ
temperature exceeded 150
o
C, most organic matter and subsequent fossil fuels were burned off. For this reason, we do not look for fossil fuels in very recent shallow sediments, nor within metamorphic rocks where temperatures were greater than 150
o
C. Thus, the ideal depth of burial to produce oil is between 3-4 kilometers. This was roughly the depth of burial of rocks in the central Appalachians which are the present source rocks for much of Pennsylvania’s petroleum and natural gas.
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80 Source rocks
: Not all rocks are buried to depths of 3-4 km with organic material still preserved in the matrix. The depositional environment that produces sandstone often leads to oxidation of all organic matter. Likewise, limestones are so permeable that oxidizing fluids move through the limestone will oxidize and ‘burn’ all organic matter. S
hales tend to preserve organic material because they have a lower permeability and are deposited in anoxic environments in deep basins. Those black shales with plenty of organic material are called source rocks
(i.e., the rocks in which fossil fuels are produced). Reservoir rocks
: Many source rocks have a finite permeability which means that although they are shales of very low permeability, the petroleum and natural gas can migrate out of the source rock. Often hydrocarbons migrate because they are less dense than ground water and, hence, are more buoyant. The hydrocarbons will rise like bubbles of air in a lake. This flow by buoyancy usually leads to the migration of petroleum and natural gas to more porous and permeable rocks such as sandstones. Those porous, permeable tocks where fossil fuels are found today are called reservoir rocks
. Reservoir rocks usually had very little organic matter during burial but once petroleum and natural gas were generated under appropriate temperature and pressure, these hydrocarbons flow to the reservoir rocks and become trapped. Porosity
: Oil and natural gas are found in the porosity or open space of rocks. Grains of sand are like marbles in that they are approximately spherical in shape. When many spheres are placed in a container, they cannot fit completely together to fill all the space of the container. The open space between the grains is called pore space
. Porosity
(represented by the Greek letter
) is a measure of the amount of pore space and is given as a percentage of the volume of the whole rock. Sand will have porosity on the order of 30% or more whereas sandstone has a porosity somewhere between 1% and 20% depending on the amount of compaction and cement in the rock. When cement is added to a sand during diagenesis
, the name given to the transformation of a sediment to a rock, cement fills in much of the pore space. Figure 1 shows an idealized cross section of a well sorted but poorly cemented sandstone with large pore space. Figure 2 is a poorly sorted and well cemented sandstone with smaller pore space. The former is like the Pennsylvania glass sand called the Oriskany Sandstone whereas the latter is like the Bald Eagle Sandstone, one of the ridge-forming sandstones of Tussey Mountain. A well cemented sandstone like the Tuscarora Sandstone is shown in figure 3. A B C
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81 Figure 1 (previous page). Examples of sorting and cementation in Pennsylvania sandstones. (A)
Well-sorted and poorly-cemented sandstone: Oriskany Sandstone (
>20%) (B)
Poorly-sorted and well-cemented sandstone: Bald Eagle Sandstone (
<10%) (C)
Well-cemented sandstone: Tuscarora Sandstone (
<2%) Seals
: Most rocks have a high enough permeability that hydrocarbons would leak out over geological time periods. Rocks which have a very low permeability are called seals
. Two types of seals are fine-grained shale and fault zone rocks. In the case of shale, capillary seals prevent hydrocarbons from flowing. Surface tension allows water to adhere to grains the fill pore throats, and petroleum and natural gas cannot flow buoyantly between the individual grains. In the case of fault zone rocks, cement that has been deposited within pore space blocks pore throats and prevents further flow. For hydrocarbons to become trapped, the seal has to surround the reservoir rock entirely. Often a complete ‘bottle
-
like’ seal is not present but a seal on top of the reservoir in the shape of an inverted cup is good enough to trap considerable oil and natural gas. Traps
: Seals in the shape of inverted cups are known as structural traps, of which there are two types. First a reservoir rock covered with a shale might be folded into an anticline in the form of an inverted cup or saucer (figure 4). Hydrocarbons are caught under the seal because they have greater buoyancy than water. Oil will float on water because of the force of buoyancy and, under a seal, oil will be found above water. Another type of trap will form if a fault has cut through the reservoir rock. On one side of the reservoir the seal might be a conventional shale, whereas on the other side of the reservoir the seal is a fault zone (figure 5). As oil will float on water, the faulted trap has oil on top of water. In either case it is important to appreciate that oil is found because a porous rock is covered with a rock that is essentially impermeable. Figure 2. Reservoir rock under an anticline. Figure 3. Reservoir rock under a fault zone.
Geologists can find structural traps using several techniques. First, by mapping surface geology, the geologist can infer the shape of subsurface structures merely by extrapolating what is seen at
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82 the surface to greater depth. Second, the geologist can use seismic cross sections to find traps. A seismic section will allow the geologist to map the location of bedding boundaries and then predict likely locations for traps. The third technique involves correlating between wells using well logs. This is the technique used in this exercise. A well log
is a record of the formations which were drilled and the depth between the formation boundaries. Part I. Exploration for petroleum and natural gas
This activity assumes that you are an investment banker looking to buy shares in recent wells drilled by the Leftwich Producing Company (LPC). You work closely with the LPC geologists and geophysicists. LPC has drilled six wells on six different plots of land. The wells are named after the land owners (Gross, Loewy, etc.). Your bank has $100,000 to spend. Your job is to advise your bank on how to invest its money. You can spend the bank’s money in $20,000 lots distributed however you choose between the six wells. Remember that you only have five lots so you cannot purchase a piece of the action in all six wells. Table 1 gives the well logs for the six wells. Each well log gives the formation names in the order in which they were drilled. The rocks closest to the surface were drilled first and listed at the top of the log. These are the rocks that outcrop. The depth at which each formation boundary was found is marked on each well in a cross section through the area drilled by LPC (figure 4). The position of each well is shown on this cross section. Part 1: Construct a cross section through the LPC field by correlating between formations using the data given in table 1. The formation names are those of the Appalachian Valley and Ridge. Each formation is characterized according to lithology. Your cross section is most easily constructed by writing out the formation names in their proper positions on each of the six logs. The lines marking the formation boundaries between each well show the dip of bedding at the boundary between each formation. Each formation consists of many beds. Part 2: Using the description for structural traps given in figures 2 and 3, locate all possible places where oil might have been trapped. Remember that each trap must consist of seal rocks in the shape of an inverted cup or saucer. A porous, permeable reservoir must be found below a seal rock for the development of an economic reservoir. Indicate the volume of trapped oil by drawing an oil-water contact (i.e., a horizontal line) 100 meters below the highest point of each reservoir. The 100-meter section of oil is known as the oil column. The volume of trapped oil is proportional to the cross-sectional area of the oil. A scale has been provided to help you draw the 100-meter column under the highest point for each trap. Part 3: Now decide how to invest your five lots on the wells drilled by LPC. Write down your plan for investing your money in the table below the cross section.
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83 Each well has a different value depending on the volume of oil that the well can extract. A rule of thumb is that wells in contact with more oil have a greater value. Although an oil column is 100 meters, not all oil wells will strike oil at the highest point within the trap. More than one well may drill into the same oil pool, but the richer well is the one touching the oil pool at a shallower depth. As an investment banker, one of your first jobs is to decide which wells have greater values (i.e., which wells are in contact with a thicker section of oil). Wells in contact with only water have no value. When considering your investment, you should not lose track of the fact that there may be fewer lots invested on wells in contact with smaller quantities of oil. Note, too, that some of the wells may be dry holes. A major part of this exercise is to state the geological rationale for your investment. Bids will not be accepted without a geological rationale. Explain your rationale in the space provided on the second to last page of the lab. Don’t forget the final thought question on the last page.
Good luck!
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84 Table 1: Well Logs for Leftwich Producing Company Well Name: Gross
Formation Name Lithology Lock Haven marine sandstone Brallier marine shale Hamilton limestone Onondaga limestone Hamilton limestone Onondaga limestone Clinton sandstone (fractured) Well Name: Loewy
Formation Name Lithology Brallier marine shale Hamilton limestone Onondaga limestone Clinton sandstone (fractured) Tuscarora sandstone (high porosity) Clinton sandstone (fractured) Tuscarora sandstone (high porosity) Well Name: Lacazette
Formation Name Lithology Onondaga limestone Clinton sandstone (fractured) Tuscarora sandstone (high porosity) Juniata shale (low permeability) Bald Eagle sandstone (high porosity) Reedsville marine black shale (source) Bald Eagle sandstone (high porosity)
Well Name: Fischer
Formation Name Lithology Onondaga limestone Clinton sandstone (fractured) Tuscarora sandstone (high porosity) Juniata shale (low permeability) Bald Eagle sandstone (high porosity) Reedsville marine black shale (source) Well Name: Younes
Formation Name Lithology Onondaga limestone Clinton sandstone (fractured) Tuscarora sandstone (high porosity) Juniata shale (low permeability) Bald Eagle sandstone (high porosity) Reedsville marine black shale (source) Well Name: Plumb
Formation Name Lithology Onondaga limestone Clinton sandstone/limestone (fractured) Tuscarora sandstone (high porosity) Juniata shale (low permeability) Bald Eagle sandstone (high porosity) Reedsville marine black shale (source)
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Figure 4 (below). Well logs with formation boundaries marked to show the dip of the formation contacts. Gross
Lowey
Lacazette
Fischer
Younes
Plumb
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Investment Plan for Your $100,000 (indicate below how much you are investing in each well. Remember that you can invest in the same well more than once): Well Name Investment Amount Geological Rationale:
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Thought question: If you were an exploration geologist assigned to a new country that had yet to be explored for petroleum resources, where would you begin? What would you look for on a geologic map, or in available stratigraphy? What sort of ancient depositional environments would be the best candidates for petroleum formation characteristics, and what are their lithological counterparts that you would look for in the stratigraphy? What stratigraphic patterns or facies stacking patterns would you look for? Think about porosity and permeability of each lithology.
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