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Instructions:
GEOLOGIC HISTORY is a book about the history of geology.
Gary Jacobson of Grossmont Community College gave permission for this lab to be used and changed.
INTRODUCTION:
Dating rocks and placing geologic events in their appropriate sequence is one of the most fundamental procedures in geology. There are two approaches that can be used to accomplish this. Absolute dating is being able to determine the age of a rock. Although this may appear to be a straightforward task, establishing the numerical age of a rock is complex due to various conditions that must be met. The most frequent method of absolute dating a rock is radiometric dating. Because you can only date a rock that originated straight from cooling magma or a recrystallized metamorphic rock, the method is limited. Even if you can’t discern a rock’s exact age, you can figure out the sequence in which a series of geologic events occurred and assign a relative age to it. This is known as relative dating, and it is the most basic idea in geology. Geologists have been putting relative ages on rocks since the 1700s, but absolute dating techniques have only been around since the late 1960s. To estimate the relative age of a rock, early geologists used the theory of faunal succession and other relative dating techniques. Long before scientists knew the actual age of the world, fossils, and relative dating concepts were utilized to build the geologic time scale. The ideas of relative dating will be the subject of this lab
RELATIVE DATING PRINCIPLES:
Differentiating older from younger events is reasonably simple thanks to a few fundamental rules. The majority of these take advantage of the well-known principle that if event “A” causes event “B” to happen, then event “B” must be older.
Superposition: When rocks are deposited on the earth’s surface, they form strata with older rocks at the bottom and younger rocks at the top. As a result, layer E is the oldest, and layer A is the youngest in Figure 1. This is true for both sedimentary and extrusive igneous rocks that have not been disturbed. Intrusive igneous rocks and rocks that have been folded or shifted by reverse faults are not affected by superposition. Sill F in Figure 2 is really younger than the layers A, B, and C that are above it. This assumes that Figure 1 serves as the starting point for Figure 2.
Horizontality: Rocks on the earth’s surface are deposited in essentially horizontal layers when they first form (Figure 1). As a result, non-horizontal rocks imply that their original horizontality was disrupted by a more recent occurrence. Because intrusive igneous rocks do not have to be originally horizontal, folding in Figure 2 would be younger than layers A-E, but not necessarily younger than Sill F
Superposition (Figure 1) Original Horizontality and Continuity (Figure 2)
Original Continuity: Rocks deposited on the earth’s surface produce strata that continue laterally in all directions until they thin out due to non-deposition or reach the basin’s border. Intrusive igneous bodies like dikes, sills, and laccoliths have some original continuity as well, but they may taper off between the rocks that surround them (note Sill F in Figure 2). Rocks that appear tilted or folded (Figure 2) have undergone a tectonic or folding event that is younger than the rocks themselves.
Cross-cutting Relationships: Geological features are older than the features through which they cut. Intrusive igneous masses, faults, and erosion surfaces are all subject to the rule. As a result, Figure 3’s erosion surface is younger than the units it cuts. When molten rock (magma) pushes through (intrudes) a body of rocks, the igneous rocks that follow must be younger than the intruded rocks. Figure 2 shows that Sill F is younger than the units above and below it. A fault is formed when an earthquake splits a collection of rocks. Later, I’ll go over the flaws in more detail.
Figure 3: Erosion on the Surface
Angular Unconformity (Figure 4)
Unconformities: An unconformity is a feature that occurs when a surface of erosion becomes buried, as G has done in Figure 4. A temporal gap is an unconformity. They might happen for a variety of reasons, but they are always caused by a halt in sedimentation. Unconformities can be divided into three categories.
1. An angular unconformity occurs when the layers beneath the unconformity are not parallel to the erosion surface (Figure 4).
Figure 5: Inconsistency
Nonconformity (Figure 6)
2. A disconformity is a structure in which the strata underneath the unconformity are parallel to the unconformity but there is a gap in time or an erosional surface (Figure 5). We know there is an unconformity above unit C because Dike x comes to a halt at the top of unit C in figure 5. Dikes and sills don’t always cease invading exactly where two units meet. As a result, the contact between units C and G can be interpreted as an erosional surface or unconformity, more precisely a disconformity.
3. Metamorphic or plutonic igneous rocks are overlain by a nonconformity (Figure 6).
In other words, any location where sedimentary rocks meet crystalline rocks.
sandstones (metamorphic or igneous).
Inclusions are particles or fragments of one rock type embedded in another, according to the law of inclusions. In a conglomerate, the cobbles are conglomerate inclusions. Sand grains in sandstone are also inclusions in the sandstone. When portions of a pluton’s wall rocks break off and become integrated into the crystallizing magma, inclusions develop in the igneous rocks. The rocks in which inclusions are found are always older than the rocks in which they are found. Unit G in Figure 7 (essentially an expansion of Figure 6) contains granite inclusions underneath it. As a result, the granite inclusions predate G. We can also deduce that the granite isn’t intrusive to G, but rather that G was deposited on top of degraded granite.
Figure 7: G has older granite inclusions than G.
The table below shows how to organize the geologic events illustrated in Figure 7 starting with the first or oldest event. Unconformities are categorized as a geologic events.
H is the newest deposit.
G-deposit
nonconformity
Oldest Granite
Reasoning:
Because there are granite inclusions in unit G, we can deduce that the granite is older than unit G based on the law of inclusions. As a result, granite is the most ancient geologic event. This logic also suggests that the granite and unit G have an erosional surface or unconformity. This unconformity is a nonconformity because granite is a crystalline rock. Because unit G is lower than unit H, G must be older than H.
We’ll concentrate on two sorts of faults in this lab: normal and reverse faults.
1. Normal faults arise as a result of the extension, or as rocks are pushed together.
They’re being pulled apart as if they’re at a dividing line. The hanging wall block, or the side of the fault that makes an acute angle (less than 90°) with the surface of the land, moves down relative to the footwall block, or the side of the fault that makes an obtuse angle (more than 90°) with the lands surface, when extension occurs (Figure 8).
Figure 8: A normal fault is depicted as a cartoon block diagram. The fault is shown by the bold angled line in the center. Under the extension, the hanging wall block (left) moves down in relation to the footwall block (right), as indicated by the arrows on either side of the fault. 2. Compression causes reverse faults to form, or you might think of it as rocks being squeezed together. pressed together, as if at a converging boundary When compression takes place, the The footwall block slides up in relation to the hanging wall block (Figure 9).
Figure 9: A reverse fault is depicted as a cartoon block diagram. The fault is shown by the bold angled line in the center. Under compression, the hanging wall block (left side) rises above the footwall block (right side), as indicated by the arrows on either side of the fault.
1. In the table provided, arrange all 8 geologic events illustrated in figure 10 in the correct order, from oldest to youngest. If there is an unconformity, specify whether it is an angular unconformity, a disconformity, or a nonconformity.
Figure 10: The tilting beds beneath unit B suggest the presence of an erosional surface or unconformity. These tilting beds were originally put horizontally, but due to a folding occurrence, they are now tilting.
The youngest is eight years old.
1. the oldest
2. What is L’s type of nonconformity? How did you figure that out?
3. Is J or T the older rock unit? How did you figure that out?
4. In the table provided, arrange all 14 geologic events illustrated in figure 11 in the correct order, from oldest to youngest. To complete the table, utilize the event bank below; each event will only be used once, and all of the specified events should be used. Only the boxes with the numbers 1 through 14 should be filled in (the box labeled “Youngest” should not be filled in).
Granite F is an igneous intrusion with a dike spreading to the surface (Figure 11). All of the beds cut by granite F are slanted, indicating that the folding event that inclined these beds was most likely caused by granite F intrusion. Because of this link, the folding event must have occurred before the granite F intrusion.
Bank of Events:
angular unconformity Deposit H Deposit J Deposit C Deposit B
Granite F disconformity Deposit E Deposit D Deposit K
I deposited G deposited A folding
Youngest 10. 5.
14. 9. 4.
13. 8. 3.
12. 7. 2.
1. oldest 11. 6.
Answer the following questions using Figure 12 as a guide.
RUBRIC |
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Excellent Quality 95-100%
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Introduction
45-41 points The background and significance of the problem and a clear statement of the research purpose is provided. The search history is mentioned. |
Literature Support 91-84 points The background and significance of the problem and a clear statement of the research purpose is provided. The search history is mentioned. |
Methodology 58-53 points Content is well-organized with headings for each slide and bulleted lists to group related material as needed. Use of font, color, graphics, effects, etc. to enhance readability and presentation content is excellent. Length requirements of 10 slides/pages or less is met. |
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Average Score 50-85% |
40-38 points More depth/detail for the background and significance is needed, or the research detail is not clear. No search history information is provided. |
83-76 points Review of relevant theoretical literature is evident, but there is little integration of studies into concepts related to problem. Review is partially focused and organized. Supporting and opposing research are included. Summary of information presented is included. Conclusion may not contain a biblical integration. |
52-49 points Content is somewhat organized, but no structure is apparent. The use of font, color, graphics, effects, etc. is occasionally detracting to the presentation content. Length requirements may not be met. |
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Poor Quality 0-45% |
37-1 points The background and/or significance are missing. No search history information is provided. |
75-1 points Review of relevant theoretical literature is evident, but there is no integration of studies into concepts related to problem. Review is partially focused and organized. Supporting and opposing research are not included in the summary of information presented. Conclusion does not contain a biblical integration. |
48-1 points There is no clear or logical organizational structure. No logical sequence is apparent. The use of font, color, graphics, effects etc. is often detracting to the presentation content. Length requirements may not be met |
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Lab Report on Geology Events Sequence |
Lab Report on Geology Events Sequence