B-Lab Report 03 Florida 2 - All Versions
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School
University of South Florida *
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Course
2000
Subject
Geology
Date
Apr 3, 2024
Type
Pages
8
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Report 3-1 Note: Activities 3.1 & 3.2 must be completed at the beginning of class and before you begin any other activity. Activity 3.1, Geologic Time and Florida O
BJECTIVE
:
To become familiar with the periods of the Mesozoic and epochs of the Tertiary, the time when Florida’s sedimentary rocks were formed. Fill in the blanks in the first three columns
of the following table, Table III-1, which summarizes the geologic periods and epochs that are important in Florida’s geologic history. Use the Geologic Time Scale on the inside front cover as a reference (5 points, ☆
). Activity 3.2, Florida Rock Summary
(2 Minutes)
O
BJECTIVE
:
To summarize the lithology of Florida rocks you determined in the last laboratory. Table III-2 is identical to Table II-1 you completed last laboratory, expanded to include several sediment samples. Transfer your answers from last week (from the graded
lab report) into the last column of Table III-1 for every row corresponding to a rock
. (2 points, ☆
) Activity 3.3, Introduction to Drilling Logs (5 Minutes)
O
BJECTIVE
:
To learn how to extract information from IC-103, the Summary of Stratigraphic Information derived from drilling logs.
Because Florida has so few outcrops, almost everything about the geology of the state is known from drilling. As the agency in charge of s
tudying and managing Florida’s geologic resources, the Florida Geologic Survey has compiled a summary of drilling logs titled Information Circular No. 103,
Shallow Stratigraphic Core Test on File at the Florida Geologic Survey. You will be using an abridged version of this book (the full book contains over 400 pages of core descriptions!) to learn about the rocks and sediments hidden from view beneath the surface. 1.
What material was recovered from a depth of 50 feet in well W-12942 in Hardee County? (2 points, ☆
) 2.
Would you characterize this material as rock or sediment? (1 point, ☆
) 3.
What minerals become increasingly abundant beneath 1000 feet at Polk County well W-10254? (In fact, it is the presence of this mineral that defines the base of the Floridan Aquifer
–
file this away for future use!) (2 points, ☆
) 4.
EXTRA CREDIT: The well-fields that supply Pinellas County with drinking water are located in Polk County. The water is supplied from big, 12-inch wells that draw water from a depth of 500-1000 feet. Does this groundwater reside in loose, unconsolidated sediment or in hard rock? How can you tell? (The aquifer in which the water is stored is called the Floridan Aquifer and is one of the most important aquifers in the United States.) Use Well W-10254 as representative of Polk County. (Answer box is on the next page.) (4 points, ☆☆☆
) Laboratory Number Three: Florida, The Land Beneath Our Feet II Name: Partners: Table III-
1, Florida’s Geologic History
Years ago Period Epoch Event, Rocks Formed Oldest Youngest 12,000 Quaternary Pleistocene Last ice age
1.6 m.y. - 10,000 Quaternary Pleistocene 5 - 1.6 m.y. Tertiary Tertiary Tertiary Oligocene Tertiary Eocene 66-58 m.y. Tertiary Paleocene 144 - 66 m.y. Cretaceous 208 - 144 m.y. Jurassic Anhydrite
Report 3-2 Where does groundwater reside? How can you tell? Activity 3.4, Miocene Sediments of Florida (12 Minutes)
O
BJECTIVE
:
To summarize the type of Miocene sediments found in Florida.
You might have noticed that Table III-2 contains many rocks of Eocene and Oligocene age but very few of Miocene and Pliocene age. The reason has to do with the difficulty in collecting core samples from poorly indurated sediment, which characterizes much of the Miocene and Pliocene material
beneath Florida. Although Miocene and Pliocene sediments are thick beneath Florida, they are not usually indurated, and they are therefore under-represented in a compilation of rock core data. To compensate for this bias, you will supplement your observations of rocks in Table III-2 with inferences drawn from IC-103 for Miocene- and Pliocene-aged sediments. Information Circular No. 103 organizes the kinds of rocks or sediment encountered when drilling in terms of formations and groups. In Florida, the most important Miocene/Pliocene units are the Hawthorn Group, and Peace River Formation. The Peace River Formation is the most important subdivision of the Hawthorn Group. 1.
Notice that some of the entries in Table III-2 are for sediments (“Sed.”) recovered from specific wells (“Well #”). Use IC
-103 to characterize the depth and lithology of these sediments. Enter the midpoint
of the depth at which the sediment occurs, and quickly summarize the kind of sediments found in the last column. Use the Hawthorn Group (Undifferentiated) or the Peace River Formation as representative of the Miocene or Pliocene sediments. Note: the midpoint is just the average of the high and low depths. (3 points each, all ☆
) Table III-2, Representative Rocks and Sediments of Florida Sample Rock or Sediment? County Depth (feet) Age Group or Formation Name of Rock or Sediment? Youngest
. FLA-6 Rock Dade 40 Pliocene Miami Fm. W-15511 Sed
Calhoun Miocene Hawthorn Grp. W-11907 Sed
Charlotte Miocene Peace River Fm. W-15509 Sed
Jackson Miocene Hawthorn Grp. FLA-7 Rock Manatee 343 Miocene Arcadia Fm. FLA-5 Rock Clay? ≈ 250
Miocene Hawthorn Grp. Siltstone
FLA-8 Rock Hardee? ≈ 100
Miocene Hawthorn Grp. FLA-9 Rock Manatee 920 Eocene Ocala Grp. FLA-10 Rock Lafayette 300 Eocene Avon Park Fm. FLA-11 Rock Citrus 35 Eocene Ocala Grp. FLA-2 Rock Citrus 280 Eocene Avon Park Fm. Dolostone
FLA-1 Rock Charlotte 1180 Eocene Avon Park Fm. Limestone
FLA-12 Rock Escambia 15847 K/J Unknown Oldest FLA-13 Rock Charlotte >10,000 K/J Unknown FLA-3 Rock Charlotte? >15,000 Jurassic Unknown Nodular Anhydrite
Report 3-3 2.
Do you think the Miocene sediments comprise an aquifer or confining unit? Defend your answer. (3 points, ☆☆
) Activity 3.5, Paleogeography of Florida (15 Minutes)
O
BJECTIVE
:
To learn how sediments and sedimentary rocks can be used to infer paleogeography, particular in Florida. 1.
Go back to Table III-1 and, for each row, enter into the last column the name of the predominant rock formed during that period. For example, careful study of Table III-2 indicates that nodular evaporite rocks were formed during the Jurassic period, so “Anhydrite” has been entered into the row for Jurassic on Table III-1. Fill in all the entries in the last column of Table III-1. (3 points, ☆
) 2.
Take a yellow colored pencil and lightly cross hatch those rows in Table III-1 that correspond to times when terrigenous clastic
sediment
was being deposited in Florida. (2 points, ☆
) 3.
What mountain range was the source of the terrigenous clastic sediments deposited on Florida? (1 point, ☆
) 4.
The Bahamas is a classic modern example of pure carbonate deposition (i.e., aragonite and calcite). Examine a map of the United States that includes the Bahamas Islands. Why aren’t the carbonate sediments in the Bahamas contaminated with terrigenous clastic sediment shed off the eastern United States? Why doesn’t this sediment reach the Bahamas? (3 points, ☆☆
) 5.
Now speculate why pure limestones, devoid of terrigenous clasts, were able to accumulate during parts of Florida’s geologic history. HINT: think about your explanation for the Bahamas, above. (3 points, ☆☆☆
) ? 6.
How can you explain the sudden influx of terrigenous clastic sediments in Florida indicated by the rows you just colored yellow in Table III-1? (3 points, ☆☆☆
) Activity 3.6, Temperatures beneath Florida (
10 Minutes
)
O
BJECTIVE
:
To learn how to calculate temperatures as a function of depth using the geothermal gradient.
While coring rock FLA-1 (Table III-2), the temperature in the boring was measured at 25.75°C. This is higher than the average temperature on the surface (20°C) because temperature increases toward the center of the Earth. The rate at which temperature increases with depth is called the geothermal gradient
. 1.
Calculate the geothermal gradient in °C/km based on the measurement of 25.75°C for FLA-1. NOTE: there are 3.28 feet /meter, and 1,000 meters in a kilometer. Show your work for full credit! (5 points, ☆☆
)
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Report 3-4 2.
Gypsum transforms into anhydrite when the temperature exceeds 50-60°C. Using the geothermal gradient calculated above, calculate the temperature of rock FLA-12 (Table III-2). Show your work for full credit!! (4 points, ☆☆
) 3.
Which mineral
–
gypsum or anhydrite
–
do you think would be stable in rock FLA-12? (1 point, ☆
) Activity 3.7, Permeability of Rocks (
12 Minutes
) O
BJECTIVE
:
To learn how to infer the permeability of rocks from porosity, and to review how to recognize and estimate porosity in thin sections.
In this activity, you will investigate the permeability
of rocks. Measuring the permeability of rocks is much more difficult than measuring the permeability of sediments, but it can usually be accurately inferred from the porosity
, which is readily observed. 1.
First examine the thin section for rock FLA-15. This rock has a very high porosity and very high permeability. How can you recognize the pores in thin section? (3 points, ☆☆☆
) 2.
Using the calibration chart on the inside back cover of your lab manual, estimate the porosity of this sample. (2 points, ☆
) 3.
For each of the following Florida rock types, estimate the ‘typical’ permeability based on its
observable porosity in hand samples. Examples of the various rock types can be found on Table III-2. (1 point each, all ☆
) Lithology Typical Permeability in Florida (High/Low) Limestone Dolostone Nodular Anhydrite Limey siltstone/mudstone Activity 3.8, Geologic Map of Florida (
7 Minutes
) O
BJECTIVE
:
To learn how to read a geologic map.
Study the Geologic Map of the State of Florida, compiled by Thomas Scott. As usual, treat the maps with care and do not write on them. 1.
What formation underlies Miami? (3 points, ☆
) 2.
What name is given to the geologic period in which the oldest rocks exposed at or near the surface of Florida were formed? Where in Florida are these rocks/sediments found? (4 points, ☆
) EXTRA CREDIT: Notice the dendritic (tree-like) pattern of Miocene/Pliocene rocks in the northern part of the Panhandle, north of Tallahassee. What causes this pattern? (3 points, ☆☆☆
)
Report 3-5 Activity 3.9, Missing Rocks (6 Minutes)
O
BJECTIVE
:
To learn how to think in three-dimensions when reading a geologic map.
The following questions are best answered by using the geologic map and cross-sections on the Geologic Map of the State of Florida together. The green patterns on the geologic map represent rocks and sediments of Miocene and Pliocene age, which are only exposed in several patches over a small portion of the state. Where do you think these rocks are over the rest of Florida? Are they missing? Where are they in these two counties? (3 points each, ☆
) Dixie County Palm Beach County Activity 3.10, Geologic Cross-Section (8 Minutes)
O
BJECTIVE
:
To learn how to read a geologic cross-section.
Look at the two geologic cross-sections shown on the second page of the Geologic Map of the State of Florida and answer the following questions: 1.
What is the vertical exaggeration for these cross-sections? (2 points, ☆
) 2.
What geologic formation (and its symbol) is exposed at the bottom of the Apalachicola River, section A-A
’
? (2 points, ☆
) 3.
What geologic formation (and its symbol) is exposed at the bottom of the Suwannee River, section A-A
’
? (2 points, ☆
) 4.
Remembering the vertical exaggeration, how would you describe the general orientation of the rock units under Florida
–
are they steeply or gently inclined, or nearly flat? (2 points, ☆
) EXTRA CREDIT: The boundary between two adjacent formations or groups is called a contact
. How deep is the contact between the Avon Park formation (Tap) and the Ocala Limestone (To) underneath Jefferson County in cross-section A-
Aʹ? Notice the vertical scal
e on the left of both cross-sections. (2 points, ☆
) Activity 3.11, Stacked Aquifers (6 Minutes)
O
BJECTIVE
:
To learn how to distinguish unconfined from stacked confined aquifers based on a cross-section of hydrogeologic units.
For all the hydrology-related activities in this laboratory you will be using the Ground Water Atlas of the United States, Segment 6, referred to as Atlas 730-G. 1.
Figure 23 on page 7 of 730-G shows a simplified cross-section of the two major aquifers underlying the extreme western part of the Florida panhandle, and Figure 45 on page 11 shows a similar cross-section showing the three major aquifers found south of Tampa Bay. Fill in the following table which summarizes the confining conditions of the three major aquifers shown in these diagrams: (2 points each, all ☆
) Aquifer Confined (C) or Unconfined (U)? Sand and Gravel (Fig. 23) Intermediate System (Fig. 45) Floridan (Figs. 23 & 45) EXTRA CREDIT: Figure 17 on page 6 shows how water flows in and out of the stacked aquifers under Florida, especially the Surficial and Floridan aquifer systems. How does water get into the Surficial Aquifer? (2 points, ☆☆
) EXTRA CREDIT: Water also leaks between the Surficial Aquifer and underlying Floridan Aquifer. Examine Figure 17 on page 6 carefully. Where does water leak upward from the Floridan into the Surficial Aquifer, along the coast or
Report 3-6 inland? How about leaking downward? (2 points, ☆☆
) Activity 3.12, Realtime Groundwater Data (16 Minutes) O
BJECTIVE
:
To learn how to read and interpret real-time groundwater data published by the USGS. The United States Geological Survey monitors many groundwater wells throughout the United States, including Florida. Some of these data are collected automatically by electronic instruments and sent via satellite to computers. The USGS then makes the data available to the general public on its web pages. For this laboratory, your instructor will provide you with printouts for several groundwater monitoring wells in southern Florida. Notice that the data are given as “stage”, in feet above datum
. The “datum”
, or reference elevation, be typically the NVGD, or National Geodetic Vertical Datum of 1929. This datum is a long-term average of sea level along the coasts of the United States. First examine the printout for Well G-580A. 1.
Near what city is this groundwater well located? (1 point, ☆
) 2.
What was the water elevation in this well above sea level on September 16? (1 point, ☆
) 3.
Approximately how far beneath the land surface was the water level in the well on this date? (1 point, ☆
) 4.
What aquifer does this water level correspond to? (1 point, ☆
) 5.
Is this aquifer a confined or unconfined aquifer? HINT: is this a ‘water table well’ or ‘artesian well’? (1 point, ☆
) 6.
Has the land at this location ever been flooded during the time when this well was being monitored? HINT: look at the Extremes for the Period of Record
. (2 points, ☆
). Now look at the printout for Well L 742. 1.
Near what city is this groundwater well located? (1 point, ☆
) 2.
What was the water elevation in this well above sea level on September 18? (1 point, ☆
) 3.
Approximately how far beneath the land surface was the water level in the well on this date? (1 point, ☆
) 4.
What aquifer does this water level correspond to? (1 point, ☆
) 5.
Is this aquifer a confined or unconfined aquifer? HINT: is this a ‘water table well’ or ‘artesian well’? (1 point, ☆
) 6.
Has the land at this location ever been flooded during the time when this well was being monitored? HINT: look at the Extremes for the Period of Record. (2 points, ☆
). 7.
Has the water level in this well risen, fallen, or remained nearly constant during the week of September 18? How can you explain this? (2 points, ☆☆☆
)
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Report 3-7 Activity 3.13, The Floridan Aquifer (18 Minutes)
O
BJECTIVE
:
To learn about the rocks in the Floridan Aquifer, and how to read and interpret a potentiometric surface map of a confined aquifer. For all the hydrology-related activities in this laboratory you will be using the Ground Water Atlas of the United States, Segment 6, referred to as Atlas 730-G. 1.
The Floridan Aquifer consists of porous and permeable rocks of Eocene and Oligocene age. Rock FLA-16 is an example of a rock from the Floridan Aquifer. What kind of rock is it? (1 point, ☆
) 2.
Do you think the porosity in rock FLA-16 is primary or secondary? Explain what this means. (2 points, ☆☆
) 3.
Go to Table III-1 and color the rows corresponding to the Floridan Aquifer rocks blue. (1 point, ☆
) 4.
The potentiometric surface
of the Floridan Aquifer (in feet above sea level) is shown in Figures 59 and 60 on page 15. The potentiometric surface map is the primary tool used by geologists who study the movement of water in aquifers. What was the elevation of the potentiometric surface of the Floridan Aquifer on the east shore of Lake Okeechobee prior
to development of the Floridan Aquifer (Figure 59)? (3 points, ☆
) 5.
What was the elevation of the potentiometric surface of the Floridan Aquifer on the east shore of Lake Okeechobee after
development of the Floridan Aquifer, 1980 (Figure 60)? (2 points, ☆
) 6.
What was the elevation of the Floridan Aquifer in Savannah, Georgia, in 1980? (2 points, ☆
) 7.
The figure on the next page is an enlargement of the area just west of Tampa Bay on Map Series No. 104, Potentiometric Surface of the Floridan Aquifer in Florida, 1980. Three dots are shown in Polk County and are all within a 20-mile radius of each other. Starting from each of these dots, trace the path of groundwater flow in the Floridan Aquifer. You might want to use a colored pencil, so your paths are easier to see. (8 points,
☆
)
EXTRA CREDIT: Suppose a well into the Floridan Aquifer located at point A becomes polluted by fertilizer from a neighboring agricultural field. Does this pollution pose any risk to a nearby community that extracts its drinking water from the Floridan Aquifer from a well at point B? Why or why not? (2 points, ☆☆
) Activity 3.14, Synthesis: Geology and Aquifers Complete Last (6 Minutes)
O
BJECTIVE
:
To synthesize the relationship between geology and hydrogeology in Florida’s Floridan Aquifer.
1.
Like all confined aquifers, the Floridan Aquifer system in Florida is both over- and underlain by confining units. Consider the permeability of Florida’s rocks (Activity 3.7) and sediments (Activity 3.4, question 2). What are the age and lithology of the upper confining unit to the Floridan Aquifer? (2 points, ☆
) Age: Lithology: 2.
What are the age and lithology of the lower confining unit to the Floridan Aquifer? (2 points, ☆
) Age: Lithology: 3.
Go to Table III-1 and lightly color in the rows corresponding to the upper confining unit of the Floridan Aquifer orange. (1 point, ☆
) 4.
Go to Table III-1 and color in the rows corresponding to the lower confining unit of the Floridan Aquifer red. (1 point, ☆
).
Report 3-8 Potentiometric Surface for Activity 3.13, Question 7