7 questionshave to get done. so all of page 107, and page 109 that’s it. I do have zoom of him going over the lab if needed and I added the slides from class.
cGOL 106 LAB 4
FOSSILS AND THEIR LIVNG RELATIVES
Group ________
Member Names
(1)_________________________________________________
(2)_________________________________________________
(3)_________________________________________________
Page
Question(s)
103
2, 4
104
5
105
1
107
All
108
3, 5
109
7 a, b, c, d
Chapter 5
Rocks, Fossils, and Time
1
Geologic Record
• The fact that Earth has changed through time
– is apparent from evidence in the geologic record
• The geologic record is the record
– of events preserved in rocks
• Although all rocks are useful
– sedimentary rocks are especially useful in
deciphering the geologic record
• The geologic record is complex
– and requires interpretation
• Uniformitarianism offers a useful approach
2
2
Stratigraphy
• Stratigraphy deals with the study of any layered
(stratified) rock
– but primarily with sedimentary rocks and their
•
•
•
•
composition
origin
age relationships
geographic extent
• Almost all sedimentary rocks are stratified
• Many volcanic rocks
– such as lava flows or ash beds as well as many
metamorphic rocks are stratified and obey the
principles of stratigraphy
3
3
Stratified Sedimentary Rocks
• Although these rocks in South Dakota are
deeply eroded stratification is still clearly
visible
4
Stratified Rocks
• Stratified rocks in California are deformed so that they
are no longer in their original position
5
Vertical Stratigraphic Relationships
• Surfaces known as bedding
planes
– separate individual strata from
one another
– or the strata grade vertically from one rock type to
another
• Rocks above and below a bedding plane differ
– in composition, texture, color
– or a combination of these features
• The bedding plane signifies
– a rapid change in sedimentation
– or perhaps a period of non-deposition
6
6
Superposition
• Nicolas Steno realized
that he could determine
– the relative ages of
horizontal (undeformed)
strata by their position in
a sequence
Youngest
Oldest
• In deformed strata, the task is more difficult
– but some sedimentary structures and some fossils allow
geologists to resolve these kinds of problems
7
7
Principle of Inclusions
• According to the principle of inclusions,
– which also helps to determine relative ages, inclusions
or fragments in a rock are older than the rock itself
• Light-colored granite
– in northern Wisconsin
– showing basalt
inclusions (dark)
• Which rock is older?
– Basalt, because the
granite includes it
8
Age of Lava Flows & Sills
• Determining the relative ages of lava flows, sills
and associated sedimentary rocks uses contact
metamorphism effects and inclusions
• How can you determine whether a layer of basalt
within a sequence of sedimentary rocks is a buried lava
flow or a sill?
– A lava flow forms in
sequence with the
sedimentary layers.
9
• Rocks below the lava
will have signs of
heating but not the
rocks above.
• The rocks above may
have lava inclusions.
9
Sill
– A sill will heat the rocks above and below.
– The sill might
also have
inclusions of the
rocks above and
below,
– but neither of
these rocks
will have
inclusions of
the sill.
10
Unconformities
• Unconformities in
sequences of strata
represent times of nondeposition and/or erosion
that encompass long
periods of geologic time,
perhaps millions or tens
of millions of years
• The rock record is
incomplete at this
location
– The interval of time
not represented by
strata is a hiatus.
11
Types of Unconformities
• Three types of surfaces can be unconformities:
– A disconformity is a surface in sedimentary rocks
separating younger from older rocks, both of which
are parallel to one another
– A nonconformity is an erosional surface cut into
metamorphic or intrusive rocks and covered by
sedimentary rocks
– An angular unconformity is an erosional surface on
tilted or folded strataover which younger rocks
were deposited
12
12
Types of Unconformities
• Unconformities of regional extent may change from one
type to another
• They may not represent the same amount of geologic
time everywhere
13 13
Sedimentary Facies
• A sedimentary facies is
a body of sediment with
distinctive physical,
chemical, & biological
characteristics from the
sediments deposited
around it.
• These distinctive characteristics help in inferring the
environment of deposition of the sediment
• Both inter-tonguing and lateral gradation indicate
simultaneous deposition in adjacent environments
14
14
Marine Transgressions
• A marine transgression occurs when sea level rises
with
respect
to the
land
• During a transgression, the shoreline moves landward as
the sea progressively covers more and more of a continent
15
Marine Transgressions
• Each laterally adjacent
depositional
environment produces
a sedimentary facies
• The facies forming
offshore become
superposed upon
facies deposited in
nearshore
environments
16
Marine Regression
• During a marine regression
– sea level falls with respect to
the continent & the
environments parallel to the
shoreline migrate seaward
• It yields a vertical sequence
with nearshore facies
overlying offshore facies &
rock units become younger
in the seaward direction
17
Walther’s Law
• Johannes Walther (1860-1937) noticed that the same facies
he found laterally were also present in a vertical sequence.
– Walter’s law states that
• the facies seen in a
conformable vertical
sequence will also
replace one another
laterally
– Walther’s law applies
• to marine transgressions
and regressions
18
Causes of
Transgressions and Regressions
• Uplift of continents causes regression
• Subsidence causes transgression
• Widespread glaciation causes regression
– because of the amount of water frozen in glaciers
• Rapid seafloor spreading,
– expands the mid-ocean ridge system, displacing
seawater and causing transgression
• Slow seafloor-spreading
– increases the volume of the ocean basins and causes
regression
19
19
Fossils
• Fossils are the remains or traces of past life forms
• They are most common in sedimentary rocks but can be
found in volcanic ash & volcanic mudflows
• They are extremely useful for determining relative ages of
strata but geologists also use them to ascertain
environments of deposition
• Fossils provide some of the evidence for organic evolution
• Remains of organisms are called body fossils. They
consist mostly of durable skeletal elements such as bones,
teeth & shells
20
Trace Fossils (or Ichno-Fossils)
• Indicate activity of the organism that produced them
– They include tracks, trails, burrows, and nests
• A coprolite is a type of
trace fossil consisting of
fossilized feces that may
provide information about
the size and diet of the
animal that excreted it
21
21
Body Fossil Formation
• The most favorable conditions for preservation
– of body fossils occurs when the organism possesses a
durable skeleton of some kind and lives in an area
where burial is likely
• Body fossils may be preserved as
– unaltered remains,
• meaning they retain their
original composition and
structure, by freezing,
mummification, in
amber, in tar
– or altered remains,
• with some changes in composition or structure
• permineralization, replacement, carbonization
• Insects in
amber
22
22
Unaltered Remains
• Frozen baby mammoth found in Russia in 1989
23
23
Altered Remains
• The bones of this
mammoth
– on display at the
Museum of
Geology and
Paleontology in
Florence, Italy
• have been
permineralized
– with minerals
added to the
pores and
cavities of the
bones
24
24
Altered Remains
• Carbon film of
a palm frond
• Carbon film of an insect
25
Molds and Casts
• Molds form
when buried
remains
dissolve and
leave a cavity
• Casts form if
minerals or
sediments fill
in the cavity
Step a: burial of a
shell
Step b: dissolution
leaving a cavity,
a mold
Step c: the mold is
filled by
sediment
26
forming a cast 26
Fossil Record
• The fossil record is the record of ancient lives
preserved as fossils in rocks
• Just as the geologic record must be analyzed
and interpreted, so too must the fossil record
• The fossil record is a repository of prehistoric
organisms that provides our only knowledge of
such extinct animals as trilobites, ammonoids,
and dinosaurs
27
27
Fossils and Time
• an English civil engineer
– independently discovered Steno’s principle of
superposition
• He also realized
– that fossils in the rocks followed the same principle
• He discovered that sequences of fossils,
– especially groups of fossils are consistent from area
to area
• Thereby he discovered a method
– whereby relative ages of sedimentary rocks at
different locations could be determined
28
28
Fossils from Different Areas
• William Smith (1769-183) used fossils to compare
the ages of rocks from two different localities
29
Principle of Fossil Succession
• Using superposition, Smith was able to predict
– the order in which fossils would appear in rocks not
previously visited
• Alexander Brongniart in
France
– also recognized this
relationship
• Their observations
– led to the principle of
fossil succession
30
Principle of Fossil Succession
• Principle of fossil succession
– holds that fossil assemblages (groups of fossils)
succeed one another through time in a regular and
determinable order
• Why not simply match up similar rocks types?
– Because the same kind of rock has formed
repeatedly through time
• Fossils also formed through time,
– but because different organisms existed at different
times, fossil assemblages are unique
• An assemblage of fossils has a distinctive aspect
compared with younger or older fossil assemblages31 31
Matching Rocks Using Fossils
youngest
oldest
• Geologists use the principle of fossil succession
– to match ages of distant rock sequences
– Dashed lines indicate rocks with similar fossils thus having
the same age.
32
32
Relative Geologic Time Scale
• Investigations of rocks by naturalists between
1830 and 1842
– based on superposition and fossil succession
– resulted in the recognition of rock bodies called
systems
– and the construction of a composite geologic
column
– that is the basis for the relative geologic time scale
33
33
Geologic Column and the
Relative Geologic Time Scale
Absolute
ages (the
numbers)
were
added
much
later.
34
Example of the
Development of Systems
• Cambrian System
– Sedgwick studied rocks in
northern Wales
– and described the Cambrian
System without paying
much attention to the fossils
– His system could not be
recognized beyond the area
• Silurian System
– Murchinson described
the Silurian System in
South Wales
– and carefully described
the fossils
– His system could be
identified elsewhere
35
Dispute of Systems
• The two systems partially overlapped!
36
36
System Dispute
• The dispute was settled in 1879
– when Lapworth proposed the Ordovician
37
37
Stratigraphic Terminology
• Because sedimentary rock units are time
transgressive,
– they may belong to one system in one area
– and to another system elsewhere
• At some localities a rock unit
– straddles the boundary between systems
• We need terminology that deals with both
– rocks—defined by their content
• lithostratigraphic unit – rock content
• biostratigraphic unit – fossil content
– and time—expressing or related to geologic time
• time-stratigraphic unit – rocks of a certain age
• time units – referring to time not rocks
38
38
Lithostratigraphic Units
• Lithostratigraphic units are based on rock type
– with no consideration of time of origin
• The basic lithostratigraphic element is the
formation
– which is a mappable rock body with distinctive
upper and lower boundaries
• It may consist of a single rock type
• such as the Redwall limestone
– or a variety of rock types
• such as the Morrison Formation (LST, Sst, Sh, Siltstone)
• Formations may be subdivided
– into members and beds
– or collected into groups and supergroups
39
39
Biostratigraphic Units
• A body of strata
recognized only on the
basis of its fossil content
is a biostratigraphic unit
• the boundaries of which do
not necessarily correspond to
those of lithostratigraphic
units
• The fundamental
biostratigraphic unit
– is the biozone
40
Time-Stratigraphic Units
• Time-stratigraphic units
• also called
chronostratigraphic units
– consist of rocks deposited
during a particular
interval of geologic time
• The basic timestratigraphic unit
– is the system
41
Time Units
• Time units simply designate
– certain parts of geologic time
• Period is the most commonly used time
designation
• Two or more periods may be designated as an
era
• Two or more eras constitute an eon
• Periods can be made up of shorter time units
– epochs, which can be subdivided into ages
• The time-stratigraphic unit, system,
– corresponds to the time unit, period
42
42
Classification of
Stratigraphic Units
Lithostratigraphic
Units
• Supergroup
– Group
• Formation
– Member
» Bed
TimeTimestratigraphic
Units
Units
• Eonothem
• Eon
– Erathem
• System
– Series
» Stage
– Era
• Period
– Epoch
» Age
43
43
Correlation
• Correlation is the process of matching up rocks
in different areas
• There are two types of correlation:
– Lithostratigraphic correlation
• simply matches up the same rock units over a larger area
with no regard for time
– Time-stratigraphic correlation
• demonstrates time-equivalence of events
44
44
Lithostratigraphic Correlation
• Correlation of lithostratigraphic units
such as formations
– traces rocks laterally across gaps
45
Lithostratigraphic Correlation
• We can correlate rock units based on
– composition
– position in a sequence
– and the presence of distinctive key beds
46
46
Time Equivalence
• Because most rock units of regional extent are time
transgressive, we cannot rely on lithostratigraphic
correlation to demonstrate time equivalence
• Example: Sandstone in Arizona is correctly correlated
with similar rocks in Colorado and South Dakota
– but the age of these rocks varies from Early Cambrian
in the west to middle Cambrian further east
• The most effective way to demonstrate time equivalence
is time-stratigraphic correlation using biozones
• But several other methods are useful as well
47
47
Biozones
• For all organisms now extinct, their existence
marks two points in time
• their time of origin
• their time of extinction
• One type of biozone, the range zone,
– is defined by the geologic range
• total time of existence
– of a particular fossil group
• a species, or a group of related species called a genus
• Most useful are fossils that are
– easily identified, geographically widespread
– and had a rather short geologic range
48
48
Guide Fossils (Index fossils)
• The brachiopod Lingula
– is not useful because,
– although it is easily identified
– and has a wide geographic extent,
• it has too large a geologic range
• The brachiopod Atrypa
– and trilobite Paradoxides
– are well suited
– for time-stratigraphic correlation,
• because of their short ranges
• They are guide or index fossils
49
49
Concurrent Range Zones
• A concurrent range zone is established
– by plotting the overlapping ranges
– of two or more fossils
– with different
geologic ranges
• This is probably
the most
accurate
method
– of determining
time
equivalence
50
Short Duration Physical Events
• Some physical events of short
duration are also used to
demonstrate time equivalence:
– distinctive lava flow would have
formed over a short period of time
– ash falls
• may cover large areas
• are not restricted to a specific
environment
• Absolute ages may be
obtained for igneous events
– using radiometric dating
51
Absolute Dates and the
Relative Geologic Time Scale
• Ordovician rocks
– are younger than those of the Cambrian
– and older than Silurian rocks
• But how old are they?
– When did the Ordovician begin and end?
• Absolute ages determined for minerals
–
–
–
–
in sedimentary rocks
give only the ages of the source
that supplied the minerals
and not the age of the rock itself
52
52
Absolute Dates for
Sedimentary Rocks Are Indirect
• Mostly, absolute ages for sedimentary rocks
– must be determined indirectly by
– dating associated igneous and metamorphic rocks
• According to the principle of cross-cutting
relationships,
–
–
–
–
–
a dike must be younger than the rock it cuts,
so an absolute age for a dike
gives a minimum age for the host rock
and a maximum age for any rocks deposited
across the dike after it was eroded
53
53
Indirect Dating
• Absolute ages of sedimentary rocks
– are most often found
– by determining radiometric ages
– of associated igneous or metamorphic rocks
54
54
Indirect Dating
• The absolute dates obtained
– from regionally metamorphosed rocks
– give a maximum age
– for overlying sedimentary rocks
• Lava flows and ash falls interbedded
– with sedimentary rocks
– are the most useful for determining absolute ages
• Both provide time-equivalent surfaces
– giving a maximum age for any rocks above
– and a minimum age for any rocks below
55
Indirect Dating
• These sedimentary rocks
– are bracketed by metamorphic and
– igneous rocks for which
– absolute ages are known
56
56
Indirect Dating
• Accurate radiometric dates are now available
– for many ash falls, plutons, lava flows and
metamorphic rocks
– with associated fossil-bearing sedimentary rocks
• These absolute ages have been added to the
geologic time scale
• Additionally, we know when a particular
organism lived
57
57
Indirect Dating
• Baculites reesidei
– biostratigraphic zone
– in the Bearpaw
Formation
– Saskatchewan, Canada
– is about 72-73 million
years old
– because absolute ages
have been determined
– for associated ash layers
58
58
QUESTIONS?
59
QUIZ
1. Record of events preserved in rocks is called _____
a) Geologic record b) Rock record c) Event record d) Earth’s record
2. The study of layered rocks is known as _________
a) Sedimentology b) Paleontology c) Palynology d) Stratigraphy
3. ____ shows period of non-deposition or erosion in rock sequence
a) Gap b) Erosive time c) Unconformity d) Parasequence
4. The missing interval of time in strata of rocks is called ______
a) Erosive surface b) Hiatus c) Bedding plane d) Fault
5. What type of unconformity is shown in the diagram below?
a) Non-conformity b) Disconformity c) Angular Unconformity
60
4:16
(9
Figure 10.16 Range chart.
Stratigraphic distribution of some genera of the foraminiferida
Genera
Periods
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Pennsylvanian
Mississippian
Devonian
7.
c.
What is the advantage, if any, of having more than
one index fossil when making age determinations?
On Figure 10.16, show by means of vertical bars the
geologic ranges for Ammodiscus, Endothyra, Fusulina,
Ammobaculites, Globigerina, Bolivina, and
Quinqueloculina.
What is the maximum possible geologic range
for rock containing only Endothyra?
d.
Which is the better index fossil, Fusulina
or Ammodiscus? Why?
b.
What is the age of a formation containing both
Robulus and Endothyra?
Chapter 10
109
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8
4:15
CS
Figure 10.12 The planktonic foraminiferida Globigerinoides.
Figure 10.13 Thin section of a fusulinid showing complex internal
structure. Length of specimen is 6 mm. (For image of a fusulinid before
thin-sectioning, see Schwagerina in Fig. 10.11.)
final chamber
aperture
ப்
suture
pores
b. Assume that the shale and sandstone have not
changed in thickness, and complete the rock
column for well B.
2. In Figure 10.15 a distinctive foraminiferida assemblage
is encountered at a depth of 410 m in
well #34. In well #62, an identical assemblage is
encountered at 400 m and again at 1200 m. In
well #71, the assemblage occurs at 1200 m.
On the diagram, draw in a fault to indicate how
faulting may have caused the repeated assemblage
in well #62.
a.
At what depth will the oil zone be reached at the
second location? State the assumptions you used
to reach your conclusion.
a.
b.
What is the name given to this type of fault? (See
Chapter 14 for a summary of fault terminology.)
Figure 10.14 Use of foraminiferida in predicting drilling depth.
B
pse
300 m
600
900
1200
1500
1800
2100
2400
2700
Oil-bearing
sandstone
Chapter 10
107
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