04 - Stratigraphy 2.pdf
Transcript of 04 - Stratigraphy 2.pdf
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STRATIGRAPHY 2Sediments in TIME and SPACE
http://www.eos.ubc.ca/courses/eosc326/content/EOSC326/
ID: eosc326
PW: ammonite
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LECTURE OUTLINE#
LITHOSTRATIGRAPHIC FORMATIONS
# FACIES
#
FACIES AND SEA LEVEL CHANGE# CASE 1: Stead State
# CASE 2: Transgression
#
CASE 3: Regression# Facies as Diachronous units
# WALTHERS LAW
#
MECHANISMS OF SEA LEVEL CHANGE# Crustal Deformation
# Isostatic Redress
# Global Eustatic Effects
#
Glaciation# Spreading Ridge Activity
# ENVIRONMENTS WHERE DEPOSITION OCCURS
#
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MID TERM 1 HEADS UP
!"#$%&"' )*+$%$,-
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$
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Learning Goals
1.# Define a lithostratigraphic formation
2.# Define a sedimentary facies and and explain how they may differ
laterally
3.#
Predict how facies will change vertically in response to sea levelrise (transgression) and fall (regression)
4.# Define Walthers Law
5.# List mechanisms of global (eustatic) and local sea level change.
6.# Relate sedimentary environmentsto the types of sediments
deposited in those environments and how this all relates to EarthSystem Science.
%
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Distinctive rock unit thathas recognizable contactswith units above and
below.
Rock type / fossilscontent / sedimentary
structures
ALSO must be able totrace it across country must be able to MAP it
Lithostratigraphic Formations
&
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Formations: 1 rocktype orassociations of
rock type, eg
Uinta Formation, Utah: composed of Sand and Siltstones
'
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How many formations would you tentatively identify?Mark them on the LHS of this photograph
The Grand Canyon (
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i>clicker: How many formations did you identify?
The Grand Canyon
A: 2
B: 3
C: 5
D: 6
E: 7
)
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LithostratigraphicFormations in the
Grand Canyon
At least 10in this
part..
probablymore
noteGroup
*
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REMEMBER: A sediment is deposited as a factor of theenvironment in which it is being deposited
EG: Near shore sands deposited by a slow advancing sea.
NOTE: although this is all the SAME TYPE OF SEDIMENT the
sediments at A were deposited BEFORE the sediments at B
!+
L*#$ M*% 7N.A- L441 B0 4GD35=6 BC=? ?3=14? F4O4;
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Develops concept of Formations a little further
Facies: part of a rock body that has characteristics from which
we can infer the depositional environment.
Consider this EXAMPLE of where sediment is beingdeposited.
FACIES: A DefinitionSee page 102 106 for additional information
!!
reverse engineer what the sediments make up this rock
sand closest to shore. heaviest. currents cant carry them further out Carbonates:sediment produced by plankton
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Turbulent (waves)High Energy
Environment
RIVER INPUT
All clasticsediments
have been
deposited
All coarsesedimentshave been
deposited
A coccolithophore: justone type of CaCO3
secreting planktonic
creature
Again in a little more detail..
Non clastic, biological sediment composedof CaCO3 Low Energy Environment
NOTE: this slope is greatly exaggerated!#
key to unravel ancient system because of the course -> fine sediment deposition
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=/# #2;F2346H4 0K :5B4;
==/#
U=V4 0K ?41=946B5;I >;5=6?===/
#
W=030>I
=R/#
Q5B4; 14DBC
R/# Q5B4; B49D4;5B2;4
SandMud and Clay
Carbonate mud
River:input of sediment
ShorelineSea level
"/# =/ ==/ =R/ R/
W/#
=/ ==/ ===/ =R/)/# =/ ==/ =R/
,/# ===/ =R/ R/
$/# ===/ =R/
!%
answer C
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HOWEVER:Lets complicate things
Plot sea level versus time:
Facies SHIFT through timedue to changes in sea level
LOCAL and GLOBAL
(Global = Eustatic)
Facies and
Sea LevelChange
COD-XX46/:=X:=
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CASE 1: the rate at which sediments are deposited keeps pacewith any changes in sea level T1 T3
RIVERINPUT
Facies boundaries inabout the same
location over time
TIME
Shoreline doesntchange location
A
A
Pebbles/GravelSand
SiltMuddy
carbonates
- facies boundaries and the location of the shoreline will notchange location over time
!'
no relative change in sea level, so the facies boundaries didnt really change
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We often can not see a cross section with all the facies exposed.
Just have a thin core of sediment in order to work out how sea
level has changed in the past
COD-XX46/:=X:=ZQ4?B4;6Z"2?B;53=5/[D> COD-XX46/:=X:=
!(
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T1
T2
T3
If you were to extract acore of sediments from
the area indicated in
case 1 at A A, this is
what that sedimentary
core would look likethe SAME facies from
the bottom to the top ofthe core.
A
A
As the sedimentary faciesare THE SAME over time
from the bottom of the
core (oldest) to the top of
the core (youngest) thenthe environmentalconditions (sea level)
MUST HAVE BEEN THE
SAME OVER TIME
Top of thesedimentary
core (youngest)
Bottom of thesedimentary core
(oldest)
!)
T1(oldest) and T3(youngest)
were sand, so it tells us the environment/sea level did not change
that much
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CASE 2: Sea Level RISES over time: A TRANSGRESSION
- Facies MIGRATE in direction of ADVANCING shore line
Shore lineat Time-rock unit B
Shore lineat Time-rock unit A
Shore lineat Time-rock unit C
!*
environment is varying
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NOTE the core of sediments you would get in this case
Progressively finersediments: Finer faciesOVERLY coarse facies:
SEA LEVEL MUST BE
RISING. Facies are saidto demonstrateonlappingbehaviour
Shore line A
Shore line B
Shore line C
#+
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CASE 3: Sea Level FALLS over time: A REGRESSION
- Facies migrate in direction of RETREATING shoreline
Progressively coarse
sediments: Coarse faciesOVERLY fine facies: SEA
LEVEL MUST BEFALLING. Facies
demonstratebacksteppingbehaviour
- NOTE the core of sediments you would get in this case
Oldest
shore line
Old shore
line
Current shore line
#!
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)/#
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##
answer B
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Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existingland
surface
Sea Level
Input ofsediment
Facies as Diachronous unitsDiachronus = time crossing
Example: with sea level rise
Shore lineT1
NOTE TIMEHORIZON T1
NOTE: Slope GREATLY exaggerated
#$
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Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existingland
surface
Sea Level
Input ofsediment
Shore lineT1
NOTE TIMEHORIZON T1
#%
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Sea Level
Input ofsedimentShore line
T2Shore line
T1
Movement of shoreline: TRANSGRESSION
As Before:- sea level rises
- facies migrate in the
direction of the moving
shoreline.
NOTE TIMEHORIZON T2
Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existingland
surface#&
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Sea Level
Input ofsediment
Shore lineT2
Shore lineT1
Shore lineT3
- Sea level continuesto rise.
Movement of shoreline: TRANSGRESSION
NOTE TIMEHORIZON T3
Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existingland
surface#'
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Sea Level
Input ofsediment
Shore lineT2
Shore lineT1
Shore lineT3
Shore lineToday
Movement of shoreline: TRANSGRESSION
Boundariesbetween differentsea floors.. T1-T3
Effectively time
horizons (red)
Boundariesbetween
different facies
(yellow)
If we just correlated the same sediment TYPE (faciesboundaries. The yellow lines) we would be CROSS
CUTTING the red time lines (T1, T2, T3)
#(
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On this diagram draw thefacies boundaries and time
lines .
Movement of shoreline: Transgression or regression?
NOTE: Slope GREATLY exaggerated
Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existingland
surface#)
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Indicate with an X theyoungest conglomerate.Indicate with a Y the
oldest carbonate.
Movement of shoreline: REGRESSION
facies
time
Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existingland
surface#*
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34R43 5? ;4D;4?46B41 FI BC=? S>2;4T \5??294 K5H=4?
F02615;=4? 5;4 R4;JH53]/
=/# %435JR4 ?45 34R43 =? K533=6>
==/#
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?45 34R43 HC56>4
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:=BC ?45 34R43 HC56>4
R/#
%435JR4 ?45 34R43 =? H06?B56B
SandMud and Clay
Carbonate mud
River:input of sediment
ShorelineSea level
"/#
=/ ===/ R/W/# =/ =R/
)/# ==/ =R/
,/# =/ ===/
$/#
===/ R/$+
answer Ebecause facies boundary
are vertical
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0;=46B5J06 0K BC4 K5H=4? F02615;=4?T
SandMud and Clay
Carbonate mud
River:input of sediment
ShorelineSea level
"/# M;09 34a B0 ;=>CB
W/#
#0:5;1? 144D4; :5B4;
)/#
M;09 ;=>CB B0 34a
,/#
W02615;I 0;=46B5J06 :0231 F4 R5;=5F34
$/#
M5H=4? F02615;=4? :0231 F4 R4;JH53
$!
answer A.
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SO WHAT IS ALL THIS LEADING TO?
We know the following facts:
1.# Facies are distributed due to changing conditions of deposition
over the surface of our planet. In our example, shallow highenergy, near shore conditions are characterized by sand.Deeper, quieter conditions are characterized by finer grained
sediments.
2.#
As conditions change (such as sea level) facies will appear toMIGRATE, following their particular environmental conditions.
3.# Over time this will lead to patterns of facies as one facies
MIGRATES OVER ANOTHER.
Walthers Law
$#
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4. This means that when we recover a verticalsuccession of rock (like the one we used in our
example) we can PREDICT the lateral equivalenceof facies
As we go from coarse, near-shore facies at thebottomof the core to off-shore, deeper water
carbonate sediments at the topof the core, sealevel (in this example) must have been RISING over
time.
silts sands Conglomerates
silts
sandscarbonates
carbonates
silts sandscarbonates pebbles
sands
silts
Carbon-ates
bottom
top
The uneven boundaries between the facies arean attempt to demonstrate that facies GRADE
into each other just as environments grade into
each other.
Conglomerates
Conglomerates
$$
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This is summed up in WALTHERS LAW
Facies that occur in a CONFORMABLE VERTICALSUCCESSION of strata, were deposited in laterally adjacent
depositional environments.
or put another wayadjacent sedimentary environments (facies) will end up
overlapping one another over time.
Sealevelfa
ll
Sealevelrise
Shore line
Beachsediments
Near shoresediments
Off shoresediments
$%
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1. Crustal Deformation (Local)
# Mountain building
# Subduction
#
Continental collision
Mechanisms of Sea Level Change
(i.e. relative sea level)
$&
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2. Isostatic redress (local)
# E.g. Removing ice sheets from Scotland
#
Scotland relative regression, England relative transgression
$'
ocean crust sag down because ice too heavy
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Scotland: Raised BeachesEngland: Big Trouble!
Depositing lots of sediment can also cause the crust to sag
COD-XX46/:=X:=
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The Michigan Basin
E#bcNN9 BC=H< =6 BC4 H46B;4
E#,4D0?=J06 K;09 )59F;=56 E d2;5??=H
$)
too much sediments deposited that the crust
sags
positive feedback. getting heavier, causing
more sag, causing more .
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3. Global Eustatic Controls
1. Glaciation
$*
ice sheet grew, sea level sink.
sea level rise, ice sheet smaller
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2. Spreading Ridge Activity
# Active spreading - Large Ocean Ridges hot and buoyant
#
Displace ocean water
%+
a lot of activity will produce a lot of mountain change, also displace water out therefore higher sea levels.
global effect not local
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Environments where deposition occurs
Terrestrial transitional Marine: see readings
%!
higher sea level affect how
river deposit sediments
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"/#
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)/# #C4 ?41=946B? :0231 F4H094 S64;
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#C4 ?41=946B? :0231 F4 90?B3I H09D0?41 0K K431?D5;
$/# #C4 ?41=946B? :0231 F4 4;0141/%#
answer c
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