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Earth History, Ch. 13 1 Cambrian System Ordovician System Early Early Middle Middle Late Late 543 495 443

Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

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Page 1: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 1

Cambrian

System

Ordovician

System

Early

Early

Middle

Middle

Late

Late

543

495

443

Page 2: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 2

Ch. 13 Review:

Early Paleozoic life & Burgess Shale fauna

• Most animal phyla originated in Cambrian;

Ordovician was a time of diversification within

clades

• Burgess Shale fauna accumulated at the edge of the

continental shelf during middle Cambrian time

• Unusual preservation of soft anatomy is attributed to

rapid burial in deep, oxygen-depleted water

• Significance of the Burgess Shale fauna

Page 3: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 3

Cambrian geography and geology

• During Cambrian time, Laurentia was a tropical, low-lying landmass

• Marine sediments around the margins of Laurentia formed concentric facies belts

– Nearshore detrital clastic belt

– Shallow water carbonate belt

– Offshore, deeper-water deposits

• Sea level was generally rising during Cambrian and early Ordovician time, producing a transgressive stratigraphic sequence

Page 4: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 4

Cambrian

sedimentation

patterns

paleoequator

Page 5: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 5

Depositional Sequences

Sauk sequence is a

record of transgression

(rising sea level) from

the margins of Laurentia

across the midcontinent

Figure 6-21 (black = nondeposition

or erosion)

Page 6: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 6

Sauk transgression

Page 7: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 7

Early Cambrian time

Page 8: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 8

Middle Cambrian time

Page 9: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 9

Late Cambrian time

Taconic island arc

Page 10: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 10

Taconic orogeny

• During Ordovician time, Laurentia remained tropical, but Gondwanaland migrated toward the south pole

– Widespread late Ordovician glaciation and drop in sea level

• Avalonia was a fragment of Gondwanaland that broke away and nearly collided with Baltica and Laurentia

– Taconic Orogeny of eastern Laurentia: 1st stage of Appalachian mountain building

Page 11: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 11

Ordovician paleogeography

Time 1 Time 2 Time 3

Page 12: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 12

Laurentia

Taconic arc

Avalonia

Baltica

Siberia

Page 13: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 13

Laurentia

Taconic Mtns Avalonia

Baltica

Siberia

Page 14: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 14

Taconic orogeny: eastern Laurentia

Accreted Avalonian island arc terranes contain “exotic”

fossils not known in cratonic Laurentia

Page 15: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 15

Laurentia in Late Ordovician

Page 16: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 16

Late Ordovician glaciation

• Evidence for Late Ordovician glaciation

– Worldwide drop in sea level, as determined by erosional unconformities

– Glacial till, glacial striations, and dropstones near south Pole (now northern Africa)

– Enrichment of 18O in seawater (16O preferentially locked up in glacial ice)

• Suggests duration of glaciation was only 0.5 to 1.0 million years

Page 17: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 17

Late Ordovician glaciation

Decrease in d18O indicates

melting of glacial ice

Increase in d18O indicates

buildup of glacial ice;

Page 18: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 18

Effects of late Ordovician glaciation

• End-Ordovician mass extinction!

• Reduction in generic diversity, but not elimination of phyla

• Affected groups were brachiopods, trilobites, corals, bryozoans, acritarchs, graptolites, nautiloids, conodonts

• Two pulses of extinction

– Tropical, warm-water forms were eliminated during onset of glaciation (this allowed for geographic expansion of cool-water biotas)

– Cool-water biotas were eliminated during return to non-glacial climate!

Page 19: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 19

End-Ordovician mass extinction

Page 20: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 20

Early Paleozoic

of Iowa

Cambrian rocks crop out

along a thin belt adjacent

to the Mississippi River

Ordovician rocks crop out

in a wider belt in NE Iowa,

with isolated exposures in north-

central Iowa

cross section

Page 21: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 21

Iowa cross-section

Precambrian

NE NW

Page 22: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 22

Early Paleozoic of Iowa

Page 23: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 23

Early

Paleozoic of

Iowa

Note: No early or

middle Cambrian rocks

in Iowa—Why???

Page 24: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 24

Cambrian Jordon Sandstone

Page 25: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 25

2006 Discovery:

Winneshiek Lagerstatten and

possible impact structure

Page 26: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 26

Page 27: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 27

Page 28: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 28

2010 NSF grant to fund

additional sample collecting

Page 29: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 29

Page 30: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 30

Page 31: Middle Ordovician System - faculty.chas.uni.edufaculty.chas.uni.edu/~groves/EHCh13lecturept02.pdf · System Ordovician System Early Early Middle Middle Late Late 543 495 443 . Earth

Earth History, Ch. 13 31

Two tons of fossiliferous shale