1. Platforms and Paleozoic life
Geology 1023
Platforms and Paleozoic life

2. Platform sequences Thin (mostly) Flat-lying “Layer-cake” stratigraphy
Laps onto the shield
Undeformed
Rocks belong to the sequences mentioned in class (Sauk, Tippecanoe, etc.)
Mostly Paleozoic rocks

3. Doing the lab. Q. 1 Two cross sections Change in sediment type
Change in thickness
How is that related to the position of the shield in each case?

4. Doing the lab. Q. 2. Detailed map showing the Grand Canyon area
Map looks complicated
But it is just a valley slicing into flat-lying Phanerozoic sediments

5. Important forms of Paleozoic life
Trilobites (extinct)
Brachiopods (a few living forms)
Graptolites (extinct)
Sponges (arose in the Precambrian but important in Paleozoic)
Corals (arose in the Precambrian but important in Paleozoic)

6. Paleozoic Life Drawing (to get your “eye” in)
Make it as good as you can, grading isn’t on the basis of artistic merit
Scales are MANDATORY, major features should be labeled.
A few assemblage questions

7. An aside about assemblage dating
Imagine 3 photos of known order (1, 2, 3)
Photo 3 taken between 2010 and 2014
Photo 2 taken between
2000 and 2014
Photo 1 taken between 2000 and 2006

8. Trilobites
Arthropods (as are insects, spiders, scorpions, crustaceans…)
Tri-lobe-ite: they have three lobes from side to side: 1 axial/central lobe and 2 side (lateral or pleural) lobes
Also divided lengthwise into head (cephalon), thorax, and tail (pygidium).
Cephalon usually recognizable due to eyes and central bulge called “glabella”

9. Trilobite (Phacops)

13. Trilobites
As a defensive strategy, trilobites were able to curl up so that the hard back wrapped around the soft and vulnerable underside (legs, antennae)
Common to find such curled up (enrolled) trilobites

16. Brachiopods Look like bivalves (clams) BUT have different symmetry
Bivalves (clams) have a plane of symmetry between the shells or are asymmetrical
Brachiopods have plane of symmetry across the shells

17. Brachiopod features Two shells or “valves”
Larger valve with a hole (“pedicle opening”) at “beak” = pedicle valve
Other valve is the “brachial” valve
Growth lines (are concentric away from beak)
Costae (ribs) fan out from beak
Sulcus and fold are deep (central) central furrows/ridges running from beak to edge

18. Brachiopod plane of symmetry plane of symmetry sulcus (furrow) costae
(ribs)
growth lines
(concentric)
brachial
valve
pedicle
opening
pedicle
valve
~1 cm

19. Growth lines (concentric)
Pedicles

20. Graptolites Colonial organism
Fossils look like pencil markings, shaped like small sawblades
The blade part called a “stipe” contained several individuals. Each “tooth” of the blade (where individual organism lived) called a “theca”.

21. Graptolite (Monograptus)
thecae (sing. = theca)
stipe
~1 cm

26. Questions?