1. Geologic Evolution of Eastern North America
Maps after slide two by Ronald Blakey, Northern Arizona University
and downloaded from
PowerPoint by Martin Schmidt
Slide 21 edited from Blakey slide 22.

2. Rodinia - about 1 billion years ago.
Baltimore Gneiss forms in Grenville Mountains, later exposed by erosion & then subsides at the continent edge as rifting occurs.
Rodinia supercontinent- about 1 billion years ago.
Source: hhmi BioInteractive EarthViewer

3. Early Cambrian
540 mya ( )
Part of South America
moving away

4. Late Cambrian 500 mya (505-495) created by subduction zone
Volcanic islands
30o S

5. Early Ordovician 485 mya (488-480) Iapetus Ocean
Islands move closer to North America
Iapetus Ocean

6. Taconic Mtns formed late Ordovician
Late Silurian
420 mya ( )
Collison of island arc creates mountains
Sediments deposited in varying shallow seas here will make the rocks we find in western MD today.
Continued motion toward North America
Taconic Mtns formed late Ordovician

7. Acadian Mtns formed in Devonian
Late Devonian
375 mya ( )
Africa
(part of Gondwana)
relativemotion
Further collisions create new mountains.
30o S
Acadian Mtns formed in Devonian

8. Early Mississippian 345 mya (350-345) Africa (part of Gondwana)
relativemotion

9. Pangaea Middle Pennsylvanian 308 mya (311-307)
Alleghanian Mtns formed about 310 mya

10. Pangaea Early Permian 280 mya (282-275)
Collision continuing over a long time creates high mountains.

11. rifting Early Triassic 245 mya (247-245)
Rifting and sediments here will later become the Frederick Valley.

12. Middle Jurassic
170 mya ( )
Africa
relativemotion
30o N

13. Early Cretaceous 130 mya (130-135) Atlantic Ocean 30o Africa
relativemotion
30o
Atlantic Ocean

14. Early (“Mid”) Cretaceous 105 mya (110-100)
Start of a long period of shoreline location movements -
deposition of sediments in shallow water creates the Coastal Plain

15. Late Cretaceous (Santonian)
85 mya (87-83)

16. Paleogene (Paleocene) 60 mya (62-58)
30o N

17. Paleogene (Eocene)
50 mya (52-48)

18. Paleogene (Eocene-Oligocene) 35 mya (36-33)
Meteorite impact occurs in what will be SE Virginia.

19. Neogene (Early Miocene)
20 mya (22-19)

20. Neogene (Pliocene)
5 mya (6-4)

21. 20,000 ya
Glaciers
Shorelines move out as ocean water becomes locked up in glacier ice on land.
During low sea levels in ice ages, Susquehanna and other rivers cut deep channels, draining toward old impact depression.

22. Present
Chesapeake Bay forms as rising sea levels flood the river valleys.