geologic period or epoch

age, m.y.

tectonic events

rocks produced

local formations

Cretaceous -> Recent

145 -> 0

US east coast a drifting passive margin. Atlantic Ocean created.

Coastal Plain sediments

none

E. to M. Jurassic

190 -> 175

Drift. Sea-floor spreading begins

Late Triassic

230 -> 208

Rift. Initial breakup of Pangea, rift valley fill

basalt flows, diabase sills, rift basin ss.

Harrisburg & Gettsburg area basalt, ss.

Late Perm->M.Trias

260 -> 230

Alleghenian orogeny. Climax of collision of N.America with Gondwanaland (Africa). Folding of foreland basin. Closure of Pro-Atlantic produces Pangea supercontinent

Miss -> M. Perm

320 -> 260

Closing of Pro-Atlantic continues; initial collision with Gondwanaland

third clastic wedge shed to the west. Coal-bearing ss & sh in foreland basin

Mauch Chunk fm, Pottsville Grp

Miss

350 -> 320

No docking.  Continued closure?

transgressive ss -> sh -> carb

Loyalhanna fm

M. Dev -> E. Miss

387 -> 350

Acadian orogeny.  Laurentia docks with Avalon plate.  Plutonism in New England, Canada

huge second clastic wedge (Catskill delta), foreland basin fill,  regressive carb -> sh -> ss. 

Marcellus, Harrell, & Brailler sh's , Chemung fm, Catskill grp, Pocono fm

E. Sil -> E. Dev

438 -> 387

Convergence continues but tectonically quiet in PA

transgressive thin shelf ss -> sh -> carb

Tuscarora ss, Rose Hill sh, McKenzie fm, Bloomsburg fm, Willis Crk sh, etc

M. & Late Ord

478 -> 438

Taconian orogeny. Laurentia docks with Piedmont, Gander, & Dunnage terranes & converges with island arc. Overthrusts in SE PA

Taconian clastic wedge shed towards west (Queenston delta). regressive carb -> sh -> ss

M. Ord ls's (incl Salona & Coburn), Antes sh, Reedsville sh, Bald Eagle ss & Juniata ss

Cambrian -> E. Ord

600 -> 478

Drift. Continued opening of Iapetus Sea, high rates of spreading??, N. Amer. (Laurentia) east coast a drifting passive margin

transgressive ss -> sh -> carb sequence on continental marginal platform

Warrior fm, Gatesburg fm, Beekmantown Grp carb's

Late Proterozoic

900 -> 600

Rift. Separation of Gondwanaland (Africa-S. Amer) from Laurentia (N. Amer) by rifting, then opening of Iapatus Sea (proto-Atlantic)

basalts & very thick rift basin (graben) ss's & volcanics

metaigneous & metasedimentary rocks of Blue Ridge, South Mtn

Proterozoic

1200 -> 900

Grenville orogeny. collision of N. Amer. with western S. Amer.

high-pressure metamorphic terrain

local basement