Historical Geology - GLY 302

Final Exam - Spring 2005

Detailed Lecture Topics - Brief Notes

After Rodinia rifted apart (~650 m.y.) the largest remnant was Gondwana
Gondwana contained what later became Africa, South America, Antarctica, India, and Australia

Laurentia had passive margins on east and west coasts beginning with the rifting from Rodinia

Appalachian Mountain Building

Taconic Orogeny (Late Ord)
metamorphic belt (e.g., Manhattan Schist) + clastic wedge
caused by collision with volcanic island arc
evidence: basaltic volcanic rx found with deformed sedimentary rocks
(e.g., the amphibolite [metamorphosed basalt] in Central Park)

Acadian Orogeny (Dev)

metamorphic belt
extensive granite from melting in deepest hottest parts of the orogen (
(e.g., granites of "The Granite State" and Maine)
clastic wedge (Catskill redbeds)
same as Caledonide Orogeny in NW Europe
The Old Red Sandstone of Britain equivalent to the Catskill redbeds
Acadian/Caledonian Orogeny the result of collision of Laurentia w/ Baltica (NW Eur)
New continent formed: "Laurussia"

Appalachian Orogeny (Penn-Perm)
produced the folds of the Appalachian Valley & Ridge province
blocks of deep basement rock uplifted - Grenvillian gneisses of the metamorphic highlands
high mountains, metamorphism beneath, clastic wedge forms on flank

Ouachita Orogeny in south-central North America

Mauritanide Orogeny in NW Africa

Hercynian Orogeny in southern Europe

Uralian Orogeny in Urals Mountains separating Europe & Asia

All of the orogenies (Appalachian - Uralian) occurred at the end of the Paleozoic as a result of continental collisions that produced the supercontinent Pangea

Paleozoic Life

the forerunners: oldest multicellular animals (metazoans): ~600 m.y., Ediacaran fauna
soft body impressions in sediment of segmented worms, jellyfish, sea pensä

Cambrian Revolution: evolution of hard parts
Early Cambrian small shellies
middle Cambrian very rapid development of most animal phyla including some bizarre

Evolution of Vertebrates - Part I, The Fishes
vertebrates are phylum chordata, subphylum vertebrata
oldest chordates were pikaia of the middle Cambrian
oldest vertebrate fossils (scales of jawless fish) are from the upper Cambrian
vertebrates have backbone and braincase
jawless fish (agnathans) had cartilage skeletons, some had bony plates on the head
lampreys and hagfish are about the only remaining jawless fish
Placoderms probably evolved in the Silurian (common in Devonian)
had jaws but no teeth - jaws modified into tooth-like shapes
cartilage skeletons and bony plates armoring their head
some very large predators
now extinct
Acanthodians probably evolved by the Silurian
cartilage skeletons
more streamlined form than placoderms
probably ancestors of the bony, ray-finned fish
now extinct
Sharks, rays & skates probably evolved by the Silurian, common in Devonian
cartilage skeletons
produce thousands of enamel covered teeth in their lifetime
sharks, rays, and skates still survive very successfully
Bony Fish - Ray-fins evolved in the Devonian (from acanthodian!?)
bony skeleton
fine bones support fins
ray-fins are the most diverse of all fish
Bony Fish - Lobe fins evolved in the Devonian
bony skeleton
muscular fleshy lobes support finer bones of the fins
the modern coelecanth and a few others still survive

Evolution of Vertebrates - Part II, Invasion of the Land

3 problems in adapting to life on the land

first land plants (ferns) and land animals (amphibians) need water for reproduction

age of fossil evidence for first land plants (pollen)
and first land animals ("bugs" & worms)

first tetrapods evolved (Late Dev) from a branch of lobe-fin fish

Carboniferous: Age of "Amphibians"

first amniotes: Carboniferous
difference between amphibian and amniote eggs
sauropsid and synapsid amniotes

Permian drying (Pangea vast interior dry regions & rain shadows)
led to the dominance of seed ferns (the first gymnosperms) and synapsids
gymnosperms ("naked seeds"), such as modern conifers, use airborne fertilization

Permian: Age of the "Reptiles"

Permo-Triassic mass extinction - the biggest known - cause: unknown

Mesozoic-Cenozoic Life

early Triassic low fossil diversity then re-diversification (adaptive radiation)
sauropsid amniotes become dominant
Mesozoic sauropsids included: turtles, crocodiles, lizards, snakes
marine reptiles (icthyosaurs, plesiosaurs), pterosaurs, dinosaurs (evolved Late Triassic)

synapsids dwindled: last remaining branch evolved into the mammals (evolved Late Triassic)
remained small throughout the Mesozoic

Mesozoic: Age of the Dinosaurs
advantage: "hole in the hip socket" allowed dinos to place legs directly beneath body
saurischian ("lizard-hipped") dinosaurs
ornithischian ("bird-hipped") dinosaurs
were all dinosaurs cold-blooded?
were dinsosaurs good parents (Barney)

Dinosaurs became extinct at end of Cretaceous (Cretaceous-Tertiary mass extinction)
all except the birds, which had evolved by mid-Jurassic from a group of saurischian (!) dinosaurs

Cause of K-T mass extinctions of dinosaurs, ammonites and many others:
question: gradual or sudden extinction? (probably sudden)
cause? volcanic vs. meteorite impact theories - "nuclear winter" scenarios
evidence: iridium, shocked quartz, glass spherules
the smoking gun: Chicxulub crater

mammals became dominant land animals of the Cenozoic following K-T extinctions
mammals diversified into 22 orders during Paleocene-Eocene
birds remained successful (and they are living dinosaurs!)

Pangea Breakup

Triassic-Jurassic rift basins (e.g., Newark Basin)
half-grabens filled with sedimentary strata (redbeds) and basaltic lava flows

oldest ocean crust in central Atlantic between Africa and North America: ~ 170-165 m.y.

passive margin sequence developed on the margins of the now separate continents

central Atlantic was restricted seaway during Jurassic, climate was arid
extensive salt deposits in subsurface of present day Atlantic and Gulf coast continental shelf
salt diapirs rising through overlying strata have formed petroleum traps

Gondwana began to break up soon after separating from Laurasia (N. Amer + Eurasia)
S. Amer + Africa, then India, then Australia, then New Zealand unzipped from Antarctica
between 155 and 85 m.y. ago (Jur & Cret)

Alpine-Himalayan Mountain Belt
As Gondwana broke up Africa/Arabia and India drifted northward toward Eurasia
India has been colliding with southern Asia and building the Himalayas since 60 m.y. ago
southeast Asia has been squeeze out of the way
Africa/Arabia has been colliding with southern Eurasia since ~ 35 m.y. ago
building the Alps Mountains
Asia Minor (Turkey) seems to be getting squeezed out of Arabia's way
The Mediterranean is the last vestige of the Tethy's Sea
The Mediterranean basin dried up ~5 m.y. ago but then re-flooded

Western Cordillera
western margin of N. Amer had been passive margin since Rodinia breakup
Devonian Antler Orogeny indicates a change to active margin, convergence, subduction
Jurassic and Cretaceous saw a great increase in rate of subduction-related igneous activity
Late Cretaceous Sevier Orogeny indicates increasing friction/compression
Latest Cret-Early Tertiary Laramide Orogeny:
massive compression, folding, thrust & reverse faults all the way across western 1/3 of North America, all the way to the Front Range of the Rocky Mountains
Hypothesis:
Jur-Cret: N. Amer. starts moving west away from new Mid-Atlantic ridge
rate of subduction increase, rate of igneous activity increases
Late Cret. N. Amer. getting closer to midocean ridge (East Pacific Rise)
young ocean crust harder to subduct
shallower subduction angle, more friction & compression
Latest Cret-Tert. midocean ridge just off shore
N. Amer grinds over ocean crust that is too young, hot, and buoyant to sink
into the mantle
extreme friction and compression
North America runs over midocean ridge and subduction stops

San Andreas Fault now connects the remaining portions of the midocean ridge from the Gulf of California to the coast of northern California

with the subduction of the ridge, a change from compression to shearing with a sense of extension has led to the development of the Basin and Range province (extensive normal faulting)

From the Greenhouse to the Icehouse

Cretaceous
Observations:
climate very warm
no icecaps
reptiles including dinosaurs to arctic and antarctic circles
sea level high - continents flooded
much ocean crust formed (very rapid seafloor spreading), voluminous hotspot activity
Explanation:
rapid seafloor spreading "inflated" midocean ridge and seafloor causing high sea level
rapid midocean ridge and hotspot volcanism outgassed much CO₂ causing warm temperature

Cenozoic
Observations:
continuing warmth in early Cenozoic gave way to cooling from late Eocene onward
rapid cooling pulses - Eocene Oligocene boundary, Plio-Pleistocene
General Causes of Cooling
seafloor spreading rate declined (reduced CO₂ outgassing)
Alpine-Himalayan and Western Cordilleran mountain building (increased weathering uses more CO₂)
Specific Causes of Cooling Pulses
opening of the Drake Passage between S.Amer. and Ant.
led to onset of Antarctic glaciation
closure of Isthmus of Panama
led to intensification of Gulf Stream and onset of northern hemisphere glaciation (2 hypotheses why)
Cause of glacial advances and retreats
Milankovitch orbital cycles
variations in Earth's precession, tilt, and eccentricity
yield variations in the amount of solar radiation striking the Earth during summer (melt season)
predicted variation in solar insolation matches actual record of temp change from oxygen isotope record
question: gradual or sudden extinction? (probably sudden)
question: gradual or sudden extinction? (probably sudden)
question: gradual or sudden extinction? (probably sudden)

Closing Comments:

- final notes on the ages of plants

- brief primer on primate and human evolution

- final comments on modern climate