Knowledge Base and Textbook Readings for Geology 02, Historical Geology
Final Exam Spring 2010
The following is a list of topics, ideas, and vocabulary that you are responsible for
learning in this class. Chapter numbers refer to Wicander and Monroe, Historical
Geology, 5e Ed.
Review the presentation pdfs. Make sure that you know the four orogenies that impacted
the eastern margin of North America and New York State and be familiar with the
geological evidence for them. Also, be aware of the effect that the rifting apart of Pangea
had on eastern North America in the Triassic and Jurassic. These tectonic events and the
evidence for them were a major focus of both lecture and lab in the course.
Plate Tectonics and the Rock Record
Wicander (Ch.3)
Tectonic plates: lithosphere (upper mantle + crust) supported by asthenosphere
Plates are driven by mantle convection, new ocean floor forms from rifting and old ocean
floor is recycled by subduction
Divergent margins, continental rifting: geologic evidence for rift valleys – faults, lava
flows, lake deposits. Evidence for passive margin – thick carbonate deposits.
Convergent margins, ocean-ocean, ocean-continent, and continent-continent collisions
Geologic evidence for plate collisions: metamorphism, granite plutons, filling of foreland
basins with eroded sediment
The Archean Eon
Wicander (Ch.8)
Archean rocks – greenstone (metamorphic volcanic sediments, banded iron formations
(BIF), granite and gneiss (pods of continental crust forming over subduction zones).
Isua rocks from Greenland – evidence for small protocontinents and volcanic island arcs
(pillow basalts, greywacke, BIFs, chert) but no large continents.
Significance of BIFs – production of oxygen, presumably by photosynthesizing bacteria,
uptake of oxygen by iron in oceans, leaving no oxygen to diffuse into atmosphere.
Archean plate tectonics – many small plates, rapid recycling of crust, small protocontinents – collision of protocontinents to produce regions of gneiss surrounded by
greenstone
Evidence for bacterial life: microfossils in chert, stromatolites (sedimentary structures –
mud mounds produced by bacterial mats), carbon isotope ratios
Apex chert – oldest preserved microfossils of bacteria? Or just inorganic carbon
smudges?
Carbon dioxide levels reduced from the Hadean due to the weathering of rock on the
continents (uses up carbon dioxide) and the formation of limestone in the oceans
(carbon dioxide from the atmosphere becomes trapped in the crust as carbonate rock).
So why didn’t the Earth freeze in the Archean under a weak sun?
Methane hypothesis – methanogenic bacteria thrived in the Archean under anaerobic
(oxygen poor) conditions. Production of methane caused greenhouse effect in
atmosphere, warming the Earth. Earth didn’t get too hot because reaction of methane
produced smog at high concentration (>1000 times modern level) blocking out
sunlight.
Pongola Group and Witwatersrand Supergroup – rock formations that show existence of
larger continents with continental shelves and terrestrial river systems.
Evidence for low oxygen in the Archean atmosphere: absence of terrestrial red beds,
presence of uraninite and pyrite in subaerial sediments.
The Proterozoic Eon
Wicander (Ch.9)
Cratonization – assembly of large continents
First extensive red beds – evidence for rise in atmospheric oxygen levels
Oxygenation of the atmosphere removed methane – reduced greenhouse warming.
Diversification of stromatolites – formation of extensive carbonate (limestone) in the
ocean leading to removal of CO2 from the atmosphere
Gowgonda Formation - first evidence for glaciation and ice age – caused by drawdown of
CO2 by carbonate formation and by loss of methane.
Late Proterozoic - Snowball Earth theory – period of wild oscillations in global climate
from extremely cold to extremely warm. Evidence for snowball Earth – glacial
sediments (till) interlayered with thick limestones (cap carbonates). Carbon isotope
evidence for high productivity in oceans prior to glaciation, followed by a drop in
ocean productivity following glaciation.
Carbon dioxide cycle – Hothouse climate and equatorial continents promote limestone
formation which removes CO2 from the atmosphere. Drawdown of CO2 causes
cooling, which slows and then stops limestone production as Earth freezes. During
Icehouse conditions, volcanoes add CO2 back to the atmosphere. By the time marine
ecosystems and limestone production recovers, CO2 levels are very high, leading to
Hothouse climate. Cycle repeats until plate tectonics move continents away from the
equator.
Evolution of eukaryotic cells by symbiosis of prokaryotes (bacteria)
Radiation of eukaryotic cells, decline in stromatolites (bacteria being grazed by protests),
evolution of sex
The Dawn of Animal Life
Wicander (Ch.9)
Increasing evidence for complex eukaryotic organisms in the Late Proterozoic.
Acritarchs – fossil cysts of marine algae (dinoflagellates)
1.0 Ga to 600 Ma – increasing evidence for evolution of multicellular organisms:
multicellular algae, carbonaceous impressions, trace fossils (simple burrows) made by
metazoans (animals)
Ediacaran fossils – appear following the Varanger Glaciations (Snowball Earth), may be
a unique radiation of animal life or may be early, non-skeletonized members of
modern marine animal groups (jellyfish, soft corals, mollusks, etc.). Preserved as
impressions in sandstones, possibly after being covered by bacterial mats.
Latest Proterozoic “shells” – calcium carbonate produced by animals? Cloudina and
enigmatic things from Namibian limestones.
Fossil embryos preserved by phosphatization – jellyfish and possible worm embryos.
Possible mass extinction of Ediacaran organisms – did they die off or just stop getting
preserved?
Phanerozoic Eon begins at 544 Ma (beginning of the Cambrian Period) – marked by
appearance of large animal trace fossil. Next come small shelly fossils – tiny plates
and shells of animals. These are followed in the fossil record by trilobites,
echinoderms, brachiopods, etc – large, recognizable animals.
Cambrian Explosion – rapid appearance of most major groups of metazoans in the fossil
record. Why did it happen? Atmospheric oxygen levels, evolutionary arms race,
evolutionary novelty triggering an adaptive radiation?
Fossil lagerstatte (extremely unusual deposits that preserve soft-bodied organisms) from
the Cambrian – Burgess Shale, Chengjiang Formation – show that almost all major
groups (phyla) of animal life evolved by the end of the Early Cambrian, including
vertebrates.
Interpreting Geologic History from Cross Section
Historical Geology Laboratory Manual
Geological Formation – formally named rock unit
Steno’s principles: Law of Original Horizontality, Law of Superposition, Cross-cutting
Relationships
Geological Events: deposition, transgression, regression, erosion, unconformity, igneous
intrusion, uplift, folding, faulting, metamorphism
Geologic History of NY – The Grenville Orogeny
Wicander (Ch.9, Geol. of NY and NJ, pg. 2-5)
Grenville Orogeny – Late Middle Proterozoic collision between eastern North America
and Amazonia (part of South America) during assembly of Rodinia supercontinent.
Metamorphic and meta-igneous rock underlying much of eastern North America
Exposed where uplifted in New York – Adirondacks, Hudson Highlands, Manhattan
Prong
Grenville Mountain range eroded during Late Proterozoic – 500 my nonconformity
formed in NY.
Geologic History of NY – The Taconic Orogeny
Wicander (Ch.10)
Cambrian – Early Ordovician: passive margin (limestone deposition).
Middle – Upper Ordovician: active tectonic margin – collision of east coast with volcanic
island arc – Taconic Orogeny
Evidence for Taconic Orogeny: rapid change from shallow water to deep water
deposition (development of foreland basin – “bowling ball on the mattress effect”)
Erosion of Taconian Mountains deposits clastic sediments westward across New
York State – shales, siltstones, and greywackes.
Eastern New York – metamorphism of rocks beneath rising Taconian Mountains –
schist, gneiss, and marble of the Manhattan Prong.
Folding and thrust faulting of Upper Ordovician and older rock layers towards the
end of the Taconic Orogeny, uplift and erosion to form angular unconformity.
Metamorphism and movement of rock layers in the Taconic region east of the
Hudson River – Taconic klippe or allochthon (a region of crust that has been pushed
out of place)
After the Taconic Orogeny: erosion of the Taconian Mountains. Unconformity spanning
most of the Silurian.
Late Silurian: sea level rise – shoreline moves westward across New York. Deposition of
Shawangunk conglomerate, return of shallow water passive margin conditions and
deposition of limestones.
Geologic History of NY – The Acadian Orogeny and the Late Paleozoic
Wicander (Ch.11)
Lower Devonian: passive margin conditions persist. Deposition of limestone in shallow
seas covering New York. Abundant marine fossils – extensive coral reefs.
Middle Devonian: beginning of Acadian Orogeny – collision of eastern North America
and Avalonia microcontinent (part of Europe).
Evidence for the Acadian Orogeny: rapid change from shallow water to deep water
deposition as Middle Devonian begins (development of foreland basin – “bowling
ball on the mattress effect”)
Erosion of Acadian Mountains deposits clastic sediments westward across New York
State – shales, siltstones, greywackes, sandstones, and conglomerates.
Deposition of enormous quantities of eroded sediment filling the foreland basin and
spreading of river systems across New York into Pennsylvania and Ohio (the
“Catskill Delta”.
Devonian metamorphism and igneous intrusion in rocks of New England and
Virginia.
“Exotic” fossils in sedimentary rocks of the Boston area and other parts of New
England – remnants of Avalonia sutured to North America.
Gilboa forest – world’s oldest known fossil forest preserved in the Upper Devonian
sandstones of the Catskill Mountains.
Mississippian: return of passive margin conditions across eastern North America after
erosion of Acadian mountains.
Pennsylvanian: Alleghenian Orogeny – collision of Africa and South America with North
America – final stage in the assembly of Pangea.
Little evidence of Alleghenian Orogeny in New York – some folding of older rock
layers in the eastern part of the state.
Most impact seen south of New York – belt of metamorphic rock between the coastal
plain and Blue Ridge Mountains, bordered by belt of folded and thrust faulted
sedimentary rock to the west. Foreland basin was farther west – filled with thick
deposits of sandstone and shale covering Kentucky, West Virginia, and western
Pennsylvania.
Pennsylvanian sedimentary rock shows evidence of high amplitude sea level cycles –
widespread transgressions and regressions – caused by the waxing and waning of
glaciers in the southern hemisphere (Gondwana). Flooding of the continental interior
during sea level rise (transgression) created extensive swamp forests that led to the
deposition of widespread coal formations.
Permian: no record exists in New York. All continents are joined as Pangea. Sea floor
spreading stops, causing a global regression. Climates across most of Pangea are arid
or seasonally wet. Seed plants and synapsids dominate terrestrial ecosystems.
End Permian mass extinction: up to 95% of all species go extinct in both terrestrial and
marine ecosystems. Extinctions likely caused by combination of sea level fall,
climate change, and climate disruption due to gases released by immense, long-term
volcanic eruptions in Siberia.
Geologic History of NY – The Mesozoic Era
Wicander (Ch.14)
Mesozoic rift basins: regions of Late Triassic to Early Jurassic rock found along the
eastern margin of North America. Formed during rifting and separation of Pangea.
Normal fault forms as crust is pulled apart and blocks of crust sink, creating large,
elongate valleys. Valleys fill with sediment as rivers and alluvial fans transport
sediments eroded from the uplands bordering the valley. Lakes form as rivers flow
into rift basins. Volcanic eruptions are common as magma rises along faults from the
mantle.
Rift basin geology: alluvial fan conglomerates, braided river sandstones, red beds,
lake shoreline siltstones (often showing dinosaur trackways), and deep lake black
shales. Basalt lava flows and diabase dikes and sills (e.g. Palisades Cliffs).
Newark Lowlands and Connecticut Valley are Triassic-Jurassic rift basins.
Cretaceous: Expanding Atlantic Ocean basin leads to development of passive margin
along eastern North America. High sea level in the Cretaceous floods the coastal
plain and deposits marine sediments far inland of the present coastline. Cretaceous
deposits are exposed along the inner New Jersey coastal plain and are present beneath
Long Island.
Geologic History of NY – The Pleistocene Epoch
Wicander (Ch.17)
Pleistocene – epoch of Ice Ages – major advances of continental glaciers.
Most recent continental glaciation was the Wisconsinan – peak at 22,000 years ago.
New York completely ice covered, landscape modified by glacial erosion and deposition.
Long Island formed by glacial deposition.
Landscape features of glacial erosion: striations and chatter marks carved in bedrock, ushaped valleys, tunnel valleys.
Depositional glacial features: drumlins, erratic boulders, moraines (till), outwash, kettle
holes and kame hills.