Sedimentation and Stratigraphy Geology 5142 Dr. Thieme

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Sedimentation and StratigraphyGeology 5142Dr.
Thieme

• Lecture 17 Land Plant Evolution, Marine
  Microfossils

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Tapeats sandstone paleochannels
Mudstone channel fills encased in tabular beds of
sand.
Lower Cambrian sandstone from the Grand Canyon
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Early Vascular Plants
Cooksonia occurs in Late Silurian and Early
Devonian beds such as the Rhynie chert in Scotland
The Early Devonian vascular plant Rhynia (A) had
stomata for regulating gas exchange (B)
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Wetland Habitat
Early vascular plants propagated vegetatively or
with spores. Both methods require that plants and
propagules remain near water throughout the life
cycle. Insects began to coevolve with early
plants before the plants spread onto dry land.
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Spore Production
Ground pine or ground cedar is a modern
lycopsid that still reproduces with spores
Spore tetrads (groups of four individual spores)
within the sporangium of the Early Devonian
land plant Aglaophyton major.
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Plants made Land

• Plants were the first biological organisms to
  invade the land (Silurian).
• Once plants established terrestrial environments,
  the next organisms to move on land (Devonian)
  were
• insects (Phylum Arthropoda, Class Hexapoda)
• amphibians (Phylum Chordata, Class Amphibia)

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Early Devonian
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Middle Devonian
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Late Devonian
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Plant Evolution summary

• Lycopsids are the club mosses and scale trees,
  such as Lepidodendron and Sigillaria
• Sphenopsids were the Paleozoic trees with ribbed
  bark which are related to modern scouring rushes
  and horsetails. Calamites was the most common
  fossil genus.

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Plant Evolution summary

• Progymnosperms were the group which first
  produced seeds for reproduction.
• Progymnosperms originated in the Middle Devonian.
• One of the most important progymnosperms was
  Glossopteris, which was restricted to Gondwana.

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Plant Evolution summary

• Gymnosperms are seed-bearing, non-flowering,
  pollinating plants with needle-like leaves.
• The modern conifers such as spruce and pine are
  gymnosperms.
• Gymnosperms originated in the late Devonian, but
  they did not spread across the land surface until
  the Permian period (295-250 Ma)

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Land Plant Evolution

• Seed ferns (progymnosperms) became extinct by the
  end of the Triassic
• Sphenopsids and Lycopods trickled through with
  small, specialized descendants
• Seedless vascular plants (ferns) and gymnosperms
  (gingkos, cycads, conifers) dominated Triassic
  and Jurassic land-plant communities

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Gymnosperms

• Cycads were palm-like plants which first appeared
  during the Triassic and now exist in tropical and
  semi-tropical areas
• Ginkgos remained abundant and still exist in
  isolated regions,
• Conifers continued to diversify and are now
  widespread in some terrestrial habitats,
  particularly at high elevations and high latitudes

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Cycads
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Ginkgos

• Ginkgos
• have changed very little
• for millions of years
• They were found
• living in some isolated habitats in Asia
• and have been transplanted elsewhere

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Conifers

• leaves simple, thin, and generally evergreen
• male and female reproductive organs in cones
• ovules transported in air

Pollen of a fir (Abies)
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Leaf of Williamsonia sp., a Cretaceous cycad
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Angiosperms

• evolved from specialized gymnosperms during
  either the late Jurassic or early Cretaceous
• adapted to nearly every terrestrial habitat from
  mountains to deserts and even to shallow coastal
  waters
• pollinated by insects (Phylum Arthropoda, Class
  Insecta) which diversified at the same time

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Fossil Angiosperms

• From the lower Cretaceous
• Potomac Group
• of the eastern United States

• Sapindopsis,
• Cecil County, Maryland

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Fossil Angiosperms

• From the lower Cretaceous
• Potomac Group
• of the eastern United States

• Aralia
• from New Jersey

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Cretaceous fossil leaves of Aralia sp. (Ginseng
family)
Cretaceous angiosperm pollen
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Angiosperms Success

• due to enclosed seeds which protect the
  propagules
• and flowers which attract animal pollinators,
  particularly insects
• now over 250,000 to 300,000 species
• account for more than 90 of all land plant
  species

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Coccoliths

• calcareous microfossils
• shells of single-celled micro-organisms now
  placed in Kingdom Protista
• coccolithophores are a type of "algae," have
  chloroplasts, and practice photosynthesis
• They were formerly placed in Kingdom Monera,
  Class Chrysophyta

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Coccoliths

• Coccoliths from the Gulf of Mexico

Miocene-Pliocene
Miocene
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The Upper Cretaceous chalk of the "cliffs of
Dover" consists mostly of coccoliths and other
calcareous microfossils
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Diatoms

• build their skeletons of silica
• made their appearance during the Cretaceous
  period
• most important and diverse during the Cenozoic
  era
• most abundant in cooler oceanic waters
• some species inhabit freshwater lakes

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Diatoms

• Diatoms from Upper Miocene rocks in Java

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Diatoms

• Diatoms were particularly abundant during the
  Miocene epoch
• Volcanic ash from many eruptions would have
  provided increased dissolved silica in seawater
• which diatoms used to construct their skeletons
• Massive Miocene diatomite is present in several
  western States

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• Outcrop of diatomite from the Miocene Monterey
  Formation, Newport Lagoon, California

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Dinoflagellates

• common during the Mesozoic
• the major primary producers in warm water today

Miocene-Pliocene, Gulf of Mexico
Eocene, Alabama
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Foraminifera

• single-celled consumers
• underwent an explosive diversification during the
  Jurassic and Cretaceous
• many genera became extinct at the end of the
  Cretaceous
• but foraminifera are still diverse and abundant
  today

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Benthic Foraminifera

• Uvigerina cubana
• Late Miocene, California

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Benthic Foraminifera

• Cibicides americanus
• Early Miocene, California

• Lenticulina mexicana
• Eocene, Louisiana

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Planktonic Foraminifera
Planktonic genera were particularly decimated by
the extinction event at the end of the Cretaceous
period.

• Globotruncana calcarata from the Cretaceous Pecan
  Gap Chalk of Texas

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Foraminifera

• major component of the Cenozoic marine
  invertebrate community
• some exceptionally large forms ("nummulites")
  lived in the warm waters of the Cenozoic Tethys
  Sea
• Shells of these larger forms accumulated to form
  thick limestones which the ancient Egyptians used
  to construct the Sphinx and the Pyramids of Giza

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Planktonic Foraminifera

• Globigerinoides fistulosus
• Pleistocene,
• South Pacific Ocean

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Forams and Stratigraphy

• Foraminifera provide the basic chronostratigraphic
  framework for ocean sediments on the sea floor.
• Planktonic foramifera shells are calcareous
  (CaCO3) and they sink to the seafloor after the
  organism dies, accumulating as sediment
• percentages of warm-water and cold-water species
  indicate past ocean temperatures

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Globorotalia menardii

• warm-water (tropical) species found only near
  the equator during periods of cooler climate
  (glaciation)

• During times of warming (interglacials) the range
  of Globorotalia menardii extended into the higher
  latitudes.

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Coiling Direction

• Some planktonic foraminifera species change the
  direction they coil in response to temperature
  fluctuations
• Globorotalia truncatulinoides coils
• to the right in water above 10C
• to the left in water below 8-10C
• Changes from right- to left-cooled and back again
  provide another way of reconstructing Pleistocene
  climate.

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Forams in Marsh Environments

• calcareous forms (Quinqueloculina sp., Ammonia
  beccarii, Protelphidium orbiculare and Elphidium
  excavatum) occur only in the lower parts of the
  low marsh
• porcellanous (miliolid) forms occur in lower to
  middle marsh, and may occur down onto the mud
  flats
• the high marsh has only agglutinated forms (e.g.
  Trochammina macrescens)

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Elphidium excavatum
Trochammina macrescens
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