((Project 2: Navajo Sandstone Revision due Thurs. 11/12 Notes on page Problem 2)) Project 4: Continental Break up in the New London-New Britain area of Connecticut


-Basics about North American craton and African Craton rift
-explain the package of rocks we see in this connecticut area
-how does continent-continent rifting work
-what sediments does it produce?

Presentation: 11/20

Geologic Bedrock Map of Connecticut

click for full size image
click for full size image


Our area of focus on this map is the very pale yellow and red areas in the center of Connecticut. Make sure not to confuse that yellow with the very light green to it's left. In the key below it, it's just the Newark Section info.

What is a rift?

When did the rift occur?
  • This event is estimated to have occurred around 190 million years ago during the Mesozoic era (early Jurassic period).
  • Rifting started in the late Triassic period and continued to completely separate Pangea to form two separate masses known as Laurentia and Gondwana.

Where did this rift occur?
  • Amongst many other areas, a large record of this rift can be found in the Central Valley area of Connecticut.

What type of rift was it?
  • Continent-continent
  • Divergent plate boundary, where a new oceanic crust formed and eventually created the Atlantic Ocean.

What types of sediments are produced here?
  • Clastic sedimentary rocks (conglomerates, arkosic sandstone, shale - early Jurassic to late Triassic in age)
  • Basalt (early Jurassic)
  • Dolerite (early Jurassic)

Why does rifting occur?



The Break-up of Pangea


The following bullets are from this source:
Historical Geology: Wicander, Reed; Monroe, James S., 2000, Evolution of Earth and Life Through Time, 3rd ed., Brooks/Cole, pp.348-354.
  • "Pangaea's breakup can be documented by the extensional structures (fault-block basins or rift valleys) that formed along the newly created continental margins." (Wicander and Monroe, 2000)
  • "As a continent begins to rift, fault-block basins are formed. Associated with these tensional structures are basaltic dikes, sills, and lava flows..." (Wicander and Monroe, 2000)
  • Basaltic oceaninc crust forms between continents that are separating (p.348)

Took place in 4 general stages:
  1. THIS IS THE IMPORTANT STAGE (the first stage in the rift): "Involved the rifting between Laurasia and Gondwana during the Late Triassic. By the end of the Triassic, the expanding Atlantic Ocean separated North America from Africa. This change was followed by the rifting of North America from South America sometime during the Late Triassic and Early Jurassic." (Wicander and Monroe, 2000)
    • "Separation of the continents allowed water from the Tethys Sea to flow into the expanding central Atlantic Ocean....During that time, these areas were located in the low tropical latitudes where high temperatures and high rates of evaporation were ideal for the formation of thick evaporite deposits." (Wicander and Monroe, 2000)


More from the book (p.354):
Eastern Coastal Region
  • "During the Early and Middle Triassic, coarse detrital sediments derived from the erosion of the recently uplifted Appalachians (Alleghenian orogeny) filled the various intermontane basins and spread over the surrounding areas. As erosion continued during the Mesozoic, this once lofty mountain system was reduced to a low-lying plain. During the Late Triassic, the first stage in the breakup of Pangea began with North America separating from Africa. Fault-block basins developed in response to upwelling magma beneath Pangaea in a zone stretching from present-day Nova Scotia to North Carolina. Erosion of the adjacent fault-block mountains filled these basins with great quantities (up to 6000m) of poorly sorted red-colored nonmarine detrital sediments known as the Newark Group. Reptiles roamed along the margins of the various lakes and streams that formed in the soft sediments. Although the Newark rocks contain numerous dinosaur footprints, they are almost completely devoid of dinosaur bones. The Newark Group is mostly Late Triassic in age, but in some areas deposition began in the Early Jurassic."
  • "Concurrent with sedimentation in the fault-block basins were extensive lava flows that blanketed the basin floors as well as intrusions of numerous dikes and sills. The most famous intrusion is the prominent Palisades sill along the Hudson River in the New York - New Jersey area."
  • "As the Atlantic Ocean grew, rifting ceased along the eastern margin of North America, and this once active plate margin became a passive, trailing continental margin. The fault-block mountains that were produced by this rifting continued eroding during the Jurassic and Early Cretaceous until all that was left was a large low-relief area. The sediments produced by this erosion contributed to the growing eastern continental shelf. During the Cretaceous Period, the Appalachian region was reelevated and once again shed sediments onto the continental shelf, forming a gently dipping, seaward-thickening wedge of rocks up to 3000m thick. These rocks are currently exposed in a belt extending from Long Island, New York, to Georgia."



It began roughly 200 million years ago.
"Pangaea began to break up around 200 million years ago with the separation of Laurasia from Gondwana, and the continents we know began to take shape in the late Jurassic about 152 million years ago. New oceans began to open up 94 million years ago (the Cretaceous period). India also began to separate from Antarctica, and Australia moved away from the still united South America and Africa. The Atlantic zippered open northward for the next few tens of millions of years until Greenland eventually tore from northern Europe. By about 65 million years ago, all the present continents and oceans had formed and were sliding toward their current locations while India drifted north to smack the south side of Asia."(http://science.jrank.org/pages/1751/Continental-Drift-Pangaea-splits.html)

"The second, major phase in the break-up of Pangaea began in the Early Cretaceous (150-140 million years ago), when the minor supercontinent of Gondwana separated into four multiple continents (Africa, South America, India and Antarctica/Australia). In the Early Cretaceous, Atlantica, today's South America and Africa, finally separated from Eastern Gondwana (Antarctica, India, and Australia), causing the opening of a "South Indian Ocean". In the middle Cretaceous, Gondwana fragmented to open up the South Atlantic Ocean as South America started to move westward away from Africa."
- (http://encyclopedia.stateuniversity.com/pages/16678/Pangaea.html)
- Apparently this is the same info on Wikipedia...



Misc Helpful Links

http://geology.com/pangea.htm

http://www.priweb.org/ed/TFGuide/NE/rocks/rock_files2/rock_pdfs/ne_rocks4.pdf
some information on the rocks found in the CT basin.


Field Trip Picutres!!

I hope this link works... http://www.facebook.com/photos.php?id=42503821#/album.php?aid=2067022&id=42503821



More Info for PP Slides


http://geology.rutgers.edu/103web/Newarkbasin/Pangea_NB.html
http://geology.rutgers.edu/103web/Newarkbasin/Pangea_NB.html


This would be good to add in near where we introduce the Pangaea supercontinent.




http://egeology.blogfa.com/post-84.aspx
http://egeology.blogfa.com/post-84.aspx

Definitely add this to the slides!!! probably somewhere towards the beginning near where we introduce Central Valley CT (Newark Basin)
When you talk about this slide, point out to the class which one is the North American plate and the African plate, then point to where the center of the rift is, and show/point out the mantle upwelling that's occurring right below the center. Also, just to please the professor, it might be good to mention that this imagine isn't drawn precisely to scale, that things are slightly squished to fit it all in a picture.


Map of the Connecticut River Basin:

http://3dparks.wr.usgs.gov/nyc/mesozoic/connecticut.htm
http://3dparks.wr.usgs.gov/nyc/mesozoic/connecticut.htm




Cross section of the Connecticut River Basin.

http://3dparks.wr.usgs.gov/nyc/mesozoic/connecticut.htm
http://3dparks.wr.usgs.gov/nyc/mesozoic/connecticut.htm

I couldn't find a stratigraphic section, but this is just as good. Definitely add these two images to the slides


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