Presentation on theme: "Amy Lombari Zoe Gentes Andew Infante Jennifer Sullivan Dennis Titterton."— Presentation transcript:
Amy Lombari Zoe Gentes Andew Infante Jennifer Sullivan Dennis Titterton
Pangaea The breakup of Pangaea is estimated to have occurred around 200 million years ago during the Mesozoic era (early Jurassic period) (Tarbuck, 2002) Rifting started in the late Triassic period and continued to completely separate Pangaea to form two separate masses known as Laurasia and Gondwana Basaltic oceanic crust forms between continents that are separating
Pangaea continued The breakup of Pangaea took place over four stages The first stage is relevant to our subject and the Connecticut rift valley: 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. (Wicander and Munroe, 2002)
Region of Interest http://sahallquist.files.wordpress.com/2008/07/ctgeomap_big.jpg Connecticut (CT) rift valley Region of continent- continent rifting Type of sediments Volcanism due to rifting Amongst many other areas, a large record of this rift can be found in the Central Valley area of Connecticut. The CT valley is a down faulted crustal segment with dimensions of 5 to 20 by 105 miles. It is split into 2 basins, each with their own sedimentary and volcanic records
Rift Valleys The central valley of CT is one of the areas affected by the continental rift between the North American craton and the African craton Continental Rifting: ○ Convection and mantle plumes are two mechanisms involved in the cause of the continental rift ○ Pangaea acted as an insulation for the mantle plume which resulted in a significant change in convection beneath the supercontinent
Basic rift model Divergent plate boundary Progressive formation of a rift valley through extension of the lithosphere and continental crust The crust responds by brittle fracture. Early rift sediments are downfaulted into the developing rift. Erosion takes place on the sides of the rift valley http://www.le.ac.uk/geology/art/gl209/lecture3/lecture3.html&usg
Sediments The Harford basin is one of several rift basins in the eastern United States that formed during the breakup of Pangaea. Over millions of years, the Hartford basin accumulated clastic sediments as well as basaltic lava Early Devonian rocks consist of marine clastic deposits with subordinate carbonates, lava flows and terrestrial deposits These sediments are located here due to the once lacustrian environment
Paleoenvironments Plant fossils and the presence of evaporites provide evidence for a climate that repeatedly altered between humid and arid (Prothero and Dott, 2002) The basin contains imprints of leaves, bark and wood that tells us that in Mesozoic times, Connecticut had a tropical climate Plants found included; conifers, horsetails, giant club mosses and cycads
Volcanisim In a Rift Valley volcanoes are not as explosive Mafic lava High viscosity, high volatile content in felsic lava makes the volcano more explosive Dikes and sills are very common in the Central Valley of CT. They were formed when cracks in the lithosphere/crust were filled with lava from beneath the rift.
Volcanism continued We can use paleomagnetic stratigraphy to determine that there were different volcanic events that occurred in the late Triassic period (Tremblay and Pinet, 2005) Basalt is found in the rift valley because of volcanism As lava flowed into lakes it formed pillow basalts http://3dparks.wr.usgs.gov/nyc/m esozoic/connecticut.htm
References Alain Tremblay and Nicholas Pinet, 2005, Diachronous supracrustal extension in an intraplate setting and the origin of the Connecticut Valley–Gaspé and Merrimack troughs, northern Appalachians. Geological Magazine, 142, pp 7-22 Donald R.Prothero and Robert H. Dott, 2002, Evolution of the Earth, Edition 6, McGraw Hill, New York, New York, p. 384 Tarbuck, Edward D., Frederick K. Lutgens, and Tasa Dennis, 2002 Earth: An Introduction to Physical Geology. 7th ed. Upper Saddle River, NJ: Prentice Hall Wicander, Reed; Monroe, James S., 2000, Historical Geology: Evolution of Earth and Life Through Time, 3rd ed., Brooks/Cole, pp.348-354.