Glacial Periods surrounding Continental Movement in Connecticut
Aversa Sheldon, Isabel Iwachiw
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The exact reasons behind the creation of glacial structures are still being hotly debated,
even though it has been over a hundred years since scientists first conceived of the northern
hemisphere ever being covered by an ice sheet. Glacio-epochs, associated naturally with severe
climate change, have been variously proposed as being caused by changes in sea salinity (Hay
and Wold, 1997 in Hay et al., 2002), ocean circulation (Berggren, 1982 in Hay et al., 2002),
aerosol content in the atmosphere, even variations in solar emissions and in concentrations of
spacedust (Hay et al., 2002). While these reasons range from the modern and well accepted
‘greenhouse gas’ to the more intriguing Milankovitch orbital motions and the even stranger
‘Cosmic Ray flux’ (Hay et al., 2002, Veizer, 2005 in Eyles, 2008), the most impressive as well as
convincing influence on glacio-epochs seems to be the creation of continental rifts (Eyles, 2008).
Eyles’ theory overpowers simply on the distribution of the evidence alone, with the Huronian
rifting of Kenorland followed shortly by glaciations, and the Neoproterozoic breaking of Rodinia
quickly subsumed by a period of glaciation (2008). Still, Eyles does not completely address all
competing issues with his hypothesis. He particularly does not deal with the rise in atmospheric
pCO2 as an alternative source of glacial cooling (Poulsen, 2007), but he also skims a little bit,
where, for instance, there is such a long time between the beginning rifts which would
eventually form the Atlantic and the glacial period following. If Eyles’ hypothesis can be seen to
have truth in it, there may be a connection between the Eastern Border Fault, Connecticut’s
failed Rift Valley, and the subsequent Cenozoic glacial activity. First we will focus on the
veracity of Eyles’ hypothesis, and then we will address the plausibility of Connecticut’s little Rift
Valley setting off, as Eyles suggests, a glacial period.
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Eyles’ hypothesis that glacio-epochs are triggered by tectonic changes is supportable
because glaciations are preferentially associated with plate tectonic processes which act to
elevate areas of continental crust (Eyles, 2008). Hay refers to a previous theory from the 1850s
when he states that uplift can be a cause of climate ‘deterioration’ which leads to a glacial
climate (2002). Preferential preservation of ice and snow occurs in areas of uplifts, which
naturally encourages the packing of glacier-type snow. Uplift changes the radiation balance,
and increases wind velocity by obstructing atmospheric circulation, especially when the uplift is
large scale (Hay, 2002). It also provides, as mentioned earlier, cooling and subsidence which
can assist in promoting glaciations (Eyles, 2008, Marshak, 761).
We have known for a while that the climate changes even without human influence,
and sometimes in newer or more extreme ways than we had thought before (Soreghan, et. al.,
2007). By looking at the stratigraphy of former rift valleys such as the Connecticut River Basin,
we can figure out when different glaciations occurred and how long they stayed. With this
information we can also estimate periods of time in which the surrounding rock was uplifted or
otherwise deformed. Eyles used diamictites found in possible-rift basins as evidence of
significant glacial movement caused by rifts, and as evidence of how many times the glacier
advanced and retreated in a given area. For instance, Eyles found diamictites in mountainous
“supergroups” on Canadian, American and South African basins (2008). The dating of those
diamictites to the same period and the knowledge of Canada, the Rockies and that section of
South Africa lying within the former Kenorland area place the plume-related splitting of
Kenorland in the same Paleoproterozoic period as the Huronian glaciation (Eyles, 2008).
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Connecticut’s history is involved only partially with the splitting of continents, but
crucially. Formed by a volcanic arc in the Proterozoic, Connecticut had nothing to do with the
rest of the current North American continent, Laurentia, until around 425 Ma, at which point
the two collided to form the Northern Appalachians (USGS, 2004). By 152 Ma, Pangaea, the
supercontinent which Connecticut had formed when joined as the Avalonian volcanic arc to
Laurentia, Baltica and Gondwanaland, was splitting apart, and an attempted rift opened which
today is known as the Eastern Border Fault, or the Connecticut River Basin. Though superseded
by what is today the proper mid-oceanic ridge, it was still powerful enough to create its own rift
valley and, possibly, be a contributor to a forthcoming glacio-epoch. Still, its rift was developed
in the late Triassic/ early Jurassic, and while according to Eyles there is a delay between the rift
flank uplift and initial rifting, major glaciations in Northern America did not start until almost 60
million years later in the Cenozoic (Eyles, 2008). This is the one weak point to an otherwise
strong argument: even given the magnitude of the true rifting of Pangea in the latter Jurassic
and Cretaceous, why did it take so long for drastic glaciation to occur?
Based on the evidence found by Eyles- that periods of glaciation followed continental
rift activity- we conclude that there is a connection between the Eastern Border Fault and the
subsequent Cenozoic increase in glaciation. Eyles’ identification of rift periods predating
glaciation by analyzing diamictite distribution presents a believable pattern of cause and effect.
Although there is a delay between the attempted rifting of Pangea along the Eastern Border
Fault and the Neogene glaciation, the circumstantial evidence points to a definitive climactic
influence, however slight.
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Bibliography
Eyles, N. ‘Glacio-epochs and the supercontinent cycle after ∼ 3.0 Ga: Tectonic boundary
conditions for glaciation’ Palaeogeography, Palaeoclimatology, Palaeoecology, 258, 89-129,
2008.
Hay, W.W., Soeding, E., DeConto, R.M., Wold, C.N., ‘The Late
Cenozoic uplift-climate change paradox,’ International Journal of
Earth Science, 91, 746–774, 2002.
Marshak, S. Earth: Portrait of a Planet. W.W. Norton Company, London, 2008.
Poulsen, C. J., Pollard, D., Montanez, I. P., Rowley, D., ‘Late Paleozoic tropical climate response
to Gondwanan deglaciation,’ Geology, 35, 771-774, 2007.
Soreghan, G. S., Soreghan, M.J, Pouslen, C. J., Young, R. A., Eble, C. F., Sweet, D.E., and
Davogustto, O.C. ‘Anamolous cold in the Pangaean tropics’ Geology, 36, 659-664, 2008.
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