A Conceptual Model of the Deglaciation of Southern Rhode Island

• Main Author: Smith, Theresa L.
• Format: Text
• Language: unknown
• Published: DigitalCommons@URI 2010
• Subjects: Block Island; Canada; Glacial Lake; Ice Sheet
• Online Access: https://digitalcommons.uri.edu/theses/2093; https://doi.org/10.23860/thesis-smith-theresa-2010; https://digitalcommons.uri.edu/context/theses/article/3054/viewcontent/Thesis_Smith_Theresa_2010.pdf; https://digitalcommons.uri.edu/context/theses/article/3054/filename/0/type/additional/viewcontent/thesis_smith_theresa_2010_Plate1.pdf

Laurentide deglaciation in southern Rhode Island (RI) is characterized by the systematic retreat of two glacial lobes: the Central Rhode Island/Eastern Connecticut (CRI) lobe and the Narragansett Basin (NB) lobe. A conceptual model of the deglaciation of southern Rhode Island is offered to provide new insights about the mode and synchronicity of retreat and to better understand the interlobate depositional environment. The study area encompasses nine quadrangles, is bounded in the south by Block Island Sound and the east by Narragansett Bay the northwest by uplands in central RI and the upper Pawcatuck River Basin. Glacial retreat is inferred from the distribution of successive ice margin positions marked by moraines and morphosequences, and from topographic relationships of glacial lake deposits, lake spillways and ice dams. This model shows that after the onset of de glaciation, 1) the ice sheet in southern New England may have undergone fluctuations resulting in the advance of both lobes at different times, 2) CRI lobe retreated rapidly north-northwest over uplands, thinned over low relief bedrock controlled topography and formed up-valley ice lobes, and 3) the NB lobe ice retreated more slowly as it occupied the deep bedrock valleys within the Narragansett structural basin. Ice recession from the terminal position probably began shortly after the ice sheet reached its maximum extent around 26 kyr BP (calendar years based on newly calibrated 10Be dates). The ice margin retreated to the Charlestown end moraine by 21 kyr BP. Although significant warming in this region did not occur until 15 kyr BP, the ice sheet began to retreat rapidly at 19 kyr BP. By 16 kyr BP, the active ice sheet had retreated from Rhode Island and by 11 kyr BP, it was in southern Canada.