LATE PLEISTOCENE DEPOSITIONAL ENVIRONMENTS AND PALEOCLIMATE, RHODE ISLAND

The maximum advance of Laurentide ice onto the Block Island shelf is marked by ridges and patches of boulder gravel of south of Block Island. Block Island is part of an interlobate recessional moraine complex formed between the Narragansett Bay (NB) lobe on the east and the Central Rhode Island (CRI) lobe on the west. Ice of the CRI lobe in Block Island Sound retreated to the Charlestown moraine recessional position and a glacial lake formed in Block Island Sound. The water plane of Glacial Lake Block Island intersects the sea floor south of Charlestown, RI 20 meters below present sea level with meltwater issuing from ice at the Charlestown moraine. The NB lobe retreated through Rhode Island Sound to a recessional position anchored on the mainland at Pt. Judith and extending eastward through Rhode Island Sound. The resulting interlobate zone in the Pt. Judith area is complex.

Calculations of sediment mass in the Charlestown moraine suggest that the moraine formed as a series of wedges deposited during ice-margin fluctuation. The timing of formation of the Charlestown moraine may coincide with an inferred cold episode based on the GISP-2 Greenland ice core (17,900 BP 14C). This would have resulted in ice-sheet advance due to climate deterioration.

The CRI lobe retreated from the stand at the Charlestown moraine north to a momentary pause marked by the Wolf Rocks end moraine correlative with the Old Saybrook moraine in eastern Connecticut. A major stand of the NB lobe formed the Congdon Hill moraine which, with is a series of large boulder accumulations trending southwestward marking the CRI lobe margin, correlate with the Ledyard moraine in Connecticut.

Ice wedge casts suggest a very cold climate immediately following deglaciation. However, the ice wedges together with the deglacial morphosequences, suggest a climate scenario of very cold winters and very warm summers for which there are no present analogs.