North-Central Section (36th) and Southeastern Section (51st), GSA Joint Annual Meeting (April 3–5, 2002)

Groundwater samples from wells on the contact between Pleistocene fill and the Antrim Shale in Fulton County, Ohio yield d-¹⁸O values much lighter (–14.5‰) than present day average precipitation (–7.5‰). We have interpreted this water to be in part "paleo" in nature, having been recharged during the time of the last glacial retreat. These isotopic values can be interpreted in two ways. Using the current relationship between the d-¹⁸O of precipitation and Greenland Ice Sheet air temperature, a mean annual temperature of approximately –2°C is predicted at the time this water was recharged. By assuming an even lighter Laurentide Ice Sheet value of –28‰, these groundwaters could be a mixture of two-thirds modern recharge and one-third ice sheet meltwater. A review of the literature indicates that our observation is not unusual for the mid-portion of the North American continent. Older studies have observed either Pleistocene age waters or mixtures of glacial melt and more modern recharge in Illinois, Iowa, Missouri, North Dakota, Ontario, Manitoba and Saskatchewan. More recent studies have made similar observations in Ohio, Michigan, Nebraska and the Northwestern Territories, Canada. Several of these paleowaters are associated with late Pleistocene lake sediments. An attempt is made to assess the volume of this water on a regional scale.