MULTIPLE PRE-WISCONSINAN GLACIATIONS ALONG THE NORTHWESTERN EDGE OF THE ALLEGHENY PLATEAU IN OHIO AND PENNSYLVANIA

Stratigraphic studies of the glacial geology of the northwestern margi n of the Allegheny Plateau of northeastern Ohio and northwestern Penns ylvania include evidence for multiple pre-Wisconsinan glaciations. Nea r the former eastern margin of the Scioto lobe at Mount Gilead, Ohio, Millbrook, Gahanna, and Chesterville tills have an inferred Illinoian age based on thermoluminescence ages of 146 000 +/- 25 000 and 124 000 +/- 16 000 BP from an overlying silt interpreted as loess. Northampto n Till overlies Millbrook Till of the Killbuck lobe and its correlativ e Mogadore Till of the Cuyahoga lobe, but does not overlie the correla tive Titusville Till of the Grand River lobe. There are signficant dif ferences in carbonate contents among these tills. Millbrook Till and i ts equivalents contain more kaolinite than other tills, and the Northa mpton Till contains more clay. Millbrook Till and its correlatives rep resent the most extensive Illinoian glaciation of the plateau, whereas the other Illinoian tills were deposited by ice that flowed a shorter distance onto the Allegheny Plateau. Butler, Mapledale, and Slippery Rock tills, formerly assigned to an Illinoian glaciation, are pre-Illi noian in age. Scarcity of materials for the dating and the lack of rec ognizable paleosols separating the tills from Wisconsinan deposits inh ibits the reliability of the chronological classification of these til ls.