The geologic origin of a distinctive layer of green, weathered clay belonging to the lower part of the Port Talbot Interstadial sediments (Port Talbot I) on the north shore of Lake Erie has been reinterpreted in relation to its clay mineralogy, carbonate content, and pollen data.In addition to illite and chlorite, both characteristic of all clayey glacial sediments in the area, the green clay contains abundant smectite probably produced by oxidation weathering of chlorite in the Bradtville Till. Carbonate contents, normally less than 1% in the green clay compared to values of 15 to 45% in the overlying and underlying sediments, indicate extensive solution weathering.The green clay layer is interpreted to be an accretion gley, weathered in a soil profile during the early part of the Port Talbot Interstadial and subsequently eroded and deposited in poorly drained depressions under reducing conditions. An abundance of oak, pine, and spruce pollen indicate a fairly temperate climate at the beginning of Port Talbot I, becoming cooler towards the deposition top of the green clay, as suggested by low percentage or absence of oak pollen.

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