Organic materials recovered from deltaic deposits confined to the Black River Valley near Marathon, Ontario, provide information on lake-level history and local ecology for the region. Radiocarbon samples provide the first age determinations (ca. 8200 BP) for the post-Minong III – IV lake phases along the northeast corner of the Lake Superior basin. A minimum of 49 Coleoptera taxa and 22 vascular plant taxa indicate coniferous-forest and riparian communities. Overbank deposition along rivers flowing from the ice margin provided temporary ponds colonized by sedges and other aquatic plants and animals. Many records for both animals and plants illustrate occurrences of western and Arctic disjunct species in early Holocene time. Some "western" Coleoptera might still be present as disjuncts in the Marathon region.