POST-GLACIAL ENVIRONMENTAL CHANGE AS RECORDED BY SILVER LAKE SEDIMENTS, LOGAN COUNTY, OHIO

A sedimentary record from Silver Lake, a small kettle lake in west-central Ohio, suggests that variations in sediment properties can be interpreted in terms of environmental change. Rock and paleomagnetic measurements, loss-on-ignition (LOI) and smear slide analysis have been used to characterize an 11.5m long sediment core. Preliminary paleomagnetic results reveal a strong, stable primary remanence. Correlation of this paleomagnetic secular variation record to radiocarbon dated paleomagnetic secular variation records suggests the sediment core spans the last 14 ¹⁴C ka BP.

Between 10.5 and 11.5 m (~13 to 14 ¹⁴C ka BP) a compact sand-size, quartz-rich lithology has high dry bulk density and low organic and diatom content. This interval is characterized by high magnetic concentration, coarse magnetic grain size and increased amount of high coercivity minerals. These sediment characteristics suggest high mineral material fluxes by fluvial and aeolian processes shortly after deglaciation.

Above 10.5 m, the sediment is generally characterized by low concentrations of magnetically fine-grained, low coercivity minerals. Organic and diatom content increases and about half of the sediment in this interval is laminated (possibly varved). Within this interglacial sediment are zones of high magnetic concentrations of magnetically coarse-grained, high coercivity minerals with a low organic content and high dry bulk density. The most pronounced of these zones at 8.8 to 9.3 m depth (10,500 – 11,500 ¹⁴C years BP) is correlative with an abrupt recurrence of spruce pollen in the pollen stratigraphy (Ogden, The Ohio J. Science, 66(4): 387, 1966). The sediment characteristics of this zone are inferred to represent a cold climatic event, possibly the Younger Dryas.