Detailed sea-level (SL) research in marshes at Bombay Hook National Wildlife Refuge suggests that during the last 5,000 years the paleo-valley of the Leipsic River was filling with transgressive marsh sequences. Foraminiferal assemblages and plant remains from peat units represent different paleoenvironments. The stratigraphy of the paleo-valley and radiocarbon dates indicate that brackish wetlands were developing in the valley from 5,000 BP until 1,000 BP, when a dramatic shift from brackish to salt marsh environments occurred.

Radiocarbon dates from basal peat were used to construct a local sea level curve and estimate rates of Holocene sea level rise. From 5,0003,500 BP SL rose at a rate of 3.8 mm/yr. From 3,500-2,000 BP, the rate of SL rise decreased to 1.7 mm/yr, and continued to decrease to 0.2 mm/yr from 2,000-1,000 BP, while from 1,000 BP to present SL rose at a rate of 2.6 mm/yr. Pb²¹⁰ analyses of the low marsh peat indicate an average accretion rate of 2.9 mm/yr for the last 160 years, which agrees with the modern rate of SL rise.

Acceleration in the rate of SL rise from 0.2 mm/yr to 2.6 mm/yr during the last 1,000 years caused change in the environments from brackish to salt marsh.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas