The Stratigraphy and Development of a Floating Peatland, Pinhook Bog, Indiana

Abstract

Pinhook Bog is an acidic, weakly-minerotrophic peatland that occupies an ice block depression in the Valparaiso Moraine in northwest Indiana. It has a floating mat approximately 22 ha in area but no central pond. Detailed stratigraphic descriptions of the peatland were made to analyze its developmental history and determine what factors may be responsible for mat formation. Stratigraphic data along four transects identified a clay-lined basin with three major sub-basins 18, 14, and 14m deep. The deeper parts of the sub-basins contain fibrous limnic peats with some intermixed lacustrine sediments deposited between 12000 and 4200 years ago. The younger, upper peat layers are composed primarily of Sphagnum and consist of the fibrous surface peat and two underlying layers of fluid, fibrous peat separated by a water layer about one meter thick. Peat materials from above the water layer have fallen through the water to form the lower layer of detritus peat. In addition to the obvious factors of climate and presence of mat-forming species, the development of extensive floating peatland mats is considered to be largely a function of deep, steep-sided basins that allow horizontal mat growth to exceed vertical peat accumulation. Other important contributing factors are clay-lined basins and the Jack of inlets or outlets. These factors may result in water-level changes in the basin and weakly-minerotrophic waters conducive to Sphagnum growth.