LITTLE FEN, BIG DATA: MORE THAN 13,000 YEARS OF DEPOSITIONAL RECORD AT QUINCY BOG, RUMNEY, NH

In 2013, for a graduate class in paleolimnology, we collected cores from Quincy Bog, Rumney, NH, Lat 43.79352; Lon -71.77637. The bog is actually a fen, now constrained by a series of beaver dams. The wetland area is about 1.6 ha and 1.7 m maximum depth. The wetland drains to the 500-year floodplain.

Ground penetrating radar (GPR) reveal up to 30 m of sediment accumulation about bedrock; of this about 7 m is wetland sediment. Three short gravity cores were collected, and one piston core 10.2 m long, extending through the Holocene sediments and into late-glacial rhythmites. All core sections, except section 8, have been split, and the work half subsampled at 1 cm-intervals. Completed analyses include loss-on-ignition, 0.5 cm resolution MSCL magnetic susceptibility, 0.2 cm resolution sediment geochemistry by scanning XRF, and X-rays. Pb210 dates obtained on the short core yields a date of A.D. 1877 at the core bottom (27 cm core depth). Radiocarbon dates on the piston core provide a surprisingly linear sediment age-depth model (based on 3 dates). Three samples were sent for C14 analyses with 525 cm sediment depth returning an age of 6086 ±96 years (cal BP). Core bottom dates are pending.

Surprising complexity appears in the early Holocene- late Glacial material, in LOI and geochemistry from the bog. Mineralogic changes suggestive of the Younger Dryas and Allerdod/Bolling warm intervals appear in core section 7, deltaic sands and silts dominate core section 8, and clays and (seemingly) organic material occur through core section 9. Section 10 is highly compacted sands and clays. The youngest sediments (less than 100 years old) closely resemble the late glacial material in magnetic characteristics and appearance. Two processes might explain this: a) residential construction near the fen mobilized glacial deposits into the bog, or b) extreme floods of the early 20th century carried Baker River sediments into the bog. While the first explanation is plausible, Pb210 ages of the uppermost meter of sediment make the second explanation, that of extreme flooding, the more unlikely explanation.

Many of these results are ‘hot off the press' at the time of submission of this abstract. These magnetic susceptibility, geochemistry, x-ray and image data bring new and important insight into early-late Holocene environments of the Baker River valley.