Report and data repository
Littleton-Bethlehem Moraine geological-calibration site
Nov. 17-18, 2007
For information about this page, contact Greg Balco
This page contains data collected on the CRONUS-Earth geological-calibration excursion to the Littleton-Bethlehem moraine complex, near Littleton, NH, on Nov. 17-18, 2007.
1. Background and literature
The Littleton-Bethlehem moraine complex is a set of prominent bouldery moraines in northern New Hampshire. The moraine complex is correlated with a till sheet. The till sheet is stratigraphically bracketed by varved lake sediments. The varved sediments are matched to the New England varve chronology, which is linked to the calendar year time scale by radiocarbon dates on individual varves. Thus, we know that the moraine was deposited 13840 +/- 250 yr ago.
Woody Thompson has written a number of excellent descriptions of the history of work on the Littleton Moraine complex, as well as the results of his more recent mapping in the area. This work is summarized in the following papers:
Historical summary: Thompson, W. B., 1999. History of Research on Glaciation in the White Mountains, New Hampshire (U.S.A.) Geographie physique et Quaternaire, 1999, vol. 53, no. 1, p. 7-24.
Full description of the Littleton moraine complex: Woodrow B. Thompson, Brian K. Fowler, Christopher C. Dorion, 1999. Deglaciation of the Northwestern White Mountains, New Hampshire. Geographie physique et Quaternaire, 1999, vol. 53, no. 1, p. 59-77
2002 NEFOP Field Guide: Woodrow B. Thompson, Carol T. Hildreth, Richard A. Boisvert, Christopher C. Dorion, Brian K. Fowler, 2002. Glacial geology and archaeology of the norther White Mountains, New Hampshire. Guidebook for the 65th annual reunion of the Northeastern Friends of the Pleistocene. Littleton, NH, May 17-19, 2002.
Link to the NE varve chronology: John C. Ridge, Mark R. Bensonen, Marc Brochu, Sarah L. Brown, Jamie W. Callahan, Glenn J. Cook, Robert S. Nicholson et Nathaniel J. Toll, 1999. Varve, Paleomagnetic, and 14C Chronologies for Late Pleistocene Events in New Hampshire and Vermont (U.S.A.) Geographie physique et Quaternaire, 1999, vol. 53, no. 1, p. 79-106.
The Ridge et al. paper above gives some description of the radiocarbon dating of the varve chronology, but it has been superseded by some newer results. These are summarized on Jack's North American Glacial Varve Project web site .
2. Existing calibration measurements:
There have been a few calibration measurements already made from this and related sites. The results, as well as a lot of information about the age control on the moraine complex, are summarized in the following paper:
Balco, G., Briner, J., Finkel, R.C., Rayburn, J., Ridge, J.C., Schaefer, J.M., 2009. Regional beryllium-10 production rate calibration for late-glacial notheastern North America. Quaternary Geochronology 4, pp. 93-107.
3. Site and sample information:
We visited the Beech Hill moraine field and collected 7 samples (see the above papers for the overall context of this site). The site is located here. It consists of a series of ENE-WSW-trending bouldery moraine ridges and intervening marshy swales. This is sort of visible on the overhead air photo. Yes, all those white spots visible on zooming in are large granite boulders. For Google Earth aficionados, the sample locations are here (.kmz file) and here (.kml file).
Folks present at the site on Nov. 17-18 included:
Overall geomorphic context of the boulders:
Everyone present at the site generally agreed that the boulders were in stable landscape positions. We were easily able to find boulders that lay on flat ground and were interlocked with other boulders in large groups, suggesting that they could not have moved since deposition. Steep slopes were present on the flanks of some of the moraine ridges, suggesting the possibility of postdepositional uncovering of boulders lying on these slopes, but we were easily able to avoid boulders in this position. All, however, were more concerned about the possibility of boulder surface shielding by vegetation or snow. The natural vegetation at the site is a dense spruce-fir forest, and we observed boulders of all sizes with 2-6 cm moss and litter accumulations on their surfaces. In several cases this litter accumulation rose to the level of 'soil' and small trees were rooted in it. It appeared that boulders with flat upper surfaces were more likely to have thick moss cover, but we did observe moss and saplings attached to a few boulder surfaces dipping at 30 degrees or more.
The site also experiences seasonal snow cover. Climatology from a long-term weather observing station in nearby Bethlehem, NH shows a mean water equivalent snow thickness, averaged over the entire year, of 2.1 cm (details of this calculation are in the 2009 paper in QG referenced above).
Taking all this into account, we agreed that we ought to be sampling relatively tall boulders (> 1.5 m), and we ought to try to avoid boulders with large, perfectly flat surfaces that might be the most efficient moss accumulators.
Boulder surface erosion:
Nearly all of the boulders had rough surfaces with 0.5-1 cm of small-scale (1-cm-scale) relief. We observed a few upstanding quartz veins on boulder surfaces. Heights of these veins above the surfaces were generally near 0.7 cm. The highest relief quartz vein we observed was 1.5 cm in relief. This suggests that boulder surface erosion has been restricted to 0.5-1.5 cm since emplacement. On a few boulders, we observed etching along joints up to 2-3 cm deep. We avoided these areas and sampled boulder surfaces that were generally flat and subject only to grain-scale roughness.
All the samples are located in the same broad lowland, and are all subject to the same topographic shielding from distant hills. The horizon description is:
Following the usual procedure, this yields a shielding factor of 0.9999.
Site and sample data:
I measured sample locations by handheld GPS, and elevations by barometric leveling from a nearby USGS benchmark using a SUUNTO Escape handheld altimeter. Unfortunately, barometric pressure changes were large both days, resulting in a large drift correction. The altimeter is temperature-compensated. A spreadsheet detailing the altimeter correction is here. I estimate 2-3 meter uncertainties on the elevation measurements. Locations, elevations, and links to sketches of the boulder and sample geometry appear in the following table.
Notes on individual samples:
Notes on individual samples reproduced from GB's field book. Please send your own notes for inclusion here. Thanks.
Photos appear on a separate page.
5. Lab details:
Sample photos (click for larger view / back button to return)
Estimated density is 2.63 g/cm^3.