Digital Varves

Varves of the Month for 1/1/2010 - 1/31/2010

Connecticut Valley Varves, Perry Hill Basin, Charlestown, New Hampshire

Scale bar in cm.

Click on image to download original image file

This month's image is the last in a series of images over the past year that showed the progressive change in varve deposition that occurred over time in the Perry Hill Basin. The Perry Hill Basin core sites, PHS and PHN which is 0.5 km further north, are in the same varve-filled basin at the west flank of Perry Hill in Charlestown, NH just south of Claremont and have very similar varve stratigraphy. The complete section contains over 500 varves from ice-proximal varves at the base that rest on till to very ice-distal varves at the top of the section that fade into sediment in which varves are difficult to discern because winter layers are erratically preserved. The general type and relative ages of the varves in the New England Varve Chronology (NEVC) in past Varves-of-the-Month images from the Perry Hill Basin (see the archive at the bottom of this page) are indicated below with the oldest varves at the bottom of the list:

  • January 2010 above NE7120 (This month) Distal (varved?) lake sediment
  • December 2009 above NE7038: Distal (varved?) lake sediment
  • November 2009 NE6985-6997: Distal varves
  • October 2009 NE6944-6953: Distal varves
  • September 2009 NE6897-6905: Distal varves
  • August 2009 NE6853-6864: Transitional varves
  • July 2009 NE6804-6818: Transitional varves + flood event
  • June 2009 NE6751-6768: Thinning transitional varves
  • May 2009 NE6687-6691: Thick transitional varves
  • April 2009 NE6652-6655: Return to ice-proximal varves
  • September 2008 NE6640-6644: Ice-proximal/transitional varves + flood event
  • March 2009 NE6631-6635: Return to ice-proximal varves
  • October 2008 NE6622-6625: Ice-proximal to transitional varves
  • February 2009 NE6590-6593: Thick, ice-proximal varves

This month's are two core images stitched together that were chosen because of the detail that they show in the upper part of the Perry Hill section (PHS core). This is a distal sequence from glacial Lake Hitchcock of the Connecticut Valley of south-central New Hampshire. The sample was collected in the summer of 2007 with a Central Mining Equipment continuous sampling system running inside a hollow-stem auger at a depth of 8.5-7.5 ft below the land surface at the core site. The core site sits along Ox Brook in a slight valley and about 8 ft of the paleo-lake floor is missing at the core site. The top of the interval shown on the image is 95.0 ft and at least 530 years above the bottom of the section at the PHS core site (NE6570) where varves rest on till. After a sporadic match, following the major flood event at ~NE6810, the Perry Hill and NEVC records again match well above ~NE6905 through NE7010. Above NE7010 the Perry Hill section could not be matched to the NEVC because of difficulties in consistently defining varve boundaries in the Perry Hill section. For this reason the boundaries and numbers of varves in the NEVC are not shown as in earlier months and a plot of the Perry Hill varves vs. the NEVC is not given. The sediment in this month's image probably correlates with sediment up valley deposited as NE7100-7200 and we estimate from the full sediment thickness in the Perry Hill basin above the interval shown on this month's image that the lake persisted in the basin to at least NE7500.

The sediment in this month's image is largely from tributary drainages and was remobilized by lake bottom currents. Sand became more prevalent at the Perry Hill sites as prograding deltas delivered more sandy sediment further into the lake basin where it was picked up by strong down valley currents. Major sources of sand to the Perry Hill basin were the Sugar River Valley 4 km to the north at Claremont and a prograding delta at the mouth of the Little Sugar River just 1.0 km to the south, while small local streams on the east side of the basin also contributed some sediment.

Varves are difficult to consistently define in this month's image. The change up section to sandy distal varves and then sediment in which varves are hard to discern is a natural consequence of ice recession, the diminished supply of sediment from the glacier, and the shoaling of the lake by sediment infilling. The sediment shown here was deposited at least 530 years after recession of the ice sheet when the ice-front had receded approximately 150 kilometers north of the PHS core site beyond St. Johnsbury, VT and Littleton, NH. The ice recession rate in the Connecticut Valley leading up to this time averaged approximately 280 m/yr, which is very rapid for a terrestrial glacier where most of the ablation is by melting. The ice began to readvance (Littleton-St. Johnsbury Readvance) at about the time the sediment in this month's image was deposited and the thin rhythmites (varves?) in the upper half of this image may represent this interval of lower glacial sediment and meltwater inputs with weaker bottom currents.

Most of the lighter gray areas on the image have stacks of graded fine sand to muddy silt beds representing melting and storm events that deposited sediment during the summer or melt season. Sediment in this interval is lightly oxidized from weathering near the land surface and the small orange and brown spots that appear on the image may be the remnants of oxidized plant fragments. In many places the light gray sediment is very regularly rhythmic (when magnified), suggesting diurnal cycles. A great example is at the bottom of the upper scale bar. In other areas are dark clayey beds that may represent late summer and early winter deposition and are probably distinct enough to define annual layering but this is not true of the entire image. Most of the clayey units are split by very thin fine sand and silt partings. The deposition of the sand and silt partings occurred prior to the end of the melt season. This means that clay deposition was initiated during the melt season and was not strictly a winter phenomenon. The bulk of clay deposition in many years may not have occurred during winter with late summer being more or as important. In the upper third of the image are a cluster of relatively thin (~0.5 cm) paired dark and light units that probably define annual layers in which case these units are much thinner varves than seen elsewhere in the entire section. As mentioned above these units may represent an interval of cooler climate and glacial readvance. In the lower half of the image, about 6-14 cm above the base of the image, are some regularly spaced clay units that also appear to define annual layers that are much thicker (1-2.5 cm) than the units above. These units may be more easily defined as annual layers than features shown in last month's image (December 2009) but unfortunately annual layers cannot be consistently defined through the whole section, which generates significant uncertainties in varve measurement. Correlative ice-proximal sediments further north in the Passumpsic and Connecticut valleys are less sandy, distinctly varved, and are easily correlated in the upper valley and to the NEVC through the whole interval of NE7000-7600.

Additional complications for varve measurement in this month's image are the small dish-shaped erosion surfaces that frequently interrupt the varve stratigraphy. The most conspicuous of these features occurs near the bottom of the image and may cut through several annual units. The erosion features also occur on a smaller scale throughout this part of the Perry Hill section. In varve sections at Newbury, Passumpsic, and Wells River, VT we have been able to analyze these structures on an outcrop and investigate their three-dimensional characteristics. In these sections they are associated with trace fossils left by fish (sculpin, char) and a crustacean (Benner et al., 2008, 2009; Knecht et al., 2009). Locomotion and resting behavior by both organisms disturb the lake floor to produce the types of erosion features see in cross section on this month's image. Some large dish structures like the one near the bottom of this image may be fish nests. Similar dish-like depressions left by sculpins have been found on the floor of Lake Superior (Johnson et al., 1984). Clearly, with this sort of organic activity and a varied community of organisms on the lake floor signal that the lake had matured to one in which the influence of the glacier was diminished tremendously from environments represented by ice-proximal varves at the bottom of the Perry Hill section.


  • Benner, J.S., Ridge, J.C., and Taft, N.K., 2008, Late Pleistocene freshwater fish (Cottidae) trackways from New England (USA) glacial lakes and a reinterpretation of the ichnogenus Broomichnium Kuhn: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 260, no. 3-4, p. 375-388. doi:10.1016/j.palaeo.2007.12.004
  • Benner, J.S., Ridge, J.C., and Knecht, R.J., 2009, Timing of post-glacial reinhabitation and ecological development of two New England, USA, drainages based on trace fossil evidence: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 272, p. 212-231. Doi:10.1016/j.palaeo.2008.10.029
  • Johnson, T.C., Halfman, J.D., Busch, W.H., and Flood, R.D.,1984, Effects of bottom currents and fish on sedimentation in a deep-water lacustrine environment: Geological Society of America Bulletin, v. 95, p. 1425-1436.
  • Knecht, R.J., Benner, J.S., Rogers, D.C., and Ridge, J.C., 2009, Surlichnus bifurcauda n. igen., n. isp., a trace fossil from Late Pleistocene glaciolacustrine varves of the Connecticut River Valley, USA, attributed to notostracan crustaceans based on neoichnological experimentation: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 272, p. 232-239. Doi:10.1016/j.palaeo.2008.10.013

Past Varves of the Month...