Digital Varves

Varves of the Month for 10/1/2011 - 11/30/2011

Varves of West Canada Creek Valley, western Mohawk Valley collected in Newport, NY

Scale bar in cm.

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This month's image is seven spliced high resolution images of an outcrop core that shows ice-proximal to distal varves of the post-Norway beds. The core was collected at Newport in the West Canada Creek valley of the western Mohawk Valley region of central New York (section 441 in Ridge and others, 1990). The varves were collected in July of 2011 as a part of research on varve sequences in the Mohawk Valley. The core was split and partially dried to better reveal differences between layers with different clay contents.

The varves were deposited in a lowered level of glacial Lake Cedarville during recession of the Ontario Lobe about 16,800 years ago. Varve thickness was controlled by glacial meltwater activity as meltwater moved southeastward in the West Canada Creek valley away from the receding Ontario Lobe. Varves became thinner as ice receded to the west and less sediment from the glacier reached the area where the core was collected.

Varves in this section (left side of core image) are generally thin as compared to other sections and are gray with subtle brown or red tones derived from the glacial erosion of red sedimentary rock formations to the west, most notably the Vernon Shale. Summer (melt season) layers in the varves are the light gray to tan units while the winter (non-melt season) layers are the dark clay beds. The summer layers of each varve are composed of a stack of micrograded units of fine sand and silt. Grain size varies within the summer layer with the coarser units (fine sand) having a lighter color.

The varve at the bottom of the core (right side of image) contains poorly sorted muddy sand that rests on stony debris flows and till (Norway Diamicton) just below the core. The bottom ice-proximal varves in the core are sandier and thicker but have thinner winter clay beds than further up section. This is possibly the result of stronger lake bottom currents when the receding ice front was closer to this site. About 16 cm from the base of the core is a horizon where mass movement on the lake floor disturbed bedding in the sediment.

The transition to more clayey and more ice-distal varves above (thicker winter layers and thinner summer layers) occurs in an interval with abundant drop sediment primarily in the form of pellets or chunks of medium to dark gray till. Included in the drop sediment are occasional light gray silt pellets that appear to be composed of rock flour or reworked lake sediment. This interval may represent a time when icebergs were still abundant near the receding ice front but bottom currents had weakened and allowed the pellets to settle to the lake floor without being broken apart. A close examination of the whole core, especially near the top, will reveal that some drop sediment is red or pink indicating a western or Ontario Lobe source.

The upper half of the core (left side of image) has thin distal varves that are difficult to count when in a moist outcrop. However, when they are partially dried in cores, like the one shown here, counting these couplets is easy and accurate. Even though these varves are relatively thin they have considerable thickness variation and show a very clear positive correlation of summer and overlying winter layer thicknesses. This indicates that the thicknesses of both the summer and winter layers is probably determined by the input of sediment to the lake during the summer. The thin varves have drop sediment sprinkled throughout but it is most common in the bottoms of summer layers and at the tops of winter beds.


  • Ridge, J.C., Brennan, W.J., and Muller, E.H., 1990, The use of paleomagnetic declination to test correlations of late Wisconsinan glaciolacustrine sediments in central New York: Geological Society of America Bulletin, v. 102, p. 26-44.

Past Varves of the Month...