The map below shows the Early T6 ice sheet extent as shown by the maroon colored shading:
This map is taken directly from the VCGI Project Sheet. The T5 margin is not depicted for sake of simplicity and scale limitations but was intermediate between the T4 and Early T6 margins.
The map below is a regional map showing the Early T6 time ice sheet (pale gray-blue shading) and ice margin (maroon colored lines, and other features as discussed in the following:
Owing to map scale limitations, the position of the Early T 6 margin on both of the above maps is highly diagrammatic.
In both the Champlain and Memphremagog Basins the T4, T5, and Early T6 ice margins represent a step-down sequence, generally of closely spaced hybrid ice margin features, (more widely distended in the Vermont Valley owing to its low gradient). Again, the maroon line on the above map approximately depicts the Early T6 margin in these basins.
By Early T6 time the Memphremagog lobe had receded to a small, remnant lobe tip in the Newport area, with the ice margin marked by numerous deep kettles which were occupied by remnant ice blocks, interspersed with stagnant ice deposits, including many ice contact deltas related to proglacial Lake Memphremagog. This is regarded as a “Disaggregated” type margin. The footprint for this lake is not shown, but its strandline was essentially the same as the Early T6 margin.
Wright (2024, ibid) mapped portions of the Memphremagog Basin in the Newport area in great detail, including the identification of ice margin and proglacial lake features. Whereas he inferred the ice sheet margin based on his interpretation of proglacial water bodies in that Basin he did not specifically delineate deglacial ice margin positions based on a correlation of ice margin features, which is the particular interest here. The recessional history in the Memphremagog Basin in T4 to T6 times is documented by VCGI mapping, as discussed for several Locales in Appendix B.
In the Champlain Basin, the Early T6 ice margin on the above maps similarly marks the bottom of a step-down hybrid sequence, with stagnant ice deposits, including many kame deltas at the Coveville Lake Vermont level, represented by the neon blue shading along the ice margin perimeter. Again, owing to the map scale, the Early T6 margin depicted on the above map is highly schematic, with more accurate depictions given by Locales as described in Appendix B. The Early T6 margin is similarly interpreted as a “Disaggregated” type ice margin, characterized by a narrow, heavily crevassed, “labyrinthian” maze penetrated by standing Coveville waters in a more or less open water corridor.
The Early T6 margin and Coveville “corridor” extended northward along the base of the Taconic foothills from the Benson Landing vicinity, around the nose of the Taconics, into the Vermont Valley in the Rutland/Proctor area, thence continuing northward along the foothills, marked in many places by kame deltas, including major Coveville deltas at Benson Landing, Castleton, Proctor, Brandon, Pittsfield, East Middlebury, Bristol, and South Hinesburg. The Bristol Coveville delta represents drainage from a T6 ice margin at the head of the La Platte Basin, and the South Hinesburg delta by drainage from Lake Mansfield, as shown, formed by an ice dam at the mouth of the Winooski Basin.
There is no evidence of calving in conjunction with this early T6 margin in Vermont. However, calving is inferred along the western margin of the Champlain lobe, related to the substantially greater depths for Coveville waters in the Champlain Basin “Deep Lake” portion of the physiographic “Trough,” as marked by the darker blue color on the above map. (This calving was part of my response to Franzi, to explain differences between the Vermont and New York records as being “schizophrenic” owing to the intervening open water body with a calving margin. It is noted that this open water and associated calving was disproven by the Addendum study, as discussed below.)
To the north in Early T6 time, in the Lamoille Basin, the early T6 margin is marked by stagnant ice deposits and kame deltas at the Lake Mansfield level. In the Missisquoi Basin, the VCGI mapping shows a highly convoluted T6 margin, marking multiple lobes of thin ice closely related to the physiography, with a major stagnant ice deposit in the Berkshire vicinity. Again, the details for this margin are provided for several Locales in the Missisquoi Basin. The Early T6 margin is correlated with the Sutton moraine in Quebec.
Thus, in sum the Early T6 margin marks a long narrow, convex lobe in the Champlain Basin. As discussed above and summarized below, remnants of this lobe persisted in later T6 time, through T7 time, continuing into T8 time. It was this long convex lobe at late glacial times that served as the impetus for the Addendum study.