Late Pleistocene Stratigraphy And Events In The Asbestos-valcourt Region, Southeastern Quebec
The stratigraphic record of the Asbestos-Valcourt region indicates that glacial sediment deposite during at least two regional glacial advances underlie Late Wisconsinan ice-contact and glaciolacustrine sediments. Glaciolacustrine sediments (unit B), which underlie surface till (drift unit C), were deposited during a rather short-lived interstade, prior to the Late Wisconsinan glacial maximum; unit B is a probable correlative of the Gayhurst Formation (Middle Wisconsinan).;Till deposited in the Appalachian Uplands during the earlier glacial advance (drift unit A) contains only rare Shield-type erratics and has a distinctive Appalachian provenance. Till geochemistry as well as till clast lithology and fabrics indicate that drift unit A was deposited by a glacier that was advancing westward from Appalachian outflow centers. However, the presence of some northwest-derived clasts in till of drift unit A provides evidence for an earlier phase of southeastward ice-flow. Ice-flow sequences recorded in drift unit A suggest that a shift of outflow centers with an Appalachian-based glacier took place toward the close of glacial phase A; it is during this part of glacial phase A that a northward ice-flow episode occurred in uplands of the Asbestos region. This glacial unit is believed to be a correlative of Chaudiere Till (Early to Middle Wisconsinan).;Till deposited during the last regional ice advance (drift unit C) commonly contains Precambrian erratics as well as abundant northwest derived local debris. Glacial dispersal trains, subtill glacitectonic deformations and till clast fabrics consistently indicate that drift unit C and its equivalent, Lennoxville Till, were deposited by ice that advanced southeastward from a Laurentide outflow center and that this ice-flow pattern was maintained until final ice-retreat.;During northward ice-retreat that followed glacial phase C, a series of recessional end-moraines (Cherry River/East-Angus, Mont Ham and Ulverton-Tingwick Moraines, in order of decreasing age) were deposited and Glacial Lakes Memphremagog and Vermont were impounded south of the ice front. Subsequent glacial retreat along the edge of the Appalachian uplands together with deglaciation of the Quebec City narrows allowed marine waters to invade the isostatically depressed Central St. Lawrence Lowland, thus forming the Champlain Sea about 12 ka.
Networked Digital Library of Theses and Dissertations