BOOK REVIEWS 183

THE LATE QUATERNARY DEVELOPMENT OF THE CHAMPLAIN SEA BASIN edited by N. R. Gadd, Geo- logical Association of Canada Special Paper 35, St John’s, Newfoundland. Geological Association of Canada, 1988. No. of pages: 312. ISBN 0-919216-35-8.

This volume is the third in a series published by the Geological Association of Canada which deals with the evolution of major water bodies in areas marginal to and deglaciated by the Laurentide ice sheet in the late Wisconsinan period (earlier volumes dealt with Lake Agassiz and the Great Lakes). It arises from a symposium held in Ottawa in May 1986, and includes a total of 21 papers. As a book it is well produced, being firmly bound and attractiveiy laid out. Artwork is generally of high quality, and I spotted very few typographic errors.

The Champlain Sea developed as a result of marine incursion into the St Lawrence lowland during and after the withdrawal of Laurentide ice from the region. This was made possible by a combination of eustatic sea level rise and glacioisostatic depression of the crust by the ice sheet. For a short period between 10800 and loo00 BP virtually all of the meltwater produced by the sector of the ice sheet between Manitoba and Quebec was routed to the North Atlantic through the Champlain Sea. The area thus plays a crucial role in theories which attribute the Younger Dryas climatic oscillation to the formation of a low salinity meltwater cap on the surface of the North Atlantic as a result of the diversion of drainage from the Lake Agassiz basin away from the Mississippi valley and into the Gulf of St Lawrence. These ideas are taken up in the paper by Teller in this volume.

Three principal themes emerge from the collection of papers included in the volume. These concern the pal- aeogeographic evolution of the area as a whole, the pattern and history of temperature and salinity variations in the waters of the basin, and the character of ice contact sedimentation in subaqueous environments. The picture which emerges is of a basin in which conditions vary rapidly in both time and space as a result of the inter- actions between a highly dynamic ice margin and its proglacial water bodies. Gadd envisages ice advancing from the Laurentian Highland forming a series of pro- glacial water bodies as it impeded northward drainage from the Appalachians. Sedimentation in these water bodies created localized soft substrates which favoured more rapid glacial advance and the development of lobate, low profile ice masses prior to the glacial max- imum when the whole area became ice-covered. Deglaci- ation is argued to have taken place by rapid downdraw as a calving bay worked its way up the St Lawrence river valley, eventually dissecting the residual ice mass. Dating these events is difficult, because the 14C activity of the total inorganic dissolved carbon in marine waters ap- pears to have been lower than that of the contemporary atmospheric CO, and marine shells appear to give anom- alously old dates (Hillaire-Marcel). Comparison of pollen assemblages in the earliest Champlain Sea sediments with regional assemblage zones for the Ottawa valley-Lake Ontario region suggests a date of 11 200 BP for the onset of marine conditions, a full 1700 years younger than the oldest shell dates (Anderson).

Palaeoecological studies of mollusca, ostracodes, and foraminifera combined with isotope geochemical studies of biogenic carbonates suggest that Champlain Sea waters were strongly stratified with respect to both temperature and salinity (Hillaire-Marcel, Wassenauer et al., Hunt and Rathburn, Rodrigues), particularly towards the end of the marine phase (believed to lie between 10 200 and 9500 B P Elson, Anderson). This stratification relates to the inflow of cold, low salinity meltwaters above cold, high salinity marine waters, particularly during the period when Lake Agassiz waters were routed through the system. There still seems to be considerable contro- versy over the possibility that there was a proglacial lake precursor to the Champlain Sea, or whether early fresh- water sediments may simply reflect meltwater dilution of saline waters in an ice-proximal tidewater glacier environment.

This debate has considerable implications for the inter- pretation of ice-contact sedimentary sequences (Sharpe, Rust, Burbidge, and Rust). Throughout much of the basin, ice appears to have terminated in standing water as it retreated and it appears to have been fringed by a zone of rapid subaqueous sedimentation. Much of this sedi- mentation appears to have taken place at the mouths of subglacial meltwater conduits on subaqueous outwash fans. Sedimentary sequences display rapid vertical and horizontal facies transitions, reflecting the abrupt reduc- tion in the transporting power of meltwater flows as they entered standing water. Sedimentation involves the ac- tion of turbidity underflows, suspension settling from overflows and interflows, plus significant reworking by retrogressive slumps which often develop into deeply channelized sediment gravity flows (Burbidge and Rust). Coarse sediments are frequently blanketed by muds which have traditionally been interpreted as distal marine sediments, but these are shown to be interbedded in places with coarser sediments and are argued by Sharpe to result from rapid settling from turbid plumes as a result of flocculation in the proximal marine environment. More speculatively, and without a lot of supporting evidence, Sharpe links the existence of turbid plumes to the former occurrence of catastrophic meltwater floods and glacier surging. Whilst this interesting idea has some support in recent process observations, its applicability to this particular setting seems to demand rather more critical glaciological appraisal than it has received hitherto.

In summary, the volume provides an excellent over- view of recent work on the Champlain Sea, which is in turn illustrative of more general thinking about the interactions between large ice sheets and marginal water bodies. These are issues which are of substantial import- ance for understanding the temporal and dynamic evolu- tion of past ice sheets and which are likely to prove critical to our evaluation of how ice sheets may respond to global warming. Nelson Gadd is to be congratulated on the production of a timely and interesting volume which should help to focus and stimulate future research.

MARTIN SHARP University of Cambridge