Champlain Sea Basin Research Articles

Using computed tomography (CT) to reconstruct depositional processes and products in the subaqueous glaciogenic Champlain Sea basin, Ottawa, Canada

In this study, depositional conditions in the glaciogenic Champlain Sea basin were inferred solely from evidence of computed tomography (CT). CT-scan images and Hounsfield unit (HU) profiles of two continuous cores in Ottawa, Canada, provided the data to identify five lithologically distinct, mud-dominated stratal units. Distinctively, all strata exhibit a repeating pattern of HU values. The upward increase and then decrease in HU values within each bed suggests upward increasing and then decreasing silt content, which collectively, is interpreted to reflect the consistent waxing followed by waning flow conditions during a single cycle of glaciogenic meltwater discharge. Mud rhythmites at the base of the succession (Unit 1) and beds of well-stratified mud at the top (Unit 4a) exhibit well-developed parallel-stratification in the lower part of each bed; they are characterized by a range of ~250–350 HU. This wide range in HU values reflects the effective partitioning of silt-rich and clay-rich parts in each bed, and therefore bed-surface and near-bed transport processes that sorted sediment mostly by grain size, followed by low-energy sediment fallout. The silt-rich part of each bed was deposited by glaciogenic meltwater-sourced hyperpycnal flows, which due to the freshwater composition of the basin, or at least in the upper part of the water column, were able to plunge to the basin floor and sort particles along the bed. In comparison, beds of bioturbated mud (Unit 2), banded mud (Unit 3), and diffusely stratified or structureless mud (Unit 4a) have a narrower range of ~50–120 HU, indicative of poorer particle sorting. These conditions, most clearly illustrated by the bioturbation, indicate a change to a seawater basin that caused meltwater inflows to instead form buoyant, sediment-laden hypopycnal flows, which aided by clay-silt particle flocculation and/or settling-driven convection, resulted in sediment deposition directly from suspension. In addition to characteristic sedimentary structures and textures, beds within each unit also exhibit similar thickness, which often doubles or triples in the abrupt transition from one unit to the next. These changes most probably reflect abrupt and systemic changes in deglacial dynamics and its control on sediment supply that often coincide with equally abrupt changes in salinity in the Champlain Sea basin.

Allochthonous sources of iodine and organic carbon in an eastern Ontario aquifer

Regional geochemical characterization of groundwaters in a bedrock aquifer in the Ottawa – St. Lawrence Lowlands of eastern Ontario has identified an iodine (I) anomaly, with values regularly exceeding 150 μg/L and a maximum observed concentration of 10 812 μg/L. The spatial distribution, enrichment mechanisms, and sources of I and organic matter were investigated using geochemical and isotopic data. High-I groundwaters (>150 μg/L) are prevalent in Na–Cl-type groundwaters at low bedrock elevations in areas overlain by thick layers of glacial sediments. I is thought to be linked to massive muds in the glacial sediments overlying the aquifer, deposited during the postglacial incursion of the Champlain Sea 12–10 ka BP. Principal component analysis of I and 18 other chemical parameters revealed correlations among I, salinity, and indicators of microbial oxidation of organic matter, suggesting that the intrusion of saline pore waters affected by decomposition of organic matter such as marine phytoplankton in the massive muds is the dominant process controlling I enrichment in groundwater. 129I/127I ratios in the pre-modern waters vary between near-marine values of 460 × 10−14 and 5 × 10−14, demonstrating that older allochthonous I derived from the surrounding Paleozoic sedimentary terrain also contributed to the I pool in the Champlain Sea basin. 14C ages and δ13C signatures for dissolved organic carbon in groundwater and disseminated organic carbon within the glaciomarine muds highlight an allochthonous source of terrestrial organic carbon predating the Champlain Sea incursion, likely transported via glacial meltwaters in tandem with I to the Champlain Sea basin.

Sedimentation in isolated glaciomarine embayments during glacio-isostatically induced relative sea level fall (northern Champlain Sea basin)

The nature of glaciomarine sediments deposited during ice margin retreat can vary according to physiographic setting and relative sea level fluctuations. To understand the effects of these two parameters on sedimentation, we analyzed the sediment records of four lakes located within former isolated glaciomarine embayments of the northern Champlain Sea basin. These lakes were initially inundated by marine water of the Champlain Sea, following deglaciation, and have subsequently experienced basin isolation owing to glacio-isostatic rebound. Three of these lakes reveal a common litho- and acoustic stratigraphic succession, characterized by an IRD-free glaciomarine to marine facies consisting of homogeneous to faintly laminated clayey silts grading into well-laminated silts with rapidly deposited layers. These two units recorded the transitional environment from glaciomarine sedimentation below multiyear shorefast ice to increased terrestrial runoff and rapid glacio-isostatic rebound once the ice margin retreated inland. During ice margin retreat, relative sea level fell concomitantly resulting in the deposition of coarser sediments in marine embayments. Upon the complete retreat of the ice margin, the supply of terrestrial sediments diminished and lake isolation, driven by relative sea level fall, led to higher biogenic content and increased bioturbation. This study provides a framework for sedimentation in isolated glaciomarine embayments which differs from deep-water sedimentation owing to the presence of shorefast sea-ice and their protected location from major ice-stream outlets.

Nouvelle Autoroute 30: a Champlain clay crust earthworks case study

The Champlain Sea Basin in eastern Canada is known for its sensitive clay and associated engineering problems through this much-developed area along the St Lawrence River. Geologically, the surface of the Champlain clay has been subjected to desiccation, frost action, and weathering. This has resulted in the reduction of the water content and sensitivity of the surficial crust layer of this very wet clay deposit sufficiently to enable it to be used as an earthworks material. However, the material is still much wetter than its optimum moisture content. By co-operative value engineering, the team on the Nouvelle Autoroute 30 project in Montréal, Quebec, investigated and achieved moisture content and degree of compaction derogations to the Ministry of Transport, Quebec specification. This allowed the successful construction of many low and high road embankments using an unprecedented 2.3 × 106 m3 of this weathered Champlain clay crust material. This paper describes how the design and construction issues associated with using this material for earthworks were evaluated and addressed.

Sequence stratigraphy of a glaciated basin fill, with a focus on esker sedimentation

A large integrated data set of cores, outcrop data, and seismic transects from the mud-buried Vars-Winchester esker in the Champlain Sea basin, Canada, was studied to gain insight into how muddy glaciated basins fill with sediment, and how esker sedimentary systems contribute to this process. Three stratigraphic units—a till sheet over carbonate bedrock, the Vars-Winchester esker , and overlying Champlain Sea mud—are identified in the data set. The till is massive, mud rich, carbonate rich, and drumlinized. The esker is also carbonate rich, and rests erosively on till or bedrock. It consists of two elements, a narrow gravelly central ridge and a broad sandy carapace. Three units comprise the overlying mud package: gray carbonate-rich rhythmites, massive bioturbated mud, and carbonate-poor, red-and-gray rhythmites. A sequence stratigraphic model is proposed to explain these observations. Emphasis is placed on gradual ice-front translation superimposed by rapid meltwater events. The esker is interpreted to have been derived from the underlying till by water that flowed through a subglacial conduit (R-channel), within which the narrow gravelly central ridge was deposited. Most mud and finer sand bypassed the conduit and was deposited proglacially on the floor of the Champlain Sea, first as sandy outwash and, farther basinward, as muddy carbonate-rich rhythmites. Gradual ice-front retreat superposed distal facies over proximal facies, generating the upward-fining succession that starts with the esker gravel and ends with muddy rhythmites. Most esker sediment appears to have been deposited during rapid, jokulhlaup-like floods that punctuated gradual retreat. Discharges are estimated to have been high, possibly on the order of several hundred to, perhaps more commonly, several thousand cubic meters per second. The chaotic and random-looking appearance of the resultant sedimentological signatures in the esker sensu stricto is sharply contrasted with the regularity of the muddy rhythmites. If the rhythmites are indeed correlative to the esker, which seems reasonable given their geochemistry and the fact that their volume scales to the volume of mud in the till, the flood events that deposited the esker must have been seasonally mediated, and the basin water must have attenuated the flood signal, resulting in a rhythmic “on-off” signature in more distal portions of the system. The regularity of the rhythmites does not betray the chaotic nature of the esker sensu stricto, and vice versa. Studying either one in isolation would lead to a very different “end-member” impression of how eskers form and how esker sedimentary systems operate during the infilling of glaciated basins.

Foraminiferal Distribution in the Central and Western Parts of the Late Pleistocene Champlain Sea Basin, Eastern Canada

Marine sediments from the late-glacial Champlain Sea have been sampled at 20 localities representing the deeper part of the basin, between Ottawa and the Rivière St-François, Québec. Foraminiferal assemblages have been extracted and a sequence of three deep water and two shallow water ecozones recognized. The lowermost zone (A) is characterized by Cassidulina reniforme, Islandiella helenae and I. norcrossi and represents a paleosalinity of 25 to 30%o. The overlying zone B is dominated by Elphidium excavatum. It represents salinities decreasing from 25 to as low as 10%o. The uppermost zone (C) contains only a sparse assemblage of a morphotype of E. excavatum. If suggests a paleosalinity of no more than 10%o. A mostly unfossiliferous silt and clay layer of variable thickness (post-C) occurs above zone C. It is probably lacustrine. Below zone A and above the Late Wisconsinan till there is a pre-A interval whose variable assemblages represent hyposaline environments east of Montréal, predominantly lacustrine conditions west of Montréal and alternating hyposaline/ lacustrine environments near and south of Montréal. Bottom water temperatures were probably "Arctic" (within a few degrees of 0°) from the pre-A interval up to zone B inclusively. The data from zone C are too poor to estimate temperatures. The shallow water zones indicate environments with high (zone EH) or low (zone EA) salinities but of shallower depths than the deep water zones. The existence of two sequences is interpreted as the result of (probably seasonal) water stratification. The data does not allow to determine the depth of the limit between the shallow and deep waters.

Quaternary Foraminiferal Stratigraphy in Sediments of the Eastern Champlain Sea Basin, Québec

Des sédiments tardiglaciaires de la Mer de Champlain ont été échantillonnés à 18 sites dans les régions de Trois-Rivières et de Québec. Deux séquences d'écozones à foraminifères (eau profonde et peu profonde), semblables à celles précédemment décrites dans l'ouest de la Mer de Champlain, sont reconnues. Le contenu faunique indique une première phase hyposaline (pré-A) avec des indices sûrs d'eau douce seulement à la limite sud-ouest de la région étudiée. Durant cette période, la salinité a dû être déterminée par l'avancée et le recul d'un lobe glaciaire dans la région de Québec. Suit la zone A (salinité : 25-32 %o), qui est en partie synchrone avec la formation de la Moraine de St-Narcisse. Cette zone a duré approximativement de 11,3 à 10,6 ka BP, peut-être jusqu'à près de 10,2 ka BP. Elle est suivie des zones B (10-25 %o) et C (2-10 %o) tandis que près des grands affluents d'eau douce, d'épaisses séries deltaïques dépourvues de foraminifères se substituent aux zones B et C. À l'est de Trois-Rivières, il semble que la zone B soit discontinue et ne se rende pas jusqu'à Québec. La zone C n'est observée qu'à un seul site, à l'ouest de Trois-Rivières. Deux zones peu profondes, EH et EA, contemporaines des zones A et B, se caractérisent par des salinités plutôt élevées (maximum annuel jusqu'à 30 %o pour EH, un peu moins pour EA), la zone EA indiquant d'autre part des étés plus tièdes. Les résultats obtenus concernant les paléosalinités ne permettent pas de détecter le détournement de l'exutoire du Lac Agassiz. Le débit estimé par certains auteurs n'a peut-être pas suffi à changer de façon détectable la salinité des eaux profondes de la dernière phase de la Mer de Champlain. Dans les eaux peu profondes, le changement pourrait avoir été plus sensible, mais sa datation est difficile à cause de la présence de carbonate ancien recyclé.

Younger Dryas‐age readvance of Laurentide ice into the Champlain Sea

Occurrences of Balanus hameri‐bearing diamicts described in this paper and pertinent (Balanus plates and pelecypods shells) 14C dates suggest that there was glacial activity in the Champlain Sea basin between 11,000 BP and 10,400 BP and that this activity can be ascribed to a climatic cooling episode correlative with the Younger Dryas of the late‐glacial sequence of northeastern Europe.

The late Quaternary development of the Champlain Sea Basin

The late Quaternary development of the Champlain Sea Basin

The late quaternary development of the Champlain Sea Basin edited by N. R. Gadd, Geological Association of Canada Special Paper 35, St John's, Newfoundland. Geological Association of Canada, 1988. No. of pages: 312. FSBN 0‐919216‐35‐8

The late quaternary development of the Champlain Sea Basin edited by N. R. Gadd, Geological Association of Canada Special Paper 35, St John's, Newfoundland. Geological Association of Canada, 1988. No. of pages: 312. FSBN 0‐919216‐35‐8

N. R. Gadd (ed.) 1988. The Late Quaternary Development of the Champlain Sea Basin. Geological Association of Canada, Special Paper 35. Proceedings of a symposium held in Ottawa, 21 May 1986. vii + 312 pp. May be ordered from: GAC Publications, Department of Earth Sciences, Memorial University of Newfoundland, St John's, Newfoundland, Canada A1B 3X5. Price C$50 (members), C$60 (non-members);

N. R. Gadd (ed.) 1988. The Late Quaternary Development of the Champlain Sea Basin. Geological Association of Canada, Special Paper 35. Proceedings of a symposium held in Ottawa, 21 May 1986. vii + 312 pp. May be ordered from: GAC Publications, Department of Earth Sciences, Memorial University of Newfoundland, St John's, Newfoundland, Canada A1B 3X5. Price C$50 (members), C$60 (non-members);

Preconsolidation pressure of Champlain clays. Part II. Laboratory determination

A series of conventional and special consolidation tests was carried out on clay samples from 11 sites in the Champlain sea basin. The results show that, for a given clay at a given depth, there is a unique preconsolidation pressure – strain rate relationship independent of the tests carried out and that the relationships obtained in different Champlain clays can be normalized.Correlations between the preconsolidation pressure values obtained from the different special consolidation tests and the conventional test are established, and a method of estimating in-situ preconsolidation pressure is suggested. Keywords: preconsolidation pressure, laboratory, testing techniques, strain rate.