The Late Wisconsinan history of ice movements is reconstructed for the region of Lower St. Lawrence and western Gaspésie based on an inventory of glacial striations and an analysis of the glacial dispersal of Appalachian indicator rocks and Precambrian erratics. The invasion by laurentide ice fom across St. Lawrence Valley appears to have been the first major glacial event. During this phase, ice moved easterly and southeasterly over the study area. Restricted glaciation may have preceded this event in higher are as; local ice caps likely covered Gaspésie and Miramichi Highlands. The development of a marine ice stream in St. Lawrence Valley radically changed the ice flow pattern. Ice now moved down-valley towards Gulf of St. Lawrence: in a northeastern direction along the valley axis and towards north or north-northeast over the study area. Decreasing discharge in the ice stream due to drawdown and accelerated calving as a result of late glacial rise of sea level caused the progression of a calving bay up St. Lawrence Valley, passing the study area between 14 and 13 ka BP. During passage of the calving bay, ice movement over the study area shifted from directions towards north-northeast and north to northwest and west. During these events, an Appalachian ice divide developed, which stretchedfrom the highlands of central Gaspésie, through northwestern New Brunswick and northern Maine, into the Eastern Townships of southern Quebec. Fossiliferous tills, observed at several places, indicate that Laurentide as well as Appalachian ice readvanced at least once after passage of the calving bay. Laurentide ice covered the coastal zone of the Rivière-du-Loup area around 11.8 ka BP and in the Rimouski area, Appalachian ice readvanced in marine waters after 12.3 ka BP.

No abstract

Three types of geological phenomena independently suggest that the TCmiscouata -Madawash Valley was affected by one or more seismic events following its deglaciation:(1) Subbottom acoustic profiling of Lac TCmiscouata and Grand lac Squatec revealed disturbance of bottom sediments by mass transport processes in both lakes. Erosional truncation of preexisting, acoustically laminated sediments and accumulation of hummocky, chaotic deposits over older hummocky surfaces or laminated sequences both result from mass transport processes. Unidirectional mass flows from several points in these symmetrical basins, in situ disruption of laminated sediment beneath flat bottoms, and the large area of the lake floors affected suggest strong similarities in sedimentation style with lakes that have been disturbed during strong earthquakes.(2) Southeast of Lac TCmiscouata, in Saint-Jacques, New Brunswick, two separate mass flow deposits, made up largely of coarse (>0.5 m), angular boulders of local bedrock, occur on opposite sides of the Madawaska River valley. These deposits have different source areas and transport directions, but occupy more or less the same stratigraphic position within sediments deposited in glacial Lake Madawaska.(3) At one site in Saint-Jacques, a near-vertical fault displaces a glacially striated bedrock surface at least 7 cm, suggesting a response to postglacial compressive stress similar to that observed on outcrops in the nearby epicentral region of the 1982 Miramichi earthquake.Although the TCmiscouata -Madawaska Valley lacks historical evidence of seismic activity, and many of the phenomena observed could, individually, have been generated by aseismic processes, we conclude that the close proximity of diverse features related to mass transport and faulting suggest that the valley has been the locus of seismic activity from the time of its deglaciation to the recent, but prehistorical, past.Trois types de phCnomknes gCologiques suggkrent, indkpendamment, que la vallCe de TCmiscouata-Madawaska a subi un ou plusieurs sCismes depuis sa dkglaciation :(1) Les sondages acoustiques du trCfonds du lac TCmiscouata et du Grand lac Squatec revklent que les stdiments de fond furent deranges par des processus de transport de masse dans les deux lacs. Les sondages acoustiques indiquent que ce transport de masse a tronqut les skdiments laminaires prk-existants, et qu'il en a r6sultC une accumulation de dCp6ts chaotiques, en creux et bosses, au-dessus de surfaces mamelonnkes plus anciennes ou qui recouvrent des skquences de laminites. La direction unique des Ccoulements en masse telle qu'indiqute h plusieurs endroits dans ces bassins symCtriques, la rupture in situ de skdiments laminaires en-dessous des couches de fond horizontales, et les fonds des lacs affect& sur une grande superficie suggkrent un style de sdimentation fortement similaire ?i celui des lacs dont les sMiments ont Ct C dCrangts par de gros tremblements de terre.(2) Au sud-est du lac TCmiscouata, dans Saint-Jacques, au Nouveau-Brunswick, deux dCp6ts de...

The clay mineral composition of a number of Saalian till samples from The Netherlands shows a large variation in smectite and illite abundances. The samples were selected according to their source area, as inferred from coarse erratic components. Specimens containing primarily rock fragments indicative of East and East‐Central Baltic areas are associated with no or low smectite percentages in their clay fractions. Those with mainly flint and rock fragments indicative of the West Baltic areas have high smectite contents in the clay. In general the smectite‐rich material is found in the lower portions of the Saalian till bed, whereas the smectite‐poor occurs in the upper portions. The linkage between very fine and coarse till components in the upper smectite‐free parts of the till suggests that this entire till has been subjected to englacial transport over distances of at least 1000 km.

Variations in composition between and within Saalian till types of The Netherlands arc dcmonstratcd with reference to grain-size distribution, fine-gravel petrography and heavy-mincrzl compo\ititrn. Several factors explain different aspects of the compositional variations. Firstly, a compositional layering rcsults from differcnces in the amount of local material that has been assimilated in successivc till hand\. Secondly, a petrographic stratification is present in the erratic components, which is most \trikingly expressed by the occurrence of flint-poor till ovcrlying till rich in flints. This fcaturc is in:crprctcd to havc becn inherited from an cnglacial debris stratification which is related to thc distribution of source rock types in the up-glacier area. Finally. a predominantly lateral variation in till compobirion 15 prcscnt.reflected best in the assemblages of the indicator pebbles, resulting from deposition by icc streams of different source and direction of flow.