ALBERT

Description: The Kamouraska Formation is a quartz-arenitic unit of latest Cambrian – earliest Ordovician age in the Quebec Appalachians that was deposited by hyperconcentrated to concentrated density flows in a meandering submarine canyon on the continental slope bordering the Iapetus Ocean, as outlined in a companion paper. Detailed petrographic study of the quartz arenites of the Kamouraska Formation combined with scanning electron microscopy of grain surface textures suggests that the quartz sands are of eolian origin having been derived from an inland desert or, less likely, a barrier beach dune system. Transport of the mature quartz-arenitic sand onto the shelf and deposition into the deep sea was not accompanied by substantial mixing with material from other sources thus preserving the inherited eolian characteristics. A modern analogue for the eolian interpretation of the deep-sea quartz-arenite beds is as follows: thick, Late Pleistocene eolian sand beds on a modern abyssal plain in the East Atlantic referred to as eolian-sand turbidites that were deposited in the deep sea during glacial sea level lowstands when eolian sand transport to canyon heads was enabled by an exposed and shortened shelf. Similarly, an established sea level lowstand at the Cambro–Ordovician boundary would have facilitated the introduction of eolian sand of the Kamouraska Foundation into canyon heads on the upper slope from where turbidity currents and related density flows were triggered. Correlation of the Kamouraska Formation with the quartz arenites of the Cairnside Formation of Quebec (Keeseville Formation in northern New York State, Nepean Formation in southern Ontario) links the deep-sea deposits with remnants of an inland dune system.

Description: During Late Pleistocene Heinrich events (H-events), distinct, decimetre- to centimetre-thick layers of ice-rafted debris (IRD) were deposited in the North Atlantic as Heinrich layers (H-layers). These layers are characterized by high detrital carbonate content, low foraminifera content, a high percentage of Neogloboquadrina pachyderma (sinistral) among the planktonic foraminifera, high magnetic susceptibility, and high grey colour values. In contrast, H-layers in the Labrador Sea reach metre thickness at core sites proximal to the iceberg source off the Hudson Strait ice stream (HSIS), and show low magnetic susceptibility and relatively low grey levels on the colour scale. To provide the reader with some background information, four hypotheses concerning the origin of H-events are discussed at the outset: (1) the binge–purge (internal forcing) model, (2) the subglacial outburst flood model, (3) the external forcing model, and (4) the catastrophic ice shelf breakup model. The higher thickness of ice-proximal H-layers is due to the supply of large amounts of terrigenous sediments that were eroded from country rocks underlying the northeastern sector of the Laurentide Ice Sheet (LIS). These sediments were transported to the deep Labrador Sea by the efficient processes of bottom-following mass and surface plume movement, where they mixed with ice-rafted sediment. Four distinct depositional facies of H-layers (Types I to IV) have been identified: Type I H-layers occur within 300 km from the presumed HSIS terminus and consist of stacked thin layers of graded muds containing IRD. The graded muds that are spiked with IRD are the result of deposition of fine-grained sediment from lofting sediment columns that collected dropstones and grains under the iceberg route. Type II H-layers occur on the slope and rise at a greater distance south of the Hudson Strait outlet, on the levees of tributary canyons to the Northwest Atlantic Mid-Ocean Channel (NAMOC). These layers consist of alternating thin mud turbidites with intercalated laminae of IRD. Type III H-layers exist on the levees of the main channel of the NAMOC, and consist of layers of IRD alternating with fewer fine-grained spillover turbidites, reflecting the lower spillover frequency from the deep channel compared to the less deep slope canyons. Type IV H-layers are made up of bioturbated hemipelagic muds with IRD, and occur in regions between canyons not reached by spillover turbidity currents, and in distal regions of the open ocean or on seamounts. The anomalously high thickness of individual H-layers on the slope and rise off Hudson Strait is explained by the transport of significant portions of H-layer sediment by suspended sediment columns lofted from sand-carrying freshwater turbidity currents (Type I), and by low density turbidity currents (Types II and III). Isopach maps for H-layers 1–3 give hints of the drift routes of the lofted suspended sediment during its ascent to the surface, and of iceberg drift directions in the Labrador Sea.

Description: Lower Palaeozoic shales and slates in the External Domain of the southern Canadian Appalachians are composed predominantly of illite and chlorite with minor occurrences of I-S mixed-layer minerals (restricted to samples with illite crystallinity, IC 〉 0·62°Δ2Θ) and paragonite (restricted to samples with IC 〈 0·42°Δ2Θ). Inverted diagenesis has occurred in the NW part of the Chaudière Nappe, indicating pre-orogenic deep burial diagenesis at the original depositional site, whereas to the SE, the diagenetic pattern was affected by synorogenic heating. Within the east-dipping thrust-fold belt and the St Lawrence Lowlands, increasing grade towards the S suggests a gradual southward increase in post-tectonic burial depth. Narrow (3–5 km) thermal haloes around the Cretaceous Monteregian intrusions show limited effects on the country rocks.The percentage of 2M1 mica polytypes and bo increase with decreasing IC. Chlorite crystallinity (CC) increases with increasing IC. Good correlations between IC, %2M1, CC and bo of micas indicate that these parameters are reliable monitors of high-grade diagenesis and low-grade metamorphism in clay-rich sedimentary rocks. IC and CC improve with increasing grain size, illustrating the effect of grain size on IC and CC. Organic material affects IC more strongly in strata with lower permeability than in those with higher permeability. In the diagenetic zone, glycolation does not uniformly produce a narrowing of the 10 Å illite peak, but may also broaden it by up to 15%, probably due to the presence of Kalkberg-type mixed-layers.

Description: The expandability of K-depleted biotite and natural vermiculite was studied using transmission electron microscopy (TEM) and X-ray diffraction (XRD). K-depletion in layer-silicates was achieved by treating ultrathin sections with 0·1 m CaCl2 and BaCl2 solutions. The natural sample of biotite, which by XRD revealed no expandability on ethylene glycol or glycerol solvation, displayed 10–15% expanded layers when viewed by TEM after alkylammonium intercalation. The proportion of expanded layers increased after CaCl2 treatment. XRD of vermiculite samples revealed two sets of expandable interlayers after alkylammonium treatment, corresponding to two types of particles with different layer structures observed by TEM. Identification of vermiculite by TEM based on basal spacings is reliable with alkylammonium treatment. Intercalation of alkylammonium ions into the interlayers of vermiculite improved the degree of stacking order of the 2:1 layers.