Volume 25, numéro 2, august 1989

FR :

Unc approche non classique de la mode'lisalion du champ gravimltrique regional est pre'sentee. Le concept mis de l'avant dans la m^thodede Griffin permettantd'extraireranomalier^siduelleestceluiquis'^Jparentele plus arapprocheproposeedans cet article. La tendance actuelle fait surtout appcl a des fonctions mathematiques et a l'analyse numerique. La m£diode proposce est compare avec d'autres techniques de representation de la regionale en prenant comme exemple la region du Mont Mejgantic. Les resultats suivants sont presented: (1) approximation du champ regional par tes polynomes du ler, 2ieme et 3ieme degr£, (2) approximation du champ regional par la m<5thode de la moyenne mobile suivant quelques versions de fenetre differentes, (3) correlations des parametres gravim£triques et lopographiques, (4) approximation des cartes de contour et des modelcs tridimensionnels pour chaque version calcul£e, (5) comparaison des r&ultats obtenus et choix me^thodologiques.

A non-classical approach towards regional, gravity-field modelling is presented, which is closest to the concept put forward within Griffin's method of isolating the residual anomaly. Current trends mainly call upon mathematical functions andnumerical analysis. The Mount Megantic area is used as an example to compare the proposed method with other techniques of representing the regional trend. Results are (1) approximation of the regional field with the help of linear, quadratic and cubic polynomials; (2) approximation of the regional field through the moving-average method using a few different windows; (3) correlation of gravity and terrain parameters; (4) approximation of contour maps and three-dimensional models for each calculated version; and (5) comparison of the results and methodological choices

EN :

The upper Middle Cambrian to early Late Cambrian King Square Formation, Saint John Group, southern New Brunswick, is an approximately 380 m thick silicilastic sequence of interbedded fine-grained sandstones and siltstones and shales. On the basis of sandstone to shale/siltstone ratios, bed thickness and characteristics, sedimentary structures and degree of bioturbation three lithofacies are recognized. These are facies KS1, thin bedded sandstone and shale lithofacies; KS2, thick bedded sandstone lithofacies; and KS3, bioturbatcd shale and siltstone with interbedded sandstone lithofacies. These lithofacies are interpreted to havebeen deposited on a wave- and storm-influenced marine subtidal shelf. Facies KS 1 was deposited essentially below wave base though in its upper horizons, deposition may have occurred above storm wave base. Facies KS2 was essentially deposited in a shallower subtidal inner- to mid-shelf environment above storm wave base and facies KS3 initially above and latterly below storm wave base. The exact nature of the currents responsible for transportation and deposition of the storm-related sandstones (geostrophic flows or turbidity currents) is impossible to determine and therefore palaeocurrent data must be interpreted with caution. The stratigraphic arrangement of the lithofacies, with facies KS1 being the oldest and KS3 the youngest, suggests that the King Square Formation represents a regressive-transgressive sequence.

FR :

La Formation de King Square (Groupe de Saint John, Nouveau-Brunswick, fin du Cambrien moyen—de"but du Cambrien tardif) est une serie terrigene d'environ 380 m d'epaisseur, constitute d'un interlitage de gres fins, de siltstones et de shales. Les rapports gres/shale et gres/siltstone, les caracteristiques et fepaisseur des lits, les structures setlimentaires ainsi que le degre* de bioturbation pcrmettent de reconnaitre trois lithofacies. Ce sont les facies KS1 (gres et shale finement lite*), KS2 (gres en bancs Ipais) et KS3 (gres interim de shale et siltstone bioturbes). On interprete ces lithofacies comme ayant £t£ deposes sur une plate-forme marine subtidale influencee par la houle et les tempetes. Le depot du facies KS 1 s'effectua essentiellement sous la zone d'amortissement de la houle quoique ses horizons superieurs puissent reliefer une sedimentation au-dessus de la profondeur d' amortisscment des ondes liees aux tempetes. Le milieu de depot du facies KS2 correspond a un site moins profond, soit la plate-forme infralittorale interne ou moyenne, exposed a faction des ondes de tempetes. Le depot du facies KS3 dlbuta au-dessus de la profondeur d'amortissement des ondes li£es aux tempetes et continue en-dessous de celle-ci. On ne pcut guere determiner la nature exacte des courants geostrophiques ou de turbidite* responsables du transport et du depot des gres lies aux tempetes; la prudence est done de mise lors de l'interpretation des donnees sur les paieocouranls. Le facies KS 16tant le plus ancien et le facies KS3 lc plus recent, l'agcncemenl des lithofacies suggere que la Formation de King Squarerepresente une seried'abord regressive puis transgressive.

EN :

The late Proterozoic Folly River Formation of the Cobequid Highlands, Nova Scotia, is a volcano-sedimentary sequence within the Avalon Terrane. The succession consists of interlayered mafic volcanic rocks and thinly laminated volcanogenic turbidites and is associated with abundant mafic dykes that are inferred to have fed the volcanic eruptions. The formation occurs exclusively between the Rockland Brook and Cobequid faults. The basalts and dykes are Fe- and Ti-rich, differentiated, within-plate continental tholeiites. Their emplacement is attributed to limited continental rifting. The Folly River Formation is similar in lithology, geochemistry and stratigraphy to the Clydesdale Formation in the Antigonish Highlands and is probably pcnecontemporaneous with arc-related volcanic sequences in both the Cobequid and Antigonish highlands. Hence it is concluded that the Folly River Formation formed in a rifting environment within a volcanic arc.

FR :

La Formation tardiprot^rozoique de Folly River (Monis Cobequid, Nouvelle-Ecosse) est une seiie volcano-s&limentaire au sein de la Laniere d'Avalon. La succession consiste en un interlitage de volcanites mafiques et de turbidites volcanogenes finement laminees. Lui sont associes d'abondants dykes mafiques qui auraient nouiri les Eruptions volcaniques. La formation ne se rencontre qu'entre les failles de Rockland Brook et de Cobequid. Les basaltes et les dykes sont des tholeiites intraplaques continentales, differenciees et riches en Fe ainsi qu'en Ti. On attribue leur emplacement a l'ouverture restreinte d'un rift continental. La Formation de Folly River ressemble, par sa litnologie, sa geochimie et sa stratigraphie, a la Formation de Clydesdale dans les Monts Antigonish. Elle est probablement penecontemporaine des series volcaniques relives aux arcs dcs monts Cobequid et Antigonish. On conclut done que la Formation de Folly River s'&ablit en regime d'ouverture a rint&ieur d'un arc volcanique.

EN :

The 1989 Colloquium of the Atlantic Geoscience Society was held at the Wandlyn Inn, Amherst, Nova Scotia on February 3-4, 1989. On behalf of the Society we thank Laing Ferguson of Mount Allison University and all others involved in the organization of the meeting.

In the following pages we publish the abstracts of talks and poster sessions given at the meeting.