Abstracts
Abstract
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.
RESUME
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.
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