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I .1 SpA DGRAPHY OF THE HUMBER ZONE
I 4 I Du: Parau!och!hQn
Grenvillian basement is overlain unconfQrmably by mainly siliciclas!ic rocks of
the Labrador Group (Precambrian-lower Cambrian; C:Jmming. 1983) (ligure 1.3) which
are products Qf Late Precambrian rifting and subsequent development of the passive
margin of [he Iapetus Ocean.
During the Cambrian period. a laterally extensive.
although narrow (Chow and James, 1987) shallow-water caroona!e platform developed
on the newly formed continental margin and remained stable until the Middle OrdQvician.
'The platformal sequenceconsiSlS Qfthe Cambrian Pon au Pon Group (Chow. 1986),!he
Upper Cambrian-Lower Ordovician St. George Group (Knight and James, 1987;
Williams et aI., 1987), and the lower pan of the lower-Middle Ordovician Tahle fkau
Group (Klappa et at, 1980; Stenzel et aI., 1990) (figure 1.3). The first indicalion of
foreland basin development occurs in the SI. George Group where a widespreau
unconformity marks the formalion of a peripheral bulge aS50Ciated with loauing of the
margin (e.g. Iacobi. 1981; Knight and James, 1987; Knight et al .. 1991). Subsequent
cQllapse of the platform caused deposition of deeper water limestones and olis!ostromal
conglQmerates of the upper, Middle Ordovician ."an of [he Table Head Group (S!enzel
et al .• 1990). These are overlain by shales of the lower pan of the Middle Ordovician
Goose Tickle group (QuiM. in preparation; Stenzel et a!.. 1990) (figure 1.3). These
shales repreliCn! the initial stages Qf siliciclastic infilling in the narrow (Bradley, 1989)
axial regiQn of a nelural foreland basin (Quinlan antl