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voup and Lower Head Form61ion.
Firs!ly.!he greater indunnion and early silica
o:menLalion of the Irishlown in comparison with lhe Maiden Poir.1 and Blow me Down
Brook Fonmlions ....-ould likely h2vc provKfed scdimenwy rock fragments rather than
loose grains. and lhe Goose: Tickle group and Lower Head Formation do flO( contain
many of the distinctive peliTic chlorite grains (although a vcry few have been observed).
Secondly. the Irishlown. as pari of the strUClurally lowest sedimentary package wilhln
the Humber Arm Allochthon. may IKIt have been in as favourable: a structural pm;ilion
10 supply detritus.
fj 3 3 Prpvroarx;t of AlIllCbrboDOU$ EilS5jve Margin SjljejdJ$ti£ Hnj!$
Although the pl(wcnance of the Cambrian sandstones is generally considered to
he weslerly and from the Grenville: basemenl, SOITIC authors ha\'C studied shales of
allochthonous units and IlOlN more subrle variations in provenance.
Evidence of a ch.1ngc: in provenance of passi,·c margin sediments through time is
provided by Bouford (l988) .....ho ncxed an increase in chlorite abundance at the base of
d~ Cooks Brook Formation (late Middle Cambrian). At the !we of the Middle Arm
Point Formalion (Trern:ldoc) he noted another change in prCM:nalJCe with shales of this
unit apparendy showing geochemical affinities to the early Middle Cambrian Irishlown
Formation.
Sucheki et al. (1977) investigatC'd the clay mineralogy of the Cow Head Group
(which is equivalent to ,he Cooks Brook and Middle Arm Point formations) and noted
lhr~ distinct clay mineral suites. They identified a late Middle Cambrian to early Lower