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restricted range of(Fe,O) +MgOIS and K:OlNaIO. The diagl'1lll of AI:OJ(CaO+ NiI,OI
vs. (Fe 10 J +MgO)i: (figureS.4) is diffICult to interprel. but shows a very wide variation
of Al 1 0 1/(CaO+Na:O) for the Lower Head Formalion. possibly ilgain relaled 10 Ihe
variation from sample 10 sample in proportions of different types of feldspars.
II is abundantly clear that the sandslones of the Goose Tickle group and Lower
Head Formalion bear no relation chemically to any of the fields outlined by Bhatu.
(1983). and the effect of gl'2in size. probably even within the range alluded to by Bhatia
(1983). is signifICant.
S 2 5 2 varjation piwjlm1 fum Roser and KOOCb (1986>
Roser and Korsch's (1986) paper resorted to the simpler approach of
discrimination of three broad fields based solely on a plot of K:O/NajO 'Is. SiOli:.
Analyses ofSJndstones of the Lower Head Formationand Goose Tickle grOl.l~ are ploned
on figures S.S and 5.6, with Roser and Korsch's (1986) fields shown. Sandstones of
both units genera.lly suaddle the boundary between the ~sive margin and active margin
fields. Several of the samples. however. plOC in the arc field, because they conlain low
SiDl S as a result of their hip arbollillte cement content. Allhough it is not clear how
much of this carbonate is of biogenic: origin. it can be inferred from lhe diSCUSSIOn in
chapter 4 thaI at least some of it is derived from dissolulion of carbonate nx:k fragments
and is hence ultimately of biogenic origin. Roser and Korsch (1986) accommodated this
problem by recalculating the major element parameters to 100% volatile and CaD free,
and by correspondingly reak:ulating the field boundaries. The Lower Head Formation