DavidRoyHunter.pdf

On
NI'W.World Island, north central N,,-vfoundland,
lin" when pur.. ly carbonatc. Th.. pur..r
cubonat" accumulations of the
formation would appear to hav.. b..en deposited In an environment free of
terrigenous detritus between "mergent vlcanics"-;;;J"-.t;hall"" ..at~r
Ordoviclan Cobbs ArlII.fo......tlon constltute" only a slDall proportion of the
~ .
dOlllnantly volcanIc and volcaniclastic strata of the ls1and arc t"rrains
chllracteTI5tic f th" Dunnag.. Zone. Th.. Cbb5 "'nIl
.
Formation is
predominantlycOIIposadof li....5tone9 thataredarkllre)-Incolourwhen
1I1x..d with volcanlc detrltus and ltght grey alldlK>recoarsely cr1sta1-
'101-
canlc sandston.." to the north: and trenchdeposlt5 to ch.. south. The result
was a carbon..t" gralnstone barrier that aubdivld..d part.. of th..
Hlddl.. Ordovtciancoaotltnaintaaland..-ardr"striCtedlallaonalenvir-
Olllll,,"t and ..n ,,,,ean..-ard open marine environment.
Ilecauseofthepres..ntlydefonoednatur.. of the New"'orld
Island rocks, sev..ral small io"0111I'I ..1:,,
Formation ..-ere ..essured and sampled.
sections of the Cobbs ArIIl
DetaIled investigallon of the lithologil!s
of the sampbs reveal..d·a s"diOientological pattern tndicatlve
ofasiightlyerra\ictranSKn,sstv"pha"cofdeposltton. llispos"ibl"
lhallhee....rgenc"ofth"arcterraillS,whichpr"cededthede p o.1tion
._-1" ,of the Cobbs"'nD Fo.....tion, and the subsequ..ntsubsidenceof the island
arctcrra{ns,whichaccOIUpaniedand " ..ccee:de:dCobbsArmFotl'!ationdepo·
sit ion, was the for.. and afteT"llath of a rldge-trent.h interaction. The
transgression resulted In a landward shift of oceanward facIes, now recorded
III
th.. vCrlide sequences of thl! CobbsAr.. formation.
The conodont fauna of the Cobbs AI"Il fonnatlon app.".r,. to be