n Alas - Alaska Division of Geological & Geophysical Surveys - State ...

and the thinning. -upward cycles
.,.1-1---:-- . .--.-.----I
cur auove rrlr: r~~~r.ne~ur~-uywlrru cycles. This
lation suggests that the sea was regressing during
at time and that the depositional cycles ended owing
channel migration. Thc upper pmt of the Shelikof
CCI ~rm ation in this area varies considerably in compositic
jn. On the north shore of Puale Bay, turbidite facies
arc e transitional to nearshore facies containing the bivalve
Corbicula sp.; on the south side, turbidite deposi-
+iqn continued to the top of the formation. The conct
with the overlying Naknek Formation Ln the Puale
y area is Shelikof siltstone overlain by Naknek
nglomerate.
The Shelikof Formation in the Big Creek area
also suggests a regressive sequence. Here, the succession
of environments is more complete. On the shore
of Wide Bay between Des Moines and Big Creeks, a
coarse channel conglomerate was reported (~apps,
1922; KeUum and others, 1945) at the base of the
Shellkof. We interpret this conglomerate to be an
inner-fanehamel deposit. The rocks at the base of
the section thin upward to shelf siltstone. The section
tween the shore of Wide Bay and the head of Big
Creek canslsts or shallow s abnerltlc sandston e, inter
-.-a:-* ,
.-^ ---I-
bedded with thick sacrrolm of siltstone that were ~FUUably
deposited on a shelf below wave ! base. T he upper
460 m of the Shelikof Formation a' t the hea d of Big
Creek is transitional from nearshore marine andstone
..nr+ nr.
to nonmarine deposits. The lower ~~nsists of
nearshore sandstone contairung the pelecypods
Corbicula sp. and Gryphaea sp.; these fossils suggest a
brackish-water to very shallow marine environment.
The upper part consists of magnetite-rich sandstone,
with inclined laminations of granules and pebbles here
interpreted to be beach deposits, overlain by carbnaceous
shale and sandstone that locally contain preserved
roots. The uppermost 60 m consists of massive
channelized conglomerate, with lenses of carbonaceous
shale and sandstone interpreted to be levee deposits
preserved within it. We interpret this conglomerate
and the associated finer pained rocks to be nonmarine
delteic or fluvial deposits. The entire section at the
northesat end of Wide Bay is about 1,500 m thick.
The Shellkoi Formation thins considerably to
only 820 m at Alai Creek near the southwest end of
Wide Bay. In this area, the base of the section consists
-Areas in south wes tern Alas :ka discussed in this volume. A tistil ~g of autt iorshlp, applicable
paging (in I parenthe ses) rela! king to the numbered tiweas follows. 1 , AU~wey 1 and Miller, fi we! 1; 2, Hild~ reth and c bthers, fig :ure 22 (g. 37-39).
figures,
i 20 and