Page 311 - Carbonate Facies in Geologic History

298 Shoaling upward Shelf Cycles and Shelf Dolomitization

1"\
Cycle top '"' " J
''', /\ :-:' ,," Bedded to nodular to lIaler anhydrite
..
Sabkha II/Ill Gray.green Iilty dolomite
evaporite
" "" ",,- Anhydrite
1\ " " "
Intertidal :>Io.y"::::::::~E Wispy laminated, mud.cracked ~
and .~.~~:::J( Feneltral ~ pellets ,'. brown - -
reltricted ~. \ CI , • • 'IJ mudltone Pellet mudltone with
.
. .
marin. O/D/", .... microbioclaltic grainl and foraml;; ','
.,,\,. , Brown foram lime wackeltone
t1i\ ,~ II\ Amphipora bioltrome Ifi0.
"" '" Brachiopod "Crinoidal oK wackestone
~"" *
Open with lithoclaltl, 0 bioturbated 51
marine Tl~ Brown ~
O~*
~'J~ Stromatoporoid IS\ bioltrome with
Stromatop- r,\~ Thamnopora V and Solenopora tdfJi
oroid
bioltromel
~
rsl
1"\ "
~y Solution breccia from dillolved anhydrite
Cycle top
A:X'"' " "
¢.J~
~-- ~~
:-;-6~·
/.0 \ _
* ,..... *
" *= Fig.X-13. Carbonate-evaporite upward shoaling
lime mudstone cycle of Duperow Formation,
c:::> r-.~ Williston basin of North Dakota. Two cycles are
shown. See Fig.III-! for additional legend

these cycles a sharp upper contact occurs with open marine beds at the base of the
next cycle but evidence of erosion or prolonged subaerial exposure is rarely
found. These cycles may be facies equivalent to oolite-grainstone cycles which lie
on the seaward exteriors of wide shelves; the micritic facies (belts 8 and 9 of the
ideal profile) usually lies more shoreward. The Arab zones of the eastern Persian
Gulf illustrate this very well. Wood and Wolfe (1969) described in detail a se-
quence of tidal flat and sabkha evaporites from the Umm Shaif field, a sequence
equivalent to the Arab zone grainstones of the Saudi Arabian mainland.
There are, however, extensive shelf areas covered by such cycles which almost
completely lack grainstone of any type. Two of these are described below.

The Duperow (Devonian) of the Williston Basin

The author (Wilson, 1967b) studied the cyclic Duperow (Frasnian) sediments of
the Williston basin in some detail. These strata formed in a vast backreef lagoon
stretching southeast behind the Cooking Lake platform and Leduc reefs of AI-