Page 308 - Carbonate Facies in Geologic History

The Smackover Formation 295

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/ GUlf Of MEXICO R Shot.li"t Ioo"d, and • .,oporlt ...
\
". 1::°:"::/:1 Sond SlOn.
f~:;:::.:;:~ Groin.ton.
, O===",,;';5 .. 0k .. ~ Peloidal wod •• ton.
\.. .. "'-,.
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Fig.X-12. Upper Smackover facies, northern Gulf of Mexico after Bishop (1968), showing the
peripheral grainstone buildup a few 100 m thick and about 75 km wide around the Gulf
grading into very thick dark lime wackestone and basinal lime mudstone which reach more
than 1000m

forms a single sedimentary cycle which is identical to an Arab zone unit, but is
much thicker (Fig. X-l1). In Louisiana an overlying thinner cycle of shelf lime-
stone is termed Haynesville A. The two cycles grade shoreward, as well as up-
ward, into the tidal flat pellet mudstone and sabkha anhydrite. A shoreward
sandy and redbed facies occurs against the edges of the old Paleozoic orogenic
belt.
The upper Smackover limestones are more oolitic than those of the Arab
zones. They were formed along a narrower belt and probably along a steeper
slope. The sand and gravel grains are largely dasycladacean or other algal parti-
cles, onkoids, and coated peloids. Shelly bioclasts are comparatively rare. A few
wells in northern Louisiana have penetrated Smackover limestone with hydro-
zoan and mollusk fragments but apparently backreef brines restricted normal
marine faunas on the narrow shelf. As in the Arab Formation, no reefs are known
from the Jurassic of the Gulf coast although the tectonic settings would seem ideal
for their development. Figure X-12, based on Bishop's studies (1968,1969), shows
the facies variations along the Smackover belt. The facies outlined by Bishop
in the upper Smackover of northern Louisiana are as follows:
Shoreward:
Buckner shaly anhydrite, quartz, sand, peloidal oolitic packstone.