Page 282 - Carbonate Facies in Geologic History

Swiss Jura Mountains 269

o IOkm
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,-_ ..... _...1'
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t

~ CORAL LIMESTONE
r; tOooJ CMUERELLE PlSOLITE
E::i3 TRANSITl~ L11'E~

I d ARGIL.1ACEOOS OFFSt£l.F LST.
~ AMMONITE LOCALITIES

Fig. IX-4. Facies of "Middle Rauracian" (Lower Kimmeridgian) showing 10 km width of
coral ramp near edge of carbonate platform and narrow belt of Caquerelly pisolite probably
at crest of shelf margin. Another narrow belt of darker thin-bedded (transition limestone) lies
basinward of the coral reef. Line of crossection of Fig. IX-3 is at extreme northeast corner of
map through Moutier. From Ziegler (1962)

Another facies, oolitic onkolitic bioclastic lime packstone-grainstone, is devel-
oped slightly shelfward along the coral knoll ramp (Caquerelle pisolite). Whereas
bioclastic debris may be coated or uncoated, well-formed ooids are seen and
onkoids are common (algal encrustation on gastropods, bivalve, bryozoan, and
ossicles of crinoids). Serpulids occur at the base and coral debris is common.
Some vague cross-bedding is seen and this sediment probably formed in a turbu-
lent environment as rapidly accumulated sand and gravel bars. This facies is
interpreted as forming the crest of the reef profile, sediment piled up to sea level
shelfward from a platform of coral heads and bioclastic debris. The low profile,
coral growth forms, and internal reef construction much resembles that seen in
Devonian strata and form a Type II shelf margin of the author's classification- a
knoll reef ramp.